United States
I:nvifonnie'ttal
Otfioe ot
Railidtiun Proyrum;,
Washington, D.C, 20460
EPA Io20/1 86019
September U>86
Mailutioh
f/EPA
Estimates of the Quantities,
Form and Transport of
Carbon-14 in Low-Level
Radioactive Waste
-------
Estimates of The Quantities. Form.
and Transport of Cacbon-14 in
Low-Level Radioactive Waste
James M. Gruhlke
James Neiheisel
Lewis Battist
September 1986
U.S. Environmental Protection Agency
Office of Radiation Programs (ANR-461)
Analysis and Support Division
401 M. Street. S.W.
Washington. DC 20460
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TABLE OF CONTENTS
Page
List of Figures iv
List of Tables v
Acknowledgements vi
Abstract vii
Introduction 1
Sources of Carbon-14 1
Nuclear Fuel Cycle Wastes 2
Institutional Wastes 8
Industrial Wastes 10
Chemical Forms of Carbon-14 in Waste 12
Nuclear Fuel Cycle Wastes 12
Institutional and Industrial Wastes 14
Transport of Carbon-14 14
Residual Materials 15
Atmospheric Transport 17
Ground Water Transport 18
Conclusions 22
References 23
iii
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LIST OF FIGURES
Figure Page
1. Fate of Carbon-14 at Low-Level 16
Radioactive Waste Disposal Sites
2. The Carbon System 20
IV
-------
LIST OF TABLES
Table Page
1. Low-Level Waste Forms 3
2. Carbon-14 in Low-Level Wastes: 5
Projected Activities and Volumes
3. Carbon-14 in Power Reactor Process 7
LLW Streams
4. Institutional Waste. Carbon-14 to 9
LLW Disposal: 1982 Estimate
5. Ground Water Parameters at LLW Sites 21
and Probable Carbon-14 Retention
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ACKNOWLEDGEMENTS
The authors would like to acknowledge the efforts of
Mr. G. Lewis Meyer, who established an interagency task force
to develop and compile data concerning the source term and
environmental fate of carbon-14 in low-level radioactive wastes
(LLW). As a result, a considerable amount of data was
contributed by numerous organizations in a relatively short
time frame. The assistance of the Conference of Radiation
Control Program Directors (CRCPD). the Department of Energy
(DOE), the U.S. Geological Survey (USGS). and the Nuclear
Regulatory Commission (NRC) is very much appreciated. The
authors are also indebted to the numerous reviewers within
EPA's Office of Radiation Programs, both at headquarters and at
the laboratory facilities in Montgomery. Alabama and Las Vegas.
Nevada. In particular, the critiques of John L. Russell.
Floyd Galpin. and David E. Janes were most helpful. Finally,
the patience of Phoebe H. Suber while typing the numerous
drafts of this paper is also appreciated.
VI
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ABSTRACT
Preliminary estimated risks from the disposal of low-level
radioactive wastes (LLW) by various shallow land disposal
methods indicated that carbon-14 (C-14) provided virtually all
of the estimated risk. The apparent predominance of the risk
from C-14 was traced to numerous conservative assumptions which
resulted from the poor state of knowledge of C-14 waste forms
and environmental transport. During 1985 an interagency group
representing many federal agencies was established to share
available data on C-14. This information has been compiled and
evaluated and is summarized in this report.
Analysis of the activity level of C-14 contributed from
the nuclear fuel cycle and non-fuel cycle sources to LLW sites
in the period from 1985-2004 provides the following
information: 2100 Ci from the nuclear fuel cycle; 1650 Ci from
institutional wastes; 2150 Ci from industrial wastes. The
chemical form of the C-14 in the fuel cycle waste approximates
75% inorganic (carbonate). 20% activation metal, and 5% organic
radiocarbons. The chemical form of the institutional and
industrial carbon-14 waste is believed to be essentially 100%
organic radiocarbon compounds.
The transport of C-14 from the low-level radioactive waste
site is believed to be largely as a gaseous release to the
atmosphere. C-14 released at LLW disposal sites is expected to
be a small percentage of that released in power reactor gaseous
effluents. Ground water transport of C-14 is probably as the
bicarbonate anion and to a lesser degree as soluble organic
radiocarbons. A suggested balance of C-14 release from LLW
sites might be two-thirds atmospheric release, one-fourth
ground water transport and less than one tenth remaining as
residual material.
Vll
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Estimates of the Quantities. Form, and
Transport of Carbon-14 in Low-Level
Radioactive Waste
James M. Gruhlke
James Neiheisel
Lewis Battist
INTRODUCTION
Carbon-14 (C-14) disposal at low level radioactive waste
(LLW) burial sites is of concern because of the estimated
potential health effects due to the amount and long half-life
(5700 years) of this radionuclide. Earlier estimates
apparently exaggerated the inventory of C-14 anticipated to be
shipped to LLW disposal sites, making it desirable to determine
a more realistic source term (En 84. NRC 81. Wi 81). In
addition the question as to the fate of this radionuclide in
the environment has to be considered. Specifically, estimates
are necessary for the fraction of C-14 in a LLW disposal
facility leaving as a gas. the fraction available for transport
by groundwater. and the residual amount left with the waste.
These are all time dependent phenomena, and are considered to
the extent possible.
In early 1985. an interagency group representing the
United States Geological Survey (USGS), Department of Energy
(DOE). Environmental Protection Agency (EPA) and Nuclear
Regulatory Commission (NRC) agreed to share available data and
information on C-14. EPA agreed to compile and evaluate this
material. The majority of the information presented in this
report came from the information received from these agencies.
the open literature and from the references obtained. An
assessment has been made of the source term and fate of C-14 in
LLW from the information and data received.
Special attention has been devoted to defining the C-14
LLW source term. Early estimates of C-14 in commercial LLW
were overestimated. Over 20 years, between 14.000 and 110.000
Ci of C-14 was predicted to be in commercial LLW, the bulk of
which was to be contributed by sealed sources (Wi 81. NRC 81).
