United States       Office of         EPA 520/4-79-007D
           Environmental Piotection    Radiation Programs      March 1980
           Agency         Washington DC 20460
           Radiation
v>EPA      Technical Support of
           Standards for High-Level
           Radioactive Waste
           Management
                                  t.

           Volume D
           Release Mechanisms

-------
  TECHNICAL SUPPORT OF STANDARDS FOR

HIGH-LEVEL RADIOACTIVE WASTE MANAGEMENT
             TASK D REPORT

   ASSESSMENT OF RELEASE MECHANISMS
      EPA Contract No. 68-01-4470
              Prepared by
        Arthur D. Little, Inc.
    Cambridge, Massachusetts  02140
              March 1980

-------
                              DISCLAIMER
This report was prepared as an account of work sponsored by the
Environmental Protection Agency of the United States Government
under Contract No. 68-01-4470.  Neither the United States nor the
United States Environmental Protection Agency makes any warranty,
express or implied, or assumes any legal liability or responsibility
for the accuracy, completeness, or usefulness of any information,
apparatus, product, or process disclosed, or represents that its use
would not infringe privately owned rights.
                                  ii

-------
                            ACKNOWLEDGMENTS
     Many individuals contributed to the work done under the direction
of Arthur D. Little, Inc., for the U.S. Environmental Protection Agency
under Contract No. 68-01-4470.  John L. Russell and Daniel Egan of the
Office of Radiation Programs at EPA served as constant guides in the
process of our work.  Dr. Bruce S. Old, James I. Stevens, and David I.
Hellstrom of Arthur  D. Little, Inc., were Program Director, Program
Manager, and Assistant Program Manager, respectively, of the overall
project.  Key individuals involved in each of the reports prepared
under the four tasks were:
TASK A
 Donald Korn
 Arthur D.  Little,
 Task Director
                                                                     Inc.
TASK B
 Robert McWhorter,
 Michael Raudenbush,
 and Lester Goldstein
 S.M. Stoller Corp.

_Edwin/ L.  Field
 Arthur D.  Little,Inc.
 Task Director
TASK C
 Robert McWhorter and
 Michael Raudenbush
 S.M.  Stoller Corp.

_Dr.  P.J.  O'Brien
 Arthur D.  Little,Inc.
 Task Director
TASK D
 Dr.  Ronald B.  Lantz
 Intera Environmental
 Consultants,  Inc.

 Dr.  John Gormley
 D'Appolonia Consulting
 Engineers, Inc.

_Dr.  Charles R. Hadlock
 Arthur D. Little,Inc.
 Task Director

 Peter D. Mattison and
 Dr.  Ajit Bhattacharyya
 Arthur D. Little,  Inc.
                                 iii

-------
                               FOREWORD


     A major Federal effort is underway to develop methods for disposal
of high-level radioactive waste in deep geologic repositories.  An impor-
tant element of this program is the development and promulgation by the
U.S. Environmental Protection Agency (EPA) of environmental standards
for the management of these wastes.

     In anticipation of its efforts to develop these standards, EPA
recognized that it would be necessary to estimate the expected and
potential environmental impacts from potential geologic repositories
using modeling techniques based upon as thorough an understanding as
possible of the uncertainties involved in the quantities and charac-
teristics of the wastes to be managed, the effectiveness of engineering
controls, and the potential migration and accidental pathways that might
result in radioactive materials entering the biosphere.  Consequently,
in March 1977, the EPA contracted with Arthur D. Little, Inc., for a study
to provide technical support for its development of environmental regula-
tions for high-level radioactive wastes.  This study was divided into
the following four tasks:

            Task A - Source Term Characterization/Definition

            Task B - Effectiveness of Engineering Controls

            Task C - Assessment of Migration Pathways

            Task D - Assessment of Release Mechanisms

     There are many national and international programs underway to
develop additional data, especially in the fields of waste forms, know-
ledge of geology and geohydrology, and risk assessment.  The information
presented in these reports has been developed on conceptual bases and is
not intended to be specific to particular conditions at geologic reposi-
tories.
                                  iv

-------
                           TABLE OF CONTENTS
                                                                  Page
Acknowledgements                                                  iii
Foreword                                                           iv
List of Tables                                                     ix
List of Figures                                                   xvi
D-1.0     INTRODUCTION AND SUMMARY                                  1
  1.1     BACKGROUND                                                1
  1.2     OBJECTIVES AND SCOPE                                      1
  1.3     SUMMARY OF RESULTS                                        2
  1.4     GUIDE TO THIS REPORT                                      2
D-2.0     GUIDELINES AND METHOD OF APPROACH                        21
  2.1     GENERAL APPROACH                                         21
  2.2     SPECIFIC GUIDELINES                                      23
  2.3     SELECTION AND CHARACTERIZATION OF GENERIC GEOLOGIES      25
  2.3.1   Bedded Salt                                              26
  2.3.2   Granite                                                  27
  2.3.3   Basalt                                                   30
  2.3.4   Shale                                                    34
  2.3.5   Dome Salt                                                37
  2.4     REPOSITORY ASSUMPTIONS                                   37
  2.5     IDENTIFICATION OF FAILURE MECHANISMS                     40
  2.6     CONCEPTUAL FRAMEWORK FOR QUANTITATIVE ANALYSIS           40
  2.6.1   Probabilities                                            42
  2.6.2   Consequences                                             42
  2.6.3   Uncertainty and Variability                              44
D-3.0     TECHNOLOGICAL FAILURE ELEMENTS                           47
  3.1     FLOW THROUGH BULK ROCK                                   47
  3.1.1   Summary                                                  47
  3.1.2   Background                                               49
  3.1.3   Flow Through Bulk Rock Failure Model                     51
  3.1.4   Flow Through Bulk Rock Release Model                     55
  3.1.5   Literature Discussion                                    68

-------
                          TABLE OF CONTENTS (cont.)
                                                                 Page
  3.2     SHAFT SEAL FAILURE                                      68

                                                                  70
3.2.1   Summary                                                 68
  3.2.2   Background
  3.2.3   Shaft Seal Failure Model                                80
  3.2.4   Shaft Seal Release Model                                87
  3.2.5   Literature Discussion                                  H6
D-3.3     BOREHOLE SEAL FAILURE                                  116
  3.3.1   Summary                                                116
  3.3.2   Background                                             US
  3.3.3   Borehole Seal Failure Model                            126
  3.3.4   Borehole Seal Release Model                            129
  3.3.5   Literature Discussion                                  154
D-3.4     UNDETECTED BOREHOLES                                   158
  3.4.1   Summary                                                158
  3.4.2   Background                                             158
  3.4.3   Undetected Borehole Failure Model                      169
  3.4.4   Undetected Borehole Release Model                      178
  3.4.5   Literature Discussion                                  191
D-3.5     OTHER TECHNOLOGICAL EVENTS AND PROCESSES               192
  3.5.1   Introduction                                           192
  3.5.2   Waste-Rock Interactions                                193
  3.5.3   Brine Migration                                        194
  3.5.4   Canister Migration                                     196
  3.5.5   Criticality                                            197
D-4.0     HUMAN INTRUSION                                        199
D-4.1     FUTURE DRILLING ACTIVITIES                             199
  4.1.1   Summary                                                199
  4.1.2   Background                                             202
  4.1.3   Future Drilling Failure Model                          208
  4.1.4   Future Drilling Release Model                          216
                                   vi

-------
                         TABLE OF CONTENTS (cont.)
                                                                Page
D-4.2     OTHER HUMAN INTRUSION EVENTS AND PROCESSES             224
  4.2.1   Introduction                                           224
  4.2.2   Solution Mining                                        224
  4.2.3   Interference with Hydrologic Conditions                225
  4.2.4   Waste Recovery                                         228
  4.2.5   Sabotage                                               228
  4.2.6   Acts of War                                            229
  4.2.7   Innocent Extraordinary Penetration                     229
D-5.0     NATURAL EVENT FAILURE ELEMENTS                         231
  5.1     FAULT MOVEMENT                                         231
  5.1.1   Summary                                                231
  5.1.2   Background                                             233
  5.1.3   Fault Movement Failure Model                           250
  5.1.4   Fault Movement Release Model                           259
  5.1.5   Literature Discussion                                  270
D-5.2     VOLCANOES                                              277
  5.2.1   Summary                                                277
  5.2.2   Background                                             278
  5.2.3   Volcano Failure Model                                  284
  5.2.4   Volcano Release Model                                  287
  5.2.5   Literature Discussion                                  288
D-5.3     IGNEOUS INTRUSIVES                                     289
  5.3.1   Summary                                                289
  5.3.2   Background                                             289
  5.3.3   Igneous Intrusive Failure Model                        293
  5.3.4   Igneous Intrusive Release Model                        294
  5.3.5   Literature Discussion                                  294
D-5.4     METEORITE IMPACT                                       295
  5.4.1   Summary                                                295
  5.4.2   Background                                             295
  5.4.3   Meteorite Impact Failure Model                         302
  5.4.4   Meteorite Impact Release Model                         304
  5.4.5   Literature Discussion                                  307
                                 vii

-------
                          TABLE OF CONTENTS (cont.)
                                                                Page
D-5.5     BRECCIA PIPES                                          308
  5.5.1   Summary                                                308
  5.5.2   Background                                             308
  5.5.3   Breccia Pipe Failure Model                             315
  5.5.4   Breccia Pipe Release Model                             317
  5.5.5   Literature Discussion                                  319
D-5.6     OTHER NATURAL EVENTS AND PROCESSES                     319
  5.6.1   Introduction                                           319
  5.6.2   Erosion                                                322
  5.6.3   Sedimentation                                          327
  5.6.4   Tectonism                                              327
  5.6.5   Uplift and Downwatping                                 331
  5.6.6   Sea Level Fluctuations                                 332
  5.6.7   Climate                                                334
  5.6.8   Salt Diapirism                                         337
  5.6.9   Salt Dissolution                                       338
LIST OF REFERENCES                                               341
APPENDICES
          Appendix D-I   Glossary                                1-1
          Appendix D-II  Repository Resaturation Times          II-l
          Appendix D-III Methodology for Dissolution Calcula-
                         tions                                 III-l
          Appendix D-IV  Methodology for Diffusion Calcula-
                         tions                                  IV-1
          Appendix D-V   Methodology for U-Tube Calculations     V-l
          Appendix D-VI  Effect of Thermally Induced Buoyancy
                         on Vertical Flow                       VI-1
          Appendix D-VII Salt Creep                            VII-1
          Appendix D-VIII Canister Capabilities for Long-Term
                         Isolation                            VIII-1
          Appendix D-IX  Thermal Stress Cracking in Salt        IX-1
                                  viii

-------
                               LIST OF TABLES


Table No.                                                            Page

  D-l       Summary of Flow Through Bulk Rock Failure Element           3

  D-2       Summary of Shaft Seal Failure Element                       4

  D-3       Summary of Borehole Seal Failure Element                    6

  D-4       Summary of Undetected Borehole Failure Element              8

  D-5       Summary of Future Drilling Failure Element                 10

  D-6       Summary of Fault Movement Failure Element                  12

  D-7       Summary of Volcano Failure Element                         13

  D-8       Summary of Igneous Intrusive Failure Element               15

  D-9       Summary of Meteorite Impact Failure Element                16

  D-10      Summary of Breccia Pipe Failure Element                    18

  D-ll      Explanation of Symbols and Terms in Tables D-l
            Through D-10                                               19

  D-12      Nominal Repository Parameters Used for Model  Calculations  39

  D-l3      Failure Element Chosen for Detailed Modeling               41

  D-14      Summary of Flow Through Bulk Rock Failure Element          48

  D-15      Model Permeabilities for Hard Rock Before and After
            Thermal Cycle                                              54

  D-16      Effective Vertical Hydraulic Gradient in Surrounding
            Geologic Media from Thermally Induced Convection
            (Granite Repository)                                       56

  D-17      Volumetric Flow Rates Through Bulk Rock (Granite
            Repository)                                      -         57

  D-18      Fluid Velocities Through Bulk Rock (Granite Repository)    58

  D-19      Fluid Transit Time from Repository to Aquifer through
            Bulk Rock (Granite Repository)                             59

  D-20      Effective Vertical Hydraulic Gradient in Surrounding
            Geologic Media from Thermally Induced Convection and
            Aquifer Interconnection (Basalt Repository)                61
                                   ix

-------
                             LIST OF TABLES (cont.)
Table No.
  D-21       Volumetric Flow Rates through Bulk Rock (Basalt
             Repository)                                                62

  D-22       Fluid Velocities through Bulk Rock (Basalt Repository)     63

  D-23       Fluid Transit Times through Bulk Rock (Basalt
             Repository)                                                64

  D-24       Volumetric Flow Rates through Bulk Rock (Shale Repository) 65

  D-25       Fluid Velocities through Bulk Rock (Shale Repository)      66

  D-26       Fluid Transit Times through Bulk Rock (Shale Repository)   67

  D-27       Summary of Shaft Seal Failure Element                      71

  D-28       Seal Material Characteristics                              77

  D-29       Properties of Possible Seal Materials                      86

  D-30       Permeability as a Function of Time for Shaft Seal
             Degradation Model                                          88

  D-31       Repository Resaturation Times (Bedded Salt Repository)     90

  D-32       Approximate Fluid Velocities and Transit Times to
             Aquifer Along Permeable Shafts During Period A (Bedded
             Salt Repository)                                           94

  D-33       Effective Vertical Hydraulic Gradient in Permeable Shafts
             from U-Tube Effect During Period B (Bedded Salt Reposi-
             tory)                                                      95

  D-34       Volumetric Flow Rates through Permeable Shafts During
             Period B (Bedded Salt Repository)                          96

  D-35       Fluid Velocities through Permeable Shafts During
             Period B (Bedded Salt Repository)                          97

  D-36       Effective Vertical Hydraulic Gradient in Permeable Shafts
             from Thermally Induced Convection and U-Tube Effect
             (Granite Repository)                                       99

  D-37       Volumetric Flow Rates through Permeable Shafts (Granite
             Repository)                                                101

-------
                             LIST OF TABLES  (cont.)


Table No.                                                               Page

  D-38     Fluid Velocities through Permeable Shafts  (Granite
           Repository)                                                   102

  D-39     Effective Vertical Hydraulic Gradient in Permeable Shafts
           From Thermally Induced Convection and U-Tube Effect  (Basalt
           Repository)                                                   104

  D-40     Volumetric Flow Rate Through Permeable Shafts  (Basalt
           Repository)                                                   105

  D-41     Fluid Velocities Through Permeable Shafts  (Basalt
           Repository)                                                   106

  D-42     Volumetric Flow Rates Through Permeable Shafts  (Shale
           Repository)                                                   108

  D-43     Fluid Velocities Through Permeable Shafts  (Shale Repository)  109

  D-44     Repository Resaturation Times (Dome Salt Repository)          111

  D-45     Approximate Fluid Velocities and  Transit Times  to Aquifer
           Along Permeable Shafts During Period A (Dome Salt Repository) 112

  D-46     Effective Vertical Hydraulic Gradient in Permeable Shafts
           From U-Tube Effect During Period  B (Dome Salt Repository)     113

  D-47     Volumetric Flow Rate in Permeable Shafts During Period B
           (Dome Salt Repository)                                        114

  D-48     Fluid Velocities Through Permeable Shafts  During Period B
           (Dome Salt Repository)                                        115

  D-49     Baseline Parameter Used by TASC in Fouled  Shaft Seal
           Calculations                                                  117

  D-50     Summary of Borehole Seal Failure  Element                      119

  D-51     Permeability as a Function of Time for a Borehole Seal
           Degradation Model                                             128

  D-52     Approximate Fluid Velocities and  Transit Times  to Aquifer
           Along Permeable Boreholes During  Period A  (Bedded Salt
           Repository)                                                   134

-------
                              LIST OF TABLES (cont.)
Table No.

  D-53     Effective Vertical Hydraulic Gradient in Permeable Bore-
           holes From Thermally Induced Convection and Aquifer
           Interconnection (Bedded Salt Repository)

  D-54     Volumetric Flow Rates and Fluid Velocities in Deep Permeable
           Boreholes During Period B as Calculated Without Considering
           Dissolution Effects (Bedded Salt Repository)

  D-55     Volumetric Flow Rates in Deep Permeable Boreholes During
           Period B Including Effects of Dissolution on Flow Rates
           (Bedded Salt Repository)

  D-56     Effective Vertical Hydraulic Gradient in Permeable Bore-
           holes from Thermally Induced Convection and the U-Tube
           Effect (Granite Repository)

  D-57     Volumetric Flow Rates Through Permeable Boreholes (Granite
           Repository)

  D-58     Fluid Velocities Through Permeable Boreholes (Granite
           Repository)

  D-59     Effective Vertical Hydraulic Gradient in Permeable Boreholes
           From Thermally Induced Convection U-Tube Effect and Aquifer
           Interconnection (Basalt Repository)

  D-60     Effective Vertical Hydraulic Gradients in Permeable Bore-
           holes Connecting the Repository and the Lower Aquifer
           (Basalt Repository)

  D-61     Volumetric Flow Rates Through Permeable Boreholes (Basalt
           Repository)

  D-62     Fluid Velocities Through Permeable Boreholes (Basalt
           Repository)

  D-63     Volumetric Flow Rates Through Permeable Boreholes (Shale
           Repository)

  D-64     Fluid Velocities Through Permeable Boreholes (Shale
           Repository)

  D-65     Approximate Fluid Velocities and Transit Times to Aquifer
           Along Permeable Boreholes During Period A (Dome Salt
           Repository)
135
136
137
139
141
142
143
146
147
148
150
151
153
                                    xii

-------
                              LIST OF TABLES  (cont.)
Table No.

  D-66



  D-67


  D-68


  D-69

  D-70


  D-71

  D-72

  D-73


  D-74


  D-75


  D-76


  D-77


  D-78


  D-79

  D-80

  D-81

  D-82
Effective Vertical Hydraulic Gradient in Permeable Bore-
holes From U-Tube Effect During Period B (Dome Salt
Repository)

Volumetric Flow Rates Through Permeable Boreholes During
Period B (Dome Salt Repository)

Fluid Velocities Through Permeable Boreholes During
Period B (Dome Salt Repository)

Summary of Undetected Borehole Failure Element

Probabilities  of Undetected  Boreholes in Buffer Zone Around
Page



 155


 156


 157

 159


 171
Selected Values of a  and ot  (Bedded Salt Repository)
 Bedded  Salt  Repository  (First  Estimate)

Effective Resistances a, through a^  (Bedded Salt Repository)  180

                                                              181

Volumetric Flow Rates Through Undetected Boreholes  (Granite
Repository)                                                   18A

Fluid Velocities Through Undetected  Boreholes  (Granite
Repository)                                                   185

Volumetric Flow Rates Through Undetected Boreholes  (Basalt
Repository)                                                   187

Fluid Velocities Through Undetected  Boreholes  (Basalt
Repository)                                                   188

Volumetric Flow Rates Through Undetected Boreholes  (Shale
Repository)                                                   189

Fluid Velocities Through Undetected  Boreholes  (Shale
Repository)                                                   190

Summary of Future Drilling Activities Failure  Element         200

Areal Borehole Densities From  Past Drilling Activities        203

Future Drilling Rate Estimates for Bedded Salt               210

Future Drilling Rate Estimates for Granite                    211
                                     xiii

-------
                             LIST OF TABLES (cont.)
Table No.

  D-83

  D-84

  D-85

  D-86

  D-87

  D-88

  D-89


  I>-90

  D-91

  D-92

  D-93

  D-94

  D-95

  D-96

  D-97



  D-98

  D-99
  D-101

  D-102

  D-103
                                                             Page

Future Drilling Rate Estimates for Basalt                      212

Future Drilling Rate Estimates for Shale                       213

Future Drilling Rate Estimates for Dome Salt                   214

Volumetric Flow Rates Through a Single Sealed Borehole         223

Summary of Fault Movement Failure Element                      232

Fault Densities for Selected Areas of the United States        254

Volumetric Flow Rates Through a Fault (Bedded Salt
Repository)                                                    261

Fluid Velocities Through a Fault (Bedded Salt Repository)      263

Volumetric Flow Rates Through a Fault (Granite Repository)     266

Fluid Velocities Through a Fault (Granite Repository)          267

Volumetric Flow Rates Through a Fault (Basalt Repository)      268

Fluid Velocities Through a Fault (Basalt Repository)           269

Volumetric Flow Rates Through a Fault (Shale Repository)       271

Fluid Velocities Through a Fault (Shale Repository)            272

Effective Vertical Hydraulic Gradient in a Fault From
Thermally Induced Convection and Aquifer Interconnection
(Salt Dome Repository)                                         273

Volumetric Flow Rates Through a Fault (Dome Salt Repository)   274

Fluid Velocities Through a Fault (Dome Salt Repository)        275

Summary of Volcano Failure Element                             279

Volcanic Phenomena with Surface Manifestation                  282

Summary of Igneous Intrusive Failure Element                   290

Summary of Meteorite Impact Failure Element                    296

-------
                              LIST OF TABLES  (cont.)
Table No.                                                               Page

  D-104    Proven or Probable Large Meteorite Impact Craters in
           the United States                                             300

  D-105    Effective Hydraulic Gradient in Extended Vertical Pathways    305

  D-106    Volumetric Flow Rates Through Meteorite Induced Permeable
           Zone                                                          306

  D-107    Summary of Breccia Pipe Failure Element                       309

  D-108    Effective Vertical Hydraulic Gradient in a Breccia Pipe
           from Thermal Buoyancy and Aquifer Interconnection (Bedded
           Salt Repository)                                              318

  D-109    Volumetric Flow Rate Through a Breccia Pipe  (Bedded Salt
           Repository)                                                   320

  D-110    Fluid Velocities Through a Breccia Pipe (Bedded Salt
           Repository)                                                   321

  D-lll    Estimates of the Rate of Erosion Under Various Conditions
           of Climate and Relief                                         333
                                      xv

-------
                             LIST OF FIGURES
Figure No.

  D-l      Rock Salt Deposits in the United States

  D-2      Repository in Bedded Salt

  D-3      Crystalline Formations in the United States

  D-4      Repository in Granite

  D-5      Repository in Basalt

  D-6      Argillaceous Formations in the United States

  D-7      Repository in Shale

  D-8      Repository in Salt Dome

  D-9      Bedded Salt Repository Showing Vertical Shafts

  D-10     Examples of Shaft Linings

  D-ll     Grouting Program for Shaft Stabilization

  D-12     Example of Section of Multi-Layered Shaft Seal

  D-13     Hydraulic Conductivity of Natural Materials

  D-14     Typical Plugged Borehole

  D-15     Electric Analog for Borehole Pathway Analysis in Basalt

  D-16     Commercial Saline Deposits in the United States

  D-17     Commercially Exploitable Organic Fuel Deposits
           in the United States

  D-18     Diagram of Salt Dome Showing Associated Oil Reservoirs,
           Wells, and Deep Holes

  D-19     Pathways Associated with the Analysis of Undetected
           Boreholes

  D-20     Migration of Brine Bubble in Thermal Gradient

  D-21     Petroleum Wells Drilled in the Contiguous 48 States,
           1976 and 1977

  D-22     Region Within Which  Canister  and Drill Hole Overlap
Page

  28

  29

  31

  32

  33

  35

  36

  38

  69

  74

  75

  83

  85

 123

 145

 162

 163



 166


 179

 195


 204

 217
                                  xvi

-------
                         LIST OF FIGURES (cont.)


Figure No.                                                            Page

  D-23     Fluid Injection for Enhanced Well Production                227

  D-24     Subparallel Faulting in Tertiary  and Quaternary Periods     234

  D-25     Basic Fault Types                                           236

  D-26     Features Associated with Faulting                           238

  D-27     Dating of Non-tectonic Fault by Bed Displacements           239

  D-28     Faulting in the Vicinity of a Salt Dome (Conceptual
           Drawing)                                                    241

  D-29     Typical Paradox Basin Salt Anticline Structure Derived
           from Seismic and Other Data                                 242

  D-30     Age of Faults in the Gulf Coastal Region                    243

  D-31     Detection of Features by Seismic Reflection                 245

  D-32     Detection of Fault by Attenuation of Refracted Signals
           Across Discontinuity                                        246

  D-33     Processed Seismic Record of Section of Paradox Basin        247

  D-34     Faulting Associated with Folding and Tilting                249

  D-35     Waste Drift Before and After Faulting                       264

  D-36     Sketch of Plutonic and Volcanic Structures                  281

  D-37     Volcanic Hazards                                            283

  D-38     Relative Crater Production Rate with Solar System Evolution 298

  D-39     Distribution of Impact Craters                              301

  D-40     Simplified Crater Geometry                                  303

  D-41     Conceptual Drawing of Breccia Pipe in Delaware Basin        311

  D-42     Characteristics of Dissolution from Above and Below
           Salt Formation                                              313

  D-43     Average Rate of Denudation of Major Drainage Areas in the
           U.S.                                                        323
                                   xvii

-------
                            LIST OF FIGURES (cont.)


Figure No.                                                             Page

   D-44     Glaciated Areas of the Coterminous United States
            Affected During Pleistocene Glaciation                      326

   D-45     Crustal Plates and Regions of the World in Which Major
            Earthquakes and Volcanoes Occur                             329

   D-46     Isostasy                                                    330

   D-47     Fresh Water Overlying Dense Sea Water                       335

   D-48     Erosion Rates vs.  Plant Cover                               336
                                 xviii

-------
D-1.0  INTRODUCTION AND SUMMARY

D-l.l  BACKGROUND

    The U.S.  Environmental  Protection Agency  (EPA)  is  responsible for
the  development  of   environmental  standards   for  the  disposal  of
high-level radioactive wastes.   As  part of its development effort, EPA
contracted with Arthur  D.  Little,  Inc.,  for  a  program  of  technical
support.  This program consists of four principal  tasks:
    Task A — Source Term Characterization/Definition
    Task B — Effectiveness of Engineering  Controls
    Task C — Assessment of Migration Pathways
    Task D — Assessment of Release Mechanisms
This report represents the results of the work done  under Task D.

D-1.2  OBJECTIVES AND SCOPE

    The purpose of Task D is to analyze the potential  for the release of
radionuclides from a deep mined  repository for radioactive wastes.  The
analysis  is  not  intended  to  correspond  to a particular  site  or
repository  design,  but  rather  it is  to  be  generic  in  nature,
representing  the  synthesis  of assumptions and data  from many sources.
The EPA wishes  to  consider  the potential performance  of  repositories in
its determination of appropriate standards.
    Repositories  in  five different geologic media  were considered  in
this  study.     These  media  include bedded  salt, dome  salt,  granite,
basalt,  and   shale.    A wide  range  of  potential  containment   failure
mechanisms have been proposed in  the  literature.   These  failure
mechanisms were evaluated  and  compared with each  other  to determine
their  relative  importance.   As  a  result of  this process,  ten  failure
mechanisms were selected for detailed modeling.  They  were chosen  with a
view toward including  those  that  appeared  to  be  the most important, as
well as ones that would span a  wide range of  risk  characteristics  (e.g.,
high probability/low consequence, low probability/high consequence). The
list includes  the following:

-------
    9  flow through bulk rock;
    •  shaft seal failure;
    e  borehole seal failure;
    •  undetected boreholes;
    •  future drilling;
    •  fault movement;
    0  volcanoes;
    •  igneous intrusives;
    •  meteorite impacts;
    •  breccia pipes.
A number of other failure mechanisms, or processes that might contribute
to failure, are discussed  in  this  report,  although detailed models have
not been developed.
    The  results  of Task D  can  be combined  with  radionuclide  transport
and  dose calculations  in  order  to  assess  the  potential  effects  of  a
repository on human health.

D-1.3  SUMMARY OF RESULTS

    Each  of  the  ten  failure  elements  was  modeled  in  terms  of  its
likelihood  of occurrence  and  its  physical characteristics.    In  six
cases, the likelihood  of  occurrence  is estimated  in  terms of an annual
probability (events/year).   However, some  failure modes are considered
sufficiently  likely  that  they  are   modeled as   deterministic   events.
Summaries  of   the  model  assumptions  and  parameters  for  each  of  the
failure  elements  are given in  Tables  D-l through D-10.    A  key to  the
symbols  that  appear in these  tables can be  found in Table  D-ll.    The
remainder  of  this report  can be  regarded  as  an explanation  of  these
tables .

D-l.4  GUIDE TO THIS REPORT

     Chapter  D-2.0  contains  a  summary of  the  methods   and  guidelines
adopted  for  this  study.    Chapters D-3.0,  D-A.O,   and  D-5.0  contain
detailed analyses of the ten failure elements that were modeled,  as well
as discussions of  other potential  failure elements.   The first appendix

-------
                                                      TABLE D-1
                              SUMMARY OF FLOW THROUGH BULK ROCK FAILURE ELEMENT



MEDIUM


Bedded Salt









Grenrte







Basalt






Shale






Dome Salt






o5
fc«
j Z
5 X
03 5
Is
p









D







D






D






P







NATURE
OF
MODEL


Cumulative occur-
rence probability








Change in permea-
bility after thermal
peak





Change in permea-
bility after thermal
peek





Change in permea-
bility after thermal
peek





Cumulative occur-
rence probability








RELEASE
MODE


Groundwater









Groundwater







Groundwater






Groundwater






Groundwater








DRIVING
FORCE


Pressure from salt
closure, thermally
induced convection.
and gradient from
aquifer interconnec-
tion




Thermally induced
convection






Thermally induced
convection and
gradient from aquifer
interconnection




Thermally induced
convection end
gradient from aquifer
interconnection




Pressure from salt
closure, thermally
induced convection.
and gradient from
lower aquifer at edge
of salt dome




SOURCE
TEAM


Uniform
concentration








Uniform
concentration






Uniform
concentration





Uniform
concentration





Uniform






PARAMETERS



1st ESTIMATE

p-0









K - 10'10 cm/sec for
t< 100 yrs
K - 10-9 cm/tec for
t > 100 yrs
17 - 10"4
A - 8xin6m2



K = 10"9 cm/sec for
t < 100 yn
K = 10"8 cm/sac for
t > 100 yn
T, = 10-4
A - BxlO^m2



K » 10"9 cm/sec for
t < 100 yrs
K - 10-8 cm/sec for
l > 100 yrs
A - s'T.oS m*



p - 0







2nd ESTIMATE

p-0









K - 10* cm/sac lot
t < 100 yn
K = 10"7 cm/sec for
1 > 100 yrs
D = 10-*
A • SxlO6*)2



K - 10"7 cm/jec for
t < 100 yn
K " 10-* cm/sec (or
t > 100 yrs
A - SxlO6!!!2



K - 10~7 cm/sec lor
t < 100 yrs
K * 10^ cm/sec for
t> 100 yrs
0 - 10-4
A - BxlO^rn2



p . 0






FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER


lit ESTIMATE

No releases need to be
calculated.








t (yn) Oltl Im3/yr)

100 1.4 XlO2
1000 8.8 xlO1
10,000 3.8x10'



t Ivnl Qltl (m3/yrl
100 1.8x10*
1000 1.5 x 10*
10.000 6.3 x 103



t (yn Oil) (m3/vr)
100 Unto*
1000 1.5x10*
10400 6 3 x 103



No releases fiMd to be
calculated.







2nd ESTIMATE

No nrioasn need to be
calculated.








tlyn)

100
1000
10.000

Oltl (m3/yrl

1.4 x 104
8.8 x 103
3.8 x 103



tlynl
100
1000
10,000
0(1) (n>3/yr)
73 x 106
7.7 x 106
6.8 x 106



tlyn
100
1000
10.000
6(tt (it.3/»rl
7SX106
7.7 x 10s
6^ xlO6



No mean need to be
olculated.









COMMENTS


The probability that the
spatial variability in
rock strength could
lead to an extensive
pathway from the re-
pository that would
fracture under the
stresses experienced
was found to be neg-
ligible.
Permeability change
after thermal peak is due
to several factors:
movement of blocks
during thermal cycle.
incomplete rebound of
material in crack*.
alteration ol minerals
in cracks.
Permeability change
after thermal peak is due
to several factors:
movement of blocks
during thermal cycle.
Incomplete rebound of
materiel in cracks,
alteration of minerals
in cracks.
Permeability change
after thermal peek is due
to seveial factors:
movement ol blocks
during thermal cycle,
incomplete rebound of
material In cracks.
alteration of minerals
in cracks.
The probability that
the spatial variabilitv in
rock strength could leed
to an extensive pathway
from the repository that
would fracture under
the stresses experienced
was found to be nee-
See Table D-11 for explanation of symbols and terms.

-------
                                                      TABLE D-2
                                      SUMMARY OF SHAFT SEAL FAILURE ELEMENT




MEDIUM


Bedded Salt







Granite










Basalt








re
o £>
£5
35
If
ss
SES
D







D










0










NATURE
OF
MODEL


Linearly increasing







Linearly increasing
permeability









Linaariy increasing
penTMebilitv










RELEASE
MODE


Groundwater







Groundwater










Groundwater











DRIVING
FORCE


Initially pressure
from salt creep.
Afterwards, U-tube
effect.





Thermally induced
convection and
U-tube effect.








Thermally induced
convection and
U-tube effect.










SOURCE
TERM


Uniform
concentration






Uniform
concentration









Uniform
concentration









PARAMETERS


1st ESTIMATE

KQ = 10 cm/sec at
time of sealing
K,- NT6 cm/sec
after 10.000 years
K increases linearly
from KQ to K, over
10,000 years '
r| - 0.1
A - 100m2, total
cross-sectional area
of shafts
KQ- ID'8 cm/sec at
time of sealing
K, • 10"* cm/sec
after 10,000 years
K increases linearly
from Kg to Kj over
10.000 years
n • 0.1
A • 100m2, total
cross-sectional area
"of shafts
KQ n 10~» cm/sec at
time of sealing
K," 10-6 cm/sec
after 10,000 years
K increases linearly
from KQ to K1 over
10,000 years
n » 0.1
A • 100m2, ton!
cross-sectional area
of shafts

2nd ESTIMATE

KQ B 10 cm/sec at
time of sealing
K,« 10"4 cm/sec
after 10,000 years
K increases linearly
from K0 to K1 over
10.000 years
n - 0.1
A - 100m2. total
cross-sectional area
of shafts
<0= 10"* cm/sec at
time of sealing
K,- 10"4 cm/sec
after 10,000 years
K increases linearly
from Kg to K j over
10,000 years
r, • 0.1
A - 100m2, total
cross-sectional aree
of shafts-
K0» 10* cm/sec at
time of sealing
K, • 10"4 cm/sec
after 10.000 veers
K increases linearly
from KQ to K j over
10,000 years
u - 0.1
A = 100m2, total
cross-sectional-area
of shafts

FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER


1st ESTIMATE

tlyrsl

200
223"
223*
1000
10,000

Q It) Im3/yrl

40 I Period
40 f0'""
w 1 creep
0.08
0.17
0.32


tlyrsl

100
1000

10,000

0 It) Im3/yrl

0.3
1.0

1.E





tlyrsl
100
1000
10.000

0 It) Im3/vrl
0.4
; 1'7
3.2






2nd ESTIMATE

tlyrsl

720
1000"
1000*
10,000

Q Itl Im3/yrl

200o| Period
>of salt
awo) creep
3.15
3.15



tlyrsl

100
1000

10,000

O Itl Im3/yrl

153
94.6

236.3





tlyrsl
100
1000
10.000

0 
-------
                   TABLE D-2
SUMMARY OF SHAFT SEAL FAILURE ELEMENT (CONTINUED)

MEDIUM

Shate




Duma SKI

£i
H|
if
£8
D




D

NATURE
OF
MODEL

Unanty Intiaaalna
parmaaMhv




Ltnaariy men—tag



RELEASE
MODE

GrounoVamr




GroundiMar


DRIVING
FORCE

Tharmatty Induced
eomactfon and
It-tuba affact.




IrdtiaHv praaBira
from alt craap.
Altannrdi. U-tuba
affact


SOURCE
TERM

Uniform
concantratkm




Uniform

PARAMETERS

la ESTIMATE

Kg » 10* cm/iac at
Ikna of Haling
K, • lO"6 cm/aac
aftar 10,000 ytari
K incraam Itnaarly
from Kg to K| ovar
10,000 vcart
r, - 0.1
A - 100m2. total
cron-sactional araa
Olfh.lt!
Kg- 10* cm/aac at
lima of aariina.
aftar 10.000 vaari
K incraaan llnaarly
from Kg 10 K, ovar
10.000 vaan
n • 0.1
A - 100m2, total
odh.lt!
2nd ESTIMATE

Kg - 10"8 cm/sac at
timaof araling
K, - 10"4 mime
ahar 1O.OOO vaari
Kmcraaanlinaarly
from KgtoK, ovar
10.000 vaari
n - 0.1
A - 100m3. total
ercts-iactional araa
of ihafn
Kg- 10* cm/aac at
tana of lading
K,- 10-* cm/a*
altar 10.000 vaari
K inuaaau linaarlv
from Kg to K| ovar
10,000 vaari
r, - 0.1
A - 100m2, total
olaS.lt,
FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER

la ESTIMATE

tlvnl
100
1000
10,000
Q III Im3/vrl
0.4
1.7
3.2



tlvnl
200
260
260
1000
10.000
O III Im3/yrl
IS ) Parted
« sr
0.04
0.10
OJ4

. 2nd ESTIMATE

tlvnl
100
1000
10.000
Q III Im3/v)
28.6
157.6
472fi



tlvnl
748
1000"
1000*
10.000

6 It) Im3'vrl
2000f Pirfod
—t sr
3.1 S
3.15


COMMENTS

reutumion.




H it comcnoiivc to
•tsumc closure bv till
creep for ihn failure
reuluraiion time would
Closure aUo impliei
itrong driving force for


-------
                                                      TABLE D-3
                                    SUMMARY OF BOREHOLE SEAL FAILURE ELEMENT


MEDIUM


bdfrdS,!,






~


Gmrin









Badt











11

_ —
fs
£S
D









D









D











NATURE
OF
MODEL


Linearly increasing
permeability








LJ nearly increasing
permeability








Linearly increasing
permeability











RELEASE
MODE


Ground water









Groundwater









Groundwater












DRIVING
FORCE


Initially pressure from
alt creep. Afterwards,
thermally induced
gradient from aquiler
interconnection for
boreholes extending
to lower aquifer.





Thermally induced
convection








Thermally induced
convection and
gradient from aquifer
interconnection for
boreholes extending
to lower aquifer.








SOURCE
TERM


Jniform
concentration








Uniform
concentration








Uniform
concentration










PARAMETERS


let ESTIMATE

C- « 10 cm/sec at
time of sealing
KI • 10"5 em/tec after
1 0,000 years
K increases linearly
from KQ to K. over
10,000 years
T; - 0.1
50 boreholes penetrate
to repository, 10 of
which continue to
lower aquifer
A - 0.1 m2/borehole
(Q » 10*3 cm/sec at
time of sealing
K, - ifl'5 cm/sec after
10.000 years
K increases linearly
from KQ« K1 over
10,000 years
n • o.i
50 boreholes penetrate
to repository
A • 0.1 m2/borehoJ*
KQ = 10 cm/sec at
lime of sealing
Kj-iO* cm/sec efter
10.000 veers
K increases linearly
from KQ to K1 over
10,000 years
F) - 0.1
SO boreholes penetrate
to repository, 10 of
which continue to
tower aquifer
A - 0.1 m2/borehoU
2nd ESTIMATE

KO- 10"8 cm/sec at
time of sealing
K . • 1 0"* cm/sec after
10,000 years
K increases linearly from
XQ to K j over
10,000 yean
r, • 0.1
50 boreholes penetrate
to repository. 10 of
which continue to
lower aquifer
A • 0.1 m2'borehole

time of sealing
Kf - 10"^ cm 'tec after
10,000 years
K increases linearly from
KQ to K| over
10.000 years
U - 0.1
SO boreholes penetrate
to repository
A • 0.1 m^/borehol*
KQ « 10"® cm/sec at
time of sealing
i<1 - 10T* cm/sec after
10.000 years
K increases linearly from
KQ to K | over
10,000 yean
r, • 0.1
50 boreholes penetrate
to repository, 10o<
which continue to
lower aquifer
A • 0.1 m2/borehole
FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER




1st ESTIMATE

tlyn)
200
223-
223'
1000
10.000






100
1000
10.000






ttyrs)

100
1000
10.000








Q (tl Im3/yrl
M i Period
\ of »it
14 f creep
0.05
0.13
0.63






0.1
0.6
2.4






0 It) tm3/yr)

o.os
1 0.4
1.6







2nd ESTIMATE

lynl '- Q (tl Im /yr)
720 100 | Pt"°°
Vof salt
1000" 100 (creep
lOOO" 19
0.000 167

|





100 . 0.9
1000 5.S
0.000 t 31.5






t (yrs) Q (t) (m3/yr)

100 2.0
1000 19.2
10.000 170.1









r-nftM4EU


e.ease o-vy t>ej<-
fter repository
on m u
-------
                                                  TABLE D-3
                           SUMMARY OF BOREHOLE SEAL FAILURE ELEMENT (CONTINUED)
MEDIUM

SM«



CHmSM



el
if
si
o *-
D



D



NATURE
OF
MODEL





LmMriv incranmg
pvmMbility


RELEASE





Ground«Mttr



DRIVING



•wfitnt from •quit*
tanrcomwction lor
bortfcota extending
to loiwr >quif tr.

InitMly prwur* from
MhcTMp. Afttnjwnh,
ttw U-tubt «ff tct.


SOURCE





unifom,



PARAM
in ESTIMATE


K,- lOrGon/MClfnr
10.000 yon
K 1 	 •• liniHlv 'rom
KQlO K^ OMT
10.000 V^l
n - 0.1
tomxxitofv. 10 oi
«hid.eootinu«
to IOVMT iquifir
A - 0.1 fnzftnnhol«
Kg -104 cm/Hen
limxrfMriing
C, - lO^antocatw
loxnovMr*
KgtoK) OMT
IQ^lOOvMrs
1 - 0.1
tonpotitory
* - 0.1 m'/bor*
100 \ P"iod
00 } ofBlt
100 I cra*>
IB
IB





I^MMllUfy (MMUIllion.

r\t\tmm only b»gJn
*lUi t^pi^ilAtr
raMturatfon. Ineon-
mn to undMKMd
m«Tt.ho(«inthiicaH
rapoiHorv and so can-
•quHvitidgiafmt
dom.
See Table O-11 for explanation of symbols and terms.

-------
                                                               TABLE D-4
                                         SUMMARY OF UNDETECTED BOREHOLE FAILURE ELEMENT


MEDIUM



BofctadSalt














Granita












Bolt














ES
n. Negligible flow in
most cases deduced
from consideration of
relative resistance of
alternative pathway*
'or 
-------
                                                            TABLE D-4
                                 SUMMARY OF UNDETECTED BOREHOLE FAILURE ELEMENT (CONTINUED)

MEDIUM



Shale















Dome Salt















It
z
_ —
Si
• w
IB
p















p















NATURE
OF
MODEL


Past drilling density
and detection re-
liability yield
probability of one
or more pertially
filled holes.











Past drilling density
and detection re-
liability yield
probability of one
or more partially
filled holes.












RELEASE
MODE


Groundwater















Groundwater
















DRIVING
FORCE


Thermally induced
convection and
gradient from aquifer
interconnection.












Second estimete
Period B flows
derive from equifer
interconnection
gradient. Other flows
negligible.












SOURCE
TERM


Uniform
concentration














Uniform
concentration















PARAMETERS


1st ESTIMATE

prob (1 hole on site)
- 0.05
("site" " repos. <•
300 m buffer zone)
prob (failure to detect)
= .01
prob (undet. hole)
= S x 10-*
K - 10-* cm/sec
1 • 0.2
A • 0.1 m
Distance from drift
n 5m but flows
assume hole through
repository. Holes
extend to lower
equifer.
exp. no. holes on site
• 3
("site" • 300 m
buffer zone only)
prob (failure to detect
indiv. hole)
- 0.001
prob (3 undet. holes)
• 0.003 (Assumes
partial dependence)
K • 10-* em/sec
n - 0.2
A - 0.1 m2
Distance from drift
• lOOm.
Holes extend to lower
aquifer.

2nd ESTIMATE

exp. no holes on site
• 9
prob (failure to detect)
• 0.01
prob (3 undet. holes)
= 0.09 (Assumes
partial dependence)
K - 10-3 cm/sec
1 = 0-2
A • 0.1 m2
Distance from drift
• 5m but flows
assume hole through
repository. Holes
extend to lower
aquifer.

exp. no holes on site
- 30
prob (failure to detect
indiv. hole)
- 0.001
prob 15 undet. holes)
= Oj03 (assumes
partial dependence)
K - 10-3 cm/sec
n - 0.2
A - 0.3 of (total)
Distance from drift
=• 100m.
Holes extend to lower
aquifer.


FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER


1st ESTIMATE
tlyrs)

100
1000
10.000











0 (m3/yrl

4.4
3.8
1.6











Negligible with respect
to other failure elements.































2nd ESTIMATE
Hyn)

100
1000
10,000











tlyrs)

1000
10.000













Q Im3/vrl

594
576
510











Q (m3/yrl

630
630














COMMENTS



Repository rasaturatlon
neoMary for releases
to begin.













Distance from drift
precludes significant
connection with re-
pository except In case
ol significant dissolu-
tion. Negligible flow in
most cases deduced
from consideration of
nrtatrv* resistance of
alter native pathway*
for water to enter and
leave repository. Re-
pository reenuratton
necessary for releases.



VO
          See Table D-11 for explanation of symbols and terms.

-------
                                                        TABLE D-5
                                    SUMMARY OF FUTURE DRILLING FAILURE ELEMENT



MEDIUM

B«dd«lSalt














Gmtita










ta.lt














SB
g|
j Z
a 5
< E
O t-
£ 0
P, O














P,D










P,D
















NATURE
OF
MODEL

Postulated determin-
istic drilling rate.
probabilistic for
hitting canister.











Postulated determin-
istic drilling rate,
probabilistic for
hitting canister.









Postulated determin-
istic drilling rate.
probabilistic for
hitting canister.














RELEASE
MODE

A. Land surface
B. Groundwater













A. Land surface
B. Groundwater










A. Land surface
B. Groundwater
















DRIVING
FORCE

A, Materials raised
with drilling mud.
B. Thermally induced
convection and
gradient from
aquifer inter-
connection.








A. Material! raised
with drilling mud.
B. Thermally induced
convection.









A. Material) raised
with drilling mud.
B. Thermally induced
convection and
gradient from
aquifer inter-'
connection











SOURCE
TERM

A, Part of canister
and fluid from
waste drift.
B. Uniform
concentration.










A. Part of canister
and fluid from
wast* drift.
B. Uniform
concentration.








A. Part of canister
and fluid from
waste drift.
B. Uniform
concentration.












PARAMETERS

lat ESTIMATE
No holes fart century;
5 holes next century;
2 holes each subsequent
century. All holes to
lower aquifer.
Holes sealed with
permeability

K = 10-4 cm/sec
rj •= 0.2, and
A - 0.1 m2.
Probability of hitting a
canister = 10*3 per hole.
with expected removal
of 1 5% contents.
No holes first century;
1 hole next century;
1 hole every four sub-
sequent centuries.
Holes sealed with
permeability
K - 10"4 cm/sec,
T) - 0.2, and
A - 0.1 m2.
Probability of hitting a
canister - 10*3 per
hole, with expected
removal of 15%
conteno.
No holes first century;
3 holes next century;
1 hole each subsequent
century. All holes to
lower aquifer.
Holes sealed with
permeability

K - 10"* cm/sec,
T) = 02, and
A - 0.1 m2.
Probability of hitting a
canister = 10*3 per hole
with expected removal
of 15% contents.

2re5 ESTIMATE
No holes first century;
50 holes next century;
5 holes each subsequent
century. All holes to
lower aquifer.
Holes sealed with
permeability

K •= 10-3 cm/sec.
T) - 0.2, and
A - 0.1 m2.
Probability of hitting a
canister = 10*3 per hole.
with expected removal
of 15% contents.
No holes first century;
10 holes next century;
2 holes every subse-
quent century.
Hota sealed with
permeability
K « ID"3 cm/sec.
TI o 0.2, and
A - 0.1 m2.
Probability of hitting a
canister - 10'3 par
hole, with expected
removal of 15%
contents.
No holes first century;
20 holes next century;
5 holes each subsequent
century. All holes to
lower aquifer.
Holes sealed with
permeability

K = 10-3 cm/sec.
TJ n 0 3.. and
A - 0.1 m2.
Probability of hitting a
canister = 10"3 per hole
with expected removal
of 15% contents.

FLUID TRANSPORTED
TO SURFACE

1st ESTIMATE
0.07 m3 /drill hole














200 m3 /drill hole










2OQ m3/drill hole















2nd ESTIMATE
1400 m3 /drill hole














5OOO m3 /drill hole










5OOO m3 /drill hole

















COMMENTS

Analysis assumes no
knowledge of reposi-
tory before, during, or
after drilling. Ground-
water releases from
post-sealing leakage are
calculated in the text
Hit are, in general, less
significant than releases
to the surface.





Analysis assumes no
knowledge of reposi-
tory before, during, or
after drilling. Ground-
water releases from
post-Mating leakage are
calculated in the text
but are. in general, (ess
significant than releases
to the surface.





Analysis assumes no
knowledge of reposi-
tory before, during, or
after drilling. Groun-
watar releases from
post-sealing leakage are
calculated in the text
but are, in general, less
significant than releases
to the surface.





See Table D-11 for explanation of symbols and terms.

-------
                                                      TABLE D-5
                             SUMMARY OF FUTURE DRILLING FAILURE ELEMENT (CONTINUED)


MEDIUM

Shita













DoimSilt









Si
II
|i
II
P.D













P, D










NATURE
OF
MODEL

. Postulated determin-
istic drilling rate.
probabilistic for
hitting canister.










Postulated determin-
istic drilling rate,
probabilistic for
hitting canister.










RELEASE
MODE

A. Land surface
B. Groundwater












A. Land surface
B. Groundwater











DRIVING
FORCE

A. Materials raised
with drilling mud.
B. Thermally induced
convection and
gradient from
aquifer inter-
connection.







A. Materials railed
wim drilling mud.
B. Thermally induced
convection.










SOURCE
TERM

A. Part of canister
and fluid from
waste drift.
B. Uniform
concentration.









ft. Part of caniiter
and fluid from
waste drift.
1. Uniform
concentration.








PARAMETERS

1st ESTIMATE
No holes first century;
5 holes next century;
2 holes each subsequent
century. All holes to
ower aquifer.
Holes sealed with
permeability
K • lO^4 cm/sec.
u - 0.2. and
A - 0.1 m2.
Probability of hitting a
canister = 10~3 per hole.
with expected removal
of 15% contents.
Jo holes first century;
» holes next century;
2 holes every
subsequent century.
Holes sealed with
permeability
K - 10-4 cm/sec.
TI * 0.2, and
A - 0.1 m2.
Probability of hitting a
canister - 10-3 per hole.
with expected removal
of 15% contents.

2nd ESTIMATE
No holes first century:
50 holes next century;
5 holes each subsequent
century. All holes to
lower aquifer.
Holes sealed with
permeability
K = 10-3 cm/sec.
rj B 03. and
A = 0.1 m2.
Probability of hitting a
canister = 10"3 per hole.
with expected removal
of 15% contents.
No holes first century;
30 holes next century;
5 holes every
subsequent century.
Holes sealed with
permeability
K - 10-3 cm/sec.
n « 0.2. and
A - 0.1 m2.
Probability of hitting a
canister = 10~3 per hole.
with expected removal
of 15% contents.
FLUID TRANSPORTED
TO SURFACE

1st ESTIMATE
200 m3 /drill hole













0.04 m3 /drill hole










2nd ESTIMATE
5000 m3/drill hole













1300 m3/drill hole











COMMENTS

Analysis assumes no
knowledge of reposi-
tory before, during, or
attet drilling. Ground-
water releases from
post-sealing leakage are
calculated in the text
but are, in general, less
significant then releases
to the surface.





Analysis assumes no
knowledge of reposi-
tory before, during, or
after drilling. Ground-
water releases from
post-sealing leakage are
calculated in the text
but are, in general, less
significant then releases
to the surface.




See Table 0-11 for explanation of symbols and terms.

-------
                                                           TABLE D-6
                                      SUMMARY OF FAULT MOVEMENT FAILURE ELEMENT



MFDIUM


Beritlrci Sad







Gran Ke




Basalt



Shale




Dome Salt



i 9
«j y
£ £
3 z
at 5
2 *
0 K
Ix O
r







p




P



9




)





MATURF
OF
MOOEI


Aft , rohabtl
nt ncruTenre ol r^rw
fault 01 rrwvemer-i
alonq olrt fj»un




Annual probability
of occurrence ol new
fauh or movement
alonq old fault.


Annual probability
of occurrence of new
fault or movement
along old fault.


Annual probability
of occurrence of new
autt or movement
along old fault.


Annual probability
of occurrence of new
ault or movement
along old fault.




RELEASE
MODE


Grnu'Vlwaf*-







Groundwatet




! round water



round water




roundwater





DRIVING
FORCE


Thermally induced
convection effect
added to gradient
from aquife' intei
connection.




Thermally induced
convection.




Thermally induced
convection effect
added to gradient
from aquifer inter-
connection.


Thermally induced
convection effect
added to gradient
from aquifer inter-
connection.


Thermally induced
convection effect
added to gradient
from aquifer inter-
connection.




SOURCE
TERM


Canine* i in fault zone
broken and subteci to
leaching. Aceumu
lated dissolved radio-
nudtdes by time ol
faulting assumed
released through fault
'roin 100-m wde zone
around fault.
^anuteri tn fault /one
broken and subject to
each ing. Accumu-
ated dissolved radio
nuclides by time of
suiting assumed
released through fault
rom 100-m wide zone
around fault.
Caniners in fault zone
broken and subject to
leaching. Accumu-
ated dissolved radio-
udtdes by time of
aurting assumed
released through fault
rom lOOm wide zone
.wound fault.
Canisters in fault zone
broken and subject to
•aching. Accumu-
ated dissolved radio-
nuclides by time of
suiting assumed
treated through fault
rom 100-m wide tone
round fault.
Canisters in fault zone
broken and subject to
eaching. Accumu-
lated dissolved radio-
nuclkits by time of
aulting assumed
released through fault
rom 100-m wide zone
wound fault.



PARAMETERS

let ESTIMATE

H * 2 « 1 0"** events/vr
Flow path 1 m wide
WOO m long
K - 10'4cmAec
i) - 0.1
tOO canisters in fault
zone. 5% repository
in affected surrounding
zone.
X = 2 x lO^eventi/yr
Flow path 1 m wide
•000m long
K - 10-2cmfc.sc
T) - 0.1
100 caniners in fault
zone. 5% repository
n affected surrounding
zone.
X • 5 x 10~7 eveno/yi
Flow path 1 m wide
4000m long
K - 10'2 cm/sac
T) ~ 0.1
100 canisters in fault
zone. 5% repository
n affected surrounding
zone.
X = 2 K lO^evants/V'
Flow oath 1 m wide
4000m long
K - 10-4cnW*ec
n - 0.1
00 canisters in fault
zone. 5% repository
n affected surrounding
zone.
X • 3 K 10*7 events/yr
Plow path 1 m wide
4000m long
K - 10"4 cm/sac
it - 0.1
100 canisters in fault
zone. 5% repository
n affected surrounding
zone.

2nd ESTIMATE

\ = 4 « 10'7 events/y
Flow path 1 m wide
4000m long
K - 10* cm/sec
n ' 0.1
100 canisters in fault
zone. 5% repository
in affected surrounding
zone.
X = IO"5 events/yr
Flow path 1 m wide
4000m long
K - 10'2 cm/sec
T) •= 0.1
1OO canisters in fault
zone- 5% repository
in affected surrounding
X - 10'5events/yr
Flow path 1 m wide
4OOOmlong
K " lO^cmfcec
T) •= 0.1
100 caniners in fault
zone. 5% repository
in affected surrounding
zone.
A - 4 x IO*7 evena/yt
Flow path 1 m wide
4000m long
K - lO^cmAec
n • 0.1
100 canisters in fault
zone. 5% repository
in affected surrounding
_
X • 10"5aveira/yr
Flow path 1 m wkto
4000m long
K - 10-*anAec
i) • 0.1
100 caniitars in fault
zona. 5% repository
in affected surrounding
zone.

FLUID FLOM RATES FROM
REPOSITORY TO UPPER AQUIFER

In ESTIMATE

1 (yr«)

100
1000
10.000
Q (tl Im3/yrl

8.2 x 10
S3 x 10*
2.5 x IO4



t lyrtl

100
1000
10,000
6 (tl (m3/yrl

6.9 x 10°
4.4 x IO6
13. IO6

tlyrd
100
1000
10.000
6 (tl (m3/yrl
8.8 x IO6
7.6 X 106
3.2 x IO6

tlynl

100
1000
10,000
6 (tl (m3/yrl

8.8 x 10*
7.6 x 10*
3.2 x 10*

t(vnl
1100
1000
10,000
0 M (m3/yil
as x io4
6.0 x 104
23 x IO4


2nd ESTIMATE

tlynl

100
1000
10.000

6 III (m3/yrl

3.9 « IO5
3.8 x 10b
3.3 x 10b



llyr.)

100
1000
10,000
6 (tl (m3/yrl

6.9 x 10°
4.4 x IO6
1.9x IO6

t(ynl
100
1000
10,000
6 (tl 
-------
                                                        TABLE D-7
                                        SUMMARY OF VOLCANO FAILURE ELEMENT


MEDIUM

bddidSelt





Granite





""•"








|i
\\
11
Is
p





P





p









NATURE
OF
MODEL

Annual occurrence
probability.




Annual occurrence
probability.





Annual occurrence
probabHity.









RELEASE
MODE

Air and land
surface.




Air end land
surface.





Air and land
surface.









DRIVING
FORCE

Direct transport by
moving gates and
molten rock.




Direct transport by
moving gases and
molten rock.





Direct transport by
moving gases and
molten roc .








SOURCE
TERM

Fraction of repository
brought to surface.




Fraction of repository
brought to surface.





Fraction of repository
vought to surface.









PARAMETERS

let ESTIMATE
X = 1 x 10-10/yr
Fraction of repository
brought to surface is
0.4%, of which 1% is
in rcapirable form. 9%
consists of fine particles
which can be easily
dbpenad, and 90% is
reburred near the
surface.
X •= 1 x 10-lo/yr
Fraction of repository
brought to surface is
0.4%, of which 1% is
in rttpirabt* form, 9%
consists of fine particles
which can be easily
dispersed, and 90% i>
nburied near the
surface.
X » 6 x 10-10/yr
Fraction of repository
brought to surface is
Dj4%, of which 1% is
in rexpirabJe form, 9%
wnsitts of fine particles
which can be easily
cnspaned, and 90% is
eburied near the
urface.

2nd ESTIMATE
X •> 1 x 10-8/yr
Fraction of repository
brought to surface is
0.4%, of which 1%is
inr*aj>irabl«formc9%
consists of fine particles
which can be easily
dispersed, and 90% is
reburied near the
surface.
X - 1 x 10-«/vr
Fraction of repository
brought to surface is
0.4%, of which 1% is
in reqiirabte form, 9%
consists of fine panidas
which can be easily
dispersed, and 90% is
roburMd naar the
surface.
X • 1 x 10-8/yr
Fraction of repository
brought to surface is
0.4%. of which 1% is
in reapirablt form, 9%
consists of fine particles
which can be easily
dispersed, and 90% is
reburied near the
surface.

RELEASE MODELING STEPS

1st ESTIMATE
Direct release





Direct release





Direct release









2nd ESTIMATE
Direchretease





Deract release





Direct release










COMMENTS

First estimate based on
national average. Lower
rates could probably be
derived from additional
siting assumption, such
as location in East or
Midwest.



First estimate baaed on
national average. Lower
ram court probably be
derived from additional
siting assumption, such
as location in East or
Midwest.




Based on Columbia
Plateau basalts.








See Table D-11 for explanation of symbols and terms.

-------
                                                     TABLE D-7
                               SUMMARY OF VOLCANO FAILURE ELEMENT  (CONTINUED)


MEDIUM

9*.






Dem Sri!


El
55
J Z
< «
£8
p






p



NATURE
OF
MODEL

Annuxl occurrence
."""•WHY.





Annual occurrence
probability.



RELEASE
MODE

Air and (and
surface.





Air and tend
surface.



DRIVING
FORCE

Direct transport by
moving gases and





Direct transport by
moving gases anrj



SOURCE
TERM

Fraction of repository
brought to surface.





Fraction of repository
brought to surface.



PARAMETERS

lit ESTIMATE
X - 1 x iO-10/yr
Fraction of repository
brought to eurfaca is
0.4%. of which 1%is
inresptrablaform.9%
consists of fine particles
which can be easily
dispersed, and 30% Is
reburied near the
surface.
X - 1 x 10-10/yr
Fraction of repository
brought to surface is
0.4%, of which 1% is
in respiratote form, 9%
consists of fine particles
which can be eastty
disparted, and 90% Et
reburied near the
surface.

2nd ESTIMATE
A » 1 x 1Cr*/yr
Fraction of repository
brought to surface is
0.4%, of which 1%is
in respirable form. 9%
consists of fine particles
which can be easily
dispareed, and 9O% is
reburied near the
surface.
X *> 1 x 1C-10/yr
Fraction of repository
brought to surface is
0.4%. of which 1% is
in rvspirable form, 9%
consists of fine particles
which can be easily
reburied near the
surface.

RELEASE MODELING STEPS

1st ESTIMATE
Direct release






Direct release



2nd ESTIMATE
Direct release






Direct release




COMMENTS

First estimate bawd on
national avtrage. Lowei
rates could probably be
siting assumption, such
as location in East or




Estimates based on
national average. Could
be refined to e lower
value for salt dome
region. First and
second estimate* are the
standpoint of volcantsm,
the Gulf region shows
no variation.
See Table D-11 for explanation of symbols and terms.

-------
                                                    TABLE D-8
                                 SUMMARY OF IGNEOUS INTRUSIVE FAILURE ELEMENT



MEDIUM

Bedded Salt




Granite




Basalt




Shale



Dome Salt




||
j|
• I
< c
*£
p




p




f




P



p





NATURE
OF
MODEL

Annual probability
of occurrence.



Annual probability
of occurrence.



Annual probability
of occurrence.



Annual probability
of occurrence.



Annual probability
of occurrence.





RELEASE
MODE

Groundwater




Groundwater




Groundwater




Groundwater



Groundwater






DRIVING
FORCE

Physical traneport of
wastes by magma to
upper aquifer.


Physical transport of
wastes by magma to
upper aquifer.


Physical transport of
wettes by magma to
upper aquifer.


Physical transport of
wastes fay magma to
upper aquifer.


Physical transport of
we net by neigma to
upper aquifer.




SOURCE
TERM

Waste material inter-
sected by magma.



Waste material inter-
sccted by magma.



Wane material inter-
sected by magma.



Waste material inter-
sected by magma.



Waste materiel inter-
sected by magma.



PARAMETERS



let ESTIMATE
X •* 2 x 10*10
Dimensions of dike:
1 mn4 km.
intenecting 0.05%
waste inventory.
x-2,10-'0
Dimensions of dike:
Imx4km.
Intersecting OJK%
w-teirr-mory.
X-Sx10~9
Dimensions of dike:
1 m x4 km.
intersecting 0.05%
WM""WMt°'Y-
Dimensions of dike:
1 m x4 km.
intersecting 0.05%
waste inventory.
V • 3 X 10*
Dimensions of dike:
1 mx4km.
intenecting 0.06%
«m««n,ory.


2nd ESTIMATE
. H « 4 x 10*
Dimensions of dike:
1 m>4 km.
intersecting 0.05%
waste inventory.
x-to-7
Dimensions of dike:
1 mx4 km.
intersecting OjDS%
wane inventory.
X - 10'7
Dimensions of dike:
1 m x4 km.
intersecting 0.05%
waste inventory.
X - 4 x 10'9
Dimensions of dike:
1 mx4 km.
intersecting 0.05%
waste inventory.
k • 5 x 10"7
Dimensions of dike:
1 m it 4 km.
intenecting 0.05%
waste inventory.
RELEASE MODELING STEPS




Material moved to aquifer and subject to leaching.
Leech characteristics of weste (uim assumed
unchanged, elthough canisters would be removed.


Material moved to aquifer and subject to leaching.
Leach characteristics of wane form assumed
unchanged, although canisters would be removed.


Material moved to aquifer and subject to leaching.
Leach characteristics of waste form assumed
unchanged, although canisters would be removed.


Material moved to aquifer and subject to leaching.
Leach characteristics of wasu form assumed
unchanged, although canisters would be removed.


Materiel moved to aquifer and subject to leaching.
Leach characteristics of waste form assumed
unchanged, although canisters would be removed.


COMMENTS




Probabilities deter-
mined as 1% of values
for faulting.


Probabilities deter-
mined es1% of values
for faulting.


Probabilities deter-
mined as 1% of values
for faulting.


Probabilities denr-
minad as 1% of values
for faulting.


Probabilities deter-
mined as t% of values
for faulting.


See Table D-11 for explanation of symbols and terms.

-------
                                                     TABLE D-9
                                  SUMMARY OF METEORITE IMPACT FAILURE ELEMENT





MEDIUM

B«*fedSalt











Graniu










Basalt










£9

ii
J Z
SI
B UJ
Is
p











p










F













NATURE
OF
MODEL

Annual occurrence
probability.










Annual occurrence
probability.










Annual occurrence
probability.














RELEASE
MODE

A. Land surface
B. Groundwater










A. Land surface
B. Groundwater










A. Land surface
B. Groundwaler














DRIVING
FORCE

A. Impact
B. Thermal convection
added to aquifer
interconnection
gradient.







A. Impact
B. Thermal convec-
tion.









A. Impact
B. Thermal convec-
tion added to
aquifer inter-
connection
gradient.










SOURCE
TERM

A, 0,1% repository
inventory to
surface.
B. 20% cumulative
teached nu elides
released to ground-
water. Continued
leaching of broken
canisters in fracture
or breccia zone
U0%) and sur-
rounding caniners
(10%).
A. 0,1% repository
inventory to
surface.
B. 20% cumulative
leached nudides
released to ground-
water. Continued
leaching of broken
canisters in fracture
or breccia zone
(10%) and sur-
rounding canisters
M0°0),
A. 0.1% repository
inventory to
urface.
B. 2O°D cumulative
leached nuclides
released 10 ground-
water. Continued
leaching of broken
canister; in Iracture
or breccia zone
(10%l and sur-
rounding canisters
(10%).


PARAMETERS



In ESTIMATE
\ c 4 ,10-1 1/ r
A = 0.8 km2
K = 10-4 cm/see
i) = 0-2








A " Q£ km2
K - 10-4 cm/sec
TJ = 0.2








X = 4 k 10"1 Vyr
A - 0.8 km?
K - 10-4 cm/sec
1 - 0.2










2nd ESTIMATE
X •= 4n I0'11'vr
A « 0.8 km2
K - 10"4 cm/sec
ij - 0.2








X - 4x 10'11 >T
A - 0.8 km2
K n 10*4 cm 'sec
1 • 0.2








A = 4x 10'n/vr
A = 0 £ km2
K = 10-4 cm/sec
n r 0.2









FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER



1st ESTIMATE
t fyri) Q (tt (m3/yrl

100 1.6x10
7
1000 , 1.4 x 10
10,000 5.0 x 106






t (yn) 6 (t) (m3/vr)

10O 1.4 x 10'

1000 8.8 x 106
10,000 3.8 x 106






t (yre) Q (t) (m3/yr)

100 13x10

1000 1.5x10
10.000 6.3 x 106








2nd ESTIMATE
fyrs) ! 6 It) (m3/yr)

100 7^*10
7
10OO 7.6 xlO7
0,000 ; 6.7 x 107
1





t(yrj) j Q U) Im3/yrl

100 1.4 x 107
:
1000 ) 8.8 v 106
0,000 i 3£ v 106
i
1





t IVTJ) 6)0 (m3/yr)
7
100 7.9x10
7
1000 7.7 * 10
10,000 6.8 x 107










COMMENTS


Water availability may
ttverely limit flows
below levels calculated.









Water availability may
tevefely limit flows
below levels calculated.









Water availability may
«verely limit flows
below levels calculated.









See Table D-11 for explanation of symbols and terms.

-------
                                                    TABLE D-9
                           SUMMARY OF METEORITE IMPACT FAILURE ELEMENT (CONTINUED)




MEDIUM

Sruto









Dorm Silt








0 Si
C Jj
5z

0 *
ES
p









p










MATURE
OF
MODEL

Anmjri oecurranei
probability.








Annuol oecurranc*
problbilltv.











RELEASE
MODE

A. Landmrhoi
B. GroundMOr








A. Undiurrtc.
B. Groundwvtw











DRIVING
FORCE

A. Impact
B. Ttumul convvc-
tloniddidto
•quite Innr-
comwclion
gradton.





A. ImpKt
B. Tlmiinl comae i
HonKfcMto
•qurhv inur-
conmctlon










SOURCE
TERM

A. 0.1% npoBtorv
inmniury to
mirtac*.
laiahid nudidis
ratavMd to ground-
wittr. Continued
(•Khingolbralun
anlaun in Iractur*
orbracctezoM
IIOKIandoir-
<10W.
A. 0.1% rapoiUorv
invomorv to
lurlira.
' taodHdnudMii
ralMMd to ground-
MUr. CormiMd
teen ing olbrokm
onlmrt Hi franuni
orbnediioni
<10%l md «ur-
110%).

PARAMETERS



in ESTIMATE
X • 4>10-"/yr
A • o£ krn^
C • 1O-4 cm/we
* ' "






X • 4« 10-"/yr
A • OJkmJ
K - tO^cm/HC










2nd ESTIMATE
X - 4«10-"/yr
A • OJkm2
K • lO^ern/HC
n • OJ






X « 4 » 10-' '/»r
A « OJkmJ
«• O^
™ w^







FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER



IB ESTIMATE
tlynl

100
1000
10.000
Q (t) (m'/yrl

1 J « 107
1i « 10J
SJ . 10S





llyn)
100
1000
lOjDOO


6 It) Im'/ytl
,*,107
141 > Id7
5.0 . 10E









2nd ESTIMATE
tlynl

100
1000
10.000

6 It) Im3/vr)

T3 K 107
7.7 x 107
SJBxIO7





tlynl
100
1000
ioxno


6 It) In3/Vrl
4JIH107
3^.107
13 * 107









COMMENTS


Wmr vrailability mty
•Mraly HmH flows
biton towli afcubnd.







•mnly limit Itom
btloo Inrii akulrad
•mMhtMlbvfnctura
zontntdgtolMlt
domt.





See Table D-11 for explanation of symbols and terms.

-------
                                                                 TABLE D-10
                                                SUMMARY OF BRECCIA PIPE FAILURE ELEMENT
MEDIUM
Bedded Salt
Granite
Basalt
State
Dome Salt
PROBABILISTIC (PI
DETERMINISTIC ID)
P




NATURE
OF
MODEL
Annual occurrence
probability.
ItA.
MA.
N.A.
NJk.
RELEASE
MODE
Upper aquifer




DRIVING
FORCE
Thermally induced
convection and
aquifer interconnec-
tion.




SOURCE

Canisters in breccia
pipe assumed to be
broken and subject
10 leaching.




PARAMETERS
IB ESTIMATE
* - Ofort<500yn
X « lO-S/yr lor
t>500yrs
K - 10-2 cm/sec
n - 0.2
A » 3* lff»mZ




2nd ESTIMATE
» Ofort<500yrs
X lO-fyyr lor
tS*SOOyrs
K - 10-2 cm/see
1 - 0.2
A - 3 « I04 n>2




FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER
IX ESTIMATE
tlyrs)
BOO
1000
10.000
Q (m'/yrl
6.107
5,107
2x107




2nd ESTIMATE
tlynl
500
1000
10.000
0 (m3/yr)
3,108
3x108
3»108




COMMENTS
Limited availability of
water from lower
aquifer expected to
significantly restrict
flows beknv levels
calculated.




00
           Sae Table D-11 for explanation of symbols and terms.

-------
                               TABLE D-ll

       EXPLANATION OF SYMBOLS AND TERMS IN TABLES D-l THROUGH D-10

K  "hydraulic    conductivity,  also  referred  to   throughout  as  the
    permeability
t = time from repository closure
n = effective porosity of flow pathway
A. = cross-sectional area of flow pathway
p « cumulative probability of occurrence
^ - annual probability of occurrence
Q » volumetric flow rate
n » n , where n is a value of  time,  t,  refers  to  a  jump  in  the  value of
    a  dependent  variable (such  as  Q)  at t  =  n.    The value associated
    with  n  is  the  limiting value  as t approaches n  through  smaller
    values  (t  v  n);  the value associated with n  is the limiting value
    as t approaches n through  larger values (t > n).
Groundwater — Aquifer overlying the repository formation.
Salt  closure  or  creep  — Tendency  of salt  to  flow plastically  under
    pressure.
Thermally  induced convection — Water heated by wastes has lower density
    and is forced upward by buoyancy effect.
Aquifer interconnection  — A pathway connecting  aquifer  above and below
    repository  can  lead   to  hydraulic   imbalance  (gradient)  and
    corresponding flow.  This  flow has been modeled upward.
U-tube effect — When at least two points in upper aquifer,  at different
    hydraulic potentials, are  connected  to  repository and to each other
    through backfilled  tunnels,  flow can result.   The new  pathway acts
    as a high resistance in  parallel to the pathway through the aquifer
    connecting the two points.
Uniform  concentration  — Average  concentration  in  water in backfilled
    repository as a  result of gradual leaching from waste package.  May
    be limited either by leach rates or by solubility limits.
First  estimate  — A parameter estimate  assuming  that the site  exhibits
    favorable  characteristics  with  respect   to  the particular  breach
    mechanism in  question (i.e., tending  to reduce  the risk).
Second estimate  — A parameter estimate assuming that the site exhibits
    somewhat  less favorable characteristics  (than  first estimate) with
    respect to  the particular breach mechanism in question, although it
    may be highly favorable  with respect  to other factors.
                                     19

-------
is  a  glossary  of  terms  that  are  used   in  the  main  text,  not  just
specialized geologic or engineering terms, but  also  terms  that are used
in  the  introductory chapters before  they can  be discussed  at  length.
The remaining appendices generally discuss processes  that  take place in
or  near  the repository and  that affect  the  quantity of  radlonuclides
that might be released  in  the event  of a breach  of containment.
                                   20

-------
D-2.0  GUIDELINES AND METHOD OF APPROACH

D-2.1  GENERAL APPROACH

    There is wide current interest in the problem of estimating  how well
deep geologic  repositories  would be  able  to  contain radioactive  wastes.
Research  on  this  problem  is  being  carried  out   by  and  for   various
government  agencies  and  other  institutions  in the  United  States  and
abroad.  The principal government programs in  the United  States  are  the
following:
    1. Environmental Protection Agency.   The Agency is responsible  for
       setting  environmental  standards governing  the disposal  of
       radioactive wastes.   Tn  this  connection,  it wants to take  into
       account,  among  other   factors,  the  estimated  performance
       capabilities  of geologic  repositories, considered  conceptually
       rather  than on a design- or site-specific basis.
    2. Nuclear Regulatory Commission.  The Commission is responsible  for
       licensing a  geologic  repository for  high-level  radioactive
       wastes. Therefore, it is developing its own modeling  capabilities
       in order  both  to  determine  appropriate  regulatory  guidelines  and
       to evaluate license  applications.
    3. Department of Energy.   The  Department  is responsible  for  siting,
       constructing, obtaining  a license for, and operating  a system for
       high-level radioactive waste disposal; and the disposal option of
       a  deep  geologic  repository  is  being  pursued  as  its   favored
       approach.      Therefore, it is  developing  modeling  capabilities
       to  use both  in  decisions  regarding  design and  siting  and  in
       making  application for a license.
Because  of  these and  other programs,  there is  an  extensive literature
base  on  the potential performance of geologic  repositories  for  nuclear
wastes. Much of  this literature is cited throughout this report.
    There are  two important aspects to the performance evaluation:
    1.  The   identification  of  scenarios  or  failure  modes  that  would
       result  in  or  contribute  to   a breach  of  the  repository
       containment.
                                     21

-------
    2. The modeling  of  identified  scenarios  and  failure modes  in  order
       to assess their  impact  on  the  environment  or on human  health.
Various  approaches  to  the  first  aspect  have  been  vigorously  pursued,
examples of which include:
    1.  The  development  of  fault trees  and,  from  them,  event  chains.
       This  approach has  received  impetus  from  the  Reactor  Safety
       Study(2) and  from  the  wide  application  of similar techniques  in
       other safety analyses.
    2. The convening of panels of experts to list every  failure element
       or scenario they  could  reasonably  imagine,  and  then to refine  and
       combine such lists.
    3. The  Identification of  scenarios  that  would be extreme  and  whose
       consequences  would be  expected  to  bound  those  of  any  other
       scenarios, the latter of which would then not need to be defined
       in detail.
The present study drew extensively on this earlier work  in  failure mode
               (3—12}
identification,       rather  than developing  sets of potential failure
elements independently.
    With respect to  the modeling  of  failure  modes,  it was not  possible
to rely  heavily  on earlier  work.  There were two principal  reasons  for
this:
    1.  Other  modeling  efforts  have generally  been  carried  out  for
       different  purposes  than  those  of  the present  study.    In
       particular, models have been developed  with  specific  sites  in
       mind, or at least with  a view  to  eventual  application  to specific
       sites.     Therefore,   these  models  can   require  detailed
       site-specific data that may  not  even be  available   at  present.
       This  study had  to  be more  general   in  perspective  and  less
       demanding in data requirements.
    2. High priority was  attached to developing models  that  would  be as
       simple as possible.  Not only  would these  be  more informative  and
       understandable to  the users of this report, but they  would enable
       the  easier  identification  of  important  assumptions  and
       uncertainties.
In spite of the  limited  applicability  of the results of  other modeling
efforts  to  the  requirements of  Task   D,  it  has  been  possible  to
                                    22

-------
incorporate  some  of  the  modeling  parameters  derived  elsewhere  into
models developed  in  this  study.  Whenever possible,  the  results of the
Task D analysis  have been compared  or  contrasted  with  results obtained
el se where.
    It is important to emphasize at  the outset that it is not the intent
of  this  study  to draw any conclusions  about  the  safety  of the disposal
of  radioactive wastes  in  geologic repositories.   Such  responsibilities
fall  to  the  regulatory  agencies  and,  more  generally,  to the  public
through  their elected government  officials.   The  purpose  of this study,
and  in  particular  Task   D,   is   to provide  modeling  techniques  and
calculational  results  that  have  been requested  as  input  for  the
regulatory  decision-making   process.    It  should  be  noted  that
uncertainties  enter  the  analysis  at every phase,  from  specific  input
data, to the validity of modeling techniques,  to the overall question of
whether  something  important  might  have been  left  out.   Tt  is  not
possible  to prove  rigorously  the   correctness or  completeness of  the
results.   However,  it  would  be  unusual  to  find  any serious  decision
process  founded on complete and totally certain information.  Therefore,
in  this  report  the intention  has been  simply to  explain  the  analytical
methods by which  the results were obtained,  to provide the rationale for
the  choice  of models  and parameters,  and  to relate these,  as  far  as
possible,  to  similar work being carried out  by other  groups.   It  is
largely  through  the peer  review process  that  studies  such as  this
receive valuable  feedback  that  can enhance the accuracy  and precision of
the  results.   An early draft  report on Task  D received  a  wide review,
which has been very valuable in the  preparation of this  report.

D-2.2  SPECIFIC GUIDELINES

    In developing a modeling strategy for nuclear waste  repositories, it
is necessary to determine  initially  the time period for  which the models
should apply.   Various time  periods have occasionally been  suggested,
ranging  from  relatively short  ones,  such as  300 years,  to rather long
ones,  such  as  10 million years.    Part  of  the  determination  of time
frames depends  on the  nature  of  the wastes  that  would  be placed  in a
repository.  Active and predominant  fission products, such  as cesium-137
                                    23

-------
and  strontium-90,  have  half-lives  on  the  order  of 30 years,  so that
after  a  few hundred  years  they will  have  decayed to  relatively l°w
levels.  Transuranic  elements,  as well as  some  fission products, such as
technetium-99,  have much longer half-lives.   Tf  spent  reactor  fuel is
placed  in  a  repository,  there  would  be  a higher proportion  of the
long-lived  elements.   The  Task A Report  discusses in greater detail how
these activity  levels  vary with  time.
    The regulatory philosophy  in evidence  in the United States today on
the subject of hazardous waste  disposal is  in  a state of flux, largely
because of  increased  quantities  of wastes  and a greater awareness  of the
pitfalls of past practice.  Nevertheless,  even new regulations  make no
attempt to  guarantee  the complete integrity  of  the  containment system in
perpetuity.  Time  periods of  30 to  100  years are generally the longest
under consideration even though many hazardous  materials do not decay or
degrade with time.   In  the case of nuclear waste repositories,   it was
decided  Jointly  by  Arthur  D.  Little,   Inc.,  and  EPA  to develop
performance models  for a period  of 10,000  years.   This was thought  to be
a  conservatively  long  time period  for  repository evaluation,  in the
sense that  even a shorter  period might be  sufficient and consistent with
regulatory philosophy utilized  in other areas.   The 10,000-year   period
allows for  the  modeling not only of direct releases  to the biosphere,
but  also of releases through  groundwater  pathways, which  can  require
very  long  times  before  harmful effects might  occur.   If  the modeling
effort were carried  even  further  into  the  future,  the  significance of
the  results  would  decrease   accordingly  because  so many factors
(available technology, population characteristics,  future medical
capabilities,  dominant  health  concerns,  etc.) might  be changed.   In
fact, the past  10,000 years  span the development of all important  human
civilizations,  and  it  does  not  seem   necessary  to carry  future
projections into longer  periods than this.
    A  second   guideline  for  this study  was  that  the  performance
evaluation  period  should  begin at  the  time the  repository  is sealed.
During the  operational  stage  of the  repository,  there may  exist some
risk of the release  of  radionuclides.   For  example,  an accident  could
                                  24

-------
occur in transporting or emplacing a waste canister.  Risks of this type
would be addressed by other regulations governing fuel cycle facilities,
but they are not addressed here.
    A  third  guideline  relates to  the degree  of  future  institutional
control  or human  knowledge  of the  repository.    Consistent with  EPA
direction,  no  control  of  the  site  after  100  years  from  repository
sealing has been assumed.   In  this  study,  this  has been taken to imply
even  the  loss of  knowledge  that  a  repository exists  on the  site.   Up
until  this  100-year  period  has  elapsed,  however,  full  institutional
control  of  the  site  has  been assumed  to  be   capable of  preventing
intrusions that  could breach  the containment system.
    The  last  specific guideline has been referred  to  earlier,  namely,
that  this  study is directed  to  the  concept  of  geologic  repositories
rather  than  to  repositories  at specific sites  or with specific designs.
Thus  it has  been  necessary  to abstract  from the  literature a  set  of
engineering  and  geologic  assumptions that represent so-called "generic"
repositories.   Because  the  question  of the  estimation and  importance of
uncertainties  inevitably enters modeling  efforts  such  as  this,  it  is
important  to note  that in the  case of  generic repositories this question
takes  an unusual  form.   Tt is not  meaningful  to  assess the  degree  of
certainty  one attaches to a parameter  for a generic repository, since by
definition  a  generic  repository  is  hypothetical  and  is  defined  by
whatever  parameters  have  been  specified.    Rather,   the  uncertainty
question  is transformed  into   the question  of  the variability  of real
sites vis-a-vis  the  parameter values used in the generic model.   In the
case  of  expected significant variability  among real  sites, two estimates
for  parameters  have  been  given  in the  generic description,  one
correspond ing  to rather  favorable  conditions (i.e., supportive of
containment)  and  another  that would  not  appear  to  be  so   favorable.
These  are  referred  to  as   the   "first"   and  "second"   estimates,
respectively.  They are discussed in Section D-2.6.3.

D-2.3  SELECTION AND  CHARACTERIZATION  OF  GENERIC  GEOLOGIES

    Based  on the site selection programs  of  the Department of  Energy and
the  supporting  research work  reported  in the  literature,  the  following

                                   25

-------
five geologic  host media  were chosen  for detailed  treatment  in  this
study:
    •  bedded salt
    •  granite
    •  basalt
    •  shale
    •  dome salt
There  are   other  rock  types   that  have  been  or  are  being  seriously
considered   for repositories,  among  which  are  welded  volcanic  tuff,
desert  alluvium, anhydrite, and seabed  sediments.          Nevertheless,
the  media   chosen  span  a  wide  range  of  geologic  structure  and  rock
properties,  and  an  analysis  based   on  them  is  believed   to  be
representative of  the  performance  capabilities of  geologic repositories
in general.  The subsequent paragraphs contain  discussions of the chosen
rock types  and descriptions of the associated geologies  assumed  in this
study.    Naturally,  there  can  be  wide variability  in  the  geologic
parameters associated with a given  type  of rock.

D-2.3.1  Bedded Salt

    Bedded  salt has been  prominently mentioned  as  a possible  nuclear
waste  repository   host  rock  ever  since  a  committee of  the  National
Academy  of  Sciences  proposed  that   waste  be buried  in  deep,  stable
geologic media.      Perhaps more research has  gone into determining the
suitability   of   salt   for  this   purpose   than  for   any   other
lithology.  >  >  »  »-     jn  Germany,  some  low-level  radioactive waste
                                                 (21)
has  already been deposited  in  unused salt mines.      This  interest in
salt is  the result of  some  of  its  unique properties, in addition to its
common  occurrence  in stable formations  at  depths  being  considered  for
 repositories  (200 ra to 1000 m)  .
     Salt  is  very  soluble.   However,   it  behaves  plastically  under
 pressure,  thereby  tending  to  creep back  into voids  and  cracks  and seal
 itself against the movement of  water.   This accounts  for  the  lack of
 water   in  most salt  mines.   Salt  is  also a  relatively good  thermal
 conductor  and thus has  the  ability  to  dissipate  the heat  generated by
                                   26

-------
the wastes.   The  sedimentary  sequences containing salt beds  generally
contain aquifers both above and below the salt.
    Salt  itself  is  frequently mined,  and   there  may  be  associated
deposits of  other minerals or  oil  and  gas.   However, because  massive
salt deposits are numerous, locations can probably be  found with minimal
economic value and with a range of other desirable characteristics.
    A map  of prominent salt deposits  in the United States is  shown  in
Figure D-i.   The generic  bedded salt  stratigraphy  adopted  for modeling
purposes is shown in Figure D-2.  It is implicit that  the  salt  formation
is  in  a stable  basin,  and  that the strata  are relatively uniform  and
continuous  beyond  the repository.   For  hydrologic modeling, both
aquifers are assumed to have identical horizontal gradients of 0.002  and
0.02 for  first  and  second  estimates,  respectively.   An average  upward
vertical  gradient  for  any connection  between aquifers  is assumed  to
exist  and  to  have  the  values  0.01  and  0.5  for   first  and  second
estimates, respectively.   (Note that a downward  gradient  may  exist  and
would,  in  general,  represent  a  more  favorable  condition  since  any
leakage  would  then be  to  strata  at  greater  depths.    However,  for
conservatism,  an upward  gradient  has  been  assumed even  in   the  first
estimate  case.)    The salt   itself   is  assumed  to be  essentially
                                 (22 23 24)
impermeable  to the  flow of water.   '  '

D-2.3.2  Granite

    Granite,  or  some  similar  monolithic crystalline  rock, is  another
important host rock.  Canadian and Swedish studies of granitic rock as a
storage medium have  provided some insight and details  into the nature of
                         O S 76 ^
this candidate  material.    '      Excavations  in  granite have  been used
for storage and military purposes.
    Granite  is an assemblage of minerals forming a  rigid and essentially
insoluble rock.   It is  relatively  strong and does not flow plastically;
thus, cracks  can remain open  to  migrating   fluids  although some become
filled with clay or  other materials.  It does not conduct heat well, but
it  does have  a high  heat  capacity.   In  addition,   the  water passing
through granite  is generally less corrosive than the brines and bitterns
associated with  salt.  Because  it  is  an  Intrusive,   and  therefore  not

                                   27

-------
oo
                                                                            ARKO BASIN
                                                                                 I
                                                                          PALO DURO BASIN
      Source: Adapted from U.S. Department of Energy, Draft Environmental Impact Statement: Management of
            Commercially Generated Radioactive Waste,  Volume I, April 1979.
                                                    FIGURE D-1  ROCK SALT DEPOSITS IN THE UNITED STATES

-------
                                                          Surface
       Surface
       Deposits
       Salt
-Repository
^-_-_- Shale
~//           ^-*.~t                            ^*- -
x// Basement
/// Complex
330 Meters
360 Meters
410 Meters
460 Meters
510 Meters
560 Meters
590 Meters
        FIGURE D-2   REPOSITORY IN BEDDED SALT
                         29

-------
stratified,  granite  is  modeled without  an  underlying  aquifer.   This
limits the mechanisms for water flow through the repository.
    Many areas of  the  country  have  granite  or similar rocks at suitable
depths for  a repository.   Occasionally,  vein minerals,  pegmatites,  or
quarry stone make granite economically important, but  the  vast expanse
of crystalline rocks suggests  that many potential site locations remain.
    A map of prominent granitic formations is shown in Figure D-3a.  The
generic granite geology adopted for modeling purposes is shown in Figure
D-4.   The  aquifer is assumed  to have  horizontal  gradients  of 0.002 and
0.02   for   first  and  second  estimates,  respectively.    Reported
permeability  values  for  granite  vary  over  a  wide  range  of  test
conditions and may be as  low as 4  x 10    cm/sec.    '        Fluid flow
is governed by fracture systems.

D-2.3,3  Basalt

    Basalt  is  another  igneous  rock  that  is  being  considered  as  a
                  (19 31)
repository medium.   '     It shares with granite many properties common
to  igneous  rocks.   It  is strong,  rigid, insoluble,  and has  a complex
mineralogy.
    The  extensive  flow basalts  being  investigated  are  unlike  other
igneous rocks in a number of important ways.  Because these basalts have
formed as  a series  of layers  over a long  period  of  time,  there  are
sedimentary  interbeds  and  other   permeable  zones  that  can  serve  as
aquifers, and  these  aquifers  would  be expected  to  exist  both above and
below any basalt  flow  in  which the  repository would be located.  Basalt
characteristically  breaks  into slender  columns  as it  cools, producing
vertical joints.   However,  weathering products  of the  rock  often fill
these cracks.  Basalt  is  rarely  associated  with mineral  resources,  and
its most common economic use is as fill material.
    The principal  flow basalts  that  are  being investigated  for possible
repository siting are  limited  to  the northwestern United States, in the
states of Washington, Oregon, and Idaho.  (See Figure D-3.)  The generic
basalt stratigraphy  assumed  in this study is  shown  in  Figure D-5.  The
hydraulic gradients  within  and between  aquifers are assumed  to be the
same as those  specified  earlier  for bedded  salt.  Reported permeability

                                    30

-------
                                             PRECAMBRIAN

                                            SHIELDGRANITES NORTHERN
                                                           (MARITIME)
                                                          APPALACHIAN.,
                                                                         CENTRAL
                                                                       APPALACHIANS
                                                                  SOUTHERN
                                                                APPALACHIANS
                                 a. Granitic Rock
               COLUMBIA RIVER BASALT
                                               KEWEENAWAN LAVAS
                                                                        TRIASSIC LAVAS
                         b. Potential Repository Basalts

Source:  U.S. Department of Energy, Draft Environmental Impact Statement: Management of
       Commercially Generated Radioactive Watte, Volume 1, April 1979.


