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                                                                 EPA 520/1-82-005
                                                    U.  Del.  Report  No.  CMS-C-1-78
                         MATERIALS  FOR CONTAINMENT

                        OF LOW-LEVEL NUCLEAR WASTE

                             IN THE DEEP OCEAN


                                    by
                             Stephen C. Dexter
                            Associate Professor
                           of Ocean Engineering
                           and Materials Science
                         College of Marine Studies
                          University of Delaware
                           Prepared August, 1978

                            Revised April, 1980

                              and June, 1983
                 This  report was  prepared  as  an  account  of
                    work  sponsored  by  the  Environmental
                   Protection Agency of the United  States
                Government under Contract No.  WA-6-99-2767-J
                               Project Officer

                               Robert S.  Dyer
                        Analysis and Support Division
                        Office of Radiation Programs
                    U.S. Environmental Protection Agency
                           Washington, D.C.  20460
ongoing effort to evaluate the low-level radioactive waste packaging
techniques and materials used in the past, with a view towards developing
packaging performance criteria and recommendations for improved packaging
materials and design.

     As part of this development process, the Office has initiated a
generic study to describe the various corrosion and degradation processes
that would be expected to affect a waste package in the deepsea.  This
report presents some preliminary results of that ongoing study.  Based
upon these preliminary results, an estimate can be made of the expected
lifetime of a conventional metal drum containing a concrete matrix. This
information can then be compared with the empirical results of the
separate, detailed analyses of various low-level radioactive waste
packages recovered from the ocean under  the direction of this Office, and
any differences will be examined.

     Readers of this report are encouraged to inform Mr. David E. Janes,
Director, Analysis and Support Division  (ANR-A61), Office of Radiation
Programs, U.S. Environmental Protection Agency, Washington, D.C. 20460,
of any errors, omissions, or other comments pertinent to improving  this
document.
                                        Gien L.  Sjcblom,  Director
                                     Office of  Radiation Programs

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                               ABSTRACT







     During the period between 1946 and 1970 the United States carried




out sea disposal of low-level radioactive waste.  A low-level waste




package was developed consisting of a plain carbon structural steel 55-




gallon cylindrical drum into which the radioactive material and a




concrete matrix was admixed.  Tie present report examines the electro-




chemical processes which corrode metals in saltwater,  factors affecting




corrosion rates in the deep sea, and mechanisms which degrade concrete




immersed in seawater.  Environmental data is reviewed on the rates and




interactive nature of these corrosion and degradation mechanisms.  For




the purposes of this report, failure of the container is considered to




have occurred as soon as seawater is allowed to contact the waste.




Based on this criterion, it is concluded that the lifetime of conven-




tional containers is likely to be short compared to the ten half-life




(50-300 years) minimum isolation period that has been considered for key




radioactive components of low-level waste, such as strontium-90, and




cesium-137.  The concept for an improved cost-efficient container




capable of isolating wastes for 50 to 75 years with a high degree of




reliability is presented.  However, it is emphasized that our present




knowledge of the mechanisms and rates of deterioration of structural




materials in the deep ocean is  insufficient to  guarantee the integrity




of even the improved containers for upwards of  300 years.

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                           TABLE OF CONTENTS


1.0  INTRODUCTION.  .  .  .  ,	1

2.0  DETERIORATION MECHANISMS	3

     2.1  CORROSION OF METALS	3

          Basic Mechanism	3
          Structural Steel  	   5
          Stainless Steels  	   7
          Factors Affecting Deep Ocean Corrosion Rates 	   9

     2.2  DETERIORATION OF  CONCRETE	17

3.0  ENVIRONMENTAL DATA	17

     3.1  STRUCTURAL STEEL  	  17

     3.2  STAINLESS STEELS  	  23

     3.3  CONCRETE	26

     3.4  EFFECTS OF RADIATION	27

4.0  LIFETIME OF CONVENTIONAL CONTAINERS 	  29

5.0  ALTERNATIVES TO PRESENT MATERIALS OF CONTAINMENT	35

     5.1  INNER CORE	36

     5.2  CONCRETE LAYER	41

     5.3  OUTER SHELL	42

6.0  REFERENCES	45

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1.0  INTRODUCTION




     The two classes of materials that have historically been used for




packaging low-level nuclear waste for ocean disposal are plain carbon




structural steel and concrete.   These were usually arranged in the form




of a two- or three-layered container starting on the outside with a 55-




or 80-gallon structural steel oil drum from which one end had been




removed.  First, the drum was partially filled with concrete.  The waste




form itself was pressed into the wet concrete and the drum then filled




with more concrete.  Some types of low-level liquid waste were mixed




directly with the concrete in the steel drum.   Occasionally the waste




form itself was a contaminated or activated piece of plain carbon or




stainless steel, which was pressed into the wet concrete.  In this




latter case, the steel or stainless steel waste form would act as an




additional containment barrier in that radionuclides would be released




to the environment only through corrosion of the steel or stainless




steel itself.  Thus, a third class of materials which must be con-




sidered, in addition to the concrete and steel mentioned above, are the




stainless steels.




     It is assumed throughout this report that typical low-level nuclear




wastes must be isolated from man and his food chain for a minimum period




of time corresponding to ten half-lives of the waste.  For example, for




low-level wastes containing Cs-137 or Sr-90 this containment period




would be a minimum of 300 years, and 280 years respectively.  Other




wastes having shorter half-lives (e.g. Co-60) would need to be isolated




for upwards of 50 years.  It is further assumed that public opinion will




not long tolerate any waste disposal program in which there is even a




small percentage of containment failures that result in premature

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release of the waste to the marine environment before the end of the




appropriate minimum containment period.




     All three classes of materials mentioned above are known to be




susceptible to deterioration in seawater environments.  The degradation




mechanisms begin immediately upon immersion of these materials in sea-




water, and appreciable deterioration by corrosion can occur in as little




as one or two years for steel and stainless steel, and in 5 to 20 years




for concrete.  These  times are much shorter than the  50  to 300 year




minimum containment period for the radionuclides discussed above.   The




purposes  of  this report are, therefore, to  (1) summarize the  current




literature  on the  seawater degradation  of these materials,  (2)  assess




what  the  lifetime  of  these materials  is likely to be in  the  deep  sea  and




 in the configurations used  for packaging nuclear wastes, and (3)  suggest




 possible  alternative  packaging techniques and materials.




      From an engineering point of view, the purpose of the outer  steel




 container is primarily to serve  as a  convenient mold for the concrete.




 Before it starts to corrode appreciably,  the steel container also




 provides  a partial barrier between the concrete and seawater.  In past




 ocean dumping this was a minor function for steel because the packages




 left the concrete exposed directly to seawater at the open end of the




 drum.  Therefore, functionally,  it matters little whether or not the




 steel corrodes.  Deterioration of the  concrete and  the  metals of the




 waste form  itself are a more  serious matter,  as they  are the materials




 which are  called upon to isolate the waste.




       In  the following sections,  the  appropriate deterioration mechanisms




 will be  outlined,  the available  environmental data on degradation  rates




 will be  summarized,  the  expected lifetime  of the  conventional  types  of

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containers will be estimated from these data, and several alternatives


to the present methods of containment will be discussed.




2.0  DETERIORATION MECHANISMS


2.1  CORROSION OF METALS


                            Basic Mechanism


     Degradation of metallic materials in marine environments by cor-


rosion can take several forms, but all of them are electrochemical in


nature.  That is, the process involves the simultaneous transfer of


electrical charges in the metal, and ions in the electrolyte (seawater


in this case) into which the metal is placed.


     The corrosion process takes place at two distinctly different types


of sites on the metal surface.  At the first of these sites, called the


anode, chemical oxidation takes place, and metal ions leave the surface


of the metal to enter the solution as illustrated in Figure 1.  It is


this loss of metal ions at the anode that leads to structural damage of


the metal during corrosion.  Of equal importance is the second site,


called the cathode, where chemical reduction takes place and dissolved


oxygen from the seawater is reduced to hydroxyl ions (OH ).  As iron

                         I i
atoms are oxidized to Fe   at the anode they liberate electrons which


travel through the metal and are consumed in the reduction at the


cathode  (Figure 1).  A simple chemical equation describes  each of  these


reactions as follows:

                                              I I
     At  the anode:              2Fe - 4e  -> 2Fe


     At  the cathode:     02 + 2H20 + 4e~ -> 40H


Combining the two, we can write  the overall  reaction as:


      2Fe + 0  +  2H 0 -> 2Fe"H" +  40H~ ->  2Fe(OH>2


The product of this reaction, Fe(OH  ),  is a  hydrated ferrous  oxide or

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                                   4 OH
FIGURE 1    Electrochemical reactions at anodic
and cathodic sites on structural steel corroding
in seawater.

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ferrous hydroxide.   It is insoluble and forms a loosely adherent green


or greenish black surface film on steel in seawater.   The outer surface


of the film, which is in contact with a ready supply of dissolved


oxygen, is further oxidized to ferric hydroxide by the reaction:


     2Fe(OH)  + H20 + 1/2 C>2 + 2Fe(OH)3


This is orange to reddish brown in color and is familiar to us as common


rust.



                           Structural  Steel


     On plain carbon  structural steel, the anode and cathode areas


described  above  shift about continuously on  the metal  surface.   The


result is  called "uniform  corrosion".  The surface becomes  generally


rusted and the metal  thickness  is  reduced almost uniformly  over  the


entire exposed surface.  It is  this  type of  corrosion  to which the outer


steel  drum of past nuclear waste packaging containers  is subjected.


Uniform corrosion of  structural steel  in  seawater will be  accelerated if


the steel is brought  into  direct contact  with a  more noble (cathodic)


metal such as a  copper  alloy,  stainless  steel,  or  titanium.  This type


of attack, called  galvanic corrosion,  or electrolysis, will be described


 in the following paragraphs.