Recent information developed by NRC and EPA indicates a
disposal of approximately 6,000 Ci of C-14 over 20 years. 0.05%
of which is expected to come from sealed sources.
SOURCES OF CARBON-14
This report examines the quantities and concentrations of
C-14 in commercial LLW which may be subdivided in three broad
categories. These include wastes from the nuclear fuel cycle.
institutional, and industrial facilities. These are discussed
in detail below.
- 1 -
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The Department of Energy (DOE) also generates significant
volumes of LLW from numerous research and defense-related
activities. Many of these facilities are one-of-a-kind and the
resulting wastes are thus more difficult to characterize in a
generic manner. DOE classifies its LLW into six categories:
(1) Uranium/thorium
(2) Fission product
(3) Induced activity
(4) Tritium
(5) Alpha (< 10 nCi/g)
(6) Other
Carbon-14 is contained only in the "Other" category, comprising
approximately 0.06% of the total radioactivity. The projected
average annual radioactivity disposal rate for "Other" LLW at
DOE/defense sites is 37.200 Ci per year. Thus. 22.3 Ci of C-14
are disposed of annually- Over a 20 year time period, this
would result in approximately 450 Ci of C-14 disposed of in
DOE/defense LLW. In addition. DOE reprocesses spent reactor
fuel, creating various high-level waste (HLW) streams, some of
which may contain significant C-14 inventories. Existing data
does not permit a determination of whether any of this C-14 may
gualify for disposal as LLW (DOE 84).
Nuclear Fuel Cycle Wastes
Nuclear fuel cycle wastes include LLW from power reactors
and associated nuclear fuel supply facilities (fuel fabrication
and uranium conversion facilities). Since commercial fuel
reprocessing is not practiced in the United States. LLW from
these facilities are not considered here. Further, fuel
fabrication and uranium conversion facilities handle only
uranium and therefore are not sources of C-14 in LLW. For all
practical purposes, then, power reactors are the sole source of
LLW containing C-14 for the nuclear fuel cycle.
Table 1 provides a listing of the principal LLW forms
containing C-14. These waste stream designations are similar
to those used by the NRC in their analysis of LLW for the 10
CFR Part 61 rulemaking (NRC-81). in fact. EPA has used the
basic information developed by NRC on LLW to construct a
simpler, more generic LLW source term (EPA-85, Gr-85). Thus.
EPA has combined similar NRC waste streams into a single waste
stream, weighting the NRC waste stream radionuclide
concentrations by their respective volumes. For example, the
NRC waste streams denoted as P-IXRESIN and B-IXRESIN (ion
exchange resins from pressurized water reactors (P) and boiling
water reactors (B). respectively) are combined into the EPA
waste stream L-IXRESIN (ion exchange resins from light-water
-2-
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TABLE 1
LOW-LEVEL WASTE FORMS
SYMBOL
L-IXRESIN
L-CONCLIQ
L-FSLUDGE
P-FCARTRG
L-COTRASH
L-NCTRASH
L-NFRCOMP*
I-COTRASH
I-LQSCNVL
I-ABSLIQD
I-BIOWAST
N-ISOPROD
N-LOTRASH
N-LOWASTE
N-SOURCES
N-TRITILFM
WASTE FORM DESCRIPTION
Nuclear Fuel Cycle
LWR Ion Exchange Resins
LWR Concentrated Liquids
LWR Filter Sludges
PWR Filter Cartridges
LWR Corapactible Trash
LWR Noncorapactible Trash
LWR Nonfuel Reactor Components
Institutional Wastes
Mostly Compactible/Combustible Trash
Liquid Scintillation Vials
Various Absorbed Liquids
Biological Wastes
Industrial Wastes
Isotope Production Wastes (Medical)
"Low Activity" Trash
"Low Activity" Process Wastes
Sealed Sources
Producers of Pharmaceuticals/
Labeled Compounds
*The EPA L-NFRCOMP waste stream combines the N-HIGHACT and
L-NFRCOMP waste streams defined in NRC analyses for the
10 CFR Part 61 rulemaking. N-HIGHACT consists of highly
activated metals from various industrial facilities and
research activities.
NOTES:
LWR
PWR
BWR
Representative of light-water power reactors
(PWRs and BWRs)
Pressurized water power reactor
Boiling water power reactor
-3-
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reactors). These concentrations are based on the NRG effort to
update LLW stream characteristics (NRG 86). Table 2 lists the
C-14 concentrations in the principal nuclear fuel cycle wastes
used by EPA in its analysis of the risks from LLW disposal (EPA
85).
Carbon-14 is a difficult-to-measure radionuclide whose
production in light-water reactor designs depends upon the
presence of nitrogen and oxygen (Fo 81, NCRP 85). Different
reactor designs, incorporating differing materials of
construction, reactor coolant chemistry, and nuclear fuel, will
produce varying amounts of C-14. Barring gross fuel failures.
C-14 produced in the fuel will remain in the fuel. Thus.
during operation C-14 produced in the reactor coolant should be
the only contributor to contamination of reactor process
streams and the low-level radioactive wastes generated
therefrom (NCRP 85). Carbon-14 may also appear in the non-fuel
reactor components (L-NFRCOMP) as activated metal wastes and
may leach from the metal matrix over extended time periods. As
defined here L-NFRCOMP are those activated nonfuel reactor core
components disposed of during the operational lifetime of the
reactor. This includes such items as control rods.
instrumentation for the core, poison curtains, and flow
channels which are replaced occasionally.
Two recent documents report on the results of the analyses
of process and waste samples from power reactors in an effort
to establish useful correlation factors between "easy" and
"difficult" to measure radionuclides (Cl 85. EPRI 85). Both
reports document the peculiar behavior of C-14 in reactors.
citing a lack of similarity with any other radionuclide in its
formation/release mechanisms and chemical/physical behavior.