       FIGURE D-3  CRYSTALLINE FORMATIONS IN THE UNITED STATES


                                      31

-------
                                                              Surface
      Surface
      Deposits
                             .,..,..--•.     -.-'j-....U-.-I.T- .-i..u     200 Meters
y^ Aquifer fyi^&®$3W$^^ ^Z&X M •>-^   230 Meters
                                                              460 Meters
          FIGURE D-4   REPOSITORY IN GRANITE
                              32

-------
                                                  -Surface
     Surface

     Deposits
 -.7 - •-. .   ..  •.-..y..---,-.T*-VTBS»-v-^>f !*•.•'. .ragr'n-p- •„.-.. ...TT7~-.T-T..-;-?a-W--T.TT^T,;-...^ www mCtCrS
fotf:*y^ y^y r^^^^jtyiy yy^^ 360 meter$



/£.?<*?'?^ ^K'';^^'^^r/;"v  • -'^\
C^~^' ~'^-~, v'\- ' '' 7«i^^^^^^^»'Rep_p^itoryi\ .,X-^\^_X460 meters


\'f i7^ ^r^ ,V^'"1 feW •:';! l^^iv, '^

A-^i^-/->;:; ^'-'':'-^-^;'>vi7-'''r^l' .'-^'••>rn

^pj^ Aquifer ^^ja^^'^^l^T^W^^g^M^BI ^ m6terS

 V^Vr^;^-r^ v- :l/^J^'^'^'^^    meter$

\^ —  D.e.if.' --v/^"^\.'\-'  / "'-y  x s~\-x  ~"~^\'— r/1 ^ — ~~ t''•t1'
','1 J^^JvV '_' ,,\- -, ^ ', \ -x / \/_\''_v^x_-x«'-/NI.'>/_V  x '
' •> \ "". s"| ^~/. ^ " \" S ^ \' I - \~ ^ ' v-~/ N~l ' ""/ N J" I I X ~ t x' " •' - ' .
 i <^ N—  'iv ix ~xi/\~/^/-x\7-\"''' ^s r \ ^i"_"\ ~ /" ' -^ i —
        FIGURE 0-5   REPOSITORY IN BASALT
                            33

-------
values  for  basalt  range as  low as  10     cm/sec, but  there is  a  wide
                                                          (19,31,32,33)
range due to variable rock properties and  test conditions.
D-2.3.4  Shale

    Argillites, siltstones, and shales are the most common find extensive
sedimentary rocks. ^34^   These  clay-rich  rocks are often  found  in thick
deposits, and they are often nearly impermeable.   Some  shales exhibit a
plastic  behavior  similar to that  of  salt, but  clay minerals  have  the
advantage over  salt  that they  are  essentially insoluble.   There  is a
very wide range in the properties of shales.
    Clay minerals have a number of properties that may be  important to
waste  containment.   Several  clays will  absorb water  into  their
structures,  swelling   in  the  process  and   sealing   the   water
passageways.   '    Similarly,   clays  can  adsorb  chemicals,  including
                                                                    (36)
radionuclides, restricting  or  essentially stopping  their movement.
However, as  they  can hydrate,   many clay minerals can be dehydrated by
heating.   This process  may  change both  their  chemical  and  mechanical
properties.
    Argillaceous (clay-containing) deposits have  a variety  of  economic
uses.  Their abundance,  however, suggests  that many  potential sites are
available where economic  and other social impacts  would  be minimal.
    A map  of  shales  and  related  argillaceous deposits  in  the  United
States is given in Figure D-6.   The generic  shale  stratigraphy adopted
for modeling purposes  is shown  in  Figure D-7.   It is  assumed  that  the
shale being modeled  is highly  indurated, which would aid the stability
of a mine while perhaps  increasing  the potential  for  fluid flow through
fractures.   While  some  shales  are nearly impermeable  to  the  flow of
water,  the  hard  shale  in  the model  is  assumed  to  have  hydrologic
properties  similar  to  those of  basalt.   Assumptions about  the aquifer
hydraulic potentials are taken  to  be  the  same as  in  the  case of bedded
salt  and basalt.    Reported  shale  permeabilities  cover  a very wide
range.(12,19,22,29,37,38,39)
                                   34

-------
                                                                      MICHIGAN
                                                                       BASIN >
OJ
                        WEST
                        COAST
                        CLAYS
                      BASINS CONTAINING
                      ARGILLACEOUS FORMATIONS
                                                                                                               TRIASSIC
                                                                                                               BASINS
            Source: U.S. Department of Energy, Draft Environmental Impact Statement: Management
                   of Commercially Generated Radioactive Waste, Volume 1, April 1979.
                                            FIGURE D-6   ARGILLACEOUS FORMATIONS IN THE UNITED STATES

-------
                                                      Surface
Surface

Deposits
         ________ .....   .   .... ..... ______ .,..•.. ...... ......  - - i.. ji. i j.-i i: • ij- 330 meters
                                                      36Q meter$
                                     Repository '-iHH?: 460 meters
        ^^Pgfe^P^l?^^:^i^^^

       FIGURE 0-7   REPOSITORY IN SHALE
                           36

-------
D-2.3.5  T)0me Salt

    Many salt deposits are not bedded, but are formations that have been
forced  up  through  overlying  rocks  from  original beds  at  considerable
depths.   These  domes  or  stacks  of  salt  are cbmposed  of  fairly
homogeneous  halite and  are  generally devoid of interbeds  or  similar
features found in bedded salt.  Typically, a salt dome will be roughly a
kilometer  in  diameter  and  capped  with  a  blanket  of  less  soluble
      ,    (40,41)
evaporites.
    Because  a  dome is injected  into  the  overlying  rock, the latter is
often shattered and disrupted  with  prevalent joints  and  fractures.  The
salt  itself  may come  very  near to,  or even  reach, the  surface;  but the
                                                                     (42)
source  of  the  salt column may extend  to  depths  near 10 kilometers.
The  geometry  of  a dome  implies  that an  aquifer  directly below the
repository will not exist.  However,  the  fracturing of the adjacent rock
indicates  that the  salt  will  be  in  contact with  groundwater  in adjacent
aquifers.    These  and other  differences  between  bedded  and dome salt
deposits indicate  that each deserves  a separate analysis.  As with
bedded  salt  deposits, domes are  frequently associated with oil, gas, and
various mineral resources.
    Salt domes are found  in  several states in  the  South,   as  shown in
Figure  D-l.    The  generic dome  salt stratigraphy adopted  for  modeling
purposes is  shown  in  Figure  D-8.   The hydraulic  conditions  in the  upper
aquifer  are assumed  to  be  the  same  as  in all  the other  cases.   For
certain  failure  elements, the lower aquifer,  while not  directly below
the  repository,  is relevant.   The vertical hydraulic  gradients  upward
between  it and the  upper aquifer have the values 0.01 and 0.2 for  first
and  second  estimates  respectively.    The  salt itself is assumed  to be
                                             / »j o  *)i  O/ \
essentially  impermeable  to  the flow of water.    '  '

D-2.4   REPOSITORY  ASSUMPTIONS

    Conceptual repository  designs have been discussed  in the Task A and
B  Reports  and continue  to be modified  and refined in  studies  for the
                      (19 43)
Department  of  Energy.   '      Based  on  this work, the parameters given
in  Table D-12 have been used  in this report.   It should be noted  that
                                   37

-------
                                                   Surface
Surface
Deposits
Country /"\
Rock  .TV. N  ,
   /  /l*x Caprock
 *   Six
          x^\  \
          ;-/\\  x
Repository  „ "I •   .      460 Meters
          ,*f ' \N.
             l\\

                      560 meters
                      590 meters
     FIGURE D-8   REPOSITORY IN SALT DOME
                      38

-------
                       TABLE D-12
NOMINAL REPOSITORY PARAMETERS USED FOR MODEL CALCULATIONS
          Depth of repository                    460 m

          Areal dimensions                   2 km x 4 km

          Number of canisters                 35,000

          Number of waste drifts                 350

          Canisters per waste drift              100

          Length of waste drift                  500 m

          Canister spacing                         5 m

          Total mined volume                   10  m

          Percent of total volume used
          for waste drifts                        90%
                           39

-------
actual  designs  might  vary considerably  from  the  values  given.   For
example, a repository  in an average-size  salt  dome  could  not occupy the
horizontal  area  specified  in  the  table.    Such  differences  are  not
important  for  the  purposes  of  the  present performance  model.   Other
parameters specific to individual  model calculations  will  be introduced
as necessary in later sections of this report.

D-2.5  IDENTIFICATION OF FAILURE MECHANISMS

    The  principal  purpose  of   Task D  is   to   identify  potential
breach-of-containment mechanisms  for  geologic  repositories  and  to
characterize them  quantitatively.  A review of the  literature indicated
a wide range of potential  failure  mechanisms that have been identified.
These  were  evaluated  and  compared to   determine  their  relative
importance;  and,  as a result,  ten were selected  for  detailed modeling.
These  are  shown   in  Table D-13.    It is  believed  that  a  repository
performance assessment based  on these mechanisms includes  the  dominant
contributors to risk and covers  the  range  from likely events with small
consequences to very unlikely events  with  large consequences.   A number
of  events  and  processes  not  chosen for  detailed  modeling  are  also
discussed  later  in  this  report.  Many  of these  are relatively  slow
geologic  processes  that  would  not   be  expected   to have  significant
effects over the 10,000-year time frame chosen  for this study.

D-2.6  CONCEPTUAL FRAMEWORK FOR QUANTITATIVE ANALYSIS

    The  quantitative  evaluation  of  potential  breach-of-containment
mechanisms includes two principal aspects:
    1.  Estimates of the likelihood or probability of  occurrence of
        various  mechanisms.
    2.  Estimates of the consequences of such mechanisms.
Naturally,  it  is  important  to  take  into account  interactions  between
various mechanisms when these appear  to be  capable  of increasing either
their likelihood or their consequences.
                                 40

-------
                                 TABLE D-13
              FAILURE ELEMENTS CHOSEN FOR DETAILED MODELING
TECHNOLOGICAL
HUMAN INTRUSION
NATURAL
                  Flow through bulk rock with altered permeability
                  Shaft seal failure
                  Borehole seal  failure
                  Undetected boreholes
                  Future drilling
                  Fault movement
                  Volcanoes
                  Igneous  intrusives
                  Meteorites
                  Breccia  pipes

-------
D-2.6.1  Probabilities

    It  is  inevitable that  probabilistic  considerations enter  into  any
performance  assessment  program  for  repositories, even  if they  do  not
enter  explicitly.   This  is true  even  for the approach  using  so-called
"worst  case  scenarios",  since the judgment  is made therein  that cases
worse  than  those treated  have  negligible probabilities of  occurrence.
Despite  the  ubiquitous  necessity of  at  least qualitative judgments  on
likelihoods and  probabilities,•efforts to systematize  and  quantify such
judgments are difficult  to carry out  and  often lacking  in precedent.
    Probabilities may be  interpreted  in  different senses, according  to
various schools of thought.      They may, for example, be  used  to refer
to  the long-term frequency of  occurrence of  certain   events.    On  the
other  hand,  they may be  taken  as subjective measures  of belief  that  a
certain event  will occur.    Statistical   analyses  usually  derive
probabilities  from  data  on frequency  of occurrence;  decision  analysis
and strategic planning often deal more with  probabilities as  measures  of
belief.  In  these and other interpretations of probabilities,  the same
mathematical  formulations  apply,  and   in  areas  where  the  different
interpretations  overlap,  the results  will ordinarily be consistent.  The
approach of the  present  study  was strictly pragmatic.  It was desired  to
use  the best  information  available  to   clarify  and  improve  otherwise
qualitative judgments, even though the result  might  fall  somewhat short
of  a  mathematically  axiomatized   probability theory.   Thus the
probabilities  assigned to  various breach-of-containment mechanisms had
to be  derived  on an  ad hoc basis.   Some result  from  crude  statistical
analyses, some from  simple  models with statistical  components,  and some
primarily from the judgment of the authors, based  on personal  experience
and a  review of  the  literature.   In  each  case  the derivation  of  the
probabilities has been explained.

D-2.6.2  Consequences

    The ultimate consequences  of concern  in  evaluating  repository
performance capabilities  are  adverse effects  on  the health of  present
                                   42

-------
and future  generations.   The  estimation  of such  consequences requires
several steps:
    1. The physical characterization of a breach of containment
       mechanism.
    2. The characterization of a source term, I.e., the radionucllde
       inventory affected by the breach.
    3. The identification and quantification of driving forces that
       would tend to move the radionuclides out of the repository.
    4. The modeling of the actual leaching of radionuclides and their
       transport through groundwater systems or through surface
       pathways.
    5. The calculation of doses to  individuals and populations.
    6. The estimation of the health effects of the calculated doses.
The  scope  of Task  T)  only pertains to  the  first  three of  these  steps.
The last  three  are  being modeled  by the EPA, based on methods described
in Task C and elsewhere.
    The  physical   characterization  of  breach  mechanisms  generally
involves considerations  such as size, depth, location, permeability, and
porosity of  the  resulting pathway.  Not  all  of these apply to all cases
since  the  mechanisms vary widely.   The characterization of  the  source
term  generally  refers to  the  extent  of  the repository subject  to the
effects of the breach.   For example, one waste drift might be  subject to
leaching  as  the  result of  a borehole  passing  through  it.   The term
"uniform concentration"  is frequently used in the  sequel to refer to the
average  concentration of radionuclides in the waste  drifts  as a result
of canister  degradation  and  leaching  of  the waste form.  Parameters and
models  relating to  corrosion  and  leaching  have been  discussed  in the
reports of Tasks B  and C. (Appendix D-VIII of this report also discusses
some  aspects  of  canister performance.)
    Driving  forces  that  enter into various release calculations  include
direct  physical transport  and transport  in groundwater.   Groundwater
flows  can  be  driven by  a  number of  factors  that  affect  hydraulic
potentials,  such as artesian conditions  in  confined aquifers, buoyancy
forces resulting from density differences, and others.  Several of  these
are discussed in the  appendices,  the principal results  being  employed  in
the main text.

                                    43

-------
    A prerequisite for  a  number  of the  release  mechanisms is  that  the
repository  and  the  surrounding  rock  return  to  a  saturated  condition
after the perturbation caused  by  the  operational  stage,  during  which any
water in  the  surrounding  rock would  tend  to flow  into the cavity  and
then  be  pumped  out.   Resaturation   times  for  all  cases  have  been
estimated in Appendix D-II.   For all  but the two repositories  in salt,
these times are not  judged  to be significant  enough to warrant  further
consideration.   However, since salt tends to flow plastically  and close
up void  spaces, the time to  establish  resaturation is closely  related to
the  total  quantity  of  water  present  under  that condition.   For  this
reason,   resaturation is  considered   in connection  with  a  number  of
release  mechanisms  in the  salt repositories.

D-2.6.3   Uncertainty.and Variability,

    The   subject  of uncertainty  analysis has  been  briefly referred  to
earlier   (Section   D-2.1),  where  it   was pointed  out  that  the  basic
question  is one   of  variability, namely,  to  what  extent  might  the
properties of  real  sites  vary  from  those  used  in  the  generic
description.    When  significant  variability  is  identified,  it  is
incorporated into  the  analysis  by  the use  of   so-called  "first"  and
"second" estimates, defined  as follows:
First Estimate  -  a  parameter estimate  assuming  that  the  site  exhibits
                  favorable   characteristics  with  respect  to   the
                  particular  breach mechanism  in  question  (i.e.,  tending
                  to reduce  the  risk) .
Second Estimate - a parameter  estimate assuming  that the site  exhibits
                  somewhat less  favorable  characteristics with  respect
                  to  the  particular  breach mechanism  in  question,
                  although it may  be  highly  favorable  with respect  to
                  other factors.
In both  cases,  models and  approximations have been  chosen  to  err  on the
conservative side, i.e.,  tending to  overestimate the likelihood  or  the
consequences of the  events.    It  is  believed   that,  for  each  first
estimate, sites will be able to  be  identified  where the  corresponding
property  is at least  as  good as  the  estimate.   Many  more  sites  can

                                   44

-------
probably be found where the property is better than the second estimate.
The use  of  relatively simple models in  the report,  rather than complex
computerized ones, facilitates the determination of the sensitivities of
results  to the various input parameters and assumptions.
    It is important  to emphasize  that  the primary emphasis  in  this study
has  been on  rough  order-of-magnitude  estimates.    Therefore specific
details  that could  only  slightly perturb the results are often ignored.
At the same time, a  number of the calculations are reported with greater
precision than  the  input  data or the goals justify.   This has been done
simply  to aid  readers who wish  to  retrace the calculations in order to
test  their understanding  of the  methods  employed.
                                       45

-------
D-3.0  TECHNOLOGICAL FAILURE ELEMENTS

    The failure elements considered in this chapter correspond either to
the degradation or failure of engineered systems or to the effect of the
repository on  the host geologic  formation.   Those  elements  chosen for
detailed modeling are all capable of providing pathways for the movement
of radionuclides  from the repository to  the aquifer system.  Failures in
some  individual  components,  such as waste  forms,  are briefly discussed
in Section D-3.5.

D-3.1  FLOW THROUGH BULK ROCK

D-3.1.1  Summary

    A  major  consideration  in  both   the  design  and  the  performance
assessment  of  a repository  is  the   fact  that high-level  radioactive
wastes  generate  considerable  quantities  of heat.  This  heat  can affect
both  engineered  barriers to  waste migration,  such  as waste  forms and
canisters, and  the  surrounding  rock.   The present model  deals with the
latter  aspect.
    In  particular, temperature changes cause stress changes in the  rock,
which can  alter  its  hydraulic  conductivity.   Examples of mechanisms for
this alteration include additional fracturing, movement along fractures,
or changes in the dimens'ions of fractures or pores.   For repositories in
salt, either  bedded  or  domed,  probabilistic calculations  were  carried
out,  based  on  a  statistical  characterization  of   spatially  varying
materials properties, to determine the probability of  a fracture pathway
developing through  the  salt.  For  the  non-salt  repositories — granite,
basalt,  and  shale —  a  simple deterministic  model  was  used  for the
variation of the hydraulic conductivity  as a function of time.
    A summary  of the analysis is  given  in Table D-14,  and  the details
follow  in subsequent sections.
                                   47

-------
                                                     TABLE D-14
                                  SUMMARY OF FLOW THROUGH BULK ROCK FAILURE ELEMENT
MEDIUM
BaddodS.lt
Granite
Baeatt
State
Dora Silt
PROBABILISTIC (PI
DETERMINISTIC IOI
P
D
0
0
P
NATURE
OF
MOD€L
Cumulative occur-
rence probability
Change in permea-
peek
Clung* in permea-
bility after thermal
pee*
Change In painiM
Witty after thermal
P-k
Cumulative occur-
rence probability
RELEASE
MODE
Groundnater
GroundMrater
Groundiwter
Groundwater
Groundwater
DRIVING
FORCE
Pressure from silt
closure, thermally
induced convtction,
and gradient from
aquifer imereonnec-
tion
Thermally induosd
Tharmalry Induced
convtctton end
gradient from aquifer
Thermalry i*iducad
gradient tram aquiftr
interconnection
Pressure from silt
etosura. rharmalry
lower aquifer at edge
ofsaHdoma
SOURCE
TERM
concentration
Uniform
Uniform
concentration
Uniform
concentration
Uniform
concentration
PARAMETERS
in ESTIMATE
p-0
K • 10'10 cm/sac for
KlOOyn
K • 10-*cm/iacfor
t> 100 yn
n • 10-*
A - 8»!0*m2
K > 10* cm/sac for
KlOOyn
K - 10* cm/sec tor
t > 100 yn
" ' 1a*-« 1
A - BxlO^m2
K - 10* em/sac for
KtOOvrs
K - 10* cm/sac for
»100yn
" ' 1 100 yrs
D - 10-*
A - BilO6"2
K - 10"' cm/we for
K 100 yrs
K ' 10"* cm/sec for
t > 100 yn
n • 10-*
A - S'lO^m3
K • 10"7 cm/tac for
t< 100 yrs
K - 10* cm/sac for
t> 100 yrs
n • 10-*
A • B»10*m2
P-0
FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER
1«t ESTIMATE
No releases need to be
calculated.
1 (yn) 6(0 Im3/yrl
100 1.4 KlO2
1000 8.8 « 10*
10.000 3.8x10'
t (ynl Qdl Im3/yrl
100 1.8x10*
1000 1.5 » 10*
10.000 6.3 x 103
t (yn CMO (m3rVI
100 UxlO*
1000 1£«10*
10JOOO 6J > 10?
No rslsaiai n«ad to be
calculated.
2ml ESTIMATE
No rslesm need to be
calculated.
t Ivn) Oh) iro'/yr)
100 1.4x10*
1000 en > to3
0.000 3.8 x 103
< (ml Olll (m3/VT)
100 73x10*
1000 7.7 x Id6
10.000 6B x 106
t (y» 6(t!  10*
10.000 68. 106
No nlaam need to be
calculated.
COMMENTS
The probability that the
spatial variability in
rock strength could
lead to an extensive
patfmiay from the ra-
portoryrhat~Hild
fracture under tha
msaas axperiancad
mas found to be neg-
ligibla.
Permaabtlitv change
after thermal oaak » dus
to savaral factors:
moMnvjnt of blocks
during thermal cycle.
material in cradu.
alteration of minerals
in cracks.
Parrnaabilrtv change
after thermal peak is dm
to savaral factors:
during thermal cycle,
incomplete rebound of
malarial In cradu.
in cracks.
Pairnaabmty change
after thermal peak is due
to savaral factors:
movamant of blocks
during thermal cycle.
material in cracks,
in cracks.
Tha probability that
rock strength could laad
to an extensive pathway
from the repository that
would fracture under
was found to be nag-
ligalla.
00

-------
D-3.1.2  Background

    Heat generation j)v_.high-level wastes.  High-level radioactive wastes
generate heat,  on  the order of up  to  several kW per canister according
to  present  packaging  concepts.   Depending  on the  average  planar heat
density at which the  wastes  are  placed in a repository (ranging from 60
to 200 kW/acre  in  conceptual designs)  and  on the  proportions of short-
and long-lived  radionuclides  in  the wastes,  the temperature  of the rock
surrounding  the repository  can  rise  considerably.   In  the immediate
vicinity  of  the  wastes,  this  rise might  be as  great  as  100-200 C,
depending on  the  age of the  waste, the  quantity per  canister,  and the
spacing  between canisters.    Representative  temperature  profiles  were
calculated and  reported  in the Task B Report  (Engineering Controls), and
simplified  approximations  to  these are  discussed  in Appendix  D-VT of
this report.
    Effects of  heat.    Heat  can  affect  both engineered  and  natural
barriers  to  waste migration.   The  focus of  this  failure  element  is on
changes in  the  rock characteristics that control the movement of fluids.
In particular,  heat can:
    • modify  basic  rock properties, such as brittleness,  ductility, and
      strength;
    • alter mineralogical  structure  (e.g.,  by dehydrating  clays),
      thereby also affecting  rock  properties;
    • cause  stress  buildups  and movement  from thermal  expansion.   New
      stresses  may cause fracturing.
These effects all  contribute to  modifications in the ability of rock to
serve as a barrier to  fluid migration.
    In  fact,   there  is not  a  simple  heating  effect,   but rather   a
heating-cooling cycle,  because  the  heat-generating wastes gradually
decay to low  levels.   This  factor  will be considered further in Section
D-3.1.3 on  the  failure model.
    Fluid flow  model.  The Task C  Report  (Migration  Pathways) contains  a
discussion of Darcy's  law and  its  application to fluid flow calculations
in  both  porous  and fractured  rock; further  discussion may  be found  In
Appendices  D-V and  D-VI of  this   report.   A  summary of  the principal
points follows.

                                   49

-------
    The flow of groundwater in saturated porous rock dan be described by
 Darcy's law, in the form of the equation:
                              Q  -  KiAc(u)
where
    Q = volumetric flow rate (volume/time);
    K « hydraulic conductivity (length/time);
    i = hydraulic gradient (dimensionless);
    A = cross-sectional area of the flow path being considered;
 c(p) =  viscosity correction  factor  (dimensionless)  that  accounts  for
        increased flow at lower viscosities.
K is frequently given in cm/sec, which is also the basic unit used here.
However,  because of  the  magnitude of  the  flows  that  result  in  the
present situation,  for  calculational  purposes K will be  transformed to
units  of  m/yr and  Q  will be  given in  m /yr.  Although Darcy's  law is
generally applied  only to relatively  homogeneous  porous media,  it  has
been found  suitable for application to fractured media  to describe  the
hydrologic  system  on  a macro  scale.   Although  the  law  may not  be
sufficiently accurate  to model  the  yield of a single  well, for example,
which depends on  the local distribution  of  fractures,  it can be applied
                                                                (28)
to describe gross water movement  over large  areas or  regions.       In
fact, the hydraulic conductivity, K, corresponding  to  fracture flow  can
be modeled analytically, using fracture parameters and the principles of
fluid mechanics,    '    although research continues into improving these
models.
    The  expression  Kic(u)  has  the  units of  velocity and  is sometimes
called the  Darcy velocity.   It  is  not  a true  fluid velocity at all,  but
rather a measure of the volumetric flow rate per unit of cross-sectional
area of  the flow path.  By  dividing  by the effective  porosity,   n, of
the  rock,   the  actual   average  fluid  movement rate  is obtained.  This
velocity,
                                    Kic(y)
                                      n
is  useful  for  estimating how  long  it  would  take  for  noninteracting
solute  to  be carried along  the  flow pathway  with the  groundwater.  Of
                                     50

-------
course, It  is  only an average value  and  therefore an approximation to
the actual  rates  in different  fracture  paths.   For porous  rock like
sandstone,  the  value  of n  may  be  in  the range of  0.1 to 0.5  .   For
fractured but tightly squeezed rock, as in  deep granitic stocks, n may
                          -4
be  in  the vicinity of  10  .    Such low values of n  mean  that  transit
times may be fast,  even  when  the hydraulic conductivity and volumetric
flow rates are  low.
    Ranges  of  parameter  values  have  been given in  the Task  C Report
(Migration Pathways) and in Chapter D-2.0 of this report.  They  will be
cited  as  appropriate  in  the  next  section,  where the  present  failure
element is  characterized  in terms  of  changes  in  K.  The parameter K is
often loosely referred to as the permeability,  especially when  the fluid
under  consideration is  known and  fixed.  In fluid mechanics,  there is
also  an  "intrinsic" permeability,  k (in  units  of  area), which  permits
the  separation  of  fluid properties from  those  of  the rock itself ; but
this  latter permeability will not  be  used  here.  Therefore,  in  keeping
with common practice,  K will often be referred  to as  the  permeability.
    Permeability measurements.  Specific permeability values are  applied
in  subsequent sections to characterize rocks or other materials.  It is
not  easy  to measure values in  the  ranges given,  especially by  in-situ
techniques,  which  would  be expected  to  represent more accurately the
fluid  flow properties   of the  bulk  rock  mass.    Thus,  the  actual
verification that  a specific  rock mass has an  approximate permeability
in  some of  the ranges  referred to may be quite  difficult.    However,
because  of  this relatively  new  need  for  measuring  very  low
permeabilities,  techniques  are  being  actively developed  for  this
purpose.

D-3.1.3  Flow Through Bulk Rock Failure Model

     The  breach-of-containment mechanism under  discussion here  refers  to
fluid movement through the  bulk rock  itself, independent  of the
development of  additional  permeable  pathways,  such  as faults,  leaky
shafts, and borehole seals.  As long as two conditions hold,  namely,
    •  the  rock has a permeability  greater than zero, and
    •  a hydraulic  gradient is present,
                                     51

-------
there will be fluid  flow through  the  rock.   If the permeability
is  sufficiently small, then  the  flow volume  can be considered
negligible.   Some of  the calculations reported  in  the next section do
lead to such negligible flows.
    The purpose of this  section  is to characterize  the permeability and
porosity  of  the rock  surrounding  the repository  for use  in  the flow
calculations of Section D-3.1.4.

D-3.1.3.1  Bedded Salt  and Dome Salt

    Relatively pure salt at  the  depths  considered  in  this study has a
permeability  that  is  so  low that  it  is  nearly impossible  to
        (22 23 24)
measure.   '  '     For  the purposes of this  study, intact salt may be
regarded  as  impermeable.    The  heat generated  by  the  wastes  is not
expected   to  change  the value, except  perhaps  to decrease  it  by
compression of pores, unless sufficient stresses are generated to  cause
fracturing.   Rock mechanics  calculations based  on uniform  rock salt
characteristics do not  predict such  fracturing  because the stresses do
not exceed  the rock strength and, in  addition,  they can be relieved by
salt  deformation.    Additional  calculations  were  carried out  with  a
stochastic  model  that  accounts  for  local  spatial variation  of rock
properties.   The  question  was whether there  might  be a combination of
weaker  zones  in  the  salt through which  a  long  fracture  pathway  might
develop.    These probabilistic  calculations,  reported  in detail  in
Appendix  D-IX,  show  that  this  probability is  negligible.   Thus the
permeability  value  of  the salt  is  assumed  not  to  increase with  time.
Because of  this  and  because  there  is negligible flow with  the baseline
salt permeability value, no  detailed  flow  calculations are  necessary.

D-3.1.3.2  Granite,  Basalt,  and Shale

    Granite and basalt  are  igneous rocks  in which  fluid flow is  almost
entirely  within  fracture systems.   Shale is a  sedimentary rock  whose
characteristics  are  extremely variable,  ranging  from relatively  soft,
plastic material to highly indurated rock similar in many  properties  to
igneous rocks.   The  latter  type  of  shale has been  assumed  for  modeling
                                     52

-------
purposes, so that fracture flow also dominates in this case.
    The following processes will, in general, occur during the period of
temperature rise:
    • expansion of rock, thereby decreasing the size of openings such as
      pore spaces, fractures, and other discontinuities;
    • compaction of fill material, (such as clays) In fractures;
    • slippage and movement along fractures; and
    • alteration of mineral content, such as by dehydration of clays.
In  addition,   new  fractures  may  develop,  but  this  Is  not  considered
likely  to  occur  to  a significant  degree  from  the  temperature changes
expected  In the  rock surrounding  the repository.   Some of  the  above
processes can  contribute  to  a decrease In bulk permeability during this
        (48 49)
period.   '      However,  no attempt  has  been  made  in  this  report  to
model this effect quantitatively.
    More important is the  fact  that after the  temperatures peak and then
begin  to  decrease,  several effects can contribute  to  a new higher bulk
rock  permeability.    For  example,  the  surfaces of  fractures  may  not
return  to  their original  position, and asperities  may  keep them apart.
Clay fill that has been compacted may  not rebound completely, leading to
open  channels.   Clays  that  have been altered may crumble  and  fail to
fill  their  original  volume.    Mechanistic  models are  not  available to
predict  the net  effect of  these  processes,  either  generically  or  in
specific  instances.    Nevertheless, by  considering  the  range  of
permeability  values  for  the  types   of  rock  formations  in  question,
modified  permeabilities  may  be  estimated.    The  values  chosen  for
modeling  purposes  are  summarized  in Table  D-15.    For  purposes  of
conservatism,  the increase in  permeability  is modeled at  the  100-year
point after repository  closure, even  though the increase is expected to
be  gradual  and may  actually occur later.   Note  that  it is difficult to
estimate  the level  of assurance with  which a given specific site can be
determined  to  have  the kind  of low permeabilities assumed  here.   This
problem  must  be addressed  in the detailed  characterization of  specific
sites.
                                        53

-------
                               TABLE D-
    MODEL PERMEABILITIES FOR TUB".
                                       BEFORE AMP AFTER THERMAL CYCLE
                               Bulk Rock Permeability (K)
                                        (cm/sec)
Basalt
Shale
                          First Estimate
Granite     t < 100 yrs**
            t >  100 yrs
            t <  100 yrs
            t >  100 yrs
            t <  100 yrs
                              10
                                -10
                              10
                                -9
10
                                -9
                               .-8
10
                                -9
            t >   100 yrs     10
                                -8
                                              Second Estimate
                      10
                                                      -7
10
                                                    10
                                                      -7
10
                                                      -7
                                                    10
                                                      -6
 Note:   Permeabilities of these rocks can be much higher than the values
        given in this  column.   The second  estimate  corresponds  in this
        case to suboptimal values, but ones  that  might  reasonably still
        be in the  range of consideration  for repository siting.

**Years after repository closure.
                                 54

-------
D-3.1.4  Flow Through Bulk Rock Release Model

D-3.1.4.1  Bedded Salt

    Because  thermal  effects  do  not  alter   the  permeability  of  the
surrounding  salt  and  because salt is essentially an impermeable medium,
all  flows  in  the bulk  rock are  negligible   in  comparison with  other
release  mechanisms.    Consequently,  no  calculations  are  presented  for
this case.

D-3.1.4*2  Granite

    Of  the  driving  forces   discussed  in the  appendices,  only  thermal
convection is  relevant  for   this  release mechanism.   This driving  force
depends  on time because  the temperature profile varies  over  time.  The
methodology  for  evaluating   this driving force  is  presented in Appendix
D-VI and the resulting effective  gradients  are shown  in Table  D-16.   As
pointed out  in  the  appendix, these values  represent  upper bounds on the
possible buoyancy forces.
    The volumetric  flow  rate can  be calculated from Darcy's  law.   The
                                                          2
values of  K  have  been given  in Section 0-3.1.3; A is 8 km  ; and c(y) is
5, in accordance with Appendix D-VI.  The results are presented in Table
D-17.
    As discussed  in  Appendix D-VI,  the  average vertical  fluid velocity
is obtained  from the equation
                                    Ki
                                   lOOun
The resulting velocities  and  transit  times  are presented in Tables D-18
and D-19.    As discussed  in  Appendix VI,  because water  may be more
readily available near the edge of the repository, the vertical velocity
may be as much as ten times higher in some locations, leading to shorter
transit times to the aquifer.
    The  source   term  for  this  failure   element  consists  of  the
concentration of  radionuclldes  that  have leached into  the  water  in the

                                   55

-------
                                TABLE D-16



           EFFECTIVE VERTICAL HYDRAULIC GRADIENT IN SURROUNDING

             GEOLOGIC MEDIA FROM THERMALLY INDUCED CONVECTION

                            (GRANITE  REPOSITORY)
                                    Hydraulic Gradient (i)





                            100 years     1000 years      10,000  years



        First Estimate        0.011        0.007          0.003



        Second Estimate       0.011        0.007          0.003
*
 Years after repository closure.
Source:   Appendix D-VT,  taking into account a ten-fold reduction because

         of the resistance of the  recharge pathway,  as  discussed in the

         last section of that appendix.
                                 56

-------
                              TABLE 0-17






                VOLUMETRIC FLOW IUTES THROUGH BULK ROCK



                         (GRANITE REPOSITORY)









                                   Volumetric Flow (Q)



                                         (m3/yr)









                          100 years    1000 years     10.000 years
                                  2            1
       First Estimate     1.4 x in     8.8 x in
3.S x 10
       Second Estimate    1.4 x 10 4    8.8 x in3      3.8 x 103
Years after repository closure.
                                 57

-------
                              TABLE D-1B

                  FLUID VELOCITIES THROUGH BULK ROCK
                         (GRANITE REPOSITORY)
                                      Velocity (v)
                                         (m/yr)
                          100 years    1000 years     10.000 years
       First Estimate
 0.20
 0.11
0.05
       Second Estimate
18.0
11.0
4.7
Years after repository closure.
                                 58

-------
                              TABLE T5-1Q

    FLUID TRANSIT TIME FROM REPOSITORY TO AQUIFER THROUGH BULK ROCK
                         (GR\NTTE REPOSITORY)
                                            Time
                                            (yrs)
                          IPO years    1000 years     10.om years
       First Estimate
1150
2100
4*00
       Second Estimate
               20
Years after repository closure.
                                  59

-------
repository during  the time  frame of  interest.    This  is  the  uniform
concentration situation described  earlier.

D-3.1.4.3  Basalt

    The two possible driving forces for this case are  thermally  induced
convection and  an  aquifer  interconnection.   Because  the temperature
profile varies  with  time,  the  magnitude  of  the combined  effect  also
varies with  time.   The methodology  used to  evaluate  thermally  induced
convection  is  developed  in Appendix D-VI,  and  estimates for  the
effective  vertical  hydraulic  gradient  are  presented  in  Table D-20.
These values  represent  upper bounds  on the possible  gradients. Using
these hydraulic gradients,  the volumetric  flows  can be calculated  from
Darcy's law.   Table D-21  presents the results  of  the  calculation.   As
discussed  earlier,  the vertical fluid  velocity  is  obtained by dividing
the volumetric flow rates  by n.   This leads to  the velocity and  transit
time estimates in Tables D-22 and  D-23.
    The  source  term for  this   failure  element  consists  of  the
concentration of radionuclides  that have leached into  the water  in the
repository during  the time  frame of  interest.   This  is  the  uniform
concentration situation discussed  earlier.

D-3.1.4.3  Shale

    All  modeling  parameters relevant   to  this  release  mechanism  are
identical  for  the shale and  basalt  repositories.    Therefore  the
discussion and calculations  for  the two  repositories are  identical.  The
results are summarized in  Tables D-24, D-25 and D-26.

D-3.1.4.4  Dome  Salt

    As in  the case of  bedded   salt,  all  flows  in  the bulk  rock are
negligible  in  comparison  with   the  other  release  mechanisms.
Consequently, no detailed  calculations  are  required  for  this case.
                                  60

-------
                               TABLE D-20

      EFFECTIVE VERTICAL HYDRAULIC GRADIENT IN SURROUNDING GEOLOGIC
   MEDIA FROM THERMALLY INDUCED CONVECTION AND AQUIFER INTERCONNECTION
                           (BASALT REPOSITORY)
                                    Hydraulic Gradient (i)
                           100 years
                                     1000 years
10.000 years
Thermally Induced
          **
Convection
        First Estimate
        Second Estimate
Aquifer Interconnection
        First Estimate
        Second Estimate
        First Estimate
        Second Estimate
                    ***
0.13
0.13
0.01
0.5
0.14
0.63
0.11
0.11
0.01
0.5
0.12
0.61
0.04
0.04
0.01
0.5
0.05
0.54
 **
***
Years after  repository closure.
t
These values are  from  Table D-VI-4, Appendix D-VI,
These values are  from  Section D-2.3.3.
                                     61

-------
                              TABLE D-21

                VOLUMETRIC FLOW RATES THROUGH BULK ROCK
                          (BASALT REPOSITORY)
                                 Volumetric Flow (Q)
                                        (m /yr)
                          100 years*   1000 years     IQ.flno years
       First Estimate
                    l.R x 104    1.5  x 104      6.3  x 103
Second Estimate     7.9 x
                                        7.7 x 106      6.8 x 1C6
Years after repository closure.
                                 62

-------
                               TABLE D-22




                   FLUID VELOCITIES THROUGH BULK ROCK

                           (BASALT REPOSITORY)
                                         Velocity (y)

                                            (m/yr)
                           100 years    1000 years     10.000 years
        First Estimate      23            19              7.9
        Second Estimate    Q.9 x 10     9.6 x 10       P.5 x 10'
*
 Years after repository closure.
                                   63

-------
                              TABLE D-23

                 FLUID TRANSIT TIMES THROUGH BULK ROCK
                          (BASALT REPOSITORY)
                                            Time
                                            (yrs)
                          100 years    1000 years     10.0^0 years
       First Estimate
4.3
  5.3
       Second Estimate
0.01
0.01
                                                          0.01
Years after repository closure.
                                 64

-------
                              TABLE D-24




                VOLUMETRIC FLOW RATES THROUGH BULK ROCK


                          (SHALE REPOSITORY)





                                                        •
                                       Volumetric Flow (Q)

                                             (m3/yr)





                                   *
                          100 years    1000 years     10.000 years
       First Estimate     1.8 x 104    1.5 x 104      6.3 x 103
       Second Estimate    7.9 x 106    7.7 x 106      6.R x 1Q6
Years after repository closure.
                                  65

-------
                              TABLE D-25




                  FLUID VELOCITIES THROUGH BULK ROCK

                           (SHALE REPOSITORY)
                                         Velocity (v)

                                             (m/yr)
                                   *
                          100 years    1000 years     in.QQO years
       First Estimate       23           19             7.9
       Second Estimate    Q.9 x lV    9.6 x ]V      «.5 x 10
Years after repository closure.
                                66

-------
                               TABLE D-26

                 FLUID TRANSIT TIMES THROUGH BULK ROCK
                          (SHALE REPOSITORY)
                                               Time
                                               (yrs)
                          100 years    1000 years     10.000 years
       First Estimate
4.3
5.3
       Second Estimate     0.01
             0.01
                0.01
Years after repository closure.
                                  67

-------
D-3.1.5  Literature Discussion

    Flow  through bulk rock has been  considered  in a  number of  studies
 (11)29) as  well  as  in the Task C Report for this project.   In addition,
some  researchers  have discussed waste- induced permeability changes.
                                (
    The  NRC/Sandia  risk program     proposes a model for stress- induced
fracturing  in  terms  of "reference  cracks."   A reference  crack  is a
vertical planar crack whose horizontal cross-section has dimensions 1 mm
x 3 km.  The  effect of  stress buildups on  the rock is measured in  terms
of  a  number  of new reference cracks.  This  number  is obtained from  the
expression  5h , where  h is  the vertical  displacement  in  centimeters.
Since  the vertical displacement is expected  to be on the order of one or
several  meters, somewhat over  500  reference cracks might  be expected.
The authors do  note large sources of error in this approximate model.
    The  BNWL/ONW1/DOE  WISAP  program      has also  noted   this  failure
element,  although quantitative estimates  of permeability  changes  have
not been reported .
D-3.2   SHAFT SEAL FAILURE

D-3.2.1  Summary

    During  the operational  stage of  the  repository,  several vertical
shafts  will  be  required  for  ventilation  and  for  the   transport  of
personnel  and materials  between the  underground workings and  the
surface.    (See  Figure  D-9).    Part of  the  process  of  sealing  the
repository  for long-term isolation  of the  radioactive  wastes requires
that  these  shafts  be  filled  with  appropriate materials  in  order  to
prevent  them  from  serving  as  pathways  for  fluid  flow  or radionuclide
migration.
    The  sealing  materials   will   need  to  be  chosen with  a specific
environment in mind so  that they may approach,  as nearly as possible,
chemical and mechanical  equilibrium with the surrounding rock.  The seal
may consist of  several layers of  completely  distinct types to provide a
multi-barrier  line  of defense  against  expected  or  unexpected forces.

                                  68

-------


Shaft 	 »

Surface
deposits



^pfi,Aquif^^|l^
	 Shale 	

Salt















-« 	 .Shaft






i;CW^&^';^v#M^!i#fe^
®.'&*a!jit.si!!'>-> •'#*"•&. Sl'.-iWfv/::!-:.'-!
	


                                                  Surface
                                                 330 Meters


                                                 360 Meters



                                                 410 Meters



                                                 460 Meters


                                                 510 Meters
£HHH?^!'L~I^-I^:£HI-~1^~^-~^^




/////"/,
       Basement

         FIGURE D-9  BEDDED SALT REPOSITORY


                    SHOWING VERTICAL SHAFTS
                       69

-------
Nevertheless, it  is reasonable  to expect  that over  a long  period  of
time,  such  as  10,000  years,  the  combination of  processes  such  as
settling,  leaching,  expansion and  contraction due  to fluctuations  in
water  content or  temperature,  earth  movements, weathering,  and  fatigue
may lead to some degradation in the integrity of the  seal.
    The shaft seal performance model  considered here  is not derived from
a  particular design.    It  is  intended  to be generic  in nature  and
conservative;  that   is,  it  is   believed   that    the  performance
characteristics  described  here can  be equalled or  exceeded  by  actual
designs for specific circumstances.
    The generic model  used  in this report characterizes  the shaft seal
integrity by  a  spatially uniform  hydraulic conductivity  K.    One
hydraulic  conductivity  value   (KQ)  is estimated  for  the  time of seal
emplacement, and  another value  (K.)  is  estimated for the  time  10,000
years later.  It is assumed that  K increases linearly from Kg to K. over
this period.  A summary of the analysis is given in Table  D-27.

D-3.2.2  Background

    The excavation  and  operation of  an  underground  repository  require
the  sinking of  a  number of  shafts  to   provide  access,  ventilation,
removal of rock, etc.   These  shafts  will  vary  in  size and construction
depending  upon  their   function  and the  rock  through  which they  pass.
Even in  relatively  simple geologic settings, such as  those represented
by  the generic  models  in  this  report,  a  variety of  construction  and
maintenance  techniques  may  be  required for the shafts to remain usable
during  the operational  life  of  the  repository.    It is  important  to
review these technologies  in  order to set  the  framework  for discussion
of the shaft sealing problem.
    Much of  the  focus  of mine shaft  engineering  is  on the problems of
hole stability and water inflow.   These problems are  often  interrelated,
and even when they are  not, some  of  the  same engineering  techniques may
be effective for both.   For example,  the  portion  of  a shaft penetrating
either  incompetent  or  water-bearing   rock,  or occasionally  an  entire
shaft, may be  lined  with  a  tubular  structure,  and  the  annular  space
between this liner and  the rock then filled with a sealer or grout.  The

                                     70

-------
             TABLE D-27
SUMMARY OF SHAFT SEAL FAILURE ELEMENT


MEDIUM


Bedded Sett






Granite








Basalt








It;
Si
S I
Is
E8
0






D








D








NATURE
OF
MODEL


Lbiaarly Increasing
permeeMlity





Linearly increasing
permeability







Linearly increasing
peimaabahy








RELEASE
MODE


Grounrhvater






Groundvwater








Grourahvatar









DRIVING
FORCE


Initially pressure
from art craap.
Aftanoards. U-tube
effect.




Thermally induced
convection and
U-lube effect.






Thermal ly induced
U-tutae effect.








SOURCE
TERM


Uniform






Uniform
Concentration







Uniform
concentration







PARAMETERS


1st ESTIMATE

Kg- 10* cm/sec at
time of seeling
K, - 10* cm/sac
after 10.000 year.
K increase* linaariy
from Kg to Kj over
10,000 years
n - 0.1
A - 100m2, total
cross seuioiial area
of shafts
Kg- 10* cm/sec at
time of sealing
K, - 1CT6 cm/sac
attar 10.000 years
K increessi linearly
from Kg to Kj over
10.000 yean
1 • 0.1
A - 100m2, total
ofshafts
Kg- 10*cm/sacat
time of seeling
K,- 10* cm/sac
aftar 10JOOO yean
K lnitsa.ii linaariy
from Kg to K, ovar
10.000 yean
T, * 0.1
A - 100m2. total
o< shafts

2nd ESTIMATE

Kg- 10"8 cm/tec »t
lima of easting
K, - 10-* cm/sec
after 10X100 years
from Kg to K^ over
10.000 year.
1-0.1
A • 100m2.total
cross-factional aree
ofshafts
Kg- 10"8 cm/sec at
time of seeling
K,- 10-4 cm/sec
alter 10.000 years
•K increases linearly
from Kg to Kj over
10,000 yean
1 - 0.1
A - 100m2. total
ofshafts
Kg- 10*cm/eacat
time of sealing
K,- ID"4 cm/sec
after 10.000 yean
Killiiessei linearly
from Kg to K, over
10.000 yean
n - 0.1
A - 100m2. total
of shafts
FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER


Itt ESTIMATE

tlyn)

200
223"
223*
1000
10.000

O It) Im3/Vrl

40 ) Parted
40 I0*""
40 ) craap
OJ08
0.17
0.32


tlyn)

100
1000
10.000

Q It) Im3/yrl

0.3
1.0
1.6




tlynl
100

1000
10.000

dlt)lm3/yr>
0.4

1.7
3.2





2nd ESTIMATE

tlynl

720
1000'
1000*
10,000


d It) Im3/yrl

^H.?
3.15
3.15



tlynl

100
1000
10^100

d 111 Im3/yrl

153
94.6
236.3




tlyn)
100

1000
10.000

0 It) Ini3/yrl
28j>

1S7i
472.6






COMMENTS


It is conservative to
assume dceure bysart
creep for this failure
laaaluiaUmi time would
be enremel Viang.
Oosurealsoinipllaa
ill oily driving fores for
release.


RriMW only DBBMI
•ftvr npository
tmnuntian.






R--.»oo*yb.^
•flaw raparitory








-------
                   TABLE D-27
SUGARY OF SHAFT SEAL FAILURE ELEMENT (CONTINUED)



MEDIUM



Stole










Dome Salt









SB

Si
32
< GC

is
D










O










NATURE
OF
MODEL



Ltntsriy mcrtatins
parrn*8biJltv









Limarlv Iner-Ming
paffsTMSblliry










RELEASE
MODE



Ground water










Groundwater











DRIVING
FORCE



Thermally induced
convection and
U tube effect.








Inilisllv pressure
from »ll creep.
Afterwards. U-uibe
effect.









SOURCE
TERM



Uniform
concentration









Uniform
concentration









PARAMETERS



1st ESTIMATE

Kg - 10 8 cm/sec at
time of sealing
K, - 10* cm/sec
after 10,000 years
K increases .inearry
from Kg to K* over
10,000 years
n = 0.1
A - 100m2. total
cron-secitonal area
of shaft i
Kg » 10"8 cm/sec at
tkne of scaling
K, - 10"6 cm/tac
after 10,000 years
K increases li newly
from Kg to KI over
10.000 years
-1 - 0.1
A - 100m2. total
crosf-tccttonaJ area
of (hafu


2nd ESTIMATE

K0= tO^em/iecat
lima of sealing
K|- lO^cm/wc
alter 10,000 years
K increases linearly
from Kg to K 4j over
10,000 years
U - 0.1
A <• 100m2, total
cross-sectional area
of shafts
Kg = 10 cm/sec at
lime of seating
K,- 10"4 cm/sec
after 10.000 years
K increases linearly
from Kg to K | over
10,000 years
n - 0.1
A - 100m2, total
cross-sectional area
of shafts

FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER



1st ESTIMATE

ttvrsl

100

1000
10.000

Q (tl .m3/yr)

0.4

1.7
3.2





Uyrs)

200
260
260

1000
10,000

6 (t) )m3/yr»

IS } Period
} of salt
15 ( creep
0.04

0.10
0.24




2nd ESTIMATE

t  of salt
2000^ CTWp
3.15

3.15






COMMENTS



Releases only begin
after repository
resaturation.








It « conservative to
assume closure by salt
creep for this failure
mechanism; otherwise
resaturation time would
be extremety long.
Closure also implies
strong driving force for
release.



-------
liner may consist  of  a  single  layer,  such  as  steel,  cast  iron, or
reinforced concrete,  or a multi-layered system.   Examples  are shown in
Figure D-10.   Other methods of  stabilization,  discussed  below, include
freezing  the  ground around  the  shaft or  filling  the  rock column  with
grout before excavation.
    Freezing  requires  the   installation  of  refrigerant   tubes  in  the
section requiring stabilization.   These  may be placed from the surface,
through  an array of  drilled  holes, from  within  the  shaft  as  a  ring
against   the   shaft  walls,  or  In  holes  drilled  from  the  shaft.
Refrigerant is then  forced  through  the  tubes,  cooling  the  ground  and
freezing the interstitial water.  Since it is the water in  the rock  that
freezes, this  method  of stabilization is suitable  only for saturated or
nearly saturated  rock.   Furthermore, if the  rock  is kept  frozen during
the  operational  life  of  the  repository,  the  distance  or  depth of
freezing  can   continue  to expand.    The permanent  effects on  the  rock
would depend,  In part,  on the  extent of  freezing,  and hence on the  time
span of the operation.
    Grouting  to stabilize soil  and  rock involves drilling a series of
closely spaced  holes  and  injecting  grout  under pressure.    The injection
pressure must  be  carefully controlled to ensure that  grout is forced a
sufficient distance into  the rock without causing additional  fracturing.
The grout  is designed to  fill voids  in the rock before  it sets and  forms
a rigid bonding agent.  The  spacing of the holes must be close enough to
permit grout  from one  hole  to spread to  the  next  and coalesce.    When
grout has  been  injected  into  all   the  holes,  a continuous  curtain or
column of  rock and  soil,  cemented by the grout, remains  in the ground.
Excavation of   the  shaft  can  then  proceed  within  the curtain  wall or
along the  column.   Figure D-ll shows a  typical  grouting  program.   Neat
cement (cement  without  aggregate) or cement with fine fillers are  the
most common grout materials.  Chemicals, such as sodium silicate gel and
epoxy and  polyester  resins, are  used  in  some  instances;  the limited
availability  of  these   specialized   products   and   their   expense   have
restricted their general  use.
    Methods used to sink  shafts  are  affected by the stability and  water
content of  the ground,  and  they affect stability  and  water content in
return.  In the fairly  competent rock expected near  a repository, rotary
                                   73

-------
(a)   Schematic of drop shaft
                 Concrete liner
                 is lowered as
                 excavation
                 proceeds
                                                                             Ground level
         .//    "
                       Floor of excavation
 Source: Arthur D. Little,Inc.
(b)   Shaft lining used in Asse Salt Mine
      Repository, Federal Republic of
      West Germany.
 / Rock
ff    ^   Concrete backfilling
          Cast iron segments


              Asphalt joint

               Steel cylinder
                                                                                 Reinforced
                                                                                concrete shell
Source: On the Safety of Disposing of Radioactive Wastes in the Asse Salt Mine.Gesellschaft fUr Strahlen
        und Umweltforschung mbH, Munich, Germany, undated.
                            FIGURE D-10   EXAMPLES OF SHAFT LININGS
                                                 74

-------
                      Shaft location
                                                  Holes for
                                                  injection
                                                  of grout
„.- .. I-  v, .   .
 ••  ••*   I    •"
• •' f  '!'-^-
 • "-••' "\:\'
 ••'•••'     \.'
   •••^~-
    1-.-J
    Zone to be stabilized
    before excavation
  Source: Arthur D. Little, Inc.
                                         Grout is injected in
                                         holes around shaft location.
                                         Sufficient grout is injected
                                         to form continuous curtain
                                         around shaft.
FIGURE D-11   GROUTING PROGRAM FOR SHAFT STABILIZATION
                         75

-------
boring  or  percussion  drilling and  explosives may  be  most  practical.
Each  technique  differs somewhat in  its  effect on the  rock surrounding
the shaft.   Typically, some fracturing of  the  wall  rock is expected as
the  stress  field  changes when   rock  is removed  from  the  shaft.
Explosives  and percussion drilling shatter rock around  the  shaft
opening,  with  the  degree   of shattering  depending  upon  the  forces
generated, rock type,  and  in-situ  stresses.    Rotary boring,  in  which
rock is more or  less continuously removed,  generally has less  effect on
wall  rock.    For  each   rock   formation,   the  relative  advantages  of
different  excavation  techniques  must  be  weighed  against   the
stabilization problems introduced by excavation in order to estimate the
most  economical  and safest  combination  for sinking  and  stabilizing  a
shaft.
    Upon closing  a  repository,  the  several  shafts  from  the surface must
be  sealed  to prevent  or  retard the vertical  movement  of  fluids  to or
from  the  repository level.   Sealing  abandoned or inactive mines  is  a
common  practice,  but   the  seals are  usually   intended  more to  prevent
humans  and  livestock  from falling   into  a  shaft,  to  permit  later
reopening of  a  mine,   or, to a lesser  extent,  to reduce  flooding  of or
outflow from a mine.   The special requirement  of  long-term isolation of
a repository, demands  that shaft seals be  placed  with  exceptional  care
and thoroughness.
    Careful preparation for  sealing  will  be important to ensure that the
shaft  seal  performs to  its full  potential.    These preparations  will
entail removal from the shafts  of operational  equipment, pipes,  cables,
guide tracks, and other hardware.    Contaminants,  such as oils  and loose
earth,  must   be  removed  from the  walls  if  these  substances  might
interfere with  the  bonding  properties of  the sealing  agents.    Also,
liners will probably have to be stripped  from  the  shafts.
    Sealing the shaft, including the possibly  altered or fractured  rock
immediately  surrounding   it,  is likely  to require  a  combination  of
materials and techniques  if  the desired impermeability and longevity are
to be achieved.  A number of studies have examined individual  aspects of
repository shaft or  borehole sealing.(11'50~55)  Some have suggested the
use of  specific  materials,  equipment,  and  procedures, as  summarized in
Table D-2R.
                                   76

-------
Material
          TABLE D-2R

SEAL MATERIAL CHARACTERISTICS

   Emp1acement Requ iremen t s
        and Practices
    Comments
Concrete

(Cement with aggregate
added)
Chemical Grouts

(Both organics: epoxy,
etc., and inorganics:
sulfur, silica gel)
Bitumens

(Tar, asphalt)
    Pumped or placed
    continuously or In
    batches.  Equipment
    and techniques are in
    common use.
    Pumped or injected as
    liquid.  May require
    catalyst or subsequent
    treatment, e.g.,
    heating.  Use is
    limited to specific
    problem areas.
    Pumped or injected.
    Often heated to
    facilitate
    emplacement.
    Technology existent
    but seldom applied.
Forms rigid mass.
Sulfate-res1stant
cements available.
Additives are possible
for specific problems
or rock/cement
interaction.  Cannot
fill fine cracks or
pores.  Strength and
permeability worsen at
high temperature.
Good longevity
expected.  Some
ability to "heal" if
fractured.

Forms rigid or
semi-rigid seal. May
be sensitive to
rock/water chemistry.
Bond to wet rock may
be weak.  Range of
viscosities permit
filling of fine
cracks, etc.
Long-term stability
uncertain.
Temperature
sensitivities range
from very low to
extreme.  Plastic
materials can
generally deform
without fracture.

Forms plastic or
viscous seal.
Insensitive to
rock/water chemistry.
Sensitive to
hydrocarbons  in  rock
formations.
                                          77

-------
                            TABLE D~2ft (continued)
 Material
 Bitumens (continued)
Emplacement Requirements
      and Practice
 Compacted Formation
 Rock
Compacted Earthen
Materials

(Clays, sands, etc.
Mixed with or distinct
from formation rock)
 Batch or continuous
 feed  down shaft.
 Continuous or
 intermittent
 compaction by
 machinery. Equipment
 and  procedures require
 development.  Crushing
 of rock may be
 necessary for
 handling.
 (Same as above)
     Comments
 Adhesion to rock often
 greater than cohesion
 of bitumen.  Viscosity
 is temperature
 sensitive.
 Contraction during
 cooling may cause
 cracks  or  separation
 from rock.   Long
 stability  expected.
 Can deform  viscously
 or "heal"  fractures.

 Forms rigid  plug.
 Insensitive to rock
 chemistry;   may be
 water sensitive.  Poor
 bond in to  rock.
 Difficulty  in  filling
 fine cracks, etc.
 Sensitive  to feed
 rate, compaction
 process, particle
 size, moisture
 content.  Temperature
 sensitivity  is  similar
 to  in-sltu  rock.
 Unless  supported or
 mixed with binder,
 strength is  low.
 Compaction may improve
 with time and
 overburden.

 Forms rigid  plug.
 Reaction with
 rock/water expected to
be slight.   Poor bond
 to  in-situ rock.
 Sensitivity  to water
 somewhat controllable.
 Difficulty in  filling
 fine cracks.
 Sensitive to feed
 rate, compaction, etc.
                                   78

-------
Material
Compacted Earthen
Materials (continued)
Melted Rock
Rock Mineral Solution

(Calcite, silica)
 TABLE D-2R (continued)

Emplacement Requirements
      and Practice
 Rock delivered to work
 face either molten or
 solid, melted in
 place, and sprayed or
 pooled.  Feed,
 melting, and  applying
 equipment and
 techniques are
 experimental.
 Same as  above  except
 that the rock  is
 dissolved  in solution,
 not molten.
 Application and
 equipment  are
 experimental•
    Comments
Temperature
sensitivity may differ
from in-situ rock.
Low unsupported
strength.  Long
stability expected.
Some plastic
deformation possible
without fracturing.
Compaction may improve
with time.

Forms solid mass.
Chemistry similar to
in—situ rock.  Most
suitable material is
low-melting-point rock
with few and
single-phase minerals
(e.g., salt) .
Cracking and
separation expected on
cooling.  May fuse or
fill small fissures in
in-situ rock.  If
properly emplaced,
good stability
expected.
Forms solid mass.
Insensitive  to in-situ
rock chemistry.  May
be sensitive  to  water
chemistry.   Implies a
single mineral phase.
Good adhesion
expected.  Low
sensitivity  to
temperature.
Solubility of solid
seal  in  question.
Good stability,
expected.  Does  not
heal.
 Sources:  References  52,  54,  55,  62.
                                       79

-------
    In general, the sealing operation will probably  attempt  to fill the
shaft  in  such a  way  that  it has  mechanical,  hydraulic, and  chemical
properties  as  near as possible  to those  of  the  virgin rock.    Some
concepts may  approach this ideal  in specific  rocks;  for example,  the
melting and  fusing of  salts  has been  suggested as  a possibility  for
shafts  through evaporites.    '  Other methods are applicable to a  wider
range of rock types,  e.g., using  compacted  earth as a seal, or  filling
the shaft with concrete and using the excavated  rock for  aggregate.   An
important  factor  in sealing  a  shaft  is  the  fact that  the   rock
surrounding a shaft is likely to differ  in certain  characteristics from
the virgin rock.   This is true not only  for  the  very short distance (say
one or  two  meters) from the  shaft,  where grouting is possible to seal
excavation-induced fractures,  but also for distances on the  order  of up
to  tens  of  meters.    The  following  are examples of changes  in
characteristics  that   must  be  considered  in  designing  and  emplacing
seals:
    •  MDisture content may change because of drainage into the shaft.
    •  Hydraulic  conductivity  may  change  because   of   leaching,
       fracturing, and stress  changes.
    •  Rock  chemistry may  change because  of  exposure  to  atmospheric
       conditions,  leaching,  and  interaction  with  grouts  and lining
       materials.
    •  Volume  changes may  result  from   pore  water  pressure  changes,
       temperature changes,  and  freezing.
After the shaft is sealed, the entire system will  move toward  chemical,
mechanical,  and hydrologic equilibrium,  and  how the system will adjust
must  be  carefully considered  in  the design.   The  effects  of various
processes on shaft seal integrity are discussed  in  the  next section.

D-3.2.3  Shaft Seal Failure Model

    Scope of Model.  For this  analysis,  the  performance of a shaft seal
is characterized  by the seal's ability to restrict  fluid  movement  along
the  shaft.    The   principal  parameter affecting  such movement  Is  the
hydraulic conductivity  of  the  filled  shaft, including the  immediately
surrounding rock.  While  the  fill material  may  vary from one point to

                                   80

-------
another,  for  simplicity and  in the  absence  of  a  definitive  proposed
design, an effective uniform hydraulic conductivity has been  assumed  to
characterize  the  sealed  shaft  or  any   portions  thereof.   Auxiliary
parameters,  such as  cross-sectional  area  and  porosity,  are  also
necessary to determine fluid  flow rates.
    The  model's emphasis on fluid  flow is not meant  to  imply  that  there
may  not be other  potentially  important  purposes  for  the  shaft  seal.
Naturally,  one  of  the  prime  purposes  of  the  seal  is to  prevent   or
discourage  accidental  entry  into an  abandoned  shaft;  however,  this  is
rather  easy to accomplish and  does  not  affect  design.   Tn addition,  it
is   possible   that   a  seal  may   be  sought   with   favorable
radionuclide-retention properties, in which case  its chemical and
mineralogical  composition  would  be  important.   This  factor  is not
included in the present model.
    The  present  model  hypothesizes  a  linear   increase  in  shaft  seal
permeability  over  a  period of  10,000 years.    Specific parameters are
presented after the following  discussion  of degradation  mechanisms.
    Mechanisms for Shaft Seal  Degradation.   Degradation  of   the   shaft
seal  over  a long period of  time,  such as  10,000 years,  is  the likely
result of a combination of  processes,  examples of  which  are discussed  in
the following paragraphs .
    Leaching, which  involves  the  removal  of material  by dissolution  in
groundwater,  has  occasionally  caused  rapid deterioration  of sealants.
Examples have recently  been  collected and documented  in which  cemented
borehole plugs have disintegrated  and  disappeared  because of leaching  of
the cementitious material,  usually by sulfate-rich or  acidic water  (see
Section D-3.3).  In  response, a number of  cements that  are resistant  to
sulfate attack have  been  developed.  "  '   '       With  the  proper
characterization of  the local  groundwater, carefully  chosen rock and
seal  materials  would  be expected  to  have very  low solubilities;
nevertheless,   increases in  temperature  and  changes   in  water pH   or
chemical composition may increase the rate of leaching.
    Pressure  and  volume changes  in  the  seal  material can  cause the
development of fractures and void  spaces. For example, thermal expansion
will  result  from  the  heat  generated by the  wastes, but  this heating
effect will eventually decrease because  of radioactive decay,  giving the

                                    81

-------
effect of a thermal cycle.   The  corresponding  stress  changes  can result
in  fractures  or  voids.  Changes  in moisture content  can  also  lead  to
similar effects;  certain clays exhibit considerable  swelling  as water is
absorbed, then crack upon drying.  Some synthetic grouts and  sealers are
formed  in  place  by polymerization  of their components.   Corresponding
volume changes often involve shrinkage, so that if the polymerization is
not complete at the time shaft filling is  resumed, or  if the  stresses in
the material are  excessive,  cracks or voids may develop.
    Degradation  from  tectonic stresses and earth movements  is a  most
difficult  engineering  problem.    Because  it is  highly unlikely that  a
site will  be  free  of  differential stresses, gradual  ground  deformation
over  time  may be  expected  even  if  no ground  movement is  felt.    For
example, pipes in  oil  fields have been knoxm to  be distorted,  crushed,
                                                         /COS
closed,  and  inclined   from  the  vertical by  such forces.       Although
some  of  these  movements   occur  along  faults,  they  may  also  occur
independently.           While  such  deformation  is  expected  to  be
relatively slow  in the stable areas being  considered  for  repositories,
the  10,000-year  time  frame is  sufficiently  long  that the  cumulative
effect could be substantial.
    Other forces  and processes that may have an  impact on  the integrity
of  the shaft  seal  include settling within  the  fill material,  changes in
overburden pressure from natural  processes  (e.g., erosion, glaciation),
chemical interaction between fill material and  surrounding  rock, changes
in  physical   properties  caused  by  variations   in  water  content,  and
chemical  changes  within  the fill  material itself  (such  as  reactions
between aggregate and  cement in a concrete) .
    Specific Model Assumptions.     The  previous  discussion  suggests  a
picture of  a shaft   seal   with  somewhat  different  appearance  and
properties after 10,000 years than immediately after  emplacement.   This
concept   is   sketched  in  Figure  D-12.    The development   of   the
corresponding  model  is  described  in  the  paragraphs below.    It  is
important  to  keep  in  mind  that  the  intention  here  is  to  present  a
generic  characterization  of  shaft  seal performance  and  that  this  has
been done by  selecting  performance characteristics  that  are  believed to
be  achievable without technological breakthroughs.  With specific
                                   82

-------
00
            Grout
                                                       ^;.  Grout
                                                                           Breccia from
                                                                           collapsed
                                                                           walls

                                                                               Voids
                                                                                                                               Fractures
                                                                                                                               from settling
                                                                                                                              Loss of adhesion
                                                                                                                              with walls
                                                                                                                              Aggregate residue
                                                                                                                              where cement leached
                                     Breccia from
                                     slumping after
                                     grout leached
                            (a)   At Time of Emplacement
(b)   After 10,000 Years
     (Degradation may be exaggerated)
                                     Source: Arthur D. Little, Inc.
                                      FIGURE D-12   EXAMPLE OF SECTION OF MULTI-LAYERED SHAFT SEAL

-------
designs  and  thorough  experimental  evaluation  even  better  shaft   seal
performance may be found to be possible.
    As  stated  earlier,  an  effective,  spatially uniform  hydraulic
conductivity has  been  used  to  characterize the  performance  of shaft
seals.  Consideration  of  seal  degradation  mechanisms indicates that  the
conductivity value will increase in time.  Therefore, the essential  step
in characterizing shaft seal performance is to determine a  function  K(t)
which  for  each time t  is  an estimate of  the hydraulic conductivity of
the  filled  shaft.   This  determination  involves  three steps:  the
estimation of the initial value KO for the time  of seal emplacement, the
estimation of  the deteriorated (i.e.,  larger)  value K, at time 10,000
years, and the  estimation of  a rule  governing  the transition from KQ to
V
    Initial  permeabilities  K^ for both  first  and second  estimates  are
taken as 10   cm/sec.  It appears  that this value can be met or bettered
by a number  of materials and  designs, as  suggested  by the  data in Table
D-29.  The performance measure is  independent of the host rock, although
the specific design  to achieve it may  well  depend  closely on the   host
rock.  (For  example, various  additives  may be used  in concrete in order
to aid bonding with the surrounding rock.)
    Estimates of  the final  permeability  K-  can  be expected  to vary  from
site  to  site,  depending  on the  harshness of  the  environment  for  the
seal, so it is appropriate that first and second estimates  be different.
The first  estimate value  is taken to be t^  =  10~  cm/sec,  which is in
the range  of permeabilities  expected of sandy  or  silty clays or clayey
sands.  That is, it is envisioned   that,  the design  of the shaft seal can
be so chosen that even with  moderate deterioration  it would be expected
to  behave  equivalently  to  such natural  soils  after  10,000  years.
Similarly, the  second  estimate value is  taken  to be K.. =  10~  cm/sec,
which lies,  for example, within the  range for  silty  sand  or silty   sand
and gravel.    The  permeabilities   of  specific   soil  types   vary greatly
depending  on  conditions  of  compaction,  but the data  in  Figure  D-13
provide a context within which to  interpret the  numbers chosen.
    Values of KQ  and ^  having been specified,  it  is  next  necessary to
estimate the function K(t) that describes the changes from  K  to K...
In  the absence  of detailed  seal  designs and  models  for degradation

                                   84

-------
00
                                      10"
                                                             Hydraulic Conductivity (cm/ssc)
                                                            fl-4     inB     ,n-6
10'7    10R    10 9
                      ,-10
1 1 1 1 1 I 1 1







1 1 1 1 1 1 1 1
Oa/
Silt
Cl»ar. Fi-ie S*"d
Coarse Sa-"1
Si'ty ?3"'1 »n'1 G'a.'-1
SiH.y Sa"H
Compacted Cl.iy *
               Sources:    Stockton, S.L. and A.M. Batch. The Utility of Petroleum Seismic Exploration Data in Delineating Structural Features within Salt
                          Anticlines.  USGS Open File Report 78-591. 1978.
                          Karoi, R.H. Soils and Engineering. Prentice-Hall, Inc., Englewood Cliffs, N.J. 1960.
                          Lambe, T.W. and R.V. Whitman. Soil Mechanics, John Wiley & Sons, Inc., New York.1969.
                          Terzaghi, K. and R.P. Peck. Soil Mechanics in Engineering Practice, 2nd Edition.  John Wiley & Sons, Inc., New York.1969.
                          Charles Stark Draper Labs., Inc. (McGowan, C. et al.). Borehole Plugging by Compaction Process, Final Report.  For Office
                          of Waste Isolation.  Y-OWI-Sub 7087-1. August 1976.
                                           FIGURE D-13   HYDRAULIC CONDUCTIVITY OF NATURAL MATERIALS

-------
                               TABLE n-29
                  PROPERTIES OF POSSIBLE SEAL MATERIALS
Seal Material    Permeability
                   (cm/sec)
                                     Porosity
                                       (%)
                                                       References
Concrete
                 10~6 - 10~12
Compacted Earth  10~6 - 10~10
                                          1-5
                                          1-15
                                                    51,56,61,62

                                                    51,54,63,64
Sand/
Montmorrillonite
Bentonite        10~8 - 10~10
Fused Salt
                 10
                   ~10
                    p      in
Chemical Grout   10-10
Bitumens
                 10
                   ~*10
                                       1-15
                                       0-0.5
                                                       30,51,64

                                                       52

                                                       51,65

                                                       51,62
 These  values  cover   the   ranges  reported  in  the  references  cited.
Testing procedures are not  uniform.   Larger variations  are  possible as
materials and conditions  are varied.
                                    86

-------
mechanisms, the simplest model,  namely  a  linear increase from Kn to K. ,
has been adopted.  This results  in the equation
                       K  .
                              0       10 4
A summary  of  the corresponding numerical formulas  in  two sets of units
is given in Table D-30.

    A constant porosity value,

                    n =  0.1,

is assumed in conjunction with the above permeability values in order to
calculate  actual fluid velocities.   This  parameter is  alsd  subject to
variation  depending  on  the design of  the shaft seal.

D-3.2.4  Shaft Seal Release Model

    A  permeable  shaft  seal  represents a  possible  pathway  for  fluid
migration  from the repository level to  the groundwater system and to the
surface.   If  radionuclides  have been leached  from  the waste package as
well,  they may  be transported to the geosphere  or  biosphere along with
the  fluid.  Releases  to the  groundwater  system would be  expected to
dominate over  those to  the  surface   for several  reasons.   For example,
the  hydrologic  assumptions  for  the  generic  repositories  admit  the
possibility  of   fluid  flow from  the  repository  to the  upper aquifer,
whereas  there  is no mechanism or sufficient  driving  potential to force
water  all  the way  to the  surface.   Transport of  radionuclides  to the
surface  could  only be by diffusion in  any water that  might be seeping
downward to  the  water  table;  diffusion  calculations (see Appendix D-IV)
show that mass transport by  this process  is  exceedingly  small.
Furthermore, radionuclides  migrating  as far up  as  the aquifer would be
largely  washed  into  it by  the  groundwater  flow.     Therefore,   only
releases to  groundwater, and in  particular  to  the upper aquifer,  have
been modeled.  Because certain parameter values  and the  dominant driving
                                    87

-------
                               TABLE D-30

                   PERMEABILITY AS A FUNCTION OF TIME
                    FOR SHAFT SEAL DEGRADATION MODEL
                                  Permeability  (K)
                       (cm/sec)
                               (m/yr)
First Estimate
Second Estimate
10 8 + 9.9 x 10""11 t
10 8 + 9.9 x 10~9 t
3.15 x 10~3 + 3.12 x 10~5 t
3.15 x 10~3 + 3.15 x 10 3 t
                                  88

-------
forces  vary  from  one  host  rock  to  another,  the  release models  are
discussed here for each of  the five geologic settings separately.

D-3.2.4.1  Bedded Salt

    Repository resaturation times for a bedded salt repository are shown
in Table D-31  based  on calculations presented in  Appendix  D-TI.  Since
the pore volume tends to decrease because of salt creep at the same time
that water seeps into the repository, these resaturation times represent
a balance point  at which  the  remaining pore volume  is  exactly equal  to
the volume  of water  that has seeped in.   Naturally  there  will  be some
non-uniformities in  water  distribution as well as  in salt  closure,  but
these factors are not included in the model.
    Since the  shafts  extend down only to  the  repository  level,  they do
not provide  a connection between  the  upper and lower  aquifers.   It  is
possible that  they may  be  coupled  with  other  pathways  from  the
repository to  the  lower aquifer, but this possibility will  be discussed
in  connection  with  these  other  pathways  (e.g.,  deep   degrading
boreholes).  The hydraulic  gradients generated in the cases of thermally
induced convection or the U-tube effect are at most on  the order 1=0.1
or  0.2  .   Furthermore, mass  transport by diffusion  is much  less.  The
effective hydraulic gradient  generated by salt creep may be estimated as
follows.  The  pressure  exerted by  the  salt on the pore water  is roughly
equal  to  (and certainly bounded by) lithostatic  pressure,  which can be
approximated  by twice  the  hydrostatic  pressure  of  a  column  of  water
extending to  the surface.   For  a  repository whose depth  is  460 meters
(recall Figure  D-9),  this   corresponds  to a  pressure  head of  920 meters
of water.  The  permeable shafts  cover  a distance  of 100 meters  from the
repository to  the  bottom of the  aquifer,  at which point the hydrostatic
pressure is roughly  30 meters of water-   Therefore, a net pressure head
of  920-100-30 =  790 meters  of  water  acts over  a path length of  100
meters, corresponding  to a  hydraulic gradient i =  7.9.   This number is
slightly  conservative  in the  sense of  overestimating the driving  force,
and hence appropriate  to the  approach  of the present report,  because as
long  as  there  is  a permeable  pathway  from  the repository, full
lithostatic  pressure  on the  pore  water  will never  quite  be  achieved.

                                   89

-------
                                   TABLE 0-T!


                         REPOSITORY RF.SATURATION TIMES

                            (BEDDED SALT REPOSITORY)
                                                         Fluid Volume at
                         Time to Resaturation            Resaturation
                                 (yrs)                         (nf )


First Estimate                    200                       1.2 x 101


Second Estimate                   720                       5.6 x 10
Source:   Appendix D-II.
                                  90

-------
It is clear  from  this  calculation that salt creep provides  the dominant
driving  force  until  the salt reaches  a  state  of approximate mechanical
equilibrium.    The  period   between  resaturation  and  arrival  at  this
equilibrated state will be  called Period A.
    The  effective hydraulic gradient  just calculated  can be  used  in
Darcy's  law  to  calculate  volumetric fluid  flow  and  fluid vplocity.   Tn
particular
                            Q =   KiAc(w),
where
          •
          Q   = volumetric fluid flow  rate through permeable  shafts;
         K   = hydraulic conductivity;
          i   = hydraulic gradient;
         A   = total  cross-sectional  area of  the  shafts;
      c(P)   =  viscosity correction  factor,  given by  .01/U,  where V  is
              the  viscosity in  poise.  (Note that  0.01  represents  the
              viscosity   of  water  at   20°C,   so  that  c(u)   is
              dimensionless .)
Values of the  function K(t) have been given in  Section D-3.2.3 and  are
summarized  there  in Table  D-30.  The  total cross-sectional shaft  area
                                               2
was also  specified  in  that  section  as  A =  100 m  .  While  the viscosity u
varies with  temperature and  hence with depth, the value y =  0.002  poise,
which corresponds  to a temperature  of  125  C, will be used throughout, so
that  c(vO  =  5.    (For further details  on temperature  and viscosity
distributions,  see Appendix D-VI.)
    It  is important to keep  in mind that  releases via  this pathway
continue  to  occur  for  a  limited   time  only,  determined  by  the  time
necessary for  essentially  all   the  water  that  has  seeped  into  the
                                   91

-------
repository to be squeezed back out.  Using the first estimate parameter
values, the cumulative outflow by  time T is given by
                         T  .
                 Q(T)  =  /  Qdt
                        200
                         T                -3            -5
                         /   3950(3.15 x  10   + 3.12 x 10   t)dt
                         200
                         0.062 T2 +  12.4 T - 4953
Complete depletion of the volume  V of  water  in the repository would be
achieved by this single  pathway  at the  time T when Q(T) = V; that is
                         Q(T)
              0.062 T2 + 12.4 T  -  4953 = 1.2 x 103
                            T   =231 years.

However,  permeable  boreholes are additional pathways. Since  these
account for  some  of the  outflow,  the  water will  be  depleted slightly
sooner.   Calculations  in Section  D-3.3.4  show that  this time  is the
                                                              •
period  from  200  to 223 years; thus the  volumetric  flow rate Q through
the  shafts is  almost 40  m /yr-   Note  that this is  only an  approximate
release  period,  not  only  because  of  variability  and  uncertainty  in
parameter values but also because the  fluid volume will  change somewhat
because of  the dissolution  of  some   of  the  salt.   Corresponding
calculations  for  second  estimate  parameter  values  require  some
modification in  the method.   These calculations  yield  a  total  water
release by a time that  is earlier than the  hypothesized  time  of complete
repository closure, given as 1000 years.  This implies  that  the rate of
closure is the controlling  factor in this case, the permeability of the
shafts  being sufficiently  high  so that   the  water  moves out  relatively
easily.   The  release  rate  will  therefore  be modeled  simply  as the

                                  92

-------
constant rate  of  void space volump  change  assumed in the closure  model
                                ATT                 1  "\
of Appendix D-VTI, namely 2 x  10  in  /10  years  or  2 x  ]0  m  /year.
    Vertical  fluid velocities  may  be  obtained by dividing  the "Darcy
velocity,"

                                Kic(u),

by the  effective  porosity n, which  was  given in Section D-3.2.3 as  n  =
0.1 .  Therefore,  the velocity v is  given by  the formula:
                                Kic(u)
                          v  =  	—
                                  n
                                nA
where the units are m/yr.  It  follows  that  the  approximate  average  fluid
velocities  and  the  corresponding  transit  times  from  repository  to
aquifer are as given  in Table  D-32.
    All the calculations  performed  so  far in this section  have been  for
Period  A,  which  represents  the period  of non-negligible salt creep.
During  this   period,  the  dominant   driving mechanism  is  the  pressure
produced by   this  process.   By  the  end of  this period,  the salt  has
reached a  state  of approximate  mechanical  equilibrium..  The  water  that
seeped  in during  the resaturation  period has  been forced  back out,  and
the  repository is  still  saturated  but  the fluid volume  is  relatively
small.    The   tunnel  backfill  has  been  compacted,  probably  to   near
equilibrium, but it still  has  some  permeability to fluid  flow.
    During  the ensuing  period  of  time,  called  Period  B,  the U-tube
effect  is the dominant driving  force.  The  effective  gradients have been
calculated  in Appendix  D-V and  are  summarized  in   Table  T)-33.   These
gradients may be  applied  with Darcy's law to  calculate the  volumetric
flow  rates  shown in  Table D-34.   (The  cross-sectional area  is  A =  50
 2
m .)   Corresponding  fluid velocities  are  given  in  Table D-35.    The
source  term  for this  failure  element consists  of  the concentration  of

                                    93

-------
                                 TABLE D-32

         APPROXIMATE FLUID VELOCITIES AND TRANSIT TIMES TO AQUIFER
                   ALONG PERMEABLE  SHAFTS DURING  PERIOD A
                          (BEDDED SALT REPOSITORY)
                                 Fluid Velocity          Transit  Times
                                     (m/yr)                    (yr)
First Estimate                        4                          25

Second Estimate                     200                           0.5
                                  94

-------
                               TABLE D-33
       EFFECTIVE VERTICAL HYDRAULIC GRADIENT TN PERMEABLE SHAFTS
                    FROM U-TUBE EFFECT DURING PERIOT) B
                        (BEDDED SALT REPOSITORY)
                                    Hydraulic Gradient (i)
                      223 years*
                   1000 years
                 10.000 years
First Estimate
Second Estimate
0.03
0.02
                                    **
Not applicable     0.004
0.004

0.0004
  Years after repository closure.
**
  Ptriod B only begins at 1000 years after repository closure in the
cast:   of second estimates.
                                   95

-------
                               TABLF. 0-34

             VOLUMETRIC FLOW RATES THROUGH PERMEABLE SHAFTS
                             DURING PERIOD B
                        (BEDDED SALT REPOSITORY)
                                  Volume trie Flow (Q)
                                        (m /yr)
                      223 years
                   1000 years
                 10.000 years
First Estimate
0.08
0.17
0.32
Second Estimate
Not applicable     3.15
                 3.15
 Years after repository closure.
                                   96

-------
                               TABLE D-35

                FLUID VELOCITIES THROUGH PERMEABLE SHAFTS
                             DURING PERIOD B
                        (BEDDED SALT REPOSITORY)
                                         Velocity (v)
                                            (m/yr)
                      223 years
                                         1000 years
                 10.000 years
First Estimate
                      0.02
0.03
0.06
Second Estimate       Not applicable     0.63
                                                          0.63
 Years after repository closure.
                                   97

-------
radionuclides that have leached into the water in the repository during
the time frame of interest.
    Dissolution along the  flow pathway  is  expected to be minimal because
of  the  limited volume of  fluid  that would come  into  contact with  the
actual boundary  of  the shaft.  In  addition,  half of  the  shaft length
between repository  and  aquifer is through a  shale  layer.   Even if  the
entire  portion  of   the  shaft  through  the  salt  were  to   be  "short
circuited" by  dissolution  pathways  along  the  edfges, the resulting  flow
would increase at most by a  factor  of  two (since the driving  potential
would  be  dissipated over  half  the  length,  thereby  doubling   the
gradient).  The  coupling of this pathway with others, such as  degrading
deep boreholes,  is  possible  during  the period before salt creep closes
the  repository,   but  the  corresponding  hydraulic  potential  would be
sufficiently  small  that   this effect  would  neither  persist  nor be
significant compared with the release model presented  above.

D-3.2.4.2  Granite

    Assuming  that repository  resaturation  has  taken place, two driving
forces  need  to be  evaluated  for  their potential contribution to fluid
flow  from  the repository to  the  aquifer.  These  forces  are  thermally
induced convection  and  the  U-tube  effect.   (Note  that  molecular
diffusion  is  always   negligible  compared  with  mechanisms   that   move
radionuclides by  fluid  flow,  and  that  there is no lower aquifer in the
generic  granite  repository.)   Both of  these forces  are  functions of
time.    Thermally  induced  convection  depends  on  time  because   the
temperature  profile changes  with time.   The U-tube  effect  depends on
time because  of  the gradual  change  in  the  hydraulic  conductivity of the
shaft seals.   The values  of the corresponding gradients,  if  calculated
independently,  are  shown  in  Table  D-36.   These values  are based on
Appendices D-V and  D-VI.  These effects interact, tending  to  move water
in  opposite  directions in those  shafts  where  the  U-tube  effect would
lead to a downward  flow.   For the present calculations, flow  rates are
based on the  larger of the two effects.   Since  the  flow pathway  for the
U-tube  effect  is  half  that  for  thermally  induced  convection,   the
                                        98

-------
                               TABLE D-36

        EFFECTIVE VERTICAL HYDRAULIC GRADIENT IN PERMEABLE SHAFTS
             FROM THERMALLY INDUCED CONVECTION AND U-TUBE EFFECT
                          (GRANITE REPOSITORY)
                             Hydraulic Gradient (i)
                            *
                   100 years           1000 years          10.000 years
Thermally Induced
Convection

  First Estimate        0.10                0.06                0.01

  Second Estimate       0.10                0.06                0.01

U-Tube Effect

  First Estimate        0.02                0.02                0.02

  Second Estimate       0.17                0.12                0.03
*
 Years after repository closure.
Source:  Appendices D-V and D-VI.
                                   99

-------
effective gradients  for  the  former need to be  more than twice as large
for that effect to dominate.
    The volumetric flow rate is calculated from the equation:
                            Q  =  KiAc(p)
where
                                        Kl - K0 t
                            K  =  K  +  ~	~
                                   u       10
                                  50 or 100
                         c(u)
and  i is  given  as a  function  of  time in  Table D-36.   The  value of
permeability K as  a  function  of  time  has been given previously in Table
                           2
D-30.   Note  that A =  50  m  in the U-tube  cases because  only half the
total  cross-sectional  shaft   area  is  used  for  transport  upwards.   The
results of the calculation are  given  in Table D-37.   By a modification
of these results one obtains  the fluid velocity from the formula

                            v  =  Kic(u)/n

                               =  Q/nA
in m/yr, where  the  porosity  n  = 0.1, given  earlier,  has been employed.
The corresponding velocities are given in Table D-38.
    The  source  term  for  this  failure  element  consists  of  the
concentration of  radionuclides  that  have leached  into  the  water in the
repository during the time frame of interest.
    No significant coupling is expected between this  failure element and
others.   In addition, the  flows  evaluated  here  are much  smaller than
those  through  the bulk  rock, and therefore  this  failure element is not
very significant  for the granite repository.
                                   100

-------
                               TABLE D-37
             VOLUMETRIC FLOW RATES THROUGH PERMEABLE SHAFTS
                          (GRANITE REPOSITORY)
                                 Volumetric Flow (Q)
                                       (m /yr)
                   100 years
                1000 years
                10.000 years
First Estimate
 0.3
 1.0
  1.6
Second Estimate
15.9
94.6
236.3
 Years after repository closure.
                                   101

-------
                               TABLE D-38
                FLUID VELOCITIES THROUGH PERMEABLE SHAFTS
                          (GRANITE REPOSITORY)
                                       Velocity  (v)
                                          (m/yr)
                   100 years
                1000 years
                 10.000 years
First Estimate
O.CP
 0.1
 0.3
Second Estimate
3.2
18.9
47.3
 Years after repository closure.
                                  102

-------
D-3.2.4.3  Basalt

    Assuming  that  repository  resaturation has taken place,  two  driving
forces  need  to be evaluated  for  their potential  contribution to  fluid
flow  from  the repository to  the  aquifer.   These forces  are  thermally
induced  convection  and   the  U-tube  effect.    With respect  to  other
potential driving  forces, note  first  that molecular  diffusion  is always
negligible  compared  with mechanisms  that  move  radionuclides  by  fluid
flow.   Second,  the  other  potential  driving mechanism—the  hydraulic
gradient  resulting  from  the  connection  between  the  lower and  upper
aquifer—cannot  result  from shaft  seal  degradation  alone  because  this
does  not  provide a  pathway to  the  lower aquifer.   It  is  possible  that
the shaft seal  failure may  interact with  other pathways to the aquifer,
such  as degrading deep boreholes, and this possibility will be  evaluated
later in this  section.  Both thermally induced convection and the U-tube
effect  are  functions of  time,  and   the  analysis  for basalt  closely
parallels  that  presented  in  the   previous  section   for  granite.
Therefore,  this  section  will  concentrate  on  a   summary  of  the
corresponding  results for the basalt repository.
    The values of  the  effective hydraulic gradients  corresponding  to
thermally  induced  convection  and   the   U-tube  effect,  if  calculated
independently,  are  shown  in  Table D-39.    As  discussed earlier,  it
follows  that  for  the  purposes  of calculating  the joint effect  the
maximum of  the individual effects may  be  utilized.  The volumetric  flow
rate  calculations  are summarized  in Table  D-40,  and   the  actual  fluid
velocities  are shown in  Table D-41.  As  in the case of granite it turns
out   that  these  quantities  are  negligible  with  respect  to  those
calculated  earlier for  flow  through  the  bulk rock, and  therefore  they
are  relatively unimportant.  The source  term for this failure  element
consists  of the concentration  of radionuclides that have leached  into
the water in  the repository during  the time  frame of interest.
    A certain  degree of  coupling between  this  failure  element,  and
others,  such  as  permeable boreholes, is  possible.   In  the  case  of
first-estimate  calculations, the  assumed hydraulic potential between the
upper and  lower aquifers (see  Chapter D-2.0) is  sufficiently small so
that  even  if  this  factor were  added  to  the gradient operative from the
                                   103

-------
                                TABLE  D-39




         EFFECTIVE VERTICAL HYDRAULIC  GRADIENT  IN  PERMEABLE  SHAFTS

           FROM THERMALLY INDUCED CONVECTION AND  TJ-TUBE  EFFECT

                            (BASALT REPOSITORY)
                               Hydraulic Gradient  (i)
                            *
                   100 years           1000 years          10.000 years
Thermally Induced

Convection




  First Estimate       0.12                0.10                0.03




  Second Estimate      0.12                0.10                0.03



U-Tube Effect




  First Estimate       0.04                0.04                0.04




  Second Estimate      0.36                0.20                0.04
*
 Years after repository closure.
Source:   Appendices  D-V and  D-VI,
                                  104

-------
                               TABLE D-40
             VOLUMETRIC FLOW RATES THROUGH PERMEABLE SHAFTS
                           (BASALT REPOSITORY)
                                   Volumetric Flowx(Qj
                                         (m3/yr)
                   100 years
                1000 years
                 10.000  years
First Estimate
 0.4
 1.7
Second Estimate
28.6
157.6
472.6
 Years after repository closure.
                                  105

-------
                               TABLE D-41



                FLUID VELOCITIES THROUGH PERMEABLE SHAFTS

                           (BASALT REPOSITORY)
                                       Velocity (v)

                                          (m/yr)
First Estimate
                   100 years
                      0.04
                                      1000  years
 0.2
                 10.000 years
 0.6
                                                                  **
Second Estimate
                      5.7
31.5
63
                                                                **
**
 Years after  repository closure.
k
 Although the maximum  volumetric  flow rate in  this  case would  result

 from  thermally  induced convection,  the maximum velocity  corresponds  to

 the U-tube effect.
                                  106

-------
U-tube or thermal convection cases the result would not be significantly
modified.   The value of  the  second estimate  for  the average hydraulic
gradient  for  the  upper  and  lower  aquifers  is   considerably  larger,
however,  namely,  0.5.     This  corresponds  to a  hydraulic  potential
equivalent  to  100 meters  of  water  acting  over the  200-meter distance
between  the  upper  and lower aquifers.   The corresponding flow would be
in the upward direction.  If a significant  portion  of this driving force
is dissipated over the  upper  half  of the flow pathway, namely, from the
repository  to  the   upper aquifer,  then it  is  possible  that  the
corresponding  gradient   over  this  pathway  is greater  than  that  from
either thermally induced  convection  or  the  U-tube  effect.  Calculations
(see  Section D-3.3)   show  that  this is  not the case, however.   In the
case  of  second  estimates,  the  permeability  function   describing  the
performance of the shaft seals is identical to  the  permeability function
describing  the performance  of the  boreholes.  Therefore the  drop in
hydraulic potential  over  the  shaft  seal  pathway from the repository to
the  upper aquifer compares  with that  over the  10 boreholes  from the
repository  to  the  lower  aquifer  in  inverse  proportion  to  the
corresponding  cross-sectional  areas.   Since these  cross-sectional areas
have  been assumed to be in  the  ratio  100 to  1,  it is  clear  that the
overwhelming fraction of the hydraulic potential drop is dissipated over
the lower half of  the pathway and  the contribution to flow in permeable
shafts  is negligible.  Therefore this  interactive  effect does not need
to be considered  further.    Even  beyond  considerations  such as  this,
however,  is  the  fact that  the  flows through  the  shafts  are themselves
small  in terms  of   both  volumetric rates and  fluid velocities  with
respect  to those through the bulk rock.

