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

                             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
                                        Gien L.  Sjcblom,  Director
                                     Office of  Radiation Programs



     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.


                           TABLE OF CONTENTS

1.0  INTRODUCTION.  .  .  .  ,	1



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



     3.1  STRUCTURAL STEEL  	  17

     3.2  STAINLESS STEELS  	  23

     3.3  CONCRETE	26




     5.1  INNER CORE	36

     5.2  CONCRETE LAYER	41

     5.3  OUTER SHELL	42




     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

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

containers will be estimated from these data, and several alternatives

to the present methods of containment will be discussed.



                            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

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

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


                           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

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

                      TABLE I

                   IN SEAWATER
    Potential vs.
Satd.  Calomel Electrode
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)
70-30 Copper Nickel
17/4 pH Stainless Steel (passive)
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)

-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

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

 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

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

                                        CORROSION  OF
FIGURE 2.  Crevice corrosion sites around a mechanical fastener.

   surface r*
                                 Oxygen, ppm
      68     10    12
      i   Temperature, C
           6.4   6.6
7.4   7.6   7.8    8.0   8.2
          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)

 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

 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

 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-

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

cases where there is appreciable suspended particulate matter in the

                         DISSOLVED OXYGEN
-c     1,000
                       A AISI 1010 STEEL
                        OXYGEN (ml/l)
                    CORROSION RATE (mpy)
 FIGURE 4.  Corrosion rate of structural steels as a
 function ot depth and dissolved oxygen. (After Reinhart6).

   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.

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-

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

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


     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,

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

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

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

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.


     The primary mechanism of degradation of portland cement type

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

of attack can and does take place.

     Destructive attack can follow either or both of the following two

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.

   3.0  ENVlROraffiNTALJDATA

        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'^

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. '

Location Depth Temperature
Pacific Ocean 1675 m 6.65C
Atlantic Ocean 1515 m 4.L8C
1.5 ml/ 9,
5.7 ml /I
Rate Reference
25 ym/y 14,15
50 ym/y 14

     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

 directly to the water.

     If dissolved oxygen is completely absent from the sediments,  the

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

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

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

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.

      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

 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.

     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.


     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

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

  % Cr
% Ni
% Fe
  % Other Major
Alloying Elements
0.2 S or Se Free machining
grade, least
resistant .
2 - 3 Mo Most resistant
                                                                 of group
9-13    Balance
               1 - 2 Mn
                     Weldable grade

     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

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

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.


     The rate of deterioration of concrete in seawater varies with the

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

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

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


      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

 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.


     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

 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

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

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

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

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.



     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.

     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

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

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

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

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

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

short compared to even the shortest desired containment  period (50


     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


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

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

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

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


     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.


     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.

     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.


     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


      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

                    Low Level  Waste
                    Imbedded  in Cement
Unalloyed  Titanium
Inner core

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

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

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


     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

  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

                                                  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.


     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

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

 the Brookhaven National Laboratory, Upton, New York.41


      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,

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

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

 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.


 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.


 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,


 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-


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

          Hall, Inc., pp. 166-193.

    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,


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.

   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,

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.

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,


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.


                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
 EPA 520/1-82-005
 Materials  for  Containment of Low-Level  Nuclear Waste
 in the Deep  Ocean
                                                           3. RECIPIENT'S ACCESSION NO.
             5. REPORT DATE
                December 1982

 Stephen C.  Dexter

                                                            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
 Office of Radiation Programs
 U.S. Environmental Protection Agency
 401 M Street,  SW
 Washington,  D.C.  20460
         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.
 Ocean Dumping/Ocean Disposal
 Low-Level Radioactive Waste Packaging
 Deepsea  Corrosion
 Deepsea  Deterioration of Concrete
                                              b.IDENTIFIERS/OPEN ENDED TERMS
                           c. COSATI Field/Group

 Unlimited Release
19. SECURITY CLASS (This Report)
                                              20. SECURITY CLASS (This page)
                                                                         22. PRICE
EPA Form 2220-1 (Rev. 4-77)   PREVIOUS EDITION is OBSOLETE