The lack of information on chemical form in process waste
streams precludes the development of a theoretically sound
correlation factor for C-14 with some other easy to analyze
radionuclide. One report speculates that some carbon activity
may be in an insoluble form, perhaps as a carbonate, and varies
with cobalt activity (Cl 85). However, analysis of the large
amount of data seems to suggest that an empirical scaling
factor for carbon-14 with Co-60 may be most useful. The
scaling factor appears to be different for BWRs and PWRs. In
any case, the concentrations of carbon-14 in reactor process
and waste streams vary greatly from one reactor to another.
Some of the higher C-14 concentrations are found on filter
cartridges, filter sludges and ion exchange resins (Cl 85. EPRI
85).
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TABLE 2
CARBON-14 IN LOW-LEVEL WASTES:
PROJECTED ACTIVITIES AND VOLUMES
Waste Form
L-IXRESIN
L-CONCLIQ
L-FSLUDGE
P-FCARTRG
L-COTRASH
L-NCTRASH
L-NFRCOMP
I-COTRASH
I-LQSCNVL
I-ABSLIQD
I-BIOWAST
N-ISOPROD
N-LOTRASH
N-LOWASTE
N-SOURCES
N-TRITIUM
Carbon-14
Concentration
(Cl/tu3)
Projected
Volume (m3)
1985-2004*
Projected Carbon-14
Activity (Ci)
1985-2004
NUCLEAR FUEL CYCLE
1.
7.
8.
1.
1.
1 .
6.
28
10
29
02
39
19
43
(-
(-
(-
(-
(-
(-
/ _
2
4
4
4
5
4
3
)**
)
)
)
)
)
)
9
3
1
1
5
4
6
-92(
.31(
.31(
.28(
.97(
.78(
.45(
4
5
5
4
5
5
4
)
)
)
)
)
)
)
SUBTOTAL:
1
2
1
1
8
5
4
2
.27(3)
.35
.09
.31
.30
.69
.15
. 10
(2)
(2)
(0)
(0)
(1)
(2)
(3)
INSTITUTIONAL WASTES
5.
2.
8.
1 .
26
(-
51(-
16
01
<-
3
4
3
2
)
)
)
)
INDUSTRIAL
7.
1.
9.
4.
2.
79
64
36
57
76
(-
(-
(-
(-
(-
5
3
4
3
)
)
)
)
1)
2
1
1
7
.82(
.50(
.11(
.52(
5
4
4
3
)
)
)
)
SUBTOTAL :
1
3
9
7
1
.48
.77
.06
.60
.65
(3)
(0)
(1)
(1)
(3)
WASTES
9
1
6
5
6
.97(
.01(
.03(
.82(
.94(
3
5
4
2
3
)
)
)
)
)
SUBTOTAL :
GRAND TOTAL:
7
1
5
2
1
2
5
.77
.66
.64
.66
.92
.15
.90
(-1)
(2)
(1)
(0)
(3)
(3)
(3)
*From PHB-85
**1.28(-2) is a shorthand notation for 1.28 E-2. or 0.0128
-5-
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Various studies and measurements have shown that almost
all of the carbon-14 In power reactor effluents {liquid, solid.
and gaseous) occurs in the gaseous form. The primary component
of this gaseous C-14 is as C(>2. Detailed measurements at
three operating power reactors indicated that C-14 gaseous
discharges would range from about 30 to 500 times the amount of
C-14 in liquid effluents (EPA 71. EPA 74. EPA 76). A recent
study at three operating power reactors in New York State
concluded that C-14 in gaseous releases was about 20 times that
in liquid and solid wastes (Ku 85). A report dealing with the
classification of LLW under 10 CFR Part 61 requirements
indicated that only a very small percentage (on the order of
1%) of the C-14 produced in the reactor coolant would end up in
LLW (AIF 83).
As indicated above, the C-14 source term used by EPA in
its analysis of LLW disposal is shown in Table 2. In order to
provide perspective, one may compare the EPA Carbon-14 source
term for routinely generated LLW (excluding L-NFRCOMP) with
other estimates, NCRP has indicated that total C-14 releases
from a light-water power reactor should be approximately 10
Ci/GW(e)-yr. of which a very small fraction (0.1% to about 3%)
appears in the liquid and solid forms. Thus, one might expect
on the order of 0.1 Ci of carbon-14 per GW(e)-yr in the LLW
from light-water power reactors (NCRP 85). Kunz has indicated
C-14 release rates (in the gaseous form) of from 9.6 to 12.4
Ci/GW(e)-yr for three power reactors in New York State, while
estimating the C-14 release rate in liquids and solids to be
less than 5% of the gaseous release rate (Ku 85). This implies
no more than 0.6 Ci/GW(e)-yr of C-14 produced in the LLW from
power reactors. Table 3 converts the EPA C-14 source term into
comparable units. Ci/GW(e)-yr. First, the C-14 concentrations
for the pressurized water reactor (PWR) and boiling water
reactor (BWR) waste streams are provided. When these are
coupled with the indicated volume generation rates, between 0.3
and 0.5 Ci/GW(e)-yr of C-14 is estimated as the production rate
in LLW from light-water power reactors. The EPA source term
falls within the range of other C-14 source term estimates and
appears to be a reasonable representation of C-14 in LLW from
light-water reactors. Finally, all of these estimates are
consistent in that they include consideration of routinely
generated LLW forms. Carbon-14 appearing as an activation
product in metallic components is considered separately (e.g.,
nonfuel reactor components or decommissioning wastes).
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TABLE 3
CARBON-14 IN POWER REACTOR PROCESS LLW STREAMS
Waste
Form
PWR
P-IXRESIN
P-CONCLIQ
P-FSLUDGE
P-FCARTRG
P-COTRASH
P-NCTRASH
BWR
B-IXRESIN
B-CONCLIQ
B-FSLUDGE
B-COTRASH
B-NCTRASH
Concentration:
C-14 (Ci/m3)*
2.25(-2)
9.80(-4)
6.97(-4)
1.02(-4)
2.70(-5)
L.85(-4)
l,44(-3)
1.22(-4)
8.32C-4)
3,50(-6)
1.5K-5)
SUBTOTALS:
Volumes
(m3/GW(e)-vr)**
17.6
123
2.2
11.0
215
110
478.8
80.7
223
179
221
105
SUBTOTALS: 808.7
*Ftom EPA-85. NRG 86
**From NRC-81
***3,96(-l) is shorthand notation for 3.96E-1.
or 0.396.