D-3.2.4.4  Shale

    With  respect  to  all  the modeling parameters relevant  to  the  present
release mechanisms,  the  basalt  and  shale repositories appear  identical.
Therefore the discussion and the numerical  computations for basalt  carry
over the shale.  Tables D-42 and D-43 summarize these  results  for  shale.
                                   107

-------
                               TABLE D-42
             VOLUMETRIC FLOW RATES THROUGH PERMEABLE SHAFTS
                           (SHALE REPOSITORY)
                                 Volumetric Flow (Q)
                                       (m3/yr)
                   100 years
                1000 years
                 30.000 years
First Estimate
 0.4
  1.7
  3.2
Second Estimate
28.6
157.6
472.6
 Years after repository closure,
                                  108

-------
                               TABLE D-43
                FLUID VELOCITIES THROUGH PERMEABLE SHAFTS
                           (SHALS REPOSITORY)
                                       Velocity (v)
                                          (m/yr)
First Estimate
                   100 years
                       0.04
                                      1000 years
0.2
               10.000 years
0.6
                                                                   **
Second Estimate
                                          31.5
                   63.0
                                                                   **
**
 Years  after repository closure.
*
 Although the maximum volumetric  flow rate in this case would result
 from thermally induced convection,  the maximum velocity corresponds to
 the  U-tube effect.
                                   109

-------
D-3.2.4.5  Dome Salt

    Repository resaturation  times for  a repository in  a salt dome  are
shown  in  Table 0-44,  based on  calculations  presented  in Appendix  D-II.
Since  the pore  volume  tends  to decrease because  of salt  creep  at  the
same time that water seeps into the repository,  these resaturation  times
represent a balance point  at  which the remaining pore volume  is  exactly
equal  to  the  volume of water  that  has seeped in.   Naturally  there will
be  some non-uniformities both  in water  distribution  and  in  salt closure,
but these factors are not included in  the model.
    The analysis  of  the dominant driving forces to  cause water  to move
from a salt dome  repository  to the groundwater is analogous to that  for
bedded salt.  Therefore this  section  will  simply  summarize differences
in  the parameter values and in the numerical  results.
    First,  for   the  period  of  extensive salt  creep  (Period A),  the
effective  hydraulic gradient  tending  to force  water  along  permeable
shafts needs to be recalculated because  the distance from the  repository
to  the upper aquifer is different  in  this case.   In particular there is
a net  pressure head  of 920-230-30 =  660 meters  of  water  acting  over  a
path length of  230 meters  (cf.  earlier calculations for bedded  salt).
This yields an effective  hydraulic gradient  of  i - 2.9.   Calculations
proceed analogously to  the case  of  bedded salt.   For the first estimate
case,  Period  A  extends from 200  to   about  260  years  after  repository
closure,  with an average volumetric flow rate Q equal to about 15 m /yr-
For the second estimate case, Period  A extends  from 748  to  1000  years
after  repository  closure,  with an average volumetric flow  rate Q  equal
               o   o
to about 2 x 10   m /yr.   The  corresponding fluid velocities and  transit
times are shown in Table D-45.  Fluid flows during  Period B result from
the  U-tube effect.     Effective  gradients  are  given  in  Table  D-46,
volumetric flow rates in Table D-47, and fluid velocities in Table  D-48.
The source  term  for  this  failure element  consists  of  the  concentration
of  radionuclides  which have  leached   into the  water in  the  repository
during the time frame of interest.
    Dissolution  along the flpw pathway  is expected to be minimal  because
of  the limited volume   of  fluid  which would  come  into  contact with  the
actual boundary  of  the shaft.   In addition, half  of  the  shaft length
                                    110

-------
                               TABLE D-44
                      REPOSITORY RESATURATION TIMES
                         (DOME SALT REPOSITORY)
                       Time to Resaturation
                              (yrs)
                   Fluid Volume at
                   Resaturation
                         (m3)
First Estimate
200
  865
Second Estimate
748
5 x 10'
Source:  Appendix D-II.
                                   Ill

-------
                               TABLE D-45

        APPROXIMATE FLUID VELOCITIES AND TRANSIT TIMES TO AQUIFER
                 ALONG PERMEABLE SHAFTS DURING PERIOD A
                         (DOME SALT REPOSITORY)
                        Fluid Velocity           Transit Times
                            (m/yr)                     (yr)
First Estimate               1.5                       150
Second Estimate            200
                                  112

-------
                               TABLE D-46

        EFFECTIVE VERTICAL HYDRAULIC GRADIENT IN PERMEABLE SHAFTS
                   FROM U-TUBE EFFECT DURING PERIOD B
                         (DOME SALT REPOSITORY)
                                   Hydraulic Gradient (1)
                   260 years
                  1000 years
                  10 .000 years
First Estimate
0.014
0.012
0.003
Second Estimate    Not applicable
                    0.004
                    0.0004
 Years after repository closure.
                                   113

-------
                               TABLE D-47

        VOLUMETRIC FLOW RATES IN PERMEABLE SHAFTS DURING PERIOD B
                         (DOME SALT REPOSITORY)
                              Volumetric Flow (Q/
                                   (m /yr)
                   260 years
                1000 years
                10.000 years
First Estimate
0.04
0.10
0.24
Second Estimate    Not applicable
                    3.15
                    3.15
 Years after repository closure.
                                  114

-------
                               TABLE D-48

        FLUID VELOCITIES THROUGH PERMEABLE SHAFTS DURING PERIOD B
                         (DOME SALT REPOSITORY)
                                    Velocity (v)
                                      (m/yr)
First Estimate
                   260 years
0.01
Second Estimate    Not applicable
                  1000 years
0.02
                    0.63
10.000 years

  0.05

  0.63
 Years after repository closure.
                                  115

-------
between repository and  aquifer  is through a  shale  layer.   Even if  the
entire   portion   of  the  shaft  through   the   salt  were   to  be
"short-circuited" by  dissolution  pathways  along  the  edges, the resulting
flow  would  increase   at  most  by a  factor  of  two   (since  the driving
potential would be dissipated  over half  the length,  thereby doubling  the
gradient) .

D-3.2.5  Literature Discussion

    The shaft seal failure model  has  also  been discussed by TASC.   '
While recognizing  that  the  condition  of  a  sealed shaft  is  both
temporally and  spatially  dependent,  they do  not  try  to  quantify this
dependence.   Instead  they  perform a number of  flow calculations based on
the assumption of  a  shaft with "failed  backfill."   The parameters used
for  the  analyses are  summarized  in   Table  D-49.    For  purposes  of
sensitivity analysis, permeabilities were varied by up to  three orders
of  magnitude,  and  porosities  by  one  order  of  magnitude.    These
parameters were not based  on specific designs  or site characteristics.
D-3.3  BOREHOLE SEAL FAILURE

D-3.3.1  Summary

    During both the  preliminary and  the  detailed  site evaluation for a
repository, a number of boreholes will be drilled to various depths at
the   site.    These  will  be  used  for  geologic  and  hydrologic
characterization of  the site as well  as  to determine the potential for
mineral and energy  resources that may be sought  on  the  site  by future
generations.    In  addition to  these  boreholes,  which will be drilled
specifically  for  repository  site  investigations,  there may be  old
boreholes  on  the  site representing  previous water,  mineral,  or energy
resource  exploration  or  exploitation.    In  some  cases,  it may  be
difficult  or   impossible  to  find  these  older  boreholes;   the  risks
associated with those that remain  undetected  are discussed as  a separate
failure  event  in  Section D-3.4.    All  old  boreholes that  are found,

                                  116

-------
                              TABLE D-49

            BASELINE  PARAMETERS USED BY TASC IN FAILED SHAFT
                            SEAL CALCULATIONS
                     Permeability        Porosity            Area
                        (cm/sec)             (%)               (m2)
                             -4               -3
Fracture zone  around        10              10                 10
  shaft through shale
                             —                _
Fracture zone around        10              10                 60
  shaft through salt

                             /                *")
Shaft with failed           10              10                 64
  backfill
Sources:    The Analytic  Sciences  Corporation  (Berman,  L.E.,  et  al.)«
          Analysis  of   Some  Nuclear  Waste  Management  Options.    For
          Lawrence  Livermore  Laboratory.  UCRL/13917;  TR-1100-1-1.
          October  10,1978.

          The  Analytic  Sciences  Corporation  (Koplik,  C.M.  et  al-).
          Information  Base  for  Waste  Repository  Design.   Vol.  I.
          Borehole  and  Shaft  Sealing.    For  U.S.  Nuclear  Regulatory
          Commission.  NUREG/CR-0495, TR  -  1210-1.  March 1979.
                                  117

-------
however,  are  expected  to  be redrilled  and replugged  according to  the
same  specifications  as the new boreholes  drilled during the  repository
site  evaluation.   The  purpose of  this section  is to present a  model  of
the  performance  of  borehole  plugs emplaced  as  part  of the  repository
sealing process.  Both  the general considerations and  the specific  model
approach parallel  to a considerable  extent the discussion on  shaft  seal
failure  presented  in  the  previous   section,   to which  reference  will
frequently be made.
    The  borehole  sealing   materials  will  need   to  be  chosen  with   a
specific  environment in mind, so  that  they may  approach,  as nearly  as
possible, chemical and mechanical  equilibrium with  the  surrounding  rock.
The seal may consist of several layers of completely distinct  types  that
provide a multi-barrier line of defense against  expected  or  unexpected
forces.   Nevertheless,  it  is  reasonable  to  expect  that   over a  long
period of time, say, 10,000 years, the  combination of processes  such  as
settling, leaching,  expansion or  contraction  from fluctuations  in water
content  or  temperature, earth  movements,  weathering,  and  fatigue may
lead  to some degradation in the integrity of the  seal.
    The borehole  seal performance model in  this report  is not based  upon
a  particular  design.   It  is intended  to be  "generic" in  nature and
conservative;  that  is,   it   is  believed  that   the   performance
characteristics described  here can  be equalled  or  exceeded  by actual
designs for specific circumstances.
    The specific  model in  this report  characterizes  the  borehole  seal
integrity in terms of a spatially uniform hydraulic conductivity K.  One
hydraulic conductivity value  (KQ) is  estimated   for  the time  of  seal
emplacement, and  another value  (K-)  is estimated for  the  time  10,000
years later.  It  is  assumed that K increases linearly  from KQ  to K,  over
this  period.   The  specific values of the   parameters  used  as  well as  a
summary of the corresponding  release models are given  in Table D-50.

D-3.3.2  Background

    Site exploration and repository monitoring will  involve  the  drilling
of a  number of  small diameter (less  than  0.5 meter) boreholes  into the
host  rock  and  surrounding   formations.    These  borings will   provide
                                   118

-------
               TABLE D-50
SUMMARY OF BOREHOLE SEAL FAILURE ELEMENT
MEDIUM










BMa.lt



= 1
_l Z
i§
C O









0



NATURE
OF
MODEL

• -
* .







(Jneerty mcreesina
pameeUllitv


RELEASE


GlUUIUWetef



nrfiM
GlUUflUlMlaf



Groui.tl*.lter



DRIVING



th.Hn...4lv.ndue.>d
osadMrnftm aquifer
borahoto emending
to tower equifer.



convection

TtwrneUy indue-
•radiem from equifer
to lower equifer.

SOURCE







Unif Drift


Uniform



PARAM
let ESTIMATE
.g

K,- 10* cm/sac after
10.000 years
K increases linearly
10.000 years
D - 0.1
to repository. 10 of
which continue to
A - 0.1 m2/borehale
r»*
KQ" 10 uii/sat al
10.000 years
K increases lineerty
from Kg to K, over
10.000 year.
i, - O.I
to repository
A - 0.1 m2/bonmole
KO- 10*cnuascet
Kj-io6 cm/asc after
10.000 yeses
from KO to Kf over
10JMO years
7 • 0.1
to repository. 10 of
which continue to
lower aquifer
A - 0.1 m2/borehale
ETERS
2nd ESTIMATE


K.- 10-4 cm/sec after
10.000 yam
K increases linearly from
KQ 10 K*! over
lO^fOOyearv
q - 0.1
to repository, 10 of
which continue to
lower aquifer
A • 0.1 m2/botehole


K,- 10"* cm/sac after
10.000 years
K inn sales linearly from
K0tO K| OMT
10.000 years
n - 0.1
A - 0.1 n>2/borehole
Kg- 10-8 cm/sec et
K,- «r4 cm/sac after
10.000 years
K0toK1oMr
q - 0.1
to repository. 10 of
which continue to
lower aquifer
A - 0.1 m2/bonhote
R
1st


200
223-
223+
1000
10.000



too
1000
10.000

tlyfal
100
1000
lOjOOO

FLUID FLOW 1
EPOSITORV TO
ESTIMATE
3

.4) Period
> of salt
"jcrasp
0.05
0.18
0£3



0.1
0£
2.4

O It) Im'/yrl
O.OS
0.4
1.6

tATESFI
UPPER t
2n


720
1000'
1000*
10400



100
1000
10.000

tlyrs)
100
1000


ROM
OUIFER
d ESTIMATE
3

100 psS;
100 (creep
19
167



03
B.S
31 .5

0 It) Im3/yrl
2.0
19J
170.1





•fttr rapontorv
reMtur.rt.on. Diwolu-
tioo in salt tav.w b
included in woond
for period after exten-
tivtialt creep.



after iepotL*UM~y letat*

RriM»onlybNm
uratton



-------
                                                       TABLE D-50
                                   SUMMARY OF BOREHOLE SEAL FAILURE ELEMENT (CONTINUED)


MEDIUM


Shale











Dome Salt








£9
- P
j 5
S £
4 orehole

FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER

In ESTIMATE

tlyra)
100
1000

10,000
Q (t) tm3/yrl
0.05
0.4

1.6







t(yrc)

200
260"
260+
1000

10,000
Q (t) (m3/yr)

5 law
S | crap
0.01
0.03

0.16


2nd ESTIMATE

.(vn)
100
1000

10,000


Q (t) Im3/vrl
2.0
19.2

170.1







tlynl

748
1000"
1000*
10,000


Q It) Im3/vr)

100 1 creep
1,6
2.8







COMMENTS

Releens only begin after
rvpofftory maturation.










Releani only begin
after repository
resaturation. In con-
trast to undetected
borehole failure ele-
ment, holes in this case
are near or through
repository and so can-
not intersect lower
aquifer at edge of salt
dome.
N3
O

-------
information on  the depth,  thickness,  lithology, geohydrology,  and
structure of the  geologic  formations at the  site.   Core  samples  taken
from the drill holes  can be used for laboratory  studies  of  mineralogy,
chemistry,  porosity,  permeability,  strength, etc.,  and  the  collective
data can  be used  in  the  evaluation of  the site's  suitability  for  a
repository.  Major  factors of  interest  include  the  effectiveness of the
geology in providing  a barrier to radionuclide escape  and the  possible
presence   of  natural  resources  that might  be  sought  by  future
generations.
    In addition to holes that are related to the repository,  a number of
boreholes may have  been drilled previously for unrelated  purposes,  for
example, to explore  or to exploit water, mineral,  and  energy resources
at  the  site.    Drilling  records  from such  holes might  also serve  to
enhance the  information obtained  from  the repository-related  borings,
particularly in  assessing  the economic  potential  of  a  site  and  the
effects of  its  loss to future generations.   Of course, it  is  possible
that one  or more  pre-existing holes may  fail  to  be  identified.   The
problem of  undiscovered boreholes is discussed  in  Section D-3.4;  this
section is concerned only with those that are identified.
    The technology  for  plugging boreholes  for abandonment  has been well
developed,  especially in response to legal  requirements  by the petroleum
producing states.   These  requirements are  primarily intended  to  prevent
the  contamination of  water  supplies  or  the  escape  of  fluids  to  the
surface.  Plugging  or  replugging  has  also  been carried  out  in  order to
seal off depleted gas  fields so  that they might be used  for  storage of
injected  gas.    In addition  to  sealing  for abandonment,  plugging
techniques  have been  developed  for a number of other purposes,  such as
separating productive  horizons, diverting  drill strings from a  blocked
.  ,     ,             . .       (51,56,62,66,67)
hole, and  preventing blowouts.
    The most common sealing materials for abandoned  boreholes are cement
and heavy mud.   They  are  usually used  in combination,  with  the cement
being placed against  permeable  or soluble  formations and  the dense mud
providing  support for the cement.   The cement  is formulated to withstand
chemical attack  and to provide adhesion  with  the  rock.   For  example,
salt is typically  added to the cement if  the  plug  is placed in a salt
formation, in  circulating brines, or  in  water  sensitive  shales.
                                  121

-------
Sulfate-resistant cements are used near evaporites or where  groundwater
contains sulfate ions,  and  other  formulations  are  available  for
different  adverse conditions.   Typical  muds  consist of  starches  and
clays suspended  in water  and  brine,  and  barite or other dense  minerals
may  be  added  to  adjust  the  mud's  density.        A cement-mud plug  is
shown schematically in Figure D-14.
    Studies examining  the  suitability of  concrete  plugs for  boreholes
into a nuclear repository have noted  some  of  the  problems that  can  arise
                                                                   (53)
in  connection  with  plug  emplacement and  long-term stability-
Furthermore, because a cement slurry has a high viscosity compared with
water,  it  is  questionable whether  cement could  successfully  seal  the
fine fissures  or permeable zones  in  the rock  immediately  surrounding  the
borehole.
    If  injection  pressure  were  to be  high enough to  force  the cement
deeply enough  into the rock to seal  fine  fissures, the  fissures might be
extended by induced fracturing.
    The  problems  involved  in designing  cement  seals  and  in  emplacing
them properly are emphasized by  some  failures  that  have been noted in
the past.  For example, in one study, the  quality of plugs in  abandoned
                                                     (fiT. ^
holes was  checked about  40 years after  emplacement.       Twenty holes
were  rebored   and  the  findings  compared  with  plugging  records.
Forty-nine plugs had been set in  these twenty wells.  The findings were:
    •  11 plugs (22%)  were missing,
    •  6 plugs (12%)  were soft,
    •  5 wells (25%) had  all  plugs  soft or missing,
    •  10 wells (50%)  had soft or missing  bottom  plugs, and
    •  2 wells (10%) had  no top plugs.
Naturally,  one  expects  significant improvements  after the  many
intervening years of development  of  materials and  engineering practices.
But it is also  true that the  degradation  referred to took place over 40
years, and  the  repository model  is  concerned  with a  period of 10,000
years.    In  any  case,   uncertainties   remain  about  the  long-term
performance capabilities  of cement  plugs.
    Along with  continuing  investigations  into  cement's  behavior  as  a
borehole plug material, work has also been conducted on the properties
of other sealants and  fillers, and  on other plugging methods.  Among  the
                                   122

-------
         Ground
                                             Steel pipe with marker or
                                 r~Ti   ^-^"  pipe cut off below plow depth
« . 1

Cement ' ^ ;
<*
Cement pluy
Mud-Tilled hole
x*
**
Cenieni pluy
Casing stub
(may or may •"
not be in hole)
Cement pluy
'&//'
yy///;
x-v^-w
-**\*ST~'

v\


ffi/'
7///<

Xt-1x^
*-H-^
^^

0
lUJI

^
^P
^
^

s. r» ^
H " outface casing


*
"~~~~~" * Fresh water strata
	 	 	 below surface casinq
Mud-filled hole
x-
w
Murl fillrrl hnln

Production horizon -May
have perforated casiny

Source: Adapted from Herndon, J. and O.K. Smith. Plugging Wells for Abandonment: A State of the
       Art Study. For Office of Waste Isolation. Y/OWI/Sub-76/99068, 1976.

           FIGURE D-14  TYPICAL PLUGGED BOREHOLE
                                      123

-------
other  materials  examined  are  a  variety  of  chemical  sealants,  natural
sealants,  original  formation  rock,  and  earthen  fills.    Emplacement
techniques  include injection,  catalyzation,  high-temperature  melting,
               (47,52,54,55,58)
and compaction.
    Some of the chemical sealants have properties that enable them to be
used  in conjunction  with cement  to  overcome  the  limitations  of  the
latter  alone.  For  example, plasticizing  resins  with viscosities as low
as  that of  water  can  fill  small  fractures  and  permeable  zones  more
effectively than  can  cement.    '   '      They also  are  frequently  more
flexible than  cement  and can  adjust to minor  rock movements.    On  the
other  hand,  many chemical sealants  have unproven  stability over  long
periods.   Some are moisture  sensitive or may  have  differing  physical
properties in different rock types.  Also, since most synthetic  sealants
contain organic compounds, there arise questions about possible  chemical
breakdown from bacterial action.
    Natural  sealants,  such  as  asphalt,  tar,  and   similar  bituminous
materials, may  have  long  life  expectancies under  a variety  of
conditions.   '     However, emplacement  of these materials  may  require
heating, which could  result in contraction of the sealant  upon  cooling.
The  contraction   could  pull  the  sealant from  the  borehole walls  and
negate  its  effectiveness.   Alternatively, a plastic  or  viscous  sealant
may  seep  out of  the  borehole into  fractures  or into  the  rock pores.
This volume loss could initiate additional movement  in other sections of
the seal column.  The organic  components of  natural  sealants may also be
subject to  some  of the same  bacterial breakdown mechanisms  as  are  the
synthetic compounds.
    The   use  of  rock   or   earthen  materials   has   also  been
suggested.   '   '     Plugging with molten rock  represents one approach,
the  intent  being  to  provide  a plug  that  is  chemically  and  physically
                                (52)
identical  to  the  in-situ rock.        To  do  this,  rock  taken from  the
formation  to  be  plugged  would  be  crushed  and   introduced  into  the
borehole.   There,  heaters would  melt the crushed rock and either spray
it on  the  walls or allow it  to pool  at  the  bottom  of  the  open hole.
Alternatively,  the rock could  first be  melted at  the surface.  Although
a  promising  concept,  this  method  has  not  yet  been  successfully
demonstrated in  practice, and  it  has  potential problems.   Cracking of
                                   124

-------
the plug  and  wall rock during  cooling  is likely.  Also,  the method  is
essentially   limited   to   rocks  with  low   melting   points  and
temperature-insensitive mineralogies, such as rock salt.  The compaction
of earthen materials represents another approach  to create a plug with a
long probable  life.  In  this  case, clays, clay-sand mixes, or excavated
formation rock would be  introduced into a borehole and compacted at the
bottom  of the hole.   A number of methods  of compaction  are possible.
Impact  compaction  could  be  accomplished  by   dropping   a   cable  tool
manipulated from  the surface  or by pneumatic  or  electric hammers within
the hole.   Static compaction might  require hydraulic  or  pneumatic rams
affixed to the sides of the hole.  Kneading of the fill could be carried
out  using rotary  drill  equipment  at   the  surface  to operate  a roller
                                        (54\
compactor at  the  end of  a drill string.      Since  the compacted earth
would consist of materials with chemical  and physical properties similar
to  those  of  the  formation rock, interaction  with the rock  may  be very
minor.   However,  as with the  molten  rock concept,  other  problems can
arise.  For  example,  compacted-earth plugging  requires  the development
of new  equipment.   Adhesion  between the plug  and the native rock may be
poorer  than for  other  seal materials,  and initial permeabilities may be
higher  than expected and difficult to control.    *
    Both  the initial quality  of a  plug  and its longevity are affected by
the  care  with which  the  borehole  is  prepared  and the  plug emplaced.
Several stages  of preparation  are involved  regardless of  the plugging
material  or  emplacement  methods.   In  general,  anything  that  might
interfere with the plug, the  rock, or  the bond  between the plug and the
rock must be  remedied.    All  foreign  matter should  be removed.   This
entails stripping from  the   hole  any  remaining  casing,  equipment,  or
debris.    If  such materials  cannot   be  extracted,  it  is  sometimes
necessary  to  overbore  the hole  or to  cut windows  in the  casings or
obstructions  so  that  sealants  may be  forced  past.   Residual drilling
fluid, mud, oil, or other  contaminants must be removed.  Both mechanical
scrubbers  and specialized  solvents are available, but their use requires
care  and  judgment  in  order  to   avoid  substituting   one  contamination
problem for another.   Next,   the walls  of the borehole should be logged
so  that the  position  and  characteristics of  the rock  along its length
are well  known.   This  step is essential in order to match sealants with
                                   125

-------
the rock, to  determine  quantities  of plugging material  to  be used, and
to select the best emplacement method.
    At present, no plugging method appears assured of providing both low
initial hydraulic conductivity and  long-term  stability.   The purpose of
the previous  paragraphs  has been  to  highlight possible  techniques and
indicate potential problem areas.

D-3.3.3  Borehole Seal Failure Model

    For this analysis, the performance of  a borehole  plug is defined by
its  ability  to  restrict  fluid movement  along  the  borehole.    The
hydraulic  conductivity  of   the   plug   is   the   principal  parameter
controlling  fluid movement.   Although the  fill  material  and  its
properties may vary from  point  to  point, for the  purpose  of this model
it is  sufficient  to assume an effective  uniform  hydraulic conductivity
for the entire length of  the filled hole.  Auxiliary parameters, such as
number and size of  boreholes  and the  porosity of  the  fill, must also be
specified  in  order to  compute  total volumetric  fluid   flows  and fluid
velocities.
    Many  of  the  same  degradation  mechanisms  that  we discussed  in the
section on  shaft  seals also  apply  to borehole seals, and  so a gradual
increase  in  hydraulic  conductivity is expected  over  time.   Therefore,
modeling plug performance  requires  the determination  of  a function K(t)
that expresses  the  hydraulic  conductivity of the plug as  a function of
time.   Determination  of  this   function  involves  the specification of
three items:  the initial value KQ for the time of plug emplacement, the
deteriorated  (greater) value  K.  for 10,000 years, and a rule governing
the transition from KQ to K, .
    Initial permeabilities, KQ,  for both  first  and second estimates are
taken as 10   cm/sec.   It appears that this value can be met or bettered
by a number of materials  and  designs, as  suggested  by the data in Table
D-29.  (See  Section  D-3.2)  This performance measure is  independent of
the  host  rock, although the  specific  design  to achieve  it  may well
depend on the host rock.  It is  further assumed that all known boreholes
are sealed  to  this  degree of  impermeability.   Previously plugged holes
must be reamed  out,  all junk, old  casings,  and  loose materials must be
                                  126

-------
stripped  from  them,  and  mud,  oil, or other  contaminants must  be cleaned
from the walls.
    Estimates  of  final  permeabilities,  K, ,  follow the  rationale  set
forth  for  shaft  seal performance.    For borehole  plugs,  however,  the
first  estimate permeabilities are  taken to be  10   cm/sec rather  than
10    cm/sec,  as  was assumed  for  the   shaft  seals.    This  difference
reflects  perceived  difficulties  in placing  and testing a borehole  plug.
Unlike  a  shaft  seal,   a  borehole  plug must be  inspected  or  tested
remotely.   The quality  of  plugs  is therefore more  suspect,  and a  more
rapid degradation is  assumed.
    The  second  estimate  for  the  final permeability, K- ,  is taken to  be
   y                                                  J-
10    cm/sec,  as  it was  for  the  shaft  seal.    This  condition  also
corresponds  to a  borehole  filled  with  silty sand,  or silty sand  and
gravel.    The  permeabilities of  specific  soil types  vary  greatly
depending  on  conditions of  compaction,   but  the   data  given   earlier  in
Figure  D-13  (see   Section  D-3.2)  provide   a  context  within  which  to
interpret these numbers.
    Values  of  K_  and K,  having been  specified, it is  next necessary  to
estimate  a  function K(t) that  describes  the change from K   to K...   In
the  absence  of  detailed  plug  designs and models  for  degradation
mechanisms,  the  simplest model,  namely a linear  increase from KO  to  K.. ,
has been  adopted.  This  results in the equation

                                       *1 -KQ
                            K  -K°+^7" "
A summary of the corresponding numerical formulas in two sets of  units
is given  in Table D-51.
    Flow volume along  a  filled  borehole  is  proportional  to  its
cross-sectional area, other factors being fixed.   Therefore,  in order  to
calculate quantities of water moving through a borehole,  a value for  its
cross-sectional area  is  required.   For the  present model, each hole  has
                                                           2
been assigned  a conservatively large cross  section of 0.1 m  •   For  this
analysis, 50 holes have been assumed to reach the  repository.   Where  the
generic  medium is  modeled  with a lower  aquifer,   10 of  these 50  holes
have  been  assumed  to reach  the  lower  aquifer.    A constant  porosity
value, n •  0.1,  Is  used  in conjunction with the other parameter values
                                  127

-------
                               TABLE D-51

             PERMEABILITY AS A. FUNCTION OF TIME FOR BOREHOLE
                         SEAL DEGRADATION MDDEL
                                        Permeability (K)
                             (cm/sec)                (m/yr)
First Estimate     10~8 + 9.9 x 10~10 t    3.15 x 10~3 + 3.15 x 10~4 t

Second Estimate    10~8 + 9.9 x 10~9 t     3.15 x 10~3 + 3.15 x 10~3 t
                                  128

-------
in order  to  calculate actual fluid velocities.   This parameter is also
subject to variation, depending on the design of  the borehole plug.
    It  is likely  that  a  repository  will be  planned  so  that  the rock
surrounding the boreholes will not be excavated.  The intention would be
to contain  the boreholes  in such pillars  as an additional  barrier to
fluid flow.  Nevertheless,  at a depth of 500 meters  there is likely to
be some uncertainty  over  the exact  location of a borehole, and so it is
possible  that  the excavation may  actually intersect it.   Furthermore,
previously  undetected  boreholes  may  be discovered  by  the  excavation
process  itself.    Because of  these   uncertainties,  it  has  been
conservatively assumed for  this analysis  that all the boreholes actually
intersect mine drifts.

D-3.3.4  Borehole Seal Release Model

    A permeable  borehole seal  represents a possible pathway  for fluid
migration from the repository level to the groundwater system and to the
surface.  If radionuclides have been leached  from  the  waste package as
well,  they  may be  transported  to the  geosphere or biosphere  with the
fluid.  Releases  to  the groundwater system would  be expected to dominate
over  those  to  the  surface  for  the  same reasons discussed  earlier for
shaft seals.  Therefore, only releases to groundwater, and in particular
to the  upper aquifer,  have been modeled.   Because both  the parameter
values  and  the  dominant driving forces  vary from one  rock  to another,
the  release  models  are discussed  here  for each  of  the five geological
settings  separately.

D-3.3.4.1  Bedded Salt

    Repository resaturation  times for a bedded salt repository have been
given in  Table D-31  (see  Section D-3.2)  based on calculations presented
in Appendix D-II.   Since the pore volume tends  to  decrease  because of
salt creep at the  same  time that  water seeps into the repository, these
resaturation times represent a balance point at which the  remaining pore
volume  is exactly  equal  to  the  volume  of  water  that has  seeped in.
Naturally, there  will be  some non-uniformities in water distribution as
                                   129

-------
well as in salt closure, but these factors have  not  been included in the
model.
    All of the driving  forces  discussed in Chapter D-3.0  are present to
a certain extent in the case of borehole  seal degradation, and different
ones dominate at different points in  time.  The  period  of  possible fluid
migration may be divided into two basic parts:
    Period A—From resaturation time  until effective closure  of cavities
              and void spaces by extensive salt  creep;  and
    Period B—Following Period A.
During Period  A,  the hydraulic  pressure generated  by salt creep  can
result in substantial gradients along permeable  boreholes.  The analysis
for the corresponding situation with  permeable  shafts  (Section  D-3.2.4)
also applies  here, yielding  a gradient  on  the order i =  7.9 in  the
portion of a  borehole connecting  the repository and the  upper  aquifer.
According to  the model  assumptions discussed  in Section D-3.3.3,  there
are 50 borehole pathways to the upper aquifer,  10 of which also connect
to  the lower aquifer.   The  10  boreholes  that  penetrate  to the  lower
aquifer  also  provide a  small  flow pathway  downward,  but  the  lower
section of  these boreholes has not  been included  in  the  calculations.
The effect of omitting  them  from  consideration  for Period A  releases is
conservative in  the sense  of  assuming that  the  fixed amount  of fluid in
the  repository  will  all  be  forced  into  the  upper  aquifer, where  the
consequences of radionuclide concentrations would be  expected to be more
significant (albeit at  the expense  of a slight  increase in the duration
of the release).
    Period A fluid  flows were  first  calculated  without  consideration of
the interactive  effect with the permeable shafts (Section D-3.2).   That
is, all  the  water  that  entered  the  repository  during  the  resaturation
period was assumed  to be forced out  through  the boreholes.   The result
of  this  calculation  is  therefore an upper bound  on  flow  through  the
boreholes; in  addition  it enables  a comparison between the  effects of
shafts and boreholes.
    The  calculations  for  first  estimate parameter values  proceed  as
                                          •
follows.  The volumetric fluid flow rate  Q is given  by

                               Q = KiAc(u)

                                  130

-------
 at  20°c,  so  that  c(u)  is  dimensionless.)
                   ;  parameters are
                     «              /
     K  =   3.15  x  10""  + 3.15  x 10    t m/yr       (from Table D-51)
where
    K  =  hydraulic conductivity, or permeability;
    i  =  hydraulic gradient;
    A  =  total cross section of all boreholes;
  c(P) =  viscosity correction factor,  given  by 0.01/P, where V is  the
viscosity in  poise.   (Note that 0.01  represents the viscosity of water
at 20°C, so that c(U) is dimension]
The values of these parameters are
    K  -  3.1^
    i  =  7.9
                          2
    A  =  50 x 0.1  =  5 m                        (from Section D-3.2.3)
  c(p) -  5                                       (from Section D-3.2.4)
It  follows  that  the  cumulative  outflow from  resaturation  time  (200
years) to an arbitrary time T is given by
                                 T
                        Q(T) = f TQdt
                               200
                                 T                3             A
                             =  f 197.5(3.15 x 10"  + 3.15 x 10  t)dt
                               200

                                              2  ,T
                             = (0.62t + 0.031t )|
                                                 200
                             = 0.031 T2 + 0.62 T - 1364.
If this  flow  pathway were to account for  the  complete  depletion of  the
water in the  repository at resaturation time, namely a volume
           V  =  1.2 x 103, m3                   (from Table D-31)
then the flow would  continue at  the increasing rate Q until Q(T) = V.
This would enable the determination of T as follows:

         0.031 T2 +  0.62 T - 1364  = 1.2 x 103
                                 T  = 278 years.
However,  it  is more  accurate  to  take  into  account the  fact that  the
outflow  pathway consists  of  both shafts  and  boreholes, so  that  the

                                   131

-------
volumetric  flow rate is  actually the  sum of  the  individual  functions
Q(T)  obtained  here and  in  Section D-3.2.4.   This  approach yields  the
function:

           Q(T)  =  0.093 T2 + 13 T - 6317.

The water available will  then be  depleted  when Q(T) - V, which  implies:
that

           0.093 T2 + 13 T - 6317  =  1.2 x 103
                               T   =223 years.

The  flow through  the  boreholes  during  this  period  (220-223  years)  is
                  o
approximately 14 m /yr.
    As  in  the  case of  shaft  seals,  the analysis  with  second  estimate
parameters is somewhat different.   Since the  shaft  seal analysis showed
that  in  this case  the  limiting  factor is the  rate  of salt creep rather
than  the  conductivity  of the flow path, the  consideration of  borehole
pathways ought not affect the flow rates.  In addition, the  permeability
functions for both shaft and borehole seals are identical,  so  that their
relative  importance  is  in  the same  proportion  as   their  total
cross-sectional  areas,  namely,  100:5.   Therefore,  the borehole pathway
is quite insignificant by comparison.  The volumetric  flow  rate  is about
      3
100 m /yr through this pathway.
    Vertical fluid  velocities  within the  boreholes may be obtained  by
dividing the Darcy velocity, Kic(vi),  by the  effective porosity  n, which
was given in Section D-3.2.3 as  n = 0.1.  Therefore,  the  velocity v  is
given by the formula:

              v  =  Kic(U)/n

                 =  Q/nA

                 -  2Q,

where the units are m/yr.  It follows that the approximate  average fluid

                                 132

-------
velocities  and  the  corresponding  transit  times from  the  repository to
the aquifer within each borehole are as given in Table D-52.
    All  the calculations  performed  so  far  in this  section have been for
Period  A,  which  represents the  period of  non-negligible  salt  creep.
During  this  period, the  dominant  driving  mechanism  is  the  pressure
produced  by this  process.   At  the  end  of  this  period  the  salt  has
reached  a  state  of approximate mechanical equilibrium.   The water that
seeped  in  during  the resaturation period has been forced  back out;  and
the repository  is still  saturated,  but the  fluid volume  is relatively
small.    The   tunnel backfill  has  been  compacted,   probably  to  near
equilibrium, but  it  still has some permeability to fluid flow.
    The  boreholes that  descend only to the  repository horizon  cease to
be  important  at   this point  compared with  those that  extend through to
the lower  aquifer and that  can still serve as release pathways.  In this
case, the  driving force consists of  the combination of the difference in
hydraulic  potentials of  the  two aquifers  and  the   thermally  induced
convection effect.   These  effects  are  essentially  additive,  so  the
effective  hydraulic  gradient in these boreholes may be obtained as given
in  Table  D-53.   By  means  of Darcy's  law,   these  gradients yield  the
volumetric  flow  rates (for  the 10 boreholes)  and fluid velocities shown
in  Table  D-54.    The  first  estimate  value  for  T  =  223 years  (the
approximate  starting  point  for   Period   B)   has  been  obtained  by
interpolation.    The values  shown  in  Table D-54  do  not  account  for
possible  dissolution  around  the  borehole,  which  could  lead  to
development of  a wider  channel  and  hence  to greater  flows.   Detailed
calculations  in Appendix  D-III  indicate   that   the   flow   rates
corresponding to  first  estimate  parameter values are  sufficiently small
that  salt  creep  is  capable of  preventing  the  development of an open
channel.   For the  case of  second  estimate  parameter  values,  however,
dissolution does  have the capability to develop an open channel through
the salt.   As a  result,  only  that  portion of  the borehole through the
upper  and   lower  shale  levels  should be  assumed  to  act as  a partial
barrier  to fluid  flow.    Since  this comprises one-half of  the  total
length  of  the borehole  between the  aquifers,  the flow rates are roughly
doubled.   Table  D-55 incorporates these dissolution  considerations into
the calculation of flow rates.
                                  133

-------
                               TABLE D-52

        APPROXIMATE FLUID VELOCITIES AND TRANSIT TIMES TO AQUIFER
                ALONG PERMEABLE BOREHOLES DURING PERIOD A
                        (BEDDED SALT REPOSITORY)
                    Fluid Velocities (v)               Transit Time
                           (m/yr)                         (yrs)
First Estimate               29                           4

Second Estimate             200                           0.5
                                  134

-------
                               TABLE D-53

      EFFECTIVE VERTICAL HYDRAULIC GRADIENT IN PERMEABLE BOREHOLES
      FROM THERMALLY INDUCED CONVECTION AND AQUIFER INTERCONNECTION
                        (BEDDED SALT REPOSITORY)
                                    Hydraulic Gradient (1)
                           100 years
             1000 years
             10.000 years
Thermally Induced
Convection

  First Estimate

  Second Estimate

Aquifer
Interconnection

  First Estimate

  Second Estimate

Effective Total
Gradient

  First Estimate

  Second Estimate
0.12

0.12
0.13

0.62
0.10

0.10
0.01
0.50
0.01
0.50
0.11
0.60
0.03

0.03
                                  0.01
                                  0.50
0.04

0.53
*Y.ears after repository closure.
Source:  First column from Appendix D-VT ; second column  from
         Chapter D-2.0.
                                   135

-------
                                TABLE  D-54

       VOLUMETRIC FLOW RATES AND FLUID VELOCITIES  IN DEEP  PERMEABLE
              BOREHOLES DURING PERIOD B AS CALCULATED  WITHOUT
                      CONSIDERING DISSOLUTION EFFECTS
                          (BEDDED SALT REPOSITORY)
                                       Volumetric Jlow     Fluid Velocity
                                                                (m/yr)
                        (m3/yr)
T = 223 years
First Estimate
0.05
0.5
                                                     *                   *
                   Second Estimate     Not applicable      Not applicable
T = 1000 years     First Estimate
                          0.18
                   1.8
                   Second Estimate
                          9.5
                  95
T = 10,000 years   First Estimate
                          0.63
                   6.3
                   Second Estimate
                         83.5
                 835
 Note:   T = 223 is not included in Period B for second estimate
            assumptions, since Period A extends to T = 1000.
                                  136

-------
                                  TABLE D-55

             VOLUMETRIC FLOW RATES IN PEEP PERMEABLE BOREHOLES
                    DURING PERIOD B INCLUDING EFFECTS OF
                         DISSOLUTION ON FLOW RATES
                          (BEDDED SALT REPOSITORY)
                                                    Volumetric Flow  (Q)
                                                        (m3/yr)
 T = 223 years          First Estimate                     0.05

                                                                  *
                        Second Estimate             Not applicable

T - 1000 years          First Estimate                     0.18

                        Second Estimate                    19.0

T * 10,000 years        First Estimate                     0.63

                        Second Estimate                    1^7.0
*
 Note:  T = 223 is not included in Period B for second estimate
            assumptions, since Period A extends to T « 1000.
                                   137

-------
    The  source  term  for  this  failure  element  consists   of  the
concentration of radionuclides  that  have leached into the water  in the
repository during  the  time frame of  interest.      Wastes would  not  be
expected to  be  placed in  or  near  the path of  a borehole, and  so none
would be expected  to  be directly  in the path  of  the flows  calculated
above.

D-3.3.4.2  Granite

    Once repository  resaturation has  taken place,  two  driving  forces
need to be evaluated  for their potential  contribution to  fluid flow from
the  repository  to  the aquifer.   These  forces are thermally  induced
convection and  the U-tube  effect.    (Note  that molecular diffusion  is
always negligible  compared with mechanisms that move radionuclides  by
fluid  flow,   and   there  is  no  lower  aquifer  in   the  generic  granite
repository.)   Both of these  forces  are  functions  of time.   Thermally
induced  convection depends  on time  because   the  temperture  profile
changes with  time.   The U-tube effect depends  on  time  because  of  the
gradual change in  the  hydraulic  conductivity of  the borehole  plug.  The
values of the corresponding gradients, if calculated  independently,  are
shown in Table D-56.   These values  are based on Appendices D-V and D-VI.
In  particular,  in  the  calculation  of  the  gradients  resulting  from
thermally  induced  convection,  the  minimal  average  density of  a water
column  from  the   upper  aquifer  to   an  unspecified  point  below  the
repository has been used, rather than that  of  a water column simply from
the  upper  aquifer  to  the  repository itself.   It is  pointed   out  in
Appendix D-VI  that the  corresponding  numerical values  represent upper
bounds on the buoyancy force.  It is believed  that  this approach is both
conservative and particularly  appropriate here  because at least  some of
the  boreholes may extend below  the repository.    By  the  reasoning
presented earlier, it  follows that,  for  the purpose  of  calculating the
joint  effect,  the  maximum of the individual  effects may  be utilized.
Therefore, the  gradient resulting  from  the thermally  induced  buoyancy
effect dominates in most cases.
                                    138

-------
                                 TABLE D-56

     EFFECTIVE VERTICAL HYDRAULIC GRADIENT IN PERMEABLE BOREHOLES FROM
             THERMALLY INDUCED CONVECTION AND THE U-TUBE EFFECT
                            (GRANITE REPOSITORY)
                                  Hydraulic Gradient (1)
                   100 years*
                1000 years
                10.000 years
Thermally Induced
Convection
  First Estimate
0.11
0.07
0.03
  Second Estimate
0.11
0.07
0.03
U-Tube Effect
  First Estimate       0.01
  Second Estimate      0.09
                    0.01
                    0.09
                    0.01

                    0.08
*Years after repository closure
Source:  Appendices D-V and D-VI
                                  139

-------
    The volumetric flow rate can be calculated from the equation

                               Q - KiAc(U)

where
    K is given in Table D-51,
    i is obtained from Table D-56,
    A equals 50 x 0.1 - 5, or 2.5 for the U-tube case, and
    c(y) equals 5.
The  results  of  this  calculation  are  given  in  Table  D-57.    The
corresponding fluid velocities are given in Table D-58.
    The  source   term  for  this  failure  element  consists   of  the
concentration of  radionuclides  that  have  leached into the water  in the
repository during  the  time  frame of  interest.    This  is  the  uniform
concentration situation referred  to  earlier.   Because a number  of flow
pathways may  exist through  the bulk rock  in the  neighborhood  of the
repository,  there  is  expected  to  be sufficient  convective movement  so
that transport  to the borehole  is not  limited  by very slow diffusion
rates.

D-3.3.4.3  Basalt

    Once  repository  resaturation has  taken  place,  there  are  three
driving forces  that  need  to  be  evaluated   for  their  potential
contribution to  fluid  flow from the repository  to the aquifer.   These
forces   are  thermally  induced  convection,  the U-tube  effect,  and  the
gradient from  an  aquifer  interconnection.    The  gradients   from  these
three forces,  if calculated independently, are shown in Table D-59.  The
gradient  values  shown  for   the   thermally  induced  convection  effect
correspond to  Table D-VI-4 in Appendix  D-VI.  They  represent bounds on
this effect for boreholes  that penetrate only to  the repository layer as
well as for  those that penetrate  all the way  to  the  lower  aquifer.  In
the  case of first-estimate parameter values, the  U-tube effect is always
dominated by thermally induced convection, and so the former will not be
considered  in  the flow calculations.   In the case of  second estimates
for  boreholes  extending all  the  way to  the  lower  aquifer,  the aquifer

                                   140

-------
                                 TABLE D-57
             VOLUMETRIC FLOW RATES THROUGH PERMEABLE BOREHOLES
                            (GRANITE REPOSITORY)
 Years after repository closure.
                                          Volumetric Flow (Q)
                                               (m /yr)
                   100 years
                1000 years
                 10.000 years
First Estimate
0.1
0.6
 2.4
Second Estimate
0.9
5.5
31.5
                                   141

-------
                                 TABLE D-58
                FLUID VELOCITIES THROUGH PERMEABLE BOREHOLES
                             (GRANITE REPOSITORY)
 Years after repository closure.
                                         Velocity  (v)
                                           (m/yr)
                   100 years
                1000 years
                 10.000 years
First Estimate
0.2
 1.2
 4.8
Second Estimate
1.8
11.0
125.9
                                   142

-------
                                 TABLE D-59

       EFFECTIVE  VERTICAL HYDRAULIC GRADIENT IN PERMEABLE BOREHOLES
             FROM  THERMALLY INDUCED CONVECTION. U-TUBE EFFECT.
                        AND AQUIFER INTERCONNECTION
                            (BASALT REPOSITORY)
                                      Hydraulic Gradient (1)
                      100 years*
              1000 years
                 10.000 years
Thermally Induced
Convection

  First Estimate

  Second Estimate

U-Tube Effect

  First Estimate

  Second Estimate

Aquifer
Interconnection**

  First Estimate

  Second Estimate
0.13
0.13
0.02
0.20
0.01

0.50
0.11

0.11
0.02

0.19
0.01
0.50
0.04

0.04
0.02

0.16
0.01
0.50
 *Years after repository closure.

**0nly applies  to the 10 of the 50 boreholes that are assumed to
  penetrate to  the lower aquifer.
  Source:   Appendices D-V and D-VI.
                                         143

-------
interconnection gradient dominates  the  U-tube effect.   In the case  of
second estimates  for  the  boreholes  that  do  not  extend  to  the  lower
aquifer,   it   is   possible  that   some  U-tube  flows   might  occur.
Nevertheless,  these would  not be  significant  compared  to  the other  flows
calculated.
    In calculating  fluid  flow rate through the  boreholes,  it  is
necessary  to  consider  the  interconnection  between the  deep boreholes
(those extending  to  the   lower  aquifer)  and the  others,  since  this
interconnection can have  the effect of  increasing  the  flow rates.   In
particular, the system may  be  analyzed  with  the  aid  of  its electrical
analog,  shown  in  Figure  D-15.     (The  use  of  electrical  analogs  is
discussed in Appendix D-V.)   Since  the relatively  large permeability and
cross-sectional area of  the repository  tunnels  imply a  relatively low
resistance, compared with  boreholes, the  system shown  in  Figure  D-15 has
been  adopted  as the basis for the  analysis.   All the resistances  have
the same value.  The driving  potential  between  points A and  B is not
dissipated uniformly  in  the vertical  direction, but in  inverse
proportion to  the  resistance of  each of the  two  parts  of the  pathway.
Therefore,  the lower part  experiences five-sixths  of the  potential  drop.
If  more  resistances were  added  in  parallel  to  the upper  part  (for
example,  by  considering additional  pathways, such as  degrading  shaft
seals) , then  the  fraction of  the   potential  drop over  the  lower  half
would  be even larger.   Therefore it  is both  conservative  and yet  not a
significant overestimate to  assume  for  the  purpose of calculation that
the  entire potential  drop  is  experienced  over  the  lower half.   The
resulting flow  in this half  also represents  the  flow in  the upper half
because  the  two  halves  are  connected  in  series.   To  effect  these
assumptions  in the  actual  calculations,  the gradients  for  thermally
induced convection  and aquifer interconnection, as given  in  Table  D-59,
should be doubled and then added to  represent  the  combined effect. The
resulting  values  are given  in  Table D-60.    Using  these gradients  in
Darcy's law yields  the  flow rates  shown in  Table D-61.    Assuming that
these  flows  all move  from the repository  to the upper  aquifer  within
boreholes  (rather  than through  shafts  or other  breach  pathways), the
actual  fluid  velocities   can  be  estimated  as   shown  in  Table  D-62.
                                     144

-------
  (a)  Basic System
                                                                                  • B
  (b)   Simplified System Ignoring Resistance of Tunnel Backfill
                                                                                  -•A
                                                                                   (50)
                                                    -0-
                                                                                   (10)
                                                     J.L.
                                                                                  -•B
Note:   Vertical resistances represent boreholes. Horizontal
       resistances represent segments of backfilled tunnels.
   FIGURE 0-16   ELECTRICAL ANALOG FOR BOREHOLE PATHWAY ANALYSIS IN BASALT
                                          145

-------
                                 TABLE D-60
        EFFECTIVE VERTICAL HYDRAULIC GRADIENT IN PERMEABLE BOREHOLES
              CONNECTING THE REPOSITORY AND THE LOWER AQUIFER
                            (BASALT REPOSITORY)
                                       Hydraulic Gradient (i)
First Estimate
Second Estimate
                      100 years
0.28
1.26
             1000 years
0.24
1.22
10.000 years

    0.10

    1.08
 Years from repository closure.
                                 146

-------
                                 TABLE D-61

             VOLUMETRIC FLOW RATES THROUGH PERMEABLE BOREHOLES
                            (BASALT REPOSITORY)
                                      Volumetric Flow (Q)
                                               ~
                                                /yr)
                      100 years
             1000 years
                 10.000 years
First Estimate
0.05
 0.4
  1.6
Second Estimate
2.0
19.2
170.1
 Years after repository closure,
                                   147

-------
                                 TABLE D-62

                FLUID VELOCITIES THROUGH PERMEABLE BOREHOLES
                             (BASALT REPOSITORY)
                                       Velocity  (v)
                                           (tn/yr)
First Estimate
Second Estimate
                      100 years
0.1
4.0
             1000 years
 0.8
38.4
                 10.000 years
  3.2
340.2
 Years after repository closure.
                                   148

-------
Consideration of  additional  flow  pathways  for  the same flow rates would
decrease the fluid velocities calculated.
    The  source  term  for  this  failure  element  consists   of  the
concentration of  radionuclides  that  have leached into  the  water in the
repository  during the  time frame of interest.   This  is  the  uniform
concentration situation described earlier.

D-3.3.4.4   Shale

    For  all the  modeling  parameters  relevant  to  the present  release
mechanism,  the  basalt  and  shale  repositories  appear  identical.
Therefore  the  discusion and the  numerical  computations for basalt  are
identical for shale.  The results for shale are shown in Tables D-63 and
D-64.

D-3.3.4.5  Dome Salt

    Repository resaturation  times  for a  dome salt repository  are
calculated  in  Appendix D-II.   As  indicated there,  these  resaturation
times represent a balance  point  at which  the  remaining pore volume is
exactly equal to  the volume of seepage water.  Non-uniformities in water
distribution and  in salt creep rates are not included in the model.
    The analysis  of  releases from a salt dome  repository  through leaky
boreholes  during  the initial period  of  extensive salt creep  parallels
very closely that  for a bedded  salt  repository.   Reference will  also be
made to the analysis of releases  through permeable shafts  in the  case of
a  salt  dome repository, which were  discussed  in Section D-3.2.4.   The
period of possible fluid migration may be divided into two basic  parts:
    Period A—From resaturation time until effective closure of cavities
              and void spaces by extensive salt creep.
    Period B—Following Period A.
During  Period  A  the hydraulic  pressure  generated  by  salt creep  can
result in  substantial  gradients  along plugged but  permeable boreholes.
The  analysis  for  the  corresponding  situation  with  shafts  (Section
D-3.2.4) also applies here, yielding a gradient on the order of  i - 2 in
the  portion of the  borehole  connecting  the  repository  and the upper

                                  149

-------
                                 TABLE D-63

             VOLUMETRIC FLOW RATES THROUGH PERMEABLE BOREHOLES
                             (SHALE REPOSITORY)
                                         Volumetric Flow (Q)
                                               (m3/yr)
                      100 years
             1000 years
                 10.000 years
First Estimate
Second Estimate
0.05
2.0
 0.4

19.2
  1.6
170.1
 Years after repository closure.
                                 150

-------
                                 TABLE D-64

                FLUID VELOCITIES THROUGH PERMEABLE BOREHOLES
                             (SHALE REPOSITORY)
 Years after repository closure.
                                       Velocity (v)
                                         (m/yr)
                      100 years
               1000 years
                 10.000 years
First Estimate
0.1
 0.8
  3.2
Second Estimate
4.0
38.4
340.2
                                  151

-------
aquifer-    According  to  the  model  assumptions  specified  in  Section
D-3.3.3,  there are  50  borehole  pathways  to the  upper  aquifer.    The
hydraulic  gradient  resulting from salt  creep tends  to  force  water from
the  repository through  these  boreholes  to  the  upper  aquifer.   At  the
same  time,  this gradient  is  also forcing  water out through  the filled
shafts.   The  combined outflow along  these  two  pathways  continues  until
the  total amount of  water  that  has  entered  the  repository during  the
resaturation  period  has been  forced  out.    (This  is  an  approximation;
there will always be some  residual water that  is not  squeezed  out.)  The
corresponding  flow rates and  time periods  can be calculated in  the same
way as they were for bedded salt.
    For the first estimate case,  the  volumetric flow rate  during Period
A  (200-260 years)  is  approximately  5  m /yr.   In  the second  estimate
case,  the flow rate during  Period A (748-1000  years)   is  approximately
100 m /yr.   It follows  from these  results  that the approximate average
fluid velocities and  the corresponding  transit  times from  repository  to
aquifer within each  borehole  are as  given  in  Table D-65.   All  these
calculations are for Period  A, which  represents the period  of  extensive
salt  creep when the  dominant  driving  mechanism  is the  pressure  produced
by this process.  By the end of this period  the  salt has  reached a  state
of approximate mechanical  equilibrium.   The water that  seeped in during
the resaturation period  has  been  forced back out  and  the  repository  is
still  saturated, but  the fluid volume is  relatively small.   The tunnel
backfill  has been compacted, probably to near equilibrium, but  it  still
has some permeability to fluid flow.
    The period following Period A has been  called Period  B.  In  the case
of bedded  salt, 10  of  the boreholes were  assumed  to  penetrate to  the
lower  aquifer  and   during  Period  B movement   of   fluid  along  these
boreholes could lead  to releases  to  the upper aquifer.   In the case  of
the  salt  dome repository,  however,  there  is no  lower  aquifer in  the
generic model.   As  a   result  there  is  no  gradient  present   in  these
boreholes  from an  aquifer  interconnection  and there  is  no  recharge
pathway available for the  thermally induced  convection  effect.   The only
driving force  expected  to  be present, therefore,  is the U-tube effect.
This is the driving  force  used to calculate  releases during Period  B.
                                  152

-------
                                 TABLE D-65

         APPROXIMATE FLUID VELOCITIES AND TRANSIT TIMES TO AQUIFER
                 ALONG PERMEABLE BOREHOLES DURING PERIOD A
                         (DOME SALT REPOSITORY)
                             Fluid Velocity (v)            Transit Time
                                   (m/yr)                       (yr)
First Estimate                       11                          21
Second Estimate                     200                         1.1
                                 153

-------
    The gradients in the boreholes which represent the vertical  parts of
the U-tube, have been calculated  by methods outlined  in Appendix D-V and
are shown  in  Table D-66.   Although the gradients  decrease with  time,
because  of a  decrease  in  the   resistance  of  the  borehole  segments
relative to that of the tunnel,  the flow rates  will  increase because the
total  U-tube   resistance  is  still  decreasing as  the  borehole  plugs
degrade.  Utilizing these gradients in Darcy's law, the  volumetric flow
rates and fluid velocities may be calculated  as shown  in Tables  D-67 and
D-68, respectively.
    The  source   term  for  this  failure  element  consists   of  the
concentration of  radionuclides that  have leached  into the water in the
repository during the time frame of interest.

D-3.3.5  Literature Discussion

    Borehole plug failure has also been discussed  by Claiborne and
Gera(3) and by TASC.(11»53)
    Claiborne  and  Gera were   concerned  with  a  specific  area  in
southeastern  New  Mexico.    On   the basis  of  their   analyses  of   site
hydrologic  data,  they  concluded   that  if  a  connection  were to  be
established between  upper and lower  aquifer by  failure of a  borehole
plug, then flow would be in a downward direction and very slow.  In the
case  of  a borehole  which extended only  to  the  repository  level,  they
argue that water in it would simply stagnate and  not exhibit a flow that
could carry radionuclides.
    TASC  addressed  borehole  failure  in the  framework  of  a threshold
definition.  In  particular, a failed borehole  was defined as one with a
permeability of  10   cm/sec.   They postulated  that   10% were   in  this
failed  condition initially,  30%  after  500  years,  and  50% after  5000
years.  They also assumed that each  failed borehole plug had a  porosity
value  of 0.01  and  that  0.5% of  the  repository was  affected  by  each
failed plug.
                                       154

-------
                               TABLE D-66

    EFFECTIVE VERTICAL HYDRAULIC GRADIENT IN PERMEABLE BOREHOLES FROM
                      U-TUBE EFFECT DURING PERIOD B
                         (DOME SALT REPOSITORY)
                                     Hydraulic Gradient (i)
                      260 years          1000 years       10.000 years
First Estimate           0.009              0.008            0.004
Second Estimate       Not applicable        0.04             0.007
 Years after repository closure.
                                  155

-------
                               TABLE D-67
            VOLUMETRIC FLOW RATES THROUGH PERMEABLE BOREHOLES
                             DURING PERIOD B
                         (DOME SALT REPOSITORY)
                                    Volumetric Flow (Q)
                                           (m /yr)
                      260 years
               1000 years
              10.000 years
First Estimate
0.01
0.03
                                                             0.16
Second Estimate       Not applicable
                  1.6
                 2.8
 Years after repository closure.
                                156

-------
                               TABLE D-68

              FLUID VELOCITIES THROUGH PERMEABLE BOREHOLES
                             DURING PERIOD B
                         (DOME SALT REPOSITORY)
                                      Velocity (v)
                                          (m/yr)
                      260 years          1000 years       10.000 years
First Estimate            0.04               0.12             0.64

Second Estimate       Not applicable         6.4             11.2


 Years after repository closure.

Source:  Appendices D-V and D-VI.
                                  157

-------
D-3.4    UNDETECTED BOREHOLES

D-3.4.1  Introduction

    The repository site selection process is expected  to  favor  sites  on
which  there  has  been little or  no  known deep drilling activity  in  the
past.    *      Nevertheless,  past  drilling  is  frequently  not well
documented and therefore  it is  possible  that  a given site  may  contain
old boreholes about which the site selection group  is  unaware.   Because
of this possibility, thorough  searches for old  boreholes  can be  expected
before and during  repository construction.  Boreholes  that  are  found  on
the  site  are expected to be  replugged  according  to the  best  available
technology;  the   effect   of these  on  repository  integrity  has  been
discussed in Section D-3.2.   Nevertheless, even after thorough  searches,
one or more undetected boreholes may remain.
    This  section analyzes the effect  of  undetected  boreholes  on
repository integrity by considering the following aspects:
    •  the probability of boreholes on a hypothetical site;
    •  the probability of detection of a borehole,  given  that it is
       present; and
    •  the physical characteristics of a borehole that might elude a
       comprehensive detection program.
A  summary  of this  analysis  is  shown  in Table  D-69.    A  detailed
explanation  of  the model parameters  is  found  in  Sections  D-3.4.3  and
D-3.4.4.   Section D-3..4.2  provides  background information  on  drilling
and detection activities.

D-3.4.2  Background

    A  potential  repository site may  contain  old  boreholes that  were
drilled for any of several purposes, such as
    •  oil and gas exploration or recovery,
    e  water exploration or recovery,
    •  geothermal  resource evaluation,
    •  brine injection or disposal of other wastes,
    •  mineral exploration,
                                      158

-------
                                                       TABLE D-69
                                    SUMMARY OF UNDETECTED BOREHOLE FAILURE ELEMENT





Bedded Salt













Granite












Basalt
















si
52
j Z
11
It
p













p












p

















NATURE
OF
MODEL

Past drilling density
and detection re-
liability yield
probability of one
or more partially
tilled holes.








Pan drilling density
and detection re-
liability yield
probability of one
or more partially
filled holes.









Past drilling density
and detection re-
liability yield
probability of one
or more partially
filled holes.













RELEASE
MODE

Groundwater













Groundwater












Groundwater


















DRIVING
FORCE

Second estimate
Period B flows
derive from aquifer
interconnection
gradient. Other
flows negligible.








Thermally induced
convection.












Thermally induced
convection and
gradient from aquifer
interconnection.















SOURCE
TERM

Uniform
concentration












Uniform
concentration












Uniform

















PARAMETERS


1st ESTIMATE
prob (1 hole on site)
- O016
("site" - 300 m buffer
zone only)
prob (failure to detect)
- 0.001
prob (under hole)
= 1j6 X 10"®
K - MT4 cm/sec

17 ° O.2
A - 0.1 m2
Distance from drift
- 100m
Holes extend to tower
aquifer.
prob (1 hole on site)
• 0.005
("site" • repos. +
300 m buffer zone.)
prob (failure to detect)
- 0.01
prob (undet. hole)
* 5 x 10~^
K •» 10~* cm/sec
n - 0.2
A - 0.1m2
Distance from drift
11 5m but flows
assume hole through
repository.
protod hole on site)
<• 0.07S
("site" - repos. +
300m buffer zone)
prob (failure to detect)
- 0.001
prob (undet. hole)
= 7.5x10
K • 10-* em/sec
n • 02
A = 0.1 m2
Distance from drift
• 5 m but flows
assume hole. through
repository. Holes
extend to lower
aquifer.

2nd ESTIMATE
exp. no. holes on site
- 3
prob (failure to detect
indiv. hole) - 0.001
prob (3 undet. holes)
- 0.003 (assumes
partial dependence)
K • 10"3 cm/sec
i) - 0.2

A • 0.3 ffl (total)
Distance from drift
- 100m
Holes extend to tower
aquifer.
prob (1 hole on site)
- 0.05
prob (feilure to detect)
- 0.01
prob (undet. hole)
- Sx10~*
K - 1(T3 cm/sec
ri - 0.2
A - 0.1 m2
Distance from drift
- 5 m but flows
aasume hole through
repository.


prob (1 hole on she)

prob (feilure to detect)
- 0.01
prob (undet. hole)
- 2 x 10"3
K - 10"3 cm/sec
u - 02
A - 0.1 m2
Distance from drift
- 5 m but flows
assume hole through
repository. Holes
extend to lower
aquifer.


FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER


1st ESTIMATE
NegtigAle with respect
to other failure elements












tlyrs)
100
1000

10.000









tlyrs)

too
1000
10.000
























6 (m3/yr)
1.7
1.1

0.5









0 (m3/yr)

4.4
3S
1.6













2nd ESTIMATE
tlytil Q(tllm3/yr)

1000 945
10,000 945










t lyrs) Q Im3,yr)
100 17
1000 11

10.000 5









t (yrs) 6 (m3/yr)

100 19B
1000 192
10,000 170














COMMENTS


Distance from drift
precludes significant
connection with re-
pository except in case
of significant dissolu-
tion. Negligible flow in
most cases deduced
from consideration of
relative resistance of

alternative pathways
for water to enter end
leave repository.
Repository resatura-
tion necessary for
releases.
Repository resaturation
nil slimy for releases
to begin.












Repository resaturation
"•! "iri'y for releases
to begin.














01
SO

-------
                       TABLE D-69
SUMMARY OF UNDETECTED BOREHOLE FAILURE ELEMENT (CONTINUED)


MEDIUM


State












Dorm Ml













£l
II
I*
o P
fZ
p












'














MATURE
or
MODCL


PM drifting dmitv
vddmcitonn>
HAHHrvWd
proMbilitvolOM
orfimptrtMy
MM hotel.








PM drill it* dm.tr
•nddmtiOfiro.
UobUtv vMd
probcMity en OM
or more ptrliilry
lilted hotel











•ELCAH
MODE


Grounrtarar .












Gfoundmmr














DRIVIM6
FORCE


Thtrrratrr inducad
conMction and
•radtem Iram miter
hmrionnonton.









Socondwinm
PvtadBflom
inwrcoMHction
•radim. OHMrllom
imiiiafcii-











SOUHCC
TEMM


Uniform
concommion











UnDorm
conanmnion














•AMAMCTCm

M ESTIMATE

arabdhoteonilnl
- aos
I" •*»- • r«K». »
300m barter ton*)
prob IbHuraio dmetl
• .01
prab lundn. hate)
• S«W*

n • OJ
A - aim'
Otrano from drift
• SmbMtMM
•gvitor.
•xp. no. hotel on sit*
- 3
btrfftr zorMonly)
prab IMkn to dract
Indta. hotel
• aooi
prob (3 undn. hotel)
' OJ)OJ(A«um«
K - 10-«cnW«K
1 • 03
A • 01 m^
DfcBnatramdrtti
- 100m.
HotamnridiotoMr
•quHtr.

hd ESTIMATE

ap.nohotaoniiu
- 9
prablteikirandmctl
• aoi
prab 13 undn. hated
pinill datttndinct)
K - 10-3on/M.
<> • 0.2
A • 0.1m2
OilSMet from drift
- SmbvlflOM
•Mrmhoklkrougk
'•pmllory. Hotet
•ttundtolowir
agurttr.
tw.no hotel an ult
- 30
prabllcikinndMoa
indh. hotel
• OM1
prob IS undtt. hotel)
- O.O3 Imunoi
UnteldlpindinLlI
K - 10"3 cm/He
A - O3mzltonll
DJ.UIH. Irom drift
• 100 m.
Hotel ntmd to toMr
•qutter.



FLUID FLOW RATES FROM
rUrOUTCWY TO UPPf R AQUIFER
Hi ESTIMATE
ilml

too
1000
10.000








NoHtejM
tOOtfMT













b(-3/rrl

4.4
18
1.6








.mthrw.1














1^ ESTIMATE
tlynl

too
1000
10.000








tlvn)
1000
10JOO












0 l-3/»r)

SH
sn
sn>








ab»3/>T>
S30
S30













COMMENTS



Hopoilio*Y (•Hiitriiion
nKBH(ly f Qf rdfjiMjij
•otMffin.










Dtanca from drift
^^^^
paotory CBCiVM in CM*
of tiinHtaMt divolit-
tton. NofUflfeto How kn
most MM dnfciMd
homcon..t.w.«tkinof

tor«iMr«o«MiVMid
IMM npMitofv. R»-

flKMwv fo> Mlmn.




-------
    •  scientific investigation, or
    •  fluid  storage.
Holes may have also been drilled for  other purposes, but  these have been
excluded from the  above  list either because they are too shallow  (e.g.,
soil  borings  for planning  foundations  of structures)  or too localized
(e.g., borings  related  to nuclear  testing).   Although  the current site
selection  process  would  generally  attempt  to avoid   locations  with
previous deep drilling (i.e.,  to  the formation  that would  contain the
repository),  documentation  of such drilling may be incomplete,  records
may be  lost or undiscovered, and  physical  evidence may be difficult to
find.(71)
    This section treats the  following topics:
    •  nature  of  past drilling activities in  the five  generic geologic
       settings,
    •  methods of detection,  and
    •  experience in  applying these detection methods in  the past.
Subsequent  sections will  provide actual  data from which to estimate the
parameters  that characterize  this  failure element.

D-3.4.2.1  Nature of  Past Drilling Activities

    Bedded Salt.  Bedded salt formations are particularly attractive for
a variety of  drilling activities.   Salt  is  a valuable commodity itself,
and it  is  also frequently associated with  other mineral  resources such
as  gypsum,  anhydrite,  and  potassium  salts.   The  range of  commercial
deposits of these minerals is indicated  in Figure D-16.   The sedimentary
sequences  containing  salt beds  frequently  contain deposits of  oil  and
gas, the ranges of which  are shown approximately in Figure D-17.  While
salt  deposits are  generally  shunned  in  the  development  of  water
resources,  permeable  strata  close  to  salt  layers  may  be penetrated by
injection wells  for  brine disposal.   Such  wells are usually abandoned
petroleum production  wells  and, therefore,  do  not  represent  additional
drilling.  Nevertheless, possible dissolution and fracturing around them
require  that  they  be  considered.   Storage  of  oil  or compressed gas in
abandoned  excavations  in  salt  is  a   relatively   recent  development.
Access  to  the  excavation   horizon  is  usually obtained  through  old
                                  161

-------
10
                        Potash
                     A   Mines
                     9   Wells
                    ---  Limit in Evaporite Basin
                          Major Mining Area
                        Salt
                     fl    Mines
                     ,    Wells
                     •    Domes
                    ~~  Limit in Evaporite Basin
                          Limit of Brine Basin
                        Gypsum
                     A    Mines & Pits
                         Plants
                         Outcrops
                         Limit in Evaporite Basin
                         Indefinite Limit
Commercial Magnesite & Brucite
Commercial Borates
                        Source:   The National Atlas of the United States of America. U.S. Geological Survey, 197O.
                                                      FIGURE D—16   COMMERCIAL SALINE DEPOSITS IN THE UNITED STATES

-------
Source: The National Atlas of the United States of America, U.S. Geological Survey, 1970.



  FIGURE D-17  COMMERCIALLY EXPLOITABLE ORGANIC FUEL DEPOSITS IN THE UNITED STATES

-------
boreholes and, therefore, this process  does  not  require the drilling of
new holes.
    Granite.   Mineral  and water  exploration are the  principal reasons
for  past drilling  into  granitic  rocks.    Precious  and  heavy metals,
including  gold,  silver, tin,  copper, tungsten,  and  lead, may  be
concentrated in enriched  zones  (veins)  in felsic rocks.   Mica, lithium
minerals, and other ore minerals may be generally distributed throughout
a granitic stock.   Because it is difficult and expensive to mine in such
rock, especially at considerable depths,  only granitic  ores with a high
economic value  have been  sought  in  the past.   Searches   for  gold  and
copper,  in  particular,  have been  carried  to  considerable  depths.
However, this has occurred only after surface exploration  suggested  the
existence  of deep  deposits.   Many  of  the  minerals  associated  with
igneous rocks are  found  in veins  at  the  contacts between  igneous rocks
and  the  surrounding  formations  or in zones  of hydrothermal alteration.
Therefore,  deep  penetration   into  a  granitic mass  devoid  of  signs  of
minerals is likely to be fruitless.
    Important crystalline  rock  aquifers  exist  in various   parts  of  the
country,  especially  in  the  Appalachians of North  Carolina,  Virginia,
Vermont, and New  Hampshire.   These aquifers  are highly fractured zones
and, if present at depths near  those  considered  for repositories, would
tend to  discourage interest  in  an area  as a potential  repository site.
There are a small  number of cases  where granitic rocks have been drilled
for  petroleum  exploration and extraction, when  the petroleum  has  been
trapped against the  flank of the  intrusive  or in its  fractures.  There
has also been more recent  interest  in geothermal resource  evaluation in
granitic  intrusions,  but  this  interest  is   sufficiently  new  and  well
documented  that undetected  boreholes  in this connection  are extremely
unlikely.
    Basalt.  Flood  basalts,  assumed  for the  generic basalt  geology in
this report,  often contain  alluvial  or  other permeable  interbeds,  and
these  may be  drilled   as  important  sources  of  water.    In  addition,
sedimentary deposits  underlying  basalt  flows may  also  contain oil  and
gas.   Nevertheless, because basalt  is difficult  and  costly  to drill
through  and because  geophysical  techniques for identifying petroleum
reservoirs are difficult  to  assess  in basalt, petroleum exploration and
                                  164

-------
exploitation  have  been  limited.    Valuable metals  such  as platinum,
nickel, chromium, and  iron  ore  are occasionally found in basalt, though
less frequently in flood basalts, and some enrichment can be  noted where
leaching and  rock alteration  have  taken place.   However, because of  the
general lack of ore-forming fluids in these rocks, concentrated deposits
              (72)
are unlikely.       (Copper  associated  with  basalt in Michigan may be an
exception.)   Geothermal  exploration  is  sufficiently  recent  not to be of
concern for  undetected boreholes;  furthermore,  source areas  rather than
the basalt flows themselves would be the principal source of  heat.
    Shale.   Shales   are  the most  common sedimentary  rocks  and  may be
associated with almost any  assemblage  of other  sedimentary  rocks.  They
generally have little or no economic value in themselves, except  for  oil
shales and  building stone, but  they may be  extensively drilled during
the exploration or  recovery of  associated  resources.   Oil and gas wells
may penetrate shale  formations, since the relatively low permeability of
the  shale  often  causes  the  accumulation   of   exploitable  reservoirs
underneath  these  formations.   Coal may  also  be  associated  with  shales,
and  previous coal  exploration  could  be the  source  of  old  boreholes.
Uranium,  vanadium,   and  phosphates  are  among   the  mineral resources
commonly  found  in   shale  or  its   associated  rocks.    Exploration   for
uranium has  intensified  over  the  last  30 years.   Shales can  also act as
aquicludes,  leading  to artesian heads  in underlying aquifers.   One of
the  most  outstanding  examples of  this  geology  involves  the  Dakota
sandstone  aquifer,  which  is  overlaid  by  thick   sections of  Cretaceous
shales.  Since this  aquifer is  one of  the principal sources  of water in
the Great  Plains, the shales  there have frequently  been penetrated in
the development of water resources.
    Salt Domes.   Salt domes,  including  the  rock  surrounding  them,  have
been of  considerable interest for drilling.  The salt  itself can be of
commercial value, as can the associated minerals, which are  similar to
those  found  with bedded salt.   Concentrated mineral deposits,  such as
sulfur,  may be  found above  or on  the flanks  of a  salt dome, since
discontinuities and  upturned  strata, which  tend  to collect  oil and gas,
often  result  from   the  intrusion  of   the  dome  through the overlying
sediments.   (See  Figure D-18.)  Deep  borings directly through the salt
are  uncommon, although  borings through  overhanging  portions  that  may
                                165

-------
                                      Surface
     Source: Adapted from Bateman, M. The Formation of Mineral Deposits, John
           Wiley & Sons, New York, 1951.

FIGURE D-18   DIAGRAM OF SALT DOME SHOWING ASSOCIATED
              OIL RESERVOIRS, WELLS, AND DEEP HOLES
                              166

-------
serve  to  trap  petroleum  below  are  frequently  carried  out.    While
geothermal resources  may be associated with  salt domes, there has  not
been  sufficient   investigation  to add  to  the risk of  undetected
boreholes.

D-3.4.2.2  Methods for Detection of Old Boreholes

    The  first  step  in  a  program of  identifying old  boreholes  is  to
review mineral claims, drilling  permits, and  leases  recorded  by various
government agencies for information on locations, depths, and  plugs.
These  records  may also  indicate unusual   situations,  such  as multiple
shafts  from  a single  surface  hole,  offshoot holes, obstructions,  etc.
Unfortunately, regulations  governing such documentation are  relatively
recent, so that while  records may  be an aid  in locating old  holes,  they
are  not  completely reliable.   Documentation  of  unsuccessful water  or
mineral exploration holes, particularly in states where regulations  have
not  been motivated by extensive  petroleum  or  mineral industries,  is
often lacking.
    Documentation  may  be supplemented  by  aerial  photographs  and
interviews with local residents.  Aerial  photographs  often  reveal  access
roads, ground damage from drill machinery,  pits for drill mud, and other
scars.   Interviews  are  particularly  useful where  obvious   traces  are
obliterated by  vegetation  or construction,  or  where  records  are
incomplete or in error.
    After  the  general location  of a borehole has been  determined,  the
hole  itself must  be  found.  Sometimes the uppermost pipe extends above
the ground or some other marker has  been  left.  Metal  detectors  can be
used  to  find  casings  and debris close to  the  surface.      Hydrocarbon
detectors can be used  to  locate  gas  escaping  from leaking holes as  well
as  traces  of  oil or  gas  that may  have  permeated  the ground  during
drilling or pumping  operations.  Even the location  of  scars  or  traces
from  guy  cables  from  the drill derrick  may be  useful in finding  the
approximate location of  an old  borehole.   Once a  possible boresite has
been  located, it  may  be necessary to remove  the  top layers of earth in
order to find the actual hole.
                                167

-------
    Underground  methods,  such as  sonar  and  radar,  are  also used  to
detect  boreholes  from  other  boreholes  or  from  excavations.    In  these
cases,  interpretation  of  reflected  signals  by skilled  personnel  may
indicate  underground  structures.   Radar uses  electromagnetic  signals  to
detect  fractures  with  anomalous electrical properties, such as empty  or
brine-filled  holes,  cracks  or  voids,  or  metals  (such  as  casings).
However,  the  cracks and voids  of fractured  rock scatter  radar signals,
and wet  rock,  with  high electrical conductivity, can  severely attenuate
the signal and thereby  limit  the  range.  In  salt or  other  dry  rock  it  is
possible  to  detect  an open,  caved,  or  brine-filled  borehole  at   a
                         (73-75)
distance  of many meters.
    Sonar, which  uses  sound waves,  is  not affected by moisture in the
rock to  the same  degree as radar.  Sonar's range through  dry,  fractured
rock may be  limited,  however, since  energy  is  lost   at  each  rock/air
interface.  Also, a filled  borehole may have acoustic properties very
similar  to those  of the  surrounding rock.
    Radar  and  sonar   use   short  wavelength   signals;  the  shorter the
wavelength, the  more  limited  the range but the better the resolution.
Experience suggests that in  fractured  or wet rock it may  be possible  to
detect a  borehole at  distances of 10 to 100 meters  away.   In  salt, the
detection capability is  over  100  meters.  Because of  the  water bound-up
in  shale minerals, even  uniform and  apparently  dry  shales   limit the
detection  capabilities  to  about  the  same   level  as  for crystalline
   ,  (74)
rocks.

D-3.4.2.3  Experience in Borehole Detection

    The petroleum and mining industries have devoted considerable effort
to  the  technology  of  detecting  (and  replugging)  abandoned  boreholes.
The  motivation for this  includes  legal  requirements  (concerning gas
leakage  from  old fields) ,  the desire  to  limit  oil and  gas   loss  into
barren  strata,  protection  of  miners  against  flooding or dangerous gas
accumulations,  and  the use   of  depleted  gas  fields  as  1535  storage
reservoirs.    Several  examples of  this  last   case  have  recently  been
          (62 ^
documented     and  are  summarized below.
                                  168

-------
    The  Webb  storage  field  in  Oklahoma had  25  old wells,  which were
found primarily through  a search of records.   The Lyons, Kansas  field,
however,  contained  many  wells   that  could  not be found  from records.
Aerial  photographs  proved useful  in  locating drilling  sites,  and then
metal  detectors  and  excavating  equipment  were  used   to   locate  the
wellbores.   The  Jackson, Mississippi  storage field  proved  even more
difficult.  About 80  boreholes  had to  be located  and replugged, but the
few existing records  were often inaccurate.  Houses and other buildings
had even  been  built  over  some  of the old  wells.   Eventually, however,
the abandoned wells  were  found  and the  field  was  successfully put into
service.

D-3.4.3  Undetected Borehole Failure Model

    The quantitative  characterization of the undetected borehole failure
element consists of  three elements:
    •  the probability of a borehole or  the expected number of boreholes
       present on the repository site;
    •  the probability of failure  to detect any such boreholes; and
    •  physical parameters to describe the nature of an undetected
       borehole so that consequence calculations may be carried out.
The  first two  factors vary  considerably  from one geologic  medium  to
another,  but  the third  has  been  modeled  independently  of  the medium,
except for the location'and length of the borehole.

D-3.4.3.1  Bedded Salt

    Number of boreholes.   First  estimate  values  are  based on  the
assumption of a site  where the major productive oil and gas horizons, if
any,  lie  above  the  formation  containing   the   repository;    mineral
resource  recovery  has  also  been  generally  limited   to considerably
shallower  depths;  and  sufficient  water is  available  near  or  at  the
surface so that deep  water wells would not have been necessary.  Much of
the Sallna and Appalachian basins, for example, meet these criteria.  In
the case of the Salina basin, it has been estimated that  holes  extending
into  the deep Silurian  salt deposits  that might  be considered  for  a

                                   169

-------
repository occur with a spatial density of about one hole per 100 square
miles  (256 km )«       Because  of the  capabilities  of  radar  and other
detection  techniques  in   salt  deposits,  boreholes  within the  actual
repository boundary  have  been assumed to have  a  negligible probability
of  failing  to  be detected.    (Because  of  the network of drifts  and
tunnels,  any  such borehole  would be  within  a few  meters  of  the  mine
opening).
    The calculations  here concentrate  on  a 300-meter-wide  buffer  zone
                                                           2
around the repository; the area of  this  zone  is about 4 km .  Boreholes
beyond  300  meters  are   assumed   to   be  too   far  away  to  contribute
significantly  to  any  risk.   Thus,  the boreholes  referred to in  this
subsection  on bedded  salt  are  assumed  to   be  in  this  zone.    The
probability of such  a  borehole  existing is thus 4 x  (1/256) = 0.016 if
the site  is  randomly chosen.   In particular,  the Poisson  distribution
describes  the probabilities of various numbers of  holes on the  site,  the
probability of N holes being given by  e ~°'016  (0.016)N/N!.  The  values
of this function for small values  of N are given in Table D-70.
    Multiple holes  are  seen  to have  negligible probabilities  compared
with a single hole,  and thus  the  event of  a single hole is  the one  that
has been  modeled  in  the  first estimate  case.   Since site  selection is
expected to favor sites with  lower  than  average past  drilling  rates, it
is  conservative  to use  the  average  rates  as  the  basis  for  the
probabilities.
    Second estimate values correspond  to  regions with  extensive mineral
and energy resource recovery activities.  Typical  of  such regions  is  the
Carlsbad,  New Mexico mining district,  where approximately 125 holes  to a
                                                                  2  (20)
candidate  repository  formation are  known  in  an area  of  166  km .
(Approximately  60% of  these  are  potash  exploration holes,  which
generally terminate above  the actual  strata that have  been  proposed  for
the Waste  Isolation  Pilot Plant.   However, the  total  number  has  been
used as an estimate  for  the generic  calculations  in  this report.)   For
               2
an area of 4 km , this leads  to an  expected number  of about three holes
per repository.
    Failure  to detect boreholes.     Statistical  analyses  of   the
effectiveness  of  borehole detection  techniques are not  available,  and
the estimates adopted here are based on very limited data.  Conventional
                                 170

-------
                            TABLE n-70

     PROBABILITIES OF UNDETECTED BOREHOLES TN BUFFER 7.0MR
        AROUND BEDDED SALT REPOSITORY  (FIRST ESTIMATE)


N(number of holes)                Probability (e~°;016)(0.016)N/N!

         0                                     0.9841

         1                                     0.0157

         2                                     1.26 x n~4

         3                                     6.72 x ]0~7

         4                                     2.69 x 10~9
                           171

-------
surface  methods  have  been   totally  effective  in  several  cases,  but
failures  are  sometimes  unknown and   often  not  documr-nted.    One
significant  failure  involved  the  interception of  an unknown  abandoned
borehole by an advancing mine  excavation.      Tn that case,  the  unknown
hole represented  one  out of  about  100 boreholes  in the area,  yielding a
detection  failure rate  of 1%.
    When  conventional  surface  techniques  are  augmented  by  techniques
such as  radar, the  detection probability  can  be  expected  to improve.
For example, with skilled operators working in dry, homogeneous salt, it
may be possible to find all boreholes out to a distance of  100 meters or
more.  However, since  operators  can  make errors  and geologic  conditions
vary,  finding all  abandoned holes  is  not an  absolute  certainty.
Instead,  it  has  been assumed  for the  case  of  both  first  and   second
estimates  that radar can reduce the failure rate to 0.1% per hole.  This
detection  failure probability has been combined with the expected  number
of boreholes as follows.
    For  the  first   estimate  case,   the  event  being  modeled   is   the
existence  of  one  undetected  borehole, whose  probability  is the  product
of the probabilities  that a  hole is  present (0.016) and the  probability
of detection failure  (0.001).   The resulting  probability is  1.6  x 10~ .
For the second  estimate case, where  more  than one  borehole is expected
on the site, the  probability  of  at least one  undetected borehole  out of
three  is  1 -  (0.999)3  =  0.003.    Note:   0.999  is the  probability of
                                             o
detecting  each individual  hole,   so  (0.999)    is  the probability  of
detecting  all  three,  assuming  independence.    While the case of  exactly
one undetected borehole is the largest  contributor  to this probability,
to  allow  for  some   dependence  among   detection   failures,   the  event
corresponding to  this probability  has been modified to  be  the existence
of three undetected boreholes  on the  site.  (It  is appropriate to make
some allowance for dependence because the causes  for detection failures,
such as  faulty equipment operation,  inadequate  coverage of the area, or
interfering  geologic  features,  may   encourage  multiple  detection
failures.)   This  is  a  rough  approximation to a more  detailed analysis
based  on  hypotheses  of dependencies in  borehole  detection; however, it
is believed  to be adequate for the purposes of this study.
                                  172

-------
    Nature of undetected boreholes.   It  is  reasonable  to  assume  that
boreholes that  escape  detection  do so because,  in  terms  of density and
water  content,  they are not  very different  from the  surrounding rock.
Thus  they can  be assumed  to be  filled or  plugged.   Their hydraulic
conductivity  has  been modeled  to  be   uniform  over  time  and  spatial
extent, and  to  have the values  of 10   cm/sec as  a  first estimate and
10    cm/sec  as a  second  estimate.   These  values  are  in  the  range
corresponding to  silty sand  and  gravel, as well  as other materials, as
shown  previously  in Figure  D-13  (see  Section D-3.2).   They represent
relatively  permeable  fill   material  such  as  might   be   expected  from
material  falling  from  the  sides of  the  hole in loose upper levels or
from  a poor  concrete-drill  mud  plug.   Their cross-sectional  area has
                   2
been taken as 0.1 m  ,  their porosity  as 0.2,  and their distance from the
nearest point of  the  repository as  100  m.    For  conservatism,  all  such
holes have been assumed to penetrate  to the lower aquifer.

D-3.4.3.2  Granite

    Number of boreholes.   Deep drilling in granite is  much less common
than  in  bedded  salt.   Granite rarely contains  reserves  such as gas or
oil  that  can  be  exploited   through boreholes.   In general,  it  is
penetrated  only when  some surface  indications suggest  that deep mining
may  be profitable,      or  when  fractures  in  the rock  are extensive
enough  that  the granite can  be  tapped  for  water.   Indeed,  there may be
locations where it  can be assumed  that no drilling  has  taken place, such
as  a National  Park.   However,   such locations  are  also  likely  to be
unavailable  or  undesirable for a  repository.
    The  first  estimate assumes  a location  that  shows no  surface
indications  of  ore  minerals deep  in the  granite,  and  where  water is
either  readily  available at  the  surface  or else past land  use  suggests
that  deep water exploration  has  not  been  carried out.   Detailed  drilling
data  for  such  regions  are  often  lacking.   For  example,   local  statutes
may  not  require  reporting of  drilling,  or  the  mineral  companies
performing  the  drilling may  be  reluctant  to  release their  information.
In the absence  of  adequate data,  it  has  been  conservatively assumed that
granite is  penetrated  to the depth  of  a potential repository one  tenth

                                  173

-------
as often as  in the  first estimate bedded  salt  situation.  This  results
in a  deep  borehole  density of  one  hole  per thousand square miles  (2560
  «
km )•  Since  the  area  of the  repository plus a 300-meter-wide  parameter
is about 12 km2,  this implies a probability of about 0.005  that there is
a borehole at  the site.   The  second estimate for  granite is  based on a
drilling rate  ten times as high as in the first estimate, resulting in a
probability of 0.05 that there  is a borehole on the site.
    Failure  to detect boreholes.    Conventional  borehole-locating
techniques are expected to  be as  reliable for  granite as  for bedded
salt,  although specific data to prove this assumption are not available.
The use  of  radar for  detection  of  features  in  granite has  not  been
demonstrated, and it is  not assumed  to  contribute to the probability of
finding  abandoned holes.   For both first and  second  estimates,  the
detection failure rate has been assumed  to be 1%, equivalent to that for
bedded  salt  without  the  advantage  of  radar.    This  failure  rate  is
combined with  the expected number  of boreholes  as  follows.   For  both
cases,  the  event being  modeled  is  the  existence  of  one  undetected
borehole, for  which  the probability  is  the product of  the probability
that  a hole  is present and the probability of detection failure.   For
the  first  estimate  the  resulting  probability  is  5  x  10     that  an
undetected  borehole  is  present.   For  the  second   estimate,  the
probability is 5 x 10   for an undetected borehole.
    Nature of undetected boreholes.   As  in the case of  bedded  salt,  it
has been assumed  that a  borehole  escaping detection  does so because, in
terms of density and water content,  it  is not  too different  from the
surrounding rock.   Thus, it has  been assumed to  be  filled or plugged.
The hydraulic  conductivity has  been modeled  to  be uniform over time and
                                           -4
spatial extent,  and  to  have the values  10    cm/sec  as  a first estimate
      ^o
and 10   cm/sec as a second estimate.  Its cross-sectional area has been
               2
taken as 0.1 m ,  its porosity  as  0.2, and its distance  from the nearest
point  of the repository as five meters.   (Five  meters  is intended to be
a conservative  estimate.   Boreholes closer than  five meters  are highly
likely  to  be  found  during  excavation,  either  by  leakage  or through
detection techniques.)
                                  174

-------
D-3.4.3.3  Basalt

    Number of boreholes.   Borehole densities  in the  basalt  regions  of
the Pacific Northwest  have  been used  in estimating the probability of  a
borehole at the repository  site.   In  that region deep drilling has been
dominated  by  water  wells,  and  reported numbers  of  wells are  used  to
derive borehole  density estimates.   The first  estimate is  based  on  a
                                      (78)
study  of  wells  in  the  Pasco Basin,     where 34 wells  were reported
reaching or exceeding  depths  of  1000  feet (300 m).  The area covered  in
                                          o
that study included  approximately 5400 km ,  and so for a repository and
                   2
perimeter  of 12 km ,  there  is a probability of approximately 0.075 that
an  old borehole  exists on  a  randomly chosen site.  The second estimate
                                                                  2
is  based  on  well  populations  for   a  larger area   (30,000  km )   of
southeastern Washington state,  where an estimated 500  wells may reach
                              (79)
depths of  1500 feet  (400  m).      For  a randomly chosen  site  with  an
               2
area of  12 km ,  this  implies  a probability  of  about 0.2  that  an old
borehole will be present.   (Multiple  occurrences have  sufficiently small
probabilities  that  they need  not  be considered.)
    Failure to detect  boreholes.  Much of the Pasco Basin area has been
under  close government control,  and  most of the deep drilling has been
supervised by  the  Federal  government.   The location  of  these holes  Is
well known and well  documented.   Although  special  techniques,  such  as
tadar, are not expected to  be adaptable  to borehole detection  in basalt,
the exceptional quality of  records  kept for this particular area should
improve the chances  of finding holes  to the degree that the  probability
of  detection failure is reduced to the level achievable in bedded salt,
i.e.,  0.001.   Combining  this probability  with the  probability  that  a
borehole is present  (0.075)results in a  first  estimate probability of  an
undetected borehole  of 7.5  x  10
    The second estimate probability of detedtion failure is  taken to  be
the same as for other  areas where surface detection techniques alone are
relied upon (0.01)  since  much of the  area  defined above for  the  second
estimate is not under  tight control and  the  location of wells may not  be
accurately known.    The probability of  an  undetected  borehole is  again
the probability of  a hole  (0.2) multiplied by  the  probability of  failing
                                                              _3
to  detect  it (0.01), with a resulting probability  of  2.0 x  10  .