      When two  different metals are placed in direct contact in seawater,


 a difference in electrochemical potential exists between them.  This


 potential difference causes a corrosion current to flow.  The more


 active of the two metals becomes the anode and begins to corrode more


 rapidly than it would by  itself.  The more noble metal becomes  the


 cathode and is protected  from  corrosion.  The accelerated  corrosion  on


 the less  noble  (anodic) metal  is called galvanic corrosion.   Table I

                                                                   2
 shows a  "galvanic series" of common metals  and alloys  in  seawater.

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                      TABLE I

       GALVANIC SERIES OF METALS AND ALLOYS
                   IN SEAWATER
Alloy
    Potential vs.
Satd.  Calomel Electrode
ANODIC
END
Magnesium
Zinc
Aluminum Alloys
Cast Iron
Steels (structural and alloy)
Stainless Steels (active-i.e. in crevices & pits)
Al - Bronze D
Naval Brass
Red Brass
Copper (ETP)
Inhibited Admiralty Brass
Manganese Bronze A
Silicon Bronze
90-10 Copper Nickel
Type 400 Stainless Steels (passive)
Lead
70-30 Copper Nickel
17/4 pH Stainless Steel (passive)
Silver
Monel 400 (Nickel-copper alloy)
Type 300 Stainless Steels (passive)
Stainless Alloy 20 cb3
Titanium and Titanium Alloys
Inconel 625
Hastelloy C-276
Stainless Alloy 6X (passive)
Tantalum
Platinum
Graphite
CATHODIC
END


-1.60 to -1.63V
-0.98 to -1.03V
-0.70 to -0.90V
-0.60 to -0.72V
-0.57 to -0.70V
-0.35 to -0.57V
-0.30 to -0.42V
-0.30 to -0.40V
-0.20 to -0.40V
-0.28 to -0.36V
-0.25 to -0.34V
-0.25 to -0.33V
-0.24 to -0.27V
-0.21 to -0.28V
-0.20 to -0.28V
-0.19 to -0.25V
-0.13 to -0.22V
-0.10 to -0.20V
-0.09 to -0.14V
-0.04 to -0.14V
-0.00 to -0.15V
+0.05 to -0.15V
+0.06 to -0.05V
+0.10 to -0.04V
+0.10 to -0.04V
+0.32 to -0.15V
about +0.2V
+0.35 to +0.2V
+0.3 to +0.2V



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For any combination of metals,  the galvanic series can be used to




predict which metal will suffer accelerated attack (anode) and which




metal will be protected (cathode).  If any two metals or alloys from




Table I are placed in contact in seawater, the one higher on the series




will be the anode, and the severity of the damage to it will be directly




proportional to the magnitude of the potential difference between the




two metals, or simply the separation of the two metals or alloys on the




chart.  Two examples illustrate  this point.  If steel is  coupled to




Monel 400  (nickel-copper alloy), the steel will be anodic and will be




damaged severely  because the two alloys are far apart on  the chart.  If




copper and silicon bronze are  coupled, damage will be slight because




they are close together on the  chart;  that  is, the two metals have  a




small  potential difference.




      It is possible  to  take  advantage  of  galvanic corrosion by  coupling




a material one wishes  to protect from  corrosion  to a more active metal.




For instance,  steel  can be protected  from corrosion  in  seawater by




 coupling  it  to zinc.   The  zinc in this case is  called a sacrificial




 anode,  and the steel will  be protected as long  as any zinc remains.  The




 protection can be extended indefinitely by periodically replacing  the




 zinc anodes  if the structure is accessible for maintenance.






                            Stainless Steels




      The behavior of stainless steels is quite different from that de-




  scribed above.   Stainless steels contain 12% or more of  chromium,  which




 make them "passive," or resistant to uniform corrosion.  Their passivity




  in seawater is caused by the  formation of a tightly adherent surface




  film of metal oxide.   Other alloying  elements in addition  to chromium




  are often added  to make this  passivity more  stable  in  a  wide range

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 of  environments  or  to  enhance  the  mechanical  and  physical  properties,  or



 both.   Nickel  and molybdenum are  two  alloying elements  commonly  added  to



 stainless  steels intended  for  seawater  service.   The  class of  stainless



 steels  most  frequently used around marine  environments  in  the  past,  the



 300-series stainless steels, has approximately 16  to  18% chromium,  8 to



 10%  nickel and up to 3% molybdenum.




     When used in seawater, stainless steels  resist uniform corrosion



 but  the chloride ions  in seawater  tend  to  cause breakdown  of the passive


                                            O  /

 film at discrete sites  on  the metal surface.  '   The  underlying metal  at



 these sites  becomes anodic, while  the vast maj.ority of  the surface



 remains passive and becomes cathodic.   Once formed, the anode  and



 cathode areas do not shift location, as they do on plain carbon steel,




 but  remain fixed.  In addition, the high concentration of  metal chlo-



 rides that builds up at each anodic site causes the pH of  the  electro-



 lyte at the  anode to become more acidic, and accelerates the rate of


                      3 4
 attack  at these sites.   '




     The result is a nigh rate of  penetration  of the metal at  the anodic



 sites while  the rest of the surface remains unattacked.  This mode of



 corrosion,  often leading to a series of small  holes which  perforate  the



metal,   is called "pitting."  As a  general rule, the fewer  pits there are



on a given surface,  the larger and deeper they will be.  As the number



of pits increases,  the  individual pits become  smaller and  shallower.



     Stainless steels are also susceptible to another form of localized



attack called crevice corrosion.   It takes place within crevices found




around  threaded fasteners,  under  washers,  gaskets,  and 0-rings, between



the faces of  riveted lap joints,  and similar places of restricted



geometry that are shielded  from the water  movements that continually

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wash the remainder of the surface with fresh, oxygenated seawater.   The

water inside the crevice becomes stagnant and depleted in oxygen, and

the surface in contact with this water becomes the anode, while the

remaining surface outside the crevice is the cathode.  The mechanism is

similar to that of pitting.  The pH inside the crevice becomes acidic

and the anode reaction becomes self-accelerating.  Corrosion starts on

the interior surfaces and hollows out the part, as illustrated in Figure

2, until its strength becomes insufficient and it fails.



             Factors Affecting Deep Ocean Corrosion Rates

     The parameters  generally recognized as  having an  influence  on  the

corrosion rates of steel and stainless  steels  in  seawater are:   dis-

solved  oxygen, temperature, salinity, pH, relative velocity  of the
                                              O  /  7
water,  and  the presence  of  fouling organisms.  ' "   Figure 3 shows  the

typical variability  of  some of  these  parameters with depth in the

Northeastern Pacific Ocean.6  Let us  consider their  effects  first  on

plain  carbon  structural steel and then  on  stainless  steels.   For pur-

poses  of  this  discussion,  the deep  ocean shall be defined as any depth


 greater than  2000 meters.

      On structural steels,  the  corrosion rate is a direct function of

 the dissolved oxygen concentration  of the seawater.      This effect is

 so strong that it tends to overshadow everything else.  The corrosion

 rate of steel is also a direct function of  temperature.  When oxygen

 concentration is the rate controlling factor, as it usually is in  sea-

 water, the corrosion rate of steel is estimated  to be halved by each

 30C decrease in temperature.4  Nevertheless, the influence of  tem-

 perature on corrosion rates is weaker  than  that  of dissolved oxygen.  An

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                                                          10
     CORROSION OF
     BOLT  HEAD
                                        CORROSION  OF
                                         WASHER
CORROSION OF
BOLT  THREADS
CORROSION
OF NUT
FIGURE 2.  Crevice corrosion sites around a mechanical fastener.

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                                                                       11
   surface r*
      500
   1000
a.
LU
a
     1500
    2000
                                                        SALINITY
          0
                                          8
                                 Oxygen, ppm
           0
      68     10    12
      i   Temperature, C
                        14
                        16
                        _L
                       18
           6.4   6.6
6.8
I
7.0
I
7.2
 I
7.4   7.6   7.8    8.0   8.2
                                                                  I
          33.0  33.2  33.4
     33,6  33.8   34.0  34.2 34.4  34.6  34.8
           Salinity, ppt
 FIGURE 3.  Variability of oceanographic parameters in
 the Pacific Ocean off Port Hueneme California (After Reinhart6)

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                                                                           12
 example  of  the  overriding  effect  of  dissolved  oxygen  in  the  deep  ocean


 is  shown in Figure  4, where  the corrosion  rate,  expressed  as mils per


 year  (mpy),  increases again  with  increasing  dissolved  oxygen concen-


 tration  at  greater  depths  despite  a  continual  decrease in  temperature.6


      The salinity and pH of  seawater have  only a  small effect  on  the


 corrosion rate  of steel.   When considered  as a function  of salinity, the


 corrosion rate  reaches a maximum at:  a value  of about 35  /oo (parts per


 thousand) salt  content and decreases gradually at higher and lower

       4
 values.   This  maximum is  the result of two  competing  tendencies.


 First, the  conductivity of seawater  increases  with increasing  salinity,


 resulting in a  greater separation  between  the  anode and  cathode areas,


 and consequently a  less protective corrosion product (rust)  film.4  This


 accounts  for the initial increase  in corrosion rate with increased


 salinity.   Second,  the solubility  of dissolved oxygen  decreases with


 increasing  salinity.  This latter  effect becomes predominant at about 35


 /oo  salinity,  thus accounting for the gradual decrease in corrosion

                        4
 rate  at  higher  salinity.    Over the normal range of open ocean salin-


 ities, however,  the changes in corrosion rate with salinity  are so small


 as to be completely overshadowed by the effects of dissolved oxygen.5"7


Within the normal slightly alkaline (pH 7.4-8.4)  range of open ocean pH,


 the corrosion rate of steel is independent of pH.   Below pH 4, the


 corrosion rate increases  rapidly with increasing acidity.  Above pH 10


 the corrosion rate decreases, and  approaches zero at pH values  greater

 than 12.4


     At water velocities  exceeding 3 to 4  meters  per second,  the cor-

                                       2
rosion rate of steel rapidly increases.    This  is especially true in


cases where there is appreciable suspended particulate matter in the

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                                                          13
  SURFACE
                         DISSOLVED OXYGEN
CARBON AND LOW
ALLOY STEELS
-c     1,000
                       A AISI 1010 STEEL
      2,500
                        OXYGEN (ml/l)
                              or
                    CORROSION RATE (mpy)
 FIGURE 4.  Corrosion rate of structural steels as a
 function ot depth and dissolved oxygen. (After Reinhart6).