Total Activity
(CiXGW(e)-yr)
3.96(-L)***
1.21(-1)
l,53(-3)
1.12(-3)
5.81(-3)
2.04(-2)
5.46(-l)
2.72(-2)
1.49(-L)
7.74(-4)
1.59(-3)
2.95(-l)
NOTE:
See Table 1 for a more complete definition of the waste forms.
The first letter identifies the waste generator: P (pressurized
water reactor). B (boiling water reactor).
-7-
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An additional category of low-level nuclear fuel cycle
wastes containing C-14 will result from the decommissioning of
commercial power reactors. Projections of the quantities and
characteristics of such wastes are difficult to make due to the
large uncertainty in future decisions relating to numerous
technical, safety and economic matters. While certain
technical factors may allow for extended operation of power
reactors, future safety-related requirements may force the
early retirement of certain power reactors. Uncertainty also
exists as to the mode, or modes, of decommissioning that will
be employed. Finally, it is not clear whether all
decommissioning wastes will qualify for low-level waste
disposal. A detailed study of power reactor decommissioning
indicates that certain reactor components will contain
extremely large radionuclide concentrations, including the bulk
of C-14 activity- Such highly activated components may be more
suited to deep geological disposal (NRC 80. NRC 81. Wi 81).
Due to these numerous uncertainties, this report does not
attempt to project the volumes and activities of low-level
wastes containing C-14 from power reactor decommissioning.
Institutional Wastes
Institutional wastes are generated by hospitals, medical
schools, universities and colleges. Such wastes have been
classified as trash, liquid scintillation vials, absorbed
aqueous and organic liquids, and biological wastes. Carbon-14
appears in a wide variety of labeled compounds. Such chemicals
are used in biological research, classroom projects, in vitro
clinical assays, and nuclear medicine procedures. An earlier
classification by NRC for its 10 CFR Part 61 rulemaking
provided estimated radionuclide concentrations and volumes for
these wastes (NRC-81). EPA has used the NRC characterization
of 'institutional wastes', though no distinction is made
between large and small generators. The EPA source term
combines volumes of large and small generators into one overall
volume for the waste in question. The radionuclide
concentrations used by NRC and EPA are based on surveys of
institutional generators and unpublished disposal site
radioactive shipment records (NRC-81) and are listed in Table 2.
Table 4 gives an estimate of the inventory of C-14 in
institutional LLW disposed of in 1982. A total of 54.9 Ci of
C-14 is calculated, based on the NRC and EPA source term
assumptions. This compares with 58.3 Ci of carbon-14
reportedly disposed of by instutional waste generators, based
on the 1982 Conference of Radiation Control Program Directors
(CRCPD) survey of waste generators (CRCPD 82). In particular.
17.6 Ci and 40.7 Ci of carbon-14. respectively, were shipped
for disposal by "medical" and "academic" waste generators
(CRCPD 82). The calculated EPA source term for carbon-14 in
institutional LLW is in good agreement with the results of the
CRCPD survey.
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TABLE 4
INSTITUTIONAL WASTE
CARBON-14 TO LLW DISPOSAL: 1982 ESTIMATE
Carbon-14 1982 C-14 Disposal
Concentration* Estimated** (Ci)
(Ci/m3) Volume (m3) 1982
I-COTRASH S.26(-3)*** 9.10(3) 4.79(1)
I-LQSCNVL 2.5K-4) 9.56(2) 2.40(-1)
I-ABSLIQD 8.16(-3) 3.60(2) 2.94(0)
I-BIOWAST 1.01(-2) 3.78(2) 3.82(0)
TOTALS: 1.08(4) 5.49(1)
AVERAGE CONCENTRATION: 5.1(-3) Ci/cubic meter
*Based on NRC 81. NRC 86. EPA 85
**1982 volumes based on NRC 86
***5.26(-3) is a shorthand notation for 5.26E-3. or 0.00526.
NOTE: See Table 1 for a more complete definition of the waste forms.
-9-
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A recent article detailing the waste management practices
at the National Institutes of Health, a large institutional
user of cadionuclides, also provides some insight as to the
average concentrations of C-14 in institutional radioactive
wastes (Ho-84). For the year 1983. 0.791 Ci of carbon-14 was
shipped for disposal in a volume of 325 cubic meters, an
average concentration of 2.4E(-3) Ci/cubic meter. This value
is in reasonable agreement with the volume-weighted average
concentration of 5.1E(-3) Ci/cubic meter for the NEC and EPA
institutional waste source term shown in Table 4. Using the
1982 CRCPD survey of waste generators, about 4500 cubic meters
of institutional waste (academic plus medical) were shipped for
disposal (CRCPD 82). Considering the estimated 58.3 Ci of C-14
shipped in that volume, an average concentration of about
1.3E(-2) Ci/cubic meter is obtained. This is slightly higher
than the 5.1E(~3) Ci/cubic meter volume-weighted average
concentration of C-14 in the EPA and NRC source term for
institutional wastes. Based on these comparisons with reported
characterizations of institutional wastes, the EPA source term
is considered to be a reasonable approximation to the overall
C-14 concentration in such wastes.
Industrial Wastes
Industrial generators of LLW include a wide variety of
activities. Such generators produce and distribute isotopes to
other industrial and institutional waste generators who
incorporate these isotopes into various products, procedures.
and analyses. Carbon-14 is an important isotope because of its
long half-life and ability to interact with biological
systems. Thus, it may be incorporated into a wide range of
organic chemicals for biological research and medical studies.