                              175

-------
    Nature of undetected boreholes.   Boreholes  In basalt are assumed to
have the same characteristics as those in granite.  For  conservatism, it
is further assumed that all holes penetrate to the lower aquifer.

D-3.4.3.4  Shale

    Number of boreholes.  First-estimate values are based on assumptions
of a  site where  productive  gas,  oil,  coal,  and water lie  above  the
shale.  Such a site is analogous to  that  assumed  for  bedded salt and so
the same borehole density applies.   However, because of poorer detection
                                                                      2
capabilities in shale, the entire area of  site  and  buffer zone (12 km )
has been used.  Therefore,  the  probability  of  a  borehole on the site is
0.05.  Second estimate values are also based on the case of bedded salt,
                                             2
leading to nine expected boreholes  on a 12-km  site.
    Failure  to detect  boreholes.    For  shale  areas,  conventional
detection  techniques  cannot  be  augmented  by  radar since  the  fractures
and  moisture  in shale  severely limit the  range of  radar  and  similar
techniques.   Therefore,  the  first and second  estimates  for  the
probability  of  failure  to  detect boreholes  are   the  same  as  for
conventional detection methods  (0.01).  As before, the probability of an
undetected borehole is calculated as the product of the probability that
a borehole is present and  the  probability  of  failing  to detect it.  For
a first estimate, the resulting probability is 5 x 10~ .  For the second
estimate, the probability of  failure  to  detect  at least one borehole in
the  expected  nine  is  about  0.09.   To   allow  for  dependence  among
failures, the event with  which this probability  has  been associated is
that  of three undetected boreholes, as in the case of bedded salt.
    Nature of undetected boreholes.  The boreholes that escape detection
are  assumed  to be  similar to  the  surrounding  rock.    Their  hydraulic
conductivity has  been modeled  as  uniform  over  time  and  space,  and to
have the values of 10   cm/sec  as a  first  estimate  and 10~" cm/sec as a
                                                                      2
second estimate.   Their  cross-sectional  area has been taken as 0.1 m ,
their porosity as  0.2,  and their distance  to  the nearest  point  of the
repository as 5 m.  For conservatism, all holes are assumed to penetrate
to the lower aquifer-
                                 176

-------
D-3.4.3.5  Dome Salt

    Number of Boreholes.   The  cross-sectional  area  of  a  salt  dome  is
generally  of  the  same  order  of  magnitude as  the area  required  for a
repository.   As  explained  in the  section  on  bedded  salt, boreholes
located within  the actual  repository  boundary are most  unlikely  to  go
undetected because of the effectiveness of detection  techniques  in salt.
Therefore, the  area that has  been modeled for  undetected boreholes  is
that of a 300 meter wide  buffer zone around  the repository.  Since  this
zone  is  expected  to  be  close to  the flanks  of  the salt  dome,  where
drilling activities are concentrated,  the total number of  holes  reported
as penetrating  the  dome will  be used as the number of holes  penetrating
the buffer zone.   Surveys of  records  for a number of interior domes  in
Texas, Louisiana,  and  Mississippi place  this number in  the  range 0  to
30.   For  the first-estimate  value,  three boreholes  have been  assumed;
for the second estimate,  30 have been  assumed.
    Failure to detect boreholes.  As in the case of bedded  salt, failure
to detect  a given  borehole has been  assumed to  have a  probability  of
0.001 for both first and  second estimates.   Thus,  in the  first  estimate
case,  the probability  of  failure  to detect  at  least   one borehole,
assuming   independence,  is  1  -  (0.999)   - 0.003.    A  simple  and
conservative  way  to  allow  for  the  possibility  of dependence  among
detection failures  is to  use  this probability  for the  event  of failing
to detect three boreholes, which has been done here..  A similar  approach
has  been  taken  for the  second estimate.   Assuming  independence,  the
probability of  failure  to  detect  at  least one  of 30 boreholes is  1 -
(0.999)   = 0.03.   Some dependence  is  roughly introduced by using  this
same probability to correspond  to  a  different event,  namely  the failure
to detect five boreholes.
    Nature of undetected boreholes.    It  is  reasonable  to  assume  that
boreholes  that  escape detection do  so  because,  in terms  of  density and
water  content,  they are  not   too  different  from  the surrounding  rock.
Thus, they have  been  assumed  to be  filled  or plugged.   Their hydraulic
conductivity has been modeled as uniform  over  time and  spatial extent,
                                •                                      o
and  to  have  the  values  of 10~   cm/sec  as  a first estimate  and  10
cm/sec as a second  estimate.   Their  cross-sectional area has been taken

                                  177

-------
         2
as  0.1  m ,  their porosity as  0.2,  and  their distance from  the  nearest
point of the repository as 100 m.   For conservatism,  all  such holes  have
been  assumed  to  penetrate  to  a  lower  aquifer  or  pressurized brine
reservoir along  the flank of  the dome.

D-3.4.4  Undetected Borehole  Release Model

    The purpose of  this  section is to analyze how undetected  boreholes
may  constitute   or  contribute  to  a breach of  the  repository.   As
discussed in the previous section,  undetected boreholes do  not intersect
repository drifts.   Furthermore,  because of the assumed reliability of
detection  techniques  carried  out   from  the  repository  itself,
conservative estimates of minimum  distances between repository  drifts
and such undetected boreholes were given  in  the previous section  as  100
meters  for  salt and 5 meters  for  the other rock types.   Consequently,
for   such  boreholes  to  serve   as  pathways  for the   release  of
radionuclides,  communication must  exist between them and the backfilled
repository drifts. An  electrical  resistance  analog  is  useful in
representing   this  situation  and  in  identifying  cases  in  which
significant levels  of  flow may take place.  The  general  situation is
represented in  Figure  D-19a.   The  quantitative analysis  for  each  of  the
two  salt formation  repositories   will  be  presented in  the  following
sections in terms  of the  diagram  in  Figure  D-19b.   Effective resistance
will  be  calculated  as  in earlier  sections and as explained  in Appendix
D-III, according to the formula a = L/KA, where  L is  the  pathway length,
K  is  its  permeability,  and  A  is  its  cross-sectional  area.    (The
unlabeled resistances  along  the aquifers are relatively low  and  do  not
enter  into the  calculations.)

D-3.4.4.1  Bedded Salt

    The  values  of  the effective  resistances  »1 through  a.^, based on
parameter values  presented  earlier,  are shown in Table D-71.   Since o^
and a^ are functions  of  time, selected  values  are  tabulated  in Table
D-72.   The values  of  a.^ and  a,  ignore  the possibility of  dissolution
                                 178

-------
   (a)   Physical Pathways
                           II
                           11
                          Ji-
I  I
      I I
        Permeable
        shafts and
        boreholes,
        fracture systems
                              Upper aquifer
                     Repository
           Permeable
           deep boreholes,
           fracture systems
                   Permeable
                    interbeds
                   or fractures
                                             Undetected
                                             borehole
                               Lower aquifer *
    (b)  Electrical Analog
                                    Upper aquifer
                         Shafts,
                         boreholes,
                         fractures
                              Upper section
                              undetected borehole
                                  Interbeds or fractures
                         Deep
                         boreholes,
                         fractures
                              Lower section,
                              undetected borehole
                                    Lower aquifer*
      Lower aquifer not present for certain rock types.
FIGURE D-19  PATHWAYS ASSOCIATED WITH THE ANALYSIS OF UNDETECTED BOREHOLES

                                   179

-------
                               TABLE D-71
                    EFFECTIVE RESISTANCES  ct  THROUGH u
                         (BEDDED SALT REPOSITORY)
                               ?                                2
            First Estimate (y/m )          Second Estimate  (v/m J_

a *   (3.31 x 10~3 + 4.70 x 10~3 t)'1   (3.31 x 10~3 + 3.31 x 10~3 t)'1

a     (1.58 x 10~5 -f 1.58 x ](T6 t)"1   (1.58 x 10~5 + 1.58 x 10~5 t)'1
                    31.75                               105.8
                    31.75                              105.8
a5**             3.2 x 106                             317.5
 *
  The  calculation  of   a    has   been   carried  out  by  considering  the
  situation of two parallel resistances, one representing shafts and one
  representing boreholes,   t is  time from repository closure.
**
  The values are based  on  the assumption of communication through one or
  more interbeds with a total effective  pathway  cross-sectional area of
  1  m ,  permeabilities  10~    cm/sec,  and  10~   cm/sec  for  first  and
  second  estimates,  respectively,  and a  length  of  100 m.   (Cf. Figure
  D-13).
                                 180

-------
                               TABLE D-72
                      SELECTED VALUES OF a  AND a
  First Estimate
        10*
       100
       500
      1000
      5000
    10,000
Second Estimate
        10
       100
       500
      1000
      5000
    10,000
(BEDDED SALT REPOSITORY)
2
Resistance (v/m )


1.

2.
4.
2.

4.
2.
3.

3.
6.
3.
6.
3.


99

11
25
13

25
13
02

02
04
02
04
02
!i

X

X
X
X

X
X
X

X
X
X
X
X


10

10
10
10

10
10
10

10
10
10
10
10
!i
i
j.
o
\J
-1
-1
-2
£,
-2
1
n
\J
-1
-1
-2
-2

3

5
1
6

1
6
5

6
1
6
1
6

.16

.75
.24
.27

.26
.32
.75

.27
.26
.32
.27
.33

x

X
X
X

X
X
X

X
X
X
X
X

10

10
10
10

10
10
10

10
10
10
10
10
A
*T
1
J
3
2
2

1
3
2
£>
2
1
1
0
*Years after repository closure.
                                  181

-------
along  the  portion of  the  borehole with  the salt  strata;  the  case  of
dissolutioning will be discussed later.
    Without performing detailed network calculations,  it  is  possible  to
dismiss  the  importance  of  the undetected  borehole  pathway,   in  most
cases, by the following reasoning.  Because a,,  is  much greater  than o^,
flows  out  of the repository  via the  undetected borehole-interbed
pathway  would be  expected  to be insignificant   compared  with  flows
through shafts and boreholes  to the upper aquifer.  Because a-  is  much
greater  than  a.,  at  least  for t  > 1000 years  in  the  case  of  second
estimates,  flows  into  the  repository  through  the  interbed  are  small
compared with those through the degrading  deep borehole seals.   (For t<
1000 years,  releases are  dominated by  salt creep,  and  other  driving
forces  are  not  important.)     In  either  case,  consideration  of  this
pathway would lead to  flows  that  are  insignificant  compared with  those
calculated in the  previous  two sections.
    The one additional possibility  that  needs to be considered  is  that
of  dissolution  around  an  undetected   borehole  and  the  resulting
consequences,  if   any,   for  repository  integrity-   Dissolution
calculations  in  Appendix D-IIT   show  that  in  the  case  of  second
                                                         _^
estimates, where  borehole  permeability is  high (K  •  10   cm/sec) and
there is  a  significant  aquifer interconnection  gradient (i = 0.5), the
potential for dissolution is  great. After  the period of  extensive  salt
creep (Period A),  releases  through an undetected borehole connected  to
the  repository as  a  result  of dissolution  can  be estimated simply  by
assuming  that  the flow  passes through  the  repository and encounters
resistance only in the part  of the  borehole  extending from the  lower
aquifer to the bottom of the  salt  stratum (since  a dissolution  pathway
extends through the  salt  and  the  part above may crumble and fall  into
that void).   Darcy's  equation,

                             Q  =   KiAc(M),
                                 182

-------
with parameters given earlier, leads to the volumetric flow rate

                             Q  -  945 m3/yr

during Period B.  (See Section D-3.2.4 for the definition of Period B.)
    The  source  term  for  this  failure  element  consists  of  the
concentration of  radionuclides  that  have leached into the water in the
repository  during the  time frame  of  interest.   This  is  the  uniform
concentration situation described earlier.

D-3.4.4.2  Granite

    An undetected borehole has been modeled at a distance of five meters
from  a  repository  drift  in  the  case  of granite.   Over  this  short
distance  the flow between the  repository  and  the  borehole cannot  be
adequately modeled by  Darcy's  law for flow through porous media,  since
this law can only be applied to fracture flow on a larger scale.  Direct
communication  through  a single  open  fracture  could  eliminate any
significant  resistance  along  this  part of the pathway.  Therefore,  the
borehole has been modeled  as  passing directly  through  the  repository,
and volumetric  flow rates  have been calculated as they were in Section
D-3.3.4.    Using  the  driving  forces  summarized  in  that  section  in
combination  with  the  pathway parameters  given in Section D-3.4.3,  the
volumetric flow rates  and fluid velocities shown in Tables  D-73  and D-74
result.
    The  source  term  for  this  failure  element  consists  of  the
concentration of  radionuclides  that  have leached into the water in the
repository during the time frame of interest.   This is the  usual uniform
concentration situation.

D-3.4.4.3  Basalt

    As in the case of  granite, flows  through  an undetected  borehole  in
the  generic  basalt   repository have  been  calculated  as  though  the
borehole passed through the repository Itself.  The flow calculations in
Section D-3.3.4 Indicated that, because  of  multiple pathways  from the

                                  183

-------
                                TABLE D-73

            VOLUMETRIC FLOW RATES THROUGH UNDETECTED BOREHOLES
                           (GRANITE REPOSITORY)
                                  Volumetric Flow (0)
                                       (m3/yr)
                   100 years      1000 years     10.000 years
First Estimate
1.7
1.1
0.5
Second Estimate
17
11
 Years after repository closure.
                               184

-------
                               TABLE D-74
              FLUID VELOCITIES THROUGH UNDETECTED BOREHOLES
                          (GRANITE REPOSITORY)
                                  Velocity (v)
                                    (m/yr)
                   100 years
           1000 years     10.000 years
First Estimate
 85
 55
 25
Second Estimate
850
550
250
 Years after repository closure.
                              185

-------
repository to the upper aquifer (e.g., permeable shafts and boreholes),
the limiting  factor  in flows through deep  boreholes  is the  resistance
over  their  lower  sections  (from  lower  aquifer  to  repository).    It
follows  that  the  driving  hydraulic  potential  is  almost  entirely
dissipated over this part  of  the  pathway.   This reasoning  was used  in
the earlier  section  to derive  the  hydraulic gradients given there  in
Table D-60.   By  using these  gradients  in  Darcy's  law,  the marginal
increase  in  fluid  flows caused by  an undetected  borehole  through the
repository  can be  calculated;  these  are  given  in   Table  D-75.
Corresponding fluid velocities, assuming that the  flow continues  to the
upper aquifer  through  the  same borehole (a  conservative  assumption  in
that it tends to overestimate the velocity)  are given in Table D-76.
    The  source term   for  this   failure  element  consists  of  the
concentration of radionuclides  that have leached  into  the water  in the
repository during the time  frame of  interest.

D-3.4.4.4  Shale

    Although the probability  of an undetected borehole differs  in the
case of shale from that calculated  for basalt, the  flow calculations for
each such borehole are  identical.   Therefore, Tables D-75  and  D-76 carry
over  to  this  case,  except  that on  the  second  estimate for shale  three
boreholes are  used.    The  results  for shale  are  given in  Tables D-77
and D-78.  The source term  is also  the same  as in the case of  basalt.

D-3.4.4.5  Dome Salt

    The analysis for a salt  dome  repository closely parallels that for
bedded  salt.    Since   an  undetected borehole  will  be  close  to the
periphery of the dome,  there  is a significant possibility that  it will
pass  through  an overhanging  flank  and make contact with  an aquifer (or
pressurized brine reservoir)  below.   This has been assumed  in the model
for  all  undetected  boreholes in dome salt.   As in  the case of  bedded
salt, the  only significant flows  can occur during Period  B and  under
second estimate model  assumptions.    In this  case, there are  five  such
boreholes and  the original hydraulic  gradient  of  0.2  (from  the  aquifer
                                       186

-------
                               TABLE D-75
           VOLUMETRIC FLOW RATES THROUGH UNDETECTED BOREHOLES
                           (BASALT REPOSITORY)
                               Volumetric Flow (0)
                                         (m /yr)
                   100 years
           1000 years     10.000 years
First Estimate
4.4
3.8
1.6
Second Estimate
198
192
170
 Years after repository closure.
                               187

-------
                               TABLE 0-76
              FLUID VELOCITIES THROUGH UNDETECTED BOREHOLES
                           (BASALT REPOSITORY)
                                 Velocity (v)
                                    (m/yr)
                   100 years      1000 years     10.000 years
First Estimate
 220
 190
  80
Second Estimate
9900
9600
8500
 Years after repository closure.
                                 188

-------
                               TABLE D-77
           VOLUMETRIC FLOW RATES THROUGH UNDETECTED BOREHOLES
                           (SHALE REPOSITORY)
                                 Volumetric Flow (0,)
                                      (m3/yr)
                   100 years      1000 years     10.006 years
First Estimate
4.4
3.8
1.6
Second Estimate
594
576
510
 Years after repository closure.
                                 189

-------
                               TABLE D-78

              FLUID VELOCITIES THROUGH UNDETECTED BOREHOLES
                           (SHALE REPOSITORY)
                                 Velocity (v)
                                     (m/yr)
                   100 years
            1000 years     10.000 years
First Estimate
 220
 190
  80
Second Estimate
9900
9600
8500
 Years after repository closure.
                               190

-------
interconnection)  leads  to a concentration of the driving  force  over  the
undissolved  and  unbrecciated section of  the borehole between the  lower
aquifer and  the point where it  enters the salt.   If  this distance  is  one
quarter  the distance between the  aquifers, the  effective gradient  is
four  times  the original value of  0.2.   The corresponding volumetric
flow  rate  is given  by

            Q =  KiAc(u)

              =   (10~3 cm/sec)(3.15  x  105 cm/sec/m/yr)(.8)(.5 m2)(5)

              -   630 m3/yr

which applies  to  Period B.
    The  source  term   for  this  failure   element  consists  of  the
concentration  of radionuclides that  have leached into  the water  in  the
repository during the  time frame of interest.

D-3.4.5  Literature Discussion

    Undetected  boreholes have  also been  discussed  by  an  NRC-Sandia
group ^  '  and  by Battelle  Pacific  Northwest Laboratory  (BNWL)^     under
the WISA.P Program.
    In the  NRC   Sandia  report,  a  general  methodology  is proposed  for
modeling  this  phenomenon.  Input requirements are the following:
     3  =   mean areal  density  of undetected boreholes
     f  -   fraction of the undetected  holes that are unsealed
     S  •   a  random variable representing the shortest distance from an
            undetected  borehole to a waste drift, whose distribution
            would be calculated from the repository geometry
  o(s)  •   a  function  describing the time required for solutioning
            along a borehole to extend  the radius to value s
  
-------
     V  -   rate of salt removal from a cavity formed by flow through an
            unsealed borehole
     W  -   rate of salt removal from a cavity  formed  by the failure of
            a sealed borehole.
                           *        3     *          3 /
The report suggests values  V - 1.5 m /yr, W - 0.15  m /yr,  and  the range
27 to 113 meters for  the distances between an undetected borehole and  a
waste  drift.   (These  parameters  apply  to  the   generic  bedded  salt
reference repository defined in detail  in the  same  report.)
    In  the  BNWL project,  it  has been  asserted that  for the  Columbia
Plateau (basalt)   the  identification  of  all  old  boreholes  to  the
repository depth should be  a relatively simple task.  In addition, it is
argued that two additional  factors  would need  to be  present in  order  for
such a  borehole to lead to a breach of  the  repository containment:   a
connection with the repository and  a  hydraulic driving force.
D-3.5  OTHER TECHNOLOGICAL EVENTS AND PROCESSES

D-3.5.1  Introduction

    Mechanisms and processes that fall into the "technological" category
are  those  related  to the presence  of  the wastes or the  repository, or
those related  to  the site  exploration  process.   In  other projects on
disposal of high-level radioactive wastes, the term "near field" effects
has been used  to include  most  of these processes.      The analysis of
such  effects  is difficult  with a  generic repository because  detailed
engineering assumptions are necessary  for a complete analysis,  and  the
repository  systems  treated here are  not defined  to  such a  level of
detail.    For example,  questions  have  been raised  concerning  the
stability of  borosllicate glass as  a  waste  form when placed  in a  salt
            (81)
environment.   '   Since  stability  is  related  to both  waste  form  and
temperature,  it Would be  necessary  to specify a  waste form and a level
of thermal  loading  for  the  repository, calculate  estimated  temperature
profiles,    and    then   determine   what   laboratory   data   and
thermodynamic/kinetic analysis could contribute to  a quantitative
assessment  of the  magnitude  of  the  potential  problem.   A  different
                               192

-------
approach  has  been adopted here, one  more  suitable for a generic  study.
Potential  problem areas have  been reviewed and,  except  in the case of
those  identified  as  particular failure  elements  in previous  sections, it
has  been assumed  that  they represent  engineering problems amenable to
analysis  and  solution.

D-3.5.2  Waste-Rock  Interactions

     Interaction between the  radioactive wastes and the surrounding rock
can  affect  both the  waste  package and the rock.   Examples of particular
effects are discussed in the following  paragraphs.
     Waste form degradation.  The waste forms under consideration in this
study  range  from  spent fuel  to  special solid  matrices  (e.g., cement,
glass,  synthetic  minerals)  for processing or  reprocessing  wastes.   In
each case and in  each geologic environment, the  effects of  the host rock
and  groundwater on the  waste forms must be addressed.  A particular case
that has  received considerable recent  attention  is  the effect  of hot
brines  on borosilicate glass.  A  straightforward  engineering solution
to  such a problem might  be to decrease  the  level of waste loading  so
that  the temperature  remains   at  a  level  where such a  reaction would
occur  at  a negligible rate,  if at  all.  Other  questions would be whether
the  altered  waste  form  is  significantly  more leachable  than  the
original,  whether the  canister  (i.e.,  the package)  might be  able  to
Insulate  the  waste form from the  environment  until the critical thermal
period  has  passed,  whether  brines  or otherwise  active  groundwater can
ever reach  the waste form,  etc.  Current research on waste  forms should
provide  the  information  necessary  to deal  with  these questions
effectively.
     Canister  degradation.  Canister research and  development work in the
United  States and abroad reflects  several  different  philosophies about
this component  of the  waste containment  system.  These  range  from the
view  that  the  canister  is  important   only  through  the handling  and
emplacement stage, to the view that the canister can  be  one of the most
important barriers  to  radionuclide release,  perhaps  for periods  up  to
hundreds of thousands  or millions  of years.   More details on canister
capabilities  may  be  found  in Appendix D-VIII  of this  report and in the
                                 193

-------
Task B Report.   In any case,  the geochemical, thermal,  and  mechanical
parameters  of   the emplacement  environment  can   certainly  affect  the
integrity  of  the  canisters,  and  therefore  these  factors  must  be
considered carefully in the engineering design of  the system.
    Rock alteration.   Rock  in  the  immediate vicinity  of  the  waste
canisters will be  subjected  to heat and radiation,  which  can  affect  it
in a variety of ways.   For example, heat can lead  to spelling,  cracking,
or decrepitation  through  differential expansion or  high vapor  pressure
of fluids  in  the  rock.  Such  fracturing would be expected to  increase
the hydraulic conductivity, but probably only within a few meters of  the
wastes.  (This increase is different  from  the  bulk rock failure element
discussed  in  Chapter   3.0, wherein  large  scale movement  along  existing
joints was  considered.)   In the special case  of  shales and some other
rocks composed of certain  hydrous clay minerals and metastable  minerals,
more   extensive   changes  are   possible.     Some  clays,   such   as
montmorillonite, contain  loosely bonded water  in  the crystal  structure,
and  this  can  be liberated at temperatures   in  the range of 100-200   C.
As  a  result  of  dehydration,  the  clay contracts,   cracks,  and  loses
strength; in addition, water is provided to the repository.  Other modes
of alteration are  also possible  but are not discussed  here since it  is
believed that they are likely to be less significant.

D-3.5.3  Brine Migration

    Salt  deposits frequently  contain fluid inclusions, which are
(generally  very small) bubbles  or  pockets of  fluid  within  the  salt
matrix.   These  inclusions occasionally have both  a liquid and  a vapor
phase.   Some  of  these inclusions may  represent connate water  contained
in the  salt since  its deposition, although  other mechanisms  may also
account  for such  inclusions.    Geochemical  studies  now  under  way may
provide a greater understanding of this phenomenon.   '
    Fluid  inclusions  can  migrate in  a thermal gradient as a  result  of
                             (83)
several  possible  mechanisms,      one of  which  is  sketched   in Figure
D-20.  In  the situation represented,  salt  dissolves  on  the left side of
the bubble and reprecipitates on the right  side because of the variation
                                  194

-------
                          Diffusional transport
                          of solute, driven by
                          concentration gradient.
Dissolution  \
Precipitation
                        Decreasing temperature
                          Bubble migration
FIGURE D-20   MIGRATION OF BRINE BUBBLE IN THERMAL GRADIENT
                             195

-------
of solubility with temperature.  This has  the  effect of moving the fluid
inclusion' to the left, toward  the heat  source.
    The  rate  of  brine  migration  and  the  total  amount  that  might
accumulate near  the hot  waste  canisters depends on  a number of factors,
such as  the  magnitude of  the  thermal  gradient  and  the  amount  of water
present  in  the salt.   The results  of modeling  efforts  and  laboratory
experimental programs  now in  progress  may provide  further  illumination
on  the  relationships  among  the parameters  and indicate the  extent  to
which this mechanism should be considered  in site  selection (e.g., fluid
content  of   salt  may  vary from  site  to  site)  and  in  the  choice  of
engineered barriers.   The potential  for migration  of brine will  be  an
important factor in determining  the requirements a  the waste  package  in
a salt repository.

D-3.5.4  Canister Migration

    Various mechanisms have been proposed  by which  canisters emplaced  in
a  salt  environment  might  physically  migrate  either upward  or
downward.    '          Representative  mechanisms  are briefly  described
below.
    Sinking because of canister density.   Because  the canister is denser
than the salt  and  because the  salt is plastic, the canister  might sink
right through  it.  (Movement might  be  slow because of the high viscosity
of the salt.)
    Sinking because of formation of a  brine bubble.  If  the canister  is
enveloped by fluid (through brine  migration,  discussed  in  the previous
section), it  would sink to  the  bottom of the surrounding  bubble.  The
higher temperatures at  the bottom,  where  the  canister  would rest on the
salt, could  lead  to preferential  dissolution  there, and  thus continue
the sinking process.
    Rising caused  by thermal buoyancy  (induced salt diapirism).     The
salt surrounding one or  more  waste canisters or  the  entire  repository
would  be expected to  expand   upon heating.    The  resulting  decreased
density  might  cause this  entire mass  to rise,  carrying  the canisters
with it.
                              196

-------
    A number  of scientists  at different  laboratories  using  different
analytical  and  experimental   tools  have  investigated  possible waste
                   (53 87—92}
migration  in   salt.   '     '   A  substantial  effort  to  characterize
behavior of the  salt  of  the Delaware Basin has been carried out  and  is
continuing  at  Sandia Laboratories.    This effort  includes  laboratory
measurements of salt creep, constitutive modeling of salt  response,  and
the application of numerical  stress  analysis  procedures for  predicting
canister movement.
    Analysis of the steady-state and transient response of  a  single  3-m
long, 30-cm diameter  canister were  performed  using lower  bound  (worst
                           (87)
case) viscosity  estimates.       The predicted  velocities are  in  the
order of  1  cm/1000 years.   The long-term  total movement  predicted  from
convective  cell  movement  is  5-10 meters  per  10   years.   The  Sandia
effort has  also  examined various  canister  and  repository  configurations
and  emplacement  schemes  with a view toward  determining the effects  of
those factors  on both individual  canister  motion  and  repository  motion.
The  studies indicate  that  movement of the salt mass  would not  cause  a
salt dome to form.
    In  the  present study  of  generic  repository designs   and geologic
formations, canister or repository movement is not  modeled  as  a  failure
element since most  recent investigations agree  that  such motions  are  not
a serious concern.   The mechanisms described  are  amenable  to engineering
analysis, based  on  the parameters appropriate to  a specific  situation
(salt viscosity,  temperature  profiles,  etc.).    If  such movement  is
predicted to be a problem  in  a particular  case, the design (e.g.,  shape
or  thermal loading  of  canisters),   can  be modified   or   a  repository
considered elsewhere.

D-3.5.5  Criticalitv
    Concentration  of  certain  radioactive material  can  result  in
self-sustaining nuclear reactions.  This condition of high concentration
is  referred  to as criticality.   To avoid  the  possibility  of  reaching
critical  levels,  waste forms,  concentrations of  fissionable material,
and  canister  spacing can be   planned with  this  factor  in mind.
Criticality calculations  are straightforward  and  well understood.
                                      197

-------
Naturally, allowance must be made  for  the  movement  of canisters and for
the  introduction  of  water,  as discussed in the  previous  sections.   The
concentration  of  fissionable  material  by  chemical  means  (i.e.,  by
dissolving out  of the waste form  matrix and  reconcentrating elsewhere)
is also  a  theoretical  possibility, but  no  reasonable mechanism has been
postulated by which this might occur in a repository.
                                         198

-------
D-4.0  HUMAN INTRUSION

    One  failure  element,  future drilling, is modeled  in  detail in this
chapter,  and  several additional  possible  failure mechanisms  are
discussed.   Some repository risk assessments have avoided quantitative
models  for  future  human  intrusion  events,  but  it  appears  that  this
approach  is  unrealistic.   There are  large uncertainties associated with
the  prediction of  future natural events or technological  failures  as
well, and  to neglect one  important  class  of events may  cause  too much
emphasis  or importance  to be  placed  on  others.   While  the estimates
given here must obviously be speculative, they would appear to be useful
not  only  for  rough estimates  of  repository performance, but  also  to
clarify  the  importance of key assumptions in the assessment process.

D-4.1  FUTURE DRILLING ACTIVITIES

D-4.1.1  _Summar_Y

    Future deep drilling on the repository site could lead to the direct
transport of radioactive material to the surface or to the establishment
of an additional  groundwater  pathway.   Estimates of the possible extent
of such  drilling  depend  on assumptions made  about future knowledge and
control  of  the  repository site.  EPA guidelines  for  this study require
the assumption that after a period of 100 years from repository closure,
control  of  the  site  is  lost  and   it  reverts   to prevailing  land  use
patterns of  the  area  in which  it  is  located.  Based on this assumption,
estimates  were  made of the  frequency  of  future  deep drilling.   Three
modes of  release  were modeled:  transport of  pieces  of canister to the
surface with the  drilling  fluid in  the case  of  a  direct  hit; transport
of fluids,  from  the repository to the  surface  during drilling; and the
establishment of  a  groundwater  pathway  from  the repository to the upper
aquifer  by  means  of  an  imperfectly  plugged  hole.     A  summary  of
assumptions, parameters,  and  calculational  results  is given  in Table
D-79.
                               199

-------
                                                        TABLE O-79

                                        SUMMARY OF FUTURE DRILLING FAILURE ELEMENT
ro
o
o



M50IUM

8^sa|i














Grwh.











Saoil













§S
p P
Si
II
§!?
K
£ 3
P, D














P, O











P, D















MATURE
OF
MOOS!,

Postulated determin-
istic drilling rate.
probabilistic for
hitting canister.











Postulatad determin-
istic drilling raw.
probabilistic for
hitting canister.










Postulated determin-
istic drilling rate.
probabilistic for
hitting canister.













RELEASE
MODE

A. Land surface
B. Groundwater













A. Land surface
B. Groundwater











A. Land surface
B. Groundwater















DRIVING
FORCE

A. Materials raised
with drilling mud.
B. Thermally induced
convection and
gradient from
aquifer inter-
connection.








A. Materials raised
with drilling mud.
B. Thermally induced
convection.










A. Materials raised
with drilling mud.
3. Thermally induced
convection and
gradient from
aquifer inter-
connection










SOURCE
TERM

A. Part of canister
and fluid from
waste drift.
B. Uniform
concentration.










A. Part of canister
and fluid from
waste drift.
B, Uniform
concentration.









A. Part of canister
and fluid from
waste drift.
B. Uniform
concentration.











PARAMETERS

1st ESTIMATE
No holes first century;
5 holes next century:
2 holes each subsequent
century. All holes to
lower aquifer.
Holes seated with
permeability

K = 10-* cm/sec
TJ = 0.2, and
A => 0.1 m2.
Probability of hitting a
canister = 10*3 pef hole.
with expected removal
of 15% contents.
No holes first century;
1 hole next century;
1 hole every four sub-
sequent centuries.
Holes seated with
permeability
K - 10"4 cm/see.
11 - 0.2, and
A - 0.1 m2.
Probability of hitting a
canister - 10"3 per
hole, with expected
removal of 15%
contents.
No holes first century;
3 holes next century;
1 hole each subsequent
century. All holes to
lower aquifer.
Holes sealed with
permeability

K • 10" cm /sec.
n - 0.2. end
A « 0.1 m2.
Probability of hitting a
canisier = 10"3 per hole.
with expected removal
of 15% contents.

2nd ESTIMATE
No holes first century;
50 holes next century;
5 holes each subsequent
century. All holes to
lower aquifer.
Hales sealed with
permeability

K = 10-3 cm/sec.
ij =• 0,2. and
A = 0.1 m2.
Probability of hitting a
canister =• 10*3 per hote.
with expected removal
of 15% contents.
No holes first century;
10 holes next century;
2 holes every subse-
quent century.
Holes sealed with
permeability
K - 10"3 cm/sec.
n - 0.2, and
A - 0.1 m2.
Probability of hitting a
canister - 10""* per
hole, with expected
removal of 15%
contents.
No holes first century;
20 holes next century;
5 holes each subsequent
century. All holes to
lower aquifer.
Holes sealed with
permeability

K =• 10-3 cm/sac.
T) *> 0.2, and
A - 0.1 m2.
Probability of hitting a
canister « 1Q-3 per hole.
with expected removal
of 15% contents.

FLUID TRANSPORTED
TO SURFACE

1st ESTIMATE
0.07 m3 /drill hole














200 m3/drill hole











200 m3/dnll hole














2nd ESTIMATE
1400 m3 /drill hole














5OOO m3 /drill hole











5000 m3/drill hole















COMMENTS


Analysts assumes no
knowledge of reposi-
tory before, during, or
after drilling. Ground-
water releases from
post-sealing leakage are
calculated in the text
but are, in general, less
significant than releases
to the surface.





Analysis assumes no
knowledge of reposi-
tory before, during, or
after drilling. Ground-
water releases from
post-sealing leakage are
calculated in the text
but are, in general, less
significant than releases
to the surface.





Analysis assumes no
knowledge of reposi-
tory before, during, or
after drilling. Groun-
water releases from
post-sealing leakage are
calculated in the text
but are, in general, less
significant than releases
to the surface.





-------
                      TABLE D-79
SUMMARY OF FUTURE DRILLING FAILURE ELEMENT (CONTINUED)


MEDIUM


Shale










Dome Salt









§1
I!

o ™

P.D










P. 0










MATURE
OF
MODEL


Postulated determin-
istic drilling rate.
probabilistic for
hitting canister.







PCM 1 y^J J^
istic drilling rate,
probabiliflic for
Mining canistar.










RELEASE
MODE


A. Lend surface
B. Groundweter









A. Lsndsurface
B. GroundMStar











DRIVING
FORCE


A. Materials raised
with drilling mud.
B. Thermally induced
convection end
gradient from
aquifer intar-
eonnactlon.





A. Msteriels raised
with drilling mud.
B Thermally induced











SOURCE
TERM


A. Part of canister
and fluid from
varo drift.
B. Uniform
concentration.






A. Pan of canistar
and fluid from
1. Uniform
concentration.








PARAMETERS


1st ESTIMATE
No holes first century;
5 holes next century;
2 holes each subsequent
century. All holes to
tower equifer.
permeability
K - 10"4 cm/mac.
1 " 0.2. and
A - 0.1 m2.
Probability of hitting a
canister- 10-3 per hole.
of 15% contents.
No holes first century:
> hates next century:
2 hales every
mosaquent century.
Hoses sealed with
permeability
K - If)"4 em/iec.
i) • 0.2, and
A - 0.1 m2.
'robetaiNty of hitting a
anister- 10-3 par hole.
of 15* contents.


2nd ESTIMATE
No holes first century;
50 holes next century;
5 holes each subsequent
century. All holes to
lower aquifer.
Holes sealed with
permeability
K * 10-3 cm/sec.
il - 0.2, and
A - 0.1 m2.
Probability of hitting a
centner -10-3 per hole.
of 15% contents.
No holes first century;
30 holes next century;
Sholes every
subsequent century.
Holas sealed with
fMrmeBbdity
K - 10-3 cm/sec.

-------
D-4.1.2  Background

    Estimates of  the  likelihood  of future penetration of a repository by
drilling  activities must  be made in  the context  of past  and  present
drilling  rates  as well as the. extent  to which the  rates,  purposes, and
characteristics of  drilling activity vary with time.   These topics are
discussed  in  this  section.    In  addition,  there  are  subsections  on
various  activities  associated  with drilling,  since  these activities may
affect  whether  an  unknown repository  is  detected  before  or  during
drilling.   They  may  also  affect  the  consequences  of  drilling  into  a
repository.
    Past drilling activity.  The  reasons for and  extent  of past drilling
into  potential  repository formations  are  relevant  to  estimating  the
potential  for  future  drilling.    Data  on  historical drilling  activity
were presented  in Section D-3.4  and  will only be summarized  here.   The
scope of drilling activities discussed  in that section includes:
    •  oil and gas exploration and  recovery,
    •  water exploration  and recovery,
    e  geothermal resources evaluation,
    «  brine injection or  disposal  of other  wastes,
    •  mineral exploration,
    «  scientific  investigation,
    •  fluid storage,  and
    •  other special  and  localized  drilling.
The areal densities  that were estimated  for  old boreholes are summarized
in  Table D-80.    They were  determined  on  the  basis  of  the  expected
dominant types of activity in the  past:   oil  and  gas, water,  and  mineral
exploration and/or recovery.
    Present drilling rates.   The  present drilling   rate  appears to  be
well  documented   only  for the  petroleum  industry-    Figure  D-21  shows
numbers  of oil  and  gas holes  drilled by  state (or groups of  states)  in
1976  and 1977.    Of  these, about  37,000 holes drilled in  1977  exceeded
                  (93)
1250 feet (385 m).      This represents  an average rate  of 0.04 hole per
                                     2
year per repository  area,  using  8  km for the  area of the repository and
         r   9
7.8  x 10  km  for  the area of  the 48  contiguous  states.    Since  this
drilling  was  generally  confined  to  potential  oil-  and  gas-bearing

                               202

-------
                                TABLE D-80
          AREAL BOREHOLE DENSITIES FROM PAST DRILLING ACTIVITIES
                                                             *
                                    Holes per Repository Area
                             First Estimate      Second Estimate
Bedded Salt                       0.08                6.0
Granite                           0.003               0.0?
Basalt                            0.05                0.13
Shale                             0.03                6.0
         **
Dome Salt                         2.0                20.0
  These estimates  are  based  on Section D-3.4  of  this report  and  refer to
  holes at  least 300-500 m  deep.   Depending  on  the rock  type,  the areal
  densities  were  given  earlier  for  either   the  buffer  zone around  the
                   2                                              2
  repository  (4 km )  or  the  repository  plus  buffer zone  (12 km ).   The
  numbers in this table have all been normalized to the repository area
  (8 km2).
**
  The holes  in  salt domes tend to  be  concentrated  near  th«  flanks  of the
  dome.   Since  the  repository would  be  in  the interior of  the  dome, the
  average density  of holes  is  a bound  on the  expected  number penetrating
  the repository area itself.  Thus, it is a conservative estimate.
                             203

-------
KJ
O
                                                                            1977 over 381 meters deep
                                                                            11/7 K.isl
                              ^---i   \     «?/
                                                             (----	i
                                               Scale  in  Kilometers  \
                                                  I	H
             Sources-  1977 Joint Association Survey on Drilling Costs, sponsored by:  American Petroleum Institute, Independent Petroleum
                       Association of America, and Mid-Continent Oil and Gas Association, February 1979.
                       1976 Joint Association Survey on Drilling Costs, The American Petroleum Institute , Dec., 1977 Edition.
                               FIGURE D-21   PETROLEUM WELLS DRILLED IN THE CONTIGUOUS 48 STATES, 1976 AND 1977

-------
sedimentary basins, the areal  density  is  far  from uniform and, In fact,
is much higher for such basins.
    Non-uniformity of drilling rates with time.  Tt is important to note
that extreme changes in drilling rates may occur with time.  Reasons for
this include the following:
    •  Scarcity of oil, gas, water, or certain minerals may
       encourage more extensive exploration.
    •  New recovery methods may make deposits attractive that
       were previously partially depleted or not worth
       exploiting at all.
    •  New drilling techniques may make it feasible to exploit
       additional formations.
    •  New resource recognition may initiate entirely distinct
       drilling programs.
    •  Demographic changes may encourage extensive drilling  for water or
       other resources in new  areas.
    •  Other purposes for drilling may assume prominence.
Examples of  these  factors  can be  seen in the evolution of the petroleum
industry.  A little  over  100 years ago there was  no  such industry, and
the  drilling of  more  than  two million  petroleum holes  in the United
                                      (94)
States  over  the  period  of  a  century     was presumably  not foreseen.
Several  thousand  holes  are drilled annually  in  search  for  uranium, and
the  recognition  of  this  resource  is   only about  forty  years  old.
Geothermal energy  is in  its  commercial infancy,  and it is impossible to
predict  to what  extent  this  industry will grow.   Population movement to
the  southwest  has encouraged  deep  drilling  for  water  in recent years,
and  with the gradual depletion  of water  stored  in certain formations,
additional resources will have to be  sought in the  future.   Furthermore,
the development of extensive drilling  programs for  new purposes, such as
monitoring or  control of  tectonic events, waste disposal, or  scientific
research, may well occur-
    Activities prior to drilling.    Tn  assessing  the  possibility  of
future  drilling  through a nuclear  waste repository, it  is relevant to
consider  whether the  repository  might be  detected  prior  to drilling.
The  extent of  such  exploration  depends  on  the  nature  of  the  resource
being  sought.   In  the  case  of petroleum,  which  is  generally  found  in
                               205

-------
specific  structural  traps,   extensive  geologic   and  geophysical
exploration usually precedes  the drilling.  In the  case  of water wells,
drilling  may  start  with  little  or no  geophysical  work,  although  the
types of  geologic  formations  being drilled would be known on a regional
basis.   Geothertnal drilling may be  preceded by detailed  area heat  flow
analyses, although it  is  not yet  clear  what practices will  be followed
when and  if this resource becomes  heavily  exploited  in the future.
    Activities during drilling.    The ways  in which  the  presence  of a
repository  might  be  recognized  during  drilling  are relevant  to   the
consequences  that  could  follow from  such  a  breach.   As  above,   this
depends on  the purpose  for  which the hole is being  drilled.   Activities
associated  with  petroleum well  drilling  are reviewed  in  the  following
paragraphs.
    Drilling  boreholes  involves a continuous  process of  investigation
and examination of the drill progress and  the geology  of  the  rocks being
penetrated.   Typically,  drilling  to  any considerable depth  into
consolidated  rock  involves  the  use  of  rotary  equipment  cooled  and
lubricated with any of a number  of fluids  (muds).   In  the  process, chips
of rock are broken at  the bottom of the hole and carried  to  the  surface
with  the  fluid.    A regular  inspection  of  the  rock  chips  is made to
determine  their  nature  and composition,  as a  guide  for  estimating  the
formation being  drilled.   Thus, the drill  crew  is constantly aware of
the nature of the  rock being penetrated.   A  written  log of rock type, as
determined  from  the cuttings,  is retained,  at least  within  the depth
range of  interest  to the exploration program.
    Other  factors  and  conditions  noted  during  drilling  with  common
rotary equipment are fluid  used, gases  and  other contaminants, drilling
rate, and  depth  of drill  string.   From this  information, a drill  crew
can  interpret   the down-hole  conditions  and  rock  formation  with
occasional  reference  to  the  material  brought  up by  the  drill  and by
correlation with other holes in the vicinity.
    Periodically,  particularly  when some  unusual  formation  is reached,
when  the  drill  stem  has been  pulled  for  some  reason,   or  when it is
suspected  that  a  productive  horizon is  being  penetrated,  the hole is
logged.   This procedure  involves  a number of  processes  and  different
equipments.   Logging  may  simply measure  the diameter  and depth of  the
                            206

-------
hole, or it may entail use of more sophisticated and sensitive equipment
to measure certain rock properties.  Specialized logging  devices  include
electric  resistance  sondes, gamma  radiation logs,  sonic logs,  neutron
logs, and magnetic and temperature sensors.  These assist  in determining
the  rock  type  at  depth,  its   physical  properties,  and  its  economic
potential.  In  some  cases, the  drill mud  and  cuttings are continuously
monitored  by  automatic  equipment to  indicate  to  the drill  crew when
petroleum, radioactive minerals, or  rock with  specific properties (such
as high density) have been reached.
    When circumstances permit and dictate  (when drilling   into competent
rock  with  important properties  or characteristics  such  as distinctive
structure or minerals) a  core of the  rock may  be taken.   This procedure
requires a special drill  bit, typically diamond faced.  The core sample
is  then  examined  and  the  results  recorded.    Important  information
obtained from cores includes not  only rock type, but porosity, strength,
permeability,  structure,  and   mineral   composition.      Some  of  this
information is found through laboratory tests performed on the recovered
cores.
    Much of  the continuous  investigation  during drilling depends upon
the experience  and expectations  of  the  drill crew.   In  locations where
other  boreholes have  penetrated a  considerable depth of unproductive
rock  in  reaching a  readily identified  horizon,  logging and mud checking
may  not  be   as conscientiously applied  as  in situations  where  the
sub-surface geology  is less well  known.   This  on-site subjectivity is
augmented  by  thorough preliminary geologic  and geophysical  surveys of
the area.  Seldom, if  ever,  is  a borehole started without a substantial
commitment of time and energy to determine the suitability of the drill
site.   The occasional  exception is when  limited finances  encourage  a
private landowner to accept the  risk of a blindly drilled  hole for water
or mineral exploration.  However, in such situations,  the  drill crew can
usually  supplement  the lack of  knowledge  with  their  own experience in
drilling other holes within the  same geologic domain.
                             207

-------
D-4.1.3  FutureJ)rilling  Failure Model

    In  accordance  with  EPA.  guidelines  on  assumptions   about  future
institutional  control  of  a  radioactive  waste   repository  site,  the
following have been  assumed  for  purposes of this study:
    0 Institutional  control of  the  site can prevent drilling for 100
      years after  repository  closure.
    • After the  100-year  period  of  institutional control, the site
      returns to the ordinary land  use patterns of the area  in which it
      is located.
It should be emphasized that  these  are model  assumptions, not assertions
about future  events.   Indeed,  one can  easily  imagine  conditions  under
which  one  or  both  of  these  would   be violated.   For   example,  the
increasing scarcity of  energy and perhaps  other resources over the first
100-year  period  could   result  in strong pressures  on the  government  to
permit  exploration  for and  recovery  of  such  resources  on  the  sits.
These resources  might  today be completely unrecognized  or  undiscovered,
or be regarded  as  commercially worthless. The  government might yield  to
such pressures and permit drilling  under controlled conditions.  Because
such a  decision would  be made  in full knowledge of  the  presence  of the
repository, however,  responsibility for any adverse  consequences  would
seem to  rest  with  those  future  decision-makers.   If  such drilling  were
undertaken,  it  is  likely  that  assurances  of its  safety would also  be
required.   Therefore,  conditions  under which  the first  assumption  is
violated have not been  pursued  here.
    The  second  assumption  may  also  not accurately  represent  the  true
situation.  It  is  highly  probable that  knowledge of  the repository will
be preserved beyond  100 years and  that this  will influence  activities  on
the  site  even   if  the  level  of  institutional   control   decreases  or
disappears.  In  the  absence of  institutional  control, however, knowledge
of  the   existence  of  the  repository  may  still  not be  sufficient  to
preclude activities  that  threaten  the  repository's  integrity.
    Obviously,  one  cannot  predict  the   future   or  extrapolate
scientifically  from  past  data  to  estimate  future drilling rates  at a
repository site.   Nevertheless, it is believed that  the probability  is
sufficiently high  of future  deep drilling at  the  site that  the question
                             208

-------
is  not  "whether" but  "how often."  That  is,  a rate of  future  drilling
should  be  a model  parameter  and  various  values  should  be  used  for
sensitivity  analyses.   The purpose of  this  section of the report  is  to
provide  nominal  values for  this  and associated  parameters under  first
and second estimate  assumptions for each of  the five geologic  host  media
being evaluated.
    Estimated future drilling  rates are presented  in Tables D-R1  through
D-85.  The drilling  rates given  in the  tables  are not the  result  of
scientific  or statistical  observation.   They  are  rough  estimates  by
members  of  the  Arthur  D. Little,  Inc.   staff who  have experience  in
resource  exploration and  recovery.  Tn  the case of exploration,  they are
generally  based  on  the  time  interval  over 'which  factors  may change
sufficiently to  justify another exploratory  drill  hole.
    The  drilling rates  are  given in  terms  of holes  per century.    For
exploratory  holes  they might be  spread  out  rather  evenly  in time,  and
for  holes for  petroleum  production  they might  be  closely  grouped  in
time.   The  choice  of  a  single  more  heavily  drilled century  was  the
result of a  two-step process.   First,  it  appears  likely  that  a valuable
resource  on  the  site will be  exploited  over a limited  period of  time.
This  period of  time  could  fall  during  any century  within  the 10,000
years over  which the repository is being  evaluated.  Thus, one  century
is hypothesized  to have a  higher drilling  rate.   The choice of the  first
century after the end  of  institutional  control  as  this period  of  heavier
drilling was based on  several  factors:
    1. Having been withdrawn  from  use for  an entire  century or more,  the
       site  is more  attractive  for exploration  since less is known  about
       it.
    2. The commercial viability of mineral or  energy resources will have
       changed over  that  first  100 years,  so that  the  new availability
       of this site may open  the door to new commercial recovery
       operations.
    3. The thermal anomaly represented by  the  repository  itself  may
       encourage drilling.
Furthermore,  it  is  in  keeping with  the  conservative  approach   of  this
modeling  effort  to  assume  drilling  at  the  earliest  possible  moment,
since  the radioactivity  levels are highest then.   A counterbalancing
                            209

-------
                                  TABLE D-81
                FUTURE  PRILLING RATE ESTIMATES FOR BEDDED SALT
                     First Estimate              Second Estimate
Characteristics  of
Resources  at  Site
  Hydrocarbons
  Water
  Minerals
Essentially none
in  the  entire
sedimentary
sequence.
  Geothermal
Abundant water
at or near
surface.
No minerals at or
below repository
formation ever
expected to become
commercially valuable,
No thermal anomaly.
Present but not of
current commercial
interest, or "depleted"
formations, or unexplored
horizons with hydrocarbon
potential (possibly very
deep).
Limited water available
at or near surface.  Deep
aquifer(s) below reposi-
tory formations even if
not potable.
No commercially
attractive reserves
in present terms.
No thermal anomaly.
Peep Holes Drilled
per Century
  First century
  after institu-
  tional control
  ends .
  Subsequent
  centuries.
                                    50
Bases for Rate
Estimates
Unsuccessful petroleum
or mineral exploration.

       210
One period of commercial
resource exploitation,
followed by occasional
exploration or water
wells.

-------
                                TABLE D-82
                FUTURE DRILLING RATE ESTIMATES FOR GRANITE
                     First Estimate
                            Second Estimate
Characteristics of
Resources at Site
  Hydrocarbons
  Water
  Minerals
  Geothermal
None in or on flanks of
pluton.
Abundant water at or near
surface.  No large
fracture system aquifers
expected at depth .
Fractures generally
closed at depth.
No expectation of signi-
ficantly valuable
mineral deposits, based
on detailed understanding
of regional geology.
No thermal anomaly.
None in or on flanks of
pluton.
Water supplies generally
from fracture systems.
None known at depth.
Limited surface water.
Mineral potential
uncertain.
Higher than average
regional heat flux.
Deep Holes Drilled
per Century
  First century
  after institu-
  tional control
  ends .
  Subsequent
  centuries.
                                   10
0.25 (i.e., one hole
every four centuries)
Bases for Rate
Estimates
Undetermined purpose,
perhaps geothermal
exploration.

        211
Water, geothermal, and
mineral exploration.
Possible geotherraal
wells.

-------
                                 TABLE  D-83
                 FUTURE DRILLING RATE  ESTIMATES FOR BASALT
Characteristics  of
Resources  at Site

  Hydrocarbons
  Water
  Minerals
  Geothermal
Deep Holes Drilled
per Century
                      First  Estimate
Essentially no  petroleum
in any  sedimentary  strata
below basalt  flow.

Abundant water  at or near
surface.
No expectation of signi-
ficantly valuable mineral
deposits, based on de-
tailed understanding of
regional geology.
No thermal anomaly.
                             Second Estimate
Unexplored  horizons with
hydrocarbon  potential,
even  if  not  presently
commercially attractive.
Limited  water at or near
surface.  Deep aquifer(s)
below repository forma-
tion even if not potable.
Mineral  potential
uncertain.
Higher  than average
regional heat flux.
  First century
  after institu-
  tional control
  ends .
  Subsequent
  Centuries
                                      20
Basis for Rate
Estimates
Petroleum or mineral
exploration.
                             212
Commercial exploitation
of petroleum resources,
with hole economy due to
difficulty in drilling
basalt.  Followed by
occasional exploration
and water wells.

-------
                                TABLE 0-R4
                 FUTURE DRILLING RATE ESTIMATES FOR SHALE
                     First Estimate              Second Estimate
Characteristics of
Resources at Site
  Hydrocarbons
  Water
  Minerals
Essentially none in the
entire sedimentary
sequence.
Abundant water at or
near surface.
  Geothermal
No minerals at or below
repository formation
ever expected to become
commercially valuable.
No good indications of
valuable minerals.
No thermal anomaly.
Present but not of
current commercial
interest, or "depleted"
formation, or un-
explored horizons with
hydrocarbon potential
(possibly very deep) .
•Limited water avalable
at or near surface.
Deep aquifer(s) below
repository formations
even if not potable.
No commercially
attractive reserves
in present terms.
No thermal anomaly.
Peep Holes Prilled
per Century
  First century
  after institu-
  tional control
  ends .
  Subsequent
  centuries
                                      50
Basis for Rate
Estimates
Unsuccessful petroleum
or mineral exploration.

          213
One period of commercial
resource exploitation,
followed by occasional
exploration or water
wells.

-------
                                TABLE D-85
                FUTURE DRILLING RATE ESTIMATES FOR DOME SALT
 Characteristics  of
 Resources  at Site
                     First Estimate
                            Second Estimate
   Hydrocarbons
  Water
  Minerals
  Geothermal
No  oil- or gas-bearing
formations in contact
with dome at any depth.
No  oil or gas of
promise in sedimentary
strata below deep under-
lying salt beds.

Abundant water at or
near surface.
No minerals associated
with dome ever expected
to be of commercial
interest.

No resource potential,
even very deep.
Present but  not  of
current commercial
interest, or "depleted"
formations or  reserves
along  flanks of  dome.
Unexplored horizons
below deep underlying
salt beds .
Limited water  at or
near surface.
Deep aquifers  with
significant  potential,
even if not  potable.
Limited dome explora-
tion, or minerals
present but  not
valuable in  current
commercial terms.
Undetermined potential.
Deep Holes Drilled
per Century
  First century
  after institu-
  tional control
  ends .
  Subsequent
  centuries.
                                      30
Basis for Rate
Estimates
Petroleum or mineral
exploration.
                214
Petroleum, water, and
mineral exploration
and/or recovery.

-------
possibility,  that during  the  first  few hundred  years  the  canisters
remain intact and  thus  the wastes are not leached  into the surrounding
repository,  should be  omitted  from the  consequence  analysis of  this
failure element  as long as the  simplifying  assumption  of early maximum
drilling is retained.
    In drawing the distinction between first and second estimates on the
subject of  water resources, a  paradoxical  situation occurs.   From the
point of view of future drilling, it is  indeed  preferable for abundant
water  to  be  available  at the  surface  or  in  aquifers  overlying  the
repository, since  this  eliminates or  decreases  the need  to  drill  deep
for  future  water supplies.   This  distinction between  first  and  second
estimates does  not mean that  from the total  perspective  of repository
evaluation  it   is  better  to  have  a  productive  aquifer  above  the
repository.  The answer  to  this latter question depends on  a  number of
considerations,  centering  on  the nature of  all  the  pathways  that  could
allow  radionuclides  to  enter  the  aquifer   system.   The  literature  of
nuclear  waste  management frequently  exhibits  the  assumption  that
                                                        (95 96}
productive  aquifers  should not  overlie  the  repository,   '    but  the
present authors  are  unaware  of  conclusive  evidence that this Is,  in
general, a  necessary or desirable  criterion.  With  respect  to  water
potability,  prospects  for  efficient  desalination  appear  to  make
potability  an unreliable factor  in evaluating  the  usefulness of aquifer
systems to  future generations.
    Consistent with previous sections of this report, the boreholes here
                                                     2
are  assumed to  have a  cross-sectional  area  of 0.1 tn   at  the  time  they
are sealed, and  they are assumed to  penetrate at least as far down as to
the lower aquifer.  After  use  they are assumed to  be sealed to the same
standards as  assumed  for  the  case  of  presently  undetected  boreholes.
This assumption  entails  hydraulic conductivities of 10~  cm/sec and 10~
cm/sec for  first and  second estimates, respectively, and  a porosity of
0.2.  The holes  are randomly distributed over the repository site.
    Assuming  that  a future drill  hole passes through  the  repository.
there is  some probability  that  it  will  actually  directly hit a  waste
canister.    This  probability depends on the  cross-sectional  area  of the
canister as well as  on  that  of  the drill  bit  and hole.   The assumed
dimensions  are as follows:
                               215

-------
                           Radius                 Area

                                                        ?
    Drill hole             0.1 m                  0.03 m"
                                                        2
    Canister               0.15 m                 0.07 m

Note that the cross-sectional  area of  the  borehole,  when considered as a
                                                7
fluid  pathway,  is somewhat larger (i.e.,  O.I m") than the area  of the
drill  bit  and  initial hole.    This  is  because some  enlargement  may take
place  over  the  period  during which  the  hole  is used  and cleaned  for
sealing. Moreover, the rock immediately  surrounding  the hole may also be
fractured and therefore augment the  fluid  flow.   The dark ring in Figure
D-22  indicates   a  region  where, if  the center  of  the drill  hole  lies
within  it,  the   drill will  intersect part  of the waste canister.   The
area of this region is

                          A =   (0.10 + 0.15)2
                            =  0.2 m2.

                                         2
Since  the area  of  the repository is  8  km , the probability that a drill
will actually hit  one of  the  35,000  canisters is  given by
                               35000 x 0.2
                                 8 x 106
                            -  0.0009
                            =  0.001.
The value p = 0.001 has been  adopted in  this  model.

D-4.1.4  Future  Drilling Release Model

    Drilling into  the repository may  lead  to the release  of  radionuclides
by several mechanisms, the principal ones  being:
    1.  Direct  transport  of  parts of  the  waste  package to the  surface in
        the case of a direct hit.
    2.  Transport  of radionuclide-contaminated water from the  repository to
        the surface.  In  the  case  of repositories in salt  formations, this
        water may  be  encountered under pressure.
                                 216

-------
           Note:  Drill hole intersects canister if and only if its center
                  is within outer circle, which has radius of 25 cm.
FIGURE D-22   REGION WITHIN WHICH CANISTER AND DRILL HOLE OVERLAP
                                217

-------
    3.  Transport with  groundwater  to the upper aquifer  through  the  filled
        but permeable borehole pathway.
The extent of releases via any of these mechanisms depends  on  the degree to
which the drillers recognize the repository and  its  associated  hazards when
they  intercept  it.    If  the  drill bit  passes directly  into a waste drift
backfilled with  densely packed yet porous  and  unconsolidated  material,  an
anomaly will  in  all  likelihood be detected by  any of several  signs, among
them:
     •  rapid downward movement of the drill  stem,
     •  loss of drill fluid,
     •  drill stem wandering and chatter,
     •  down-hole temperature changes caused by  increased cooling of the
        drill by water in repository.  (This  would only be  detected in
        the case of constant thermal monitoring, as  presently practiced
        in some geotherraal exploration work.)
The  unconsolidated  zone  identified by these  anomalies  might  be
interpreted as  an  extensive  shear zone or, if  there is  some  idea of a
repository  in the  area,  it  might be identified  as such.    If  it  is
identified  as part   of  the  repository,   caution  would presumably  be
exercised  in  either  sealing  the hole  or  continuing   to  drill.   For
example, samples of rock and water could be taken, down-hole logging and
geophysical techniques  could be  employed,  and the repository section of
the hole could be grouted or cased to seal it off during subsequent use
of the hole.
    Even  if  the  repository were  not  recognized  as such,  it  is likely
that  the  hole  would be  cased  through  the  backfilled   level  at least
during the active life of the well.   In  case  the drill  passes through a
rock pillar rather  than a mined opening,  recognition of the repository
is much  less  likely.   Pre-existing  fractures  or  fractures  induced  by
drilling could establish  sufficient  interconnection with a nearby drift
to lead to fluid changes or loss of drill mud.
    Despite  the foregoing  discussion,  model  calculations  have  not
assumed  recognition   of  the  repository  by  future  drillers,  although
alternative  assumptions  could  be  used  to modify parameters  in a
sensitivity analysis.  This approach  is based on three considerations:
                            218

-------
    1. Although the mined portion of the repository  occupies  only  25%  of
       the total cross-sectional area, inclusion  of  portions  of  the
       pillars in close proximity to the drifts significantly increases
       this fraction.
    2. The earlier assumption about loss of  control  and  knowledge  of  the
       repository site makes it likely that  the repository would simply
       be interpreted as a zone of incompetent rock.
    3. Ignoring considerations about recognition  leads to a simple and
       conservative model.
Specific  parameter  values  to model  fluid  or  radionuclide  releases are
given in  the following paragraphs.

D-4.1.4.1  Direct Hit

    In  case  a drill  bit hits  a  waste  canister,  some  fraction  of the
canister's contents  will be transported  to  the  surface.   Based on the
geometry  presented in Figure D-22, the expected fraction of the  canister
intersected by a drill  hole  whose  center is  randomly located within the
dark ring is approximately  0.15,  which can  be derived  by  a  lengthy but
elementary geometric analysis.  It  is possible  that the  drillers will
notice  that  they have  hit  a strange  object,  either by examination  of
chips at  the  surface, deflection of the drill  stem, or clogging of the
cutters  on  lead  or  other  materials  that may form  part  of the  waste
package.  However,  this  observation by the drillers is  not assured, and
so  it has not  been assumed  in  the  model.    Consequently,  the drill has
been  assumed   to  pass  right  through  the  portion  of   the  canister   it
intersects, which implies that the fraction  0.15  also corresponds  to the
expected  volumetric  fraction  of  the  canister  that is raised  to  the
surface.

D-4.1.4.2  No Direct Hit — Fluid Released During Drilling

    The  analysis  of  this   situation  depends  on  the  nature  of  the
repository host rock.
    Bedded Salt. As  discussed  in  Appendix  D-II,  water is  expected  to
seep gradually into the backfilled repository through slightly permeable
                           219

-------
shaft and borehole seals.  (There may also be seepage along some natural
pathways, such  as interbeds.)    In  addition, fluid  inclusions  in  the
seemingly intact rock may migrate because  of  thermal  gradients, thereby
increasing the  water content of  the backfill  close  to  the  canisters.
Therefore, whenever  the  repository  is penetrated  by  a drill  hole,  the
accumulated  fluid may  leak out,  taking  with  it any  radionuclides  that
may have leached out  of the waste package.  The  amount  of fluid present
at  any  moment  is  a  function of  time.   There  is  an increase  in  this
amount during resaturation  and  then  a decrease  as salt  creep  tends  to
squeeze  some  of  it  back out.   For  simplicity  of  calculations,  the
maximum  amount,  which  is  the  amount present  just as  the  resaturation
condition is  reached,  has been assumed  to be present  whenever a drill
hole  intersects  the  repository.  This  simplifying assumption  tends  to
overestimate  the level  of  release.    These volumes  are calculated  in
Appendix D-II and are as follows:
                                              3  3
                      First estimate: 1.2 x 10  m
                                              5  3
                     Second estimate: 5.6 x 10  m .
By  means of  the  parameters given in  Table  D-12  (Chapter D-2.0),  the
fluid volume  per  canister  and per waste  drift can be calculated.  While
such volumes  only  represent  averages  and  do  not  account  for
inhomogeneities  in fluid  distribution, they  are  believed  to be adequate
for modeling  purposes.
    The  first estimate for fluid volume released during drilling is
       3
0.07  m  per drill hole.   This  is based  on  the low  porosity  and fluid
availability  in  the  first estimate  case,  because of rapid  salt creep,
and  the  assumption  that  at most  the  fluid associated  with  the  two
nearest  canisters would  leak out.   For  simplicity, this value is also
applied  to  the case where  a drill  hole  does not pass through a waste
drift, but  rather through another backfilled room (other  than a waste
drift) or a pillar.  Possible  fracturing or dissolution during drilling
do  not permit adequate assurance  that a drill hole  through a pillar will
not  communicate  with  a  waste  drift.   The  second estimate  for fluid
                                          3
volume released during drilling  is 1400  m  per drill hole, based on the
total fluid volume of one waste drift.
     Granite.  The fluid  volumes per  canister and per waste drift remain
constant after repository resaturation, with the approximate values
                                     220

-------
    3            3
50 m  and  5000  m  respectively.   The first  estimate for  fluid  volume
released  during  drilling is based on the assumption of backfill material
that is cohesive and  will not easily wash into  the  drill  hole.  In this
case, the integrity of  the backfill is expected to prevent more than
     3
200 m  from  flowing  into  the drill  hole.  (This  is, for  example,  the
quantity  of water  contained  in  a 20-m long section of  the waste drift,
centered  at the  drill hole.)   The second estimate value is based on less
cohesive  backfill, the  possibility that the  hole  is being  drilled  for
water, and the  possibility that  the  drilling crew  pump  the repository
horizon  to test  it as  a  source  of water.   It would not  prove  to  be a
desirable water  supply,   but the  test might  well  empty most  of  the
contents  of one  waste drift,  or 5000 m .
    Basalt.   The  assumptions for  basalt  are identical  to  those  for
                                                           3           3
granite,  resulting in  fluid  flows to the surface of 200  m  and 5000 m
as the first and second estimates, respectively.
    Shale.  The  assumptions for shale are identical  to those for granite
                                                            3
and basalt, resulting in fluid flows to the surface  of 200 m  and
      3
5000 m  as the first  and second estimates, respectively.
    Dome  Salt.  The analysis  for  the  case of dome  salt  is analogous to
that  for bedded  salt,  except   that  the  available  fluid volumes  are
slightly  different.  Total fluid  volumes  for  the resaturated repository
are calculated in Appendix D-II to be:
                                              2   3
                     First estimate: 8.7 x 10  m
                     Second estimate:   5 x 10  m
                                                                      3
The  first  estimate for the  fluid released per drill hole  is  0.04  m ,
based on  the  fluid associated with two canisters.   The second estimate
         3
is 1300  m , based on  the fluid in one waste drift.
D-4.1.4.3  Fluid Flows After Plugging of Borehole

    If the  hole drilled  is  an unsuccessful  exploratory hole,  then  it
would be  expected  to be  plugged  soon  after being  drilled.   If  it  is
suitable for some resource recovery operation, it will probably be cased
where it passes the repository  (interpreted as a horizon of incompetent
or soluble rock).  The casing will prevent  leakage during the production
stage.   After  this  stage,  sealing  will  take place.   In  either  case
                                        221

-------
(initial plugging or plugging  after  production),  there may be subsequent
fluid migration  along  the sealed borehole  up to the  overlying  aquifer.
This  pathway is  analogous  to borehole  pathways discussed  in  Sections
D-3.3 and D-3.4.  First and second estimates  of hydraulic conductivities
have  been  taken  to be  the  same  as  for   present  undetected  boreholes
                           A                —3
(Section D-3.4),  i.e., 10~   cm/sec  and 10~   cm/sec,  respectively.  By
adopting  the  methods  and  results  of  Sections  D-3.3 and  D-3.4,  the
volumetric  flow  rates  shown  in Table  D-86  have  been  obtained.    The
radionuclide  source  term  for risk calculations! based  on  these  flows is
the average  concentration in  the fluid in the  backfilled  repository.

D-4.1.5  Literature Discussion

    Quantitative  estimates  of the  likelihood and consequences of  future
drilling  activity  do  not   seem to  appear  in  other  repository risk
assessments,  although  there  is  the  realization that  this may  be  an
important failure element.
                                     (12)
    The  NRC/Sandia  risk  assessment      does  not  treat  this problem
quantitatively,  although  it does argue  that  the associated  hazards  are
small.   The reason given   is  that  the first   exploratory  hole   would
probably lead to recognition of the  repository  and  reeStablishment of
administrative control.   Local contamination by material  brought  to  the
surface would be  recognized and  decontamination would  be  carried out.
    Claiborne and Gera    argue  that  even if  a future  drilling  crew were
too  unsophisticated  to  detect  radioactive  material  brought  to  the
surface, the resulting contamination would  only be  local  and limited in
consequence.
                          ( 7 fi ^
    The Swedish  KBS study     argues  that  their  proposed  repository is
in  one of   their most common  types  of rock (granite)   and "does  not
contain any  valuable minerals which could  conceivably be considered  for
profitable extraction."  The  depth and low  water  content  also make water
exploration  unlikely.    They also   argue  that  future  drilling   would
probably  be preceded by  exploration work that  would  detect  the
repository.
                             222

-------
                                TABLE D-86
          VOLUMETRIC FLOW RATES THROUGH A SINGLE SEALED BOREHOLE
                                                 Volumetric Flow
                                                     (m3/yr)
Rock Type
Bedded Salt
           (1)
Granite
       (2)
Basalt
      (3)
Shale
     (4)
Dome Salt
         (5)
Time
(yrs)
250
1000
10,000
100
1000
10,000
100
1000
10,000
100
1000
10,000
Firs

2.0
1.7
.6
1.7
1.1
0.5
4.4
3.8
1.6
4.4
3.8
1.6
                                                    Second Estimate
                                                    Not applicable
                                                         189
                                                         167
                                                          17
                                                          11
                                                           5
                                                         198
                                                         192
                                                         170
                                                         198
                                                         192
                                                         170
                                                                  (6)
                                 Negligible at all times
(1)
(2)
(3)
(4)
Based on gradients in Table D-53, Section D-3.3., and corresponding
discussion of dissolution.
Based on Table 0-73, Section D-3.4.
Based on Table D-75, Section D-3.4.
Based on Table D-77, Section D-3.4, dividing by 3 since only
one hole is modeled here.
   Cf. Table D-67, Section D-3.3, and corresponding discussion.
(6)For this case, Period B only begins at 1000 years after closure.  See
   Appendix D-TI.
                             223

-------
D-4.2  OTHER HUMAN INTRUSION  EVENTS  AND PROCESSES

D-4.2.1  Introduction

    The most  common and  widespread  human  activity  that could  affect  a
deep  geologic  repository  is  drilling  for  oil, water,  and  other
resources. This has already been  examined  as  a specific failure element.
It  is  natural  to consider  whether  future human  endeavors  other  than
drilling programs may  add substantially  to the risk of  releases  from  a
repository. Since  future incentives, technologies,  and opportunities to
intrude into a  repository can be only imagined  now,  the discussion must
be  speculative.  It is  believed  that  detailed  modeling of  these  other
phenomena would  not contribute significantly to  the  assessments made in
this generic study.

D-4.2.2  Solution Mining

    Because  of  its  high  solubility,  salt  is  often  extracted  from
underground  formations  by  solution  mining.  In this process,  water,
usually  heated,  is  forced  through  wells  into the   salt.  The  water
dissolves the  salt  and  the solution is pumped  to the surface, where the
salt  is  removed and  the water  reinjected. This  technique can  also be
used  for  certain other  minerals,  such as sulfur.   Solution mining is
applicable  to  both dome  and  bedded  salt  deposits.    Some  abandoned
solution cavities  are used  for  the  storage  of hydrocarbons,  and  other
cavities  have  been developed exclusively for  this  purpose.   It is
possible that in the future  solution cavities will be developed and used
for  additional  purposes,  such  as   the  disposal  of  chemical wastes or
energy storage in the form  of  compressed  air.
    The potential hazard  associated  with  solution mining is apparent. An
extraction  well passing  near or  through  a  repository  would circulate
large volumes  of water  that  could  accelerate leaching and transport of
the  stored  waste. The brine, with  any  waste material dissolved  in it,
would be  brought directly  to the  surface and  distributed  to  any  of  a
number of  users,  such  as  the  food and  chemical  industries.  Although

                              224

-------
quality controls and purity requirements of the consumers may detect the
unusual  radioactive  constituents  before  they  are dispersed,  it  is
questionable whether  such measures  can be  relied  upon.   Furthermore,
when solutioning  is carried out  for the primary purpose  of  creating a
cavity, as  for  example  for hydrocarbon  storage,  little  or no attention
is paid to the composition of the waste brines.
    The  cavity  developed  in  solution  mining  operations   is  typically
"carrot"  shaped  if  a  single  well  is  used  for  water  injection  and
extraction. The usual dimensions of  a  single well  cavity  are  about 15
meters  (diameter)  and 76  meters (height), although diameters twice this
                           (97)
size  have  been  reported.        Paired  well  mining,   where water  is
introduced  through  one well  and brine is extracted from another nearby,
produces tunnels  or lateral  cavities. Wells are  spaced  from  100 to 400
meters  apart  and  are connected by  hydrofracturing the  rock  between.
Tunnel  dimensions  range  from  a few  to perhaps  100  meters in  cross
         (97)
section.      Crude oil storage cavities constructed in salt domes have
diameters of more  than 70 meters and heights of more than 200 meters. If
future  solution mining were  carried out at a repository site, canisters
located  in  the  dissolution  zone could  collect  near the bottom  of the
cavity,  possibly  generating more concentrated heat and radiation. These
effects  would  depend largely  upon  canister  size, spacing,  original
source  term, and  age.
    Solution mining has not  been analyzed as a separate failure element
because  the exploratory  drilling  and  testing  usually  performed before
mining  facilities  are  installed  are  likely to  detect  a  repository.
Furthermore, since  salt is such a common mineral, the likelihood of this
activity at a repository  site appears to  be  extremely low.

D-4.2.3  Interference with Hvdrqlqe;ic Conditions

    Recovery or injection of  fluids in  the  rocks  bounding  the repository
can  alter  hydraulic  conditions,  possibly changing  flow characteristics
and  apparent  rock strength. The risk to a repository from interference
with groundwater  is distinct  from direct drilling risks.
    Active  control of hydraulic  conditions is practiced  in  both  water
and  petroleum production. This  technique is used to increase secondary
                                    225

-------
recovery of  oil,  for example, where  water  or brine  is injected into a
production zone through a nonproductive well. The water,  under  pressure,
displaces  the  petroleum  and  forces  it  toward  production  wells,  as
illustrated by  Figure T)-23.  In a similar manner, recharge wells  in arid
regions provide conduits   for  surface water  to  replenish  depleted
aquifers.
    Changes  in  the  hydraulic  regime  in aquifers bounding  a  repository
are  not,  strictly  speaking,  failure  elements,  but  they  do affect
modeling parameters.  The degree  to which  changes   could  occur  depends
upon several  indeterminate  factors  such  as  amount and  pressure of fluid
injected or  discharged  and  the  duration  of interference.  In  general,
pumping of  aquifers adjacent  to a  repository  would  have  only a local
effect, perhaps to a range of  hundreds of meters. The  effect would be to
change  flow  rates and  direction for  a  brief period  compared with the
total  life of the repository. Since  wells  affecting a repository would
have to be very  near  or directly  over  the  site,  their  probability  of
occurrence  has  already  been  considered   in  Section D-4.1,   and  the
additional risk from changes in flow rates is insignificant.
     Variations  in  rock strength due  to water  content are difficult  to
quantify.  To produce  meaningful estimates,  such factors as pore water
pressure  and  contact   area  between  rock particles  must  be  known.  A
repository  would be  essentially  unaffected,  however,  by  strength
variations in the rock of the overlying  aquifer. Lowering the  strength
of  the aquifer would,  at   worst,   increase  fracturing  in  this rock.
Fractures would  increase  the permeability of the aquifer somewhat, but
would  not   lead  directly to  water  flow to  or  from  the  repository.
Changing rock strength  and  volume  in  the  underlying aquifer by  pumping
would  be preceded by drilling  through the  repository level,  a  failure
which  has already  been examined.  Nevertheless, the  potential  for
inducing fractures between the repository and the underlying aquifer may
exist  for  a  given site and  should  be considered  in the site  selection
process.
                              226

-------
Production

  Well
                                                      Injection

                                                       Well
                                                                      I
                                                                      I
   -.1 I
  •. n
   -1'i
Petroleum
                 Petroleum

                  Stratum
                                            Water
     FIGURE D-23    FLUID INJECTION FOR ENHANCED WELL PRODUCTION
                                  227

-------
D-4.2.4  Waste Recovery

    It  is  possible that radioactive waste  may be considered  a valuable
resource  sometime  in  the  future,  especially   if  the  waste  includes
unreprocessed  spent  reactor  fuel.  Therefore, the  possibility  that  the
waste  may be  sought  for   some  useful  purpose  in  the future  deserves
consideration.
    Since authorized  reentry  of  the repository for  recovery implies both
consent of  the responsible  government  and  substantial understanding of
the  situation,  it  can  be   assumed  that  appropriate  precautions  and
technologies would be employed  in this  case.  This suggests  that  future
sanctioned  entry  would  provide  safeguards  at  least  as  good  as,  and
perhaps better  than,  existing ones.  In any case, responsibility for  any
adverse  consequences  would  seem  to   rest  with  the  future  society.
Unauthorized recovery operations are discussed in  the  next  paragraph.

D-4.2.5  Sabotage

    The  potential for  buried waste  to  be used  as  toxins  or for  the
construction of nuclear explosives raises the  question  of  a repository's
susceptibility  to  sabotage or unauthorized  intrusion.   The  waste  forms
would  preclude any convenient conversion  into nuclear explosives,   and
if the wastes  were used to  contaminate  a water supply,  the  effects  would
become  apparent only  after  a  considerable delay.  Nevertheless,  it is
possible that  the  waste might be perceived  as a  resource by terrorists.
However,  reaching  a  repository would  require  unusual  resources  and
expertise.  Sinking  a mine shaft  would  involve many people,  much
specialized  equipment,  supplies,  energy,  planning,   engineering  and
operating  skills,  and uninterrupted access to  the  site for  periods of
months.  If  the repository  were  finally breached,  removing,  processing,
and using  the  stolen waste would involve planning and engineering on  a
similar  scale.  Also,  unless  the people involved possessed  exceptional
skills, they would be  placing themselves at great  personal  risk from the
waste  they  would be  attempting  to  recover.  Therefore,  unauthorized
recovery of waste material  does  not appear  to be a credible scenario.

                               228

-------
    If the intent were simply  to  pollute  a  water  supply with the waste,
the  saboteurs would still  need  substantial   drilling  equipment,
specialized  workers,   free  access  to  the  site,   and  a  great deal  of
patience,  since  the  effects  of  their  act  would  not  be apparent  for
years, if at all.  Sabotage of visible and accessible objectives, such as
a chemical plant  or a surface  nuclear  facility,  would be more likely.
Less time, material,  skill,  and  organization,  with  far  less  risk to the
saboteurs, would  be required  to  obtain substances with  the  equivalent
potential for terrorism.

D-4.2.6  Acts of War

    Similar to the question of sabotage is the question of damage to the
repository through  some  act  of  war. The  only credible  act  that  could
even fracture the rock down  to  about  500  meters would  be the detonation
                                                     (98)
of at  least  a  ten-megaton or  larger  nuclear  device.       During  a war,
it is  hardly  likely that bombs would be  aimed at a  repository.  Cities
and  strategic installations  are  far more attractive  targets.  In
addition,  the  effects on the biosphere from  a damaged  repository would
be  insignificant  compared with  the  other  damage inflicted  in such  a
conflict.

D-4.2.7  Innocent Extraordinary Penetration

    No buried  repository of   the  sort considered  in this  study has (to
present  society's knowledge)   ever  existed.  However,  a  similarity  can be
drawn  between  a  repository and other hidden  artifacts.  The  possibility
remains  that  curiosity   or   other  motivation could  encourage  future
penetration or exploration of a repository.
    For  example,  archeologists  have excavated under pyramids  and other
traces  of human  activity;  tunnels  for  transportation  are  common  in
mountainous  terrain,   and  subway  tunnels  underlie  many  cities.  The
possibility of treasure is also a strong motivation.  The classic example
is the recurring  effort  to discover whatever may  be at  the  bottom of a
shaft  originally  dug  two or  more  centuries ago on  Oak  Island,  Nova
       (99)
Scotia.       While  nothing   of  great  value  has  ever  been   recovered,

                             229

-------
persistent  attempts during  the  last century  to reopen  the mysterious
shaft have  reached  depths  of  100 meters  or more.
    While a repository  is  not  the equivalent of a treasure trove,  future
generations may  have no knowledge  of its function  and  may be  intrigued
by  signs of  mining and  the  unusual  care with  which  the  openings are
sealed.  There is  no firm basis for  determining  if  a  repository will
become an  attractive site  for explorers  in  the  future.  However,  if it
were  to  be  entered by an astute  investigator,  its  function  and  the
nature of  the canisters should  become apparent.  It is  more than likely
that steps would  then be  taken to return  the  repository to its original
integrity.
                              230

-------
D-5.0  NATURAL EVENT FAILURE ELEMENTS

    A  number  of natural  events  and  processes   are  modeled  In  this
chapter, with additional ones being discussed in lesser detail.  Most of
these are geologic phenomena, although  some  are not, such  as  changes in
climate or the impact of  large  meteorites.   In all cases the  models  are
simple and  only intended  to  enable  very approximate  quantitative
judgments.   For  the  evaluation  of  repositories  at  specific  sites,  it is
possible that quite different models, based on extensive data  gathering,
might  be  appropriate.   Nevertheless,  for  the evaluation  of  the
performance  of  generic  repositories,  it  is believed   that  the  models
developed here are adequate.

D-5.1  FAULT MOVEMENT

D-5.1.1  Summary

    The  repository  site selection  process  is expected  to favor  sites
that  are  relatively  stable geologically   and  where  renewed  or  new
faulting is  unlikely.      Nevertheless, old faults are  common geologic
structures in  almost any  location  and  may  be  expected  at or  near  any
repository site.   They  may only intersect  strata above  or   below  the
repository formation, and some may even  go  undetected  through  the  entire
site  evaluation   process.    This analysis   assumes  the presence  of  a
certain number of faults on  the  site  and,  on the  basis of  their age  and
density, estimates:
    •  the probability of renewed movement  along the old faults,
    •  the probability of the occurrence of new faults.
The model  consists  of a  constant  annual rate based on the age of  the
most  recent   fault  activity.    In  addition,  physical parameters  that
characterize the groundwater flow pathway along the fault are  estimated.
Releases  from  the repository are assumed  to be by groundwater flow to
the  upper  aquifer.    Sufficient  displacement  to   move the entire
repository  into   contact  with  the  aquifer  or to the  surface is  not
considered possible in the  time  frame considered  in this  report (10,000
years).   A  summary  of  the  analysis  is given  in  Table D-S7.   Section
                               231

-------
                TABLE D-87
SUMMARY OF FAULT MOVEMENT FAILURE ELEMENT


MEDIUM



Bedded Salt




Granite



Basalt


Shan



Dome Salt



If
si
3 z
S3 S
< e
i£
£ 0
P




P



P


F



P




OF
MODEL



Annual probability
of occurrence of new
fault or movement
along old fault.

Annual probability
of occurrence of new
fault or mowsjmant
along old fault.


Annual probability
of occurrence of new
fault or movement
along old fault.

Annual probability
of occurrence of new
fault or movement
along old fau.s.

Annual probability
of occurrence of new
fault or movement
along old fault.


RELEASE
MODE



Groundweter




G^ound water



Groundwatar


Grour*d water



Groundwatar




DRIVING
FORCE



Thermally induced
convection effect
added to gradient
from aquifer inter-
connect ton.

Thermally induced
convection.



Thermally induced
convection effect
added to gradient
from aquifer inter-

Thermally induced
convection effect
added to gradient
from aquifer inter-
connection.

Thermal ly induced
convection effect
added to gradient
from aquifer inter-
connection.


SOURCE
TERM



banisters in fault zone
broken and subject to
leaching. Accumu-
lated dissolved radio-
nuclides by time of
faulting assumed
released through fault
from 100-m wide zone
around fault.
Canisters in fault zone
woken and subject to
leaching. Accumu-
lated dissolved radio-
nuclidn by time of
faulting assumed
released through fault
From 100-m wtda zone
around fault.
Canisters in fault zone
broken and subject to
caching. Accumu-
lated dissolved rsdio-
nuclicte by time of
faulting assumed
released through fault
from 100-m wide zone
around fault.
Canisters in fault zone
iroken and subject to
leaching. Accumu-
lated dissolved radio-
nuclides by time of
faulting assumed
released through fault
from 1 00-m wide zone
around fault.
Canisters in fault zone
broken and subject to
leaching. Accumu-
ated dissolved radio-
ituclides by time of
faulting assumed
rvleated through fault
Irom lOO-m wide zone
wound fault.

PARAMETERS


1st ESTIMATE

X - 2,,O^^M
Flow path 1 m wide
000 m long
K - 10~*cmftac
1 " 0.1
100 canisters in fault
zone. 5% repository
in affected surrounding
zone.
X " 2x10~8events/yi
Flow path 1 m wide
4000m long
K - 10'2 cm/sec
u • 0.1
100 canisters in fault
zone. 5% repository
in affected surrounding
zone.
X. - 5 xlO'7 events /yi
Flow path 1 m wide
4000 m long
K => 10"2 cm/sec
17-01
100 canisters in fault
zone. 5% repository
•n affected surrounding
zone.
X - 2x10-8evena/y
Flow path 1 m wide
4000m long
K = 10'4 cm/sec
n . 0 1
100 canisters in fault
zone, 5% repository
in affected surrounding
zone. '
I • 3x10-7evants/yi
Flow path 1 m wide
4000 m long
K - 10-4 cm/sac
n • 0.1
100 canisters in fault
zone. 5% repository
in affected surrounding
zone.


2nd ESTIMATE

X *> 4 x 10~7 events/yi
Flow path 1 m wide
4000m long
K - 10'4 cm/sec
TJ ° 0.1
100 canisters in fault
zone. 5% repository
in affected surrounding
zone.
X *= lO^events/yr
Flow path 1 m wide
4000m long
K = 10"2 cm/sec
T) = 0.1
100 canisters in fault
zone. 5% repository
in affected surrounding
zone.
X = 10"5events/vr
Flow path 1 m wide
4000 m long
n = 0 1
100 canisters in fault
zone. 5% repository
in affected surrounding
zone.
X • 4 x 10'7 events/yr
Flow path 1 m wide
4000m long
K - lO^cmfsec
100 canisters in fault
zone. 5% repository
in affected surrounding
zone.
X - 10'sevents/yr
Flow path 1 m wide
4000 m long
K - 10-* cm/sec
100 canisters in fault
zone. 5% repository
in affected surrounding
zone.
FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER


1st ESTIMATE

tlynl

100
1000
10,000
t(yrs)
100
1000
10X100
0 (t) (m3/yrt

8.2 x 10*
6.9 x 10*
2.5 x 104
6 (t) (m3/yrl
6.9 X 106
4.4 X 106
1.9 x106

tlyrsl
100
1000
10,000
tlynl

100
1000
10,000
tlyrs)

1100
1000
10.000
6 It) Int3/yr)
8.8 x 106
7.6 x 106
3.2 x 106
6 III Im3/yr)

8.8 x 104
7.6 x 104
3.2 X104
6 It) (m3/yrl

8.2 x 104
6.0 x 104
2.S x 104


2nd ESTIMATE

tlyrs!

100
1GGO
10.OX)
tlyrsl
100
1000
10,000
6 (t) (m3/yr)

3.9 x 105
3.8 x 105
3 J x 10S
6 it) (m3/yr)
6.9 x 106
4.4 X 106
15 x 106

tlyrel
100
1000
10.0OO
tl^l

100
1000
10.000
tfyn)

100
1000
10,000
6 (t) Im^yr)
4.0 x 107
3.8 X 107
3.4 x 107
Q (t) (m3/yr|

4.0 x 10
3.8 x 10b
3.4 x 105
6 M (m3/yrl

2.0 x 10°
1.7 x 10S
1.5 xlO5






Fault may seal if flow
rate is tuff iciently small
Flow may be restricted
by availability of

Flow may be restricted
by availability of water.



Flow may be restricted
by availability of water.


Flow may be lesiiimed
by availability of water.



Fault may seal if flow
rate is sufficiently small.
Flow may be restricted
by availability of warn.


-------
D-5.1.2 provides a brief review of background  material  on the occurrence
and detection of faults.   Detailed  explanations of  the model parameters
are given in Sections D-5.1.3 and D-5.1.4.

D-5.1.2  Background

    Definition and examples.  A  fault is a fracture within  the  rocks  of
the earth's  crust  along  which  relative  movement of  the two sides has
taken place.  Faults can range  in  length from less  than  a centimeter  to
hundreds of kilometers.       Very  small faults, on  the order of  tens  of
meters or  less  in  length,  are  not  important  for  the present analysis.
In depth, faults may  intersect  only  a single geologic formation  or  part
thereof, or they may extend  all  the  way from the surface to  deep  in the
basement  rocks.   Cumulative displacement along  faults,  whether in the
horizontal or vertical direction, can range  up to tens of kilometers  or
more, representing the sum of relatively  small  individual movements  over
an  extended  period.   Notable examples  of large  faults  in the United
States include  the  San Andreas fault,  whose  length exceeds  600  km, and
the Lewis overthrust  fault, representing  the  east side of the Rocky
Mountains  in  Montana, with  a cumulative vertical  displacement  of  more
than 12 km.   '  '  Often,  a large  fault is associated with  a multitude
of  smaller  fractures, and  both large  and  small faults  may occur as  a
series of  subparallel  features  reflecting a distinct  trend.        (See
Figure D-24.)  Faults are very common features  in most geologic  settings
and it  is  unlikely that any repository site  can be found  that  will  be
completely free  from past  faulting  activity.    For  example, a detailed
geologic study of the  area  surrounding  the proposed Charlestown nuclear
power plant in Rhode Island  led to the  identification of  one  major fault
and  over  2600  minor  faults   and   joints  within five  miles.
Additional  faults  are  generally expected  to  be  encountered on  plant
                                      (22 102  103)
sites once the  overburden  is removed.    '   '       The  important issue
is whether additional  movement  along faults on  (or  under)  the site  can
be expected and whether new  faults might also develop.
    Nature and types of faults.   Faults  are  the result of differential
compressive stresses in the  crust  that  exceed  the strength  of the  rock
formation.  The geometry of  faults can  be  categorized  into  three  types,

                                   233

-------
(A) Nevada (Basin and Range Province)
(B) Gulf Coast Region
               ."TEXAS
LOUISIANA


                               -'^••'  GULF
                                      of
                                   MEXICO
  Source: Adapted from USGS Map M.F. 916.