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                                                                             14
   seawater that might lead to abrasion of th
   corrosion product films.   Deep ocean currents,
   much smaller  velocities  than this  (3 to 30 cm per  second  is  typical8)
   and  are  not expected  to play a  substantial role  in determining  the
   corrosion  rate.

       Macroscopic marine fouling organisms do not usually have an adverse
   effect on the corrosion rate of structural steels.   In fact, a complete
   cover of hard-shelled sedentary (sessile) fouling organisms may decrease
   the corrosion rate by acting as a barrier through which dissolved oxygen
  must  diffuse to reach the  metal surface.4'6'7  Such a complete layer of
  organisms is  rare  in the deep ocean.   There are  fewer biofouling organisms
  present at  great depths, and  those  that  are present near the  bottom  tend
  to  attach as opportunistic  individuals,  causing only  a  slight pertur-
  bation of the  corrosion rate  in  their  immediate vicinity.9'10 Fouling
  is expected, therefore, to have only a minor effect on  the overall cor-
  rosion rate of steels in the deep ocean.
      Marine microorganisms can influence  the corrosion rate of steels
 only in restricted  areas where they can change the chemistry of the
 surroundings.   For  instance, the corrosion rate of steel can be appre-
 ciable in  anaerobic bottom  sediments if sulfate-reducing bacteria are
 present.   The mechanism of  this type of attack will  be considered later
 in this report.
     These same parameters have different effects  on the corrosion rate
 of stainless steels, which corrode by pitting and  crevice corrosion
 rather than by uniform attack.4'6  The factors that  influence  these
 localized  forms of attack are primarily those that allow or discourage
differences in the environment from place  to place on the metal surface.

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                                                                          15
Dissolved oxygen has a major effect only when differences in it are per-


mitted to develop along the metal surface.   This happens most readily in


stagnant or zero velocity conditions or when crevices, such as shown in


Figure 2, are built into the mechanical design.  Seawater velocities of


1.5 to 2 meters per second can suppress the initiation of pitting


corrosion altogether by keeping the surface uniformly immersed in oxy-

              2
genated water.   Water velocity has little effect on crevice corrosion,


however, because the corroding surface is shielded from the flow of


water.


     The above effects are in direct contrast  to the case for plain


carbon steels, where an increase in velocity brings more oxygen to the


corroding surface and increases the corrosion  rate.  Another direct


contrast to the case for plain carbon steels is that of fouling organ-


isms.  On plain carbon steels these organisms  tend to decrease the


corrosion rate by acting as a diffusion barrier for dissolved oxygen.


On stainless  steels, however, unless the fouling layer  is complete and


uniform, it creates localized oxygen-shielded  regions and promotes


crevice  corrosion beneath  the organisms.


      Temperature has the same effect on stainless  steels that  it has  on


plain carbon  steels, and to a first approximation, the  salinity and  pH


of seawater have little effect on  the  rate  of  pitting and crevice


corrosion  of  stainless  steels.


      Historically,  when stainless  steels have  been present  in  low-level


nuclear  waste packages  from ocean  disposal,  they have been  as  part  of


 the  waste  form itself  embeddec  in  the  concrete.  Thus,  the  environment


 to which stainless  steels  have- been subjected  is neither  open  ocean


 seawater nor  bottom sediment, but  rather  seawater-saturated concrete,

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                                                                          16
the pH of which is normally 32 to 14.  This alone should suppress the


initiation of pitting, because- hydroxyl (OH ) ions have been found to

                                                        4
be effective inhibitors for pitting in stainless steels.   The alkaline


pH will also inhibit corrosion if the core is made of structural steel.


As long as the dissolved oxygen level is maintained uniformly low and


the pH uniformly high over the- entire surface of the metal, very little


corrosion might be expected whether the metal is made of structural


steel or stainless steel.


     There are two ways in which this desirable low oxygen, high pH


environment may be lost.  The first way is if the concrete itself


deteriorates according to one of the mechanisms discussed in the next


section.  If the concrete becomes fractured and allows oxygenated sea-


water to contact part of the metallic waste form, corrosion will start.


For stainless steel, the exposed area will become cathodic and the re-


maining surface still shielded by the concrete will be susceptible to


crevice corrosion.  For structural steel, uniform corrosion will start


on the surface exposed to ambient seawater and the wedging action of the


corrosion products, which are more voluminous than the steel from which

          3
they form,  will tend to pry the concrete away and progressively expose


more steel.


     The second way the desirable environment can be lost involves


changes in internal chemistry that; occur as the concrete absorbs sea-


water over a period of time.  Recent evidence   indicates that as the


pores (or voids) in the concrete become saturated with seawater, chlo-


ride ions from the absorbed seawater break down the protective film on


the metal surface and initiate corrosion.  As corrosion proceeds, the

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                                                                           17
metal-chloride corrosion products, which are acidic, both reduce  the pH



of the pore water, and produce the wedging action mentioned above.  Both



these effects tend to produce still more corrosion.





2.2  DETERIORATION OF CONCRETE



     The primary mechanism of degradation of portland cement type


                                        12
concretes in seawater is sulfate attack.    In waters with more than



about 2000 ppm sulfate, destructive chemical reactions can take place


                                                12 13
with the cementing constituents of the concrete.  '    Since the average



concentration of SO   ions in the Atlantic Ocean is 2810 ppm,  this type


                                  12
of attack can and does take place.



     Destructive attack can follow either or both of the following two


      12
modes:   (1) cracking due to the formation of a calciura-sulfoaluminate



hydrate called ettringite,  or (2) surface softening due to the formation



of gypsum.   The first type of attack can take place in portland cements



containing more than 5% of tricalcium aluminate (3CaO'Al?0^).  The



sulfates react with hydrated 3CaO*Al 0  in the presence of calcium



hydroxide (Ca(OH) ) to form ettringite (3CaO-Al 0 3CaO-SO 32H 0).



Ettringite has a strong tendency to absorb water.   This causes it to



expand and results in cracking of the concrete.  In the second type of



attack,  acidic sulfates cause the conversion of Ca(OH)? to gypsum



(CaSO *2H O"1 according to the following reaction:



     Ca(OH)   + MgSO -7H 0 -> Mg(OH)  + CaSO 2H 0 + 5H 0



This is accompanied by surface softening and spalling of the concrete.



The types of attack discussed above are aggravated by high porosity as



well as by high 3CaO*Al 0  and Ca(OH)   contents in the cement phase.

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                                                                             18
   3.0  ENVlROraffiNTALJDATA
   3.1  STRUCTURAL STEEL

        There is a considerable volume of data on the corrosion of plain
   carbon structural  steel  in  natural  seawater.   The  bulk of  these data  are
   for  shallow coastal water exposures.   In  general,  the  shallow water
   data show  initial uniform corrosion rates as high  as 380 micrometers  per
   year (llm/y), decreasing with tirae to a constant value  of 75  to  125 Mm/y
   after two or three years of exposure. 2>5'-  Jhe ^ ^ ^ ^
  uniform corrosion rate decreases depends upon how quickly the barrier
  film of corrosion products,  carbonaceous deposits,  and  fouling organise
  builds  up,  and upon how effective this  film  ls  in preventing dissolved
  oxygen  from reaching the  bare metal  surface.  Once  this film has forced,
  factors  which may cause the  corrosion rate to vary  outside  the 75  to
  125 Wy limlts  are pollution (especially by sulfides) ,  high  water
 velocities, or variations in water temperature.   In addition, very low
 dissolved oxygen can reduce the rate to less than 75 pm/y.
      The corrosion is not always entirely unifo.  Located attack In
 the for. of broad shallow pitting has frequently been reported with
 penetration rates of up to 10 tu.es the  uniform  corrosion rate.
 Occasionally,  a  very deep  p,t  WLU be  observed.   For instance,  a pit
 with a depth  of  4 mm was observe,,  on  one  panel that  had  been  exposed
 for 16 years  in  the Pacific Ocean  at  the Panama  Canal Zone.17   The
 Plttlns type of attack tends to be more severe in polluted seawater
 and on material  from which the mill scale is not cleaned off properly/''
     1" the deep ocean,  which is the primary focus of this report, the
corrosion rates of ,,laln carbon steels
i, surface waters.5'^

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                                                                          19
waters, as it does in shallow water, starting at 50 to 100 ym/y and



decreasing to 12 to 50 ym/y.     Several factors favor lower corrosion



rates in the deep ocean.   The most prominent of these is low dissolved



oxygen.  The decrease in dissolved oxygen with depth is more pronounced



in the northeastern Pacific Ocean than it is in the northwestern



Atlantic, where the minimum in dissolved oxygen is generally not as low,



and where the value at great depths can be as high as, or higher than it


                  5 18
is at the surface. '     Table LI shows that for plain carbon steel ex-



posed at similar depths in the Atlantic and Pacific Oceans, the corrosion



rate is doubled in the Atlantic because of the higher dissolved oxygen.



For a given oceanic site, therefore, the concentration of dissolved



oxygen must be known before any prediction of the corrosion rate can



be made.