Of the many categories of industrial LLW generators
included in the NRC and EPA analyses of LLW. five categories
generate LLW containing C-14 (NRC-81. NRC-86. EPA-85. Gr-85):
N-ISOPROD Isotope (Medical) Production Waste
N-LOWASTE Low Specific Activity Process Wastes
N-LOTRASH Low Specific Activity Trash
N-SOURCES Discarded Sealed Sources
N-TRITIUM Producers of Pharmaceuticals/Labeled
Compounds
Table 2 further identifies these wastes as to average C-14
concentrations and projected waste volumes expected in the
period 1985 to 2004. These concentrations are based on
previous NRC analyses (NRC-81. NRC-86) except for discarded
sealed sources. For this category, the EPA source term relies
in part on a recent NRC update of the data base supporting the
10 CFR Part 61 rulemaking and an examination of sealed source
usage among NRC medical, academic, and industrial by-product
material licenses (NRC-86. EPA-80).
-10-
-------
Examination of Table 2 illustrates that about 90% of the
C-14 in industrial wastes originates from the N-TRITIUM waste
category- Though the N-TRITIUM waste stream is dominated by
tritium (an estimated 220 Ci/cubic meter of tritium versus
0.276 Ci/cubic meter of carbon-14). the C-14 content of
N-TRITIUM makes it the largest contributor to the inventory of
C-14 to be disposed of from 1985 to 2004 (see Table 2).
Some data are available on the waste shipped by large
tritium and C-14 manufacturers of Pharmaceuticals and other
labeled products. New England Nuclear Corporation (NEN) is a
major generator of non-fuel cycle C-14 wastes both in terms of
volume and activity (Ke 85. NRC 83). Waste volumes from NEN
have decreased over the last few years: 696 m3 (1979). 354
m3 (1981). 42.5 ra3 (1983). Carbon-14 in waste activities
from NEN have shown considerable variability over recent years:
150 Ci (1980). 47 Ci (1981). 178 Ci (1983). 11.1 Ci (1984).
Prior to the implementation of 10 CFR Part 61 (late 1983).
NEN's waste volumes ranged well into the hundreds of cubic
meters and waste activities were in the range of 100 Ci C-14
(Ke 85. NRC 83. ER 83). This implies an average C-14
concentration of a few tenths of a curie per cubic meter of
waste, similar to the value used in the EPA LLW source term for
the N-TRITIUM waste stream (Table 2).
In 1984 the total C-14 activity in NEN wastes dropped
significantly to a little over 11 Ci. Although the waste
volume for 1984 was not available, it also dropped
significantly, judging by the 60% decrease in the number of
waste packages shipped from 1983 to 1984 (Ke 85). This
decrease in waste shipped is probably the combined result of
many factors. Implementation of 10 CFR Part 61 forced waste
generators to re-evaluate the processes generating waste and
the treatment and packaging of wastes. It is possible that
many waste generators decided to ship stored wastes in addition
to routine process wastes prior to 10 CFR 61 implementation.
It is known that NEN has stored some of its higher activity
C-14 wastes since January 1984 awaiting approval of a new waste
package design that would allow 8 Ci of C-14 per package (Ke
85)*- An additional factor has been the evolution of
commercial disposal site restrictions on many institutional
wastes (DOE 82). This has also encouraged waste generators to
dispose of certain waste forms sooner than normal, further
distorting reported waste volumes and activities over the
last few years. Finally, it is reported that NEN has
implemented certain process changes to improve production
efficiency and reduce waste generation (Ke 85). In summary.
numerous factors have forced waste generators to introduce
changes in waste management practices. The EPA source term for
N-TRITIUM appears representative of the C-14 concentration in
these wastes prior to the implementation of 10 CFR Part 61.
* NEN is reported to have approximately 6.4 Ci C-14 in
inventory at the present time.
-11-
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Various data sources ace used to characterize the
remaining industrial LLW streams. The low activity trash and
process waste radionuclide concentrations and volumes are based
on the NRC characterization of such wastes in the 10 CFR Part
61 rulemaking (NRC 81). These wastes are meant to characterize
the industrial equivalents of institutional wastes, i.e..
liquid scintillation vials, absorbed liquids, and biological
wastes. Characterization of medical isotope production wastes.
N-ISOPROD. is based on a review of 1983 radioactive waste
shipment records (NRC 86).
For industrial sealed sources. N-SOURCES. the data base
has always been very limited. As a result, the first
characterization of N-SOURCES for NRC's 10 CFR Part 61
rulemaking (NRC 81) relied upon certain assumptions regarding
the radionuclide composition and total activity
(Wi 81). This resulted in an exaggerated carbon-14 source term
for N-SOURCES. In preliminary analyses of LLW disposal by EPA
and NRC. approximately 99% of all the carbon-14 in LLW was
attributed to N-SOURCES (En 84. NRC 81).
Additional information has been used to derive a revised
characterization of N-SOURCES. The NRC update of LLW source
terms (NRC 86) does provide information on the allowable
activity in C-14 sealed source designs, which is relatively
small. To obtain a representative concentration for carbon-14
in discarded sealed sources. EPA examined the records of 65 NRC
byproduct material licenses to establish a frequency
distribution of radionuclides used in sealed sources (EPA 80).
Assuming disposal is in proportion to usage, the radionuclide
composition of discarded sealed sources waste can be
approximated. In the case of C-14. 1.9% of the sealed sources
in use (and therefore disposed of) are carbon-14 sealed sources
(EPA 80). The average activity of the largest carbon-14 sealed
source category is 0.05 Ci (NRC 86). When one considers all
sealed sources, however, the weighted average carbon-14
activity in a single hypothetical sealed source becomes 1.9% x
0.05 Ci. or 9.5 E(-4) Ci. This is termed a hypothetical sealed
source because it is meant to depict, in one sealed source, the
relative activities of nuclides used in all sealed sources and
disposed of by shallow land disposal techniques. For the sake
of calculation, this weighted average carbon-14 activity.
9.5E(-4) Ci. is disposed of in one 55 gallon drum (i.e.. 0.208
m3). resulting in the disposal concentration of 4.57E(-3)
Ci/cubic meter shown in Table 2. This revised source term for
carbon-14 in sealed sources also illustrates that this source
of carbon-14 contributes only about 0.05% of all carbon-14 in
LLW (See Table 2).