  FIGURE D-24   SUBPARALLEL FAULTING IN TERTIARY AND QUATERNARY PERIODS
                                        234

-------
reflecting the stress system giving rise to the fracturing.  (See Figure
D-25).  Normal faults occur  when the  maximum compressive stress, 0 , is
vertical and the minimum compressive  stress, o   is horizontal.  Reverse
and thrust faults (the former steeper than 45°, from the horizontal, the
latter  flatter  than 45   occur   when  the maximum  compressive  stress  is
horizontal and the minimum vertical.   Strike-slip  faults occur when the
maximum and  minimum  compressive stresses are both  horizontal.   Oblique
faults represent a combination of vertical and horizontal movement.
    Evolution of regional stress systems.   Many geologic  processes can
contribute to the development of stress  systems that may cause faulting.
Examples  of  these  processes,   some   of which  are   related,  are  the
following:
    •  Plate  tectonics,   involving  the  movement  of   crustal  sections,
       called plates, toward or away  from each other-
    •  Slowing of  the  earth's  rotation, with corresponding  changes  in
       centrifugal forces.
    •   Earth tides, resulting  from gravitational   interaction  with the
       sun and moon.
    •  Changes in heat flow and  temperature in the earth's crust.
    •   Increases in  overburden stress, caused by sediment  deposition,
       lava  flows, glaciers, rises  in sea level, etc.
    •    Decreases   in  overburden   stress,  caused   by  erosion,  glacial
       melting, retreat of seas, etc.
    •  Volcanic activity, involving movement of magma  through the crust.
    •  Diapirism,  involving  the penetration  of plastically flowing rock
       (such as salt or shale) through overlying rock.
    •  Dissolution,  leading  to   settling or  collapse  into  the resulting
       voids.
    •  Folding and downwarping  associated with the movement of the  crust
       toward  mechanical  equilibrium after some  of  the  processes
       mentioned above may have  caused differential stresses.
The above list is only intended  to  give  some representation of the  range
of  processes with  which  faulting  may  be  associated.   Two important
conclusions  can  be  drawn.   First,  because at a given location many of
the  processes  listed  occur  only  during specific periods  in geologic
history, if  at all, many  (probably most) faults  have  exhibited movement
                               235

-------
        (a)   Normal (Gravity) Fault
       (b)   Reverse or Thrust Fault
       (c)   Strike-Slip Fault
Note:   (o^ = maximum stress, a2 = intermediate stress, o3 = minimum stress)
                          FIGURE  D-25 BASIC FAULT TYPES
                                       236

-------
only  during  particular  periods and  have not  been  reactivated  during
later periods with different stress regimes.      Second, an analysis of
the geologic evolution of a region and the corresponding regional stress
patterns  is  important  in predicting  future  faulting  or fault movement.
It should be pointed out, nevertheless,  that faults do represent a zone
of weakness, and  therefore  reactivation  is occasionally experienced and
even reverse movement has been  noted.
    Movement along faults.  Movement  along existing faults  depends on a
number of  factors  besides  the  relative  levels  of  stress.   Among these
are the lithology, the fluid  pressures within the fault, and the nature
and quantity of  material,  such as rock  dust, that may  fill  the fault.
Movement may take  the  form  of  a continual slippage (creep)  or recurring
abrupt  jerks (stick-slip).    '       Creep  may  pass  unnoticed  unless
detected  by measuring  cumulative  displacement, whereas stick-slip
movements are often  accompanied by  sensible  seismicity.  Depending upon
types  of  faults,  lithology,  confining  pressure,  temperature,  rate  of
movement, and other  factors, the rock bounding a  fault may be fractured,
polished  (slickensides),  folded (drag folds), or essentially unchanged.
These features are represented  in Figure D-26.  The rate of displacement
over  time can  vary  considerably.    The  San Andreas  fault has  shown
occasional displacement  of up to  five   centimeters  per year  although
maximum  rates  of  one or  two  centimeters per  year  are probably  more
common•
    Ages of faults.  Two at»es  that are important  in studying a fault are
the time when the  fault  began  and  the time of its  most  recent movement.
In many cases, these may be estimated on  the basis of  stratigraphy, as
sketched in Figure D-27.  Since the fault shown there does not intersect
bed C, it must have begun sometime since  the  deposition  of  that bed.  On
the other hand,  since it does not intersect bed A,  it is highly unlikely
that  it has  moved  more  recently than  the period when  A was deposited.
(In  rare  circumstances  it  could have  moved below A  without actually
moving A, although generally  some manifestation  of such movement, e.g.,
deformation,  would  be  found   in  A.)    Faults   may  also  be  dated  by
associating them with a  specific geologic  process whose  age  is  otherwise
well determined.   For  example,  the  salt  domes of the Gulf  region caused
extensive faulting and  fracturing  as they pushed through the  overlying

                              237

-------
(a)   Drag Folds
 (b)  Gouge, Breccia, Slickensides, and Subsidary Faults
                                         V
 (c)   Parallel Shear Zone
            FIGURE D-26   FEATURES ASSOCIATED WITH FAULTING
                                     238

-------
                                 /
                                Fault
                                 239
                                                                     Surface

                                                          -•'" '"' •'£  Marker bed A

                                                              iiSi  Marker bed B
                                                                  Marker bed C
                                                                Bedrock
FIGURE D-27   DATING OF

-------
rock.   (See  Figure D-28.)   Similarly,  both  the development and the upper
surface  dissolution of  the salt  anticlines  in  the  Paradox  Basin have
caused  most  of the faulting  that  has  been  observed  there.   (See Figure
D-29.)   Other  faults  in  the  Gulf region  were  caused  by  slippage  and
settling  of  new  sediments  as  the shoreline migrated southward.   Thus,
these  faults parallel the  shoreline  and  decrease in  age as  one  moves
southward.   (See Figure D-30.)  There  are also  radiochemical, magnetic,
and mineralogical techniques for  studying  faults with a view to learning
about the history of their movement.
    The  age  and  nature  of  the most  recent  movement  are generally  the
most  important data in  determining  whether  additional  movement can be
expected.    Active  faults   are  those  that   have experienced  relatively
recent  movement  by  geologic standards  (with the period of  10,000  years
often chosen as  the  criterion)  and that  may be expected  to show future
movements.   Young faults  include those  whose  most  recent  movement is
within  the Quaternary  Period (extending  back about L.8 million  years).
The  dating   of  faults and  the  determination  of  their  capability  for
further movement  are difficult  problems with  significant  uncertainties.
There  is no  universal  agreement  among  earth  scientists  on  criteria
defining  a fault  that  is capable of further  movement; moreover,  paucity
of  geologic   data leaves  considerable  uncertainty  about  the  age  and
extent of previous fault movement.
    Identification of faults.  Some faults,  particularly young ones,  are
easy to recognize by surface observation because their displacements  are
manifested in  escarpments or other offsets  that  have  neither been eroded
away  nor  covered by  later  sedimentary deposits.    Because faults may
either be particularly permeable or act  as  a barrier  to  groundwater flow
along  permeable strata  (by offsetting   them),  changes  in  surface
vegetation in  linear patterns  often  indicate  the possible presence of a
fault.  These  and other  linear  features (lineaments) visible on  aerial
photographs  are   frequently  used   to  detect  faults.    Surface  geodetic
surveys  may   indicate  changes  over  time  that  imply  ground   movement,
possibly along faults.  The angles and  depths of marker  beds as  observed
at outcrops  or in a series of boreholes may  also  indicate  whether  some
offset has taken place.   Trenches can be dug  across areas  of  interest
                                240

-------
                                  «OUNO SORfACE

                                                                 SANDSTONE •   " - -*





FIGURE D-28   FAULTING IN THE VICINITY OF A SALT DOME (Conceptual Drawing)

-------
                            Kilometers
Source: Stockton ,S.L. and A.M. Balch.The Utility of Petroleum Seismic Exploration
       Data in Delineating Structural Features Within Salt Anticlines. USGS Open
       File Report 78-591,1978.
FIGURE D-29 TYPICAL PARADOX BASIN SALT ANTICLINE STRUCTURE
              DERIVED FROM SEISMIC AND OTHER DATA
                               242

-------
NJ
                                                                                                 Circum—Gulf
                                                                              T     Older than late Cenozoic (>15 million years)




                                                                              TT    Late Cenozoic (last 15 million years)




                                                                             TTT   Quaternary (last 1.8 million years)






                                                                             T t/   Late Quaternary (last 500,000 years)
            Source: Adapted from USGS Map M.F. 916.
                                                       FIGURE D-30   AGE OF FAULTS IN THE GULF COASTAL REGION

-------
and  be examined  carefully for  signs of  displacement.   Natural stream
cuts may  serve  a  similar  purpose.
     Geophysical  techniques such as  seismic,  electrical  resistance,  or
magnetic  surveys  can  also be  used  to  detect deep  faults  that  do not
appear  at the  surface.  For  example, seismic profiles  can be developed
from recordings of mechanical  shock waves propagated through the rock to
an  array  of receivers  (geophones)   as  diagrammed  in  Figure D-31.   The
timing  and  amplitude  of waves reaching  the geophones  can be interpreted
in  terms  of the  depth and  orientation  of  reflective  surfaces  in the
rock.   If,  instead of measuring  the  reflected  signal,  the refracted  wave
is  examined,  faults  may also  be identified,  usually by the attenuation
of  energy  across  the  fault  face,   as  shown  in  Figure D-32.   Whatever
techniques  are  used,  the  scale  of   the  features  to be  detected  depends
basically  on the wave  length  of   the  seismic  wave.    This  is  itself
determined  by  the energy loss  through  the  rock,  with   shorter  wave
lengths having  a  greater  energy loss   than  longer ones.   The possible
resolution  is   approximately  one-half  the wavelength  or,  in  practical
                                   (22)
terms,  in  the range of  ten meters.       Thus,  a vertical displacement  of
roughly ten meters is  required  before   a  fault  can be  distinguished  by
seismic  surveys.    An  interpreted   seismic profile is  shown  in  Figure
D-33.
    Electrical  resistance  surveys  measure the conductivity of  rock  or
soil and  compare  the measurements with models of  the  expected results.
Irregularities  between the measured and  expected  electrical resistance
may  indicate  the presence  of  a  fault  or  other structural  feature.
Electrical  resistance  mapping  of   a potential  repository site would
probably  use measurements  taken  through an array  of boreholes across the
site.   By determining  the resistance  of representative strata  or  rock
types  at  differing orientations, detecting and determining the position
of  structural  faults  is made easier-   Unfortunately, electrical
resistance  surveys  are  complicated by  a  number  of   factors.    Since
resistance  surveys  measure deviation from a  model, the accuracy of the
survey  is  limited by the  precision  of   the model.  Results tend  to  have
several possible  interpretations and are usually  simplifications of  real
conditions.  Features  must  also have   electrical  properties  different
enough  from the intact rock  that  the  contrast can be  measured.   Large
                              244

-------
Source
                                               Geophones-
                                              No reflection
                                              received from
                                              marker bed
                                                            Longer signal time
                                                            due to offset of
                                                            marker bed
                                                       Reflecting marker bed
                      Fault offsetting
                      marker bed
       FIGURE D-31   DETECTION OF FEATURES BY SEISMIC REFLECTION
                                     245

-------
Source
                      Refracted
                      signals
                                                                                /




                                                                              Marker
                                                                   .->:•//..** V-'.?.-".Vf.tv,v
                                                                   ..-. '/.:•:•:: ,.::•:. .V.'.:
                                                           Refracted signals
                                                           attenuated due to
                                                           discontinuity in bed
         FIGURE  D-32    DETECTION OF FAULT BY ATTENUATION OF REFRACTED
                         SIGNALS ACROSS DISCONTINUITY
                                          246

-------
(a)  Uninterpreted
    30—~~ .."""• •• iiss:."";;"^;^;^ '.%*."

 (b)  Interpreted to Show Structure





         SW
NE
    20

                                    1     !    I
                                                    KILOMETERS
       Source: USGS Open File Report 78-591.




       FIGURE  D-33  PROCESSED SEISMIC RECORD OF SECTION OF PARADOX BASIN
                                        247

-------
shallow  features  generally  show  more  contrast  than  small  or deep
features, and  normal  variation in  the  rock's  electrical resistance may
                                                    (22)
obscure the electrical vibration caused by a fault.
    Lastly, since most earthquakes  are  generally  thought  to  be caused by
movements along  faults,  a  record  of  the seismicity  of  a region can be
helpful in  understanding the  potential  for  active faults.   In
particular, the  foci of  earthquakes  tend  to  lie  along  linear trends,
which  can  then be  studied  further for the identification  of  specific
faults.
    New faults.   While  faults  are among  the  most  common  structural
features in geology,  few (if  any)  new  faults  have been reported in the
literature.  Most  apparent  new faults  have turned  out to be  extensions
of old or unmapped faults.  Nonetheless, locations with a propensity for
faulting may  be  suggested   by  identifying  other  characteristics
indicative of  the  stress  differential  necessary  for  faulting.    For
example,  in-situ  stress  measurements  can  be  made  to determine  the
direction and  intensity  of  lithic stress at a  particular location.  If
the  stresses  approach  the  fracture strength  of  rock,   or  if  stresses
increase in  time,  faulting is possible.        Alternatively,  folding,
which  is  indicative of stress  change  (see Figure  D-34), also  suggests
that  faulting,  particularly  parallel   to  the  fold axis,  is  possible.
Other geologic indicators,  such  as  block  tilting  or warping of  a basin,
suggest  that   stress  intensification  may  be  occurring.   Conversely,
locations showing  little tectonism in  the  recent  geologic  past may  be
expected to have a  reduced  likelihood of  future faulting because of the
time delay involved before  sufficient stress for  faulting could  build.
    Availability and reliability of information.   The mapping  of faults
has  considerable  importance.   For  example,  faults  may  form traps that
contain petroleum,  or  they  may pose  safety  risks  to  industrial
facilities such as nuclear  power plants.  The U.S.  Geological  Survey has
published geologic maps of  all  portions of  the country and  continues  to
update  them  as  new information  becomes available.   A  national map  of
young  faults was  published  in  1978,  based on  1975 data.       As this
reference points out, the availability of data is very uneven  across the
country.  For  example,  far  fewer recent  searches for young faults have
been made in the mid-continent than in California.   Even  where  extensive
                               248

-------
                                                          /Present surface
"Tensional"
normal faulting
(Undifferentiated
   sediments)
                            Compressional"
                           thrust faulting
                                                                 "Tensional"
                                                                 normal faulting
                                "Tensional"
                                normal faulting
   FIGURE D-34     FAULTING ASSOCIATED WITH FOLDING AND Tl LTING
                                 249

-------
surveys have been made, considerable uncertainty often remains.  Much of
the variability depends both on the  intensity  of  exploration and on the
field workers'  interpretations  of what constitutes  a "mappable fault."
Usually, only faults  that  can be discerned  at the  surface  are mapped,
and these only  if  they show significant displacement.   Furthermore, as
most faults  caused  by a particular  stress regime  are roughly parallel,
they are  occasionally identified  as a  single  large  fault,  rather than
many individual  ones.  Therefore,  the  actual  number  of faults  may be
significantly higher  than  the  number  mapped.    As a  supplement  to the
geologic maps  published by  the USGS,   this  report  has  drawn  upon the
safety  analysis  reports for  proposed nuclear power plants,  wherein more
detailed  evaluations   of  fault  capabilities  in   particular   areas  are
reported.

D-5.1.3  Fault Movement Failure Model

    The  quantitative   characterization  of  the  fault movement  failure
element consists of three parts:
    •   the probability of renewed movement along any old faults that may
       be present at  the repository site;
    •   the probability of the development of new faults at the site; and
    •   physical  parameters to describe  the groundwater flow pathway
        resulting from fault movement.
The general  method  used for estimating  the probabilities is the same for
all geologic settings  and   is  described  in  the  next paragraph.   Its
application  to   specific settings will  then be  discussed  in  subsequent
paragraphs.
    Renewed  movement  along old  faults.  Suppose  an old fault  is present
at  the  site  and  that  its most recent movement  has  been reliably dated at
about N years before  the present.   The  model uses the reciprocal  1/N as
an  estimate of  the  annual  probability of   renewed  movement  along  that
fault.   The  rationale for  this approach  is  as follows.  Movement  along
faults  may  be   regarded  as  a  stochastic  process,   with  the  intervals
between movements  analogous to the  time  between failures of  mechanical
components  in classical reliability theory.        The simplest model for
                                   250

-------
such a stochastic  process  is based upon  a  constant  annual failure rate
X, approximately representing the probability of failure between times t
and t + 1 given that  the  component  has  not  failed  (fault has not moved)
by time  t.    According  to  this model,  X  is the reciprocal  of  the mean
time to failure.  That  is, if a type of component is known to fail after
an average  duration of n, then X = i/n  ±s  the  value of the parameter X
consistent with this  observation.
    Applying  this  analogy  to the fault  case,  suppose  it  is  known that
over  the  history  of  the  fault,  times  of  n ,  n  .  .  .  . ,  n,  elapsed
                                             1   £.            K.
between movements.  One should also  add  to  this  list the period  N since
the  last movement.    Since  fault  movement  has  not  yet  recurred,  N
underestimates  the  true value of the  time  to the next movement,  which
may  even  be  infinite  (i.e.,  no  new movement  ever  occurs).    If  the
process   were  truly  stationary   in  time   (i.e.,   having   failure
probabilities dependent only on the  time elapsed  since the  last  event
rather  than  depending  also  on  historical  time)  then  a  reasonable
estimate of  the mean  time to failure would be the average of the  numbers
n, , n2» . .  .,  n, ,  N.  (It  would  be biased on  the  low side  because of
the  bias  involved  in  using N,  as  mentioned   above.   This would  be
consistent with the conservative  approach adopted  in  this  study.)   The
corresponding failure rate would then be the reciprocal of this  average.
However, as mentioned in the previous section, movement along a fault is
strongly affected by  the long-term evolution of regional stress  patterns
associated with slow  geologic processes.  Because  of these changes with
time,  in  estimating  the mean  time  to failure  one might wish to  use a
weighted  average  of  n, , n-,  •  •  -,  n,, N,  weighting  the more recent
observations more heavily.   In  the  cases  to be  considered below, N,  the
time since the  most recent movement,  is  generally  sufficiently  great in
geological terms (tens  or hundreds  of millions  of  years) that in itself
it  covers  the  entire  period  of   site  history  relevant  to  whether
additional  fault  movement  will occur.   Thus,  the appropriate  weighted
average of  n,, n2»...nK,  N  assigns  all  the  weight  to N,  implying a
failure rate  X  =•  1/N.  This  implies  that N is  the  only observed value
needed to estimate  the  failure rate from renewed fault movement.
    It  is  not uncommon  for  geologists  to   assign, implicitly  or
explicitly,  a  zero  probability  for  renewed movement  in the near future
                            251

-------
to  certain  old faults  that  are well  dated and understood.        Thus,
the estimation  of  a  small  positive probability by the above algorithm is
believed  to  be  consistent  with  present  practice  and  somewhat
conservative.   It  should be  noted that this discussion  further assumes
that  the geology  of a  site  is well  understood  and  that new evolving
processes  that  could  lead  to  renewed  fault  movement  will  not  be
significant  over  the 10,000-year  period  of repository evaluation.   (On
the other  hand, it  is  also  possible  that  in  specific  cases,  regional
site  investigations  may lead to higher fault movement estimates,  based
on a detailed understanding of  the geologic  processes  at  work.)
    New  faults.   A  region containing  a potential  repository site may
have  had several  episodes  of  faulting in  its  geologic  history.   For
example,  there might  be  contemporaneous  faulting  during a  period  of
sedimentation,  followed  by tilting  and block  faulting  associated  with
tectonic  forces.    In  attempting   to  estimate  the  probability  of new
faulting  in  the  region,  it  is reasonable  to  consider   only  the  most
recent  episode  of  faulting,  because  previous processes  are   even  less
related  to the present state  of the  region.   If  this  most recent  episode
of  faulting  and  fault  movement spanned  the  period  from M  to N  years
before  the  present and  if  a fault  density of f  faults  per  repository
area  (or some  other measure  of density)  is observed, then the  average
rate  of  new  faulting over the  last M years  is  given by  f/M faults per
year  per  repository area.     In  a  location  with   a  long history  of
stability  since the  last  faulting  episode, and  where  no new geologic
processes  offer  countervailing  evidence,  this  average  rate  can  be
interpreted  as  a conservative  estimate of  the  rate  governing the  more
recent past  and the  near  future.   In fact,  M  is often  more difficult  to
determine than N,  the latter  being  of  greater  concern in any  case; and
since  N is  less  than  M,  the  larger  rate, f/N,  has  been adopted for
modeling purposes.   As  was mentioned  for  the  case  of renewed  movement
along old faults,  in  site-specific circumstances  there may be  reason  to
estimate a different rate.
    Combined estimate for reactivated and new faults.     Suppose  it  is
observed that  as  a  result  of the  most  recent  episode of faulting  in a
given region (excluding minor surficial  faulting),  faults occur with a
density  of  about  f  per  repository  area.   Assume  further that  the most
                               252

-------
recent movement is dated at about N years before  the  present.   Then the
previous two  subsections  each lead to  occurrence rates of  f/N,  in the
first case  for old  fault  movement and  in  the second  for  new  faults.
(The  second  calculation is probably more conservative  than  the  first.)
Then the combined rate of occurrence of either type of fault movement is
given by :
                                    N
With  respect  to  the  estimation of  the  parameter  f,  there  are
insufficient  reliable data  on which  to base  a  statistical  analysis.
Some  evidence  for  appropriate values  of  f  can  be obtained  from  the
following :
    •  Examination of fault densities from surface surveys at various
       locations.  Examples are shown in Table D-88.
    •  Fault maps prepared in  connection with a number of power plant
       applications .
    •  Seismic  surveys for parts of the Delaware Basin.
    •  Reported  spacings of  faults  along anticlines  in the  Columbia
       Plateau.
On  the  basis of  these  data,  it appears  that  for most  locations it is
very  unlikely   to  find  faults  spaced  less  than   about   one   to  two
kilometers  (10  to  15 kilometers   is  more common) .    Hence  the first
estimate  f =  2  faults  per repository  and the  second  estimate  f  = 5
faults  per  repository have  been   adopted  for  all  geologic settings.
Therefore,  the  sections on the specific geologies  simply associate dates
with  these periods  of faulting  so as  to calculate  values  of  A,  the
faulting  failure  rate.
    Flow  pathway.   The reference repository has dimensions 2 km  x 4 km.
It  is assumed for the sake of  conservatism that a  fault intersecting the
repository  cuts  through parallel to the long side, so  that  the length of
the intersection is 4000 m.   The  width of the fault zone  is  assumed to
be  one meter.   The widths of fractured  zones associated with faults vary
widely.   Many  are very  small (a  few  centimeters) although some  extend
100 meters  or   more.         In light  of  the  assumption  of relative
                                  253

-------
                                 TABLE D-88
          FAULT DENSITIES FOR SELECTED AREAS OF THE UNITED STATES
                                            Density
                                           (per km )
         Montana
         San Juan, Utah
         Central Oregon
         Nevada Test Site
         Karnes, Texas
         Sweetwater, Wyoming
         Coconino, Arizona
         North Michigan
         Western Massachusetts
         Eastern Kentucky
         Bonneville, Idaho
         Eastern Pennsylvania

Source:   Geotechnical Engineers,  Inc.
0.0236
0.2807
0.154
0.058
0.0567
0.0998
0.1737
0.1993
0.0871
0.0031
0.820
0.370
                             254

-------
geologic stability  and  careful'selection of a repository site,  for  both
first  and   second  estimates  a width  of  one  meter  is believed  to  be
adequate to model  all fault  movements  that could reasonably occur  over
the  next  10,000 years.   Larger  zones are  in  fact generally associated
with  growth during extended  periods  of activity.   The porosity of  the
fault  zone  has  been assumed  to be 0.1.   This parameter is used  only for
velocity calculations  and even with this relatively high value  (tending
to  underestimate velocities). transit  times to  the  aquifer system  are
quite  short.   The  only rock-specific  parameter in  the model  is  the
permeability of the fault.   This  depends on the  strength of  the  rock and
will be discussed below  for  the various cases.

D-5.1.3.1   Bedded Salt

     The first  estimate for bedded  salt  assumes  most  recent faulting  to
be  of  Permian  age, and  hence at  least 230 million years  old.   This  is
generally  a valid  assumption  for the Delaware  Basin,  for  example,
and  there  is evidence that  in much of  the Salina Basin the most recent
faulting is even of Pennsylvanian age (280 million years old).     '
                            g
The  assumption  N =  2.3 x 10   years  yields  the value
               A - — -	 -  2 x 10~  events/year.
                    N   2.3 x 108
The  second estimate  is  based on  mid-Tertiary faulting  in the Paradox
Basin, corresponding  to  N = 2.5 x 10  years.  The corresponding failure
rate is
                         4 x 10   events/year.
There  has been  more  recent faulting  in some  evaporlte basins.   For
example,  faulting  associated with  salt dissolution in the Paradox Basin
may be  of Quaternary age  (1  million  years old); however, the faults do
not appear to cut  through  the salt beds.     '    '      There  is probably
significant Cretaceous  faulting (63 million years  old)  in parts of the
Salina  Basin,  and  there  is  an active  fault suspected  to  have moved
                               255

-------
within 100,000  years  in western  New  York.        Therefore,  the second
estimate used  for  the calculation  of X is  not  a "worst  case,"  but is
intended to represent a general  type  of area being seriously considered
for repository siting.
    The permeability of the fractured  zone  associated  with a fault in a
salt repository  could vary  widely.    In  fact,  it  is  highly possible for
the salt  simply to  deform  to  relieve the  stresses  that  would  induce
fracturing in adjoining strata,  rather  than  for  the  salt to fracture at
all.   Since  salt is  rather  weak, any  fracturing  would be  expected  to
lead to fairly well crushed  salt.  The permeability of compacted crushed
salt has been  estimated  at  about 10    cm/sec,      which  is  the value
adopted  here   for  both  first  and   second  estimates.    Crushed  shale
actually may  have  a  lower  permeability (depending  upon the degree  of
crushing), but  for  conservatism the entire  fault  pathway,  even through
the overlying  and  underlying  shale  beds,  has  been assumed to  have the
same permeability as the pathway through the salt.

D-5.1.3.2  Granite

    The  first  estimate  for  granite  is  based  on  the  assumption of  an
ancient,  stable batholith  or other pluton.    Some  faulting would
generally be  expected  since emplacement or  metamorphosis.   In western
Massachusetts, Triassic  faulting was the most recent  faulting identified
in  the  geologic exploration  associated with  the  Montague Power Plant
application.          Adopting  this   age,   IRQ  million  years,   the
corresponding failure rate is:
                                   — 8
                             2 x 10   events/year.
The second  estimate is  based  on a  more active  site in  the  basin and
range  province.    Assuming  that  site  selection  avoids  areas  with
Quaternary  faulting ("young faults"),  the  age  would be at  least one
million years, giving
                         X =  10   events/year.
                               256

-------
Less stringent site selection  or  inaccurate site characterization could
lead to a still higher rate.
    The permeability  of  the fractured  zone is based  on the assumption
that the granite  is brecciated and fractured  more  than pulverized, due
                                                         _2
in  part  to  its high  strength.  It  is believed  that 10    cm/sec  is a
reasonable estimate  for  this  permeability,  although a large  range is
possible.  This value of  permeability corresponds to the high range for
silty  sand   and  gravel  (Figure D-13;  see  Section  D-3.2)  and  to the
parallel plate model of ten parallel  smooth fractures per meter, each of
aperture 0.5 mm.(47'50)

D-5.1.3.3  Basalt

    The  first  estimate  for  basalt  is based upon relatively  stable  areas
of  the  Columbia  Plateau, where  at  least  the  uppermost  basalt layers
 (dated  at eight million years) show large areas  free of faults.  It is
possible  that the most  recent faulting  is still  older than this, but
because  of active  tectonic  forces in  the  general region it is  believed
that eight million years  is a  reasonable age  to  assume.  This age yields
the value:

                       ^  *  5  x 10~   events/year.

 There  are certainly areas of more  recent faulting within this
area.       For example,  a scarp  in  the  Horse  Haven uplift indicates
                     (31)
 Quaternary movement.       The second  estimate is based on  a site  in an
 area where the most  recent  faulting  is at  least  earlier than Quaternary
 age (one million years),  yielding  the value

                         *  =   10~   events/year.

    For  the  same  reasons as in the case of granite, the permeability is
                _2
assumed  to be 10   cm/sec through  the fault zone.
                                        257

-------
D-5.1.3.4  Shale
    The  first  and second  estimates for  shale are  based upon  the same
geologic assumptions as for bedded  salt,  and therefore the failure rates
are
                           —8
                X =  2 x 10    events/year (first  estimate)
                X =  4 x 10    events/year (second  estimate).

    A permeability  of  10    cm/sec  has  been  assumed,  based on  the high
range  of  the  permeability  of  compacted  crushed  shale evaluated  for
,   ..... (112)
backfill.
D-5.1.3.5  Dome Salt
    The  first  estimate  for  dome  salt  is  based  on  contemporaneous
faulting  in  the  Gulf  Interior  region,  where  faulting continued  even
after  the  domes  stablized.       The  youngest faults  identified  in one
detailed site evaluation       were  dated at 13 million years.   This age
yields the value
                       X =  3 x  10    events/year.
As one  moves  down to the  Gulf  Coast, more recent  sedimentation  has  led
to  contemporaneous faulting  even in  the Quaternary  period.   Assuming
that  the  site selection rules  out areas  with Quaternary  faulting,  the
minimum age of one million years  to  the  last  movement  implies the value

                       X =   10    events/year,

which is taken as  the second  estimate  value.
    The permeability of  a  fault through a salt dome  repository has been
           -4
taken as 10   cm/sec, as in  the  case  of  bedded salt.
                               258

-------
D-5.1.4  Fault Movement Release Model

    The purpose  of  this  section is  to  calculate  fluid  flows through an
assumed ruptured fault.  Parameters  to characterize the physical pathway
have been  estimated  in the previous section.   A  number of conservative
assumptions (i.e., tending to overestimate flow rates) have been made in
the analysis so  that the net  effect  may be to overestimate flows by one
or  more  orders  of  magnitude.    For   example,  the  capability of  the
associated aquifers  to produce  or  receive the estimated fluid flows may
be highly  restricted.  Faults may heal either by the plastic deformation
of the  surrounding rock  or by the accumulation of  fill  material in the
fractures.   For  the  sake of  simplicity in  the  present  model,  these
factors have  not  been included.    If  it is  determined  that  the  risk
(accounting  for  both  probability  and   consequences)  indicated by  the
bounding calculations  carried out  here  warrants more  detailed analysis,
then it would  be necessary to  conduct  a wider survey of specific fault
characteristics  in order to improve  the  precision of the estimates.  The
present level  of detail is believed to be  sufficient  for  this generic
analysis.  For  further  simplification, repository  resaturation  is
assumed to have  taken  place in  all cases by the time the fault movement
occurs.
    In  addition  to   transport   of  radionuclides  by  groundwater  flow
through  the  faulted  rock,   there   is  the  possibility that  continued
movement of the  fault  may  lead  to physical transport of a portion of the
repository to  the  surface.  Rate estimates show that  this process would
be extremely  slow, however.   Further discussion  is provided  in Section
D-5.6.

D-5.1.4.1  Bedded Salt

    It is  unlikely that fault movement  would occur  during the period of
extensive  salt  creep  and  repository resaturation  since  the mechanical
stability  of the site  would be  expected to be  most certain in the time
period  closest  to  the present.   (This  period has  been  referred  to as
Period A  in  previous  sections).   Furthermore, the pressures resulting
from salt  creep  are  sufficient  to  cause the  relatively rapid "squeezing
                               259

-------
out"  of  fluid  through  degrading  shaft  and borehole  seals  during  this
period  as  well,  and  so the  addition  of another  pathway,  such as a
ruptured fault,  would not significantly  alter this process.   The fault
does  have  the  capability,  however,  to   lead  to  additional  releases
through  groundwater movements,  and these  are the  movements  that  have
been  modeled  for  faulting  at any point  in  the  10,000 year  period of
evaluation.   The dominant  driving  forces  are thermally induced
convection  and  the  gradient  from interconnecting  the  upper  and  lower
aquifers.
    The values of  the combined effective  gradients tending to move fluid
through a  fault  are the same  as  those  given earlier in  Table  D-53  (see
Section D-3.3).   When  these  gradients  are used  in Darcy's law,  along
with the other  parameters given  in Section D-5.1.3, the  volumetric flow
rates  shown in  Table D-89  are   obtained.   Since  these  flows are not
nearly  so small  as  those  calculated  for a number of  other failure ele-
ments,  it is  natural  to ask  whether  the conservative viscosity correc-
tion factor

                               c(u)  =  5,

corresponding  to pressurized   water  at  about 125°C,  should  be
re-estimated  as  a function  of time here  so  as to  give  more  realistic
flow  rates,  especially  at  later  periods, when  radioactive decay will
have  reduced  the  heat  output  from the wastes.   From  Table D-VI-2 in
Appendix D-VI,  it  is seen  that  even reducing  the  fluid  temperature to
60   (50   is  the  average  temperature  at  10,000  years), the  viscosity
correction  factor  would be  reduced by  only  a  factor  of  about two.
Therefore  the  original value  of  c(u)  is retained  for the  sake  of
simplicity.
    Another area of concern  that  arises is whether  the  calculated fluid
flows  might  lead  to  considerable  dissolution  along the pathway.  The
implications of this might include:
    •  a decrease  in the  distance between the flow  pathway  and  waste
       canisters,  either by widening of  the  pathway or  gradual  plastic
       flow of  the salt and  repository  toward  the fault  in order to
       replace salt that had been  carried  away;  and
                            260

-------
                                  TABLE  89

                   VOLUMETRIC FLOW RATES THROUGH A FAULT
                           (BEDDED SALT REPOSITORY)
                                    Volumetric Flow (Q)
                                        (nrVyr)
                   100 years
1000 years
10.000 years
First Estimate     8.2 x 10'
6.9 x 10'
2.5 x 10'
Second Estimate    3.9 x 10"
3.8 x 10'
3.3 x 10'
 Years after repository closure.
                              261

-------
    •  an  increase  in  fluid  flow rate  from  the  widening  of the  flow
       channels.
This  is  indeed a  possibility.    However,  another  factor offsets  these
problems, namely,  the  tendency  of fractures  in  salt to heal  themselves
by plastic flow and recrystallization.   While it is beyond  the scope of
this  report  to attempt to  prove, by an analytical model or  otherwise,
that  the healing  effect more than offsets  the dissolution, the present
model  may  be  interpreted  as  being  based  on  this assumption.   Other
reports have  also  noted  the  healing potential  for breaches  in  a salt
           (11,18)
repository.
    The  volumetric fluid  flow  rates  in  Table  D-89  lead  to  the
interstitial velocities given in  Table D-90,  based on a porosity of 0.1
in the fault zone.
    Estimation  of  the  source  term  for  this  failure  element requires
consideration  of  several  processes.   First, because of  the possible
leaching of radionuclides prior to the fault  event,  the water  saturating
the  backfilled  repository  will  contain  an  approximately uniform
concentration  of  each  species   (see Figure  D-35a).  The value  of  the
concentration  may  vary  from one  radionuclide to  another  depending on
leach  characteristics  and possible  solubility limits.   When  the fault
pathway is established  (Figure  D-35b),  some  of  the fluid will mix with
the  fluid  moving  up  from below  so  that some of  the  radionuclides in
solution will be released.  This effect decreases with distance from the
fault.  It is  assumed  for modeling  purposes  that  the  zone  of influence
is a  band extending 50  meters  from each  side of the fault.  Such a zone
is  expected  to contain 5%  of  the repository area and  inventory.   For
conservatism,  it  is assumed  that the initial fluid  flows  through the
fault  from  the  repository to   the upper  aquifer  contain  all  these
dissolved radionuclides  at their  initial uniform concentration.    (That
is, this inventory  is assumed  to be  depleted somewhat more  rapidly  than
would actually be the case.)
    Second,  any  canisters  in  the  actual   path   of  the  fault  may be
damaged,  and  so  the waste form  is assumed to  be  subject  to  direct
leaching.    (Other  canisters  might be  given  credit  for  container
integrity.)   The  material expected  to be  leached from canisters in the
direct flow pathway should  be  added  to  that calculated according  to the
                              262

-------
                                TABLE D-90

                     FLUID VELOCITIES THROUGH A FAULT
                         (BEDDED SALT REPOSITORY)
                                           Velocity  (v)
                                              (m/yr)
First Estimate
Second Estimate
                   100 years
205
975
1000 years

    173

    950
10.000 years

    63

   825
 Years after repository closure,
                               263

-------
(a)   Backfilled Watte Before Fault Event
                                  Surrounding rock
                                                Backfilled drift;
                                                radionuclide concentrations
                                                approximately uniform (in space)
            ggg

Canisters in
drilled holes
in floor
                 %>».•>

                                                                    1
(b)   Backfilled Waste Drift Intercepted by Fault
         FIGURE D-3S     WASTE DRIFT BEFORE AMD AFTER FAULTING
                                         264

-------
previous paragraph.   It  Is  assumed that  100  canisters fall into  this
category.
    Third, continued  leaching  from other canisters is also  expected  to
occur, with movement of the radionuclides by diffusion and  fluid  mixing.
This contribution to the releases is expected to be much smaller  than  in
the previous two cases, so it is not included in the model.

D-5.1.4.2  Granite

    Thermally induced convection is the dominant driving force for  fault
pathways  through  a  granite  repository.   The  effective gradients have
been calculated as  0.11  at 100 years, 0.07  at  1000  years, and  0.03  at
10,000 years.    (See  Appendix D-VI) .   Using  these  gradients   in
conjunction  with  the  parameters  given  in  the previous  section, the
volumetric flow rates  shown  in Table D-91 may be  calculated by  Darcy's
law.   Corresponding  fluid  velocities  are  given  in  Table D-92.   The
source term  in this  case may be  treated  according  to  the same procedure
as that given for bedded salt.

D-5.1.4.3  Basalt

    The  effective hydraulic  gradient  in the  case  of basalt  is the
combined  result  of  thermally  Induced  convection and an  aquifer
interconnection.  The  values  have been  given  in Table D-59 in  Section
D-3.3.   Using  these  gradients  in conjunction with the  parameters  given
in the previous section,  the  volumetric flow rates shown  in Table D-93
may be  calculated by Darcy's  law.   Corresponding  fluid velocities are
given  in  Table  D-94.  The  source term  in this  case  may  be calculated
according to the same procedure as that given for bedded  salt.

D-5.1.4.4  Shale

    The  effective hydraulic   gradient  in  the  case   of   shale   is the
combined  result   of thermally  induced  convection  and an  aquifer
interconnection.  Their values are the same  as  for basalt.  Using  these
gradients  in conjunction  with  the parameters  given  in  the previous
                               265

-------
                                TABLE  D-91

                   VOLUMETRIC FLOW RATES THROUGH  A FAULT
                            (GRANITE REPOSITORY)
                                     Volumetric Flow
                                            (tn/yr)
                   100 years
First Estimate     6.9 x 10
Second Estimate    6.9 x 10
1000 years

4.4 x 106

4.4 x 106
10.000 years

1.9 x 106

1.9 x 106
 Years after repository closure.
                              266

-------
                                TABLE D-92

                     FLUID VELOCITIES THROUGH A FAULT
                           (GRANITE REPOSITORY)
                   100 years
First Estimate     1.7 x 10
Second Estimate    1.7 x 10
Velocity (v)
 (m/yr)

1QOO years

1.1 x 104

1.1 x 104
10.000 years

4.8 x 103

4.8 x 103
 Years after repository closure.
                              267

-------
                                 TABLE D-93

                   VOLUMETRIC FLOW RATES THROUGH A FAULT
                             (BASALT REPOSITORY)
                                    Volumetric Flow (Q)
                                            (m3/yr)
                   100 years
First Estimate     8.8 x 10
Second Estimate    4.0 x 10
1000 years

7.6 x 106

3.8 x 107
10.000 years

3.2 x 106

3.4 x 107
 Years afer repository closure.
                               268

-------
                                TABLE D-94

                     FLUID VELOCITIES THROUGH A FAULT
                            (BASALT REPOSITORY)
                                       Velocity  (v)
                                         (m/yr)
                   100 years*
First Estimate     2.2 x 10"
Second Estimate    9.9 x 10*
1000 years

1.9 x 10A

9.6 x 104
10.000 years

7.9 x 103

8.5 x 104
 Years after repository closure,
                                 269

-------
section, the volumetric flow rates shown in Table D-95 may be calculated
by Darcy's law.  Corresponding fluid velocities are given in Table D-96.
The source  term in this  case  may be calculated  according  to  the same
procedure as that given for bedded salt.

D-5.1.4.5  Dome Salt

    It can reasonably  be  assumed that a fault  intersecting  a salt dome
will  extend  beyond  the   flank  of  the  dome  on  one  or   both  sides.
Consequently, a connection will be established between the upper aquifer
and the lower  aquifer  (or  pressurized brine reservoir) extending to the
side of the dome.   This interconnection provides  for two driving forces
whose  effect  is additive.   First, an  aquifer  interconnection gradient
tending to move fluid  upward has  been assumed  in  the generic repository
setting in dome salt  (see  Chapter D-2.0).   Second, adequate recharge is
available to permit the establishment of  a thermally induced convection
cell.   The  values  of  the effective gradients  are  given in  Table D-97.
Using  these  gradients  in conjuncion wih  the  parameters given  in the
previous  section,  the  volumetric flow rates shown  in Table  D-98 may be
calculated by  Darcy's  law.   Corresponding  fluid velocities are given in
Table  D-99.    The discussion  of healing  and  dissolution  that  was
presented in  the  case of  bedded salt also  applies to  this  case.   The
source  term  in  this  case  may  be  calculated  according  to the  same
procedure as that given for bedded salt.

D-5.1.5  Literature Discussion

    Faulting models and  parameters  have been  reported  in  a number of
other  studies, several of which are summarized below.
    Battelle Pacific Northwest  Laboratory,  working under the ONWI/WISAP
program,  has developed general models  for faulting  at a  hypothetical
site in Columbia Plateau Basalts.   '  Components of  the model include:
    *  probability  of  significant changes  in regional  tectonic forces
       over the next million years;
    a  probability  of  changes in  local  strain ratios  over the next
       million years;
                                    270

-------
                                TABLE D-95

                   VOLUMETRIC FLOW RATES THROUGH A FAULT
                            (SHALE REPOSITORY)
                                    Volumetric Flow  (Q)
                                          (m3/yr)
                   100 years
First Estimate     8.8 x 10
Second Estimate    4.0 x 10'
1000 years

7.6 x 104

3.8 x 105
10.000 years

3.2 x 10A

3.4 x 105
 Years after repository closure.
                            271

-------
                                 TABLE D-96

                     FLUID  VELOCITIES THROUGH A FAULT
                             (SHALE  REPOSITORY)
                                        Velocity (v)
                                          (m/yr)
                   100 years
First Estimate     2.2 x 10'
Second Estimate    1.0 X 10"
1000 years

1.9 x 102

9.5 X 102
10.000 years

8.0 x 101

8.5 X LO2
 Years after repository closure.
                             272

-------
                                TABLE D-97




             EFFECTIVE VERTICAL HYDRAULIC GRADIENT IN A FAULT

                   FROM THERMALLY INDUCED CONNECTION AND

                          AQUIFER INTERCONNECTION

                          (SALT DOME REPOSITORY)
                   100 years
                                     1000 years
                 10.000 years
Thermally Induced
          **
Convection
  First Estimate
                    0.12
  Second Estimate     0.12
0.07



0.07
0.03



0.03
Aquifer

Interconnection'
             ***
  First Estimate
                    0.01
  Second Estimate     0.2
Total
  First Estimate
                    0.13
  Second Estimate     0.32
0.01
0.2
0.08
0.27
0.01
0.2
0.04
0.23
 **
***
 Years  after  repository closure.
it
 From Table D-VI-4,  Appendix D-VI.

 From Chapter D-2.0.
                               273

-------
                                 TABLE D-98

                   VOLUMETRIC FLOW RATES THROUGH A FAULT
                           (DOME SALT REPOSITORY)
                                     Volumetric Flow (Q_)_
                                           (m3/yr)
                   100 years
First Estimate     8.2 x 10
Second Estimate    2.0 x 10'
1000 years

5.0 x 104

1.7 x 105
10.000 vear;s

2.5 x 104

1.5 x 105
 Years after repository closure.
                              274

-------
                                TABLE D-99

                     FLUID VELOCITIES THROUGH A FAULT
                          (DOME SALT REPOSITORY)
                                       Velocity  (v)
                                          (m/yr)
                   100 years*
First Estimate     2.0 x 10"
Second Estimate    5.0 x 10
1000 years

1.3 x 102

4.3 x 102
10.000 years

6.3 x 101

3.6 x 102
 Years after repository closure.
                              275

-------
    •  probability of  an undetected fold as a function  of  both distance
       from the site and degree of  site  investigation;
    •  probability of  a  fault  associated with  an undetected anticline;
    •   probability of shear deformation along pre-existing  joints,  the
       cause being movement in an undetected anticline;  and
    •  probability of  rupture of a  fault in the  basement strata.
The last probability in  this list is estimated at

                         X =  10    events/year.

The determination of various probabilities is  associated with seismicity
data.
    TASC,  in  work  for  Lawrence  Livermore  Laboratory,      modeled
movement along old faults in a shale repository  as having an  annual rate
of

                         X «  5 x 10   events/year.

They  argued  that  for  bedded  salt   the  probability   would  be  less.
Consequence modeling  parameters  included permeabilities of  10   cm/sec
      -4
and 10   cm/sec through  the repository and barrier layers,  respectively,
with partial healing after 70  years reducing  these values by two orders
of magnitude.  Fault zone porosity was estimated at  10
    Claiborne  and  Gera  evaluated faulting  probabilities for  a site  in
southeastern New Mexico.     They estimated a faulting rate of

                         X =  4 x 10    events/year,

based on  the  regional  tectonic  data  and  geometrical   analysis.   They
further argued that containment failure by faulting  is even less likely,
involving  a  reduction  of about  two  more  orders  of magnitude  in  the
failure rate.
                              276

-------
    The KBS study' "' in Sweden estimated a  fault movement  rate  of

                        X =  10   events/year

          2
for a 1-km  repository in that country.
    A University of  New Mexico  study     for  the EPA  considered  the
possibility of  faulting  in  shale and  salt  repositories  in the Delaware
Basin.  The following occurrence rates were given

                       X =  2.2 x 10   events/year     (shale)
                       X =  1.4 x 10   events/year     (bedded  salt).

The  model was  based on  13  years  of  earthquake  data  and  a  relation
between  earthquake  magnitude  and   faulting   parameters,   in  order  to
estimate  an  annual  average fault surface  area over which movement has
been experienced.  This value was used to estimate  the net  faulting rate
as a product of  three probabilities
                           Pj  x  p2  x  p3

where:
           average fault surface moving per year
    "l  =   total surface of Permian-Penn. faults
    p«  "  probability of an old fault beneath repository
    p,  »  probability  of  a rupture in old fault extending as far up as
           repository.
                                                    242
For bedded salt the respective values  are 0.012 km  /10   km  ,  0.6, and
0.2, leading to the X value given above.
D-5.2  VOLCANOES

D-5.2.1  Summary

    The  repository site  selection  process is  expected to  avoid sites
where future volcanic activity is at all likely.  Nevertheless, volcanic
                               277

-------
trends can cover  large distances  over  a  period  of time, and occasionally
completely  new  volcanic  centers  erupt,  even  within  stable  crustal
plates. This section of  the  report  is  concerned with the intersection of
a  repository  by  a  volcanic structure  that vents  to  the surface.  The
case  of  subsurface intrusive  structures  is  treated  in Section  D-5.3.
The  model  adopted here  consists  of  a  constant  annual  rate  for
penetration of  the  repository  and  transport  of material to  the  air and
land  surface.   Rates are  estimated by  counting the number of vents in
various areas, dividing by their  age to  obtain  vent formation rates, and
multiplying by  the probability  that  such  a   vent  would  intersect  a
randomly cited  repository  in the  region of  interest.   A summary  of the
analysis is given in Table D-100.

D-5.2.2  Background

    A volcano is  generally  defined  as  a hill or  mountain resulting from
accumulations of  congealed lava  or other ejecta  that  have been  spewed
from  a vent by deep geologic pressure  and  heat.  From  the point  of view
of  a  repository,  the  physical  form  is  less  important  than  the
probability of  recurrence,  the  nature  of the eruption, and  the range of
influence.   Figure D-36 illustrates  a number of volcanic or  igneous
features •   Several  important surface  phenomena  are  described in Table
D-101.
    Volcanism  is  usually related to  areas of  crustal  plate  collision,
where magma from a subductlon zone  can be  freed  up  through  the  overlying
crust, or to areas under tensional  stress, where rift zones  can develop.
These  conditions generally are  found  along  continental  margins  and
mid-oceanic rises,(         although  intracontinental  rifts  are also
found.  (See Figure D-45 in Section 5.6.)  Most  such activity therefore
follows linear or arched trends.
    During  the  last   ten  million  years,  the  only  volcanism  in  the
coterminous 48  states  has  been in  the  West.   Most of  this  activity has
paralleled the  Pacific  Coast,  but  some  has  followed  the graben  of the
Rio  Grande,  arched southward  from  Albuquerque  toward Las  Vegas,  or
extended  westward  from  Yellowstone Park.    These trends  are shown in
Figure D-37.    There  have been  only  three  eruptions  in  the  48  states
                             278

-------
            TABLE D-100
SUMMARY OF VOLCANO FAILURE ELEMENT



MEDIUM


Bedded Sell





Granite





Basalt







SS
So «
35
1
s§
ES
p





P





p








NATURE
OF
MODEL


Annual occurrence
probability.




Annual occurrence
probebilrty.





probability.









RELEASE
MODE


Air and lend
surface.




Air and lend
surface.





Air and land
surface.









DRIVING
FORCE


Direct: tramport by
moving 0M> *nd




Direct tramport by
mowing OMMMd
molten rock.





moving gmt *nd
moJ ton rock.









SOURCE
TERM


Fraction of repository





Fraction of repository
brought to surfece.





Fraction of repository
irought to surface.








PARAMETERS



1st ESTIMATE
X - 1 i 10-10/yr
Fraction of repository
brought to surface is
0.4%, of which 1%h
in reeuiieule form, 9%
consists off Ins pertides
which can be easily
dispersed, end 90% is
reburled near the
surface.
Fraction of repository
brought to surface is
0.4%, of which 1%l.
consists of fine pertides
which can ba amity
Opened, and 90* is
report ed near tha
surface.
X - 6 x 10-1uYyr
Fraction of repository
irougtrt to surf ace is
M%. of which 1% is
nreepirablefonn.t*
xmsira of fins pertides
•nidi cen be eerily
aspersed, and 90% Is
aburied near the
urfece.


2nd ESTIMATE
X • 1 x 10 • 1 x 10-8/yr
Fraction of repository
brought to surfece is
0.4%. of which 1% is
hi rtapireW. form. 9%
consists of fine particles
which cen be sesiry
dlspsrsed.end9(mis
raburiad near the
surface.
X - 1 x 1f»*/yr
Fraction of repository
brought to surfece is
(U%. of which IK is
inreaplrableform.9X
consists of fine pertides
which eanbaeetlty
dtwened.andOOXit
reburiedneerthe
surfece.

RELEASE MODELING STEPS



lit EST MATE
Direct release





Direct release





Direct releese









2nd ESTIMATE
Direct relaese





Direct release





Direct releese










COMMEffTS


First estimate based on
natkmel svsrn).. Lower
rates could probebh/ ba
shing easumption, such
eslocatlaninEastor
Midwest.



First enhnsta based on
nettonel an*raga> Lower
retascouW probsoh/ be
siting assumption, such
as location In East or
Mijmaet



Based on Columbia
Plateau basalts.








-------
                                                        TABLE D-100
                                      SUMMARY OF VOLCANO FAILURE ELEMENT (CONTINUED)

MEDIUM


S»l»





DomtStlt




LISTIC (PI
INISTIC (Dl
s*
ss
ss
p





p




NATURE
MODEL


Annual occurrence
probability.




Annual occurrence
probability.





MODE


Air and land
surface.




Air and land
surface.





FORCE


Direct transport by
moving gases and
molten rock.




Direct transport by
moving gases and
molten rock.





TERM


Fraction of repository
brought to surface.




Fraction of repository
brought to surface.




PARAMETERS


In ESTIMATE
X = 1 x I0-10/yr
Fraction of repository
Drought to surface ts
0.4%, of which 1% is
in respirable form, 9%
consists of fine particles
which can be easily
dispersed, and 90% is
raburied near the
surface.
\ " 1 x lQ-10/yr
Fraction of repository
brought to surface is
0.4%, of which 1% is
in respirable form, 9%
consists of fine particle*
which can be cosily
dispersed, and 90% to
reburied near the
surface.


2nd ESTIMATE
\ - 1 x 10-8/yr
Fraction of repository
brought to surface is
0.4%, of which l%i$
inreapirabJeform.9%
consists of fine particles
which can be easily
dispersed, and 90% is
reburied near the
surface.
X = 1 x 1O-l°/vr
Fraction of repository
brought to surface is
0.4%, of which 1%is
in re»p treble form. 9%
consists of fine particles
which can be easily
dispersed, end 90% is
reburied near the
surface.
RELEASE MODELING STEPS


to ESTIMATE
Direct release





Direct relasie






2nd ESTIMATE
Direct release





Direct release





COMMENTS


First estimate based on
national everage. Lowe)
rotas could probably be
derived from additional
siting assumption, such
as location in East or




Estimates based on
national average. Could
be refined to a lower
value for salt dome
region. First and
second estimates are the
same since from the
standpoint of volcanism.
the Gulf region shows
no variation.
to
00
O

-------
         LAVA
         MESA
                               VOLCANIC NECK WITH
      LAVA     ASH CONE WITH      RADIATING DIKES
     PLATEAU    VOLCANIC DOME        /            CALDERAWITH
                                                 CINDER CONE
CINDER
 CONE,
                                                                   ON FLOOR
COMPOSITE
 VOLCANO
Source:  U.S. Geological Survey. Atlas of Volcanic Phenomena.
        FIGURE D-36  SKETCH OF PLUTONIC AND VOLCANIC STRUCTURES
                                       281

-------
                                TABLE D-101
               VOLCANIC PHENOMENA WITH  SURFACE  MANIFESTATION
Type

Basaltic
Eruptions
Andesitic
Eruptions
Silicic
Eruptions
Phreatic
Eruptions
Maars and
Diatremes
Fumarole
Geyser
Characteristics

Mild eruptions; fluid  lava;  small
gaseous component; silica  deficient;
regular or continuous  eruptions.
                          «
More violent than basaltic eruptions;
viscous lava; gaseous; much  ash and
cinders.  Forms composite  cone; may
be explosive; irregular eruptions;
often long dormant.  Most  prevalent
type.

Nearly rigid lava; may be very
gaseous; forms domes and spines.
Gas, fumaroles, and geysers  may
be only manifestation  of magma.

Steam or gas explosion.  May create
crater resembling impact crater, or
may shatter existing cone.   Most
ejecta fragmented, or  dust and gas.
Caused by contact of water with
hot magma.

Eruption crater in country rock from
violent eruption.  Steam explosion
and jet erodes crater  and  ejects
limited volume of volcanic material
and shattered country  rock.

A crack or vent in a lava  flow or
volcanic region emitting gas and fine
ejecta.  May be connected  to main magma
source or may be the result  of trapped
gas and steam from recent  eruption.  A
small feature building little or no
cone.

Steam and water emitted from a channel
connecting a heat source at  depth to
the surface.  Little or no solids are
ejected; often displays regular cyclic
eruptions.
 Examples

 Hawaii, Columbia
 Plateau, Stromboli
 Mt. Ranier,
 Tamboro, Vesuvius,
 The Andes,
 Paricutln, Katmai
 Mt. Pelee, Crater
 Lake
 Taal, Krakatoa
Hole-in-the-ground,
 Crater Elegante.
 Numerous
 Yellowstone Park,
 Steamboat Springs.
                                232

-------
                          ni--           y<-'
                       •:  v   --4^A
                                           r=^T -—;"""'"   ''';":V;:'~v-^-.
                     MAP EXPLANATION
       LARGE VOLCANO~Bu1lt mostly by repeated eruptions
           at a central vent and probably active within
           the last 100,000 years.  Eruptions range from
           quiet to explosive.  Volcano flanks 
-------
recently enough  to  have  been witnessed and documented: at Lassen Peak in
1915  and  Mount  St.  Helens  in   1857  and   at  present   (1980).    The
composition  of  most  recent  eruptions  from  the  continental  volcanic
systems has been  andesite  or rhyolite.

D-5.2.3  Volcano  Failure Model

    Of concern  for  a repository are the frequency  and predictability of
new volcanism,  since there  are  no  present plans to  consider repository
sites  within the  range  of  influence of  known volcanoes.   With  few
exceptions, new volcanism  will occur close to existing volcanic features
and in regions  experiencing tensional  stress.  The exceptions stem from
the possibility of  maar eruptions  (see  Figure  D-36) initiated by  the
release of gases  or steam  from a subterranean  heat  source.   These  types
of  eruptions appear to  be  less  sensitive  to  regional  stresses,  but
represent a very  small percentage  of eruptions.
    Areas of future activity can be defined only  very approximately,  and
predicting  the  timing  of  this  future  activity  is  even   less  exact.
Future  estimates of  the   expected  frequency  of  eruptive   activity  at
volcanoes  or in volcanic  regions  are  generally  based  on  historical
records and geologic investigation, both of which vary widely in detail
and reliability  from one  volcanic  region   to  another.        All of  the
geologic media considered  in this  study, except salt domes,  can be  found
both close to and far  from areas of recent volcanism.
    There  are  many site-specific  factors  that  can enter  into  an
estimation  of  the  likelihood  of  future  volcanism  at  a  repository
location.   These include  the distance to  the nearest  recent activity,
whether  the site  lies  in the  direction   of  a  trend, regional  stress
patterns and  the way  they  have evolved  over geologic time,  heat  flow
measurements, etc.   The  model  used  here  does  not  incorporate geophysical
parameters, but  rather  utilizes  a simple  counting  technique for roughly
estimating the order of  magnitude  of the  likelihood of future volcanism.
    Figure D-37  shows all  mapped  vents in the  coterminous  states  that
have shown activity within the last  10 million years.  As noted earlier,
these  are  all  restricted   to  the  western third of   the  United States.
These vents actually formed over a longer  period than 10 million years.
                             284

-------
However, in  estimating  the  rate  of  formation,  it is conservative to use
this lower,  more  readily available  figure.   The map shows approximately
                                                 6   2
1300 vents  over  this  western area  of  3  x  10  km .   Thus,  a gross
regional average  rate of vent  formation is
                                            62       7
                   X =  1300 vents per 3 x 10  km  per 10  years
                             -11         2
                     =  4 x 10    vents/km /year.
                               2
For a  repository  of  area 8 km ,  the  corresponding  rate of intersection
would be 8 times  the above, or
                   X =  3 x 10    intersections/year.
This number  does  not  represent  either a  first or  second  estimate  for
model purposes, but  is  used  as an  example  calculation  to represent  the
model equation
                   x =  8V/AT intersections/year,
where  V is  the number  of  vents  formed in  the area A  over  a  period at
least as long  as  T.   This  equation  will be used  for various regions to
estimate appropriate values  of X.  The 10-million-year cutoff  for  data
on vents was chosen  to be consistent  with the USGS  use of  this  time
frame for  their volcanic hazards maps.
    A simple first estimate value  of  X for all  media  except basalt  can
be derived  from  the  assumption  that,  with careful site  selection,  it
should  be  possible to  locate  a  repository so  that the  probability of
future  volcanism  is  less  than the national  average.   This  is because
bedded salt,   granite,  shale,  and  salt  domes  are  either  widely
distributed  or  concentrated in  areas of negligible volcanic  activity.
The national average is thus  a conservative estimate of  X.   This value
is  obtained  exactly as  above,  except  that   the  entire area  of  the
coterminous  states is used, so that

                            (81(1300)
                        (7.83 x 106)(107)
                      =  1 x 10~    intersections/year,
Basalt is not covered by this reasoning because the only basalt deposits
being  seriously  considered  for  a  repository  are  located  in  a  single
region, namely,  the Pacific Northwest.   By their  mere  presence, these
                              285

-------
basalts  are  indicative of  significant volcanic  activity in  the past.
Most  of  the Columbia  Plateau  flood basalts  were  apparently  deposited
about  14  to  17  million years ago, but  some  volcanic activity continues
in locations such as Mount Lassen  farther  to  the  west.   Regional stress
studies  suggest  that  there  may  be locations  in  this region  where  the
probability  of  future volcanism  is  low.   First   estimate  calculations
consider the states  of Washington, Oregon, and Idaho, exclusive  of  the
north-south  volcanic  trend  represented  by  the  Cascade  and  Klamath
Mountains.   (This  latter  zone is  probably associated with an existing
subduction zone and  hence a  different  tectonic zone  from the  region  of
greater  interest.)   From  the  map   in Figure  D-37,  the  following
parameters have been estimated:
                            A = 4 x 105 km2
                            V = 300 vents
                            T = 107 years
The resulting value of X from the model equation is

                  X = 6 x 10    intetsections/year.

This number is the first estimate for  basalt.
    Second estimate  values  correspond  to repository  sites  in  locations
of modest volcanic activity  over  the past 10 million years.   A number  of
volcanic fields shown  on Figure D-37 were  considered, with  values of  A,
V, and T  being  estimated  for each.   For  example,  for the  Flagstaff,
                                                                   2
Arizona area, 85 vents are  estimated  to exist  in  a region 6400  km   in
area, and  the time  over which  these developed  is  thought to be at least
10  years. These parameters  yield the  value

                              X = 1 x  10~8.
It is  important  to  note that such values  should  not be applied  to  the
specific  volcanic  fields  from whose  parameters  they have been
calculated.    They  represent   only  averages,  and  detailed site
investigations  could  introduce other  factors  that  might  significantly
alter the estimate for an individual  site.   They  are,  however, believed
to be reasonable for generic  calculations.
                               286

-------
    Many  of  the other calculations yielded  similar values, and so  this
                   —8
value,  X  = 1  x 10  , has been  adopted as  the  second estimate for  all
media except salt  domes.  In  the  case  of  salt domes, which  are  not  found
in any  of the volcanic regions,  the  second  estimate value is  identical
to the  first,  i.e.,  1 x 10~10.
    It  should  be  noted  that  in  the  calculation  of  the  volcanic vent
formation  rate,  X, the choice  of regions to be  considered has a great
effect  on the resulting  numerical  value.   For  example,  application  of
the above procedure to the eastern United  States would yield essentially
zero rates.  Since the values  calculated by  this procedure  are  generally
very  low, it  did  not seem desirable  to  refine them  by  making further
site  selection assumptions.   Simple modifications,  such  as eliminating
from consideration the vents  along the  Pacific coastal volcanic mountain
zone, would indeed lower  the  rate for  the  rest of  the  country.  However,
since this modification only  changes  the result  by about a factor of  2,
it  is  not  deemed important  in  these  order-of-magnitude  calculations.
Another  modification  would  be  to  cbnsider  only  intra-plate silicic
eruptions.  While  the consequences of  these would be  more severe, they
would   also  involve  lower  probabilities  than   the  already   low  ones
calculated,  as well  as  the  possibility  of detecting  developing  magma
chambers  that  could  lead  to silicic  eruptions  over  the  next  10,000
years.

D-5.2.4   Volcano Release Model

    The dominant  release  mode for the interception of a repository by a
volcanic  vent  is  the transport of  radioactive material  directly to  the
surface.  Since the  size  of  the vent  and the nature of the eruption  can
vary  considerably,  this analysis  simply estimates parameters that would
characterize an "average" new vent.
                                              A  2
    The area of the vent  is taken to be 3  x  10  m  ,  corresponding to  the
area  of  a  circle with radius 100 m.   This cross-sectional  area also
characterizes  the  portion of  the repository that  would  be affected,  or
0.4%  of  the  repository  inventory.    Of  the  affected contents,  it  is
assumed that 1% is widely dispersed as  fine  particulates or gases,  9% is
included  with  unconsolidated ash or  cinder on  the  surface,  and 90%  is
                             287

-------
incorporated  into  solidified  lava or welded ash.  Most  recent  eruptions
in  America  have involved andesitic  ejecta  with fragmented, molten, and
gaseous  components.   The  fractions  assigned  to  each  component  are
thought  to  be  reasonable  for such  a typical  eruption.   Explosive and
calamitous  events,  such  as the obliteration  of Krakatoa and Mt. Mazama
(Crater  Lake),  are not  only  exceptional, but  they  are apparently more
likely with  large,  established volcanic  systems than  with  newer
eruptions.    Similarly,  maars require  abundant water,  a  condition not
expected  at most  candidate  repository sites.   If  it were  desired  to
model  the  "worst  possible"  case in  terms  of consequences,  then  the
probabilities would need to be revised downward  accordingly.

D-5.2.5  Literature Discussion

    Volcanism  has  been  discussed in  a  number of  repository studies.
However, models  and quantitative  analyses are usually not included, and
ones that are included are difficult  to compare  with  those derived here.
    The  University of New Mexico/EPA study      characterized volcanic
                                                       -12            -12
events with annual probabilities  ranging  from 2.4 x 10   to 8.1 x 10
for disruption  of a  repository.   These  probabilities are  based  on  an
estimate of renewed volcanism in  the Delaware Basin with an annual rate
           -9
of  5  x  10   , in  combination with  a geometric argument  on repository
intersection.
                        (3)
    Claiborne and  Gera,     also  in  an analysis of  the Delaware Basin,
simply state  that  volcanism  in  such a stable  area  is much less likely
than formation  of a  "great  fault."    In  addition,  they argue  that  the
consequences would be less than for a giant meteorite  impact.
    Recent  probability  calculations  carried  out  for  a  potential
repository  site at  Yucca Mountain  on  the Nevada  Test Site  yield  an
                 _9                                        M2i)
annual rate of 10   for repository disruption by volcanism.
    Some  of  the  calculations carried  out  in  other  studies  appear  to
count volcanic  craters  rather than  individual  vents, which may explain
why some of these other rates are lower than  those calculated here.
                              288

-------
D-5.3  IGNEOUS INTRUSIVES

D-5.3.1 Summary

    The  previous  section  on  volcanoes  discussed  extrusive igneous
activity  (movement  of magma  out  through  vents to  the  surface or  the
atmosphere). The repository might also be disrupted by intrusive Igneous
bodies (magma that moves through the earth's crust  but  never reaches  the
surface) .  The  important  difference  between  extrusive  and  intrusive
activity  is   that  while  extrusive  activity, volcanism,  can  transport
waste directly to the biosphere, intrusive activity requires groundwater
as a secondary transport mechanism.
    The  model in  this  section  assumes  that  a planar  intrusive body
intersecting the repository will transport a fraction of  the intersected
waste to  the  overlying  aquifer. Waste within the  aquifer will then be
leached and moved by the natural flow of groundwater. The model  requires
two  parameters:  the probability  of an  intrusive intersecting the
repository, and  the dimensions of the intrusive.  Intrusives are common
structures,  particularly  in volcanic and  crystalline rocks;  but,  by
their very nature,  their  emplacement  has not been  directly  observed and
there is  little information from which probabilities for  intrusions may
be  estimated.  In  the  present   model,  the probability of  an intrusive
intersecting a repository is modeled as a fraction  of the probability of
faulting. Dimensions of  intrusives used in the model  are  consistent with
those reported  in  the  literature.  It is assumed that  the waste is not
sealed  into  the  resolidified igneous  rock,  which may be  heavily
fractured especially in zones  where  it encounters  groundwater.  Detailed
explanations of the model are  given  in  Sections D-5.3.3  and D-5.3.4.  A
summary of the analysis  is given in Table D-102.

D-5.3.2  Background

    Definitions and examples.  Intrusive igneous  rock masses are  created
when  magma or  molten  rock is  injected  into  crustal  rock  below  the
surface,  as  opposed to  extrusives,  which  erupt   at  the surface. Some
intrusive bodies may be  the result of extreme metamorphism and partial
                              289

-------
                                                       TABLE D-102
                                      SUMMARY OF IGNEOUS INTRUSIVE FAILURE ELEMENT





MEDIUM


Bedded Salt




Granite




Basalt




Stole



Dome Salt




sa
0 SJ
ES
(O _
si
< ec
00 tU
it
a. O
p




p




p




p



f







NATURE
OF
MODEL


Annual probability
of occurrence.



Annual probability
of occurrence.



Annual probability
of occurrence.



Annual probability
of occurrence.



Annual probability
of occurrence.







RELEASE
MODE


Groundwater




Groundwater




Groundwatw




Groundwater



Groundwater








DRIVING
FORCE


Physical transport of
wastes by magma to
upper aquifer.


Physical transport of
wastes by magma to
upper aquifer.


Physical transport of
wastes by magma to
upper aquifer.


Physical transport of
wastes by magma to
upper aquifer.


Physical transport of
wastes by magma to
upper aquifer.






SOURCE
TERM


Waste material inter-
sected by magma.



Waste material inter-
sected by magma_.__



Waste material inter-
sected by magma.



Wane material inter-



Waste material inter-
sected by magma.





PARAMETERS



1st ESTIMATE

X=2x10-10
Dimensions of dike:
1 m x 4 km.
intersecting 0.05%
waste inventory.
X = 2 x 10'10
Dimensions of dike:
1 m x 4 km.
intersecting 0.05%
waste inventory.
X - 5 x 10'9
Dimensions of dike:
1 m x 4 km.
intersecting 0.05%
waste inventory.
Dimensions of dike:
t m x 4 km.
intersecting 0.05%
waste inventory.
X = 3 x 10"9
Dimensions of dike:
1 m x 4 km.
intersecting 0.06%
waste inventory.


2nd ESTIMATE

X = 4 x 10"®
Dimensions of dike:
1 m x 4 km.
intersecting 0.05%
waste inventory.
» . ID'7
Dimensions of dike:
1 m x 4 km.
intersecting 0.05%
waste inventory.
X - ID'7
Dimensions of dike:
1 m x 4 km.
intersecting 0.05%
waste inventory.
X = 4 x 10~9
Dimensions of dike:
1 m x 4 km,
intersecting 0.05%
waste inventory.
X o 5 x 10"7
Dimensions of dike:
1 m x 4 km.
intersecting 0.05%
waste inventory.


RELEASE MODELING STEPS





Material moved to aquifer and subject to leaching.
Leach characteristics of waste form assumed
unchanged, although canisters would be removed.


Material moved to aquifer and subject to leaching.
Leach characteristics of waste form assumed
unchanged, although canisters would be removed.


Material moved to aquifer and subject to leaching.
Leach characteristics of waste form assumed
unchanged, although canisters would be removed.


Material moved to aquifer and subject to leaching.
Leach characteristics of waste form assumed
unchanged, although canisters would be removed.


Material moved to aquifer and subject to leaching.
Leach characteristics of waste form assumed
unchanged, although canisters would be removed.




COMMENTS





Probabilities deter-
mined as 1% of values
for faulting.


Probabilities deter-
mined as 1% of values
for. faulting.


Probabilities deter-
mined as 1% of values
for faulting.


Probabilities deter-
mined as 1% of values
for faulting.


Probabilities deter-
mined as 1% of values
for faulting.


10
v£>
O

-------
melting  of older  rock,  and  therefore  are not  truly igneous.  However,
this distinction  is not important for  the purpose of generic modeling,
and  so,  for  the sake of simplicity,  all  intrusives will be regarded  as
igneous  throughout  the discussion.
     Intrusives  may  be  classified according  to  a number  of features,
including  size,  orientation,  and  petrography.    The  most  important
classifications  are  discussed  here  and  illustrated  in Figure  D-36
(Section  D-5.2).   The generic  term,  pluton,  refers  to  any intrusive
igneous  rock body,  independent  of  structure  or mode  of emplacement.
Sills  are  planar and  parallel to rock  strata or  contacts.   Dikes are
also  roughly planar, but  they cut  across strata.   Laccoliths  can  be
described  as very  thick sills  that  cause doming of the overlying rock.
Stocks are vertical masses,  roughly round in cross section, that pierce
the  country rock. Batholiths  are very large stocks, apparently formed  at
considerable depths.
     Plutons may intrude  any  rock: sedimentary, igneous, or metamorphic;
and  they may have  any  igneous petrography.  Examples  are  found  of both
acid and basic  rocks  forming  all  types of intrusive structures. Usually,
however,  magmas of  low viscosity  tend   to  form dikes  and  sills while
those  of  higher  viscosity   form the  thicker  laccoliths and   stocks.
Batholiths are  most  often granitic in composition, apparently the result
of  melting of  older  continental  rocks.  Local  stresses at the  time  of
emplacement may also  affect the morphology of  intrusives;  high vertical
stresses  favor  the formation of  dikes  and other discordant bodies, and
low vertical stresses favor the formation of  sills.
     Effects on  country rock.  The  viscosity,  temperature,  and chemistry
of  the magma  influence  the  range  of  effects  accompanying  intrusion.
Forcible injection  tends to  break free pieces  of the surrounding rock,
incorporating these rock fragments  in the intrusive  mass as xenoliths.
Intrusion  often produces secondary fracturing  of  the country rock. These
fractures  are typically, but  not  always,  filled by the  fluid magma. The
temperature differential between  the hot  magma  and  the  cool invaded rock
may  produce  a  zone of  chilling  in the   intrusive  and heating  in the
country  rock, creating  local areas  of metastable minerals as the rocks
pass rapidly through the stable temperatures  for  such minerals.  Chemical
alteration (metasomatism) of  both magmatic and  country  rock occurs where
                              291

-------
water and other volatiles  in  one or both rocks react  in  the  vicinity of
the  intrusive  contact.  The  term  "contact  metamorphism"  is  used  to
describe the  change  in  the mineralogy or fabric of  the original  rock as
a  result of  the  intrusion.  The area  of  contact  metamorphism  may be
extensive  and  contain  a  variety of  economic minerals,  depending,  of
course,  on the  composition  of the intrusive  and the  accompanying  fluids.
    The  sizes  and  extent of intrusives  can  vary  widely.   Some  sills and
dikes have dimensions  reported  in centimeters, while  others extend for
                                           (58  122  123)
many kilometers and are many meters thick.    '    '      Classic examples
of the  latter  are  the  Palisades sill along  the Hudson River,  the dikes
near  Shiprock, Arizona,   and  the  dike  swarms  across  Scotland  and
England.(123>124'125)   Batholiths,  such as  the   Idaho  batholith,  have
                                    2
areas   on   the  order   of  100  km   or   larger,  while  stocks  are
   ..    (58,126)
smaller.
    Intrusives are frequently associated with volcanism, as evidenced by
the numerous  sills  and dikes radiating  from  or  concentric  to volcanic
vents. However, not  all  intrusives  show this relationship, although the
relationship can also be obliterated by subsequent erosion.
    Depth  of  igneous emplacement  also varies  over  a wide  range.  Some
plutons, particularly  those  associated  with  volcanism,   may  have  been
emplaced very  near  the  surface. Others  cooled slowly and at depths  of
several  kilometers,  as  indicated by  their  minerals  and  their  crystal
     (122)
size.       As the distance  from the magma  source  increases, plutonic
intrusion clearly becomes  less  likely.
    Detection of intrusives.  Intrusives  are  most  generally identified
through  field  surveys by stratigraphic and petrographic comparison with
surrounding rock. These basic techniques may be supplemented  by drilling
and geophysical investigations  of magnetic and gravitational anomalies.
Intrusives  often differ markedly in magnetic properties and density from
many sedimentary rocks  and may  be readily  detected  in some  situations.
The  geologic   history  of  plutons  near  a  repository  site  gives  some
indication  of  the  potential for  future  activity.   Furthermore,  current
magmatic activity  near a  repository  site  may be  detected  through
geothermal  heat flow measurements. In general, heat  gradients across the
United  States  indicate  that,  except for  a  very  few  locations,  rock
melting  is  not likely  within  several  kilometers of  the surface/
                              292

-------
Measurement of surface rise or ground tilt may also  be used  to  interpret
magmatic movements  at  depth.        However, to maintain a  conservative
approach  and because rates of  magmatic movement are  too  poorly
understood, the potential advantage of geothermal  or geophysical  surveys
is not considered in the present  model.
D-5.3.3  Igneous Intrusive Failure Model

    The model developed for igneous intrusions  is  analogous  to  that used
for faulting in that it requires:
    •   the probability of new intrusions  intersecting  a  repository; and
    •   the physical parameters  to describe  transport of  waste by an
        intrusive.
The actual  formation of intrusives has  seldom, if ever,  been witnessed,
although  some  have  been  inferred  near volcanic  centers.  Only  a few
investigators have reported the number, size, and spacing of plutons in
                    (122  127)
different  regions.    '        Therefore,  an  approach  using  areal
densities  and  ages  of plutons  to  establish the probability  of  their
occurrence  is  difficult  to  apply.  Many plutons  apparently  form  at
considerable depths, suggesting  that  the number  reaching  a relatively
shallow  repository would  be  far  fewer than  indicated  by a  count  of
plutons visible at  the surface  after  extensive uplift  and erosion. For
example, in  one study  of  a granitic region, dikes were  reported at the
rate  of  three  per  linear  mile,  or approximately  10  per  square
           (122)
kilometer.        However,  as  they  had been  emplaced  roughly 6.5
kilometers  below the surface,  it  is clear  that extrapolation  to
establish  representative  probabilities for  Intrusions  into  a shallow
formation would be of questionable validity.
    Alternatively, the  argument  has been made that the  rate of  intrusion
is a fraction of  the rate of  faulting,  since most intrusives apparently
fill faults  or  joints, while many  faults  or joints have no associated
           (12)
intrusives.       Conditions are envisioned  similar  to  those for normal
faulting,  where   vertical  stress  is   greater  than  horizontal stress.
Vertical  faults could  form,  intersecting  the  repository and  admitting
magma in the form of dikes. The magma  could  then  carry the waste to the
upper  aquifer.  Horizontal  flows  of   magma  through  a  repository are
                            293

-------
considered  less  important  since  they  would  not  carry  waste to  the
aquifers or nearer to the  surface.
    Very limited data permit only a  rough estimate of the ratio of dikes
to  faults.  Further analysis  based  on geophysical  considerations  may be
possible  for  a particular   region.    However,  to  be   consistent  with
                                         (12)
estimates  proposed in  similar studies,      the  present  model  assumes
that dikes are  one percent as frequent  as faults.  The probability of an
                                                                       _2
Igneous intrusion disrupting the repository  is  thus estimated to be 10
times  the  rate of faulting   for the  geologic  medium,  as  determined  in
Section D-5.1.

D-5.3.4  Igneous Intrusive Release Model

    The dimensions of  an  intersecting dike  are  used  to  determine  the
fraction of stored waste  transported to  the aquifer  by  the molten rock.
For  the  sake  of  conservatism,  it  is assumed  that a dike  would cut  the
                                                                   2
repository across  its longest dimension.  For a repository  of 8 km with
sides  of  2 km and 4 km, the dike would be 4 km  long.   The thickness of
                                   (122)
the dike is assumed  to  be 1   meter.        The dike would then intersect
0.05%  of the  repository.  Also for  conservatism,  it  is  assumed that this
entire fraction is carried  to  the  overlying  aquifer and  is  not  sealed
into  the  matrix of  the dike. Because  this  transport mechanism assumes
immediate  introduction  of the waste  into the aquifer,  the contribution
of groundwater  flow along  the contact  is  Insignificant by comparison  and
may be neglected.  Furthermore,  it  is likely that  this  boundary will be
resealed by melting  of the  country  rock.
    This model  is  independent of the  host rock.   Accordingly, the same
parameters apply  for all media discussed  in  this  study.

D-5.3.5  Literature Discussion

    Igneous intrusives  have  been modeled  as possible failure  mechanisms
in  several other studies,  which   are mentioned below.  Most  of  these
studies  have  not  identified  igneous  intrusion  as  a  separate failure
mechanism, but as a  variation of  volcanism.  '   '  '       Two sources
distinguish  between  extrusive  and   Intrusive  magmatlc  activity,   citing
                             294

-------
the  additional  requirement  of  groundwater  to  transport  waste  after
                                            (12 128)
magmatic intrusion as  the main distinction.   '      These  studies  also
discuss qualitatively the effects of concentrated  geothermal heat  on the
natural  groundwater  regime  and  possible  local  perturbations  in  flow.
                                                        (12)
Only one study develops  a failure rate for intrusives,      and this  is
the basis for  the approach used here.
D.5.A  METEORITE IMPACT

D-5.4.1  Summary

    The  impact  of  a  large  meteorite  could  cause  a  breach  of  the
repository  either  by directly  releasing material  to  the  air or  land
surface  or  by  fracturing  the  surrounding  rock,  thereby  permitting
greater  groundwater  access.   Meteorites  large  enough  to  create  such
breaches  are  very  uncommon.    Furthermore,  the potential  hazard
associated  with  repository   releases  would  appear  to  be  negligible
compared with  the possible effects on  surface  Installations,  the
environment, and  the  surrounding population.  Therefore, the  following
discussion  is  more  abbreviated  than  that  for most  other failure
elements.  A summary of the parameters used  to  characterize  this  failure
element is given in Table D-103.

D-5.4.2  Background

      In the history and  evolution of  the solar  system,  meteorites  have
been very common, representing a  process  that has had measurable  effects
on the planets and their satellites.   Indeed, it  has  been theorized  that
some  meteorites  over  1000   km  in  diameter  may  be   responsible  for
                                                                   (129)
variations in the thickness of the crust  on  the earth and the  moon.
From observations of  cratering  history  on  the  inner  planets   and  their
satellites  and  by  correlation  with  the  ages  of  portions   of  their
surfaces  (e.g.,  by lunar  rock   samples),  estimates  have been made  of
meteorite fluxes since the formation  of  the solar system.  Figure  D-38
shows how  this  rate  has slowed  since  the  early period of   the  solar
                             295

-------
                                                       TABLE D-103
                                       SUMMARY OF METEORITE IMPACT FAILURE ELEMENT




MEDIUM

BeddadSaM











Granite










SataH










si
!§
J Z
II

II
p











p










p












NATURE
OF
MODEL

Annual occurrence
probability.










Annual occurrence
probability.










Annual occurrence
probability.













RELEASE
MODE

A. Lend surface
8. Groundwalar










A. Land surface
B. Groundwater










A. Land surface
B. Groundwater













DRIVING
FORCE

A. Impact
B. Thermal convection
added to aquifer
interconnection
gradient.







A. Impact
6. Thermal convec-
tion.









A. Impact
B. Thermal convec-
tion eddad to
aquifer inter-
connection
gradient.









SOURCE
TERM

A. 0.1% repository
inventory to
surface.
B. 20% cumulative
leeched nudktn
refeasfd to ground-
water. Continued
leaching of broken
canisters in fracture
or breccia zone
110%) and tur.
rounding canisters
110%).
A. 0.1% repository
inventory to
surface.
3. 20% cumulative
Inched nudides
released to ground-
water. Continued
leaching of broken
canisters in fracture
or breccia zone
(10*1 «nd sur-
rounding canisters
110%).
A. 0.1* repository
inventory to
surface.
B. 20% cumulative
leached nudides
released to ground-
water. Continued
leaching of broken
canisters in fracture
or breccia zone
110%) and sur-
rounding canisters
110%).

PARAMETERS



1st ESTIMATE
X . 4x10-H/yr
A - 0.8 km?
K - 10-«cm/stc
n - 03








X - 4x 10-H/yr
A - 0,8 km?
K " 10~* cm/fee
n - 03








X • 4 x IO-1 '/yr
A - 0.8 km?
K - lO-'cm/sac
1 • 03










2nd ESTIMATE
X • 4x10-11/yr
A - 0.8km2
K - IO4 on/tec
r, « 03








X - 4x10-1'/yr
A " 0.8 km2
K - 10-4 cm/tec
n - 02








X - 4x10-1'/yr
A • 0,6 km2
K • 10-« cm/sec
fl - 02








FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER



1st ESTIMATE
tlvra)

100

1000
10.000
Q III (m3/vr)

IjSxIO7
•j
1.4 x 10'
5.0 x 106






tlyrsl

100

1000
10.000

6 It) (r»3Avrl
f
1.4 x 10'

e.8 x 10°
32 x IO8






tlyrs)

100

1000
10.000
Q It) Im3/yr)

1 J x IO7
•j
1.5 x 10
6J x IO6








2nd ESTIMATE
(yrsl

100

1000
0*00

0 It) Im3/yr)

7£.107

7^ x 10'
S.7 x IO7






t(vn)

100

1000
10.000

6 It) lr»3/yr)

1.4 x 10

8.8 x 10*
3JB x I06






tlvnl

100

1000
10.000
6 It) Im3/yrl

73 x 10
7
7.7 x IO7
&JBx107









COMMENTS


Water availability may
severely limit flows
below levels calculated.









Water availability may
severely limit flows
below levels calculated.









Water availability may
severely limit flows
below levels calculated.









VD

-------
                                                           TABLE D-103
                                    SUMMARY OF METEORITE IMPACT FAILURE ELEMENT (CONTINUED)

MEDIUM

Shale







Dome Salt







5i
a HI
Is
p







p








NATURE
OF
MODEL

Annual occurrence







Annual occurrence
probability.








RELEASE
MODE

A. Lendeurface
B. GroundMter







A. Landawfece
B. GroundMeter








DRIVING
FORCE

A. Impact
B. Thermal connec-
tion added to
aquifer Inter-
connection
gradient.





A. Impact
B. Thermal convec*
tton added to
aquifer inter-
eormaciion
gmtitnt.







SOURCE
TERM

A. 0.1%rapo>itorY
inventory to
eurface.
B. 20% cumulative
Hater. Continued
leeching of broken
caniaten in fracture
or breceie zone
rounding canMan
<10%l.
A. ai«repoaitarv
•Memory to
aurfece.
1. 20»CMaetfve
leeched nudidei
M^ConttMcT
laachlni of broken
cenlalen in fracture
or breccia zone
(WMUandaur-
roundlai cankMn
now.

PARAMETERS

l« ESTIMATE
X - 4x10-"fVr
» - 0£kn>2
B - OJ






X - 4x10-"/yr
A - aSkn.2
* - OJ








andESTMATE
X • 4x10-"/yr
A - OJBkml
K - 10-*cm/eec
n - OJ






X • 4x10-'1ryr
A - OJBkmZ
K - 10-*cm/aac
n - 0.2







FLUID FLOW RATES FROM
REPOSITORY TO UPPER AQUIFER

1
100
1000
10,000
6 It) Im3/Vr)
1 J x 107
U.,107
6J x 106





tlyfe)
100
1000
ioxno

0 It) .107
24»107







COMMENTS

Weterenllabllrryiney
arMntv limit flam







•enerely limit f torn
bekM NHeb cakulaled
eetablitfiad by fracture
aoneatedgaofaah
dome.






ro

-------
    c
    0>
    £
   a.
    o
   cc
   *
    n
   tr
    o
uuu
000
100
10
1
p
i
•
i
\



i
\
V
^




k










^^
i 4 3 2 1 0
                                   Billions of Years Ago
            Note: Graph is for lunar cratering but it is representative for inner planets.
            Source:  Hartmann, W.K., Cratering in the Solar System. Scientific
                    American 236:84, January 1972.

FIGURE D-38   RELATIVE CRATER PRODUCTION RATE WITH SOLAR SYSTEM EVOLUTION
                                  298

-------
system,  when  interplanetary debris  was rapidly  being  removed  by  the
gravitational attraction of the planets*   The  rate  appears  to  have been
roughly  constant for the last  two billion years.
    Meteorite impacts  have been much  more common on  earth  than  may
generally be realized.   The surface geology of  the earth is  so  active
that even  very  large  craters  are  eroded  or buried  with time.    Table
D-104 lists all proven  or  probable impact craters  in  the United  States
with diameters  of at  least one kilometer.   Proven  structures  involve
meteorite remnants, and probable structures are determined from evidence
of  shock  metamorphism.  Many  other possible  impact craters  have also
been identified.       The  list of  impact  craters worldwide includes  a
number  over  100 km  in diameter.   Figure  D-39 is  a map of proven and
probable impact  craters.    The  highly  non-uniform  spatial  distribution
can be attributed to the varying geologic stability of different  regions
as  well as  to  differences in  the degree  to  which  areas  have  been
investigated for craters.
    The rate  of cratering, by  size, has been  studied  rather  carefully
because  comparison  of  this   rate with  actual  counts  of  detectable
features yields information on the history and evolution of a planet and
its  surface.   For craters  at  least 1  km  in diameter,  the  frequency of
occurrence appears to be roughly inversely proportional to the square of
the  diameter.    This   rule  has  both   an  empirical  and a  theoretical
justification/130'131)  Calibrating with  data from well studied  stable
regions of  the  earth,  a cratering  production  rate, $ ,  has  been
determined to be given by the equation

                       log1Q    =  -11.85 - 2 log1Q D.

Here D  is  crater diameter  in km and    <)>  is the number  of  craters per
square  kilometer per year at least as large as D.   In particular,  for
                        -12
D «  1 km,   =  1.4 x 10    .  This means  that for  a  land  surface of  7.8  x
   6   2
10   km  ,  the area of  the 48 coterminous  states,  there should be  about
1.1  x 10~   falls  per year of meteorites capable  of creating craters at
least 1 km in diameter.   The mean time between such occurrences  is the
reciprocal of this rate, or about 90,000 years. It should be noted  that
D»l  is  near  the lower  limit of  applicability of the given formula, but
                                       299

-------
                                 TABLE D-104
              PROVEN  OR PROBABLE LARGE METEORITE IMPACT CRATERS
 Location
Kentland, Indiana
Manson, Iowa
IN THE UNITED STATES
Diameter
(km)
rizona 1.2
:, Missouri 5.6
Missouri 6
Tennessee 3.8
iana 13
32
Kentucky 6
N. Dakota 9
, Ohio 6.4
, Texas 13
nnessee 14

Age


(millions of years)
0.025
320 +
300
360 +
300
70
300
200
300
100
200 +

80

20






100
Source:  Grieve, R.A.F. and P.B. Robertson.  The Terrestrial Cratering
Record. Icarus 38:212, 1979.
                              300

-------
Source:   Hughes, D.W. Earth's Cratering Rate. Nature 281:11. September 6,1979.
         Based on: Grieve, R.A.F. and P.B. Robertson. The Terrestrial Cratering
         Record.  Icarus 38:212,1979.

           FIGURE D-39   DISTRIBUTION OF IMPACT CRATERS
                                301

-------
for present purposes,  where the emphasis is on orders of magnitude,  the
formula suffices.
    The geometry of  craters is  relevant  in  determining  their  effect on  a
nuclear waste repository.   There  are  simple bowl-like craters, as well
as ones with  complex  structures,  including ringed  ridges  and peaks in
the interior and depressed  sections  along the boundaries.   Craters up to
about  4 km in diameter in  crystalline  rock and 2-3  km in  sedimentary
strata are usually simple,  while larger  ones have complex structures.   A
schematic  representation of a  simple crater, shown  in  Figure  D-40, forms
the basis  for the analysis  in  this section.  For a  repository about
500 m deep, as in the  generic  models,  a  crater diameter  of  at least 1 km
is a reasonable cutoff for  defining  meteorite events of  interest.