     Other factors favoring low corrosion rates in the deep ocean are



low water velocities and low temperatures.  The decrease in corrosion



rate with time is usually more gradual in the deep ocean than it is



in surface waters because protective surface films form more slowly



under deep ocean conditions.   The low temperature and more acidic pH


                                                                  5 19
retard the rate of deposition of carbonaceous type mineral scales, '


                                        9 10
and fouling films form slowly Lf at all. '
TABLE 11


CORROSION RATE OF STEEL AFTER 3 YEARS EXPOSURE
Location Depth Temperature
Pacific Ocean 1675 m 6.65C
Atlantic Ocean 1515 m 4.L8C
Dissolved
Oxygen
1.5 ml/ 9,
5.7 ml /I
Corrosion
Rate Reference
25 ym/y 14,15
50 ym/y 14

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                                                                          20
     Since the low-level nuclear waste containers that have previously



been deposited in the ocean are sitting on the bottom partially embedded



in the sediments, corrosion rates in these sediments are an important



consideration.  Generally, corrosion rates of steel in the sediments



will not differ greatly from those in the water immediately above


the sediments.5  However, there are several factors that can cause



corrosion rates in the sediments to be different from those in the


water.  These factors include:   (a) a difference in concentration of



some chemical species, such as dissolved oxygen, between the sediments



and the water,  (b) the presence or absence in the  sediment of  sulfate


reducing bacteria under anaerobic  (no dissolved oxygen) conditions  and,



(c) the presence of bottom currents strong enough  to  keep  appreciable



particulate matter in suspension.  Each  of these factors will  now be



discussed  in  more detail,  first  for an unpainted steel  cylinder, and



then  for  a painted steel  cylinder  similar  to  the radioactive waste  con-



tainers under consideration.


      The  dissolved oxygen concentration  is often lower  in  the  sediments



than  in the water.   This  difference  produces  what  is  commonly  called an


oxygen concentration cell.   Whenever  such a  concentration  difference



exists,  it sets up a potential difference resulting in the area of


 lower oxygen  concentration becoming anodic and the area of higher  oxygen



 concentration becoming cathodic.  For an unpainted steel cylinder,  the


 portion of the surface exposed to the lower  oxygen concentration (i.e.,



 the portion buried  in the sediments)  would become anodic and suffer a



 moderately accelerated rate of attack compared to that portion exposed


                       4
 directly to the water.

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                                                                          21
     If dissolved oxygen is completely absent from the sediments,  the


                                                                     4,20
corrosion rate of steel in the sediments would normally be negligible




but may be accelerated in the presence of anaerobic,  sulfate-reducing




bacteria.   Such bacteria are almost universally found in the sediments




under shallow natural waters, where the dissolved oxygen is used up by



                        20
decaying organic matter.    In deep sea conditions where the amount of




decaying organic matter may be very low, however, the presence of




sulfate-reducing bacteria may be more variable.  In the presence of




these bacteria, corrosion rates of steel can be increased by as much as




several orders of magnitude.  Under anaerobic conditions, the cathodic




reaction shifts from the reduction of oxygen described earlier (Section




2.1) to reduction of hydrogen according to the reaction:






                              H+ + e~ -> H






Without sulfate reducing bacteria present, the cathodic surface quickly




becomes covered with a monolayer of neutral hydrogen atoms  (H), and




corrosion stops.  Sulfate reducing bacteria, however, strip off the




hydrogen layer, thus allowing corrosion to continue, a process called



                        21
cathodic depolarization.     The bacteria utilize hydrogen in  their




metabolism to  reduce sulfates from decaying organic matter  to sulfides.




The  sulfides,  in  turn,  form an iron-sulfide scale on the  steel which  is




cathodic to a  bare  steel  surface.  The  sulfide  scale thus leads to an


                                                 20
additional galvanic corrosion of  the  bare  steel.    Sulfate-reducing




bacteria are  rendered  inactive, and  their  effect  on corrosion is




stopped, by the  presence  of even  trace  amounts  of dissolved oxygen.




Thus,  the mechanism of  corrosion  described above requires both  com-




pletely  anaerobic conditions and  a  source  of  sulfates.

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                                                                           22
      For an unpainted steel cylinder,  the differences discussed above



 between the water and sediments will cause accelerated corrosion of



 that portion of the steel exposed  to the sediments.   For  a painted



 steel drum, however,  the inverse may be  found  due  to  the  presence of



 the  paint itself.   The  paint exposed to  the water  is  in a more  dynamic



 environment and may deteriorate more quickly than  that exposed  to the



 sediment,  due to surface abrasion  and  biological fouling.   This  allows



 corrosion to  begin more quickly on the surfaces of the druir exposed to



 seawater,  while the sub-surface paint  coating  continues to  protect  the



 drum.   This appeared  to be  the  case  for  the container  recovered  from



 the  northwestern Atlantic Ocean during the  1976 Atlantic  dumpsite survey.



 It suffered very little corrosion  on the  portion of the cylindrical



 surface that  had been buried  in the  sediments  because  the paint  coating


                            22
 remained  in good condition.     Coatings,  however, cannot  be made  perfect



 enough  to  provide  dependable  long-term (greater than about  15 years)



 protection  as will  be discussed  later  in  this  report.



     Higher rates  of corrosion  can also occur  just above  the bottom



 sediments  if  the seawater currents close  to  the bottom  are  sufficiently



 strong  to keep appreciable  paniculate matter  in suspension.  In  this



 case, the sediment  particles gradually abrade  away corrosion product



 and mineral scale or paint  films, thus constantly exposing fresh bare



metal.  This often happens  in shallow coastal waters as a result of



 tidal current or wave action.   It would be unusual to encounter deep



ocean currents of sufficient magnitude to cause such abrasive action.



However, turbidity currents set  up by underwater landslides moving



large volumes of sediment at considerable velocity may produce this



abrasive action.

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                                                                          23
     In light of the above discussion,  the important factors to be


considered when evaluating corrosivity to conventional structural


steel containers placed in deep sea dumpsites are:  the dissolved


oxygen concentration in the water and sediments;  the presence or


absence of sulfates and sulfate-reducing bacteria; and bottom currents


or turbidity currents.



3.2  STAINLESS STEELS


     Stainless steels are not susceptible to uniform corrosion in


seawater.   They corrode by localized breakdown of their protective


passive film at pits and crevices as discussed in an earlier section


of this report.  The resulting penetration of the surface is deeper


and more rapid than it is on plain carbon steel.


     Many types of stainless steel are available today, and a number


of these perform well in both the marine atmosphere and in the splash


zone above mean high tide level.  Nearly all of the conventional alloys,


however, perform poorly when fully submerged in quiet seawater for periods


exceeding one or two months. '  '    Several recently developed stainless


alloys have superior performance when fully submerged in seawater.  These


alloys will be discussed in a subsequent section.


     With one exception, it has not been possible to identify which


of the available stainless st.eel alloys have historically been disposed


of as nuclear waste in the ocean.  That exception is the pressure vessel


of the N/S Seawolf reactor, which was dumped in the Atlantic 2800m


nuclear waste dumpsite in 1959, and was constructed of Type  347

                0 ^
stainless steel.    For the purposes of this report, therefore',  it


will be assumed that only tht- more resistant of the commonly available

-------
                                                                          24
grades (300-series stainless steels) were used and our discussion will

be limited to stainless steel alloys 302, 303, 304, 316, and 347.  The

nominal compositon of these alloys is given in Table III.

     As explained in an earlier section, the environment surrounding the

inner stainless steel waste form is initially seawater-saturated concrete

at a pH of 12 to 14 rather than ambient seawater itself.  There are

no long-term data available for seawater corrosion of stainless steel

in concrete, but it is expected that as long as the concrete remains

intact and the chloride ion concentration remains low, corrosion rates

will be low due to the uniform alkaline environment.   If the concrete

should spall or crack, however, and expose the stainless steel to ambient

seawater, or if chlorides become sufficiently concentrated in the pore

water, accelerated attack on the stainless steel may take place.



                              TABLE III26

          NOMINAL COMPOSITIONS OF 300-SERIES STAINLESS STEELS
 Alloy
  % Cr
% Ni
% Fe
  % Other Major
Alloying Elements
Comments
302
303
304
316
17-19
17-19
18-20
16-18
8-10
8-10
9-12
10-14
Balance
Balance
Balance
Balance
-
0.2 S or Se Free machining
grade, least
resistant .
-
2 - 3 Mo Most resistant
                                                                 of group
 347
17-19
9-13    Balance
               1 - 2 Mn
                     Weldable grade

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                                                                          25
     All the 300-series stainless steels suffer rapid localized attack




by pitting and crevice corrosion in quiescent seawater.  Rates of pene-




tration in shallow water as high as 11.5 mm/y by pitting and 1.3 mm/y by



                                     5 27
crevice corrosion have been reported.  '    In the deep ocean, the




penetration rates tend to be lower (up to 4 mm/y by pitting and 0.3




to 0.75 mm/y by crevice corrosion) due to the lower dissolved oxygen


                5 27
and temperature.  '     The rate of attack can be strongly influenced by




seawater velocity.   An increase in seawater velocity inhibits pit




initiation but accelerates pit growth after the pit has already formed.




But a stainless steel form encased in concrete would be shielded from




such effects.  The rates cited above could be considerably higher if




less corrosion resistant grades of stainless steel such as the 400-series



were involved.