CHEMICAL FORMS OF CARBON-14 IN WASTE
Nuclear Fuel Cycle Wastes
Seven nuclear fuel cycle waste streams containing C-14 are
listed in Table 1. With the exception of the L-NFRCOMP waste
-12-
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stream which represents activated metal, the chemical form is
not precisely known, although it is reasonable to assume that
the major portion of the remaining waste streams is in the form
of a carbonate and a very minor portion as organic radiocarbon
compounds.
The primary component of the initial gaseous release of
C-14 from LWR's is anticipated to be as C02. as reported for
BWR's and various percentages of offgas from PWR's (EPA 74. EPA
76. Ku 85). Although the solubility of C02 would be very low
in the reactor coolant at the operating conditions of power
reactors, a small fraction would form carbonate and bicarbonate
ions. These ions would either be removed by the anion
exchanger resins in the coolant purification system or could
form trace insoluble carbonates with some of the corrosion
products, subsequently removed by other liquid treatment
components. In PWR's it can be postulated that the hold-up of
C02 in the offgas system, in the presence of large amounts of
hydrogen and radiation, allows for the conversion of C02 to
methane and other low molecular weight molecules.
The most stable form of C-14 delivered to a LLW site is
the L-NFRCOMP waste stream, which is in the form of a metal
matrix. This source constitutes a projected 415 Ci or
approximately 20 percent of the nuclear fuel cycle C-14 waste
to the year 2004. The National Council on Radiation Protection
and Measurements is of the opinion that the quantity of C-14
formed in core hardware at power reactors will remain in the
metal (NCRP 85). They also assume that because of other
activated radioactive products in the hardware the metal will
be disposed of in a manner which will prevent release of C-14.
This constitutes a firm basis for any quantification of the
fate of a residual source of C-14 at a LLW site.
The remaining six waste streams, comprising approximately
80 percent of the projected nuclear fuel cycle C-14 waste
activity, consists of materials collected as solids on resins.
filters, or in sludges at light water reactors. Although the
material has been adequately inventoried for C-14 by liquid
scintillation counting techniques, the chemical form of the
C-14 in these waste streams has not been sufficiently
documented, primarily due to the extremely low mass
concentrations measured. Some differences regarding the
L-IXRESIN waste stream are also apparent; this ion exchange
resin waste stream comprises approximately 60 percent of the
fuel cycle waste C-14 activity shown earlier in Table 2. Two
recent reports examined hundreds of process and waste samples
from power reactors, including numerous ion exchange samples
(Cl 85. EPRI 85). In many instances, reactor coolant ion
exchange resins contained elevated C-14 concentrations as
compared to C-14 activity in the reactor coolant. Kunz
however, reporting on a Boiling Water Reactor (BWR) in New York
State, found no detectable removal of C-14 by the ion-exchange
resins on analysis of a limited number of primary coolant
samples from that particular BWR (Ku 85). In an assessment of
-13-
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C-14 control technology for the light water reactor (LWR) fuel
cycle. Bray discusses the formation of calcium carbonate as the
principal solid formed and the methods used for its collection
as the waste product (Br 77). While removal of solid waste in
existing LWR's differs from the methods prescribed by Bray in
his earlier assessment, it is reasonable to assume that C-14
exists primarily as a carbonate in the six fuel cycle waste
streams as previously stated. Mackenzie suggests that
compounds such as formaldehyde, formic acid, and acetic acid
may be produced in small amounts in the PWR wastes and perhaps
form as much as 2 to 5 percent of the solid waste components
(Ma 85).
Institutional and Industrial Wastes
Institutional and industrial sources account for about 28%
and 36% of the carbon-14 activity in LLW. respectively (Table
2). Among these generators the greatest contributor of C-14 is
expected to be N-TRITIUM. manufacturers of tritium and C-14
labeled compounds. New England Nuclear Corporation (NEN) is
the largest waste generator among the manufacturers of tritium
and C-14 labeled chemcials. accounting for greater than 70% of
the C-14 waste activity in 1983 from this category (Ke 85).
Approximately 100 organic radiocarbon compounds are available
for sale (MEN 85).
Institutional and industrial waste comprises approximately
64 percent of the projected total inventory of C-14 to the year
2004 (Table 2). Most of these compounds are varieties of
organic radiocarbon compounds. As all organic matter, they
decompose at various rates when exposed to bacteria and other
natural processes, collectively called biodegradation. Organic
matter has a relatively short life time in contact with soil.
Organic materials yield either carbon dioxide or methane as end
products of the biodegradation process depending upon the
nature of the bacteria, and whether the redox state of the
system is an oxidizing or reducing environment. Since both of
these compounds are gases, they are able to diffuse away from
their source, with the major portion ultimately escaping to the
atmosphere. Carbon dioxide may also fractionate between a
vapor and water phase. The transport of C-14 from a LLW
repository will therefore have at least two pathways from the
site (Co 82. Fr 84).
TRANSPORT OF CARBON-14
The C-14 buried at a LLW site is comprised of the organic
radiocarbon compounds from the institutional and industrial
wastes and the inorganic carbonate and activation metals from
the nuclear fuel cycle wastes. The decomposition of these
wastes begins upon exposure to trench moisture and soil
bacteria after release from the isolation of their container.
-14-
-------
The process of decay of the organic radiocarbons should proceed
in a manner similar to the decay of any organic wastes in a
sanitary landfill (Ov 82). The activation metals from the
nuclear fuel cycle C-14 waste will constitute the residual
portion of the waste. The transport of the inorganic carbonate
will be governed to a large extent by the chemical composition
of the ground water and the pH and Eh of the trench
environment. The three major transport considerations may be
divided into the three categories depicted in Figure 1 as
residual, atmospheric, and ground water transport. These are
estimated as proportional releases to the various pathways.
Residual Materials
The C-14 in the activated metals, comprising approximately
seven percent of the total C-14 budget, is the only material
apt to remain residual at a LLW site. While some of the
organic hydrocarbons have a longer residence time than others.
none are residual over the long term (thousands of years).