D-5.4.3   Meteorite  Impact  Failure Model

    The failure model concentrates on meteorites giving rise  to craters
of  diameter  1-2 km  because  the  frequency  of  meteorite  cratering
decreases  rapidly with increasing  size,  and the larger  size  impacts  are
even more  likely  to cause  widespread environmental  effects  of greater
importance than breaching  a waste repository.  The  target area has been
                 2
taken  to be 24 km.,  corresponding to  the repository area  (2  km x 4  km)
and a  one-kilometer wide buffer  zone around  it.   The failure element
consists of the center of the  crater lying  within this area.  Using  the
                                    —12         2
production  rate  of    <(>  =  1.4  x  10    per km  per yr  for  craters of
diameters  at least 1 km, the annual  failure rate is  given by

                           A = 1.4 x 10~12  x 24

                                     —11
                            = 3 x 10     events  per  year.

This rate  is assumed to be  independent of the host  rock  formation, since
variations in  geophysical properties are not  significant  for   the
purposes of these rough  calculations.   Moreover,  there are  no distinct
first  and  second estimates  in  this  case,  since this is a  statistically
derived estimate and is independent  of location.
                                        302

-------
   D = Crater Diameter
Source: Adapted from Innes, M.J.S. The Use of Gravity Methods to Study the Underground
       Structure and Impact Energy of Meteorite Craters. J. Geophysical Research,
       66 (7), July 1971.
        FIGURE D-40    SIMPLIFIED CRATER GEOMETRY
                                303

-------
D-5.4.4  Meteorite  Impact  Release Model

    A  meteorite impact  crater formed  on the  repository  site  would be
expected  to  be smaller  than  the  repository,  since  crater  sizes  are
biased toward  the  lower end of the  range  under  consideration.  A crater
of  1-km diameter would  have a cross-sectional area at the  surface of 0.8
km2.
    The  breccia zone  would  not   even  reach  500  m in  depth, and  the
fracture  zone at  that  depth would  be very  small.   (See  Figure  D-40.)
For a  crater  with  a diameter of  2 km,  the breccia  zone  would intersect
the repository.   Based on  the  simple geometry  in  Figure D-40,  the area
                                        2
of  intersection would be roughly  0.8 km ,  corresponding to a circle 1 km
                                                                       2
in diameter.   For modeling  purposes, this  area of  intersection, 0.8 km ,
has  been  taken  as  a  conservative estimate  of   the  portion  of  the
repository  directly affected  by  the meteorite  event.   It has  further
been assumed  that  there is sufficient  fracturing  or brecciation down to
the repository depth for direct releases  to  the  surface to occur.
    Because  of the higher  probability  of meteorites  at  the  low  end of
the size  scale being  considered,  the expected direct  release  to the  air
and land  surface is probably very small.   Although there does not appear
to be an analytical or  empirical  model  for predicting this event,  it  has
been assumed  that  1%  of the wastes  in  the affected zone  (i.e.,  0.1% of
the repository inventory)  would  be  released to  the  land  surface.  The
remaining wastes are subject  to enhanced  leaching  by groundwater because
of  permeability  increases  in the  surrounding  rock.   The  hydrologic
parameters assumed  for  this  pathway  are:
                       K =  10    cm/sec
                        n =  0.2
                                                  2
and the cross-sectional area is again  A = 0.8 km •  Flows through this
zone can be calculated  analogously to Section D-5.1.4 on fault pathways,
and in other  sections.   In particular, Darcy's  Law is  applied  with  the
hydraulic gradients given  in  Table  D-105. The  corresponding  fluid flow
rates  are given in Table D-106.   These would very  likely be restricted
well below the  calculated values  because  of  limitations on the amount of
water present.
                              304

-------
                                TABLE D-105
        EFFECTIVE HYDRAULIC GRADIENT IN EXTENDED VERTICAL PATHWAYS
                   100 years
1000 years
10.000 years
Bedded Salt
  First Estimate      0.13
  Second Estimate     0.62
   0.11
   0.60
   0.04
   0.53
Granite
  First Estimate      0.11
  Second Estimate     0.11
   0.07
   0.07
   0.03
   0.03
Basalt
  First Estimate      0.14
  Second Estimate     0.63
   0.12
   0.61
   0.05
   0.54
  First Estimate      0.14
  Second Estimate     0.63
   0.12
   0.61
   0.05
   0.54
Dome Salt
  First Estimate      0.13
  Second Estimate     0.32
   0.08
   0.27
   0.04
   0.23
 Years after repository closure.
                               305

-------
                                 TABLE D-106
      VOLUMETRIC FLOW RATES THROUGH METEORITE INDUCED PERMEABLE ZONE
                                      Volumetric Flow Q
                                          (m /yr)
Bedded Salt
Granite
Basalt
Shale
                       100 years
                     1000  years
                     10.000 years
  First Estimate
  Second Estimate
1.6 x 10'
7.8 x 10'
1.4 x 10'
7.6 x 10'
5.0 x 10C
6.7 x 10y
  First Estimate
  Second Estimate
1.4 x 10
1.4 x 10'
8.8 x 10
8.8 x 106
3.8 x 10
3.8 x 106
  First Estimate
  Second Estimate
1.8 x 10'
7.9 x 10'
1.5 x 10'
7.7 x 10'
6.3 x 10"
6.8 x 10y
  First Estimate
  Second Estimate
1.8 x 10
7.9 x 10'
1.5 x 10
7.7 x 10'
6.3 x 10l
6.8 x 107
Dome Salt

  First Estimate
  Second Estimate
1.6 x 10'
4.0 x 10'
1.0 x 10'
3.4 x 10'
5.0 x 10
2.9 x 107
                                                6
 Years after repository closure.
                                   306

-------
    The source term  for  the  groundwater  release has several components.
First,  radionuclides  that may  have  leached out  into any  water  in the
repository before  the  meteorite event would be able to move  with that
water  up   through  the  permeable  pathway.    Second,  canisters  in  the
affected zone of the repository would  probably  be broken up and subject
to direct  leaching after  the  event.   Third,  canisters in other portions
of  the  repository  could  also   continue   to   contribute  leached
radionuclides to the water in the repository.  These radionuclides could
gradually  migrate  through  the  backfilled  tunnels  and drifts  to  the
actual  release pathway.   The  third  effect  is   expected to  be  the  least
important  by  far,  and  so it has  not been  modeled.    To  account  in  a
conservative  and   simple  way  for the  other source  terms,  it  can  be
assumed  that  the  cumulative  leached  radionuclides  from  20%  of  the
repository are released into  the  pathway  at  the time of the breach, and
that thereafter 20%  of  the  repository is  subject  to continuous leaching
in the groundwater  flows calculated.

D-5.4.5  Literature Discussion

    Various estimates  for the  likelihood of  a  meteorite breaching  the
                                                              (26 ^
repository are found in the literature.  The Swedish KBS study^    cites
a rate
                             —13       2
                       X = 10    per km  per year
for craters at  least  100 meters deep, and  on  this  basis  dismisses this
                                      (12)
failure element.  The NRC/Sandia study     uses the rate

                                 -13
                       X = 2 x 10    per repository per year

                                2
for impacts on  an area  of  8 km ,  a  value attributed  to  Claiborne  and
Gera.     These   latter  authors  assume a  reference  crater  at  least  2
kilometers in diameter-      The University of New  Mexico  study     for
the EPA suggested a rate

                                 -13
                       X = 1 x 10    per repository per year

           2
for a  10-km  repository.  A source term for consequence calculations was
                                307

-------
given in this  last  study as 5% of the  repository inventory to  the  air
and 5% to the land surface.
D-5.5  BRECCIA. PIPES

D-5.5.1  Summary

    Deep dissolution processes in bedded  salt deposits can lead  to  the
development  of brine-filled  cavities  on  the  lower  sides  of  the
formations.  These cavities, after reaching  a certain critical size,  can
cause  the  collapse  of  the overlying  rock  and  the  propagation of a
                                                    (22  132 133)
chimney of broken rock up to or toward  the  surface.    '    '       Such a
chimney  structure  is called a  breccia pipe.   It provides a  permeable
pathway through which groundwater can  flow  and  leach radionuclides  from
the  waste canisters.   The model  described  here  assumes that  breccia
pipes develop at a constant annual rate, except that none can  breach the
repository for the first 500 years after sealing because their incipient
development would be detected during  site investigations.  Fluid  flows
are  assumed  to be  upward,  with release  of radionuclides to  the  upper
aquifer.    Significant  dissolution of  the  salt  formation  around  the
breccia  pipe  is   assumed  not   to   occur,  based   on  qualitative
considerations of water  availability and  degree of  salt saturation,  but
healing of  the  column  by cementation and recrystallization is  also  not
assumed.  A summary of the analysis is given in Table D-107.

D-5.5.2  Background

    Salt  is  a very soluble  mineral,  and  every  salt  deposit  shows
geologic  or  topographic  features  associated  with  various  dissolution
phenomena.  The Delaware Basin in New Mexico contains massive salt beds,
for  example,  but  it has been estimated that  this  represents  only about
                                              (133)
half  of  the salt  originally deposited  there.       In  fact,  essentially
all  the salt  in  the Rustler Formation  in  that basin  has been leached
out.  Saline  groundwater,  springs,  or  streams associated with most salt
basins are further  indications of continuing dissolution.
                                   308

-------
                                                            TABLE D-1O7

                                             SUMMARY OF BRECCIA PIPE FAILURE ELEMENT
MEDIUM
Bedded Seta
Gtenne
BeBlI
SMe
OomeSelt
PHCWABILIITIC (PI
DETERMINISTIC (Ol
f




NATURE
Of
MODEL
Annual occurrence
probebilltv.
N.A.
N.A.
N_A.
N.A.
RELEASE
MODE
Upeereqiiner




DRIVING
FORCE
ThermeUv induced
convection end
equifef imerconnec-
lion.




SOURCE
TERM
Ceniners in brecct*
pipe ettumed lo be
broken end subject
to leeching.




PARAMETERS
let ESTIMATE
* - Olort<500vTi
X . l(T«/vt for
t>600»r.
K - IO-2 cm/eec
1-0-2
A - 3 » 10* m'




2ml ESTIMATE
X . OlortSOOyn
K - 10-2 cnVsec
n • OJ
A • 3 » IO4 m^




FLUID FLOW RATES FROM
REPOSITORY TO UTTER AQUIFER
let ESTIMATE
tlynJ
600
1000
10.000
6 Im3(y»l
6« 107
S» 107
2 i 107




2nd ESTIMATE
t
-------
    Because salt  deposits  can be massive  (tens to  hundreds  of meters
thick,  with  some  interbeds)  and  nearby groundwater  flows may be
relatively low,  dissolution may be an extremely slow process.  In fact,
because  salt  is  practically  impermeable   to  the  movement  of  water,
dissolution generally  takes place only  at  the  boundaries of  the
deposits.  Slow average rates of dissolution would not lead to breaches
of  the  repository  for  tens  or  hundreds   of  millions  of years.
However,  there  are  certain localized dissolution  features that result
from much higher than average rates of salt removal. These  features are
generally caused by  the collapse  of  the  overlying rocks into cavities or
voids  in the  soluble  rocks  below.  Depending  on  the  size  and  other
characteristics  of  these  collapse  structures,  they  are  known by  a
variety of names: kettles,  sinks, swales, collapse chimneys, and breccia
pipes. The last  two  terms  are used  to denote structures that originate
near  the bottom of  soluble  strata and  extend  toward  the surface, being
somewhat taller than they are  wide and  filled with rubble  (breccia) from
the overlying  rock.  Although  the term  "breccia  pipe"  is  also  used to
describe  a  distinct geologic structure of  volcanic  origin, some early
investigators  of the  dissolution  phenomenon  have  used  the  term  to
indicate  collapse features  with  considerable  vertical  extent, and this
meaning  is adopted here.
    Physical  Characteristics.   Breccia  pipes are roughly  circular
features  from  a  few  tens  of  meters  to  more  than 0.5  kilometer  in
                                                            f 132)
diameter, with  an  average  depth three  times  the diameter.        The
upper portions  are  filled with broken rock  ranging from small granulars
to blocks  a  meter or more  across.  (See Figure D-41.)   These  features
have  usually  been recognized  only when  they  have  reached the  surface,
and limited tests have  suggested that the  pipes bottom  near the lower
margin of the salt strata.        Only a  few not  reaching the surface are
reported  in  the literature,  although  it is possible  that many remain
undiscovered.
    Sometimes,  breccia  pipes  are seen  as  domes or  topographic highs,
contrary  to  the general  expectation  for  a  collapse  feature.  One
hypothesis suggested to  account  for this structure  is that dissolution
of the surrounding  salt  has lowered  the  elevation of the  area below the
more  resistant  brecciated column. This process  is enhanced  by anhydrite
                                     310

-------
       MAGENTATS:
       DISTANCE or
           MAGENTA
            COLLAPSE 1 •?
    HORIZON 0»  SU«ttCE
     rciv i
          H III BLANKET «*tCCi*.'.*AV4V*

            AMI            MECCIA
 SURFACE  EXPRESSION


 COLLAPSED
   OUTLIER
                                                        LEVEL OF PIPE IN
                                                          MISS  CHEM CO  MINE
(A = Anhydrite,  H = Halite)
           BELL CANYON
 Source: Adapted from Anderson, R.Y. Report to Sandia Laboratories on Deep Dissolution
         of Salt, Northern Delaware Basin, New Mexico, April 1978.


FIGURE D-41   CONCEPTUAL DRAWING OF BRECCIA PIPE IN DELAWARE BASIN
                                 311

-------
in the breccia  reacting  with available water and  catalyzed  by bacterial
or organic  processes to  form calcite, which  may  be  more  resistant  to
     i  ,   (133,135)
dissolution.     '
    Hvdrologic  properties.   Relatively  few measurements  have been
performed on the breccia  filling  the pipes  to  ascertain their hydrologic
properties. However,  existing data indicate that  very broad  spectra  of
porosities  and  permeabilities are  possible.  Pipes within  the  Carlsbad
mining district  in New Mexico have  shown properties ranging  from  those
of  the  intact   evaporite  section  to   those  of  typical  gravels,  with
hydraulic conductivities  from 10    to 10   cm/sec and porosities from
20%  to  1%.(104'133)    At  the   time   of  formation,   higher hydraulic
                                                ~3                (132}
conductivities are expected,  in  the range of 10    to 1.0 cm/sec.
    Mechanisms of dissolution.   When salt  or  other soluble material  is
attacked by a solvent, the shape  of the dissolved  void  and  the direction
in which dissolution  progresses  depend  upon a  number of conditions. For
example, water in  contact with the upper  surface of a  salt mass  tends  to
spread laterally.  In  the  case of water reaching the lower boundary of a
salt  mass,  dissolution is upward,  forming a  vertical cavity,  provided
relatively  fresh water  is supplied and brine  is  removed at  the  bottom.
These phenomena  can  be  explained in terms of brine  density.  (See Figure
D-42.) Water  in contact with  salt dissolves  the  salt until it nears
saturation. The  saturated  brine  is  denser than undersaturated water and
tends to  sink.   If  it  is  at  the  upper  salt surface,  the  brine  forms a
stratified  layer at the  interface,  inhibiting further dissolution.  On
the other hand,  water dissolving the salt  from below  becomes saturated
with salt and  sinks  away, to be  replaced with fresher water, promoting
further dissolution.  This latter situation  sets  a convection cell into
motion (driven  by  density differences) ,  and the  rate  of convection can
be  expected to  increase  as  the water  density  differences  are  more
pronounced.  Initially, the  cavity thus formed  at  the  bottom of  the salt
is not  large  and  is able to support  itself.   However, if  dissolution
continues,  the  cavity  may   reach  a  critical size,   become  unable   to
support the overburden, and  collapse.
    Implicit in  this  explanation for  a dissolution  mechanism developing
a vertical cavity is the need for sufficient hydraulic  head  to raise the
underlying  water to  the  salt layer.  Furthermore,  fresh  water  must  be
                              312

-------
(a)  Dissolution from above.
    Denser brine accumulates
    and spreads out along top
    of salt formation.
    Saturation limits further
    dissolution.
Water Saturated Rock
         Brine Zone
                                               Salt Bed
(b)  Dissolution from below.
    Density difference
    between brine and fresh
    water leads to convection
    cell and transport of salt
    away by lower aquifer.
                                                Salt Bed
                             •V'.•".'•;./. ©•'-.-.
                                   *  *      »\  s''
                                                      Fracture Pathway to Lower Aquifier
  FIGURE D-42  CHARACTERISTICS OF DISSOLUTION FROM ABOVE AND BELOW SALT FORMATION
                                            313

-------
supplied and  saturated  brine removed  if  dissolution is  to  continue at
any appreciable  rate. Thus,  an  impermeable  barrier separating the water
from the salt could effectively prevent cavity growth or propagation.
    Detection of Breccia Pipes.   Interest  in  detecting  and  surveying
breccia  pipes  and  similar  deep  dissolution  features  is a  relatively
recent  development.   In general, the  earlier discussions of detection
methods  (see  Sections  D-5.2 and D-5.1)  apply to  breccia pipes.   The
generally  small  scale   of these  features,  however,  limits   the
effectiveness  of  techniques such  as   gravitational,  resistivity,  and
magnetic  surveys,  except  when  such a  feature is  suspected.   Seismic
investigations  are  better  able  to  detect  collapse structures,
particularly when the breccia or other filling material is characterized
by a different  seismic  velocity than the surrounding rock,  or when  the
collapse  has  disrupted  a  distinctive  marker  bed.   The difficulties
presented by seismic work  are typically related to  the  area  that can be
investigated within  an actual  exploration program,  and  to  resolution
loss with  depth,  which may limit   interpretation  of seismic records.
This is particularly true when attempting  to detect breccia pipes in  the
                           (22)
early stages of formation.
    Finding  breccia   pipes  within  a  large  area   may  most  easily  be
accomplished  through  the  use  of  aerial  or  Landsat  photographs.
Domes,  sinks,  and  other topographic relief can be  located and selected
for further  investigation  on the ground.   A number of  pipes have been
detected in  this way,  and  sites for more  intensive seismic  exploration
have been  selected.        The features seen on photographs  are  not  all
collapse  structures,  and  not  all  collapse structures  are  deep
dissolution  features.   Nevertheless,  many  apparent dissolution
depressions suggest a location deserving further study.
    Of  all the  detection methods discussed previously,  radar  and
drilling may be the most precise for confirming the presence  of  breccia
pipes.         Since radar  works well  in  salt  and  could  be used from
exploratory  shafts  and  tunnels,  it is  likely that  scanning the rock
below a repository  site  could detect any dissolution cavity in its  early
stages.  The reported  effective range of radar is  in excess  of the salt
thickness  in  the generic  repository model.   Proponents of   radar have
suggested  that  targets  as  small as  a drill  pipe  can  be detected at
                               314

-------
hundreds  of meters;  therefore, it  is  likely that  natural  brine-filled
cavities  of a  similar  size  could be discovered at a lesser range.
    Drilling,  while  not  an  efficient  method   for detecting  collapse
structures, may  sometimes  be  necessary  to  confirm the  indications  of
radar or  other detection methods.   Drilling into a selected target would
confirm the existence of a  breccia pipe and  could be used to  test the
Structural and hydrologic conditions of the feature.

D-5.5.3  Breccia Pipe Failure Model

    The  failure model  for  a  breccia pipe  consists  of  estimates  of
hydrologic properties  and probabilities  of  occurrence.   As  noted
earlier,  bedded  salt  is the only  medium to which this failure element
applies.
    Probability of occurrence.    The  probability  of   occurrence   of  a
breccia  pipe  on  the repository site is specified  in terms  of a  constant
 annual rate,  A,  after an initial  period  of 500  years  during  which the
 probability is  0.   An  initial period of  zero  probability results from
 the  fact  that it  takes  some time  for  a  critical cavity to develop, and
 if  one were   already  at a  significant stage of growth at  the  time the
 repository was  sealed,  then it would  have been detected by geophysical
 techniques, such  as  radar,  operating  from  the  mine.   The  time  required
                                                                    (132)
 for  critical  cavity growth  is probably much larger than  500 years,
 but   this  conservative  value  has  been  adopted  to  account   for the
 probability of waste  (heat)  induced  acceleration of dissolutioning.  The
 values adopted are as follows:
                           _Q
 First Estimate:      A  = 10    events/year/repository
                         for  t  >.  500 years
 Second Estimate:      *  = 10    events/year/repository
                         for  t  L  500 years
 The  second estimate  will be discussed first because the first  estimate
 was  derived   from  it.    It  comes   from previous studies    '     and has
 been  normalized  here  to account  for a different repository area.  The
 method   used  to  derive this  estimate  can be  briefly  summarized  as
 follows.   Information  on  areal densities of  possible breccia  pipes  in
 several  evaporite  basins was collected from the  literature and  from the
                                         315

-------
study  of  aerial  photographs.   The volumetric rate  of salt  removal  via
deep  dissolution was  then  estimated, based  on the  time period  during
which  this dissolution has  been occuring.   By comparing  this  rate with
estimates of  critical cavity size  necessary  for chimney  initiation  and
propagation  at  least  to an  upper aquifer,  estimates  of  the rate  of
formation were calculated.   These numbers are  comparable  to  estimates
developed in other more empirical  surveys, based simply on the  number of
features,   basin    area,    and    time   period    of    dissolution
          (132 133 135)
processes.     '   '       Field  investigation  to determine  whether  the
features  were  deep seated was  generally  not  carried  out.   While some
shallow features  are  surely  included  in  the  counts,  there  are  probably
also deep features for which surficial indication was  either not present
or not recognized.  In spite  of these limitations  and  sources  of  error,
the  resulting  rate  still  appears  to be  a  reasonable  "best  estimate"
based on available data.  This  number was  adopted as  the  second  estimate
because it is  assumed  that the  avoidance  of  features  that could lead  to
deep  dissolution will have  high priority  in  the  repository site
selection process,  and therefore  a chosen  site should  be  at  least  as
good as a randomly chosen one.  (This would be the case,  for example,  if
the  potential  for  deep  dissolution  is   difficult  to  estimate  for a
particular  site.)   The  first  estimate  assumes   that  the structures
underlying a potential repository  formation  are simple and  well mapped,
and that  any underlying aquifers are  heavily  saturated with salt, slow
moving, at relatively  low  piezometric head, and well isolated  from  the
host salt formation in the vicinity of the repository.   It  is believed
that  these  conditions can  be verified   with  sufficient  certainty  to
reduce the occurrence  rate  by  two  orders of magnitude,  which  leads  to
the first estimate cited above.
    Hydrologic processes.  The  following  parameters  have been chosen  as
representative  of conditions  in a newly formed breccia pipe
             _2
     K  =  10   cm/sec          (hydraulic conductivity)
     n  -  0.2                   (effective porosity)
                 4  2
     A  -  3 x 10  m            (cross-sectional area)
The hydraulic  conductivity is the  value  recommended  in Reference  11  and
is in  the  range  given in Reference 132.  In  fact, breccia pipes have a
tendency  to  heal over  time,  due  to  recrystallization  of  salt   and
                               316

-------
cementation  of  the broken pieces  of rock.   Since dissolution  is  also
possible,  depending  on the available groundwater, healing  has  not  been
assumed  for  the  present   model.    The  values   of  porosity   and
cross-sectional area are also consistent with those in the literature.

D-5.5.4 Breccia Pipe Release Model

    If  a  breccia pipe were  to  develop from underneath  the repository.
eventually part  of the repository  would  either slump or fall  into the
chimney-like structure.   Physical  damage to the waste  package  would  be
expected  in  this  process,  since  the  rock  itself  is generally  rather
thoroughly broken.   At  this  point  the canisters would  be subject  to
leaching by  groundwater  circulating from  and  back to an aquifer below
the repository.  The present model does not treat separately releases  to
the lower  aquifer.  Rather,  since  chimney  growth propagates rapidly,  it
is  assumed that  a connection  is  established  between  upper and  lower
aquifers,  and   that  water  flows  upward,   driven by both  an  aquifer
interconnection  gradient  and  thermal  buoyancy.   The  counterbalancing
effect  of  increased   density   from  salt  dissolution  is  difficult  to
quantify;  in  the  interest  of  bounding   the  flows,  it  has  not  been
included.  Significant additional  dissolution  could in  fact lead  to the
leaching  of  a  significant  portion  of  the  salt formation,  and  it  is
probable that some sections of salt deposits that are  known  to have  been
removed  did  so  by this  process.    Nevertheless,  field observation  of
recrystallized  and  cemented breccia  pipes  through  salt formations
suggests that in  a carefully chosen site, this  would be  most  unlikely.
As has been mentioned in the previous section,  no healing of the breccia
pipe is assumed in the model.
    Upward  flows  are  calculated by Darcy's law  using the  parameters
given in the previous section and the hydraulic gradients given in Table
D-108.  As in other sections, the version of Darcy's  law here includes a
factor  of  5 to  account  for  the lower viscosity  of  water  at  elevated
temperatures.    As  was   discussed  in  Section D-5.1.4,   even  as  the
temperatures in  the repository decrease  after the   thermal  peak,  this
factor does  not  appear to introduce excessive  conservatism.   Estimated
volumetric  flow  rates  and fluid  velocities  are  summarized in  Tables
                               317

-------
                                   TABLE D-108

            EFFECTIVE VERTICAL HYDRAULIC  GRADIENT IN A BRECCIA PIPE
               FROM THERMAL BUOYANCY AND  AQUIFER INTERCONNECTION
                            (BEDDED SALT  REPOSITORY)

                                     Hydraulic Gradient (i)
                      500 years*
1000 years
10.000 years
Thermal Buoyancy
  First Estimate        0.11
  Second Estimate       0.11
Aquifer
Interconnection
  First Estimate        0.01
  Second Estimate       0.50
Total
  First Estimate        0.12
  Second Estimate       0.61
  0.10
  0.10
  0.01
  0.50

  0.11
  0.60
  0.03
  0.03
  0.01
  0.50

  0.04
  0.53
 Years after repository closure.

Source:  First effect is from Appendix D-VI, interpolated  to give values at
500 years.  Second effect is from Chapter D-2.0 of this Report.
                              318

-------
D-109 and D-110, respectively.  It is  important  to note  that,  as  in the
case  of  faults,   water  limitations  from  the  lower  aquifer  may
significantly reduce  these  flows.  Therefore,  in a real  site,  aquifer
capability may  be   the  limiting  factor, although  it  is not simply  the
lower aquifer closest to the repository that needs to be considered.
    The  canisters   in  the   breccia  pipe   include  about  0.4%  of  the
repository inventory, based  on  the cross-sectional area given earlier,
and  these   are  subject  to  direct   leaching.    Furthermore,   any
radionuclides that  had  previously leached  out  of  the  waste  packages
would  also   be  washed  out   with  the  groundwater  flowing  through  the
brecciated zone.  It is  assumed that an area with  twice  the  diameter of
the  pipe  itself is affected by  this  process,  so  that the cumulative
leached  inventory  for  1.6%  of  the canisters  should be  assumed  to  be
released to groundwater upon the occurrence of  the failure  element.

D-5.5.5  Literature Discussion

One model used in the literature has already been referred  to in Section
D-5.5.3.  While  there has been  considerable recent geologic  Interest in
learning more about the breccia pipe phenomenon, it does  not  appear that
other  models  for  their occurrence  or  consequences  have  yet  been
published.
D-5.6 OTHER NATURAL EVENTS AND PROCESSES

D-5.6.1  Introduction

    In addition  to  the natural events and processes modeled  earlier  as
specific failure elements, other processes could have some impact  on the
repository in a time frame much  longer  than  the 10,000 year  period  used
as the principal focus for this study.  No location on earth  is  expected
to be completely stable over very  long  periods  (hundreds  of  millions  of
years or more).  Parts of  the  Appalachian Mountains  were  once low-lying
swamps, not unlike the Florida Everglades, and  the Rocky  Mountains  also
arose  from what  must have  been  warm  shallow seas.    Not  only  have
                            319

-------
                                  TABLE  D-109



                  VOLUMETRIC FLOW RATES  THROUGH  A BRECCIA PIPE

                             (BEDDED  SALT REPOSITORY)





                                  Volumetric Flow (Q)



                                       (m3/yr)



                      500 years            1000 years           10.000 years



First Estiamte        6 x 107              5 x 107              2 x 107



Second Estimate       3 x 108              3 x 108              3 x 108
*
 Years after repository closure.
                            320

-------
                                  TABLE D-110

                    FLUID VELOCITIES THROUGH A BRECCIA PIPE
                             (BEDDED SALT REPOSITORY)
First Estimate
Second Estimate
                      500 years
1 x 10
5 x 10
                                   Velocity  (v)
                                       (m/yr)
                    1000 years
9 x 10
5 x 10
10.000 years

3 x 103

5 x 10A
 Years after repository closure.
                              321

-------
tectonic  forces raised  such  mountains, but.  other forces have worn them
down.   The  ancient Appalachians  once  had  peaks  reaching 4000 meters,
roughly twice  as  high as at  present.   Some natural processes  occur more
rapidly  than the growth  and  decay of  mountains;  for  example, glaciers
can  come  and go in a  cycle  of tens  of  thousands  of  years.  The purpose
of  this   section  is to  survey a  range of natural  events and processes
that  have not  been modeled  in detail  in this  study  and  to  give some
indication of  the  rates  at  which they occur.

D-5.6.2   Erosion

    The most prevalent natural  process on land  is  erosion.   Gravity  is
the  driving  force,  and  wind,  water,  and  ice provide  the vehicles for
rapid movement  of  rock and  soil.
    Fluvial  erosion (erosion by water)  is  the most important  process  at
work.  No  part  of  the United  States  is completely  devoid of rainfall.
Rain  striking  bare  earth  dislodges  soil  fragments  and  suspends them
momentarily, moving them downhill with  the  general flow of water.  When
water is  confined  to a stream  or  river channel,  its  greater volume and
velocity  can move more  and  larger fragments  greater  distances.   One  of
the most  dramatic  examples  of fluvial erosion is  the  Grand  Canyon  of the
Colorado  River,  which is roughly  20 kilometers  wide  and  1.6  kilometers
deep.  It was  incised  during  the last  two  to ten million years, with  an
                                          -4               -4
average  rate  of downcutting  of  8  x  10    to  1.6   x   10   meters per
year.   '      Although  higher rates  of erosion  have been reported for
brief  periods  for  unconsolidated  sediments,  this  erosion  rate  of the
Colorado  River  is  the  highest for  any major river system in the country,
as indicated  in Figure D-43.   At  its  sustained rate, the  Colorado River
would require  more  than  500,000 years  to  strip away  the  overburden from
a  repository   located  directly  below the   canyon.     Since  long-term
drainage patterns  are  fairly predictable,  having remained  largely
unchanged for millions of years,  it  is unlikely  that  river  erosion would
be a serious  concern for a repository  even  over a time  span longer than
that considered in  this  report.
    Glaciers,  which  are  moving  masses  of  ice,  can  remove  great
quantities of  rock and  soil  in a  relatively  short  time.  A glacier can
                               322

-------
                              Rates of Denudation (cm/1000 yrs.)
Source: Gilluly,J., A.C. Waters, and A.O. Woodford. Principles of Geology. 3rd edition.
       W.H. Freeman and Co., San Francisco, 1968.

FIGURE D-43   AVERAGE RATE OF DENUDATION OF MAJOR DRAINAGE AREAS IN THE U.S.
                                    323

-------
usually be  classified  as  alpine or continental, depending  on whether it
is confined  to  a mountain valley  or  covers a broader  region.   Glaciers
form  when  snowfall  exceeds  melting  and  evaporation,  causing an
accumulation of  ice.   Eventually,  the  ice becomes thick enough  for the
bottom layers to move  plastically under the weight of  the  overlying ice
and snow.   The  ice  freezes around rock and  soil,  breaking  them free and
grinding  them  against  the  bedrock.    These  combined  mechanisms  of
breaking and  grinding  make a  glacier an extremely aggressive  erosional
force.  Also, because  a glacier is  a  relatively  solid  mass, it  can  alter
the course  of  streams and rivers  by diverting or damming  them.   The
scablands of Washington and Idaho were formed when continental  glaciers
diverted the Columbia  River many  times during cycles of  ice  advance and
retreat.  The enormous weight of  glaciers has apparently depressed  some
regions  up  to  several   hundred   meters,  and  rebound  has   also  been
             1 Q £
detected.   '   '        It   is  possible  that  crustal  adjustments  for
depression and rebound  could cause fracturing or  renewed  movement along
existing faults .
    The  alpine  glaciers  that carved  California's  Yoseraite Valley and
many  of  the  valleys  in the  Cascade Range  and  the Northern  Rockies,
gouging  the  land  to depths  of hundreds  of meters,  did so  during their
relatively  short  (roughly  10,000-year)   lives.    The duration of these
valley glaciers is  not  well determined,  since there  was  apparently more
than  one episode  of  glaciation,  nor  is  the erosional  depth  exactly
measured,  since  the  original  topography   is  not  precisely known.
However, a rate of  erosion  can be  estimated  from  the volume of  material
carried  off  by  meltwater  streams.    One  such   estimate  for  the Muir
Glacier  in  Alaska suggests  that  the average  rate of erosion may be as
high  as  1.9  cm/year.        At this  rate,  500 meters  of  rock  could be
removed  in  25,000 years.  A  study of two  Icelandic  glaciers determined
                                                                (137 139)
that  their  average  erosional  rates  were  0.06  and   0.6  cm/yr.     '
Between  6  and 60 meters  of  cover  could  be removed  by  such  glaciers
during a 10,000-year ice age.  Thus, a repository buried  directly under
a valley prone to  glaciation could be seriously Jeopardized within tens
of thousands of years  after the  onset of  moving  ice.  While such times
are not  much more  than  the time  frame chosen for  this study, the hazard
                             324

-------
can be eliminated by  ensuring  that  a site is selected where there  is  no
expectation of alpine glaciation.
    Continental  glaciers,  such  as  those  that  covered   the  northern
portions of the  United  States  several times during the Pleistocene  age,
account for more widespread erosion  than  do  valley  glaciers, but erosion
depths  are harder  to estimate.   It  is  likely that  their movement  is
slower than valley glaciers'  since  the  driving force would depend  upon
differences in ice  thickness between the  glacier center and edge, rather
than  the  gradient  of  a valley  floor.    Rates  of   ice  advance are  more
difficult  to  establish  than   ice   retreat  since  advancing  ice often
obliterates  evidence  from which dates can  be determined.   Erosion  by
continental glaciers  is  non-uniform and  varies widely, but rates are  in
general much less than for valley glaciers.
    In addition  to its  erosional  power,  a  glacier is expected to  have
effects reaching far  beyond the limits  of the ice  itself.  For  example,
the increased  precipitation  often associated with  periods of  glaciation
and  the  runoff  of glacial  meltwater can  increase  fluvial  erosion  in
advance of  the ice.  Furthermore,  the  presence of ice and accompanying
water will affect both surface  and  groundwater  hydrology in a  variety  of
ways: diverting  rivers,  recharging  aquifers, and forming lakes.
    The  timing  of the  next  glacial  epoch is  speculative,   at best.
However,  the  frequency  of  major glacial advances  in  the  last  several
million  years   suggests   that   another  continental  glacier  is  a   real
possibility in  less than  100,000  years,  the average  cycle time of ice
ages during the  last 850,000 years.       Thus,  effects of a glacier  upon
a repository could  appear in a  geologically short  time.   Nevertheless,
locating a  repository some distance  from the  boundaries  of Pleistocene
and  recent glaciation,  shown  in   Figure D-44, could  provide  adequate
long-term  control  against disruption  of  a   repository   from  glacial
processes, if necessary.
    The wind   can  transport fine   sands  and  silts long  distances and
against the  general  trend  of   fluvial  erosion.  However,  the depth  to
which  the  wind  can  erode  is  limited,  especially  compared  with the
erosional power  of  water or ice.   From the standpoint of a repository,
aeolian (wind)  erosion  is of  little consequence,   as  it  is essentially
unable to  remove the  overburden.    The  two more  likely  effects of the
                              325

-------
to
                                                                                                                        GLACIATED AREAS
                                                                                                                        GLACIAL LAKES
                                                                                 MIUS
                                                                            0  160  321  482
                                                                               KIIUMUtRS
                                                                                                      |— t
                                        FIGURE D-44  GLACIATED AREAS OF THE COTERMINOUS UNITED STATES
                                                       AFFECTED DURING PLEISTOCENE GLACIATION

-------
wind are  stripping  of vegetation at the  site,  which would increase  its
susceptability to fluvial  erosion,  and obliteration of site markers  and
survey  points,  which  would increase  the  chances  of  the repository's
existence and location being forgotten.

D-5.6.3  Sedimentation

    Sedimentation is  the complement of erosion.  Material removed from
one place is deposited in another.  Final deposition is typically in  the
ocean, but  there  may be many  intermediate  depositional  stages,  such as
stream beds, terraces, and sand dunes.
    The  effect  of  sedimentation  on  a   repository  is   likely  to  be
positive.  That is, any process that thickens the overburden and further
Increases the distance from the repository  to the biosphere is likely to
aid the isolation of  the wastes.   However, some detrimental effects  are
possible.   Not  only  can extensive deposition  obliterate  site markers,
but the added weight of  thick sediments can, by increasing the stress on
the buried  rocks,  induce  fracturing   or,  in the  case of  less  brittle
rocks, plastic  deformation.   Since it is  expected  that  the  repository
will  be  backfilled,  the   damage  that  could  result  from  an  extreme
increase  in vertical  stress  is  expected  to be  slight,   and  a  general
compaction of the repository and  its  contents  is  most likely.   Possible
displacement  of  the  repository  through  differential  sedimentation is
discussed in Section D-5.6.8.

D-5.6.4  Tectonism

    Mountain  building and  the formation  of continents,  which  involve
many related  processes under the general  description  of  tectonism,  may
alter overburden  thickness,  ground and surface water  patterns,  erosion
rates,  and  permeabilities.   Examples  of  tectonic  phenomena  include
faulting, folding,  tilting, uplift,  and  subsidence.   These  structural
changes in  the  earth's  crust  are  explained, for the  most part,  by  two
compatible theories: continental drift and  isostasy.   Continental drift,
or  plate  tectonic  theory,  explains  the  forces   necessary  to  cause
structural  changes  on  the basis  of   collision between thin  plates of
                              327

-------
crustal rock.  While the relative velocities of the colliding  plates are
very low, their huge masses produce extraordinary  forces,  sufficient to
rupture the  crust.   Since  the deformation is  primarily  along  the  plate
margins,  which are relatively specific locations, future folding,
faulting, volcanism, and the  like are expected to be  confined  to  these
limited margins, shown in Figure D-45.
    The theory of isostasy views  the  continents as bodies  of  relatively
low density material floating  on a dense mantle.   If  some portion of the
crust is higher than the rest,  there  must be  a proportionally deep mass
of crustal  rock below the rise  to provide  the  necessary buoyancy,  as
depicted in  Figure  D-46.   If  some process, such as  erosion,  alters the
land contour and hence  the buoyant equilibrium, the  crust  will  rebound.
A  rebound  in brittle  rock  may result  in faulting,  whereas  rebounding
softer rocks can deform by folding.
    Both theories suggest that deformation, by folding or faulting, will
be more  likely  in regions of  previous  tectonism  and high relief  since
these  regions   represent  local  areas of  high stress  in  a  state  of
disequilibrium;    either plate margins under compression or thick  zones
of  the  crust.    The  importance  of tectonic  forces  upon  a  repository
depends upon the rate at which structural processes may occur.   Faulting
and  folding  may  occur  in  the same  settings and  at  the  same  rates.
However,  faulting  is perceived  to be  more consequential than  folding
since  folds may leave the  overburden  at  its  original  thickness,
requiring considerable  erosion to  expose a  deeply  buried repository,
while a  fault  transecting a  repository may  raise  it  to  the  surface.
Therefore, the  following  discussion  will focus on the  possible  results
of  severe  tectonic  faulting.   The  possibility of  a fault  permitting
water that may  have contacted the buried wastes to  enter  the biosphere
has been consided as a failure element.
    It  is  also  possible that  repeated vertical  displacement along  a
fault could bring part  of  the repository itself to  the  surface.   Using
an extreme rate of  fault movement  yields  a conservative  estimate of the
time required to  exhume the  repository.  An  example of  a fault with a
rapid vertical  displacement  is the fault  forming  the east boundary of
Colorado's Front  Range.  This  fault  is approximately 20  million  years
old and has moved roughly 1000 meters over that period.  At that rate, a
                                      328

-------
to
                                LEGEND
                                     MAJOR EARTHQUAKES
                                     OTHER SEVERE
                                ?%%  EARTHQUAKES

                                :••*    VOLCANOES


         Sources:   Dewey. J.F., Scientific American. May 1972. Williams, H., Scientific American. November 1955.
                  FIGURE D-46  CRUSTAL PLATES AND REGIONS OF THE WORLD IN WHICH MAJOR EARTHQUAKES AND VOLCANOES OCCUR

-------
Note:   Elevation of surface is reflected in deepening of crust.
                                FIGURE D - 46    ISOSTASY
                                   330

-------
fault  through the  repository would  require  about  10  million years  to
raise  part of the repository  to  the  surface.
    It is  possible  that a  fault could divert  a  stream or  river  course
and make the stream  follow the trend of  the fault, as the  Snake  River
follows  the  fault forming  the  face  of the Teton  Range in Wyoming.   In
such a case,  the combined river erosion and  fault movement would  reduce
the time before  the  repository might be  exposed.   However,  this  more
rapid  mechanism would  commence  only  after   the  creation  of  the
transecting  fault.   Given  the very low  probability  of  a  new  fault
occurring  and the long  time before  the repository could be exposed,  this
mechanism  appears to  be much less significant  than the faulting  failure
element discussed in  Section  D-5.1.
    Earthquakes  generally  are  the  manifestation  of  movement  along  a
fault but, unlike a fault, their effects  are felt over a wide area.  In
examining  the possibility of  damage to a  repository from  quaking  it was
found  that   damage   is  typically   limited   to  surface  structures  and
features,  and that damage to underground workings is slight,  if  present
at  all.        For open  underground workings, damage  from very  strong
earthquakes  was  seen  only in  the   portals  and shallow  tunnels.    Deep
excavations  showed  no damage  at all.   A backfilled repository could be
expected to  endure  severe shaking with essentially no adverse effects.

D-5.6.5 Uplift  and Downwarping

    Relative movement  of  large regions,  such as orogeny, or  mountain
building,  may  contribute  to  a general degradation of  the repository-
This degradation might  occur  through fracturing and faulting and changes
in  the hydraulic regime  surrounding the repository, in  addition  to the
tectonic mechanisms already  discussed.   The geologic  record  shows that
in  the  United  States,  present  mountain  ranges   have  arisen from the
remains of ancient mountains, and these areas  would be most susceptible
to future  uplifts.   The time  for such pronounced  events as the emergence
of  a mountain  range  or   high  plateau  are  moderately  long,  even  in
geologic terms.   For example, the Laramide  orogeny, which created  parts
of  the Rocky  Mountains,  started  in  the  Cretaceous  period  and has
continued  into the Quaternary,  spanning more than 50 million years.  If
                                         331

-------
such  a  long  period is deemed  appropriate in evaluating  the performance
of  a  repository,   the  model  of  geologic  failure  elements  previously
developed would require substantial  changes  to  accomodate the structural
changes possible over such  spans of  time.
    More immediate  effects  of  changes  in ground level  would be shifts in
stream and river direction  and the rate of  stream erosion.  However, as
has  already  been  indicated,  the  presence of  a  stream  near  or over  a
repository would  not immediately  affect  the  repository.   The  rate  of
land  tilt and stream shift  would be  so  gradual  as  to be insignificant.
    A  region experiencing  downwarplng  or  subsidence is  likely to  be
eroded  more   slowly than  higher  ground  and   may  become  a  region  of
deposition.   In general,  subsidence  or deposition at  or  on a  repository
is not  a  disadvantage  and  may increase the  isolation of  the  contained
waste.   A problem  may  arise,  however, if  subsidence and  accompanying
sedimentation occur near a  repository in salt.   This  is discussed  in
Section D-5.6. 8.

D-5.6.6  Sea Level  Fluctuations

    The  relative  elevations  of a repository  and  sea  level  can  alter
conditions of erosion,  sedimentation,  and hydrology.   Usually  the  "base
level" of erosion is sea  level.   Erosion does  not generally occur  below
that  base level; instead,  sedimentation takes place.   The  slope of  land
toward  the  sea  affects  the  rate of  erosion,  higher  slopes  having  a
higher rate of erosion,  as  shown in Table D-lll.  If  the sea  level  were
to rise, a repository  sited in a high  plateau  area  may  see a  reduction
in the average slope (over  the  long  run) and a  corresponding decrease in
erosion.  Conversely, lowering the sea level would  lower the  base  level
of erosion and  increase the  gradient,  increasing the rate of  erosion.
However, for  an  inland  repository site,  the effects  of  changes  in  base
level would be slight, if apparent at  all.
    The most  recent and best  recorded  sea level fluctuations  have  been
attributed to changes  in  the  water volume  of  global ice  caps.   During
the  last  ice ages, sufficient  water  was withheld  from the   oceans  to
produce an  approximate 100-meter  decline in sea  level.   Since then, a
general warming  trend  has  prevailed.   If  this trend  continues, the sea
                              332

-------
                               TABLE D-lll
             ESTIMATES OF THE RATE OF EROSION UNDER VARIOUS
                    CONDITIONS OF CLIMATE AND RELIEF

Physiographic setting                    Estimated Rate of Erosion
                                                  (cm/1000 yrs)

Lowlands—Gradient -  0.001 or less

  Hot moist climate with dry season                       3.2
  Climate with cold winter                                2.9
  Intermediate maritime climate                           2.7
  Equatorial climate (dense rain forest)                  2.2
  Hot dry climate (Mediterranean, New Mexico)             1.2

Mountains—Gradient « 0.01 or more

  Hot moist climate (Guatemala-Mexico border)            92
  Extremely snowy climate (Southeastern Alaska)          80
  Semi-humid, near-glacial climate                       60
  High Mediterranean mountains                           45
  Hot dry climate (Southwestern                          18
    United States, Tunisia)

Source:  Press, F. and R. Siever. Earth.
         W.H. Freeman & Co.. San Francisco. 1974.
                             333

-------
level  could  rise as much  as  50 meters.       A repository  less  than 50
meters  above  present  sea  level would  be inundated, but  one  higher  than
50 meters would  be  relatively  unaffected.
    What  may  be most  important to an inundated  site  is the  effect  on
groundwater with an advance of the  ocean.   Eventually,  a layer  of  salt
water  would  spread  over  the  repository and  separate  it  from  fresher
water  floating  on top, as  shown  in  Figure  D-47.   Before equilibrium  is
reached,  however,  the encroaching seawater  may  cause a  reversal of  the
previous  groundwater flow  on the  site.   However, the  changes  in gradient
and groundwater  velocity would be expected  to be slow  and their  effects
minor.

D-5.6.7  Climate

    Of  all natural processes  influencing  a  repository,   weather  and
climate are the  most variable  and rapid.  Climate  affects virtually all
surface processes  and,  indirectly, many subsurface processes.  The most
important characteristic of climate  is precipitation, and its  effect on
hydrology and on erosion and sedimentation.
    Precipitation  affects  both surface  and  groundwater flows.   Changes
in rates  of infiltration and in the level of surface  bodies  of  water can
modify  the  water table and  the hydraulic  potential  throughout confined
and unconfined aquifers.   Changes in hydraulic potential  can  alter rates
and directions of flows.
    A more subtle influence of  climate  includes the types and density of
vegetation.     Vegetation  exerts   some   control   on  erosion  and
sedimentation.  As  shown in Figure D-48, the amount of  material stripped
from the  surface actually  decreases  with  increased  rainfall.   This is
because  a protective  cover  of  plant   growth  prevents  raindrops  from
striking  bare soil  and  dislodging dirt.  Also, plant roots and detritus
slow running water, entrapping  soil being carried with  the runoff.
    More  important for  a  repository,  however,  are  the more dramatic
effects of climatic change.  Glaciers, for  example, are  the  result of a
shift  in  climate,  and  their disruptive  effects have  already been noted
In  Section  D-5.6.2.   During  the  last  ice  age,  glacial advances were
accompanied  by an abundance of  precipitation  and  a reduction in
                               334

-------
Land Surface
FIGURE D-47    FRESH WATER OVERLYING DENSE SEA WATER
                     335

-------
     1000
      800
T5 — .
"3 ju
>  E
c  £
E  S
   -

600
      400
      200
              Desert
              Shrub
                                               Forest
                     10         20         30         40
                               Effective Precipitation (inches)
                                                            50
60
       Source:  Gilluly, J., A.C. Waters, and A.O. Woodford.
               Principles of Geology, 2nd edition.  W.H.
               Freeman & Company, San Francisco.  1958.
               FIGURE D - 48    EROSION RATES VS. PLANT COVER
                                336

-------
evaporation,  giving rise to  many  lakes and  ponds that have  now dried
altogether  or have shrunk to relative  insignificance.   Great  Salt Lake
is  the  dessicated remnant of Lake  Bonneville, which was  deeper by 300
meters  and  covered  roughly  eight  times  the  area of  the  present lake.
Another  lake,  Lake Missoula,  was  formed by an ice dam preventing normal
flow  into  the Columbia  and  Snake  Rivers.  Several  times,  when  the dam
broke,  the  rush  of  water  rapidly  carved  channels  and   formed  giant
ripples  in  the  lake bottom.   A new  glacial age  could  also bring about
the  return  of lakes such  as  Bonneville and Missoula.   If  these lakes
were  to  develop  over a  repository  or over the recharge area of aquifers
passing  through  the site,  decided  changes   in   groundwater  hydraulic
gradients could  occur.
    By  selecting  a site  without  indications of previous  lacustrine
environment or where no  geographic  barriers form  an  enclosed basin,  any
problems associated with future   lake  expansion  can be minimized.
However,  the  importance  of   this  site  selection factor  has  not  been
investigated  quantitatively in this  study.

D-5.6.8  Salt Diapirism

    Because  salt deforms plastically,  it  can  be  displaced, carrying  a
repository  with  it.   If the displacement  is  vertical, the repository
waste could  actually be carried to  the  surface.   The presence  of  salt
domes and anticlines in  various parts of  the  country  is evidence of  the
fluid behavior of  this  rock.
    Studies in salt tectonism have concluded that  certain conditions  are
essential   before salt  flow can  proceed.   '    '        Among these
conditions  are  an  overburden of  sufficient  thickness  to provide  the
necessary stress differential for  flow  to  start, and a salt  bed  thick
enough  to   react  to  the  stress.    While  there   is  no  clear  minimum
thickness  or  depth,  diapirism  apparently needs  a  salt   thickness  of
300-400  meters  and a burial  depth  of at  least 2000  meters.  The  salt
thickness cannot increase after  the  salt  deposit is  formed, but  the
depth of burial  may  increase  with  subsidence  and  sedimentation.  For  a
bedded  salt  formation   under  about  500  meters   of  cover, additional
deposits 1500 meters thick would have to accumulate  before the onset  of
                              337

-------
dlapirism.   If  deposition and  downwarping of  a  region proceed  at  the
same  rate,  it may  be possible  to  determine  the  minimum  delay between
siting a  repository in salt and the first  salt  flowage.  The section of
the United  States  with  the most rapid  downwarping  bounds the  Gulf  of
Mexico and has  a average rate of approximately  5-10  mm/year.        With
sedimentation  keeping  pace with  this  downward movement  150  thousand
years would  elapse  before the  overburden  would increase  by  the  extra
1500 meters necessary even to  start  salt flowage.
    Where salt diapirs  have already  formed, less or  no  added  overburden
may be necessary to  restart  upward  movement.   Stabilized  domes may  be
either  in  static  equilibrium  or   may  have  exhausted  the  supply  of
underlying salt.   In the  latter case,  no further movement  is  possible,
but in the  former  case, movement may  be expected to keep  pace  with  the
rate  of  sedimentation.  For many of the salt domes  of the Gulf  Coast,
diapir  growth  appears  to have  occurred  at  about  the  same  rate  as
sedimentation.       For these  domes,  the  subsidence has   increased  the
distance  between the top  and  bottom of  the  dome while maintaining  the
top in nearly the same  relation  to sea  level.

D-5.6.9  Salt Dissolution
    High solubility  is  a distinctive  property of salt.   If  water were  to
have  free  access  to  salt  containing  a  repository,  eventually the
isolating rock would  be dissolved away and water  could  attack the waste
directly.  Both the bedded  and dome salt  deposits  typically have caprock
deposits or  dissolution surfaces  indicating that  part  of  the  salt has
dissolved.   Sometimes  the  salt  has been  lost  from the  entire formation;
other  times   the  salt  is   lost  along  a  horizontally  moving  front  or
dissolution wedge.   For some specific  locations,  the rate  of  salt loss
has  been  estimated.   For example,  approximately  half   of  the  salt
originally  present  in the Delaware  Basin  may  have  dissolved  and  a
dissolution wedge has  moved eastward  in  one  formation at  a rate between
5 and  20 miles  per million years.    ^    Similarly,  the  Palo Duro Basin
has  active  dissolution fronts   moving   horizontally on  the  order  of
centimeters per year  and vertically at the rate  of a  few millimeters per
year.       Very  large  volumes of caprock mantle some salt domes.  These
                              338

-------
thick caprock deposits can indicate that as much as 6000 vertical meters
of salt  dissolved  from a single  dome, although lesser  amounts of  salt
loss are more common.  In some locations within the Salina Basin and the
Michigan Basin, salt beds have disappeared entirely, with remnant gypsum
indicating their previous presence.       Since the rate of salt loss  is
controlled by  local conditions  and is  a  continuous  process,  the  time
that would be necessary for the dissolution of a significant quantity  of
salt can and should be determined from site-specific data rather than  by
repository model parameters.
                             339

-------
                          LIST OF REFERENCES
1.    U.S. Department of  Energy.   Draft  Environmental  Impact  Statement.
     Management  of   Commercially  Generated   Radioactive  Waste.
     DOE/EIS-0046-D. April 1979.

2.    U.S.  Nuclear  Regulatory Commission.   Reactor  Safety Study.
     WASH-1400; NUREG-75/014.  October 1975.

3.    Oak  Ridge National Laboratory  (Claiborne,  H.  C.,  and  F.  Gera).
     Potential Containment Failure Mechanisms and Their  Consequences  at
     a  Radioactive Waste  Repository in  Bedded  Salt  in  New  Mexico.
     ORNL-TM-4639.  October  1974.

4.    U.S. Department of  Energy.   Draft  Environmental  Impact  Statement.
     Waste  Isolation Pilot Plant.  DOE/EIS-0026-D.  April 1979.

5.    Girardi,  F.,  G.  Bertozzi, and  M.  D'Allessandro.  Long-Term  Risk
     Assessment of  Radioactive Waste Disposal in Geological Formations.
     Transactions of the American Nuclear Society 26:  1-610,  1977.

6.    Battelle  Pacific  Northwest Laboratories (Schneider,  K.  J., and  A.
     M.  Platt) .   High-Level  Radioactive Waste Management Alternatives.
     BNWL-1900.  May 1974.

7.    Energy Research and  Development Administration.   Alternatives for
     Long-Term Management  of  Defense  High  Level  Radioactive  Waste,
     Savannah  River Plant, Aiken, S.C.  ERDA  77-42/1.  May 1977.

8.    Proske, R.  Contributions  to the Risk  Analysis of a Repository for
     High  Level Radioactive  Waste  in  Geologic   Salt  Formations.
     Transactions   of  the  American  Nuclear  Society  26:  1-610,  277.
     1977.
                                      341

-------
9.     deMarsily,  G.,  et al.  Nuclear Waste Disposal:  Can  the  Geologist
      Guarantee Isolation?   Science 197:  519-527.   1977.

10.   University   of  New  Mexico  (Logan,  S.  E.  and  M.  C.   Berbano) .
      Development  and  Application of  a  Risk  Assessment  Method  for
      Radioactive Waste Management.   For U.S. Environmental Protection
      Agency.  EPA 520/6-78-005.   July  1978.

11.   The  Analytic  Sciences  Corporation (Berraan, L.  E. ,  et  al.).
      Analysis of  Some Nuclear  Waste  Management  Options.   For  Lawrence
      Livermore Laboratory. UCRL/13917;  TR-1100-1-1.   October 10,  1978.

12.   Sandia Laboratories  (Campbell,  J.  E.,  et  al.).  Risk Methodology
      for Geologic Disposal of Radioactive Waste:  Interim  Report.   For
      U.S. Nuclear Regulatory Commission NUREG/CR-0458;SAND 78-0029  RW.
      October 1978.

13.   Nevada Operations Office, U.S. Dept. of Energy.  Annual  Report on
      Nevada Waste Isolation Program.   1978.

14.   Clynne, M.  A.,  and R. W. Potter II.  P-T-X Relations  of  Anhydrite
      and Brine  and  their  Implications  for the Suitability  of  Anhydrite
      as a Nuclear Waste Repository Medium.   In:  Scientific  Basis  for
      Nuclear  Waste  Management.  G. J.  McCarthy, ed. Plenum Publishing
      Corporation, New York. 1979.

15.   Storage  and Disposal  of  Radioactive  Waste.  Hearing before  the
      Joint Committee  on  Atomic Energy, Congress of  the  United States,
      Ninety-Fourth Congress. November 19,  1975.

16.   Sandia  Laboratories.   Seabed Disposal  Program.  Annual  Report -
      Part 1, January-December 1976.  SAND 77-1270.  October 1977.

17.   National  Academy  of  Sciences/National Research  Council.    The
      Disposal  of  Radioactive  Waste  on  Land.    Publication  519.
      NTIS-PB130035/AS.  September  1957.
                                      342

-------
18.   National Academy of  Sciences/National Research  Council.   Disposal
     of Solid Radioactive Wastes  in  Bedded  Salt  Deposits.   NTIS-PB  265
     197, November 1970.

19.   U.S.  Department of  Energy.    Technology  for  Radioactive  Waste
     Management.  Vol. 4.  DOE/ET-0028.  May 1979.

20.   Sandia  Laboratories   (Powers,  W.,   et  al.)«     Geologic
     Characterization Report, Waste  Isolation  Pilot  Plant  (WIPP)  Site,
     Southeastern New Mexico, Vols.  I  and  II.   SAND-78^1596.   December
     1978.

21.   On the  Safety of Disposing  of Radioactive Wastes  in the  Asse Salt
     Mine,  Gesellschaft  fur Strahlen  und  Umweltforschung  mbH,  Munich,
     Germany, Undated.

22.   Geotechnical  Engineers  Inc.   Uncertainties   in  the  Detection,
     Measurement,  and  Analysis  of  Selected  Features Pertinent  to Deep
     Geologic Repositories.   For Lawrence Livermore Laboratories.
      September 13, 1978.

23.   Gloyna, E.  F.,  and T. D. Reynolds.   Permeability Measurements of
     Rock Salt.  J.  Geophysical Research 66:3913. 1961.

24.   Dames & Moore*   Technical  Support  for GEIS:   Radioactive  Waste
      Isolation  in  Geologic  Formations.    Vol. 4:    Baseline  Rock
      Properties  -  Salt.  For Office of  Waste  Isolation, Union Carbide
      Corporation.  Y/OWI/TM-36/4.  April 1978.

25.    Tomlinson,  M.,  et al.    Paper  presented  at  IAEA  International
      Conference  on Nuclear  Power  and Its Fuel  Cycle, Salzburg, Austria,
     May 2-13,  1977.  Atomic Energy  of Canada, Ltd.  AECL-57CG. 1977.

26.    KSmbranslesMkerhet  (KBS).   Handling  of  Spent Nuclear  Fuel and
     Final  Storage  of  Vitrified  High  Level Reprocessing Waste.
      Stockholm,  Sweden,  December  12, 1978.
                                       343

-------
27.    Dames  & Moore.   Technical Support  for  GEIS:   Radioactive Waste
      Isolation  in  Geologic   Formations.  Vol.  5:   Baseline  Rock
      Properties  -  Granite.     For  Office  of  Waste  Isolation,  Union
      Carbide  Corporation.  Y/CWI/TM-36/5.  April 1978.

28.    Brace,  W.  F., J.  B.  Walsh, and W.  T.  Frangos.   Permeability of
      Granite  under High  Pressure.    J.  Geophysical  Research 73:2225.
      March  15, 1968.

29.    Dames  & Moore.   Technical Support  for  GEIS:   Radioactive Waste
      Isolation  in Geologic Formations. Vol.  21:   Groundwater Movement
      and Nuclide  Transport.    For   Office  of  Waste Isolation,  Union
      Carbide  Corporation.  Y/OWI/TM-36/21.  April 1978.

30.    KarnbranslesMkerhet  (KBS).    Handling  and  Final  Storage  of
      Unreprocessed  Spent Nuclear Fuel.  Stockholm, Sweden. 1978.

31.    Rockwell Hanford  Operations.     Basalt  Waste   Isolation  Program
      Annual Report-FY 1978.  RHO-OWI-78-100.  October 1978.

32.    Rockwell Hanford  Operations.     Basalt  Waste   Isolation  Program
      Annual Report-FY 1977.  RHO-ST-9.  September 30, 1977.

33.    Dames  & Moore.   Technical Support  for  GEIS:   Radioactive Waste
      Isolation  in  Geologic   Formations.  Vol.  7:   Baseline  Rock
      Properties  - Basalt.  For  Office of Waste  Isolation, Union Carbide
      Corporation.   Y/CWI/TM-36/7.   April  1978.

34.    Pettijohn,  F. J.   Sedimentary  Rocks.   Harper  &  Row Publishers,
      Inc.,  New York.  1975.

35.    Grim,  R. E.   Clay Mineralogy.   McGraw-Hill Book  Company, New York.
      1953.
                                       344

-------
36.    Erdal,  B.  R.,  et al.   Sorption  and  Migration of Radionuclides in
      Geologic  Media.    In:   Scientific  Basis   for  Nuclear  Waste
      Management.   G. J. McCarthy,  ed.   Plenum Publishing Corporation,
      New York.   1979.

37.    Dames & Moore.   Technical  Support  for  GEIS:   Radioactive Waste
      Isolation  in  Geologic  Formations.  Vol  6:   Baseline Rock Properties
      -  Shale.    For  Office  of  Waste  Isolation,  Union   Carbide
      Corporation.   Y/OWI/TM-36/6.   April  1978.

38.    MIT Research  Report 75-28  (Martin,  R.T.). Feasibility of Sealing
      Boreholes  with Compacted Natural Earthen Material.  For Office of
      Waste Isolation,  Union Carbide Corporation.   June  1975.

39.    Sandia  Laboratories   (McVey,  D.  F.,  et  al.).  Test  Results  and
      Supporting Analysis of a Near  Surface  Heater  Experiment  in  the
      Eleana Argillite.

40.    Gera, F.  Review of Salt Tectonics  in Relation  to the Disposal of
      Radioactive Waste  in Salt  Formations.    Geological  Society of
      America Bulletin 83:3551. December 1972.

41.   Bateman, A. M.   The  Formation of Mineral Deposits.  John Wiley &
      Sons, Inc., New York.   1964.

42.   Atwater, G.I.   Gulf Coast Salt Dome Field Area in  Saline Deposits.
      Geological Society of  America.  Spec.  Paper  88:29.  1968.

43.   Steams-Roger Engineering  Company.   National  Waste  Terminal
      Storage Repository for Storing  Reprocessing Wastes  in a Dome  Salt
      Formation.  Conceptual Design Report. For U.S.  Dept.  of  Energy,
      Oak Ridge, Tennessee.   November 9, 1978.

44.    Kenney, J. F., and E.  S.  Keeping. Mathematics of  Statistics,  Part
      Two.  D. Van  Nostrand  Company, Princeton, New Jersey.   1963.
                                     345

-------
45.    Freeze,  R.  A., and J.  A.  Cherry.  Groundwater.   Prentice -  Hall,
      Inc.,  Englewood  Cliffs,  N.  J.   1979

46.    Sharp, J.  C.,  and Y. N.  T.  Maini.  Fundamental  Considerations  on
      the Hydraulic  Characteristics  of  Joints  in Rock.    In:   Proc.
      Symposium  on Percolation  Through  Fissured  Rock.   Stuttgart,
      Germany. 1972.

47.    Snow,  D. T.   Rock Fracture Spacings,  Openings, and Porosities.  J.
      of the  Soil Mechanics and Foundations Division,  Proc.  of  American
      Society of  Civil Engineers.  99(SMI):73.  January 1968.

48.    Karnbranslesakerhet (KBS).  (Lundstrom, L.  and H.  Stille.)   Large
      Scale Permeability  Test of  the  Granite  in  the  Stripa Mine  and
      Thermal Conductivity  Test.  Technical Project  Report  No.  2.   For
      Swedish Nuclear Fuel Supply Co. and Lawrence  Berkeley  Laboratory.
      LBL-7052;  SAC-02, TID-4500-R66.  July 1978.

49.    Lawrence Berkeley Laboratory  (Carlsson, H.) .   A  Pilot  Heater Test
      in  the  Stripa  Granite,  Technical Project  Report  No.  6.    For
      Swedish Nuclear Fuel  Supply  Company  and  Lawrence Berkeley
      Laboratory.   LBL-7086;  SAC-06.  August 1978.

50.    Battelle Pacific  Northwest Laboratory    (Stottlemyre,  J. A.,  et
      al.).    Waste  Isolation Safety  Assessment Program - A Conceptual
      Simulation Model  for Release  Scenario Analysis of  a  Hypothetical
      Site  in Columbia Plateau  Basalts.  Oral  presentation  and working
      paper presented at WISAP Review Meeting, Seattle. August 1979.

51.    Dowell  Division  of  Dow Chemical  Co.   (Eilers, L.  H.).  Borehole
      Sealing, Final  Report.   For Office  of  Waste   Isolation,  Union
      Carbide Corporation.   ORNL/Sub/15966-73/1. October 31,   1973.

52.    Westinghouse Astronuclear Laboratory (Black, D. L. et al.).  Study
      of Borehole Plugging  in Bedded Salt by  Earth Melting   Technology.
      For Oak Ridge National Laboratory.  ORNL/Sub-75/76230.   June  1975.
                                      346

-------
53.    The Analytic  Sciences  Corporation  (Koplik,  C.  M.,  et al.)«
      Information Base for  Waste Repository Design.   For U.S.  Nuclear
      Regulatory Commission.  NUREG/CR-0495;  TR-1210-1.  March 1979.

54.    The Charles  Stark Draper  Laboratory,  Inc.    (Fernandez,  R. ,  et
      al.).   Borehole Plugging by  Compaction Process,  Final  Report.  For
      Office of Waste Isolation,  Union Carbide Corporation.   Y-OWI-Sub
      7087-1.  August 1976.

55.    The Pennsylvania State  University  (Roy,  D.  M.,  and W.  B.  White).
      Borehole Plugging by  Hydrothermal  Transport.   For  Office of  Waste
      Isolation, Union Carbide Corporation. ORNL/Sub-4091/3.   May 1975.

56.   American Petroleum Institute.  Oil Well Cementing Practices in the
      United States. 1959.

57.   Significance  of Tests  and  Properties of  Concrete  and  Concrete
      Making  Materials.  American  Society  for Testing  and  Materials.
      ASTM Special Technical Publication, No. 169-A. 1966.

58.   Gilluly,  J.,  A.  C.   Waters,  and  A.   0.  Woodford.  Principles  of
      Geology,  3rd  edition,   W.H.  Freeman  &  Company,   San  Francisco.
      1968.

59.   Flint, R.  F.,  and  B. F.  Skinner.  Physical  Geology. John  Wiley &
      Sons, Inc., New York. 1966.

60.   Billings, M.P.  Structural Geology.   2nd Edition.   Prentice-Hall,
      Inc., Englewood Cliffs, N.J. 1954.

61.   Standard  Handbook  for  Civil  Engineers.    F.S.  Merritt,  ed.
      McGraw-Hill Book Company,  New York.  1976.

62.   Herndon,  J.  and D. K.  Smith.   Plugging  Wells for  Abandonment: A
      State  of  the  Art  Study.    For  Office of  Waste Isolation,  Union
      Carbide  Corporation.  Y/OWI/Sub-76/99068.   1976.
                                     347

-------
63.    Lambe,  T. W.,  and  R. V. Whitman.   Soil Mechanics.   John Wiley &
      Sons, Inc.,  New York. 1968.

64.    Terzaghi, K.,  and  R.  P.  Peck.   Soil  Mechanics  in  Engineering
      Practice.  2nd Edition.   John Wiley & Sons, Inc., New York.  1968.

65.    Karol,  R. H. Soils and Engineering. Prentice-Hall, Inc., Englewood
      Cliffs, N.J.  1960.

66.    Modern  Petroleum  Technology.   I.  Hobson  and   G.  Douglas,  eds.
      Institute of Petroleum,  London.  Halsted Press.  1973.

67.    Pasini, J.,  et al.  Plugging Abandoned  Gas and  Oil Wells.  Mining
      Congress Journal.  December 1972.

68.    Personal Communication,  Herbert Einstein, MIT, 1978.

69.    Erickson, H.  Chemical Grouting  at NORAD.  In:  Proc. 6th Symposium
      on Rock Mechanics, U. of Missouri, Rolla, Mo. 1964.

70.    Environmental Evaluation Group,  State  of  New Mexico (Goad, D.). A
      Compilation  of Site  Selection  Criteria,  Considerations  and
      Concerns  Appearing  in  the  Literature  on  the  Deep  Disposal  of
      Radioactive Wastes. EEG-1. June 1979.

71.    Bureau  of Mines  (Johnson,   K.,  et  al.).  How  to  Find  Abandoned
      Wells: A Manual.  BU Mines 1C 8578.  March 1973.

72.    Barnes,  H.  L.,  ed.   Geochemistry of  Hydrothermal Ore Deposits.
      Holt, Rinehart, and Winston, Inc., New  York.   1967.

73.    Stewart,  R.  D.,  and R.  R. Unterberger.   Seeing through Rock Salt
      with Radar.  Geophysics 41:123.   1976.

74.    Unterberger,  R.  R.   Looking  through  Rocks  with  Radar.   Mining
      Congress  J.  63:38.   1977
                                      34«

-------
75.    Cook,  J.  C.   How to  Locate Water  Hazards  in  Salt Mines.   In: Proc.
      4th  Symposium on Salt,  Cleveland.  Proc. Northern Ohio Geological
      Society  2:27.   1974.

76.    Netherland,  Sewell & Assoc., Inc.   Preliminary Regional  Study of
      the  Present  and  Possible Future  Oil  and Gas  Development  in the
      Areas  of  Thick Rock Salt and  Shale Deposits  of  Michigan, Ohio,
      Pennsylvania, and Western New York.  For  Office  of Waste Isolation,
      Union  Carbide Corporation.   ORNL/SUB-4091/3.  February 28,  1976.

77.    Personal Communication.  William  Mallio,  Resource  Engineers,  Inc.
      November 1979.

78.    W. K.  Summers & Associates,  Inc.  (Summers, W.K., and  P.A. Webber).
      Description of Wells Penetrating the Wanapum Basalt Formation in
      the  Pasco   Basin  Area,  Washington.    For  Rockwell-Hanford
      Operations.  RHO-BWI-C-22.  April  1978.

79.    Personal  Communication.  John  Swerta,  Washington  Department of
      Ecology.  June 1979.

80.    Office  of Nuclear  Waste  Isolation  (Burkholder,   H.C.). Waste
      Isolation  Performance   Assessment  -  A  Status  Report.  ONWI-60.
      November 1979.

81.    McCarthy, G.  J.,  et al.   Interactions  Between Nuclear  Waste and
      Surrounding Rock. Nature 273:216. May 18, 1978.

82.    Roedder,  E. ,  and H. E.  Belkin.   Application of  Studies of  Fluid
      Inclusions  in  Permian  Salado  Salt,  New Mexico,  to Problems of
      Siting  the  Waste  Isolation  Pilot Plant. In: Scientific  Basis for
      Nuclear  Waste  Management.   G.  J. McCarthy,  ed. Plenum  Publishing
      Corporation, New York.  1979.
                                      349

-------
83.    Battelle  Laboratories  (Olander,  D.  R.,  and  A.  J.   Machiels) .
      Thermal  Gradient Brine  Inclusions:  Migration in  Salt Study:
      Gas-Liquid  Inclusions  - Preliminary  Model.  For Office  of  Nuclear
      Waste  Isolation. ONWI - 85.  October  1979.

84.    U.S.  Geological Survey (Bredehoeft,  J.   D.,  et  al.).    Geologic
      Disposal  of  High-Level   Radioactive  Waste  -  Earth  Science
      Perspectives.  USGS Circular 779.   1978.

85.    Hyder, C.  On  Diapirs and Diapirism.   Southwest Research and
      Information Center, Albuquerque, N.M.  Paper presented at Hearings
      before  the  United  States  Senate,  Subcommittee on Science,
      Technology, and Space of  the  Committee  on  Commerce,  Science and
      Transportation,  Albuquerque,  N.M.,  March  31,   1978.   Serial No.
      95-92.

86.    Stewart,  D.  B.,  and W.  R. Potter,  II.  Application  of  Physical
      Chemistry  of  Fluids  in  Rock  Salt  at  Elevated  Temperatures and
      Pressures to Repositories  for  Radioactive  Waste.  In:  Scientific
      Basis  for  Nuclear  Waste  Management.   G.J.  McCarthy,  ed.  Plenum
      Publishing  Corporation, New York.  1979.

87.    Sandia Laboratories  (Wawersik,  W. R.).   Interim Summary of Sandia
      Creep  Experiments on  Rocksalt  for  the  WIPP  Study Area,  SE  N.M.
      SAND  79-0115.   February 1979.

88.    Sandia Laboratories  (Dawson, P. R.) .   Constructive  Models Applied
      in the Analysis  of Creep of Rock Salt.  SAND-79-0137. June 1978.

89.    Sandia Laboratories  (Dawson, P.R., and P.R.  Chavez). COUPLEFLO -A
      Computer  Code   for  Coupled   Creeping   Viscous   Flow  and
      Conductive-Convective   Heat   Transfer,  Part  I,  Theoretical
      Background. SAND-78-1406.  November 1978.
                                      350

-------
90.   Sandia Laboratories (Dawson, P. R., and J. R. Tillerson). Nuclear
     Waste Thermally Induced Motion. SAND 78-0566.  June 1978.

91.   Dawson, P. R., and J.  R. Tillerson.   Salt Motion Following Nuclear
     Waste Disposal.  In:   Proc.  International  Conference on the
     Evaluation and Prediction of Subsidence,  Pensacola, Fla.  January
     15-20, 1978.

92.   Sandia Laboratories  (Dawson,  P.  R. ,  and  J.  R.  Tillerson).
     Comparative  Evaluations  of  the  Thermomechanical  Responses for
     Three High  Level Canister Emplacement  Alternative. SAND  77-0388.
     December  1978.

93.   American  Petroleum Institute.  1977 Joint  Association  Survey on
     Drilling  Costs.  February 1979.

94.   Halbouty, M.  T.    The  U.S.  Is Not  Drilled  Out.   The Wall  Street
     Journal.  December 27,  1979.

95.   U.S.  Geological  Survey  (Ekren,  E.   B.  et  al.).  Geologic and
     Hydrologic  Considerations  for  Various  Concepts of  High   Level
     Radioactive  Waste Disposal  in the  Conterminous  U.S.   USGS  Open
     File  Report  74-158.  1974.

96.   U.S.  Nuclear Regulatory  Commission.   Disposal of  High-Level
     Radioactive  Wastes in  Geologic Repositories. Draft 10  of Planned
     Addition  to  10 CFR 60.  January 9, 1980.

97.   Solution     Mining Research  Institute  (Walters,  R.  F.).    Land
     Subsidence   in   Central  Kansas  Associated   with  Rock   Salt
     Dissolution.  Flossmoor,  Illinois. June  1976.

98.   Erode,   H.   L.   Rock  Mechanics Considerations  in the  Design  of
     Underground  Protective  Structures.  In:  Proc.  International
     Conference  on State  of Stress  in the Earth's Crust. Santa Monica,
     California.  June 13-14,  1963.
                                      351

-------
99.    Snow,   E.  R.   Ghosts,  Gales and Gold.  Dodd,  Mead &  Company,  New
      York.  1972.

100.   U.  S.  Geological  Survey.  Preliminary Map  of  Young Faults  in  the
      United States  as  a  Guide  to  Possible Fault  Activity.  USGS  Map
      MF-916. 1977-

101.   New England  Nuclear  Power  Co.  Preliminary Safety Analysis Report.
      Charlestown  Station,  Units 1 and 2.  February 1979.

102.   Northeast Nuclear Energy  Co.   License  Application and Preliminary
      Safety Analysis Report,  Vol.  2,  Montague Nuclear  Power  Station,
      Units 1 and  2.  July 12, 1974.

103.   Baecher, G.  B.   Site Exploration, A Probabilistic Approach. Ph. D.
      Dissertation,  Department  of  Civil Engineering,  Massachusetts
      Institute of Technology. 1972.

104.   Byerlee, J.  D., and W.  F.  Brance.  Stick Slip,  Stable Sliding,  and
      Earthquakes. J. Geophysical Research 78:6031. 1968.

105.   Sbar,  M.  L.,  and  L. R. Sykes.  Contemporaneous  Compression Stress
      and Seismicity in Eastern North America: An Example of  Intra-Plate
      Tectonics.  Geological  Society of  America Bulletin  84:1861.  June
      1973.

106.   Hillier,  F.  S. ,  and  G.  J. Lieberman.  Introduction to Operations
      Research. HoIden-Day,  San Francisco. 1967.

107.   Davies, J. V.,,The Astoria  Tunnel Under the East River  in New York
      City.  Trans. American  Society of Civil  Engineers  80:594-674* 1916.

108.  Personal    Communication,   Stanley  E.   Norris,   U.   S.  Geological
      Survey. December 1979.
                                     352

-------
109.   U.  S.  Geological Survey (Norris', S. E.). Hydrologic Environment of
      the Silurian  Salt  Deposits  in  Parts of  Michigan, Ohio,  and New
      York.  USGS Open-File Report 78-684. June 1978.

110.   Personal  Communication,  Robert  J. Hite, U.  S.  Geological Survey.
      November 1979.

111.   U.  S.  Geological Survey (Stockton,  S.  L.,  and A.  H.  Balch). The
      Utility  of  Petroleum  Seismic   Exploration  Data  in  Delineating
      Structural Features Within  Salt  Anticlines.  USGS  Open-File Report
      78-591. 1978.

112.   Bechtel  National,  Inc.  Regional Characterization  Report  for the
      Paradox Bedded  Salt  Region  and  Surrounding  Territory. For  Office
      of Nuclear Waste Isolation, Battelle Memorial Institute, Columbus,
      Ohio.  ONWI/SUB-78/42507/1. May 1978..

113.   The Analytical Sciences Corp. (Giuffre, M. S. et  al-)« Information
      Base  for  Waste Repository  Design,  Vol.  5:  Decommissioning  of
      Underground Facilities.  For U.   S.  Nuclear  Regulatory Commission.
      NUREG/CR-0495; TR-1210-1. March  1979.

114.  Bechtel  National,  Inc.  Regional Environmental   Characterization
      Report  for the Gulf Interior  Region  and Surrounding Territory. For
      Office  of Nuclear Waste  Isolation, Battelle Memorial Institute,
      Columbus,  Ohio.  ONWI/SUB-78/512-01600-1. November 1978.

115.  Louisiana Power  and  Light Co. Preliminary Safety Analysis Report,
      Waterford  Steam Electric Station, Units  3  and 4.  Docket  50382-2.
      January 1971.

116.  Macdonald,    G.  A.    Volcanoes.  Prentice  Hall,  Inc.,   Englewood
      Cliffs, N. J.  1972.

117.  Civetta,  L. et al., eds. Physical Volcanology.  Elsevier  Scientific
      Publishing Co.,  New York.  1974.
                                     353

-------
118.   Catalogue   of  Active  Volcanoes  of  the World.    International
      Volcanological Association, Naples, Italy.  1955.

119.   U.  S.  Geological Survey (White,  D.  E.,  and D. L. Williams, eds.).
      Assessment  of   Geothermal  Resources  of  the  United  States.  USGS
      Circular 726.  1976.

120.   U.  S.  Geological Survey (Millineaux, D. R. ). Preliminary Overview
      Map of  Volcanic Hazards in the  United  States.  USGS Miscellaneous
      Field Studies  Map, MF 786.  1976.

121.   Nevada   Operations  Office, U.   S.  Department of  Energy.   Nevada
      Nuclear Waste  Storage Investigations, July through  September 1979.
      NVO-196-12. December 1979.

122.    Fowler-Billings,  K.,  and  M. P.  Billings.  Geology of the Gorham
      Quadrangle, New Hampshire  - Maine. N.  H. Department of Resources
      and Economic Development Bull. 6. 1975.

123.   Geology Society of Great Britain. Geological  Map of  Great Britain,
      Second Edition. 1957.

124.    Bowen,  N. L.    Evolution of Igneous Rocks.   Princeton University
      Press, Princeton, N. J. 1928.

125.   Shelton,  J. S.   Geology Illustrated.  W. H. Freeman  &  Company,  San
      Francisco.  1966.

126.   U.  S.  Geological Survey (Maldonado, F.  ). Summary  of  the  Geology
      and  Physical  Properties  of the Climax  Stock,  Nevada Test  Site.
      USGS Open-File  Report 77-356. 1977.

127.  Eaton,   J. P.,  and K.  J. Murata.   How Volcanoes Grow.  Science
       132:925.  October 7S 1960.
                                       354

-------
128.   Battelle Pacific Northwest  Laboratory   (Scott, B. L. et al.).   A
      Summary  of  FY-1978  Consultant   Input   for  Scenario  Methodology
      Development.  For  Office of  Nuclear  Waste  Isolation  PNL-2851.
      November 1979.

129.   Hartmann,   W.  K.   Cratering  in  the Solar  System.   Scientific
      American 236:84. January 1977.

130.   Grieve, R.  A.  F.,  and P. B. Robertson.  The Terrestrial Cratering
      Record. Icarus 38:212. 1979.

131.  Hughes, D.  W.  Earth's Cratering  Rate. Nature 281:11. September 6,
      1979.

132.  Geotechnical Engineers,  Inc.  Geological Studies Pertinent to Site
      Suitability  Criteria  for High-Lev el  Waste Repositories.  For
      Lawrence Livermore Laboratory, UCRL 13741. May 25, 1977.

133.  Anderson, R. Y.  Report  to  Sandia Laboratories on Deep Dissolution
      of Salt, Northern Delaware  Basin, New Mexico. April 1978.

134.  Swenson,  E.  A.   Rates of  Salt  Dissolution  in  the Permian Basin.
      USGS J. of  Research 2:253.  1974.

135.  Personal   Communication, Thomas  Gustavson,  University  of  Texas.
      December 1979.

136.  Brochie,  J.  F.,  and  R. Sylvester.   On  Crustal  Flexures.    J.
      Geophysical  Research  74: 5240. 1969.

 137.  Flint,  R. F.   Glacial and  Quaternary Geology.  John Wiley & Sons,
      New York.   1971.

 138.  Reid,  H. F.   Studies  of  Muir Glacier, Alaska.  National  Geographic
      Magazine   4:19.  1892.
                                    355

-------
139.   Okko,  V.   Glacial Drift  in Iceland,  Its Origin  and Morphology.
      Comm.  Geol.  de Finlande Bull.  170:133.  1955.

140.   Rozen,   A.    Response  of  Tunnels  to  Earthquake  Shaking.    S.M.
      Thesis,  Massachusetts Institute of  Technology.  1976.

141.   Ewing,   M.,  and  J.   Ewing.  Rate  of  Salt Dome Growth.  American
      Association  of Petroleum Geologists Bull. 46:708

142.   Press,  F., and R. Siever.   Earth.  W.  H. Freeman  &  Company, San
      Francisco. 1974.

143.   Landes,  K. K., et al.   Geology of  the Mackinac  Straits Region.
      Michigan Geological  Society, Publ.  44.  1945.
                                    356

-------
APPENDIX D-I
  GLOSSARY

-------
                               APPENDIX 0-1

                                 GLOSSARY
Andes!tic
Anticline



Aquiclude



Aquifer



An 1sotrophy


Argillaceous
Barlte
Basalt
Batholith


Breccia
Andesitic refers  to volcanoes and  related  features
with composition  part way between  basalt and
silicic rock,  suggestive of  the mixture of wet
basalt and continental rocks at a  plate subductlon
                        zone *
A geologic  structure having  rock folded  into an
arch.  The  opposite is a syncline which has the
rock folded downward into a  trough.

A relatively Impermeable geologic formation which
effectively prevents the passage of water.
Contrasts with an aquifer.

A rock formation or stratum  of relatively high
permeability that may readily yield or transmit
water-

Having properties which are  not the same in all
directions.

Clay bearing. Here argillaceous is used  to
describe any of a range of sedimentary rocks with
clay as a major constituent, including shale,
mud stone, argilllte, and slltstone.

Barium sulfate, BaSO,. A dense mineral and chief
source of barium, barite Is  used in the deep
drilling industry as an additive to drill mud to
increase its density.  This  helps to buoy the
weight of a long drill string and to increase the
pressure at the bottom of the hole which assists
in preventing blow-outs.

A dense, dark, hard, fine-grained igneous rock
containing  iron and magnesium rich minerals and
lacking free silica. In this study, basalt is
taken to be a family of fine-grained Igneous rocks
without specifying a particular mineral
assemblage.

A body of intrusive igneous  rock larger  in area
than 100 km.

Broken rock with fragments larger than sand.
                                    1-1

-------
Breccia Pipe
Catalysis
Cement with Fine
Fillers
Connate Water


Creep


Critical Cavity




Criticality
Crust
Crystalline Rock
Darcy's Law
A geologic structure steep sided and roughly
circular in plan composed of breccia. In the
context of this report, a breccia pipe is a
feature in salt formed by the collapse of
overlying rock into a cavity formed by
dissolution.

The modification of the rate of a chemical process
through the use of an agent which is not consumed
in the process .

Portland cement or similar material mixed with
clay and silt-sized inert particles instead of
coarser aggregates.

Water entrapped in a rock at the time of its
formation. Contrasted with meteoric water.

Slow plastic or viscous fluid deformation of rock
under stress.

The maximum void or cavity in rock salt able to
support itself.  Cavities larger than the critical
cavity will experience the fall of rock blocks or
breccia into the cavity.

The conditions necessary for a self sustaining
nuclear chain reaction to start or continue.
Criticality is reached when a necessary quanitity
of nuclear material is brought and held in close
proximity.

The exposed rocks of the earth. The relatively
rigid outer layer of the earth exhibiting
relatively slow seismic velocities. The crust
varies in thickness from about 60 km under certain
mountainous parts of the continents to about 5 km
under the oceans.

Referring to igneous or highly metamorphic rocks
composed of minerals with crystals large enough to
be distinguished by the unaided eye.

A mathematical description of laminar fluid flow
through a permeable medium, to the effect that
flow is proportional to the hydraulic gradient*
In particular, Q = KiA, where Q is the volumetric
flow rate through a surface of area A, orthogonal
to the flow, under a gradient i.  A factor c(y)
must also be included when viscosity can vary
significantly.
                                     1-2

-------
Diapir
Differential Stress

Dike Swarm
Drilling Mud
Drill String
A geologic structure formed by the  forceful
intrusion of one geologic material  into overlying
material, especially the non-igneous  intrusion of
a relatively plastic or  fluid material, such  as
salt •

Stress differences  in different directions.

A cluster of dikes  oriented roughly parallel  or
radiating from a common  point. Parallel dike
swarms are noted in the  British Isles and the
Pacific Northwest.  Radial swarms are  common near
volcanic centers.

Fluid used to cool  and lubricate the bit of a rock
drill and to float  the cuttings to the surface.
Muds may be water or organic fluid based with a
number of possible  additives including clays,
starches, and density modifying materials.

A length of steel pipe segments joined together
and used to operate a drill bit suspended below
the surface.
Evaporite
Fault
Felsic Rocks
First Estimate
Graben
Gravity Fault
A rock or mineral deposited when the waters  in
which it was dissolved evaporated. Common
evaporites include salt, gypsum, sulfates, and
potash salts.

A fracture showing displacement of the material on
either side along the plane of the break.  Faults
are distinguished from joints, the latter showing
no relative displacement.

Igneous rocks composed primarily of feldspars and
free silica (quartz), such as granite.

In this study, the conditions or event
probabilities appropriate to a repository site
selected for its particular advantages regarding a
specific criterion.  For example, a first estimate
with regard to abandoned boreholes would assume a
site with no history of deep well development and
conditions unfavorable for gas or oil reserves.

A block of rock bounded by parallel gravity  faults
which has moved downward in relation to  the  blocks
on either side.

A synonym for a normal fault. A sloped geologic
fracture along which the overlying (hanging  wall)
rocks have apparently moved downward with respect
to the underlying (foot wall) rocks.
                                    1-3

-------
Head


Horst



Hydraulic Conductivity



Hydraulic Gradient


Igneous rock

Incompetent Rock



Indurated



Intrusion
Joints
Lithology
Lithostatic Pressure
Magma
Hydraulic pressure  represented  by a column of
water of a given height.

The counterpart of  a  graben.  A fault-bounded
structure which has moved  upward  in relation to
the rocks on  either side.

The coefficient of proportionality, K,  in Darcy's
Law.  In this  report,  it  is used  synonymously with
permeability.

The rate of change in  hydraulic head  with respect
to distance.

A rock formed  by the  cooling  of melted  rock.

Rock unable to support  itself or  an applied  force.
In engineering, incompetent rock  requires
additional support.

Solidified into a massive  rock.   Usually  used to
describe sediments which have hardened  into  rock,
e.g. indurated clay is  shale  or mud stone.

A rock body forcibly injected into  pre-existing
rock or soils.  Generally  intrusion denotes  an
igneous rock which invaded surrounding  rock but
never reached  the land  surface.

Fractures or separations in a rock  having no
apparent displacement  parallel  to the plane  of the
fracture.

The character  of rocks  and rock formations,
particularly their gross features  such  as
structure, color, mode  of  emplacement,  fossil
content, and stratigraphy.  Also,  the study  of
rocks.

Pressure applied by the weight  of the overlying
rock.  Lithostatic pressure at a  given  depth  can
be estimated by multiplying the weight  density of
rock by the depth below the surface.

Melted rock beneath the earth's surface.
                                   1-4

-------
Mantle
Metastable
Mine Drift
Montmorillonite
Near Field
Neat Cement


Normal Fault



Permeability



Petrography



Piezometric Head
The layer of the  earth between  the  core  and  the
crust, starting about 3400 km from  the  center.
The mantle has higher seismic velocities  than the
crust and is apparently  composed  of dense iron and
magnesium rich rocks.

Temporarily stable.  Metastable is  used  to
describe minerals or other phenomena which are not
in equilibrium with their surroundings but which
require a finite disturbance to initiate  a change
toward equilibrium.  A typical  example  is a
supercooled liquid which remains  liquid  until made
to solidify upon  the addition of  a  grain  of  the
solid phase.  Metastable is not synonomous with
unstable which denotes a shift  toward equilibrium
without the addition of energy  or a disturbance.

A tunnel or horizontal mine opening.  Particularly
a blind tunnel not connecting to  others  at one
end.

A clay mineral (hydrous aluminum  silicate),
generally the weathering product  of  lava,  with the
capacity to readily absorb water between  crystal
layers causing marked expansion.

Within the vicinity of the waste  or  the  repository
tunnels.  Near field effects are  those caused by
the presence of the waste or the  repository  and
are contrasted with far field effects which  are
essentially unrelated to the repository or its
contents .

Portland cement mixed without fillers or  aggregate
and generally used as a grout or  sealing  agent.

Synonym for gravity fault.  An  inclined  fracture
along which the rocks above have  apparently  moved
downward with respect to the rocks  below.

A measure of the ease with which  a  fluid  can pass
through the continuous voids of a material.  (See
hydraulic conductivity.)

Description of a rock including mineral
composition, grain size and shape,  fabric, and
evolution.

The height to which water in an aquifer  rises or
could rise if penetrated by a well.  The  hydraulic
head.
                                    1-5

-------
Planar



Plastic


Pluton

Poise Units


Polymerization




Productive Horizon



Resaturation
Second Estimate
Shale
Shear Stress
Silicic
Forming  a plane  or  flat  surface.   Used  here,
planar describes  features  or  structures which are
wide, long, and  roughly  uniform in thickness.

Capable of being  permanently  deformed without
rupture.

A body of intrusive  igneous rock.