     Crevice corrosion can be avoided by welding parts together rather




than using threaded fasteners.  Unless the welding is done properly,




however, the material can be made sensitive to another type of corrosion




called intergranular attack or weld decay.   This occurs in the heat-




affected zone of  the weldment.  While the metal is at high temperature




during welding, the chromium in the alloy is scavenged out of solid




solution by an internal precipitation reaction, leaving a network of




chromium-rich particles embedded in an alloy that is no longer stainless




(because of the depleted chromium).   Corrosion then proceeds rapidly




in the depleted regions on either side of the weld, while the remainder


                               3
of the part remains unaffected.   Intergranular attack can be minimized




by using specially stabilized grades of stainless steel such as types




304L (low-carbon),  316L, 321 and 347 for any part where welded joints

-------
                                                                           26
are anticipated.   These stabilized grades have resistances to pitting



and crevice corrosion comparable to other type 300-series stainless



steels but are more expensive because of the addition of stabilizing



elements such as tantalum and columbium (Types 321 and 347), or because



of a more complex manufacturing process (Types 304L and 316L).   Because



of the difficulties discussed above, the conventional 300 series stain-



less steels are seldom recommended for applications in seawater re-



quiring full immersion for durations exceeding about six months, unless



some corrosion protection measures are feasible.





3.3  CONCRETE



     The rate of deterioration of concrete in seawater varies with the



formulation of the material.  Most of the published data on deteriora-


                                                                       12
tion rates comes from blocks of concrete immersed in Los Angeles Harbor



in 1905 and subsequently inspected after 27 and 67 years, and a similar


                                              28
series of tests near Trondheim Harbor, Norway,   started in 1936 to



1943.  The sulfate type of attack described earlier leading to  cracking



or surface softening was most severe in tests on high permeability



concretes where losses in compressive strength of up to 10% were ob-



served.12'28  The sulfate type of attack was negligible for high quality



formulations using portland pozzolan or portland blast-furnace  slag



cements of low permeability, low alkalanity and low 3CaO-Al20^  content.



Losses in compressive  strength due  to sulfate attack and/or water  ab-



sorption in these high quality concretes rarely exceeded  10% and a

                                 1 '>  90
strength gain was often reported.  ""'    Damage  by rock-boring mollusks



was  limited to superficial  surface  scouring if  a  granite  aggregate was



used.

-------
                                                                            27
      The  factors  of  most  significance  to  the  problem of  nuclear  waste




 containment  are water  absorption  and permeability.   Most concretes




 tested at depth were estimated  to  absorb  a  total  of  1 to 3  percent  by




 weight of water over an extended  period of  time  (several months  or


      29
 more).    Superimposed on  this  absorption,  all concretes were  permeable




 to seawater  to some  extent.  Permeabilities have  been calculated  from




 the changes  in buoyancy with time  for  hollow  concrete spheres  moored at



                            27  30
 various depths in the ocean.  '    This permeability  to  seawater  leaves




 open  the possibility of a hollow concrete container  eventually becoming




 filled with  seawater and the subsequent leaching  of  contaminated  water




 back  into the environment.  For these  reasons, unmodified concrete  alone




 should not be relied upon to isolate even low-level waste for  a period




 as long as 300 years, whether the waste is mixed  in with  the wet  con-




 crete, or placed in a cavity inside a  concrete shell.






 3.4  EFFECTS OF RADIATION




     There are no data in existence on the effects of either high or




 low-level radiation on corrosion rates in the deep ocean.  The data that




 are available in the open literature are concerned with  the effects of



                                                             3] 32
 radiation on corrosion rates in nuclear reactor environments.  '     For




 stainless steels,  these data indicate  that radiation  generally does not



                              '52
 accelerate the corrosion rate."    There can even be a slight retardation




 of the corrosion rate of stainless steels if the radiation intensity is




 large enough to break down the water surrounding the  corroding metal.




 Breakdown of the water provides more oxygen for repairing the passive



                                32
 film,  thus inhibiting corrosion.    The opinions relative to the  effects



                                             32 33
of radiation on plain carbon steel are mixed.   *     There is some evi-



                                                                     32
dence that the corrosion rate is accelerated under high neutron flux,

-------
                                                                           28
but this is a much different environment than that to which a low-level




radioactive waste container would be exposed in the deep ocean.




     It is probably safe to conclude that the radiation intensity pro-




duced by low-level waste is unlikely to cause a significant increase in




the corrosion rate of either plain carbon or stainless steels in the




deep ocean where the temperature remains low and the pressure high.




Under deep ocean conditions, it would take a level of radioactivity




approaching that found in and immediately around nuclear reactor cores




to cause a change in the corrosion rate.

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                                                                          29






 4.0  LIFETIME OF CONVENTIONAL CONTAINERS




     Based on the data presented in the previous section, an attempt




 will now be made to estimate the useful and reliable lifetime over which




 one can confidently predict that the conventional type of low-level




 nuclear waste container made from steel, concrete and stainless steel




 will be able to isolate the waste from man and his food chain in the




 ocean.  For the purposes of this report, the criterion of failure for




 any given layer of the container will be that it either allows water to




 contact the next layer in such a way that it will start to deteriorate,




 or it allows water to contact the waste itself.  In order for the en-




 vironment to be contaminated, water must not only reach the interior of




 the container but must also find its way back out.   The time scale of




 this process depends upon the failure mode of the container, and can




 range from a few seconds for a container that fails by implosion to




 several decades or more for one that fails by seepage (leaking or




 leaching)  through concrete and/or by corrosion of a metallic inner waste




 form.   In the following discussion,  the entire container will be con-




 sidered to have failed as soon as it allows water to contact the waste,




and the time for the contaminated water to return to the environment




will be neglected.




     In some cases,  there will be so many unknown factors that it will




be impossible to accurately estimate the lifetime.   In such instances,




the only prudent course of action will be to identify the worst possible




combination of conditions and the most rapid deterioration mode, assume




that if there are a large number of  containers these worst-case con-




ditions will occasionally be met,  and base the estimated lifetime on




this worst case.

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                                                                           30
     Consider first the outermost mild-steel shell.  If we assume a



worst-case deep-sea corrosion rate of 100 ym/y for the first year



decreasing to a constant 50 ym/y thereafter, a 1.5 mm wall thickness



will be entirely consumed in 29 years if the corrosion is uniform.



Usually> however, there is some broad shallow pitting in which pene-



tration rates are up to 10 times faster than the uniform corrosion rate.



Thus, the wall could be penetrated locally in as little as about  three



years.  In most instances, the steel will last considerably longer than



this, as was the case for the containers recovered during the  1976


                          22
Atlantic dump site survey.    But there is no assurance that this will



be the case for all containers.



      In actual practice, the steel was not meant to  isolate the  concrete



at all as one end was left open.  Even if the end  were closed, however,



one  should not rely on  the mild  carbon steel to keep seawater  from the



concrete  for more  than  three years.



      Consider next the  layer of  concrete.   It has  been estimated that an



originally dry, hollow  sphere with 15 cm  thick walls of high quality



concrete  would be  penetrated by  seawater  (as evidenced by  liquid drop-



lets apppearing  on the  inside  surface)  in one  to  two months under a


                                                        34
pressure  head corresponding  to a depth  of 3,660 meters.     It  has also



been estimated  that  the same concrete wall  would  be  saturated  with


                            o /

 seawater  within  six  months.    By the present  definition  of  failure,



 therefore,  a conventional  type container  having  nonmetallic waste mixed



 in concrete,  and the concrete  exposed  to  seawater on one  end  would have



 failed by allowing water from the environment  to  contact  the  waste



 within two to six months after deployment.   If the open end of the outer



 steel container were closed,  the time to penetration could be extended

-------
                                                                          31
by three years, but this is still short compared to the desired 50- to




300-year isolation period.




     For containers with structural steel or stainless steel inner waste




forms, the initial saturation of the concrete by seawater would not




constitute failure because it would not immediately create a situation




in which the structural steel or stainless steel would begin to corrode.




Corrosion may start shortly thereafter, however, if chloride ions become




sufficiently concentrated in the pore water of the concrete, or if the




concrete deteriorates further by cracking, spalling or sulfate attack.




     Cracking and/or spalling of the concrete can sometimes take place



                                                                       35
even before deployment of the container due to shrinkage during curing.




This problem can be aggravated by the almost inevitable rough shipboard




handling which is well known to all seagoing personnel.  The outer steel




drum helps to minimize such damage, but even with special handling




precautions,  one would expect the concrete in a small percentage of




conventional type containers to be cracked prior to disposal.




     Sulfate attack takes place gradually over a time period of tens of


      -i 9 10 90

years.   '   '     Based on our accumulated experience as outlined in




section 2.2,  one would not expect a 15 cm wall thickness of high quality




concrete,  in the absence of chloride ions, to be sufficiently damaged by




sulfate attack to allow an underlying steel or stainless steel waste




form to corrode for at least 75 years,  and perhaps as long as the




desired 300 years.   The difficulties are that (1) in the configuration of




conventional low-level nuclear waste containers, the cracking problem




may occasionally render the concrete prematurely useless as a corrosion




barrier for any interior metals, and (2) not enough is currently known




about the  chloride ion problem to allow us to predict how long it will

-------
                                                                          32
take to initiate corrosion.   Almost certainly,  however,  the time will be



short compared to even the shortest desired containment  period (50




years).



     Let us now examine what might be done to increase the reliability



of these containers in their conventional configuration.  The methods



available for increasing the lifetime of marine structures fall into



four categories.  These are:  (1) isolation of the structure from the



environment by coatings, (2) elimination or control of corrosion by



cathodic protection,  (3) use of chemical inhibitors (which can be ruled



out  in the present open ocean situation because of the volume of in-



hibitor that would be required) and  (4) use of materials more resistant



to deterioration, which will be taken up in the following  section on



alternative packaging methods.



      Coatings protect against corrosion either by  isolating  the metal


                               O 

substrate  from  the  environment,    or, in the case  of metallic coatings,



by  creating a galvanic  corrosion  couple where  the  coating  is  sacrificial


                  9  (->
to  the substrate.     Nonmetallic  marine coating systems have been



improved over the last  10 to  15  years, but none of the  currently



available  systems are capable of  protecting  the substrate  from  seawater



under fully  submerged conditions  for more  than about  10 years without



periodic maintenance.