Several persistence classification schemes have been devised
for organics based on their volatilization, hydrolysis, biotic
degradation, and other abiotic degradation processes; however.
such classification schemes do not mean much when organic
compounds contain C-14 with its 5700 year half-life. With the
breakdown of the organic compounds, the C-14 atoms take on the
chemical characteristics of the organic decay products. Thus,
the seven percent residual C-14 (the fraction of C-14 in
L-NFRCOMP) constitutes the only reasonably firm guantitative
base in any budget regarding the fate of C-14 at a LLW disposal
site. If. as is believed, the C-14 exists as elemental carbon
in the activated metal then this material would probably be
unavailable to biological activity.
As discussed earlier, L-NFRCOMP consists of activated
nonfuel reactor core components occasionally shipped as LLW
during the operational lifetime of a power reactor. Examples
include discarded control rods, in-core instrumentation, poison
curtains, flow channels, or any other in-core metallic
components separated from the fuel assembly. Most of these
components are stainless steel. By far. the largest
contributor to C-14 in these metals is the activation of
nitrogen impurities, resulting in single carbon-14 atoms
dispersed throughout the metal matrix (Da 77. Navy 84, NCRP
85).
Corrosion of steels has been reported in regard to LLW
packaging and the disposal of defueled, decommissioned
submarines (Co 79. Navy 84). In general, corrosion resistant
alloys like stainless steel exhibit pitting penetration rates
on the order of a mil per year in soil. Weight loss rates are
much less since this represents the thickness of metal lost as
-15-
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ATMOSPHERIC '
"V-V •,'••: •',*.", '-vV-r;
\*.. • : >•. vv.' ; -K . > ./.
CYCLE
LLVJ
Q
FIGURE 1. FATE OF CARBON-14 AT LOW-LEVEL RADIOACTIVE WASTE DISPOSAL SITES
-------
if the corrosion had occurred uniformly over the surface area
in question. Once the metal has corroded, the availability of
any C-14 would depend on the chemical characteristics of these
corrosion products. It is reported that, in general, the
corrosion products of structural stainless steels are not very
soluble in either seawater or freshwater (Navy 84).
Considering that many of the nonfuel reactor components are
stainless steel and have thicknesses on the order of an inch or
less (Vepco 73). a considerable amount of metal in the
components may corrode within a few half-lives of C-14 (10.000
to 20.000 years). Furthermore, considering that most of these
corrosion products are reportedly insoluble in freshwater.
coupled with the presence of C-14 as elemental carbon (i.e..
unavailable to biological activity), implies that for all
practical purposes, the C-14 in activated nonfuel reactor
components will remain in the vicinity of such components
disposed by shallow land disposal techniques.
Atmospheric Transport
The primary source of the C-14 that eventually leaks off
as carbon dioxide and methane gas to the soil and atmosphere is
from the organic radiocarbons of the institutional and
industrial waste categories. Francis describes in some detail
the significant role microorganisms play in the generation of
radioactive gases directly through their metabolic activity (Fr
84). Methanogenic bacteria in anoxic conditions that may
prevail in the trenches release methane and tritiated methane.
With increased availability of oxygen, carbon dioxide is the
final product of decay of organic radiocarbon compounds (Fr 84).
Dayal reports that at the Maxey Flats LLW site leachates
from the trenches exhibited varying degrees of anoxia
characterized by negative redox potentials, low dissolved
oxygen, elevated alkalinity, sulfate concentrations, ammonia.
dissolved iron and manganese, and dissolved organic and
inorganic carbon (Da 85). Under such conditions methane gas
might be expected; with migration of the gas into oxygenated
soil space the methane would be oxidized to carbon dioxide. At
the West Valley. NY. LLW site Husain cites high levels of both
carbon dioxide and methane in the trenches (Hu 79). Francis
reports tritated methane as the most abundant detected seepage
gas to the atmosphere from the West Valley site burial trenches
(Fr 84).
While some of the carbon dioxide released to the moisture
in the trench and soil will be converted to carbonate and
bicarbonate anions under favorable environmental conditions.
the preponderance of carbon dioxide will be released to the
atmosphere.
-17-
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The amount of C02 converted to carbonate and or
bicarbonate anions is dependent upon the pH and Eh of the soil
moisture, the partial pressure of the C02 in contact with the
moisture and the chemical species present in the water, many of
which would tend to remove, by precipitation, the above
mentioned anion apecies. However, since experience has shown
that gaseous biodegradation products are generally released
from sites of decaying matter, the majority of the C02
produced is anticipated to eventually migrate to the surface
and be released to the atmosphere. Of the total organic
radiocarbons acted upon, only a minor amount is expected to be
available for conversion to the bicarbonate anion or to soluble
organics for ground water transport. Thus in a budgetary
consideration it is estimated that the major portion of the
institutional and industrial C-14 waste is available for
release to the atmosphere.
Upon release to the atmosphere the carbon dioxide
generated from the LLW radiocarbon waste is diluted with the
normal atmospheric gases. The amount of carbon dioxide
generated from the LLW sites is only a fraction of that
released to the atmosphere from operating nuclear power
plants. As discussed earlier in the report, only a very small
percentage of the C-14 generated at a light water reactor is to
be found in the LLW. Even with the addition of C-14 from
industrial and institutional LLW generators, the amount of C-14
in all LLW will still comprise a small percentage of that
released to the air from power reactors. The inventory of C-14
released to the atmosphere by commercial power reactors
(1976-2000) has been estimated to be approximately 10.000 times
lower than the sustained steady state atmospheric C-14
inventory from cosmic ray production (Fo 81). Thus, the amount
of C-14 released to the air at LLW disposal sites would be a
tiny percentage of that deriving from naturally-produced C-14
in the atmosphere.
Ground Water Transport
The ground water transport of C-14 is of primary concern
in the assessment of the fate of C-14 from LLW sites.