A measure of  fluid dynamic viscosity.    1 poise =
1 gm/cm-sec.

Formation of  long chain  molecules  from  short
molecules.  Through  polymerization,  certain light
volatile molecules combine to form more rigid
dense ones.

A stratum from which mineral  wealth  is  recovered;
especially a  stratum from which petroleum or  gas
is taken.

The filling of a  repository with water. If a
repository is partially  back-filled  with rock
materials, resaturation  denotes the  filling of the
void spaces within the backfill.

In this study, conditions appropriate for a
repository sited  in  circumstances  unfavorable in
regard to a specific criterion.  For example, a
second estimate for  undetected abandoned boreholes
would assume  a site  within a  long  abandoned gas or
oil field.

Sedimentary rock  formed  from  clay  and silt and
that is laminated and fissile.  In this study,
shale is intended to denote all fine-grained  clay
rich clastic  sedimentary rocks including
argillites, mudstones, siltstone,  graywacke,  and
so forth.

A stress or force acting to cause  slippage of two
adjacent parts of a  body past  one  another.

High in silica.   Silicic refers to silica rich
magmas which  are  typically viscous,  and confined
to regions of continental crust, suggesting that
they are the  result  of reraelting of  crustal rocks.
Typical rocks from silicic magmas  are granites,
granodlorides, and their fine-grained equivalents.
                                      1-6

-------
Sonde
Source Term



Spall



Stochastic process


Stock
Stratum
(PI. Strata)
Stress
Subcircular
Subduction
Subparallel
Tectonic
Thermally Induced
Buoyancy
Uniform Concentration
A device to obtain and  transmit  remote
measurements.  A borehole sonde may be used  to
determine the properties of  rock penetrated  by  the
hole.

The quantity and composition  of  radioactive  waste
contained in a repository or  subject to release by
a particular breach mechanism.

To fracture concentrically,  to form "onion skin"
joints where movement  is largely perpendicular  to
the plane of the fracture.

A process or model whose evolution over time is
governed by probabilistic factors.

An igneous intrusive which is smaller than a
batholith, steep sided, and  assumed to be
cylindrical or widening with  depth.

A layer of rock, especially  a layer of uniform
characteristics distinguishable  from overlying  and
underlying strata.

A force acting to deform, usually measured as
force per unit area;  may vary with direction.

Not circular in the mathematical sense but
describing a figure which is  closed and convex,
approximately circular, as the cross section of a
tree trunk is subcircular-

The forcing down toward the  mantle of the earth of
crustal rocks at the junction of two colliding
crustal plates.

Not parallel in the mathematical sense but near
enough to parallel that linear features do not
actually intersect.

Pertaining to the earth's broad  structural
features.

Upward forces brought  on by  expansion of material
when heated resulting  in a lower density than that
of the surrounding material.  The low density
material will tend to  rise through the denser
material.

Average concentration  of radionuclides in
backfilled repository  as a result of gradual
leaching from waste packages.  May be limited
either by leach rates  or by  solubility limits.
                                     1-7

-------
U-Tube Effect           A term to describe water movement  through  a
                        repository involving water entering  from an
                        overlying-aquifer at the upstream  side of  the
                        repository and returning to  the aquifer at the
                        downstream side.

Virgin Rock             Rock which is unaffected by  drilling or mining.

Waste Drift             A mine tunnel or drift containing waste.
                                1-8

-------
        APPENDIX D-II
REPOSITORY RESATURATION TIMES

-------
                              APPENDIX D-II

                      REPOSITORY RESATURATION TIMES

A.  INTRODUCTION

    Many of  the mechanisms  that  permit the  transport  of radionuctides'
from  the  repository to  the upper  aquifer require  that  the hydrologtc
system  be  in a saturated  condition.   Before  repository construction,
essentially  all  the  rock helow the water  table (defined  in the generic
repositories by the  level  of the  upper aquifer) is saturated with water
at  pressure  at  least   equal  to  hydrostatic  pressure.     (See  Figure
D-II-1).
    The excavation  of  the  repository disturbs  this  saturation because
water  flows  from  the  surrounding  rock into  the resultant  cavity, as
shown in Figure D-II-2.  During the operational  phase of  the repository,
this  water,  if  significant, will  be pumped  out,  as  is commonly  done
during  mining   operations.   After  the backfilling  and  closing  of  the
repository,  water  flowing down the filled  shafts  and/or  in through the
rock  walls  will  gradually fill  the  pores  of  the backfill  until
saturation is again  established.   The  purpose  of this discussion is to
estimate the time required  for  such  "repository resaturation"  to  take
place.

B.  SIMPLIFICATIONS

    The repository will  be  modeled as  a rectangular solid with base  area
AR, height  h,  mined fraction M,  and backfill  porosity  1.   Thus,  the
volume of pore  space needing to be resaturated  is:
For the present calculations, the following values will be used

                               A.  -  8 km2  -  8 x 106 m2
                                II-l

-------

X
X
X
X
X
X
X
X
X
X
X X
X X
Siitui
X X
X X
X
X
illlHl
X
X
X
X
/OIM!
X
X
X
X
X
X
X
X
X
X
X
X
                                        Liitul surface
                                       Top of upper ;u|uit
-------
                                      5 m
                                M  -  0.25

                                n  =  0.2 .

                                               6   3
These values  lead  to  a pore volume V  = 2 x 10   m".   Resaturation also
requires  filling  of  the  pores  in   the  unsaturated  zone  of  rock
surrounding the repository  and  in  the  backfilled  (or  sealed)  shafts and
boreholes.  These  latter volumes  are negligible  in relation to the pore
volume  of  the  repository  cavity and  so  will   be   omitted  from  the
analysis.   The resulting  calculation  is  conservative, in  that  it will
predict recharge slightly earlier  than  in the real case.
    The flow into  the mined repository is driven by a pressure gradient.
The repository  is  initially at atmospheric pressure while  the water  in
the  surrounding  rock exceeds  this by  its  corresponding  hydrostatic
pressure.   This hydrostatic  pressure   will  be modeled  as  that  from  a
column of water extending  to the top of the upper aquifer-  The pressure
in  the  repository  would gradually   rise  during  recharge,  thereby
decreasing  the effective  gradient.   However,  for  the  sake of  these
simple  conservative   calculations,  this  effect  will  be  ignored.   For
flows  through the rock  itself (as opposed  to flows  through permeable
shafts  or boreholes),  it   will be assumed  that  recharge  also  occurs
through the bottom of  the  repository and  that  this is  equal to recharge
through  the  top.   With  respect  to  the  latter,  it  will be  assumed  to
occur through the  column of rock immediately above the repository.  Edge
effects  are  assumed  to  be  insignificant and, in  any case, more than
balanced  by  the conservative  assumption  of equal  flow up  through the
floor.

C.  OUTLINE OF COMPUTATIONS

    The outline of the steps  in   the   calculation  of  recharge times  is
shown in  Figure D-II-3.    To  illustrate the steps,  several preliminary
calculations will  be carried out below.
                              II-3

-------
SI
Oi'tt'imiiio hytliaulii:
tliadiunl (liivini) iiH:liai<|r
S2
Dclui mino total flow
rato into repository via
all pathways
S3   Determine cumulative
     inflow as a function
     of time
S5   Determine the time at
     which cumulative inflow
     reaches required volume
                                                S4    Determine water
                                                      volume necessary to
                                                      saturate repository
      FIGURE D-ll-3   COMPUTATIONAL SEQUENCE FOR RECHARGE TIMES
                                 II-4

-------
1.  Two  repository-aquifer distances are represented  among  the  generic
    repositories.  For  bedded  salt, shale,  and  basalt, the  top  of  the
    upper aquifer  is  130  meters  above the repository.   This determines
    the  driving  hydrostatic head.   The  head is essentially dissipated
    entirely  over  the  100-meter  barrier layer,  so  that the  effective
    gradient  is:
                                 -12JL
                                 100
    In the case of granite and dome  salt,  the  gradient  is:
                                  230
2.  Total  flow  rate  into the repository is  assumed  to be the sum  over
    all possible recharge pathways.  Each pathway  is characterized  by  a
    permeability (which may vary with  time)  and  a  cross-sectional  area.

    In  the case  of  shaft  recharge,  the  permeabilities  are  based on
    Section D-3.2.   For  the  first  estimate,  K  degrades  linearly  from
    10   cm/sec to 10    cm/sec  over 10  years.  The permeabilities are
    more convenient to deal with  in units  of meters per year, to  which
    the conversion is  accomplished by multiplying by  3.15 x 10 .   The
                                        —3                      —1
    linear  degradation  from  3.1*5  x  10    m/yr  to  3.1")  x  10     m/yr
    corresponds to the equation:

                      K(t)  =  3.15  x  10~3 + —
                                                 104
                                 3.15  x  10~3 -t-  3.12  x  10~5  t  (m/yr)

                                                           —8
    For the  second  estimate, K  degrades linearly  from 10   cm/sec  to
      -4               4
    10   cm/sec over 10  years.  In this case, one  obtains:
                             II-5

-------
                  K(t)  -  3.15xlO-+--
                                            10*
                           3.15 x 10~3 +  3.15 x  10~"  t  (m/yr)
    The total cross-sectional  area  of the  shafts  will  be taken as 100
     2
    m  (e.g., four shafts, each of which is 5 m x  5 m).
    In the  case of  borehole  recharge,  the  first estimate  calls for

    degradation from  10    cm/sec  to 10    cm/sec  over 10  years, which

    is represented  by the equation:



             K(t)   -  1.15 x 10~3 + 3.15 x 10"4 t  (m/yr).


                                                      ft                /
    For  the  second  estimate,  degradation  from  10    cm/sec  to  10
                  4
    cm/sec over 10   years, is given by:



             K(t)   =  3.15 x 10~3 + 3.15 x 10~3 t  (m/yr).
    Each borehole has a cross-sectional area of 0.1 m".


                                          •
3.   The  output  of Step  2  is  a function  Q(t)  representing the rate of

    flow into the repository at  time t.   This  rate  is  calculated by

    Darcy's law:
                                     100M
    where v is  the  water viscosity  at the  ambient  temperature in the

    rock.  For  these calculations,  u  will be  conservatively taken as
                        •
    0.002 poise  so that  Q has the form:
                                     5 KiA
    for  each pathway.  The  integral  of  this function from 0 to t gives

    the  cumulative inflow by time t.
                             II-6

-------
    4.  The required water volume has already been calculated to be
                                  V  =  ARhMn
        which has the numerical value

                                  V  -  2.0 x 106 m3

        for  the  parameter values  that  have been adopted.  This  represents
        the  initial pore  space  at  the  time of repository sealing.   Tn  the
        case of  salt,  which is  a  plastic medium that tends  to  flow under
        applied stress, the pore space  will  decrease  as  a function of time
        due  to the overburden pressure.   The modeling of creep behavior is
        discussed in greater detail in Appendix D-VII, where representative
        numerical results are estimated.  For the present calculations,  the
        pore space  has  been  assumed  to  decrease  linearly  to  0  (an
        approximation)  over  a   certain  period  following  sealing  of  the
        repository.  For  first  estimate  calculations,  this  period  has been
        taken  to be  200  years.  For  second  estimate  calculations,  this
        period has been taken to be  1000 years.   The  slower  rate  of creep
        represents  a less  desirable  situation  with  respect  to this
        mechanism because  more  water can  enter  the  repository before  the
        salt has effectively sealed itself tight.

    5.  The  equation:

                               Q(t)  =  V

        is solved for t in order to determine the recharge time.

D.  BEDDED SALT RESATURATION TIMES

    For a  repository in  bedded  salt,   resaturation  would  generally be
restricted to two sets of  pathways: permeable  shaft  and  borehole  seals.

                              II-7

-------
The bulk rock permeability is too low to contribute significantly  to  the
inflow.
    First estimate.  Using  parameters  given earlier,  the  Inflow due to
shafts is given by:

                               QL  -  5 KiA

                                   -  2.048 + 0.02048  t

so that the cumulative amount of water present is:

                               Q   -  2.048t + 0.01024 t2 .
Similarly,  assuming  60 borehole  pathways (50  to  upper aquifer,  10 to
lower), they contribute an amount of inflow given by:

                               i$   -  0.123 + 0.0123 t
so that the cumulative amount of water present is:

                               Q2  -  0.123t + 0.00614 t2 .


Since the pore space in the first estimate case is given by:

                      Q  -  (2 x 106)(200 - t)/200
for t  between 0 and  200  years,  resaturation Is  achieved  at  the time t
which satisfies the equation:

                      Q  -  Qx + Q2 .
                               II-8

-------
This  value  of  t   is  approximately   200 years  (199.883)  and  the
                                      3   3
corresponding water  volume  is  1.2 x  10   m"  (1171).
    Second  estimate.  Second estimate parameters  lead to the formulas:
                          •
                          Qj_   =  2.048 + 2.048t

                          Q1   =  2?048t  + 1.024 t2

                          •
                          Q2   =  0.123 + 0.123t

                                                  2
                          Q2  =   0.12^t +  0.061 t
                                  (2 x  106)(1000 - O/1000
The  resaturation  time in  this  case is  approximately  720 years,  with a
                                      5  3
corresponding water volume of 5.6 x  10   m .
E.  GRANITE RESATURATION TIMES

    For  a repository  in granite,  there are  three sources  of inflow:
permeable  shaft  seals,  permeable  borehole  seals,  and  flow  through the
bulk rock.   Because the cross-sectional area  for  flow through the bulk
rock is so much larger  than for shafts and boreholes (almost five orders
of  magnitude),  and  because  this  difference  is not balanced  by  a
correspondingly  lower  permeability,  the  flow  through  the bulk  rock
dominates.
    The  permeability  values  given  in  Section  D-3.1 for  the  first
estimate case  lead  to the formulas:

                     Q  =  5 KiA

                                    3  3
                        =  2.8 x 10" m /yr  for  t  < 100 yr

                        -  2.8 x 104 m3/yr  for  t 1 100 yr

                                          7   3
The value of  A used  here  is 1.6 x  10   m  ,  twice  the  area  of the
repository,  to  account for  recharge  from  both   above  and below the

                               II-9

-------
repository.  The cumulative  inflow by  100 years  after repository closure
is thus:

                       Q(100)  =   2.8  x  103  x ]02

                               =   2.8  x  105  m3

In order  for resaturation  to be  complete, an  additional  inflow equal  to
          f   O
1.72 x  10  m  is necessary,  in order  to give the required  total of 2  x
10  m .   At  the  rate of 2.8 x 10  nf /yr,  this would take  an additional
61  years, so  that  the  resaturation  time  would be  approximately 161
years .
    For the second estimate  case,  the  inflow over the  first 100 years  is

                          Q  =  2.8 x  105 m3/yr

so that resaturation takes place almost  immediately,  i.e.,  about 7  years
after  closure.    Since  the  calculated value  is  so small,  it  does not
extend  into the peak  thermal  period.    Therefore,  the  conservative
viscosity assumption  (0.002  poise)  is overly conservative.   This
observation also applies to  subsequent calculations, but  since the  times
would be  rather  short  in any case,  there  is no need for a  more refined
calculation.

F.  BASALT RESATURATION TIMES

    As  in the  case  of  granite, the  dominant inflow for  resaturation  is
through the bulk rock.
    The parameter values  given in Section D-3.1  for the  first estimate
case lead to the inflow rate:

                          Q  =  3.3 x  10 4 m3/yr

over the  first  100 years,  which implies  resaturation at  about 61  years
after repository closure.  In the  second  estimate case,  the permeability
                               11-10

-------
is two orders of magnitude  higher,  so that resaturation takes place in
less than one year  (0.6 year).

G.  SHALE RESATURATION TIMES

    The parameters  that govern  resaturation times  are  identical to  those
for basalt.   Therefore,  the  first  and second estimates of  resaturation
times  for  a  repository  in  shale   are  61  years  and  0.6  years,
respectively.

H.  DOME SALT RESATURATION TIMES

    The  analysis  of  resaturation  of  a  repository in  a  salt dome is
similar to the case of bedded  salt.   There  are  two parameter changes to
be  accounted  for.   First, since there  is  no lower aquifer immediately
below  the  repository,  only  50  borehole pathways  should  be   included.
Second the vertical gradient in  shafts  and boreholes  is 1.1 instead of
1.3.    Using  the  same  notation  as   earlier,   the  first   estimate
calculations yield  the functions:

                        Qj  =  1.73t + 0.0086  t2

                        Q   =  0.086t  + 0.004 t   .
 Since the pore space is
                               (2  x 106)(200 - t)/200
for t between 0 and 200 years  after  repository  closure,  resaturation  is
again achieved at  the  time t which solves  the  equation
                             Q  -  Q! + Q2 •

This  value  of  t  is  approximately  200  years   (199.91)  and  the
corresponding water volume is 865 m .

                                   11-11

-------
    Similarly, for the second estimate, the following functions apply:

                           Q   =  1.73t + 0.86 t2

                           Q2  =  .086t + 0.04 t2

                            Q  =  (2 x 106)(1000-t)/1000 .

The result  is a  resaturation  time of  748 years  with a  corresponding
water volume of 5.0 x 10  m .

I.  SUMMARY OF CALCULATIONS

    Resaturation  times calculated earlier  are  summarized  in Table
D-II-1.

J.  QUALIFICATIONS

    The numerical results of this section  have been derived  under  a  set
of specific assumptions  and  parameter  values.  Depending on  the manner
in which  the  repository is designed,  the  resaturation  times  calculated
here may  or may  not  be reasonable estimates  of  the time before  which
certain release mechanisms can  become  operative.   A  particularly
complicating  factor is  the  fact that  engineering choices which may  add
to repository integrity with respect to one breach mechanism may detract
from  its   integrity  with  respect  to  another.   Examples  of  this  are
discussed  below.
    Porosity of backfill.  Since the rate of inflow to the  repository is
fixed by the  pathway parameters, the recharge  time  will be increased if
the volume V of  water  required  to  saturate the repository  is increased.
                                                         7   3
The limiting  case of  no backfill yields  a volume V =  10  m  and  hence
recharge   times  five  times  as  long   as  those   calculated  above.
Nevertheless,   the  use  of highly  porous (and  hence  permeable)  backfill
would  aid  the movement of  radionuclides  through the  repository  should
some breach pathways be established.
                               11-12

-------
                              TABLE D-II-1

                      CALCULATED RESATURATION TIMES
Medium                  First Estimate           Second Estimate
                            (yrs)                      (yrs)
Bedded Salt                  200                        720
Granite                      161                          7
Basalt                        61                          0.6
Shale                         61                          0.6
Dome Salt                    200                        748
                                 11-13

-------
    Bulkheads.  It  is  possible  that  the repository designs will include
sealing  off  waste drifts  and   segmenting  tunnels  with  carefully
constructed bulkheads.   These  measures will  reduce the  potential  for
water and  radionuclide transport   through  the  repository.  At  the  same
time, if these barfiers are  essentially impermeable, they also  seal  off
portions of  the  repository from  certain  inflow sources,  such  as
permeable shafts and boreholes.  The result will be  that the segments of
the  repository  which  include  (or  are  close  to)  the water  sources  may
become resaturated rather soon.  In this case, mechanisms for hydrologic
transport of  radionuclides  may become  operative  sooner  than  envisioned
from  the  times  calculated  earlier.    For  repositories  in  which
resaturation  through  the   bulk rock   dominates,   this  factor  is   not
important.

K.  CONCLUSIONS

    While resaturation mechanisms may delay  the  initiation  of  potential
radionuclide transport from the repository, for the reasons cited  in  the
previous section  it  is recommended that considerable care  be  exercised
in applying  credit  for this delay in assessing  repository  performance.
It  is  a matter  that  should  be investigated  when  specific  repository
plans  are  being  evaluated,  at which  time  the  uncertainties  may  be
sufficiently resolvable to  allow greater credit for  this  factor  in  the
repository performance assessment.
                             11-14

-------
             APPENDIX D-III
METHODOLOGY FOR DISSOLUTION CALCULATIONS

-------
                             APPENDIX D-III

                METHODOLOGY FOR DISSOLUTION CALCULATIONS

A.  INTRODUCTION

    The  dissolution  mechanisms  discussed  here   apply  exclusively  to
repositories in salt.  Similar problems do not arise with the other host
rocks under consideration.
    Breach  mechanisms that permit  water to  flow from a  repository in
salt to an  aquifer may develop  either  by gradual  processes (e.g., shaft
seal degradation)  or abrupt events  (e.g.,  faulting).  In  either case,
the water may  dissolve  and carry off  some  of the salt,  thereby perhaps
worsening  the  breach.     The   harmful   effects   could  consist  of  the
formation of  a less  resistive  pathway  for the water  and  hence greater
water  flow,  the  accessibility of  more  canisters  to  leaching,  or
structural changes in the surrounding rock.
    The purpose of  this  appendix is to estimate  the  rate  at  which such
dissolution could  take  place,  consistent with other  assumptions  in the
report.   Throughout, the  following  constant value for  salt  (NaCl)
solubility in water  is used:

               0.37  gm/cc water  =  0.168cc salt/cc water.

This is the solubility of  salt  at about 100 C.  The concern here is for
boreholes and  shafts  that  have  been filled and sealed  according  to the
specifications given elsewhere   in  the  report.   Dissolution  during the
operational phase of  new wells drilled  in  the future  is  assumed to be a
problem  that   the  drillers  will  have  to meet   in  engineering  their
systems.  For  the sake  of conservative calculations  (i.e.,  tending to
overestimate the dissolution),  it will be assumed  that water leaving the
salt layer through the breach pathway is saturated with salt.
                              III-l

-------
B.  BOREHOLES

    In  Section  D-3.3,  the degradation  of  a  sealed  borehole has been
modeled as a deterministic process.  The parameters  assumed  were:

                                               2
                             Area, A  =  0.1 m
                         Porosity,
0.1
                     Permeability, K  =  10
   -8
                                                     -  10
                                                         -8
                                                     10
                                          (for  the  first  estimate,
                                           t  in years,  K  in  cm/sec)
                                   K
 10
-8 + 10   - 10
        10
                                                          8
                                           (for  the  second  estimate,
                                           t  in  years,  K in cm/sec)

These  parameters  enable  the   calculation  of  flow  as  a  function  of
hydraulic  gradient.   For  conservatism,  the viscosity  will be taken as
0.0022 poise, which has been used elsewhere  for flow  calculations.  (See
Appendix  D-VI   for   the  dependence  of  viscosity  on  temperature.)
Dissolution  is  expected to be  greatest  at  the  point  where  unsaturated
water enters  the salt layer.   As  a consequence,  it  is conservative to
assume uniform  dissolution in  estimating  dissolution  at  the  repository
level.  Calculations  here  are consistent with  the  generic  stratigraphies
and repository assumptions given earlier in  the report.
                        •
    A water  flow rate  Q  through the  filled borehole  corresponds to a
                                       •
salt dissolution rate equal to 0.168 Q.   If  the  borehole has radius r
                           III-2

-------
and length L  through  the  salt,  then  the  rate  of change of the radius is
            3

given by:
                              dr_ =   0.168  Q

                              dt       2-rrrL
                                            s
For  bedded  salt,  L  =  100 m  for  a  borehole  extending  to  the  lower
                    S

aquifer.   For  dome  salt,  L   =  230  for  a  borehole  extending  to  the
                          •   s

repository.  Recall  that  Q  is given  by:

for a  hydraulic  gradient i.   The  computational procedure is  to  proceed


as follows :
    1.  Compute  Q(t)  =
    2.  Compute Q(t) by  integrating Q(t)  and  using  the  initial  condition


        Q(0) S0.


    3.  q(t) = 0.168 Q(t)  is  the  cumulative volume  of salt  removed.


    4.  Compute r(t) from  the  formula
        where  r   is  the  initial  radius.   This  formula simply  derives


        from volumetric considerations.



    5.  Compute -7^ , if it is of  interest,  from the  earlier  formula
                         _ q(t)
                      dt   2irr(t)L
                                  s
                                               •
For ease  of  computation, the  integration  of  Q(t)  is worked  out  below,



                                 III-3

-------
                                                             4
where K is assumed to degrade linearly  from KQ to  K^ over 10  years:

                                  K     K
                  K(t)  =   [K  +   ^-7- °  t] [10"2][3.15 x 107]
                             0     104

                                                                       _2
where  KQ  and  K,  are  in  cm/sec  and K is  in m/yr -    The   factor  10
converts  centimeters  to  meters  and  the  factor  3.15  x   10   converts
seconds to years.  As long  as the other parameters remain constant,
                              f~                     r\            -j
             Q(t) - Q(0)  =   J[K  +   1 "   °  t] [10"  ][3.15  x 10
                              Q  U      ^Q^
                                    K    K
                    Q(t)  =   [Knt +  1-  ?  t2] [3.15  x 105] [.~
                               u    2 x 1(T
Note  for  future  reference that the  expression inside the  integral  sign
    •
is  Q(t) .  Note  also  that dissolution may change  the value of  A  for the
section of  the borehole  within the salt, but  as  long  as  the  changes are
very  small,  corrections for  this  change need not  be introduced.   For
significant dissolution  over a large  extent  of the  borehole,  Darcy's law
would  no  longer apply  since  there would  essentially be a  conduit  for
water flow.
     Using  the  scheme  just  outlined,  the  numerical results  shown  in
Table D-III-1 are  obtained.   These  calculations  suggest  that, at least
within  the   parameter  range  under  consideration,   the  change  in  r  is
relatively slow.  Therefore,  the derivative  dr/dt may be  approximated by
the formula:

                           ll  =  0.168  Q
                           dt  =  2irr  L
                                     o s
                               III-4

-------
                              TABLE D-III-1
          CHANGES IN BOREHOLE RADIUS AS A RESULT OF DISSOLUTION
                 (Using a gradient i - 0.01, rQ - 0.18))
                    Time
                   (years)
                    First Estimate
                       r(meters)
                Second Estimate
                  r(meters)
Bedded Salt
   100
   500
  1000
  5000
10,000
0.1800
0.1800
0.1800
0.1803
0.1811
0.1800
0.1800
0.1801
0.1826
0.1903
Dome Salt
   100
   500
  1000
  5000
10,000
0.1800
0.1800
0.1800
0.1801
0.1805
0.1800
0.1800
0.1800
0.1812
0.1846
                                III-5

-------
instead of by the original formula:

                           T     0.168Q
                          dt
                                     s
The difference is in using r , the original  radius,  instead  of r, which
always  results  in  a  conservative  calculation  (i.e.,  tending  to
overestimate dr/dt)  because r is greater  than  or  equal to rQ.   For  the
case of bedded salt,  using L   =  100  m and r  - 0.18 m,  this  yields  the
                             S               O
formula:
                             =  1.485 x 10~3 Q
Similarly, for dome salt, using L  - 230 m and r  =0.18 m, one obtains

                          ~  -  6.458 x 10"4Q .
As an example of the application of these formulas, consider the value Q
= 0.875 m /yr, which is  the value  calculated  in  Section D-3.4 for first
estimate fluid  flows  at 1000 years  after repository  closure.    Tn  the
                                                                _3
case of  bedded  salt,  the resulting value  of  dr/dt is  1.3  x  10   m/yr-
This slow rate  of  increase  is or  would  probably be compensated  for  by
salt  creep,  which would  tend   to  close  any  channels created  by
dissolution.  For example, rough calculations  suggest  that dr/dt for  an
                                                          _3
open borehole at repository  depth  would be about  -3 x 10  m/yr, which
would more  than balance  the  dissolution.  Further discussion  of salt
creep may be found  in  Appendix D-VII.
    Dissolution around other breach pathways can be analyzed in a manner
exactly analogous to  the examples  worked out  above  for boreholes.  The
values  in Table D-III-1 roughly scale  with  the  gradient, so  that  the
effects of  the  larger  second  estimate  gradients  in  certain  cases  are
apparent.
                                III-6

-------
             APPENDIX D-IV
METHODOLOGY FOR DIFFUSION CALCULATIONS

-------
                              APPENDIX D-IV

                  METHODOLOGY FOR DIFFUSION CALCULATIONS

A.  INTRODUCTION

    In the  case  of  a breach of  a  nuclear waste repository, either  by a
gradual process  (e.g., borehole plug  degradation)  or a  distinct  event
(e.g., faulting),  there  are basically  two  processes  for movement  of
radionuclides  from  the  canisters  to  the  release  pathway.   These
processes   are  convection  and  diffusion.   Convection,  the carrying  of
radionuclides  by moving  water, may be  driven  by several  mechanisms,
which  are  discussed  elsewhere   in this  report.   Molecular  diffusion,
driven by  a concentration gradient, is  the  principal  subject of  this
appendix.
    A  simplified  plan view of  a  portion  of  a  repository is shown  in
Figure D-IV-1.   The  canisters   of  wastes are  emplaced  in holes in the
floor  of  the waste drifts.   For purposes  of  this appendix it has  been
assumed that the  waste drifts are  5  m  x 5 m  in  cross  section,  although
most of the  formulas  will  first  be worked out  in  terms  of a  parametric
cross-sectional  area  A.   The waste  drifts may be  quite  long, say 500
meters, and  the  canisters  may be  placed  at  intervals  on  the  order  of 5
to 10 meters.
    Potential  breach  mechanisms,   such  as faults  and  boreholes,  may
intersect   the   waste  drifts,   the main  tunnels,  or  simply  the  rock
pillars.     (The  pillars   are  expected  to  cover  50-90%   of  the  total
repository  area.)      The  drifts  and  tunnels will  be backfilled  with
porous material.   The pillars  may also  be  porous,  due either  to  basic
rock porosity or to  fracture  systems.   In any case, diffusion is through
porous media, not simply through bulk fluid.

B.  BASIC  PRINCIPLES AND HYPOTHESES

    The basic goal here is to calculate  the rate  of  mass  transport from
a "source"  to  a  "sink".    The source  is one or more canisters of nuclear
waste, and  its  strength is  determined  by  the  concentration of material
                                   IV-1

-------
       •    Waste drift
Waste drift   •  •
                                 Main
                                 tunnel
       •    Waste drift   •
Waste drift    •  •
                                                             Canisters
FIGURE D-IV-1  PLAN VIEW OF PORTION OF REPOSITORY (NOT TO SCALE)
                                  IV-2

-------
at  Its  boundary.   In  general,  this  concentration  will vary  from one
radionuclide  to  another.    The  concentration  will  be  bounded  by the
solubility limit of  the relevant  species,  which in many  cases is very
small,  and  it  may  be further  limited  by the rate at  which the species
can be leached from  the  canister/waste-form  package.   The sink consists
of a release pathway, such as  the  portion  of a borehole passing through
the  repository.    (Transport  along  the release  pathway  is  generally
dominated by  convective  forces,  which  are  discussed  elsewhere  in this
report.)
    Molecular diffusion  is  driven  by a  concentration gradient  in the
same way  that heat  conduction is  driven  by a  temperature gradient  or
fluid flow by a pressure gradient.  The basic mathematical model is thus
a  partial differential  equation,  which for  steady-state  problems  is
simply the Poisson equation  (reducing  to the Laplace equation away from
sources and  sinks).   The purpose  here  is  not  to derive  or assume this
body   of   mathematical  theory,   but  rather  to   present   simple,
self-contained  models  that  are  sufficiently accurate  to  predict
diffusional  mass   transfer   in   the  present  case.      Geometric
simplifications,  always  intended  to err on  the conservative side, will
be  employed  freely.   The purpose  is  generally  to reduce  problems  to  a
single dimension.
    The fundamental principle that the diffusion rate is proportional to
the concentration gradient  takes  the form:
                             J  =  D
                                     dx
in one dimension,  where
    J  =  flux  rate  (mass  per  cross-sectional  area per  time) .   The
          direction of  movement  is  understood  to  be  from  regions of
          higher concentrations  to lower  ones.  With  this convention, no
          minus sign is needed  in  the  equation.
    D  =  diffusion constant.   This depends  on  the  fluid,  the  porous
          medium,  the diffusing  solute,  and  the conditions  present.
  C(x) =  concentration of the  solute  at  distance x  from the  sink.
This equation,  called  Pick's law, is exactly  analogous to Darcy's law
                                   IV-3

-------
for fluid flow  in  a porous medium.   J will  be  a function of  x.    The
total mass transport rate  q through  any cross-sectional area A will be
obtained as the product  JA.   The  two  sections  that immediately follow
use  Pick's  law  to calculate  diffusion  rates   in  certain fundamental
cases.

C.  DIFFUSION THROUGH  A TUBE OR  TUNNEL  (MODEL  A)

    Consider  the  situation sketched  in  Figure  D-IV-2a.   Suppose  the
concentration at the left end  is kept fixed at C2 and that at the  right
end at C, , where C« >  C, .  The  corresponding  concentration gradient  and
flow  is  strictly  one  dimensional,  and may  be   modeled  as  in Figure
D-IV-2b.  As  long  as  the  porous medium is uniform (an assumption used
throughout),  the   concentration  will change   uniformly,  so  that:

                                 C(x)  - £ (C  - C )

  Thus the diffusive flux is:
                                         D(C  - C.)
                                    J  =  	±	±_
  and the mass  transport  rate  q  is:
                                       D(C2 -
  where A is  the  cross-sectional  area.
      While  it would be  desirable  to have measurements  of the diffusion
  coefficient  D for  the  given  solute in the given  medium,  such data are
  not generally available  for  the materials  of interest  in  this  study.
  Indeed,  the diffusion rates in water  are not  well known and must often
  be approximated  from other known values.   Given  the  diffusion  rate in
  water,  the  rate  in   the water-saturated   porous  medium may  be
  approximated.     We  shall   do  this  by  multiplying  the   tunnel
  cross-sectional area  A by  the porosity n of the backfill material, since
  nA better  represents the  effective  cross  section  through  which  the
  diffusive  flux  acts.   The effective  pathway  through a  real  medium is

                                     IV-4

-------
       Source boundary
       (Concentration
                                                              Sink boundary
                                                            (Concentration C1)
(a)
(b)
                              TUNNEL






                                         C(x)
              FIGURE D-IV-2   DIFFUSION ALONG A TUNNEL
                               IV-5

-------
also not  expected  to be the  straight  line suggested  in  Figure D-IV-2b,
but  this  distance  multiplied by  a  "tortuosity" factor.   Since for many
porous media this  factor is  still less  than 2,  it  is not  incorporated in
the  present  analysis.  Therefore,  accounting for porosity  but ignoring
tortuosity, the mass  transport  may  be  calculated  approximately by:
                        q  =
                              D(CZ - c1)An
This formula and the corresponding model will be  called  Model A.

D.  DIFFUSION IN AN ANNULAR REGION  (MODEL  B)

    The  situation  to  be analyzed  in  this  section is  shown in  Figure
D-IV-3a.  The cylindrical source will be used to  bound  the contributions
from  several point  sources  located  on  or  outside  such  a  cylinder.
Because  of  symmetry,  flow is strictly  horizontal  and  radial  and  may  be
analyzed with the  aid  of Figure D-IV-3b.  Steady-state  flow requires  an
identical rate  of  mass  transport  through  every  intermediate  boundary.
As x increases,  the boundary  area  increases proportionately,  so  for the
same mass transport  rate, a smaller  flux  rate holds.   Since  flux  rate
                      \
and  concentration  gradient  are proportional,  the  concentration  varies
non-uniformly in this  case.
    The  reasoning  just  described  actually  enables the  calculation  of
mass transport.   Whatever the  steady-state  overall mass  transport  rate
                          •
may be,  it must hold that q is  the rate of material movement through any
intermediate cylindrical boundary; that  is, for all x,
                                   JA
                                    (D 3-)
                                      dx
                                 IV-6

-------
                                  Borehole passing through
                                      repository (sink)
                                                                 Repository
                                                                 horizon
Cylindrical source of material
 diffusing toward  borehole
                                              Intermediate boundary
                                              at radius x
                                              Source
        FIGURE D-IV-3
CYLINDRICAL SOURCE AND SINK LEADING
TO DIFFUSION IN AN ANNULAR REGION
                               IV-7

-------
where h is  the height  of  the cylinders.  Therefore:
     dC       q
     rr~  "  ~  o  i-
     dx     D • 2irh
                                           •  constant
Simply calling the  constant B,  it  follows that!
                            dC   =  B_

                            dx      x
                           C(x)   -  Bin x + E





for  another  constant E,  yet to  be  determined.   If  boundary conditions


are  specified  in  the  form:
C(r1)
C(r_)  «  C-
                                                                   (sink)
                                                                (source)
where  r.,  and r_  are  the radii  of sink and  source respectively,  it is


easily seen  that:
                          ~ C
                                      tn(x/r
                                  IV-8

-------
The corresponding mass transport rate is thus:
                 •     •
                       D •    (r ) • 2irr.h
                           dx   1       1
                       D .
                       D
                           C  - C,
                                 i.     .    2-rrr-h
Cancelling the r,'s and now inserting the porosity factor,  we obtain:
                       2irDhn(C2 -
This formula and the corresponding model  will  be called Model B.   Note
that for  conservative  calculations  one  wants to  err  on  the  side  of
underestimating r2  and  overestimating r, .


E.  EXAMPLE:  DIFFUSION INTO MAIN TUNNEL

    Consider the situation  previously shown in Figure D-IV-1.   If flow
through  the main   tunnel  is   initiated  by   some  mechanism,  such  as
degrading shaft seals at either end, the release of material along waste
drifts to  the  tunnel may be  primarily from diffusion.   We shall model
this  situation  as  shown  in   Figure  D-IV-4  for  radionuclides  whose
concentration is limited by a relatively low solubility limit C^*  It is
conservative  to replace  the   first  canister  by  a  planar  source  at
concentration  C~,   and  fill   the entire  waste  drift   cross  section.
Furthermore, the remaining  canisters in the drift  cannot contribute to
the  mass   transport,  since   the  hypothetical  source  has  maximal
concentration.   (There could not be a net concentration gradient driving
                                 IV-9

-------
                                Hypothetical
                                sink


                                  Hypothetical
                                  source
                                                    First canister
FIGURE D-IV-4   GEOMETRY FOR DIFFUSION INTO MAIN TUNNEL
                           IV-10

-------
material  toward  it from  the  right).  We  take  as  the sink  the  entrance
from the main tunnel  to the waste drift.   This  is  the situation  in Model
A.  Nominal parameters will he taken  as follows:
A -
n =
D =
C2 -
Cl "
L =
25 m
0.2
io-6
io-5
0
20 m
2

2
cm /sec
Ci/m3 (Ci

9
                                     curies)
The corresponding mass transport is  found to be:
              q  •  8 x 10~9 Ci/yr.
This represents the maximum  contribution of one waste drift to  the main
tunnel by diffusion, according to the parameter values given above.
    It  is  important to  compare  this mass  transport  with that  possibly
driven by other forces.  In particular,  consider the  following question:
What hydraulic gradient  acting  along a  waste  drift  would result in  the
same transport rate?   A  permeability of K - 10~  cm/sec  and a viscosity
of  v -  0.005 will  be  used in answering this.  The  unknown gradient  1
causes fluid flow at the rate
                       Tot"
Assuming that this water is saturated with  the  solute  in  question,  i  may
be found to be:

                    8 x 10~9  -  1.6 x IO3  x  i  x  10~5

                           i  -  5 x 10~7.
This is an extremely low  gradient  and suggests that much care  should  be
                                  IV-11

-------
exercised before diffusion is  regarded  as the  dominant  transport
mechanism.

F.  EXAMPLE:   BOREHOLE THROUGH A PILLAR

    The  repository pillars  may  be  considered  as  long  rectangles  of
constant width w; a borehole drilled  randomly through such a pillar will
have its  expected distance from a wall  approximately  equal  to w/4.  For
the present  calculations we  shall take w =  16 m,  so that  the  expected
shortest  distance  from borehole  to  drift will  be  4 m.   In fact,  the
borehole may receive material from the nearby drift as well  as  from the
one on  the opposite side of the pillar.  An upper  bound  on diffusional
transport may be  obtained by using  Model B, with nominal parameters as
follows:
rl •
C1 •
1
h =
r2 =
C2 =
n -
D =
0.2
0

5 m
4 m
io-5
10
io-6
m




Ci/ra3

O
cm Is
The corresponding mass transport is found to be:

               Q  -  3.3 x IO"11 Ci/yr

As earlier, it is important to compare this with  the potential transport
by a  convective process.   By  the  analogous structure  of Darcy's  and
Pick's laws, the equation corresponding to Model  B for fluid flow rate Q
may be written:
                        ZirKhAp
                     100p«,n(r2/r1)
                                      IV-12

-------
where Ap Is the head difference and p is the viscosity.
Taking u - 0.005 and K - 10~9 cm/sec, this yields:
                       Q  »  7 x 10"3 x Ap m3/yr.
                                   —5      3
If  this  fluid is  saturated at  10   Ci/m ,  say,  then Ap  may be  found
from:
              3.3 x 10~U  =  7 x 10"8 x Ap
                5 x 10   m =  Ap
Along a distance of 5 m of the borehole, the pressure drop corresponding
                                             -3
to a  gradient  of 0.001, say, will be  5  x  10   m.  Therefore, no matter
what  the pressure  in  the  waste  drift,  it will  differ  from that in part
 of  the borehole by  at  least   2.5  x  10~ ,  which is  five  times the
difference needed  to  approximate diffusional  transport.   This suggests
that diffusion will not dominate this  process.
 G.  TRANSIENT BEHAVIOR

    If  the  repository  is  breached some  time after  the  canisters have
 corroded  and  radionuclides have  diffused through  the repository, then
 initially the  mass  transport  out through  the release pathway will be
 greater  than  its  steady-state  value.    This is  because  the maximum
 concentration C* determined by solubility  limits may  be experienced very
 close to  the breach, leading  to  a high concentration  gradient  and hence
 a  high  diffusion  flow.    The  initial  flow is  best approximated  by
 assuming  it is  at  concentration  C~ of whatever other  initial values may
 be estimated for that point in time.
    Exit  flows  at  concentration  C2  should  continue  to be  used in the
 models until steady  flow has been  obtained.   A conservative  approach for
 dealing with this  factor may be developed  as follows:
    1.   Determine the  radionuclide  flow  rate (in Ci/yr,  say) out the
        release path.
                                    IV-13

-------
    2.   Determine  the  initial  stored  radionuclide  content  in  the
        diffusional  pathway  being modeled.    (Concentration limits  x
        water volume).
    3.   Determine how long it would take for the quantity calculated in
        Step  2 to be  removed  by the rate  from Step 1.
    4.    The   time  calculated in  Step  3 may  be  used  to  shift  to  a
        steady-state  diffusion  model.   In  fact, for  the  Model  A
        situation, one half of this time  suffices.
This  calculation is  not  intended  to  determine   the  time  at  which
steady-state  behavior  is achieved, but  it shifts the mass transport rate
in time so that  the cumulative amount  released by  any  point in  time is
greater than  or  equal  to  the actual  value.    In  this sense  it is  a
conservative  approach.
                                    IV-14

-------
           APPENDIX D~V



METHODOLOGY FOR U-TUBE CALCULATIONS

-------
                              APPENDIX D-V

                   METHODOLOGY FOR U-TUBE CALCULATIONS

A.  INTRODUCTION

    The  purpose of  this section  is to  analyze  the  flow  through the
repository  for  the  conditions  outlined  in  Figure  D-V-1,  where the
degrading  shaft seals  and  the  permeable  tunnel backfill  lead  to an
alternative path from point A to B.  While this additional path may  tend
to  decrease  slightly the driving potential  (head) between points A and
B,  it  is  conservative  to   ignore  this  effect.    Since  the  overall
resistivity  of the  alternative  path is  in general  still considerably
higher than  that of  the aquifer,  this  assumption is  probably not overly
conservative.

B,  MATHEMATICAL FORMULATION

    Darcy's  formula  will  form the basis  for the present  analysis.   In
its simplest form, it appears as follows:

                               Q  -  KiA

where
    •
    Q - flow rate through pathway cross section
    K « hydraulic conductivity, also referred to loosely as the
        permeability
    i - hydraulic gradient
    A " cross-sectional area
The hydraulic  conductivity,   in  units  of  length  per  time,  depends not
only  on  the medium through  which  water  is flowing, but also  on the
water's viscosity, which varies with temperature.  The numbers reported
in  the  literature  are  ordinarily  for  water  at  relatively  low
temperatures (a20°C) at which the viscosity  is approximately 0.01 poise.
Since  the  hydraulic  conductivity  is   inversely proportional   to  the
viscosity, the reported K values  must  be  divided  by the ratio y/0.01

                                   V-l

-------
                     Flow
                    Gradient i
Shaft
                   Mine tunnel
Shaft
                                                        Aquifer
   FIGURE D-V-1    TYPICAL U-TUBE SITUATION
                        V-2

-------
when  the  viscosity  U  is  expected  to deviate  significantly from  0.01
poise.  This might be  the  case,  for  example,  with  water flowing through
the  repository  during  its  period  of high  thermal  output.   A  table  of
viscosity values is given as Table D-V-1.  Dependence on pressure is not
sufficiently important  to require consideration for present  purposes.
    Consideration  of  viscosity,  as  outlined  above,  leads  to  the
following revised form  of Darcy's law:
                               0  _
                               *     100U
    where the dimensions are as follows:

    K       length /time
    i       dimensionless
    A       length squared
    100P    dimensionless (actually, poise/0.01 poise)
    •
    Q       length cubed/time
The factor
                              lOOy
is sometimes called the Darcy velocity.  It has the units  of length/time
but should be interpreted as a flux: volume per cross-sectional  area  per
unit  time.   When  the  Darcy velocity is divided by the porosity n,  an
approximation to the average fluid velocity is obtained.
    Darcy's  law may   be  considered  from  the point  of  view  of   its
electrical analog,  Ohm's law:
                                     I-
where
      R = resistance,
      E « the voltage over the resistance, and
      I = the current.
In the present case, the porous medium  is  the  resistance,  the  head  drop
is the voltage!  and the flow  rate is  the  current.   If the gradient  i
                                 V-3

-------
                   TABLE D-V-1
VISCOSITY OF LIQUID WATER AT ATMOSPHERIC PRESSURE
     Temperature                  Viscosity
        (°C)                       (poise)
          20                        0.0100
          40                        0.0065
          60                        0.0047
          75                        0.0038
         100                        0.0029
         125                        0.0022
         150                        0.0018
     Source:   American Institute of Physics Handbook, 1972.
              Data compiled  from other sources.
                     V-4

-------
originally derives  from  a head  drop A  over a length L,  that  is,
then the basic equation  is
                                   _
                                *      100UL
 from which  the parameter  correspondence  is  seen  to  be:
    resistance

    voltage

    current
This  correspondence  is  useful  in  analyzing  series  and  parallel  flow
paths, as  in  the present problem.

C.  ANALYSIS  IN PARAMETRIC FORM

    The following  symbols will be  used  for  the  parameters  characterizing
the situation shown  in Figure D-V-1:
    A  head drop from A to B
    D,  distance from A to B which also  equals  length  of mine  tunnel
    K^  permeability of filled mine  tunnel
    A.  cross-sectional area of mine  tunnel
    n,  porosity of  filled mine tunnel
    D«  length of  each shaft
    K2  permeability of filled shafts
    A-  cross-sectional area of each  shaft
    ^2  porosity of  filled shafts
As  mentioned  earlier,  the  slight  change  of  head  difference  between
points A and  B, due  to  the  development of an additional pathway  between
                                V-5

-------
 them will  be  omitted  from the analysis.   Thus,  the  problem amounts to


 three resistances In series,  as  sketched  In Figure D-V-2.


 The flow rate Is thus:
Interstitial velocities  In  each  segment are given by:
                             v.  .--a.
                             v
                              2
Head drops over Individual  segments are proportional to the resistances,


so that:
                              A   -
                              2
where  the  subscripts   1  and  2  correspond  to  tunnel  and  shaft,


respectively.
                               V-6

-------
  left shaft                     tunnel                   right shaft






                              100MD,
FIGURE D-V-2   SERIES RESISTANCE MODEL FOR U-TUBE CALCULATIONS
                          V-7

-------
D.  NUMERICAL RESULTS

    Of  particular  importance  in  this  report   is  the  upward  vertical
gradient i, in  the  so-called  right shaft.  On  the basis  of  the  previous
discussion, this can be calculated  from  the equations:
                                        "2         A
                                     a. +  2cu     L,
                                       i      z       t
                                     al + 2°2     L2
where  i  is   the  gradient  in  the  upper  aquifer.    For  calculational
purposes,  the variable  inputs  will generally  be i,  K. , and K_.   The
gradient  i will vary between  first and  second  estimates,  taking the
value 0.002  and  0.02, respectively.  K,  has the  value  10~  cm/sec for
             j                           •*-
salt and 10   cm/sec  for granite, basalt, and shale.  K-  is  a  function of
time due  to   the assumed  gradual degradation of the  shaft  seals.   The
first estimate is:

                   K2  -  3.15 x 10~3 + 3.12 x  10~5  t
and the second estimate is:

                      K2  -  3.15 x  10™3 +  3.15  x 10~3  t,

both based on Section  D-3.2.3.   The  other parameters  have been  given
previously in this  appendix.   Corresponding values  of i« are summarized
in  Table  D-V-2.   Note that while  the  gradients decrease with time, the
flow rates would  actually  increase since the  total  resistance of  the
series pathway is decreasing.
    A similar U-tube effect occurs  with  sealed boreholes.   Assume that
50  boreholes  penetrate  to  the repository  and  that  they  are  located
randomly.  Then the  resulting  flow would be  downward in  roughly 25  holes

                                V-8

-------
                                  TABLE D-V-2
          HYDRAULIC GRADIENTS IN VERTICAL SHAFTS DUE TO U-TUBE EFFECT
                                               Hydraulic Gradient (1)
Medturn
Years*
First Estimate
Second Estimate
Bedded Salt
Granite
Basalt
Shale
Dome Salt
100
250
1,000
10,000
100
1,000
10,000
100
1,000
10,000
100
1,000
10,000
100
250
1,000
10,000
0.033
0.030
0.019
0.00 A
0.017
0.017
0.017
0.040
0.040
0.036
0.040
0.040
0. 036
0.016
0.015
0.012
0.003
0.036
0.015
0.004
0.0004
0.167
0.121
0.033
0.363
0.200
0.036
0.363
0.200
0.036
0.032
0.015
0.004
0.0004
*Years after repository closure.
                               V-9

-------
and upward in  the  other 25,  and the mean distance  (projected  to  a  plane
parallel  to  the  direction of  aquifer flow)  between  the  boreholes  in
these  two sets  would  be  2000  m,  half the  length of  the  repository.
Using  area  and  permeability  parameters given  in  Section  D-3.3.3,  the
vertical gradients shown in Table D-V-3 may be calculated.
                              V-10

-------
             APPENDIX D-VI

EFFECT OF THERMALLY INDUCED BUOYANCY
           ON VERTICAL FLOW

-------
                             APPENDIX D-VI

          EFFECT  OF  THERMALLY^INDUCED BUOYANCY ON VERTICAL FLOW

A.   INTRODUCTION

    The heat  generated  by  radioactive  wastes  in  a repository  will
decrease the density  of any water  present.   The  reduced  density  will
result  in  an  upward   force  (due  to  buoyancy)  for  any water  column
extending  from  the repository to  the upper aquifer.   The water column of
interest may include all the water contained in rock pores or fractures
above the  repository,  or may be  the  water present in a specific breach
of  containment  pathway  such as  a  slightly  permeable  borehole.   The
situation  is illustrated in Figure D-VI-1.  Note that  the emphasis is on
the water  above  the  repository,  not  on the  rock  itself, and therefore
reference  is to the (generally  moving) column of water.   This phenomenon
has been discussed  elsewhere  *  '  ,  although various conclusions  have
been drawn concerning  its significance.  These previous discussions have
been  based  on  numerical  solutions  to two-dimensional  fluid-flow
equations  and on other fluid-mechanical  techniques.   The purpose of this
appendix  is  to  discuss  the  question  in  terms  of basic physical
principles, without  numerical  simulations  or advanced  analytical
techniques.  This approach should serve  to clarify the important factors
and  lead  to useful numerical  approximations of the  forces  created  by
this buoyancy effect.

B.  SIMPLIFICATIONS

    Any vertical movement   of  the water  in  the  rock surrounding  a
repository will  be  superimposed  on  the  prevailing,  largely horizontal
flow  pattern.   However, the water  velocities  through  the  surrounding
rock are sufficiently  small that  these horizontal  forces  and  motions can
be  omitted  from the  analysis  without  significantly  affecting  the
results.   In  fact,  it is  also conservative  to  ignore  such  motions
because they  tend  to  decrease  the  density gradient  and hence  the
buoyancy effect.   In the absence of horizontal flows induced  by regional
                                      VI-1

-------
                                                    Land surface
                                                    Aquifer
                         !;^— Water column acted on by
                         ll     upward buoyancy forces
                               t
                            Repository


FIGURE D-VM  CONCEPTUAL FRAMEWORK FOR BUOYANCY ANALYSIS
                           VI-2

-------
groundwater movement,  there will still  be horizontal flows  induced by
the differential vertical forces that result from density differences in
the water  column under  consideration.   The resulting flow pattern has
the general  shape shown  in Figure  D-VI-?.   However, these horizontal
components may also be  ignored  for  the present  approximate analysis, as
becomes especially clear by redrawing the previous figure with Identical
horizontal and vertical scales.  See Figure D-VI-3.

C.  OUTLINE OF APPROACH

    The  structure  of this  analysis is  illustrated  by the  sequence of
drawings in Figure D-VI-4.  Figure D-VI-4a shows two vertical columns of
water  connected  by a tube  at  the bottom.   Heating of the  left  column
results  in  a  lower density,  so there is  a  tendency for  water  to move
through the connecting  tube from right to left.   The  driving force for
this motion can be maintained approximately constant by inlet and outlet
pipes  to  maintain constant  water levels, as  shown in  Figure D-VI-4b.
The same driving force  and flow  rate  can  be obtained by considering an
equivalent  difference  in  water  levels,  rather  than water  densities.
This difference  is shown  in  Figure D-VI-4c.   In  order for  the  flow to
achieve a steady state,  the driving force must be  balanced  by an equal
and  opposite  resisting  force.   In  the  present  case,  the  dominant
resisting  force  comes from  the low permeability of  the  medium through
which  the  water  flow?.   While  it may be  argued  that  the corresponding
repository situation  implies  that this resistance  should  be present in
both columns  of  water,  at  the  outset of  the analysis  the conservative
assumption of resistance  only in the rising column will  be  used.   This
is shown in Figure D-VI-4d.  The driving force can be represented by the
effective hydraulic  gradient over  this  vertical  column,  calculated by
dividing  the  excess  height  of  the  right  column over that  of the left
column  (= head)  by  the  length  of  the  left  column.  (The  effect  of
resistance in the right column  is discussed later  In this  appendix.)
                               VI-3

-------
                                                 Land surface
                                                Aquifer
      \    N        /    /   /
         =M=      •
• Repository
         /     /
     FIGURE D-VI-2   CONVECTIVE FLOW PATTERN
M   t   I   I    I    I!   I    I    1

                                  SCALE: 1 cm = 460m
   FIGURE D-VI-3  SCALE DRAWING OF REPOSITORY
                                                    • Land surface
                                                    • Aquifer
                      VI-4

-------
(a)
                                                  "2
     /\
     Heat
/\
Heat
(0
(d)



I
1









 FIGURE D-VI-4  CONCEPTUAL DEVELOPMENT OF BUOYANCY MODEL
                        VI-5

-------
D.  OUTLINE OF COMPUTATIONAL APPROACH

    In  order  to  apply the  conceptual  model  described  earlier,  the
following data are needed:
    •   Temperature distribution  in the  overlying  rock  at  the time of
       interest.
    •  Water density as  a  function  of  temperature.
    •  Water viscosity as  a function of temperature.
    •  Permeability of  the water  column pathway.
    •  Effective porosity  of the  water column pathway.
These data enter  into  the  computational  framework illustrated  in Figure
D-VI-5.   The output  of such  computations  consists of  volumetric  flow
rates and travel times for water  from  the repository to  the aquifer when
driven by  the  thermally induced  buoyancy effect.   For  the purposes of
this study,  this  output may be interpreted  as  a lower  bound on travel
time  and hence a  conservative  estimate.  The equivalent hydraulic
gradient is  also  important for comparing this  driving  force with other
driving forces.
    In  addition  to  model  limitations  previously noted,  the  following
factors are also not included:
    •  Effect of dissolved material on density and viscosity.
    •  Effect of fluid flow on underlying temperature distribution.
Dissolved material  could have a  significant  effect on  density in case
the water passes  through a highly soluble medium such as salt.  In this
case,  the  vertical column moving upward would contain  more dissolved
material, and this would tend  to  counteract  the buoyancy effect.  It is
therefore conservative  to  omit  this  factor.   The effect  of dissolved
material on viscosity is too small to warrant consideration.  It is also
conservative  to   omit   the effect  of  fluid  flow on   the   temperature
distribution,  since  this  effect  is   to  decrease  thermal,  and  hence,
density gradients.  Furthermore,  the amount of heat transfer  that can be
accomplished by  the  fluid  flow appears  to  be  rather  small  (<10%)
compared with the total heat transfer.
                               VI-6

-------
81
S2
S3
S4
86
S7
89
     Pick time t.
     Obtain temperature
     distribution from
     other documents.
     Compute corresponding
     density distribution.
     Compute mass of
     vertical column
     of water
                                                     85
Compute mass of column
of water at normal tem-
perature.
     Determine vertical force
     on column and corres-
     ponding pressure.
     Convert to equivalent
     hydraulic gradient.
                                                     88
Compute water
viscosity for ambient
conditions.
     Determine flow rates and
     interstitial velocity by
     Darcy's law.
810
     Determine travel time
     from repository to aquifer.
 FIGURE D-VI-5   INFORMATION FLOW CHART FOR BUOYANCY COMPUTATIONS
                                    VI-7

-------
E.  DISCUSSION OF INDIVIDUAL STEPS

    SI:    Because   the   temperature  profile  varies  with  time,  these
    calculations need to be repeated for  the  points  in time that are of
    interest.

    S2:  Temperature distributions for various points  in time have been
    given  for  salt  and  granite  in  the Task  B  Report.  Temperature
    distributions  for  basalt,  granite, and  shale  have been  given
              (A)
    elsewhere.    These  distributions  depend  significantly on  several
    factors, such as:  age  and  composition of wastes, areal  density of
    waste,   thermal  conductivity  of  surrounding  rock,  heat capacity of
    surrounding rock, etc.   For  purposes  of the present calculations, we
    will  assume  the temperature  distributions  indicated  in  Figures
    D-VI-6 through D-VI-10,  which are "generic" approximations based on
    the aforementioned  sources.

    S3:  The  density of  liquid  water may be  estimated from  standard
    reference data.  Table D-VI-1 summarizes  selected  numerical  values.
    Pressures are not given with  these data,  but the  effect  on  density
    of pressure changes in  the  range of  1 bar (atmospheric)  to  50 bars
    (approximate hydrostatic  pressure  at 500m depth)  is  too small  to
    warrant consideration in this approximate analysis.   One  notes that
    50 bars is sufficient pressure to prevent  boiling at  250°C.

    Given the  temperature  distribution in a  vertical  column of  water,
    the corresponding density distribution is  then calculated by means
    of the  data in Table  D-VI-1.

    S4:  Previously, the  column of water under consideration  has always
    extended  from  the  repository level  to  the upper  aquifer.    In  the
    case of many breach-of-containment mechanisms, there  is no  question
    about  this  choice.   For  some  calculations, however,  it  may  be
    preferable to consider  a  column of  water  extending   from the upper
    aquifer down to  some  point below the  repository.
                                  VI-8

-------
360
-5 460
f
560
                  Time:   10 yr.
                (100,460)
                        I
               100       200       300
                 Temperature °C
360
                                             460
                                           f
                                           w
                                           Q
560
                                                                Time:  100 yr.
                                                          (50,360)
                             (250,460)
                                                          ),560)
                                                         100       200
                                                           Temperature °C
                                300
360
•§ 460
a
0)
Q
560
Time: 1,000yr.
% (100,360) 360
\ I
\ (150,460) | 460
/ 1
/
/ (100,560) 560
-
-
-
Time: 10,000 yr.
(50,360)
(50,460)
(50,560)
I i |
               100       200       300
                 Temperature °C
                                                         100       200
                                                           Temperature °C
                                300
     FIGURE D-VI-6   TEMPERATURE DISTRIBUTION FOR BEDDED SALT REPOSITORY
                                  VI-9

-------
                   Time:  10 yr.
    260
    460
f
    660
           (20,230)
(100,460)
            (20,660)
                  I
        _L
                 100        200
                   Temperature °C
                               260
€
I   460
                           a
                           0>
                           a
                              660
                                            Time:  100yr.
                                      (20,230)
                                                          (20,660)
                                             I
                  300
                            _L
                 100        200
                  Temperature °C
                     (250,460)
                                                                300
   260
J 460
OJ
Q
   660
                     Time:  1000 yr.
               (35,230)
  (125,460)
                 100        200
                    Temperature °C
                              260
   460
                                               £
                                                  660
                                            Time:  10,000 yr.
                                       (20,230)
(50,460)
                                      I (30,660)
                  300
                                            100        200
                                             Temperature °C
                                     300
        FIGURE D-VI-7   TEMPERATURE DISTRIBUTIONS FOR GRANITE REPOSITORY
                                           VI-10

-------
   360
I





I
0)
O
460
   560
                  Time:  10 yr.
                                             360
          a
          4)

          •§  460
                                          a
                                          Q)

                                          O
                                             560
                 I
                        I
                                                             Time:  100 yr.
                          •I
                                                                        I
                100        200


                  Temperature °C
                                 300
                                                          100       200


                                                           Temperature °C
                                             300
   360
w


I  460
   560
                   Time:   1000 yr.
                                             360
                                          .§  460
                                             a
                                             a>
                                             Q
                                             560
                                                          Time: 10,000 yr.
               100
                       200
300
                                                             100
200
                                                                             300
                  Temperature °C
                                                           Temperature °C
        FIGURE D-VI-8   TEMPERATURE DISTRIBUTIONS FOR BASALT REPOSITORY
                                        VI-11

-------
  360
-460
  560
                 Time:  10 yr.
          (20,410)
(100,460)
                I
      I
               100        200
                 Temperature °C
               300
                           360
          I
          1  460
          f
          V
          Q
                           560
                              Time:  100 yr.
                        (50,360)
                         100       200
                          Temperature °C
(250,460)
   300

360
S
0>
,§ 460
£
0)
Q
560
Time: 1000 yr.
\ (100,360) 36°
\ 8
) (150,460) ^ 46°
/ °
/(100.560) 560
I I I
Time: 10,000 yr.
—

••
-
(50,360)

(50,460)
(50,560)
               100
    200
300
                Temperature C
                                       100       200
                                         Temperature °C
                                                                               300
         FIGURE D-VI-9  TEMPERATURE DISTRIBUTIONS FOR SHALE REPOSITORY
                                      VI-12

-------
                   Time:   10 yr.
  260
.§ 460
(100,460)
           (20,510)
                 I
         I
                100        200

                  Temperature °C
                  300
                               260
S 460
                                               a
                                               0)
                                               a
                                                 660
                                          Time:   100 yr.


                                          (30,230)
             (30,660)
               	L_
                                                                          I
                 100        200

                  Temperature °C
                                                                                (230,460)
                                                                300
  260
E 460
  660
                   Time:   1000 yr.
  (110,460)
                  (80,660)
                            I
100        200

  Temperature °C
                                     300
                              260
•=• 460

f
0)
Q
                              660
                                             Time:  10,000 yr.


                                        (50,230)
                                                           (50,230)
             (50,230)


                  I	I
                                            100        200

                                             Temperature °C
                                     300
          FIGURE D-VI-10   TEMPERATURE DISTRIBUTIONS IN SALT DOME REPOSITORY
                                          VI-13

-------
     TABLE D-VI-1
DENSITY OF LIQUID WATER
Temperature (°C)
20
30
40
50
60
70
80
90
100
110
120
130
Density (gm/cm )
.99823
.99568
.99225
.98807
.98324
.97781
.97183
.96534
.95838
.9510
.9434
.9352
                      Temperature (°C)
                            140
                            150
                            160
                            170
                            180
                            190
                            200
                            210
                            220
                            230
                            240
                            250
Density (gm/cm )
    .9264
    .9173
    .9075
    .8973
    .8866
    .8750
    . 8628
    .850
    .837
    .823
    .809
    .794

-------
The following two principles should be kept in mind:
     a.   The  vertical velocity of  the water  column is proportional
         to the effective hydraulic gradient acting upon it.
     b.  The effective hydraulic gradient acting on a vertical water
         column  (due to  buoyancy)  is proportional to  the average
         density of  the column.
These principles will now be  applied  to  a repository whose vertical
thermal  profile  has  the  form  given   in  Figure  D-VI-lla.    The
corresponding density profile is given in Figure D-VI-llb.  A column
of  water  extending  down  just  to  the repository  has  some average
density Pj, as shown in Figure  D-VI-llc.  The slightly longer water
column shown  in Figure D-VI-llc has  a lower average density because
the addition  has  a  density  P_  which is  less  than PI .   To confirm
that  this  would increase  the  velocity  of  the column,  simply note
that  the  relatively high  buoyancy force  in the  lower segment would
tend  to  "push"  the  column above  it.   This  effect  continues  to
require consideration of longer  columns until  a  point  is reached
where the  average  density of  the  column equals the  density  of  the
next  additional increment.     In  calculations  of this  type,  the
maximum point will  often  be only roughly approximated.   Examples of
situations  in which such  longer  water columns  will  need   to  be
considered include  the following:

     •  Baseline flow through repository (no breaches).
     •  Boreholes penetrating some distance below repository.
     •  Faults extending below  repository.

The determination  of the  proper water  column  to   consider  and  its
average density  provides  the   information  needed  to  determine  its
mass  (or,  equivalently,  mass   per  unit  cross-sectional  area).  The
numerical differences resulting from consideration of  longer water
columns are generally not  very  large.
S5:  The density of a  corresponding  column of unheated water may be
conveniently and  conservatively estimated  as 1 gm/cm  .   With this
density, the mass of a column is easily determined.
                               VI-15

-------
                    Depth
                 a)

               Upper
               aquifer
            Repository
M
        Depth
       b)
   Upper
   aquifer
Repository
c)
d),—t
e)
                                                                                                              P2
                              Temperature
                Density of water
                       FIGURE D-VI-11   DETERMINING WATER COLUMN WHOSE VERTICAL VELOCITY IS MAXIMAL

-------
S6:   Let  L  represent the  length  of  the  water  column under
                                                        o
consideration and let p* be its  average density in gm/ctn .   Then for
every square centimeter of cross-section,  the gravitational force is
P*Lg, where  g  is  the  acceleration  due to  gravity.    The  opposing
buoyant force due to a  column of unheated water  is  1-Lg, and so the
difference is (1-P )Lg.
S7:  This force corresponds to a hydrostatic head of
                           (l-P*)Lg
                              Pg
 when  measured  in  terms  of water   at  an  arbitrary  density  p.
 Variations in  p  between p* and 1  do  not significantly affect this
 value,  so  that the computationally convenient value,  p  = 1 g/cm ,
 will be used.  Thus, the equivalent head is given by

                            (l-p*)L
 This yields a  hydraulic gradient i given numerically by
                               i -  l-p*.
  Note that i is dimensionless.  It is strictly equal to the quotient
  (l-p )/l, where  1 and P* ai
  cancellation of  the units.
(l-p  )/l, where  1  and  P*  are both  in  gm/cm  ,  thereby leading to the
  S8:   The viscosity of water  is  relatively insensitive to pressure
  in  the range under consideration.  Its dependence on temperature is
  shown in  Table D-VI-2.

  Because  of  this  temperature dependence,  no  single viscosity value
  actually  covers the entire water column.   Nevertheless, an estimate
  based  on average temperature  can  be made in order  to  permit the
  application of Darcy's law  (see below).

  S9:  The  vertical  flow of the water column will be approximated by
  Darcy's  law:
                        n  -  Ki
                        Q   Too"
                                    VI-17

-------
                  TABLE D-VI-2
VISCOSITY OF LIQUID WATER AT ATMOSPHERIC PRESSURE
     Temperature                     Viscosity
        (°C)                          (poise)
         20                            0.0100
         40                            0.0065
         60                            0.0047
         75                            0.0038
        100                            0.0029
        125                            0.0022
        150                            0.0018
 Source:   American Institute of Physics Handbook,  1972.
          Data compiled from other sources.
                       VI-18

-------
     where:
          *                     32
          Q  - flow quantity (cm /cm /second)
          K   - permeability   (hydraulic  conductivity  for  water  at
              viscosity 0.01,  in cm/sec)
          i  - hydraulic gradient (dlmensionless)
          W   - viscosity (poise, equal  to  gm/cm/second)
     The  denominator   100P  allows  for  corrections  due  to  different
     viscosities,  although  the numerical effect is at  most about half an
     order of magnitude.  Furthermore,
     S10:  The travel  time T from the repository to the upper aquifer is
     given by the  quotient
     where  D  is  the  distance  and  v is the velocity.   Note that D is the
     correct  parameter  here even if a longer column of water  (i.e., L >
     D)  is  under consideration.

P.   SAMPLE CALCULATIONS

    The  detailed computation of thermally induced convective flows is a
matter    for    the    consequence    calculations    in   specific
breach-of-containment  mechanisms.  Several examples will be worked out
here.

    1.   Baseline Flow Through Granite Repository  at 100 Years

        The temperature distribution shown in Figure D-VI-7 corresponds
    to  the  density distribution  shown  in Figure  D-VI-12.   Calculations
    show that  a  water  column of approximate length L • 305m has maximum
    vertical  velocity.   In  particular,  a  running  average  density  is
    recorded  as  the  column  length increases from L-0, and the Increases
    are  terminated  when the  density  equals (approximately)  the density
                                    VI-19

-------
           210
           260
           310
           360
           410
       3  460
       I
       Q
           510
           560
           610
           660
                                          I
                     I
              .78   .80    .82    .84
.86     .90    .92     .94

 Water density (gm/cm )
.96     .98    1.00
FIGURE D-VI-12  WATER DENSITY DISTRIBUTION FOR BASELINE GRANITE REPOSITORY AT 100 YEARS
                                             VI-20

-------
of the next  increment.   The corresponding average density value  is
P* =• 0.899.  This yields a hydraulic gradient of
                             .  i  =»  i - p* = 0.1.
    The other parameters  will  be  taken  as follows for this  sample
    calculation:
                               —9
                         K = 10   cm/ sec
                         U = .0022 poise  (taken at 125°C)
                         n = 10~4
                         D = 230 meters
    These numbers lead to a fluid velocity:
                         v
                             4.5 x 10   cm/sec
                           ~ 1.4 m/yr
    and hence a travel time:
                           = — = 162 years.
                                         —8
    Note that if the permeability were  10    cm/sec,  then  the  travel
time would be about 16 years.
2.  Flow Through Leaky Borehole Penetrating to a Bedded Salt
    Repository at 1000 Years

         In  this  case, the  length  L is  fixed at  100 meters,  the
distance from the repository to  the  upper  aquifer.   The temperature
range is  100°C  -  150°C,  as  shown  in  Figure  D-VI-6.    It   is
sufficient to estimate the average density to be P* = 0.94, based on
Table D-VI-1.  This  results  in a  gradient  i   =  0.06.    Other
parameters will be taken as follows:

                          K = 10   cm/sec
                          M = 0.0022 poise
                          v =• 0.1
                          D - 100 meters
                                 VI-21

-------
    These numbers lead to a fluid velocity:
                          v =• 2.7 X  10~5 m/sec
                            =8.5 m/yr
    and hence a travel time:
                          T = 12 years.

3.  General Results

    Tables D-VI-3 and D-VT-4  show the effective hydraulic  gradients
on  vertical  columns  of water  extending between  the upper aquifer
and the repository or some  point  below it.   (The difference between
these two cases is  usually  not very  great  and is  often blurred by
the interaction between breach pathways.)

G.  CALCULATION OF RELEASE TIMES

    The transit times  calculated  earlier are  useful  for estimating
the  instantaneous  transport  rates  at  particular moments  in  time.
However, if several hundreds  or  thousands  of years are  required for
the distance  from repository  to aquifer to  be traversed, the change
in velocity over time must be accounted  for.   As  an example of this
kind  of calculation,  consider the  case of  a gradually degrading
borehole seal.  The question is:  when do radionuclides  first appear
at the  aquifer?   For a granite repository,  ignoring  the effect, if
any,  of  repository resaturation time,  the  permeability of  the
                                                                  -8
borehole is assumed  (second estimate)  to degrade  linearly from 10
     -4               4
to 10   cm/sec over 10  years.  A formula for K is thus:
                                    -4      -8
                             -8   12 - =
                           10
                           10"8 + 10~8t
                           io~8 (i+t)  .
                        VI-22

-------
                              TABLE D-VI-3
            EFFECTIVE HYDRAULIC GRADIENT DUE TO .BUOYANCY OF A COLUMN
                 OF WATER BETWEEN UPPER AQUIFER AND REPOSITORY
Bedded Salt

Granite

Basalt

Shale

Dome Salt
10 years

0.02

0.01

0.02

0.02

0.02
                                    Time after closure

                                  100 years    1000 years
0.12

0.10

0.12

0.12

0.12
0.10

0.06

0.10

0.10

0.07
10,000 years

0.03

0.01

0.03

0.03

0.03
                                VI-23

-------
                                  TABLE D-VI-4


        MAXIMUM EFFECTIVE HYDRAULIC GRADIENT DUE TO BUOYANCY OF A COLUMN
         OF WATER BETWEEN UPPER AQUIFER AND SOME POINT BELOW REPOSITORY


                    10 years      100 years    1000 years    10,000 years

Bedded Salt         0.03          0.13         0.11          0.04

Granite             0.02          0.11         0.07          0.03

Basalt              0.03          0.13         0.11          0.04

Shale               0.03          0.13         0.11          0.04

Dome Salt           0.03          0.13         0.08          0.04
                               VI-24

-------
The average density of  the water  column  would  be approximately that
at the 350 m depth  (at  least  for  all times after 100 years).   From
the  data in  Figure  D-VI-7,   this  can  be  estimated as  on  Figure
D-VI-13.   The  analytic  approximation  to  the  temperature  curves
enables  straightforward computations.  Now  we  perform a  sequence of
velocity calculations  according  to the  earlier  outline.    The
porosity  is  taken  as  0.1.    The  results  are  summarized in  Table
D-VI-5;   and  it can  be seen   that for  the  first few hundred  years
(excluding about  the first  50-70 years),  the average  velocity  is
approximately 1 m/yr.   Thus,   it  requires  about  200 years to  cover
the distance from repository to aquifer.   The  first  releases  by this
mode  would  then  be  expected  at  about 250-300 years   after
emplacement.

H.  RESISTANCE  OF RECHARGE PATHWAY

    The model which has been  used in the calculations thus  far  was
sketched  as  Figure D-VI-4d and  is repeated as  Figure  D-VI-14a  in
this  section.    The  true physical  situation is  more  closely
represented by  Figure D-VT-14b,  in which  the  column on  the right,
called  the  recharge  pathway,  is  also  modeled  as  offering   some
resistance to fluid flow.   In  this case,  the total driving potential
remains the same, but it is dissipated over the two  columns,  so that
the potential  acting  on  the  release pathway  (the  left   column)  is
less.  It was  pointed out earlier that  to  ignore  this  factor is  a
conservative approach.    The  purpose  of  this  and  the  following
sections  is to  estimate the  degree of conservatism  involved and  to
provide a more  realistic model to  use where appropriate.
    The representations in Figures D-VI-4 and D-VI-14 are useful  in
determining  the effective  pressure  differential  tending  to move
fluid through the system, but  once this has been determined (as  in
previous sections)  it  is simpler  to use the model in Figure D-VI-15a
with  the electrical  series  resistance  analog  in Figure D-VI-15b.
                               VI-25

-------
        120
t 90
ui
oc


I
£

I
         60
         30
                       100
                               T * -30log10t
                                                T * - 60 Iog10t + 270
                                                 I
                            1000

                          TIME (t)
10000
FIGURE D-VI-13  APPROXIMATE TEMPERATURE PROFILE AT 350m IN GRANITE
                             VI-26

-------
                                                                    TABLE D-VI-5
                                                        CALCULATION OF VELOCITY FOR VARIOUS TIMES
<
l-l

N>

t
100
200
300
400
500
1000
2000
3000
4000
5000
10000

T(at 350m)
120
111
106
102
99
90
72
61
54
48
30
it

.943
.950
.954
.958
.959
.965
.977
.980
.986
.989
.996

i
.057
.050
.046
.042
.041
.035
.023
.020
.014
.011
.004

P
.0023
.0026
.0027
.0029
.0029
.0033
.0039
.0047
.0050
.0056
.0082

K(cm/sec)
1.0 x 10~6
2.0 x 10"6
3.0 x 10~6
4.0 x 10~6
5.0 x 10~6
1.0 x 10~5
2.0 x 10~5
3.0 x 10~5
4.0 x 10~5
5.0 x 10"5
1.0 x 10~4

v(m/yr)
.8
1.2
1.6
1.8
2.2
3.3
3.7
4.0
3.5
3.1
1.5

-------
(a)
                      (b)
                                                      1
                                                      I
FIGURE D-VI-14  RECHARGE RESISTANCE INCORPORATED IN EARLIER BUOYANCY MODEL
                               Flow direction
(a)
                   Recharge
                               Discharge
(b)
-~-vwvwv—vwvwv-
     FIGURE D-VI-15  SIMPLIFIED CONCEPTUAL MODEL FOR RECHARGE RESISTANCE
                                  VI-28

-------
(The  electrical  analog  has  been discussed  at  greater  length  in
Appendix D-V.)  The resistance of a pathway segment is given by
                         .-IL-
                             KA
where  L  is  the  length,  K  is  the  permeability,  and  A  is  the
cross-sectional area.   Non-uniform pathways may be  approximated  by
series  or  parallel  combinations of resistances,  which  may then  be
reduced  to an  equivalent  simple resistance.   In  cases  where  the
water  viscosity  changes  appreciably  during  transit  (because   of
temperature  gradients),   this   factor  may  be  incorporated  in  the
resistance term:
                         a a L • IQOU
                               KA
where p  is  the  viscosity  (in  poises).   For a potential drop  (head)
over a series of resistances,  the drop  over each .one  is  proportional
to its resistance.  In particular, for a drop A over  ct  and a**  the
effective potential acting on  the discharge path is
                                          "2
                                               A.
The  calculations of  the  previous  sections  were  based  on the
conservative assumption ou « a. so that A.  - A.
    The  following sections  will  discuss  the  application  of the
present model  to  particular  breach-of-containment mechanisms.  The
estimation of appropriate values of A- and L_ can  be quite difficult
because   of  the  complicated  geometry  of the flow  patterns.
Furthermore,  one must be  careful in applying  steady state models  to
systems in which parameters are changing over time.

I.  RECHARGE  THROUGH  BULK ROCK

    The approximate shape of  the streamlines for  the baseline flow
through  granite  is  sketched   in  Figure  D-VI-16.    The  shortest
recharge  pathway  would  be from  the  aquifer  rather   close  to the
repository and  its length could be almost  as small  as that of the
                          VI-29

-------
                                              Land surface
                                              Aquifer
FIGURE D-VI-16  QUALITATIVE ESTIMATE OF STREAMLINES
                        VI-30

-------
discharge path.  A  longer  length would generally be associated with
larger cross-sectional  areas for the  same  flow,  thereby tending to
counteract the  effect  of longer length or  resistance    ( <*= L/KA).
As  a consequence,  one can  imagine recharge  paths  with  as little
resistance as  the  discharge  path,  which  would entail  dividing the
earlier calculated  flows  by a factor  of  2.   This difference is not
significant in the order-of-magnitude  calculations being carried out
here;  consequently, this  effect has  not  been taken into account in
determining first  arrival  times at  the  aquifer  from  the  thermally
incuded convection mechanism.
    For determining  long-term cumulative  releases to  the aquifer it
is  important   to check whether the  present  calculations  grossly
overestimate  the flow  rates and,  if so,  what  correction  factors
might be appropriate.   In order  to simplify the geometry,  the model
shown in Figure D-VI-17 will  be  used.   The  repository is modeled as
                                                                 2
a hemispherical surface with  radius 1  km, giving an area of 2^(1)  =
     2                                                             2
6 km ,  or slightly  less  than  the  real  repository  area of  8  km".
(The  smaller  area  in  the  model  will  tend  to slightly overestimate
the  recharge  resistance.)   The  recharge paths  are  assumed  to  be
oriented  radially,   so  that  the  equipotential  surfaces  would  be
hemispherical.   (This  underestimates  recharge  near  the  aquifer and
overestimates it deep  in  the rock.)  Thus,  the hydrostatic head, h,
is a function of r alone in  this model.
     If water passes  through  the  repository at the flow rate  §, then
in   fact  the   same  flow  must  pass through  every  concentric
hemispherical surface.   Since by Darcy's law,  flux  is proportional
to pressure or head  gradient, it follows that

                        Q  =  K.  ^ • 2,r2
                                 dr

and  that  this  quantity is  actually independent  of  r.    (K is the
permeability; h  is  the head.)   Viscosity  is assumed  to be  that at
low  temperatures, so no correction factor is  incorporated.   It would
be  possible  to   incorporate  lower  viscosities  near  the repository,
due  to  higher  temperatures.   In comparing  the relative resistances
of  the  recharge and discharge  pathways,  this  factor  would  tend to
                                 VI-31

-------
a) Three dimensional view
                                                   Repository
                                                        Equipotential surface
                                                        for recharge streamlines
b) Two dimensional side view
                                                Repository
                        Recharge streamlines
FIGURE D-VI-17  HEMISPHERICAL REPOSITORY RECHARGE MODEL
                            VI-32

-------
increase the  relative weight of the recharge  pathway.   Integration
of the above differential equation for h, between arbitrary radii r.
and r_, yields
                      Ah  -  h(r2)  - Mr,)   . ^ < JL - JL )   .
 An equivalent resistance for the recharge path is  then

                             Ah      11    Is
                       M  <•»  	  M
                             Q       *
 The cumulative resistance from r. - 10 m  to r_ » »  is therefore

                       a          .  JL   _L_
                        recharge     2rrK

 It has previously been seen that the discharge resistance is given by

                                             L
                              Discharge  "  KA
                                                6   9
 and in the present case, L « 230m and A - 8 x  10  nr.  Therefore,

                       o   .       -  1.6 x 10~4 x   K
                        recharge

                       "discharge -  2.9 x 10~5 x   K
 In this case the recharge resistance is larger by roughly a factor of
 20.
                                VI-33

-------
    The cumulative fraction of  the  total resistance between  r^  - 1 and
an arbitrary value r- is given  by the factor
                      1  - l/r2

for which  selected values  are  shown in  Table D-VI-6.   It  is clear that
the preponderance  of the resistance  to  recharge  flow is  close  to the
repository.  The  reason is  that the effective  cross-sectional  area for
recharge  increases  faster  than  the  corresponding distance from  the
repository.
    The implication  of  a recharge  pathway resistance  of 10  or  20 times
that for discharge would be to decrease  the  corresponding  flow rate by
the same factor.  Whether this  factor  should  be incorporated depends on
an additional factor, which is  discussed  in the next section.

J.  NON-STEADY-STATE FLOW

    The calculations in the previous  sections have  been  based  on the
assumption  of  steady  state flow.   This  assumption  may  underestimate
actual flow  in case  there are  transient  sources of fluid  closer to the
discharge  path.   A  potentially important  source  consists of  the void
spaces in  the repository backfill and  in the  surrounding rock.   Changes
in temperature and hydrostatic  pressure in a rock mass can cause changes
in  void  space  volume  with  the  result   that  water  can  be stored  or
released.    If  the  potential changes  in   total stored  water  are
substantial,  compared  with the volumetric flows  being calculated  for
certain  failure   elements,  then  the recharge  resistance  assumes less
importance  because  the  water   may  be coming out  of  storage  instead.
Figure D-VI-18  illustrates  a  potential  storage release  mechanism.  The
                                 VI-34

-------
              TABLE D-VI-6
FRACTION OF TOTAL RECHARGE RESISTANCE
    BETWEEN rx - 1 km AND GIVEN r2



   r2 (km)            fraction (1 - l/r2)


      2                       1/2

      3                       2/3

      4                       3/4

      5                       4/5
                              n-1
                              "
                    VI-35

-------
(a)
(b)
      Rock with fractures
      and pores before
      repository resaturation
       Expansion of openings
       by hydrostatic pressure
       during resaturation
                          (0
                            Partial contraction of openings
                            due to decrease in hydrostatic
                            pressure from heating of water
                            and corresponding density change
                 FIGURE D-VI-18  PORE WATER RELEASE MODEL
                                        VI-36

-------
extent of this mechanism obviously depends on the timing of resaturation
compared to  the  peak thermal period, both of  which depend on many site
and repository parameters.
    Since the  purpose  of this section  is  primarily to estimate whether
the quantities  of water  available from  storage could be  an important
factor  to  consider,  two example  calculations  will  be  carried out, one
for the  water  stored in  the repository backfill and  one  for the water
stored in the rock itself.
    From  Appendix D-II,   the void  space  volume  in  the  backfill  is
                            f Q
expected to be about 2  x 10 m .   The actual volume  is a function of the
effective stress  on  the backfill,  which equals  the total  stress minus
the effect of fluid pressure.  If the overburden has shifted so that the
backfill  has  voided  mechanical   equilibrium,   then the  total  stress
remains  essentially  constant, so  that  changes  In  fluid  pressure imply
equal changes  in effective stress, although in  the opposite  direction.
These changes  in effective stress change  the  volume,  primarily because
of  grain movement.   The  parameter that  measures   this  effect  is  the
compressibility  a, defined  as   the  fractional  volume  change  per  unit
change  In effective  stress.  Representative volumes are  shown in Table
D-VI-5,  which  also shows  the compressibility  of water.   The change in
hydrostatic  pressure  due to  changes  in density  of  the overlying water
has been discussed  earlier  in  this  report.   For  a granite  repository
with a distance of 260m from  the repository to the water table, a change
from P  - 1  to P  « P*  « 0.95 results in  a pressure change of 17 psi at
the repository depth.  With  a normal  compressibility of 10   psl  , the
                                          3
corresponding volume change  would  be  340m .   This number is larger than
a  number of  flow rates  calculated  in the  main  text,  in  which  case
recharge resistance might not be an important factor.
    Similarly, the storage  capacity  of  the bulk rock may be  considered.
                             -4
Using a  porosity  value  of  10  ,  the void space volume in the  rock below
the repository down to a depth of 1000m is given  by
                        V -  (8 x 106m2)  (540m)10~4
                                  5 3
                          - 4 x 10 m
                              —7     -1
With a  compressibility of  10   psl   and a pressure  change of 17 psi,
the water released would equal the change in rock volume, given by
              7.3 x 103 -  (8  x 106m2)(540m)(10~7  psi"1)(17 psi).
                                    VI-3 7

-------
Note that since  the  rock volume is so much larger  that  the water volume
stored  in voids,  the  compressibility  of  the  water  itself  has  little
importance here.   At the rate  calculated  above,  the  flows  through bulk
rock could not be met for long using this source of water.  Obviously, if
the  parameters  were  different,  then  possibly the  compressibility could
have some effect on the flow calculations.

K.  CONCLUSIONS ON RECHARGE RESISTANCE

    For  the  case  of  flow  through granite,  it  appears appropriate  to
decrease  by  an  order  of magnitude  the  effective hydraulic  gradients
                                      *
calculated by  the  formula  i  =  1- P ,  in  order   to   account  for  the
resistance of  the  recharge  pathway.    In basalt  and  shale,  water  is
available from the lower aquifer.   For  large breaches, such  as  faults,
recharge can occur through  the  fault  itself,  and no  recharge  resistance
should be included.  This appears  to be  a  conservative  approach, but  not
overly so.   For small  breaches, such  as boreholes,  sufficient  recharge
resistance can  be assumed  through the  repository,  so  that  significant
resistance along this part of the system cannot  be assumed.
                                 VI-38

-------
REFERENCES APPENDIX D-VI

1.  Dames   &   Moore.    Technical  Support  for  GEIS:  Radioactive Waste
    Isolation  in  Geologic  Formations.  Vol.  21:   Ground Water Movement
    and Nuclide Transport.  For  Office of Waste Isolation, Union  Carbide
    Corporation.  Y/OWI/TW-36/26.  April 1978.

2.  Ka'rnbra'nslesa'kerket (KBS).   Handling of  Spent Nuclear Fuel and Final
    Storage  of Vitrified  High  Level Reprocessing  Waste.   Stockholm,
    Sweden.  December 12, 1978.

3.  Apps,  J.A., et al.   An Appraisal of  Underground Radioactive Waste
    Disposal  in Argillaceous  and Crystalline  Rocks:  Some  Geochemical,
    Geomechanical, and Hydrogeological Questions.      Lawrence Berkeley
    Laboratory.  LBL-704.  June  1978.

4.  Dames   &  Moore.   Technical Support for  GEIS:    Radioactive Waste
    Isolation  in  Geologic  Formations.  Vol. 20: Thermomechanical  Stress
    Analysis and  Development  of  Thermal  Loading Guidelines.  For  Office
    of  Waste  Isolation,  Union   Carbide  Corporation.   Y/OWI/TM-36/20.
    April  1978.

5.  Chemical Engineers Handbook.  R.H. Perry and C.H.  Chilton, eds.   5th
    Edition.  McGraw-Hill Book Company, New  York.  1973.

6.  Freeze,  R.A.  and J.A.  Cherry.   Groundwater.   Prentice-Hall, Inc.,
    Englewood  Cliffs, N.J.  1979.
                                     VI-39

-------
APPENDIX D-VII




  SALT CREEP

-------
                               APPENDIX D-VII

                                 SALT CREEP

A.  INTRODUCTION

    When  subjected  to  loads  for  extended  time  periods,  many  materials
undergo gradual  plastic  deformation subsequent to  the  initial elastic and
plastic response.  This  gradual  deformation is known as  creep and,  of the
geologic media under consideration, it appears significant only in the case
of salt  deposits.   This  suggests  a possible  advantage of salt  for waste
containment because certain  breaches may tend to  be "self-healing" through
plastic  creep.   This  appendix  provides the  basis for  analysis of  this
healing process  by  examining the creep  closure of  cylindrical openings in
salt.   The principal  mathematical method  used  is a  standard engineering
approach for the analysis  of three-dimensional creep.      In the following
analysis, this method is combined with empirical data and a stress analysis
of a circular opening to produce estimates of  closure times.

B.  MATHEMATICAL CHARACTERIZATION OF STEADY-STATE CREEP

    This analysis will be based  on a steady-state uniaxial creep law due to
       (2)
Heard.     The law may be stated as follows:

                           -    in-6  -11833/6   5.5                      (1)
                    e  =  3  x 10   e          a                        v  '

where

     ° »  applied stress (bars)
     9 =  temperature ( K)
     e =  strain rate (sec   )

After  conversion of  stress  units  to  psi  and  evaluation  at  60°C,  the
equation becomes

                           e  =  1.1 x ICf20  a5'5
                                    VII-1

-------
    Since  this  is  a  uniaxial  law,  it  is  necessary  to  develop  a
generalization  to describe  creep  in  response  to a three-dimensional stress
field.    In the  development,  the  stress  field  is  represented by  three
mutually  orthogonal  principal  stresses  denoted  o.,  a^t  a$  an<*  their
corresponding  strains  e ,   e.,   e  .     The  basic  assumptions,  based  on
observations of  plastic  flow,  are that during  creep  there is  no change of
volume and  that  the principal  shear  strain  rates are proportional to  the
principal shear  stresses.   Under  the  assumption that  the  strains are  small
compared  to unity and that  there  is  no rotation of the strain  axes,  these
assumptions may be expressed mathematically as
or                           ei "*" £2
                        - °2     °2 * °3
where  C is a  constant  at a  given point and  time in  the stressed  body.
Together, equations (2)  and (3)  imply that
                           -  f C
In order to  fully  characterize  the three-dimensional creep, it  remains  to
determine the constant C based on the  uniaxial  creep  law of  Equation  1.