      Sacrificial metallic coatings such  as zinc  (galvanizing) have  been



used to protect steel successfully in seawater for short  periods of



 time.  As  a  rough rule of  thumb,  a zinc  coating  0.025 cm  thick is



 sufficient to protect steel from corrosion in seawater  for one year.



 Heavier coatings can extend the  protection to two  or  three years.  As



 was the case with nonmetallic coatings,  however,  longer-term protection

-------
                                                                          33
requires periodic maintenance,  and this is not practical for a structure


sitting unattended on the seafloor.   Thus, coatings are considered


capable of extending the lifetime of the present type of low-level waste


container for only about 10 to  15 years.


     Cathodic protection is the most effective means available for


controlling metallic corrosion.  It  is the only way to reduce the


corrosion rate to zero and maintain  it that way over an extended period

        4
of time.   Cathodic protection  is achieved by applying an external


electrochemical current to the  corroding system.  The polarity of the


external current is opposite to that of the natural corrosion current.


The applied current opposes the tendency for metallic ions to enter the

                                                                    4
seawater, and if made strong enough, will stop corrosion altogether.


The applied current must be supplied by either an external electronic


power supply or by a sacrificial anode such as aluminum, zinc or mag-


nesium.  Unfortunately, either  type  of system requires that the struc-


ture be accessible for periodic: maintenance.  External power supplies


need a source of current and must be monitored periodically to make sure


that the proper amount of current is being supplied.  Too little current


allows some corrosion to take place, while too much current can damage


the structure being protected.   Galvanic anodes become exhausted and


must be replaced every one to three  years.  For these reasons, cathodic


protection is not a practical way of controlling corrosion on structures


which must be able to survive for more than a few years unattended in


the deep ocean.  Thus, it is not expected that cathodic protection will


contribute significantly to extending either the average lifetime or the


reliability of conventional low-level nuclear waste containers in the


ocean.

-------
                                                                          34
     Based on the discussions above, the performance of an average low-




level nuclear waste container as previously configured for ocean dumping




is expected to be as follows.  Starting from the open end of the con-




tainer, the concrete should become saturated with seawater within about




six months.  The condition of the concrete then becomes critical.  For




most of the containers in which the concrete is not cracked or other-




wise damaged, the inner waste form, be it structural steel or stainless




steel, should not start to seriously degrade for 75 years or longer.




The careful application of marine coatings might extend this time by




about 15 years.   It is even conceivable that a substantial portion of




the containers might succeed in isolating their waste from the environ-




ment for the desired 300-year period.  It is probable,  however, that the




concrete in a small percentage of containers will become cracked before




disposal in the ocean due to shrinkage upon curing, or rough handling or




both.  In this case, the inner waste form should not be relied upon to




resist corroding for more than a few days if made of structural steel,




or a few months if made of stainless steel.   These times are short




compared to even a 50-year containment period.




     While marine coatings are capable of adding to the lifetime of the




average container whose concrete does not crack, coatings can do nothing




about the cracking problem itself.   Coatings are thus incapable of




improving the reliability of the present containers.  The containers are




likely to have the same rate of early failures  with or  without coatings.




     In order to significantly increase both the reliability of the




containers and the public's confidence in the waste disposal system,  it




will be necessary to change either  the materials of construction or the




configuration of the container or both.

-------
                                                                          35
5.0  ALTERNATIVES TO PRESENT MATERIALS OF CONTAINMENT




     Before any scheme for nuclear waste disposal can be considered to




be a viable alternative, it must be capable of winning public confidence.




In the case of low-level waste disposal on the deep-sea floor, that




confidence must be based upon the public's perceived reliability as




well as the actual reliability of the waste package.  The problem of




nuclear waste is such an emotional issue that the public's confidence,




based upon the perceived reliability, is likely to be low unless the




actual reliability is very nearly 100%.   If ocean disposal of low-level




waste is to be resumed, convincing evidence must be presented to show




that the probability of a total package failure, allowing the seepage




of contaminated water into the environment, is negligible over the




necessary containment period, even for a large number of packages.




     In order to achieve such confidence, a multi-layered package having




the following characteristics Is recommended:  (1) the waste should be




encapsulated in an inner core made of an impervious material that will




resist corrosion for the duration of the required containment period




even if inadvertently exposed to seawater during or shortly after




disposal.   (2) The inner core should be surrounded with at least




15 cm of an incompressible nonmetallic material that will neither




crack nor absorb seawater but that will provide a uniform environment




for the core if seawater does get in.  (3) The package should be one




solid incompressible mass to eliminate the possibility of implosion




under pressure.  (4) The outer shell should be of a noncorrodirig




material capable of withstanding shock loading and rough treatment




at sea.

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                                                                          36
     For the 50-year containment period,  it should be possible to build




such a waste package.   It is not the purpose of this paper to present a




detailed design,  but some recommendations based upon the characteristics




outlined above can be made.   A schematic cross section of a conceptual




package design is snown in Figure 5.







5.1  INNER CORE




     Consider first what would happen if the inner core were made of




plain carbon steel or one of the 300 series stainless steels.  In either




case, corrosion could begin as soon as chloride ions from the aeawater




caused the pH of the pore water in the concrete to fall below about 4.




For  structural steel, this will be uniform corrosion.  Sucn a core might




last a relatively long time compared to stainless steels.  For example,




if a wall thickness of 6.5 mm of a particular  structural  steel is needed




to resist deep ocean pressures, then at normal deep  ocean corrosion




rates, a total wall thickness of 13 mm should  last about  125  years




before the  inner core implodes  or begins  to leak.  A total wall  thick-




ness of  2.5  cm might be  expected to last  the desired 300  years if the




corrosion remained  uniform.   If there were any non-uniformities  to  the




distribution of  the corrosion over  the  surface however,  the  penetration




rate would  be faster  than that  for  uniform corrosion.   The  increase in




the  penetration  rate would  be proportional to  the degree of  non-uniformity




and  could vary from 1.5  to  100  times  the uniform corrosion penetration




rate.



      If the core material were  a  300  series stainless  steel, either




 pitting or  crevice corrosion or both could take place,  although crevice




 corrosion is more likely to be  the dominant mode in this case because

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                    Low Level  Waste
                    Imbedded  in Cement
Polymer
Impregnated
Concrete
                                                            37
Unalloyed  Titanium
Inner core

         Outer Shell
         (see  below)
                         Concrete
        Solid Polyethylene jacket
              Polyethylene foam
        Outer Polyethylene skin
Figure 5. Schematic cross section of
proposed low-level waste package.

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                                                                          38
of the restricted geometry.  For either the crevice corrosion or pitting




modes, it is difficult to predict how fast the stainless steel core




would be penetrated, as the corrosion rate depends on a number of




unknown factors.  One of the more important of these is the amount of




stainless steel surface area that is exposed to ambient seawater.  This




area will become the cathode, and the larger it is, the more rapidly




will the rate-controlling oxygen-reduction reaction be able to proceed.




The exposed area could range from less than 1 square millimeter in the




case of a small crack up to several square centimeters if a large chunk




of concrete spalls off.  Assuming the worst case conditions, where a




substantial area of 0.5 cm thick stainless steel is exposed, the data




presented earlier in this report suggest  that penetration of the con-




tainer could take place in as little as 5 years by a pit on the cylin-




drical surface  or 35 years by crevice corrosion.  These numbers could be




adjusted up or  down for different wall thicknesses, but again,  they  are




shorter  than the desired lifetime of 50 to 300 years.




      In  addition, there  is another  mode of attack which could  be even




more  rapid.  This would  involve corrosion at  the point where  a stainless




steel core was  sealed  after  emplacement of the waste.   If  sealing  were




accomplished by bolting  the  end cap to a  flange  containing  a  rubber  CD-




ring  or  a  gasket,  then crevice  corrosion  may  take  place preferentially




 in the groove  holding the  0-ring or gasket in place as  has  often been




 the case with  pressure casings  for  oceanographic instrumentation.   Once




 corrosion  has  tunneled under the 0-ring,  the  container  will leak,




 resulting  in failure by the present definition.   Such failure in stain-




 less steel instrument casings similar  in size to a hypothetical waste




 container  core have sometimes occurred within 6 to 18 months of seawater

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                                                                          39
service.   In oceanography, these casings are used only for relatively




short-term immersions (1 hour to 1 month) and are given periodic pre-



ventive maintenance.  Such maintenance is not presently available for a




low-level waste container once it has been placed on the sea floor.  One




can conclude then that plain carbon structural steel and the conventional



300 series stainless steels are not suitable for use as inner core




materials.  There are, however, other metals with increased corrosion



resistance.



     The metals and alloys most resistant to both uniform and localized




corrosion in seawater include gold, platinum, tantalum, unalloyed



titanium and some higher strength titanium alloys, Hastelloy C-276,



Inconel 625, and several recently developed stainless steels.  The



corrosion behavior of all of these has been studied extensively in


         2 4-6 37-39
seawater. '    '       Gold and platinum can be eliminated because of



their low strength and prohibitively high cost.  Tantalum, while offer-




ing excellent corrosion resistance, is also ill-suited for use as a




structural material due to its high cost, low availability and low



strength.  It is used mostly as a liner in containers for severely




corrosive chemicals.  The titanium alloys, Hastelloy C-276, Inconel 625



and the new stainless steels, however, are all possible candidates for




use as inner core materials.



     Unalloyed titanium and two high strength titanium alloys are



commonly used in marine environments.  The two alloys are Titanium 6 Al,



4V (6-4) and Titanium 6 Al, 2 Cb, 1 Ta, 0.8 Mo (6-2-1).  The 6-4 alloy




has an excellent strength-to-weight ratio but would have to be down-



graded for nuclear waste applications because of a slight possibility of



stress corrosion cracking in seawater environments.   The 6-2-1 alloy

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                                                                            40
  has  good  strength and  was  formulated  as  a  replacement  for  alloy 6-4  to




  avoid  the  cracking problem.   Lt  is  a  much  newer  alloy,  however,  and




  there  is less  long-term  seawater experience with it.   For  these  reasons,




  unalloyed  titanium is  probably the  preferred choice from the  titanium




  alloys group.  Its moderate strength  of  50,000 to 90,000 psi  should  be




  adequate for the  present application, and  it has withstood more  than 30




  years of service  in seawater environments  at 0C to 30C without any




  reported instances of corrosion of any type.   The major disadvantage of




  all the titanium alloys is their relatively high cost as compared to




  structural steel.