Preliminary, conservative, estimates indicate that potential
health effects from ingestion by drinking water could occur in
the long term if all of the C-14 disposed of at a LLW site were
transported by ground water. As previously discussed however.
the predominant forms of C-14 for potential transport include
the inorganic carbonate and bicarbonate ion from the nuclear
fuel cycle waste and the soluble organic radiocarbons of the
institutional and industrial wastes.
The dissolution of calcium carbonate from the fuel cycle
waste in the hydrogeologic setting of the LLW sites takes place
in accordance with the following reactions (Wi 74):
HC03
-18-
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The bicarbonate anion (HCOg) is the predominant carbonate
species under pH conditions of typical ground water (pH=6.5 to
9). As observed in the pH-Eh diagram of the carbon system
(Figure 2). carbonate species can be stable even under reducing
redox conditions that might occur in LLW trenches. Studies
conducted by Dayal at the Maxey Flats LLW site provide evidence
that inorganic carbon concentrations in the trench are greater
than would occur under the normal atmospheric partial pressure
of carbon dioxide (Da 85). Therefore the ability of ground
water to transport dissolved carbonate from the fuel cycle
carbon-14 LLW would most likely be enhanced in the trenches
over conditions existing in surface waters at the site.
A comparison of ground water parameters at four LLW sites
(Table 5) shows a marked difference in the bicarbonate and
calcium content at the Barnwell site as contrasted with the
West Valley. Beatty. and Sheffield LLW sites. The difference
in the ground water parameters relates to an impoverished
carbonate terrain at the Barnwell LLW site. The lower pH and
undersaturation as regards bicarbonate anion should result in
faster transport of the fuel cycle carbonate waste containing
C-14. Investigations of Allard et al. in Sweden oh sorption
characteristics support this view in that increased sorption of
C-14 was observed with an increase of the calcium content of
the solid on host media (Al 81). Gamier in an investigation
of C-14 retention in a column study found evidence of retention
of C-14 in the presence of carbonate material in the range from
0.8 to 2.9 ml/g of calcium (Ga 85). Factors that increased the
retention also included greater retention with greater ionic
strength. Thus from the foregoing investigations and the
ground water parameters it is apparent that the Barnwell LLW
site would favor more rapid ground water transport of C-14 from
the site than the other LLW sites as is indicated in the
estimated K^ shown in Table 5. Sites having alkaline
conditions or carbonate minerals in the soil or high calcium
and bicarbonate ion content in the groundwater would tend to
favor precipitation or hold-up of carbonate anions. The high
calcium and bicarbonate content of the ground water at the
Beatty. NV. West Valley. NY. and Sheffield. IL. sites would
favor retention of [H ^-4C03] as compared to a more rapid
transport of this species at the Barnwell. SC. site.
Recent investigations on the transport of organic
materials at LLW sites conducted by Fruchter disclosed that low
molecular weight hydrophilic organic compounds comprise from
0.05 to 2.6 percent of the total organic compounds transported
by ground water (Fu 85). This indicates that the process would
favor the likely transformation of most of the institutional
and industrial organic radiocarbons which are predominantly low
molecular weight compounds to carbon dioxide or methane gas
-19-
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10 I? (4
FIGURE 2. THE CARBON SYSTEM (after Be 71)
-20-
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TABLE 5
GROUND WATER PARAMETERS AT LLW SITES
AND PROBABLE CARBON-14 RETENTION
HC03- mg/1
Ca mg/1
SI mg/1
PH
Probable
Kd ml/g
Barn well, SC
Saturated
20
3
3
6.5
0
Beatty, NV
Saturated
389
24
4
7.7
3
West Valley, NY Sheffield, IL
Saturated Saturated, Unsaturated
200
47
7
7.5
3
340
86
9
6.7
3
455
122
7
7.5
3
Notes: 1. Ground Water Parameters from United States Geological
Survey from wells located near the LLW sites (USGS 85).
-------
rather than having it available for ground water transport. A
recent investigation on landfill leachate also supports the
view that biological oxidation products constitute the primary
contribution to organic material transported by ground water
(Ve 85). In general it is concluded that the institutional and
industrial wastes contribute a minor fraction of radiocarbon to
ground water transport as compared to the amount that undergoes
major decomposition and conversion to gas and eventual
atmospheric release.
The Sheffield. IL, LLW site has evidence of ground water
transport of both tritium and C-14 to locations in only one
direction up to 1000 feet off site. The levels of C-14 are in
the range 0.1 to 0.4 nCi/liter. While these values are not
excessive they are clearly related to ground water transport
(Fl 85). Piciulo describes the geology of the site and points
out that transport from the site was by ground water via a
sandy member of the Glasford Formation which constituted a
highly permeable pathway (Pi 84). Assessment is currently
being made of the nearly 3 million cubic feet of LLW waste
buried in 21 trenches at the site during the period from August
1967 to April 1978. The on-going investigation will
undoubtedly provide more insight into the nature of ground
water transport of C-14 at LLW sites.
CONCLUSIONS
Analysis of the activity level of C-14 contributed from
the fuel cycle and non-fuel cycle sources to LLW sites in the
period from 1985-2004 provides the following information: 2100
Ci from the nuclear fuel cycle; 1650 Ci from institutional
wastes; 2150 Ci from industrial wastes. The chemical form of
the C-14 in the fuel cycle waste approximates 75% inorganic
(carbonate). 20% activation metal, and 5% organic
radiocarbons. The chemical form of the institutional and
industrial carbon-14 waste is believed to be essentially 100%
organic radiocarbon compounds.
The transport of C-14 from the low-level radioactive waste
site is believed to be largely as a gaseous release to the
atmosphere. C-14 released at LLW disposal sites is expected to
be a small percentage of that released in power reactor
effluents. Ground water transport of C-14 is probably as the
bicarbonate anion and to a lesser degree as soluble organic
radiocarbons. A suggested balance of C-14 release from LLW
sites might be two-thirds atmospheric release, one-fourth
ground water transport and less than one tenth remaining as
residual material.
-22-
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Al 81
Be 71
Br 77
Cl 85
Co 79
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CRCPD 82
Da 77
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References (Continued)
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