    There are  a number  of  approaches to  this,  but  a  standard  technique
(supported   by   experiment)   is   to  assume  that   in  steady-state
three-dimensional creep,
                                       VII-2

-------
                                       «„*)
            *
      •
where e , o   are,  respectively, the octahedral  strain rate and octahedral
stress as defined by:
              o* -    -  ((al - a2)  +  (o2 - a3)  +  (o3 - o^]

    Combining this  with  Equation 4  and the  uniaxial law,  Equation  1, it
follows that:
                   1.1  x  10~2°(o*)4'5[a1  - i
                   1.1 x 10~20(o*)4'5[o2 - f
              e3 »  1.1  x  10"2°(o*)4'5ta3  - | (ax +  o2)]
This  provides  the  required  description  of  three-dimensional  creep  in
response to a general stress field.

C.  APPLICATION TO CLOSURE OF A LONG CYLINDRICAL OPENING

    In order  to model the  creep  closure of a borehole or tunnel shaft, the
above result can be interpreted for the case  of a long circular cylindrical
opening.   The stresses result  from the  ambient  lithostatic pressure.  It
will be  assumed  that the creep is  steady state, the  medium is isotropic,
and the  cylinder  is very  long  in relation to  its  radial dimension.  From
                      (3)
the literature  (e.g.    ),  it can  be demonstrated  that,  based  on  these
assumptions  and  if  the  pressure  in  the  borehole  is  much  smaller than
lithostatic pressure, the following principal stresses are present  at  the
                                    VII-3

-------
boundary.
                                  Q0  =  2p                      (6)


                                  ar  -  °




where p is the lithostatic pressure and the principal stress directions are


taken along the cylindrical coordinate axis.



                                            *
    It follows that the octahedral stress, a  is given by




                 r                                        I


          °*  =  -r [(ar - °e)2 + <°r - °z)2 + (oe - °z)2]2



              = 1.2p
Application of Equation 5 implies that the radial strain rate is given by




             er = 1.1 x 10'2°(o*)4-5[ar - \ 
-------
assumptions were made.   Some  of  the most  important  are:

    •  The  creep closure is characterized as  a steady-state  process,

    •  The  surrounding  salt is completely homogeneous.

    •  The  creep behavior  is  described  as
            **              -20    SS-1
            e    -   1.1 x 10   (a*) ° yr
where
            e*  =   octahedral  strain  rate
             *
            a  =   octahedral  stress
    •  The  creep  process  occurs  without  net  change of volume.

    •  The  principal  shear  strain  rates  are  proportional to the principal
       shear  stresses.

    The first  two assumptions are  made to permit an analytical estimate of
closure rates for  a  generic  repository.    To  eliminate  these assumptions
would require detailed finite  element analysis, which is  not feasible in
the  absence  of  site-specific  information.   Such  an  analysis   is  not,
however,  expected  to  alter the order of magnitude  of the results.   The
third assumption  is based on  the most  recent empirical  impure  data  obtained
for  the  WIPP  project  and  is felt  to represent  the  best available
information on salt  creep  under expected conditions  in  the  vicinity of a
repository.  The  final  assumptions are standard in the analysis of plastic
creep  and  are  based  on  extensive  observations  of creep processes.
    The  result  of  the   analysis  is  that   the  opening   will  close
according  to  the  following  relation:
                                        VII-5

-------
                          ,  „          -1.1 x 10~2  t
                         r(t)   =•  r  e
where

         r   «  initial radius
          t  =  time since opening was created
       r(t)  -  radius at time t .

The breach-of-containment mechanisms discussed in this report involve holes
in  the  range of  10  cm  to  5  m  in  radius.   Table D-VII-1  summarizes  the
resulting closure of holes in this size range.
    From  the  governing equation  it  is  clear  that both  radius  and
cross-sectional area,  considered  as  functions of time, are  concave up, so
that  between  any two  points  they  are  bounded  by  the  linear  function
connecting those  points.   For simplicity, therefore,  cross-sectional area
can be modeled as a  linear  function  of  time, equal to 0 at a time when the
opening may be regarded  as  essentially  closed.   Since  for long tunnels or
holes the  volume can  also  be modeled  in  this  fashion.   For non-circular
openings, closure can be considerably faster  than  for  circular  ones and it
is, in general, conservative  to  use  the closure  rates  for  the latter.  For
backfilled openings, the fractional  rate  of  change of  the pore space will
be  taken  to  be  the  same as for the open holes.   To cover  all these cases,
two very  simple  rules have been adopted, therefore.   For  first  estimate
calculations, the void space of  an  open or  backfilled opening  in  salt is
assumed  to  decrease linearly  to  approximately  zero  in 200  years.   This
number  is consistent  with  the  above  calculations.  For  second  estimate
calculations, the void  space  is assumed to  decrease to approximately zero
in 1000 years.  Slower creep could result from the nature of  the overburden
and interbeds, as well as from impurities in  the salt itself.
                                      VII-6

-------
                              TABLE D-VII-1
         ESTIMATED CLOSURE RATES OF CYLINDRICAL OPENINGS  IN  SALT
                                                      Radius  (m)
Percent/closure    Times  (vrs)
  50
  90
  99
 60
210
420
                   O.lm initial
5 x 10
                                                -2
1 x 10
                                                -2
1 x 10
                                                -3
5 m initial









    2.5






    0.5






    0.05
                                        VII-7

-------
                              REFERENCES
1.  Finnie, I., and W.R. Heller.  Creep of Engineering Materials.
    McGraw-Hill Book Company, Inc., New York, 1959.

2.  Sandia Laboratories (Dawson, P.R. ).  Constructive Models Applied in
    the Analysis of Creep of Rock Salt.  SAND 79-0137.  Jan., 1978.

3.  Timoshenko, S., and J.N. Goodier.  Theory of Elasticity.  McGraw-Hill
    Book Company,  Inc., New York, 1951.
                                   VlI-3

-------
          APPENDIX D-VIII

CANISTER CAPABILITIES FOR LONG-TERM
             ISOLATION

-------
                             APPENDIX D-VIII

              CANISTER CAPABILITIES FOR LONG-TERM ISOLATION

A.  INTRODUCTION

    The  systems  under consideration  for  nuclear waste  isolation  offer
many barriers  for waste  containment,  including the waste  form itself,
the  canister and  overpack  materials,  the  vault  sleeve and  backfill
materials,  and  the  geologic   formation.     The  geologic  environments
currently being  investigated  are salt and hardrock  formations,  as  well
as sediments on  the  ocean  floor.   The waste may be directly disposed as
spent fuel  rods  or may be altered  to  a different form.   This  appendix
will consider the  protection that may  be  expected  from the canister and
overpack layers.

B.  CANISTER SYSTEM DEVELOPMENT

    There  are  four   steps  in  the  development  of  a  canister  system:
         1.  performance criteria development and environmental
             specifications;
         2.  materials development;
         3.  canister design; and
         4.  system demonstration.
These steps may be worked  on concurrently  but they must be completed in
sequence.
    The development  of performance  criteria  will  set lifetime goals for
the canister.  It  must be  determined  whether the canister should remain
intact  for  (a)   retrlevability  purposes,  about  25  years, (b)  the  high
radio/thermal activity period,  500-1000 years, or  (c)  the radionuclide
lifetimes, up to 10  -10  years.   The  controlling failure mechanisms and
rates   for  a  given  material  will  depend  upon  many  environmental
parameters, which in  turn will vary with the geology and the waste form.
Estimates  for  several parameters  are given  in Table D-VIII-1.   These
estimates  have  not  been  designated  as design  criteria but have  been
useful guides for experimentation.
                               VIII-1

-------
                             TABLE D-VTII-1
                         ISOLATION ENVIRONMENTS*
Geologic Formation     Maximum
   and Waste Type     Temperature   Pressure    Chemistry
Bedded Salt

  Transuranic-Low
  Level Waste
                         30
  Spent Unreprocessed
  Fuel                70-100
  High-level Waste
                         250
Sub-seabed Sediments

  High-level Wastes      200


Shale, Hardrock,  Tuff

  High-level Waste   250-300
14.5 MPa   Dry (1/2%) 95% Nad
                                    17.9 MPa   Dry (1/2%) 9«%
17.9 MPa   Dry (1/2% H,0) , 98% NaCl
           with potential localized
           intrusion of
           NaCl-KCl-MgCl. brine (due
           to thermally induced
           brine migration)
                                    55   MPa   Seawater-saturated
                                               sediments (40% solids)
                                  Atmospheric  Air + steam for » 100
                                               years,  then possibly
                                               inundated groundwater
*Does not take radiolysis  into  account
Source:
         Braithwaite,  J.W.,  and  N.J.  Magnani.   Corrosion Considerations
         for Nuclear Waste Management.   In:  Scientific  Basis  for Nuclear
         Waste  Management, G.J.  McCarthy,  ed.,  Plenum Press,  N.Y. ,  1979.
                              VIII-2

-------
    Once the design  goals  and  service conditions are set, input from  a
materials development program  is  necessary.   Laboratory  experiments  can
generate general  corrosion  rates,  but it is also  important  to  quantify
the susceptibility of materials to  localized  corrosion that  will result
in accelerated corrosion rates.  Localized  corrosion mechanisms  include
pitting,  crevice corrosion,  and  stress-corrosion cracking.    The
following sections will summarize the materials development  work in  the
United States and Sweden.
    When the materials are sufficiently characterized,  an integration of
the information  should  result  in  a  canister design  that can meet  the
lifetime goals in the specified environment.  It is not  clear whether  a
single  barrier   or  a multi-barrier system will  be  preferred.    A
multi-barrier system must be designed carefully,  so that  the  presence or
failure of  one  barrier  will  not  inadvertently  hasten  the  failure of
another-  This effect  could occur  by galvanic  corrosion if two metals
are in  contact  or when  the corrosion product of  one  barrier could be
especially aggressive to another barrier.

C.  U.S. MATERIALS DEVELOPMENT PROGRAMS

    The materials development  program  in  the United  States is  in an
early stage.  Many materials are being evaluated  but no specific systems
have yet been  singled  out.  The broadest-based  U.S.  study  has  been at
Sandla  Laboratories  where  a  number  of  metals  have been evaluated as
                                                    (1 2)
potential   high-level  waste  canister  materials.  '      Laboratory
investigations there have  measured  coupon weight losses   for periods of
2-8  weeks   in autoclaves.    The   solutions  modeled  brine   from   salt
formations  and  seawater   from sub-seabed sediments.   Temperature,
dissolved oxygen,  and  moisture content  were also varied.   Sandia  has
also been active  in bench-scale heated salt block experiments as well as
full-size heated  field  tests.   As  a  result, Sandia has  selected  eight
metals for  further study.   The criteria for selection  included corrosion
resistance  as  well  as  metal  cost  and availability.   The eight metals
are:   1018 mild steel;  Corten A  steel,    ;  lead;  90-10 cupronickel;
SS-Ebrite 26-1,(b);  Monel  400,(c);  Inconel  600,(c);  and Ticode 12.(d)
                               VIII-3

-------
Table D-VIII-2  summarizes  the corrosion  rates  of these materials  in a
brine and a seawater solution.
    It appears possible to design an overpack material to last thousands
of  years  if  general   corrosion  is  known  to   be   the  only  corrosion
mechanism at work.  This conclusion  is  similar  to that presented in the
Task  B  Report.   Autoclave  experiments  provide  general  corrosion rates
but are  not  very helpful in providing  accelerated  rates  resulting  from
local corrosion mechanisms.
    Work under  way at  Battelle's  Pacific Northwest  Laboratories (PNL)
will  complement  the results  from Sandia  and  continue  the  broad-based
approach.      Autoclave  experiments  will  provide further data  on
corrosion  rates  utilizing  both  groundwater solutions  and  brine.   PNL
will  investigate ceramic and  polymeric materials as  well as  metals.
    The materials  development  program at  Savannah River Laboratory  has
been  limited  to  studying  canisters   for  vitrification  (through  either
continuous or in-can melting).     The  canister  lifetime goals have  not
been  in  the range  of  thousands of  years but  rather are  intended  for
interim storage and shipping  purposes.  Overpack materials  are  not being
studied.
Trademarks:    (a)  U.S.   Steel  Corporation,   (b)  Allegheny  Ludlum
             Industries, (c)  Huntington Alloys,  and  (d)  TIMET.
                              VIII-4

-------
                               TABLE  D-VIII-2

                CORROSION RATE IN BRTNE  AND  SEAWATER OF THE
                         EIGHT CANDIDATE MATERIALS
                                    Brine                    Seawater
                                   (mm/yr)                    (mm/yr)

1018 Mild Steel                     1.7                       0.4

Gotten A Steel                      0.9                       0.2

Lead                                0.5                       0.3

90-10 Cupronickel                   0.14                       0.07

SS-Ebrite 26-1                      0.016                     0.005

Monel 400                           0.03                       0.1

Inconel 600                         0.009                     0.005

Ticode 12                           0.0006                     0.005
Source:  Braithwaite, J.W., and M.A. Molecke, High Level Waste Canister
         Corrosion  Studies Pertinent  to  Geologic Isolation.   NRG
         Conference on High Level Radioactive  Solid Waste Forms, Denver,
         December 19-21, 1978.
                              VIII-5

-------
D.  SWEDISH PROGRAM

    The  Swedish  Corrosion Institute and  its  research group  seem  to be
somewhat  ahead  of  the  United  States  in regard  to  the  four  steps  of
canister  development.   Granite  rock has been  specified  as  the geologic
environment.  Three specific alternatives for the disposal of spent fuel
in hardrock formations have been recommended:
    1.  reprocessed waste in a 6 mm-thick titanium canister  with a
        100-mm thick lead lining,
    2.  spent unreprocessed fuel in a 200-mm thick pure copper canister;
        and
    3.  spent unreprocessed fuel in 100-mm thick aluminum oxide canister
        produced by hot isostatic pressing.
    The  feasibility of  manufacturing  aluminum oxide  canisters  by  means
                                                          (4)
of hot  isostatic pressing  (HIPing) has been  demonstrated.      HIPing  is
a  process that  produces  very  dense  ceramic  bodies  without  excessive
grain  growth but  is  normally   applied  to  much  smaller samples.    An
aluminum  oxide  lid  can  be sealed onto the main  body, also  by  means  of
HIPing.   The flat  surfaces  that  form  the seal must  first be polished  to
a flatness of + 25 ym.
    Aluminum oxide  is in  its highest  oxidation  state and  is therefore
very  stable  in  groundwater.   It will, however, be  hydrated  on surfaces
in contact  with  water,  which may result  in  flaking.   This  reaction  is
very  slow  and   aluminum  oxide  should  easily  resist  the  action  of
groundwater  for  a  million years.    Being  a  ceramic,  it  is  very
susceptible to  slow  crack growth,  which could lead to delayed  failure.
In order  for this to  occur,  a surface defect  and  tensile stresses,  both
of sufficient magnitude,  must be present.   The  stresses may be due  to
residual stresses from  fabrication or applied  stresses  from  rock
movement.   Care must  be taken during fabrication of  these  canisters  to
minimize  defects  and  residual  stresses.    Nondestructive  evaluation
techniques may  be  used  to verify  the  maximum defect size  before  final
disposal.
    A  copper   canister  was  also  designed  for  the  isolation  of
unreprocessed spent  fuel  assemblies.   '      It  is to be made  from very
pure oxygen-free high conductivity (OFHC) copper.   The fuel  rods  are to
                              VIII-6

-------
be stripped  from  the metal  components of the assembly to maximize space
usage.  After the rods are placed in  the copper container, the spaces in
between will be  filled  with lead.   Three  copper  lids are then electron
beam welded  to seal the can.
    Copper is a  relatively  noble metal  and  free  oxygen  and  sulfide are
the  only  constituents  of  groundwater  that can potentially  cause
corrosion.  Considering all of the sources of free oxygen and sulfide in
the  repository,  a  weight loss  estimated  at 60  kg  will occur  after  a
million years.   This  loss corresponds to an average  corrosion  depth of
0.5  mm or a maximum depth  of  2.4  mm  if   the top  of  the  canister is
attacked more heavily.  Copper  is not highly susceptible to  pitting but
it  can occur in some  cases.    Using an  empirical  model,  the  maximum
attack depth after  one million years  is  predicted  to  be  60 mm or 30% of
the wall thickness.
    In Sweden, the  storage container  for vitrified reprocessed waste has
                                                       /a \
been designated  to  be  a  lead-lined   titanium canister.     The  waste is
to  be  cast  into  or melted  in a  stainless  steel   cylinder.    These
stainless  steel  cans  will be placed  in  the  prefabricated lead-titanium
canister and  any extra space  filled with molten  lead.   The  container
will be  sealed  by  a welded-on  titanium  lid.    Both  the lead  and  the
titanium are to be very pure.
    Titanium develops  a  passivating  layer  of Ti02»  which  forms
spontaneously  and  protects  against corrosion.    Assuming  a  constant
corrosion  rate,  the 6-mm thick  casing  should last beyond thousands of
years.  Pitting, crevice  corrosion,  and stress-corrosion cracking do not
appear to be problems.  The initial  prediction of lifetime was thousands
          (8)
of  years,     but a recent  report  has  downgraded  the lifetime of  the
               (9)
titanium shell.      This  revision was based  on  a  slight  risk of delayed
failure  from the   presence  of  hydrogen,  causing  penetration  of  the
titanium  in  a  rather  short  time.    Hydrogen can  diffuse   through  the
titanium and  become concentrated at defects.   This action  results in
embrittlement, and  possibly  delayed  fracture, at  tensile  stresses much
lower than those  normally involved.   Small  amounts  of  hydrogen will be
present in the  fabricated titanium  and  hydrogen  may also   evolve  as  a
corrosion product.  It  is  very difficult, however, to predict the extent
to which this evolved hydrogen will  be absorbed.   Although this type of
                              VIII-7

-------
delayed  failure  has  never been  found  in unalloyed  titanium,  it  is not
completely understood,  and thus,  the  risk of  its  occurring  cannot be
eliminated completely.  Therefore, no  lifetime  limit has been predicted
for the titanium casing.
    Pure lead is also very corrosion-resistant.  Because of the titanium
casing,  any   attack   on  the  lead  would  be  localized,  with  the  rate
dependent  upon   the  amount  of  available  oxygen.    Estimates of  this
quantity lead to a predicted  lifetime  of  thousands of years for the 100
ram-thick lead lining. According to  Swedish estimates, the total lifetime
of the lead-lined titanium canister in groundwater is given as thousands
of years, although it probably will be tens of thousands of years.

E.  SUMMARY

    The canister development program in  the United  States is  not  at the
stage where  it  is possible  to make  an  estimate of  canister  lifetime.
Specifications for the  service  conditions  must be  set  and  considerable
materials development work is still needed.  When this is all  integrated
into  a canister design, a  lifetime evaluation  will be  possible.
However,  from results  to date of  the  U.S.  program  and  taking  into
account the  Swedish  work  on  specific canister  systems,  it  seems  highly
likely  that  it  is possible to  design a  viable canister  that  will  last
thousands and possibly tens of thousands  of years.
                              VIII-8

-------
REFERENCES - APPENDIX VIII

1.   Braithwaite,  J.W.,  and N.J. Mag nan1.   Corrosion Considerations for
    Nuclear Waste Management.   In:  Scientific Basis for  Nuclear  Waste
    Management, G.J.  McCarthy,  ed.   Plenum Publishing  Corporation, New
    York.  1979.
2.   Braithwaite,  J.W.,  and  M.A. Molecke.   High  Level Waste  Canister
    Corrosion  Studies Pertinent  to  Geologic  Isolation.   Presented  at
    Conference on High Level Radioactive Solid  Waste Forms, sponsored by
    the Nuclear Regulatory Commission,  Denver,  Colorado, December 19-21,
    1978.
3.  Personal communication, MaxKrelter, Pacific Northwest  Laboratories.
4.   Savannah  River  Laboratory (Rankin, W.N.)   Compatibility  Testing  of
    Vitrified Waste Forms.  Report DP-MS-77-115 (rev. 2/15/78).
5.  Mattsson,  E.   Corrosion Resistance of  Canisters  for Final  Disposal
    of  Spent  Nuclear  Fuel.    In: Scientific  Basis  for  Nuclear  Waste
    Management, G.J.  McCarthy,  ed.   Plenum  Publishing  Corporation,  New
    York.  1979.
6.   Karnbranslesakerhet  (KBS).   Handling  and  Final  Storage  of
    Unreprocessed  Spent Nuclear Fuel.   Stockholm,  Sweden.   1978.
7.  Ibid.   Copper as Canister Material  for  Unreprocessed  Nuclear  Waste
    Evaluation with Respect  to Corrosion.    Technical Report  90,
    Stockholm, Sweden.  1978.
8.  Ibid.  Handling of Spent Nuclear  Fuel and Final Storage of Vitrified
    High Level Reprocessing Waste.  Stockholm,  Sweden.  1978.
9.  Ibid.   Corrosion Resistance  of Titanium Canisters  Lined with  Lead
    for Final  Disposal  of  Reprocessed  and Vitrified  Waste from  Nuclear
    Reactors.   Technical  Report  107,  (in Swedish),  Stockholm,  Sweden.
    1978.
                              VIII-9

-------
        APPENDIX D-IX
THERMAL STRESS CRACKING IN SALT

-------
                              APPENDIX D-IX

                     THERMAL STRESS  CRACKING  IN  SALT

A.  INTRODUCTION

    The purpose of this appendix is  to present  a set of rock mechanics
calculations undertaken to assess  the possibility that  fracture pathways
would develop  from  the repository to  the  upper aquifer, especially in
the  case  of  a repository  in  salt.    Two types  of stress  have been
addressed:   thermal  stresses and stresses  around mined openings in rock,
with emphasis on the former.
    The existence of a repository and the  heat  released  by it alter both
the state of stress  and the mechanical properties of  the host formation.
While  stress  concentrations around  underground  openings have been
studied extensively,  thermal  stresses complicate the problem; for much
of  the  time,  these  thermal stresses  are  dominant.    Should  the total
applied  stresses  exceed  the  strength of formations  surrounding  the
repository,  fractures may breach the geologic barrier.

B.  BASIS FOR ESTIMATION

    Analysis  of  stresses   about  manmade  underground  works  has  been
undertaken  with  varying  degrees  of  sophistication for  about   thirty
       (1  2  3)
years.   '  '     In-situ  stress  measurements  generally confirm the
predictions  of analytical models within the normal limits of accuracy of
geomechanics.
    With  few  exceptions,  analyses  of  stresses  and  strength  in
geomechanics are  deterministic.   Material properties  are specified as
constant over  large regions;  it is then possible  to  analyze and  compare
them with strengths.   Results are  expressed  as the ratio of available
resisting strength to  driving load  in specified models  of failure; the
ratio  is  commonly  called  the "Factor  of  Safety"  (FS).   Because no
sources of  uncertainty  are  included  in   these analyses, quantitative
estimates of  probabilities  of failure  are not  possible.  Through  long
experience,   rules of  practice for   acceptable  Factors  of  Safety  have
                                    IX-1

-------
emerged.   The  extrapolation    of  "acceptable" FS  to unique  cases  is
difficult, however.
    The most important  mode  of  failure  considered  in  estimating  the  risk
of high-level waste  (HLW)  escaping the repository is  the formation  of
continuous  channels  connecting  repository and  aquifer.   Traditional
stress  analyses  predict  zones of  failure,  rather  than fractures.
Generally, the stress  field  is  compared with rock  strength  and for these
regions in which strength is exceeded by stress,  the rock  is said to  be
                                                                    (4)
"failed" or "plastic".   A typical  result  is  shown in Figure D-IX-1.
The conclusion of  this  type  of  analysis is  that  zones of  failure develop
adjacent to the repository, but  beyond  about  one  opening diameter  from
the repository  (expected) stresses  do  not exceed  (expected) strengths.
The expected FS against failures that  extend  beyond  the  failed  zone  is
typically much greater  than  1.0.
    Stress analysis  can be  made  with varying  levels  of  sophistication.
Assumptions can be  made about  alternative  deformation behavior (e.g.,
elasto-plastic,  strain-hardening,  strain-softening,   etc.),  about  the
influence of  jointing,  and  the like.  Yet,  the predictive results are
qualitatively the  same:    in  some  regions  adjacent  to  the   opening,
stresses exceed  strengths;  in regions away  from  the opening, stresses  do
not exceed  strengths.    The shapes  of  failed  zones  are  sensitive  to
geometric details  (i.e.,  sharp  corners  concentrate  stresses  locally).
For the  purpose of  estimating  risks  such conclusions  are Inadequate,
since they do not follow  the development  of  the  fracturing all  the way
to the aquifer.
    At present, there  are  no  modeling  techniques for  rock fracturing
that  incorporate uncertainty.   Thus,  an  approach to  this problem was
developed specifically for  the  present analysis.   This  approach treats
rock  properties as  random variables,  and  calculates  the reliability  of
host   formations   against  failure  in  particular  modes,  under
deterministically  predicted  stress  fields.   The  approach  and  its
underlying assumptions  are presented  below.
    The  purpose  of this   analysis cannot be to  calculate  precise
probabilities  for   a  breach  of   the  geologic   barrier   through
overstresslng, because  such  calculations  are not possible in the present
state of geomechanics.  Rather, the purpose is  to establish whether the
                                 IX-2

-------
      0 yr
0.1  vr
1.0  vr
5.0  vr
30 .vr
Note:   Dotted areas indicate regions within the rock for which applied stresses
       exceeded strength.

Source: Mathab, M.A., J.L. Ratigan, and D.R. McCreath. Stability of a Radioactive
       Waste Repository in the Canadian Shield.  18th U.S. Symposium on Rock
       Mechanics, 1977.
  FIGURE D-IX-1   RESULTS OF STRESS ANALYSIS STUDIES PERFORMED FOR WASTE
                   STORAGE IN FORMATIONS OF THE CANADIAN SHIELD
                                     IX-3

-------
 inherent  uncertainties  in  rock  properties within  a bedded  salt  formation
 chosen  for its  uniformity lead  to important uncertainties on breaching.
 A limiting  equilibrium model  is constructed  which, while  typical  of
 geotechnical  models, is  only one of  many  that  could have  been  used.
 Reasonable  estimates  of  material  property  uncertainty and  spatial
 variability  are  propagated through the model.   Average  salt properties
 are  sufficient to protect  the repository against breaching; the question
 is  whether there is  a  significant probability  that worse-than-average
 properties may  occur  in   such  a  way  that  breaching  becomes  possible.
 This analysis  yields  a  prediction  that  is more qualitative  than
 quantitative; the  numerical  results  are  accurate,  not  to an  order of
 magnitude, but to a  few orders of magnitude.
    Many  numerical  models have been  developed for  studying  stress and
 temperature distributions  around potential repository openings, and many
 mechanisms of breaching failure have been studied.  All of these studies
 have  led   to  consistently  high deterministic  factors of  safety.   The
 present analysis  estimates whether such  factors  of  safety may  lead to
 significant probabilities  of the development of release pathways.

 C.  FAILURE THEORY FOR ROCK

    Rock,  including salt,   is a frictional material the strength of which
 depends  on  two   properties:    one  independent  of  ambient  stresses,
 generally called the "cohesion"; and one  dependent on ambient  stresses,
 generally   called  the "friction  angle".  Rocks display greater  strength
 under confinement than when unconfined, and  this  increase  in strength is
dependent  on  the  confining stress.
    The Mohr  failure  criterion for  rock  is  shown  in  Figure  D-IX-2,
plotted  with  normal  stress as  abscissa  and shear  stress as  ordinate.
 Following   this  criterion,  failure  occurs when  the   shear  stress  on  a
plane, T,   exceeds  some  monotonic  function  of  the normal  stress  on the
plane, a,

                              T  ra  g(o)                         (1)
                               IX-4

-------
           SHEAR
           STRESS
                r
                                                       •FAILURE
                                                        ENVELOPE
  (TENSILE)
 °3            °
NORMAL  STRESS
(COMPRESSIVE)
Note:  Semi circles represent loci of stresses for planes of varying orientation with major
      principal stress o\, minor principal stress o3, and intermediate principal stress Oj.
       FIGURE D-IX-2 MOHR FAILURE CRITERION FOR ROCK
                            IX-5

-------
    Equation 1 is sometimes approximated by the linear relationship

                              T  «  C + a  tan  •

where C is  the "cohesion", and   4>,  the "friction angle".  Equation 2 is
commonly called  the  Naviser-Coulomb  criterion.   The  Mohr  failure
criterion  (Equation 1)  has  been  empirically verified,  and  is  widely
used.
    Under  high pressures, Mohr envelopes  for  rocks  typically  become
flat, and  the  materials  behave  cohesively.  Failure strengths  cease to
be dependent  on  normal stress.  While the slope  of  the  Mohr  envelope
gradually  changes,   a  bilinear approximation   is  often  used  Instead
(Figure D-IX-3).   The  inferred  transition pressure between  frictional
and  cohesive  behavior  depends  on  the particular  rock  and the  ambient
temperature.  Transition  pressures  decrease with increasing temperature,
with the  rate  of decrease dependent  on  the particular rock.   In salt,
strength behavior above  some  transition  pressure is usually  assumed  to
be purely  cohesive,  while in  other rocks  (e.g.,  crystallines)  strength
at high  stresses  still exhibits slight  stress  dependence.   Transition
stresses  for  salt  are  anticipated  to be  within the  range of  stresses
predicted for repositories at  460 meters.
    Intact  rock  is  not perfectly elastic, but displays  ductility (i.e.
nonlinearity  in  stress  vs.   strain)   at  high  shear  stresses  (Figure
D-IX-4).    Post-failure  behavior  can  range  from  strain-hardening  to
strain-softening, with some materials like salt displaying  more  ideal
plasticity.
    Deformation  properties of   rock  are  not  important  in  comparing
stresses with strength, but they are important  in predicting stresses in
the  first  place.   According  to elasticity  theory,   elements  of  rock
continue to  withstand  and transmit stresses  in a linear way up  to  and
(theoretically) beyond  what are known to  be  their  failure limits.   In
reality,  however,  rock  is  not perfectly elastic,  and  incremental
stresses  are  redistributed  around  failed  elements,  replacing  sharp
stress concentration with broader bands of lower stress.
    Much work  has been performed over the  past  ten years  in numerical
analysis  of  subsurface stresses   using  assumptions  of  various

                            IX-6

-------
                 to
                 00
                 Lul
                 QC
FRICTIONAL

BEHAVIOR
                                             COHESIVE
BEHAVIOR
                                         'TRANSITION
                                          PRESSURE
(EXPANSIVE)
      NORMAL STRESS
     (OPPRESSIVE)
    FIGURE D-IX-3  Bl LINEAR APPROXIMATION TO CURVED MOHR ENVELOPE
                             IX-7

-------
              oo
              LL)
              OH
              OH

              Sj
                   VOLUMETRIC
(EXPANSIVE)
    STRAIN
(COMPRESSIVE)
   FIGURE D-IX-4
TYPICAL DEFORMATION BEHAVIOR FOR

BRITTLE ROCKS
                       IX-8

-------
complexities  (e.g.   elastoplastic  analysis,  plastic  analysis,  etc.).
Changes of  these  assumptions lead to  changes  in predictions of  stress
distributions  and  failure  zones.   Of  course,  as  pointed out  before,
changes in  failure  zones predicted by a  totally deterministic  analysis
have little practical  importance in an  overall safety  analysis  program.
It is useful, however, to emphasize the point that assumed relationships
of deformation affect stress predictions.
    The  cost  and  effort   involved   in  performing  stress  analysis
incorporating  complicated  deformation properties must  be balanced
against  the  increase in  information, actually derived.  With few
exceptions,  inelastic stress  calculations  must be  made  numerically,
typically using finite element or finite difference  techniques.   Besides
estimating bulk and shear moduli for the rock,  one must estimate various
transition  stresses  and moduli   in  each   zone  of  the  stress-strain
relationship.
    All of these properties can be reasonably estimated for a particular
site,  although  the  accuracy of the estimates  depends  on  the extent  of
the  exploration  and  testing  program.   Tn  performing  non-site-specific
studies, however, such estimates are difficult;  this difficulty extends
to estimating  an  appropriate modulus  for the  elastic  case.   Therefore,
one must ask whether more sophisticated deformation  relations are useful
in  the present  application.   In  any  case,  uncertainty  in  estimating
moduli probably leads  to more  uncertainty  in stress  predictions than  do
the differences among different deformation models.
    Rock masses  differ from  intact rock  in that the  former  are  cut  by
pervasive  and  nonpervasive  fractures  and  inhomogeneities  that  affect
mechanical behavior.  Most important of these features  are joints, i.e.,
one or more sets of  subparallel  fractures  separating  the rock mass into
blocks.    Joint systems  are  geologic  in  origin  and  exist  prior  to
repository construction, with  their  character  and  extent  determined  by
lithology and geologic history.
    Joints  affect  the behavior of  rock masses  by  lowering deformation
moduli  and by  introducing  planes  of  weakness.   The degree  to which
either of  these  effects  occurs depends on  the density of joints, their
sizes, and  their  physical properties (i.e.  shear and  normal stiffness,
and  frictional  resistance).  All of these properties are site-specific.
                                IX-9

-------
    Common practice in analyzing the behavior of jointed rock masses is
to  use  continuum models, but  to modify  deformation  moduli and strength
parameters by  reduction   factors.    Sometimes anisotropy  is  also
introduced.  Discontinuum  models  for jointed  rock  require  information
specific to the  rock mass and  opening geometry.   '
    Salt is a low-viscosity material that can  flow  under  stress  and in
which fractures  heal quickly.  Therefore, salt formations are thought to
be sparsely jointed, if at  all.   Variations  introduced  by assuming salt
to  be  intact  are  probably  within  the  error band of present  analysis,
which  among other uncertainties  includes those  from  site-to-site
variability.

D.  EMPIRICAL DATA  ON SALT  STRENGTH

    1.  Rock Salt Properties

        The literature was  searched  for  empirical data on the mechanical
    and thermal  properties  of  in situ salt,  in  order to estimate  values
    for the following parameters:
            1.   thermal conductivity and heat capacity,
            2.  Young's (deformation) Modulus and Poisson's  Ratio,  and
            3.   strength parameters  (cohesion and friction angle).
        Such  an  estimate  was  difficult   because of  the  lack  of
    comprehensive   published  information on  the  subject,  and because
    these properties vary  with temperature and the  strain rates.   Some
    simple  assumptions  were therefore  made  in  the  study.   Where
    necessary,  the  available  published  data were  extrapolated  to  the
    conditions  of  the model repository,  which were  taken  to  be:
                              _                        y       i o
    temperatures  from 0 to  300 C; strain rates from 10   to 10    min-1.
    2.  Thermal^Properties

        Thermal  conductivity has  been measured  in  several studies
    dealing with waste  repositories/7'8'9'10^   Findings  from  the
    literature  are  summarized  in Figure  D-IX-5.    Reported  values  of
                                 IX-10

-------
      10
       8
   .c
CO

>-
   o
   Q
   §   4
   o
                                            estimated range
                                            at roon  temp.
                       polycrystalline
                        latural  rock salt **
                              ingle crystal
                                  NaCl  t
                assumed  for
                analysis *
                                                   estimated
                                                   range at
                                                   room  temp.
                  100      200      300      400

                            TEMPERATURE (°C)
                                                    500
600
700
Sources:  * Arthur D. Little, Inc. Task B Report.
       **Westinghouse Astronuclear Laboratory, A Study of Borehole Plugging in
         Bedded Salt Domes by Earth Melting Technology. WANL-TME-2870, 1975.

       t Kaufman, D.W. (ed.) Sodium Chloride: The Production and Properties of Salt and
         Brine.  Reinhold Publishing Co., N.Y., 1960.
                FIGURE D-IX-5   THERMAL CONDUCTIVITY OF ROCK SALT
                                    IX-11

-------
thermal conductivity are  in  the  range 1-10 Btu/(f t-hr-°C), and  the
values decrease with increasing temperature.    '
    Many of the laboratory data reported in the  literature are  from
tests   on   single  crystals  of  salt,   so   the   properties   of
polycrystalline salt  (i.e.  rock  salt)  had  to be  estimated  from
sparse  data.   The curve  labeled  "rock salt"   in Figure D-IX-5  was
extrapolated from  tests  on polycrystalline salt at  room  temperatue
(24°C), using the  trend  observed  in single  crystal  tests.
    Specific heat  data are shown in Figure D-IX-6.    '      Reported
values of specific heat  are in the range 8-11  Btu/(gm-  C),  which is
in  the upper  range   of  values   for   other  rocks,  and   are
temperature-dependent.     Specific  heat  increases   with  increasing
temperature.
    Density data are shown in  Figure D-IX-7.   '     While the  data
are sparse,  a  range of  1.95-2.2 seems appropriate.   As  expected,
this  range  is  somewhat  below  that of most  rocks.    As  with other
properties  of  salt,  density  is  temperature-dependent,  decreasing
with increasing temperatures.

3.  Mechanical Properties

    Estimation of  elastic  properties  for  salt, Young's Modulus  and
Poisson's  Ratio,  is complicated by temperature-dependence  and
viscosity.  Creep  from  viscosity at  low strain  rates decreases  the
deformation moduli reported in  the test results.
    Published values of Poisson's  Ratio  for  rock salt are  shown in
Figure  D-IX-8.(11'14'15)     Within  the  range  of  temperatures  of
interest  for  the   repository,  a Poisson's  Ratio of  about 0.22  is
appropriate.   It  should  be  noted that thp  Poisson's Ratio  enters
                                            2  _i
stress  calculations through  the  term  (1-v  )    (where  v  is   the
Poisson's  Ratio)  which  means  that  stress   predictions are  not
sensitive to minor uncertainties in the ratio.
    Published  data  on  Young's Modulus  for rock salt  are  shown in
Figure  D-IX-9.    '   '      Temperature  trends in  both  dynamic  and
static  testing  are  similar,  the modulus  decreasing slightly  with
increasing temperature for the range 0-300°C.   The  disparity between
                            IX-12

-------
X
                     CM
                   I  O-
                  CD
                     CV
                     CO
                  O
                  LU
                  O- I--/
*

**
TOO
200
300
400
  500
                                                                                      600
700
                                                              TEMPERATURE:  (°c)
                                                                                                              melting
                                                                                                              temperature
800
900
inno
                   Sources:   "Arthur D. Little, Task B Report.

                            **Gera, F. Review of Salt Tectonics in Reaction to the Disposal of Radioactive Waste in Salt Formations.

                              Geological Society of America. 83,1972.

                             tKaufman, D.W. (ed.). Sodium Chloride:  The Production and Properties of Salt and Brine. Reinhold Publishing Co.. N.Y., 1960.
                                          FIGURE D-IX-6   SPECIFIC HEAT OF ROCK SALT VS TEMPERATURE

-------
 I
M
*-
   2.4
   2.2
   2.0
   1.8
o>
s1'6
'Z
c
tt)
   1.4
   1.2
   1.0
                                                                                               melting I temperature
                                                                  I
                  100        200       300         400        500

                                                        Temperature (°C)
                                                                                             600
700
800
900
1000
   Sources:    'Arthur D. Little, Task B Report.
             **Gera, F. Review of Salt Tectonics in Reaction to the Disposal of Radioactive Waste in Salt Formations. Geological Society of
               America. 83,1972.
              tKaufman, D.W. (ed.). Sodium Chloride:  The Production and Properties of Salt and Brine. Reinhold Publishing Co., N.Y., 1960.
                               FIGURE D-IX-7   DENSITY OF ROCK SALT VS. TEMPERATURE

-------
l/i
              0.4
              0.3
           as
           CC.
           O
'§.
              0.2
              0.1
                               I
                                 I
 I
I
I
                              100
                               200
300
                       600
                        700
                                                                                                                 melting
                                                                                                                 temperature
                                                                                                            I
                                                               800
                                                                                                                        900
                                                      400        500
                                                  Temperature   (°c)
Sources:  Westinghouse Astronuclear Laboratory, A Study of Borehole Plugging in Bedded Salt Domes by Earth Melting Technology. WANL-TME-
         2870,1975.
         Hunter, L., and S. Siegel. The Variation with Temperature of the Principal Elastic Moduli of NaCI Near the Melting Point.  Physical
         Review, 61,1942.
         Starfield, A.M., and W.C. McClain.  Project Salt Vault. J. Rock Mechanics and Mineral Sciences, 10, 1973.
                                                                                                                                                1000
                                                  FIGURE D-IX-8  POISSOIM'S RATIO VS. TEMPERATURE

-------
o    5
x
ji

I    4

ui
"5
2!    3

                            •Dynamic Modulus — Average Values for Polycrystals.
                             (derived from Single Crystal Data of Reference 14)
_]••— Elastic (reload) static modulus (data from Reference 16)

      Static value for Lyons, Kansas Rock Salt (from Reference 15)
          Initial  static modulus (data from Reference 16)
     k«-Backfigured from in-situ test (from Reference 15)
          'Static" Modulus - Values for Grand Saline, Texas Dome Salt (from Reference 8)
                                                                                   I
                                                                                  li
                                                                                             Melting
                                                                                             Temperature
         100       200       300       400        500       600

                                            Temperature (°C)
                                                                              700
800
900
1000
           FIGURE D-IX-9   YOUNG'S MODULUS OF ELASTICITY VERSUS TEMPERATURE

-------
dynamic  and static  testing  is  much  greater  than  the  temperature
effect, which  suggests  that strain rate and not  temperature  is the
dominant test variable.
    To determine  the variation  in  Young's  Modulus with  strain rate,
it was  necessary to make  several  assumptions  and to use  published
creep test data.  It was  assumed  that  static moduli  reported  in the
literature  (Figure  D-IX-10K   '     were tested at a strain rate  of
         -2     -1
about  10    min  .    This  would   correspond  to  10% strain  in  10
minutes.   It was also  assumed  that dynamic moduli  reported  in the
                                                 4
literature correspond to strain rates of about  10  per  minute.
    In addition,  values of  elastic moduli  have been  back-calculated
from published unconfined creep tests.      Uniaxial  creep  tests for
rock salt,  as  shown in Figure  D-IX-11,     were used to  determine
the  strain  at  various  compressive  stresses  and  temperatures
corresponding  to  strain rates of  10~ , 10~ ,   and  6 x 10~   min   ,
from which values of Young's Modulus  have  been determined  (Table
D-IX-1) .
    Finally, the  strain-rate dependence was estimated by  rearranging
Starfield  and   McClain's  equation  for  empirically  observed
deformation  in rock salt pillars,
e - (0.65 x 10~37) (    )°*25  (T + 273)9'5 o3'0
                                                              (3)
where
    c « strain
    t - time in minutes
    T « temperature in  C
and
    a = uniaxial stress in psi, into the form
      u.5o
                           IX-17

-------
                  106
M
x
t-«
oo
               J  10s
               jo
               LU
              •S  1Q4
               o
                   103
                          Figure
                          D-IX-9
                      104
                                  Estimated
                                  Value of E
                                         •
                                  Versus e
                              Temperature °C
                           20°  65°   100°  200'
Hendron
Starfield
•
A
O
A
V
                   102               1              10'2             10^            ID"5            1Q-8
                                                     Strain Rate (cm/cm/mm)
Sources:  Hendron, A.J. Mechanical Properties of Rock. In: Stagg, K.G., and O.L. Zienkiewicz, eds. Rock Mechanics in
         Engineering Practice.  John Wiley & Sons, New York, 1968.
         Starfield, A.M., and W.C. McClain. Project Salt Vault. J. Rock Mechanics and Mineral Sciences, 10,1973.
                                                                                                                                    10-
                                 FIGURE D-IX-10   YOUNG'S MODULUS OF ELASTICITY OF ROCK SALT VS. STRAIN RATE

-------
TOTAL
STRAIN
  (*)
                                   e =  10"4/hr
                                                                            e =  10"5/hr
                         400           800
                            TIME (hours)
1200
1600
 •Temp. 65°C
"Temp. 23°C

Note: Stress is indicated along curves in kg/cm2.

Source: Hendron, A.J. Mechanical Properties of Rock. In: Stagg, K.G., and O.L. Zienkiewicz, eds.
       Rock Mechanics in Engineering Practice. John Wiley and Sons, New York, 1968.
       FIGURE D-IX-11  UNIAXIAL COMPRESSION CREEP TEST FOR ROCK SALT
                                  IX-19

-------
              T°C     E(105psl)
              23
              65
ro
o
               20
               100
               200
                        10
                        10
                          -5
  -6
                       6x10
                          -5
                           -7
10
10
                          -6
                       6x10
                           -7
               20(7)     4x10
                            -4
 10
 10
 10
-5
-8
 10
 10
                            -11
                            -5
  10
  10
  10
  10
                            -8
                            -11
-5
-B
-11
                                    525
                                    750
                                    2800
                                     525
                                                                  TABLE  D-IX-1
                                                  UNIAXIAL COMPRESSIVE CREEP TEST DATA
                                               0.(
In) E(10 psi) a(p>l) e(ln/ln)
TEST DATA(2*
11 5.25 1750 0.008
0.0135
" 0.0155
n 3.75 " 0.023
0.0355
" 0.0425
TPCT nATA^- '
E(105pst)

2.19
1.30
1.13
0.761
0.493
0.412

                                                0.0075
9.99
9.92
9.27
9.83
8.56
3.72
7.46
2.27
0.28
                                                              3.73
                                                                          4500   0.0125
                                                          BACK-CALCULATED FROM CREEP EQUATION
                                                                                             3.60
                                                                                            (19)
                                                                           1750
9.72
7.73
2.54
6.16
1.38
0.158
7.33
0.078
0.0079
                                                                               o(pei)
                                                                                                         2250
                                                                                                         2250
                                                                                         e(ln/ln)
                                                                                          0.020
                                                                                          0.0435
                                                                                          0.0/.85
                                                                                          0.0115
                                                                                          0.065
9.41
6.16
1.38
4.30
0.701
0.075
0.359
0.037
0.0037
                                                                                 I .13
                                                                                 0.517
                                                                                 0.464
                                                                                 0.714
                                                                                 0.346

-------
where  strain rate, e,  is in rain"  .   Values  of  modulus from  this
equation  were  computed  for  various   stress   levels  at   room
temperature,  for  strain rates of 10  , 10~8,  Id'11  (Table D-IX-1).
Although these values  differ from those back-calculated  from  creep
test data, the trends are similar.
    Combining information from each of the above  sources  leads  to  a
best estimate of modulus over the temperature and  strain-rate ranges
of  interest, as  shown  in  Figure  D-IX-10.   This  estimate would
suggest  an approximately constant modulus in the range  below  10
min  ,  which is  the  range  of  thermally  applied  stresses   for  the
repository.   The value of E  in this range  is about 3 x 10 psi.
    Published values of  the  coefficient of linear  thermal expansion
                  (18 )
were    reviewed.    '    The  coefficient    is    only   slightly
temperature-dependent  (increasing with  increasing  temperature),  but
over the range of  interest  (0-300°C)  the values vary only from 4.03
to  4.7  x  10     C  .    For the  purposes  of this  analysis,   the
coefficient of expansion was assumed not to vary with temperature.
    Rock  salt  sheared  at   constant  temperature  and  strain  rate
exhibits  either  brittle  or  ductile behavior,  depending  on  the
confining  stresses.   Above  the  brittle-ductile boundary, the  Mohr
envelope is flat, (i.e., a constant shear  strength for all confining
stresses).   In the  ductile range, however,  the shear  behavior  is
strain-hardening.
    The brittle-ductile  transition was assumed to occur, as  shown in
Figure  D-IX-12,  where  the   curved Mohr  envelope for  peak  behavior
crosses  the   residual  envelope,  oriented  at  the  angle  of  sliding
         (19  20 21)
friction.    '*'  The angle of residual friction was derived  from
Figure D-IX-13 to be about 29°.<16»17»22)  Reports in the literature
vary from  as  low as 20°  to as high as 40°, with most estimates lying
between 25° and 35°.
    A  simple  (c,)  linear approximation  to the Mohr envelope called
the  Mohr-Coulomb  Criterion (Figure  D-IX-14)  was  conservatively
                                IX-21

-------
                                                                                      20'
M

?
[S3
                                                               o   (psi x  1000)
             Note:   TEMP°C   *  24°                             n ^
                               #150°
                              "250°
                             ##300°
            Sources:   Handin, J., and R.V. Hager, Jr. Experimental Deformation of Sedimentary Rocks Under Continuing Pressure: Tests at High Temperature.
                      Bulletin, American Association Petroleum Geologists, 42: 2892-2934,1958.
                      Stokes, R J. Mechanical Properties of Polycrystalline NaCI. Proceedings British Ceramics Society, 6:  187—207,1966.
                      Baidyuk, B.V. (ed.). Mechanical Properties of Rocks at High Pressure and Temperatures. Consultants Bureau Translation, New York, 1967.
                                        FIGURE D-IX-12   SUMMARY OF PUBLISHED SHEAR STRENGTH DATA

-------
NJ
U>
                                                                                     n (kg/cm2)
                Sources:    Fodor, I., and K. Tokes, Neve Forschungen Uber die Physikelischen and Mechanischen Eigenschaften des Rumanischen Steinsalzes.
                           Theme 3, No. 78: 705-709.  Proceedings 1st Congress International Society Rock Mechanics, Lisbon, 1966.
                           Serata, S., S. Saknrai, and T. Abachi. Theory of Aggregate Rock Behavior Based on Absolute Three-Dimensional Testing (ATT) of Rock Salt.
                           Proc. 10th Symposium on Rock Mechanics, 1969.
                           Hedron, AJ. Mechanical Properties of Rock.  In: Stagg, K.G., and O.L. Zienkiewicz, eds. Rock Mechanics in Engineering Practice.
                           John Wiley and Sons, New York, 1968.
                                        FIGURE D-IX-13  MOHR COULOMB ENVELOPE AT LOW STRESS LEVELS

-------
                     Td
uniaxial
tension
test
         tension,  a.
                                                        model  peak/
                                                                                ductile
                                           ad =
compression, a
              n
                                                tan
                FIGURE D-IX-14  LINEAR MOHR - COULOMB ENVELOPE STRENGTH MODEL

-------
    assumed  to predict peak shear strength for constant temperature and
    strain  rates.   This  model  is  expressed as
             o  tan
              n
P IT,
I d
where

C 2




Td - °t/2
2t ,
d j. ,
a. tan <}>
L t u _
                              O. • T,/tan d>
                               ad      p
                                                                       (5)
                                 n >
                                                                      (6)
    tan 
-------
    800
    600
 o
o
 oc

 i
 LU
    400
    200
                           STRESS (kg/cnr)
   FIGURE D-IX-15  STRENGTH LIMITS OF ROCK SALT VERSUS TEMPERATURE
                             IX-26

-------
where T   is the ductile  shear strength and  o   the tensile strength.


    These  values of  shear  and  tensile  strength  were used  in  the

strength model previously discussed, so that:
for                                   v
°a < °d
J4.8 x 103 -540> /tan
|T(°C) + 74 )
T • C(T) + o tan 4> K(T)
p v ' n P
where ,



C(T) -

2

7.07 x 106


T + 1160
» •
5
4.79 x 103
T + 74

4.79 x 105


T 4- 74
**
A
540 1 7'08 X 10 3£(
J*tW T JW\
T + 1160
*y (10)
(11)


. + tan .79 x 10'
T + 74
- 540
-I
r.os x 10;
 T •»- 1160
                                                 360o  tan

                                                  (13)
 where T is temperature  in  C,

 o  is norrail srress,
  n
 o  is the brittle-ductile transition stress,  and

 $  is the residual  fraction angle.
 For
                Tp   Td     T +  74
                     - 540
                           IX-27

-------
    The strength model  is,  therefore, in  terms  of only  two  exogenous
    variables  (temperature  and applied normal  stress)  and  one material
    constant  (the residual sliding coefficient of friction).

E.  STRESS  PREDICTIONS

    To make  predictions on  the  behavior  of  a  rock  mass,  both  the
mechanical  rock  mass  properties  (strength,   deformability,   and
permeability)   and  the  state  of  stress   must  be  estimated.    These
parameters  and  stresses  are not independent.

    1.  In-situ Stresses

        Prior  to construction,  a repository site will be  in  some  state
    of stress  depending on  the  rock formations  and  recent  geologic
    history.   For flat-lying  sites  in tectonically quiet  regions,  the
    principal  stress  directions  will be very  nearly vertical  and
    horizontal.   Figure D-IX-16 presents data  summarizing in-situ
    vertical  stress measurements  from several  sources  and from  sites
                                      (23)
    distributed  across  North  America.       The  common  assumption  of
                                                                 2
    gravity stresses  for the  vertical direction,  about  0.23 kg/cm /m (1
    psi/ft)  of  depth, is  slightly below  the  average   of  these
    measurements, but the scatter  in the  data  is large.  Among  other
    sources of this scatter  are  large measurement errors  from the  way
    in-situ stresses are measured  (see, e.g., (2).
        Typical  densities for rock masses are in the range of
             3                                             3
    2560 kg/in  .   Salt is somewhat lower, or about 2240 kg/m .   Thus,  the
                          2
    assumption  0.23  kg/cm  /m  (1  psi/ft)   is  reasonable,  particularly
    since the analytical results  are insensitive  to moderate  changes in
    vertical  and horizontal stresses.
        Horizontal  stresses  within  a  given  profile typically vary
    proportionally  with vertical stresses.   The ratio  of  horizontal to
    vertical  stress  is  therefore defined  and assumed  to be  constant
    either  for an entire profile or  for individual strata  or  sequences
    of strata,
                                    o,
                              K  =  -£                         (15)
                                    a
                                     v

                                     IX-28

-------
DEPTH  (m)
        0
    150  1
    304
    460
    610
     760
     915
                                            assuming  deqsity of
                      assuming
                      stress
                      .23 kg/cm /m
                      70          140        210         280        350

                          VERTICAL STRESS  (kg/cm2)
 Source: Lidner, E.N., and J.A. Halpern. In-Situ Stress Analysis. 18th U.S. Symposium on
        Rock Mechanics, 1977.
     FIGURE D-IX-16   APPROXIMATE VERTICAL STRESSES FOR SEVERAL
                     SITES IN NORTH AMERICA

-------
Figure  D-IX-17  shows data  summarizing in-situ measurements  of
                                            (23)
horizontal  to  vertical   stress  ratio,  K.        As  for  vertical
stresses,  the  data  show wide  scatter.    Typical  values  of  K,
particularly in tectonically quiet regions, were  assumed  to be  from
0.5 to 2.0  (i.e., the average horizontal stress varies  from half  to
twice the vertical stress).  A best estimate of the stress ratio was
taken to be 1.0.
    Salt,  having  low viscosity,  deforms continuously  under  small
shear  stresses,   and  within short  geologic  times (i.e.,  hundreds
rather than tens  of thousands  of years).   Thus, for the  purpose  of
non-site-specific analysis,  a  stress ratio  of 1.0 is  appropriate.
Any other stress  ratio would produce  shear  stresses, induce viscous
flow, and  over  time  neutralize stress differences.  A  stress  ratio
of K = 1.0 was used  in analysis,  and the sensitivity of  results  to
variation within the range of 0.5 1. K L 2.0  was tested.

2.  Concentration of Stress

    Construction of  an  opening  within  a uniform stress field
concentrates the stresses, with the  exact  form of the  concentration
a  function of  the   geometry  of  the  opening  and the  deformation
properties of  the rock mass.   Typical results  for elastic media are
shown in Figure D-IX-18.   Analytical expressions of the concentrated
stress field exist  for elastic isotropic and  anisotropic  media and
                       (24)
many common geometries.       Analytical expressions do not exist for
most  inelastic  assumptions,   although   solutions  can  be  obtained
numerically.
    Waste repositories will not have a single  opening,  like a long
cylinder, but  will have a  series of  parallel openings approximating
a  rectangle in the  horizontal  plane.   Stress distributions  about
this series of openings  will  be  more  like those  from an infinite
series of  holes  in a  medium  rather  than  a single  one  (Figure
D-IX-19).   The present  analysis considered only  a single opening,
however.
                                IX-30

-------
 DEPTH  (m)
                             AVERAGE   oh  /  a
Source:  Lindner, E.N., and J.A. Halpern. In-Situ Stress Analysis. 18th U.S. Symposium on Rock
       Mechanics, 1977.
         FIGURE D-IX-17  MEASURED STRESS RATIOS FOR SEVERAL SITES IN
                        NORTH AMERICA:  HORIZONTAL STRESS *
                        VERTICAL STRESS
                                  IX-31

-------
PRINCIPAL
STRESS
V  r^;^^O
  \yVv^"^^  I
 ^^^fefci£7
                   QX>
                      ^%*,.>$S?'(iv '?$^~^£g.
                     II'!     I
  SHEAR
  STRESS
 Source: Savin, G.N. Stress Distributions Around Holes. NASA Technical
      Translation, TTF-607.
 FIGURE D-IX-18  STRESS CONCENTRATIONS ABOUT CIRCULAR
             OPENINGS IN HOMOGENEOUS, ELASTIC MEDIUM
             UNDER VERTICAL STRESS FIELD
                      IX-32

-------
         maximum  tangential stress  at wall
       -3
            ^A^r^*-
                                  H O  ®  O =
      0123456

                   S/r
                                    If  If t It  t  I
                                     Hsh-
                                     o  00

                                    h  n M  n  »
       0    12    345    6
                  S/r
Source: Savin, G.N. Stress Distributions Around Holes. NASA Technical
      Translation, TTF-607.
FIGURE D-IX-19  STRESS CONCENTRATIONS ABOUT A ROW OF OPENINGS
             IN ELASTIC MEDIUM
                     IX-3 3

-------
    The bases  for choosing  to consider  a single opening  were  the
following:
         First, use of analytical expressions available for stresses
    about a single opening  reduced  computational effort  and allowed
    larger parametric studies.
         Second,  the  region   of  significant  stress  concentration
    extends  only  to  about  one  diameter  away  from  the  opening.
    Series of openings at separations greater than two diameters  can
    be modeled  as  if each  were  isolated.    Increases  in  maximum
    stress  concentrations  for multiple openings spaced at  one
    diameter  (i.e.,   2  diameters   o/c),   over   single  openings  in
                                           (2)
    elastic  materials is   less  than  10%.       Therefore,  errors
    introduced by considering only one opening were small.
         Third,  uncertainties  in the  conclusions of  this  analysis
    are dominated  by uncertainties  in  material  properties  and  the
    thermal field.
    Stresses  generated  about  an opening in  a  homogeneous  medium
depend on the deformation properties of the medium, in particular on
whether  the  material  is  elastic or  inelastic   (and on  the  form of
inelasticity  in the  latter case) ,  and  on the   ratio  of moduli  and
Poisson  ratios  if the material is  anisotropic.   The simplest case,
of course, is elasticity.
    While elastic  solutions, as used in the present analysis, depend
on assumptions  that  are  not  precisely  correct for real rock masses,
there are several  arguments for their use.
    First, any  stress-strain  relationship must  be verified for real
conditions.   In  many cases  inelastic relationships are as  difficult
to  verify  as  elastic  ones.    Given  many  alternative  inelastic
relationships,   each leading  to   a  somewhat  different   stress
distribution,  a  choice  must  still be  made  among  them.    Errors
introduced by using  an  elastic  assumption may  not be  any greater
than errors associated with various  inelastic assumptions.
    Second, appropriate moduli values are difficult to estimate even
in the  elastic  case.   Estimation  is more difficult  for  inelastic
cases, and  more  moduli  must  be  estimated.    Errors  introduced  by
selecting poor  parameter values may  be  larger than those introduced
by using elastic  theory.
                                 IX-34

-------
    Third,  elastic  solutions are  analytically and  computationally
convenient.   Therefore,  larger  parametric uncertainty is a primary
source  of predictive  uncertainty  in  this analysis;  results  from
parametric studies are likely to bound  predictions made using other
models.
    Fourth, given the  widespread use  of elastic analyses, there is
accumulated  experience  with   these  solutions,  which  aids  in
interpreting  the results.   This  also means  that  results  of  the
present analysis are  more easily interpreted  by those who were not
directly  involved in obtaining them.
    For these  reasons, stress distributions in  the present analysis
were  calculated  using elastic theory,  and parametric studies were
used  to bound the range of uncertainty.

3.  Thermal Stress

    The major  source of  stress in  geologic media about a  repository
appears to  be  the  thermal field.  Salt has a  coefficient of linear
thermal expansion, a ,  of  about  40  x 10~   0C~ .  Rock temperatures
predicted by  several  studies,  including the present one, may reach
200-250°C at the repository wall.  Because deformation of  repository
formations  is  constrained,  this  thermal  field  will  induce
significant stresses.
    Prior to repository construction,  the  in-situ  thermal  field will
be  uniform,  but increasing  linearly  with depth.   For geologically
stable  regions  (i.e.,  nonvolcanic),  a  temperature  gradient  of 1 C
for 60-80 m is typical.   Ambient  temperature at 450  m (1500 ft) in
bedded salt is expected to be about 30 C.
    Heat  generated  within  the  repository  will  be a  function
primarily of  (1)  waste   type  and  age at  burial,   (2)  time after
                                            O S  96^
burial, and (3) spatial  canister  density.v"'       The  conditions
considered were  10  years aging  and 150 kW/acre for  heat  generation
density,  consistent  with the"  Task  B report.    For  analysis,  a
                                 1X-35

-------
temperature (increase) profile  similar  to the Task  B  results were
used.  This profile  was  expressed analytically as:

                      AT(°C)   =  222 exp  (-1.1 x 10~5 r2)    (16)

where r = distance from  repository.

This profile was assumed  to .be isotropic  in the salt.

    The  time for peak  mine temperatures  differs  in different
analyses;  fracturing  probabilities are  related  primarily to  the
temperature profile  and  not  to time  (relation  of  shear  stresses
through viscous  flow  was  neglected,  which  is  a conservative
assumption).   Therefore,  the  results  of stress  analyses in  the
present case  are  not  significantly  affected  by   these   time
differences.   For analyses,   a  time of  100  years  to  maximum mine
temperature was  assumed.
    Stresses generated by the thermal field were calculated assuming
the  repository  salt  formations to be   isotropically  elastic with
uniform deformation  properties.   Parametric  analyses were  performed
by varying deformation moduli.
    Elastic thermal  stresses  around the  underground repository were
derived by  adapting a solution  for the  thermal stresses  in a thin
                (27)
circular disc.        This  solution  is  valid  for  temperature
distributions  symmetric  about  the  center of  the  repository,  and
requires  that  the  modulus  of   elasticity,  Poisson's  Ratio,  and
coefficient of  thermal  expansion  be constant with  temperature and
location.
    Expressions  for  radial  and tangential  thermal  stresses  are:
                                                              (17)
VI~IT
~/T(r)dr
                                 IX-36

-------
            6  1-v-
                   -«  /"
                     ~
                T(r)dr + aT(r)
(18)
where: E
      v
      a
      r
      R
    T(r)
modulus of elasticity
Poisson's Ratio
coefficient of thermal expansion
radial distance from center of repository
radius of repository
temperature increase above ambient at radius  r
Rewriting equation 16  in general form as:
                    T =  T    e
                         max
                              -Br'
                                             (19)
    where: T= maximum temperature  increase (at repository wall)
           in 3. A
            B = constant
    Substituting into  the equations for stresses yields,
          •,-&($*  [•-*-•*])
                                                         (20)
          'e
                              IX-37

-------
        Radial  thermal  stresses  are zero at the repository wall  (r  -  R)
    and  at  infinity,  and  are  compressive  everywhere in  between;
    tangential  stresses  are  maximum  at the  repository  wall,  zero  at
    infinity, and may be  compressive  or  tensile in  between.
        It  is  Important   to  note  that   thermal  stresses  .ire  directly
    proportional  to the modulus  of elasticity of the rock salt.   Errors
    in this  modulus result in equally large errors  in  thermal  stresses.
    Since there are little data  on the  elastic modulus of rock  salt  at
    high temperatures  and low strain  rates,  the potential for  error  in
    estimating  thermal  stresses  is  large.
        Since  all  stress  calculations assume elastic material  behavior,
    total stresses  around the  repository are obtained by superimposing
    the region (in-situ  plus  stress  concentrations  around  the  cavity)
    and thermal stress  fields.

F.  STOCHASTIC  FRACTURE MODEL

    1.  Model Construction and Assumptions

        The probability  of   fracturing  between  the repository  and  an
    overlying   aquifer  was  analyzed  by  modeling  rock  properties  as
                                               ( 2 8}
    second-order  homogeneous random  processes,     and calculating  the
    reliability  of potential  fracture  paths against  shear failure
    (Figure D-IX-20).
        The assumption of second-order  homogeneity* for  rock  properties
    implies  that   mean  properties  are  constant   in   space  or  may  be
    described   by  a deterministic  trend,  that  the point  variance  of
    properties  is  spatially  constant,  and  that the autocorrelation  of
    properties  (i.e.,  the degree  to  which  adjacent points  in  the  rock
    mass have  similar properties)  is  a  function only  of  the  vector
    *"Homogeneity" and "stationarity" are equivalent terms for spatially
    varying and  temporally varying parameters,  respectively.   Although
    usage  varies, "homogeneity" has been adopted in this report.
                                IX-38

-------
DEPTH (m)
    0
                       surface
380


460

540
                          repository
          __  .     -j.   aq'u}fer
                                                          £iii
 FIGURE D-IX-20   POTENTIAL FAILURE PATHS BETWEEN REPOSITORY
                AND AQUIFER
                          IX-39

-------
distance separating points (Figure D-IX-21 presents  these concepts).
Second-order  stationarity assumptions  for geologic  materials  are
                   (29)
generally accepted.
    Three  sets  of  rock  properties  are  important  for  analyzing
reliability:    strength  parameters,   deformation  parameters,   and
thermal parameters.  The first set controls the available resistance
of rock  to  various modes of  failure,  while the  latter  two  control
stresses  generated  in  the  rock.   In  the present  analysis,  only
strength  parameters were  assumed  to be stochastic; deformation  and
thermal  parameters  were assumed  to be deterministic.   This means
that analyses were performed on a  stochastic strength  field  subject
to deterministic stresses.  The errors introduced  by this limitation
are thought to be within  the  scope  of  the desired objectives of  the
study.  In more precise  studies, and in particular for  site-specific
analyses,  techniques  for  incorporating   uncertainty  in  the  stress
field  should  be  used.    Because  analysis of  stochastic  stresses
involves differential  rather than  integral fields, their  solution is
more complicated.
    A failure mode analyzed  in the present study was  the  development
of shear zones between repository  and  aquifer.   For  this  analysis,  a
limiting  equilibrium  approach was  used   with  driving  forces along
potential shear paths balanced  against resisting  forces.   Kinematic
admissibility was not considered  (i.e.,  potential shear paths  were
not  limited  to those  on which continuous relative movements  were
possible) .  The requirement of kinematic  admissibility, constraining
the  set  of  potential  shear surfaces, would  yield somewhat  higher
reliabilities than those from the  present  analysis.
    Alternative modes of  fracturing,  in  particular  the  development
of propagating  cracks  by redistributing  stresses at  increments  of
                          (31)
crack were not considered.      Pre-existing anomalies  in repository
formations  (e.g.,  faults)   are   treated   in  Section  D-5.1.    The
limitation of  other  failure modes, other than  limiting  equilibrium
shear  failure,  affected  numerical  results,  but  differences   are
thought   to  be  within   small  multiples  rather  than  orders  of
magnitude.   Site-specific  analyses  should   include  both   the
probability of  non-flaw  inhomogeneities  and progressive  fracturing.
                                IX-40

-------
                      horizontal  axis
                                            randomly
                                            variable
                                            material
                                            property
                                      mean
                     point  variance
     autocorrelation     '
     distance
FIGURE D-IX-21  SCHEMATIC DESCRIPTION OF ROCK STRENGTH
                         IX-41

-------
Both of  these  are important in predicting  stress  fields and should
be  treated  in  conjunction  with  spatially  varying  deformation and
thermal properties.
    Figure D-IX-20 illustrates plane strain failure paths considered
in  this  analysis.   Various fracture  geometries were  analyzed,  of
which  the  least reliable was  selected  for  detailed  analysis.   The
failure path geometry  used  in  detailed analysis consisted  of  a log
spiral  emanating  from  the  repository  at   an  angle  (45  -  4>/2),
connecting to a vertical line  continuing  to  the  aquifer.  This is a
                                               (32 33)
geometry of fracturing observed in model tests .   '     In analyzing
failures for a given set of  parameters, a search routine was adopted
that searched  for  the minimum reliability  surface.    In  general,
minimum reliability and minimum FS surfaces  are not the same.
    Overall reliability against plane  strain  shear  faiure  was  taken
as  that of  the  least  reliable  surface.   With  an infinite  number  of
potential surfaces, the reliability of  the  least  reliable  path  is
only an  approximation  to the  reliability of  the system.   However,
due to high correlation of  stresses  and  strengths  along  adjacent
surfaces   and  the  spatial  narrownesss   of  low  FS  clusters,
correlations of  FS  for alternative paths are high.   Therefore, the
reliability of  the  minimum  surface  is  a good approximation to the
system reliability.
    The  reliabiity of an  individual  path   to  shear   failure  was
determined by  integrating  predicted shear stress  along  the surface
and  comparing  this driving  force  with  the  integral of  available
resisting shear  stress.  (Figure  D-IX-22.)   The driving  force was
determined by decomposing the  stress field  at each  point  along the
failure surface into a normal stress, s , and a shear stress, t, and
numerically integrating over the surface,
                    DP
                         S
'./  "*•
where DF  is  the  total  driving force  along  path  S,  and ds  is the
differential curve length.
                           IX-42

-------
DEPTH (m)
    0
surface
                          shale
  380
  460
                          aquifer
                                '
                          repository
  540
                          aquifer
        FIGURE D-IX-22   STRESS AND RESISTANCE ALONG POTENTIAL

                      FAILURE SURFACE
                             IX-A3

-------
    The  resisting  force was  determined  by  decomposing the  stress
field and integrating over  the failure criterion,
                   RP -   /*[C(T) + a u(T)]ds
                        eJ           R
where  RF  is  the  resisting  force  along  path  S,  C(T)  is  the
temperature-dependent  cohesion  parameters,  and  {J(T)   is  the
temperature-dependent coefficient of friction (y(T) = tan 4>(T)).   A
tilde indicates a random variable.
    Resisting force, a function of  two random variables,  is  itself a
random variable with some mean and variance.  The  reliability  index
of shear failure along path S was defined  as:
where E[ ]  indicates  expectation,  and V[  ],  variance.   A  reliability
index was used because  it  is  non-parametric (i.e., does not depend  on
distribution assumptions).
     With no  loss  in generality,  thermal  reduction  factors  K(T) and
H(T) may be introduced such that
                    C(T)  = K(T)C(24°)  = K(T)c,
                    W(T)  - H(T)y(24°)  = H(T)p.
K(T) and H(T) were assumed to be monotonically decreasing  functions  of
temperature,  evaluated  on  the  basis  of  empirical  evidence.
     Using reduction  factors,  moments of  the  resisting  force  along  path
S can be derived  as:
                              IX-44

-------
               E[RF]  »  J{K(T)E[c]  + o ,H(T)E[M]}ds
                       S               nl
               VfRF]  -/^>{K1(T)Kj(T)Cc(r)  + 0^(1)0^

                        •(I)Cp(r)}d.1dSj                    (23)

where  subscripts i and j indicate  arguments for the double integration,
and
    Cc(r) = autocovariance function of cohesion

    Cu(r) = autocovariance function of coefficient friction

       r  = surface  distance between  points i and j.

    On the basis of  empirical evidence, a bilinear Mohr-Coulomb failure
criterion was  assumed.   Up  to  some transition  stress,  a, (T2),  the salt
was assumed to have  a  failure criterion specified by the parameter pair
(C,  w) ;    above the transition stress,  a perfectly  cohesive  failure
criterion specified  by the  parameter pair  (C,  u  - 0) .   The  transition
stress  was  assumed  to  be  monotonically decreasing  with   increased
temperature.
     Introducing  a transition from frictional  to purely cohesive
behavior  required  that the potential  breach  path be divided  into  two
segments,  one  on  which  a  >o,(T)   and  one on which  a 
-------
    The analysis  was expanded  to three  dimensions  by  considering
cylindrical  failure surfaces  formed by translating  the least
reliability  plane-strain  path  (Figure D-IX-23).   As  a first
approximation, the failure surface was taken as  one  autocorrelation
distance (r ) wide.  The question addressed in  the three-dimensional
analysis was how much the plane-strain reliability index  is  reduced
by  considering  the  potential  for  failure  anywhere  around the
repository.
    Considering only one opening of  the repository,  there is  an
infinite number of potential  failure  surfaces because the assumed  r
wide surface  could be  anywhere  along the  opening  length.  Let the
surfaces be indexed by the location of their  center points.   Because
adjacent surfaces  overlap,  their  total  resistances  can be highly
correlated*
    The total shear resistance  is calculated  as for  the  plane-strain
path, but  now averaged over a  larger  two-dimensional  surface.  Thus,
the variance  in  the  total resistance  is  reduced from  that  of the
most  critical path.    For a  surface  of width  r   this variance
reduction   is  to  37%,  and  the  corresponding  standard deviation
reduction  to 61%.(28)
    Assigning the total resistance of a  surface to  its  midpoint  at
the repository wall, a  correlated one-dimensional random  process  is
defined.  Breaching  occurs if  at any  place  along the  opening, the
resistance drops  below  the driving  forces.  This is equivalent  to
the  one-dimensional  random  process   crossing  a  level  (J standard
deviation  from the mean,  where  6 is  the  single-surface  reliability
index.  For large 6, the probability of .at least  one level crossing
in length  L of repository  opening is:
                  Pr = L exp(-B2/2)                           (25)
                              IX-46

-------
FIGURE D-IX-23   THREE-DIMENSIONAL MODEL
               IX-47

-------
where   6   is  a   length  measure  formed  by   integrating   the
autocorrelation function between negative and positive infinity (for
                                     /2 g\
exponential autocorrelation <$ = 2r ).
    Applying Equation 25 yields the probabilities of failure at peak
thermal stresses.  If  the  peak thermal stresses  occur  at  about 100
years,  and  if  the cumulative  probability  of failure is  assumed  to
increase linearly with time,  the failure rate over the first hundred
years would be two orders of  magnitude lower than the values implied
by Figure D-IX-24.
    The  results  of  the  analysis  for  the  reasonable  and  somewhat
conservative 20% variation  in salt properties  indicate exceedingly
low probabilities  of breaching  failure  even when  multiple failure
surfaces  are  considered.   These  probabilities  are obviously  not
precise and should be considered only as indicators.

2.  Parametric Inputs and Results of Analysis
    Parameter values  chosen for  sensitivity  studies bounded  those
values found in the literature  (Table D-IX-2).   For a specific site
these  values  would   have   to  be  evaluated  from  exploration  and
testing.   Results were  not sensitive  to Poisson's  Ratio,  lateral
stress ratio,  the  anisotropy  ratio of autocorrelation, or  the form
of the autocorrelation function.
    Results  of plane  strain analyses  for coefficients  of variation
in material properties, are shown in Figures D-IX-24 and D-IX-25.
    Trends within the results are the following:

    1.    Thermal   stresses  predominate,  thus  the  probability  of
        fracturing is  sensitive  to the  thermal field.   Time trends
        in reliability reflect  time trends in rock temperatures.
    2.  The probability of fracturing interconnecting repository and
        aquifer  decreases  as   the  separation  distance between
        repository and aquifer  increases.   The relationship  is not
        linear; by  decreasing  the  separation some  proportion,  the
        probability is increased by a greater proportion.
                              IX-48

-------
                                TABLE D-IX-2
           PARAMETER VALUES USED IN ANALYZING RELIABILITY AGAINST

                SHEAR FAILURE BETWEEN REPOSITORY AND AQUIFER
Parameter

Young's
  Modulus
   (psi)

Poisson
  Ratio

Point Coefficient
  of Variation*
Autocorrela-
  tion Length*
  (feet)

Lateral
  Stress Ratio
                      Low
                   5.0 x 10'
                    5/50
Most Probable

  5.0 x 104
                                     0.22
                                      10
   10/100
  High

5.0 x 10!
 20/200
                     0.5
     1.0
  2.0
  Standard deviation divided by mean.
**                                          -1
  Distance at which correlation reduces to e
                              IX-49

-------
oa.
x"
I
If
20


16

12

 8

 4

 0
       0.1
                            10
                         Time (yrs)
100
         FIGURE D-IX-24  CALCULATED RELIABILITY INDEX AS A
                         FUNCTION OF TIME
    12

    10
oa.
x   8
0)
=5    4
QC
     2

     0
                   50          100
                     Distance to Aquifer (m)
                                           20%COV
                                               40%COV
                                       150
            200
        FIGURE D-IX-25   CALCULATED RELIABILITY INDEX AS A
                         FUNCTION OF DISTANCE TO AQUIFER
                             IX-50

-------
        3.   Probabilities of  fracturing  are sensitive  to deformation
            modulus  and  point variance  of  strength properties.   Care
            must   be  taken   in  estimating   these  parameters  for
            site-specific studies.

G.  RECOMMENDATIONS FOR STOCHASTIC ANALYSIS  IN SITE-SPECIFIC STUDIES

    Stress  analyses  of  site-specific repositories  should incorporate
uncertainties.  In general, this is not now done.  Current analyses are
primarily deterministic, allowing estimates  only of mean safety factors
and  not  probabilities.   The  analysis  performed  here,  owing  to
limitations  of  time  and  effort  and in  keeping  with  the  overall
objectives of the present study,  serves only  as  a first approximation to
a comprehensive stress  analysis of a particular  repository.
    In analyzing a specific repository, the  present  analysis  should be
expanded to account for the uncertainties discussed below.

    1.  Stress Field  Uncertainties

        Uncertainties in the stress  field are generated by  uncertainties
    in deformation and  thermal  properties of repository formation, and
    by uncertainties in the regional   stress  field.   These  sources of
    uncertainty are coupled.  Moreover, for a specific  site, uncertainty
    will be contributed by estimation  error.  Despite  the  extensiveness
    of site  exploration programs,   uncertainties always exist  in site
    characterization.  These estimation uncertainties  are increased by
    the conflicting objectives  of placing as  few new borings as  possible
    into the geologic barrier.
        The approach to  modeling  uncertainty in stresses would  be to
    approximate  deformation  and  thermal  properties  as  second-order,
    homogeneous stochastic  processes,   and solve the differential  field
    equation for  means  and variances.   These  solutions  would most  likely
    be numerical,  as through uncertain finite  element  analysis.   This
    would result  in  process  statistics  for stresses  as  a  stochastic
    field (e.g.,  (30).    Using  a model of  this sort,  estimation  error
    based on sampling could be  quantified.
                              IX-51

-------
2.  Crack Propagation Analysis

    The  present  analysis  has   treated  limiting  equilibrium  shear
failure as the criterion  of  fracturing.  Alternative  criteria should
be considered.  Of particular importance would be the  consideration
of  fracture  propagation  in  which  stress  concentrations  are
recalculated for  increments  of  fracture  extension.   The  same
stochastic model  of  strength,  deformation,  and  thermal properties
could be used to yield probabilistic  predictions.

3.  More Accurate Geometric  Model  of  Repository

    The present  analysis has used  a  simplified  idealization of the
repository  as   a  cylindrical opening  in  a  uniform material.
Site-specific  studies  should  model  repository  geometry based  on
actual  layouts.    Although  this  would  add  analytical complexity,
certain  idealizations  (e.g.,  infinite  rows of  identically shaped
openings) are tractable.

4.  Elasto-plastic Media

    For specific  sites,  more  complicated  deformation models should
be introduced, based  on test results  on  site materials.

5.  Jointing and Pervasive  Inhomogeneities

    Salt  has  been  modeled  using  continuum mechanics.  In materials
other  than salt  (e»g., basalt, shales), jointing will  significantly
influence  the  mechanical behavior of  the  rock mass.   Appropriate
allowances  must  be  made  for  the  effects  of  Joints,  either  by
augmenting bulk mechanical  properties or by  introducing discontinuum
models.(5'17»3>
                          IX-52

-------
    6.  Pore Water Pressures

        Pore  water  pressures  affect  rock  mass  strength  by  reducing
    available  frictional  resistance  in  accordance  with the  effective
    stress concept,

                       T - C + (a - u) tan 6,

    where T = the available shear resistance and
          y - the pore water pressure.

    No  consideration has  been  given  to  pore  water  pressures  in  this
    analysis.   Recent  work  indicates  that  water  pressure  may  be
    incorporated in  stochastic analyses.

H.  DERIVATION OF STOCHASTIC REDUCTION FUNCTIONS

    For the derivation of mean and variance of stochastic resistance for
constant temperature, cohesive condition,  consider an elemental volume i
(Figure  D-IX-26)  along   the  potential  failure  path   L:(a,  b).    The
resistance to  shear displacement  at  this point,  assuming  Mohr-Coulomb
failure criterion, is:

                                                                 (26)
                       Tr,i = Ci + ai tan *i
where
      T    » the maximum available resisting shear stress,
       r»1
c. and .  » the cohesion and friction angle at the point, and
       a   = the  stress  normal  to the potential failure  path  at  i.   o.
             is  assumed  known,  based  on  stress  calculations;  however
             both c. and tan $  , the material properties, are assumed to
             be second-order homogeneous random variables.
The maximum available resisting shear force along path L  is the integral
of the available shear resisting stress, or
                             IX-53

-------
  -60
                                                                15%COV
  -50
   -40
.o
(D
•§  -20
oT

 o

 O)
 O
   -10
                                                               20%
                                                               30%
                                                               40%
                   10
       100

Total Length of Opening
1000
                                                               m
                   FIGURE D-IX-26   PROBABILITY OF BREACHING
                              IX-54

-------
           RF(L) -  / Tr ± ds  -  /  ct + o± tan $± ds           (27)
        The expectation of Equation 27 is
E[RF(L)] - E[/ c± + o1 tan ^ ds]                    (28)
         - / Elc^ds  + / o^ E[t
                                            an
    Defining the new variable,
                    = tan
the expected resisting shear force becomes
              E[RF(D]  - / Elc^ds  +  /a1Elwi]d.              (29)
This value is easily  calculated  once  o   is  known  as  Etc.]  and E[w.]  are
constant across space, given the assumption of statistical  homogeneity.
The variation of Equation  26 requires somewhat more  labor  to  determine.
By definition,
             V[RF(L)] -  E[(RF(L) - E[RF(L)])2]
                                  IX-55

-------
                        - E*[RF(L)J                               (31)
                 4 + o^ds  • f(c± + otv
               - [/Etc.] - ot ElVi] ds]
                                •  - -,  c   + o c y v ) ds^sj      (32)
                                     ds]2
                                                                  (33)
                Cc
-------
along  any  potential failure  path.   Correlation  lengths  will  of  course
differ  for  different paths, based  on  the  orientation  of the chord joining
their endpoints.   Second,  the  path  length  between any  two points  i and j is
used in  calculating correlation rather than the chord length between them.
This  allows line  integrals to be  taken  along the path.   As  long  as  the
correlation  length,  r  ,  is small  relative  to  the path  curvature this second
assumption  introduces  little error.
                                            (35)
    Following  the  arguments  of Popoulis    , the  double  integral  of
Equation  34 can  be reduced to  a single  integral.   The function Cc(i,J)t
depending only on the distance  r » li-jll,  is  constant  within the shaded
area of Figure D-IX-27:

                         Cc(i,j)  - Cc(r)                           (35)

    The area of  this strip is (L -  r)dr when  L is  the total path  length
from a to b.
    Thus Equation 34 becomes
    V[RF(L),  .  //^((J) ds.ds.,   - / (L - r) ee(r) dr       <36>
                                       r-0
    For the common autocovariance  function  (Figure  D-IX-28)

                     C.(r)  -  °l e'r/ro                            (37)
        2
where       is  ttie  Point   variance;  the  variance  of  resisting  force
becomes:
                                     IX-57

-------
                             L-r
FIGURE D-IX-27   REDUCTION OF DIMENSION IN VARIANCE
                 CALCULATIONS
                        IX-58

-------
0.5
0.4
0.3
0.2-
0.1 -
                                                 e-(r/r0)
0.1        0.2          0.3
                                                    i           i
                                                   0.4        0.5
     FIGURE D-IX-28    NORMALIZED VARIANCE OF AVERAGE STRESS
                       FOR TWO AUTOCOVARIANCE FUNCTIONS
                                 IX-59

-------
   V[RF(D]   -   f  (L-r)  o 2e"r/r°dr
                J n          C
                r-0

                                                                   L

                                                                   o  (38)
                                        +  1)  -
,L

'o
Dividing by L   leads  to the variance in the  average  resisting stress,

which is a function only of the ratio l/rQ»
 This  is  graphed  in  Figure D-TX-29.
     For  the  autocovariance  function:
                    C (r)  -  a
                                                                   (40)
                                    IX-60

-------
II



f-H
o
•p
o
O


•o
   0.0
                          TOO
FIGURE D-IX-29
APPROXIMATE REDUCTION FACTOR AS

FUNCTION OF AUTOCORRELATION DISTANCE
                        IX-61

-------
                          L

           V[RF(L)]   -   f  (L - r)  a^ e      °   dr

                         o
                                *•     i *
                         -..«/ »'  fe
                                                                 (42)
Substituting the approximation
                                                         2
              erf(z)  =  1  -  (0.3A8t - 0.09587(+0.74785t)e~z       (43)


                              t -  [1 + 0.47047Z]"1

allows Equation 42  to be  calculated numerically.
                                  IX-62

-------
                              REFERENCES

!•   Jaeger,  J.C.,  and  N.G.W.  Cook,  Fundamentals of  Rock Mechanics.
     Methuen,  London,  1969.

2.   Obert ,  L.,  and W.I.  Duvall,  Rock  Mechanics  and the  Design  of
     Structures in Rock.  John Wiley & Sons, New York,  1967.

3.   Stagg,  K.G.,  and  O.L.  Zienkiewicz  (eds.),  Rock  Mechanics  in
     Engineering Proctice. John Wiley &  Sons, New York,  1968.

4.   Mathab,  M.A.,  J.L. Ratigan,  and  D.R. McCreath.  Stability of  a
     Radioactive Waste  Repository  in  the  Canadian  Shield.  18th  U.S.
     Symposium on Rock Mechanics, 1977.

5.   Goodman,  R.E.,  R.E.  Heuze,  and  G.J. Bureau, On Modelling Techniques
     for the Study of Tunnels  in  Jointed Rock.  14th U.S.  Symposium on Rock
     Mechanics, 1973.

6.   Hoek,  E. ,  Structurally Controlled  Instability  in Underground
     Excavations.  18th U.S.  Symposium on Rock Mechanics, 1977.

7.   Oak  Ridge National  Laboratory,   R.L.  Bradshaw,  and   W.L.  McClain,
     Project Salt Vault:   A Demonstration of  the Disposal of High-Activity
     Solidified Waste in  Underground Salt Mines.  ORNL 455.

8.   Bradshaw, R.L.,  T.F. Lomenick, W.L.  McClain,  and  F.M.  Empson, Model
     and Underground Studies of the Influence of Stress,  Temperature, and
     Radiation on Flow and Stability in Rock Salt Mines. Proc. 1st Congress
     on Rock Mechanics, Lisbon, 1966.

9.   Parsons, Brinckerhoff, Quade, and Douglas, Inc.,  Thermal  Guidelines for
     a  Repository  in  Bedrock.  Y/OWI/SUB-76/16504,  Office  of  Waste
     Isolation, September, 1976.

10.  Oak  Ridge National  Laboratory,   R.D.  Cheverton,  and  W.D.   Turner,
     Thermal Analysis of  the National Radiation Waste  Repository:  Progress
     through March 1972.   ORNL 4789.
                                    IX-63

-------
11.   Westinghouse Astronuclear Laboratory,  A Study of Borehole Plugging  in
     Bedded Salt Domes by Earth Melting  Technology.  WANL-TME-2870,  1975.

12.   Kaufman, D.W.,  (ed.), Sodium Chloride:  The Production and  Properties
     of Salt and Brine. Reinhold Publishing Co.,  New York,  1960.

13.   Gera, F.,  Review of Salt  Tectonics   in Relation  to  the  Disposal  of
     Radioactive Waste  in  Salt Formations. Geological Society of America.
     83.

14.   Hunter,  L.,  and  S.  Siegel,  The  Variation  with Temperature  of the
     Principal  Elastic Moduli  of  NaCl Near  the  Melting  Point. Physical
     Review, 61, 1942.

15.   Starfield,  A.M.,   and  W.C. McClain,    Project  Salt  Vault,  J.  Rock
     Mechanics & Mineral Sciences,  10,  1973.

16.   Serata,  S.,  S.  Saknrai,  and  T.  Abachi,   Theory  of  Aggregate  Rock
     Behavior  Based  on  Absolute  Three-Dimensional Testing of  Rock  Salt.
     Proc. 10th Symposium on Rock Mechanics, 1969.

17.   Hendron, A.J., Mechanical  Properties  of Rock.  In:    Stagg, K.G., and
     O.L. Zienkiewicz  (eds.), Rock Mechanics in  Engineering Practice. John
     Wiley & Sons, New York, 1968.

18.  .Department     of  Transportation,  Office  of  High Speed  Ground
     Transportation,  G.B.  Clark, et al., Rock  Properties  Related to  Rapid
     Excavation. Final Report, PB  184756.

19.   Handin,  J.,  and R.V.  Hager,  Jr., Experimental  Deformation   of
     Sedimentary  Rocks  under  Continuing Pressure:    Tests at  High
     Temperature:  Bulletin, Americal  Association Petroleum-Geologists. 42:
     2892, 1958.

20.   Stokes,  R.J.,  Mechanical  Properties  of Polyerystalline  NaCl.  Proc.
     British Ceramics  Society, 6: 187,  1966.
                                     IX-64

-------
21.  Baidyuk,  B.V.  (ed.),  Mechanical Properties of  Rock at High  Pressure
     and Temperatures. Consultants Bureau Translation, New York,  1967.

22.  Fodor, I., and K.  Tokes,  Neve Forschungen Uber  die Physikelischen and
     Mechanishcen  Eigenschaften  des  Rumanischaften  des  Rumanischen
     Steinsalzes.  Theme 3,  No.  78:  705-709.  Proc.   1st  Congress  on  Rock
     Mechanics, Lisbon, 1966.

23.  Lindner,  E.N.,  and J.A.  Halpern.  In-Situ Stress Analysis. 18th  U.S.
     Symposium on Rock Mechanics, 1977.

24.  Savin, G.N.,  Stress  Distributions Around Holes. NASA  Technical
     Translation, TTF-607.

25.  Arthur D. Little,  Inc.   Technical  Support of  Standards  for  High-Level
     Radioactive  Waste Management.    Task  B  Report.    "Effectiveness  of
     Engineering Controls".  Cambridge, Massachusetts.  March-August  1977.

26.  Cohen  B.L.,  The  Disposal  of Radioactive Wastes  from Fission Reactors,
     Scientific American, 236  (6), June 1977.

27.  Timoshenko,  S.P.,  and  J.N.  Goodier,  Theory  of Elasticity, McGraw-Hill
     Book Company, Inc., New York, 1943.

28.  Vanmarke,  E.H.,  Stochastic  Modeling of Soil  Profiles.  J. Geot.  Div.
     ASCE 103, 1977.

29.  Agterberg,  F.,  Autocorrelation  Functions in Geology.    In:  Meriam,
     (ed.),  Geostatistics,  Methuen,  London,  1970.

30.  Beran,  N.J.,  Statistical  Continuum Theories.  John  Wiley  & Sons, New
     York,  1968.

31.  deary, M.P.,  Fracture  Discontinuities  and  Structural  Analysis  in
     Resource Recovery Endeavors. AIME J.  Pressure Vessel Technology (Paper
     77 - Pet 3),  1977.
                                     IX-65

-------
32.  Hener,  R,E.,  and  A. J.  Hendron,  Geomechanical  Model  Study of  the
     Behavior of Underground Openings  Subjected  to  Static Loads. Contract
     Report  R-69-1,   U.S.   Army  Engineers  Waterways  Experiment  Station,
     Vicksburg, Mississippi, 1969.

33.  McCutcheon, A.,  The  Behavior of Rock  and Rock Masses  in Relation to
     Military Geology. Quarterly Colorado School of Mines, 1949.

34.  Gelhar, L.W., Effects  of  Hydraulic Conductivity  Variations  on Ground
     Water  Flows.  2nd Int'l. Conference on Stochastic Hydraulics, London,
     1976.

35.  Papoulis, A.,  Probability, Random Variables, and  Stochastic Processes.
     McGraw-Hill, New York, 1965.
                                     IX-66

-------