      Hastelloy C-276 and  Inconel 625 are both nickel-based  chromium-




 molybdenum alloys, which  have  long-term seawater  corrosion  resistances




 and costs  roughly  comparable to  those  of  the  titanium alloys.2'37'39




 Use of  these  materials, or  one of the  titanium  alloys,  would  maximize our




 confidence  in the  long-term integrity  of  the  inner core.  The titanium




 alloys  have the added advantage of being  the  lowest  in  density of any of




 the candidate inner core  materials.  Their  low  density  would  help to




 minimize the  overall package weight, a matter of  considerable  importance




 in  shipboard  handling.





     A  series of stainless  alloys has  recently been developed  having




 greatly improved resistance to crevice corrosion  and pitting in seawater38




 as  compared to  that of the conventional 300 series stainless steels.




 These are the ferritic and duplex (part ferritic and part austenitic)




 stainless steels.   The most resistant of  these are the ferritic stain-




 less steels with 27 to 30% Chromium,  3 to 4% Molybdenum and less than 1%




Nickel.   These alloys have crevice corrosion resistances under labora-




 tory conditions comparable to that of Hastelloy C-276,  although there is

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                                                                          41
                                                  o o
far less service experience with the newer alloys.     Other ferritic


alloys with 25 to 28% Chromium,  2 to 4% Molybdenum and up to 4% Nickel;


plus some of the duplex alloys with 20 to 26% Cr,  5 to 25% Ni and 3 to


7% Mo may also prove to have adequate crevice corrosion resistance.

These newer ferritic and duplex alloys have the advantage of being less


costly than Hastelloy C-276, Inconel 625 and the titaniums.  Their

disadvantages are that there is yet far less service experience with


them and they are not yet as widely available as the more established


alloys.  Both these latter two factors are expected to change dramati-


cally, however, within the next 5 years.

     There are, thus, a number of alloys now available with greatly


improved corrosion resistance compared to the conventional 300 series


stainless steels.  Any one of the alloys discussed above could probably


be used successfully as an inner core material.  The final choice of the


best alloy will depend on many factors outside the scope of this report,


and must await a more detailed package design.

     In order to eliminate the possibility of implosion of the inner


core under pressure, no matter what its material of construction, it is


recommended that once the waste has been placed in the core, cement be

injected under pressure to fill any voids and create a solid mass.  If


the waste were liquid, it could perhaps be mixed with cement, injected


into the core and then allowed to set.



5.2  CONCRETE LAYER

     The concrete used outside the core should be of high quality, with


a low  permeability and a granite aggregate as described previously.


Water  absorption of  the concrete can probably be eliminated by using one


of the polymer-impregnated concretes that are under development at the

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                                                                           42
 U.S. Naval Civil Engineering Laboratory, Port Hueneme, California,40 and




 the Brookhaven National Laboratory, Upton, New York.41






 5.3  OUTER SHELL




      The outer shell should serve two basic functions and perhaps a




 third.   It should serve first as a mold for the concrete, and second as




 a shock absorber to shield the concrete from the effects of rough




 handling.   It is recommended that the shell be constructed of a rigid




 polyethylene  foam sandwich material as shown by the inset in Figure 5.




 The outer  skin and  foam layers will provide shock resistance.   These




 layers  will be collapsed onto the inner solid polyethylene jacket by the




 great hydrostatic pressure of the deep ocean,  but this will be of no




 consequence as they will already have served  their function.   The




 polyethylene  should be  stabilized against  ultraviolet  radiation using




 carbon  black  to  prevent  deterioration by sunlight between the  time of




 manufacture and  of  emplacement.   Marine exposures of polyethylene for up




 to  seven years usually have  resulted  in no  detectable  degradation,10 and




 polyethylene  has  one of  the  lowest rates of water absorption of  all  the




 polymers that  have  been  tested.   In addition,  polyethylene  is  relatively




 immune  to marine  borer attack when not  immediately adjacent to a  piece




 of wood.    This material  is far  less  likely to degrade over a 50-year




 period  than is a  conventional structural steel shell.  A  third possible




 function would be for the  inner polyethylene jacket to serve as an




 additional moisture barrier if some way could be  found to seal the outer




 shell after insertion of the core and concrete.




     Such a container could be either cylindrical or spherical in shape.




A sphere would be preferable because, under hydrostatic compression,




 tensile and shear stresses would be minimized.  The cylinder, however,

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                                                                          43
might be more economical and convenient,  since tubular mill forms of



most materials are readily available.   In addition, the cylindrical



shape would be easier to handle at sea.   There could be a high degree of



confidence in such a container of either  shape for 50 to 75 years



because there is experience with:  (1) concrete in seawater for that



length of time;  (2) titanium, Hastelloy C-276 and Inconel 625 in sea-



water for about half that time; and (3)  the newer candidate materials



for at least a few years.  It is not possible, however, given our



present knowledge of the mechanisms and rates of deterioration of



structural materials in the deep ocean,  to guarantee the integrity of



even this improved container for 300 years.  Selected individual con-



tainers might well last that long or longer, but there will be uncer-



tainty involved.  Therefore, when the desired period of isolation of



even low-level nuclear waste in the ocean exceeds the 50- to 75-year



period over which actual material exposure tests exist, it is recom-



mended that the waste be disposed of in such a manner that the disposal



environment itself provides another barrier to migration of the waste,



rather than relying strictly on the packaging materials themselves to do



that job.



     While a full discussion of additional options to the present



methods of nuclear waste disposal is beyond the scope of this report,



one would be remiss in making this recommendation without indicating



briefly that there is at least one possible additional method already



under consideration.  Disposal of low-level radioactive waste in stable


                                      42
geologic formations of the deep seabed   would seem to be an option



compatible with the concept of not requiring or expecting the physical



container to permanently isolate the waste.  Such depositories are being

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                                                                           44
 discussed and evaluated mainly for high-level waste disposal.  However,




 their most attractive feature - the potential of being able to chemi-




 cally bind the waste and thus to isolate it from man and his marine food




 chains for long periods of time after the deterioration of the original




 container - should apply to low-  as well as  to  high-level waste.




      At  the  present time then,  the most  logical  course  of  action might




 be  to:   (1)  attempt to  develop  cost-efficient  nuclear waste  packaging




 systems which  could demonstrably isolate  and contain the wastes for




 specified  periods of time, preferably fifty to three hundred or more




 years; and (2) couple this packaging system to a carefully selected




 environmental isolation system (deep-sea disposal site)  to provide for




an additional measure of isolation and containment of the waste after




the man-made packaging system has begun  to release its  contents.

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                                                                          45
6.0  REFERENCES




 1.  Dyer,  R.  S.,  1976,  "Environmental Surveys of Two Deepsea Radio-




          active Waste Disposal Sites Using Submersibles", International




          Symposium on the Management of Radioactive Wastes from the




          Nuclear Fuel Cycle,  IAEA,  Vienna, IAEA-SM-207/65, Vol. II, p.




          317-338.




 2.  Tuthill,  A.  H.  and C. M.  Schillmoller, 1971, "Guidelines for




          Selection of Marine  Materials", 2nd Edition, May, 1971, The




          International Nickel Co.,  Inc.




 3.  Fontana,  M.  G.,  and N. D. Greene, 1967, Corrosion Engineering,




          McGraw-Hill.




 4.  Uhlig, H.  H.,  1971, Corrosion and Corrosion Control, Second Edi-




          tion, Wiley-Interscience.




 5.  Fink,  F.  W.,  and W. K. Boyd,  1978,  "Corrosion of Metals in Marine




          Environments", Metals and  Ceramics Information Center, Battelle




          Columbus  Laboratories,  Columbus, Ohio, MCIC Report No. 78-37,




          March,  1978.   (See also the earlier DMIC Report No. 245, May,




          1970, AD  712585.)




 6.  Reinhart,  F. M., 1976, "Corrosion of Metals and Alloys in the Deep




          Ocean",  U.S.  Naval Civil Engineering Laboratory, Technical




          Report R-834,  February,  1976.   (See also LaQue, F. W., 1975,




          Marine Corrosion, Wiley-Interscience.)




 7.  Dexter, S. C.,  and C. Culberson, 1980, "Global Variability of




          Natural Sea Water",  Materials Performance, 19 No. 9, pp. 16-




          28.




 8.  Knauss, J. A.,  1978, Introduction to Physical Oceanography, Prentice




          Hall, Inc., pp. 166-193.

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                                                                             46
    9-   Dexter,  S.  C.,  1974,  "Microbi dogica!  Fouling  and  Its  Control  in




            Coastal Water and  thu Deep Ocean", Woods  Hole Oceanographic




            Institution Technical Report WHOI-74-64,  September 1974.




            Unpublished manuscript.





  10.  Muraoka, J. S., 1964_67, "Deep_0cean Biodeterioration of Materials -




            Parts 1 to VI",  U.S.  Naval Civil Engineering Laboratory, Port




            Hueneme,  CA,  Technical  Reports:  R329 (November, 1964)  AD608939;




            R393 (August,  1965) AD619014;  R428 (February,  1966) AD631078;




            R456 (June,  1966) AD636412; R495 (November,  1966)  AD'642838;




            R525 (May,  1967)  AD65U24.





  H.  Dehghanian,  C.,  and C. E. Locke, 1982,  "Electrochemical Behavior  of




            Steel in Concrete as a Result of Chloride  Diffusion into




           Concrete:  Part 2",  Corrosion, Vol^J8_No^, p. 494.    (See




           also Part 1 of the same study in Ref.  No.  3 of the quoted




           article, and Paper No.  52 by Hartt and Voshardt presented at




           CORROSION/81,  Toronto,  Canada,  April,  1981.)




 12.   Mehta, P.  K.,  and H. H. Haynes,  1975,  "Durability  of Concrete in




           Seawater",  Journal of the  Structural Divison, ASCE,  101, No.




           ST8,  Proc.  Paper 11516, August,  1975,  p.  1679-86.




 13.   Haynes, H. H., and R. S.  Highberg, 1976, "Concrete Properties at




           Ocean Depths", Presented at ASCE  National Water Resource and




           Ocean Engineering Convention, San Diego, April, 1976.




14.  Reinhart,  F. M., 1966,  "Corrosion of Materials in Hydrospace", U.S.




          Naval Civil Engineering  Laboratory, Technical Report R-504.




15.   Reinhart,  F.  M.,  1967,  "Corrosion of Materials in Hydrospace,  Part




          I -  Irons,  Steels,  Cast  Irons and Steel Products", U.S.  Naval




          Civil Engineering Laboratory, Technical Note N-900,  July,
          1967.

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                                                                           47







16.   Southwell,  C.  R. ,  and J.  D.  Bultman, 1975, "Corrosion of Metals  in




          Tropical Environments", Part 10, Final Report of 16-Year




          Exposures,  Naval Research Laboratory, NRL Report 7834,




          January,  1975.




17.   Southwell,  C.  R.,  and A.  L,.  Alexander, 1968, "Corrosion of Structural




          Ferrous Metal in Tropical Environments - 16-Year's Exposures




          to Sea and Fresh Waters", presented at 1968 NACE Conference,




          Cleveland,  Ohio.




18.   King, C.  A. N.,  1962, An Introduction to Oceanography,  p. 89-90.




19.   Park, K.,  1966,  "Deep-Sea pH", Science 154, p. 1540-1542.




20.   Miller, J.  D.  A.,  1970, Microbial Aspects of Metallurgy, American




          Elsevier, p.  63, New York.




21.   Uhlig, H.  H. ,  1971,  Cojr_ro_sio_n and Corrosion Control, Second-Edition,




          Wiley-Interscience, p.  96.




22.   Dexter, S.  C.  , 1979, On. ISoajrd Corrosion Analysis o_f a. Recovered




          Nuclear Wa_st_e Container, U.S. Environmental Protection Agency,




          Office of Radiation Programs, Report No. ORP/TAD-79-2, Washington,





          DC 20460.




23.   Lennox, T.  J., Jr.,  M. H. Peterson,  and R.  E. Groover,  1968,




          "Marine Corrosion Studies - The  Corrosion Characteristics  and




          Response to Cathodic Protection of Several Stainless  Steel




          Alloys in Quiescent Seawater",  Naval Research Laboratory




          Memorandum Report No.  1948, AD  684073, November,  1968.




24.   Lennox, T.  J., Jr.,  and M.  H.  Peterson, 19.76, "Inherent Corrosion




          Resistance and  Response  to  Cathodic  Protection  in Seawater of




          Recently Developed  Stainless  Steel Alloys",  Naval Research




          Laboratory Report No.  8016, August,  1976.

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                                                                              48
   25.  Dyer, R. s. , Personal Communication, April, 1980.  From:  Special
             Subcommittee Hearing on Industrial Radioactive Waste Disposal
             of the Joint Committee on Atomic Energy,  1959, p. 3092.
   26.   The Metals Handbook,  1961,  Eighth Edition, Vol.  j
             for Metals,  Metals  Park,  Ohio,  p.  409.
   27.   Reinhart,  F. M.,  1971, "Corrosion of Materials  in Hydrospace,  Part
            VI  - Stainless Steels", U.S.  Naval Civil Engineering Laboratory,
            Technical Note N-1172, September, 1971.
  28.  Gjorv, 0. E., 1972, "Long-Time Durability of Concrete  in Seawater"
            Proceedings - American Concrete Institute,  Vol. 68, p.  60-67.'
  29.  Haynes,  H. H.,  R.  s.  Highberg,  and B. A.  Nordy,  1976,  "Seawater
            Absorption and Compressive Strength of Concrete at Ocean
            Depths", U.S.  Naval  Civil  Engineering  Laboratory,  Port Hueneme,
            California, Technical Note N-1436, April, 1976.
 30.  Haynes, H. H., and  R. s.  Highberg,  1978, "Deep Ocean Study of
           Concrete Spheres", presented at  the FIP Eighth World Congress,
           April-May,  1978, London.
 31-   Jenks, G.  H., 1957, "Effect  of Radiation on Corrosion", presented
           at HRP Civilian Power Reactor Conference,  Oak Ridge, May,
           1957, U.S.  Atomic  Energy Commission  Report TID-7540.
 32.   Byalobzheskii, A. V., 1970, Radiation  Corrosion,  Translated from
           the Russian by  Israel Program for Scientific  Translations,
           Jerusalem.

33.  Uhlig, H.  H., 1971,  Corrosion and Corrosion Control, Wiley-mterscience,
          p. 145.

34.   Haynes, H.  H., Personal Communication,  November,  1977.  Estimate
          based  on experience at the U.S. Naval Civil  Engineering
          Laboratory,  Port Hueneme,  California.

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                                                                          49
35.  Haynes, H. H.,  Personal Communication, November, 1977.




36.  Hunger, C. G.,  1975, "Marine Coatings", in F. L. LaQue, Harine




          Corrosion, Wiley-Interscience, p. 283-317.




37.  Reinhart, F. M.,  1967, "Corrosion of Materials in Hydrospace, Part




          II - Nickel and Nickel Alloys", U.S.  Naval Civil Engineering




          Laboratory,  Technical Note N-915, August, 1967.




38.  Streicher, M. A., 1983, "Analysis of Crevice Corrosion Data from




          Two Sea Water Exposure. Tests on Stainless Alloys", Materials




          Performance, Vol. 22, No. j, p. 37.




39.  Dexter, S. C.,  1979, Handbook of Oceanographic Engineering Materials,




          Wiley Interscience,  New York.




40.  Haynes, H. H.,  and Eckroth, W. V.,  1979,  "Lightweight Concrete




          using Polymer-Filled Aggregate for Ocean Applications - An




          Exploratory Investigation", U.S.  Naval Civil Engineering




          Laboratory,  Port Hueneme, California, Technical Note:  TN No.




          N-1565, December, 1979.




41.  Kukacka, L.  E., 1977, "Production Methods  and Applications for




          Concrete Polymer Materials", Presented at AIChE Symposium on




          Degradation of Concrete and Ceramics, New York, NY, November,




          1977.




42.  Hollister, C. D. , 1977, "The Seabed Option", in Oceanus, VpJl_._J20,




          No_,	_1,  "High Level Nuclear Wastes in  the Seabed?", Woods Hole




          Oceanographic Institution, Woods Hole, Massachusetts.

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
1. REPORT NO.
 EPA 520/1-82-005
                              2.
4. TITLE AND SUBTITLE
 Materials  for  Containment of Low-Level  Nuclear Waste
 in the Deep  Ocean
                                                           3. RECIPIENT'S ACCESSION NO.
             5. REPORT DATE
                December 1982
             6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)

 Stephen C.  Dexter
             8. PERFORMING ORGANIZATION REPORT NO.

                CMS-C-1-78
9. PERFORMING ORGANIZATION NAME AND ADDRESS
                                                            10. PROGRAM ELEMENT NO.
 College of Marine Studies
 University of  Delaware
 Lewes, Delaware  19958
             11. CONTRACT/GRANT NO.
                Contract No. WA-6-99-2767-J
12. SPONSORING AGENCY NAME AND ADDRESS
 Office of Radiation Programs
 U.S. Environmental Protection Agency
 401 M Street,  SW
 Washington,  D.C.  20460
             13. TYPE OF REPORT AND PERIOD COVERED
                Final
             14. SPONSORING AGENCY CODE
                ANR-461
15. SUPPLEMENTARY NOTES
16. ABSTRACT
         The United States  ocean  dumping regulations  developed pursuant to PL 92-532,
    the Marine Protection,  Research,  and Sanctuaries  Act  of 1972, as amended, provide
    for a general policy of isolation and containment of  low-level radioactive waste
    after disposal into the ocean.

         In order to determine  whether any particular waste packaging system will meet
    this general requirement, and for how long, it is necessary to know what materials
    were used and how those materials will behave in  the  deep sea.

         This report discusses  the  mechanisms of marine corrosion of structural  and
    stainless steels, the degradation mechanisms acting on  concrete in a marine
    environment, the interaction  between metal and concrete combined as a low-level
    radioactive waste package under deep sea conditions,  and the effect of
    environmental parameters such as  dissolved oxygen, temperature, and water velocity
    on  deep sea degradation processes.  A concluding  discussion presents various
    improved metal alloys and concrete additives which may  result in greater resistance
    of  a low-level radioactive  waste  package to deep  sea  deterioration processes.
17.
                  DESCRIPTORS
 Ocean Dumping/Ocean Disposal
 Low-Level Radioactive Waste Packaging
 Deepsea  Corrosion
 Deepsea  Deterioration of Concrete
                                              b.IDENTIFIERS/OPEN ENDED TERMS
                           c. COSATI Field/Group
18. DISTRIBUTION STATEMENT

 Unlimited Release
19. SECURITY CLASS (This Report)
     Unclassified
21. NO. OF PAGES
       58
                                              20. SECURITY CLASS (This page)
                                                   Unclassified
                                                                         22. PRICE
EPA Form 2220-1 (Rev. 4-77)   PREVIOUS EDITION is OBSOLETE

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