United States
Environmental Protection
Agency
Office of
Radiation Programs
Washington DC 20460
Technical Note
ORP/fAD ;<) 2
v>EPA
Radiation
On Board Corrosion Analysis
of a Recovered Nuclear
Waste Container
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TECHNICAL NOTE
ORP/TAD-79-2
ON BOARD CORROSION ANALYSIS OF A RECOVERED
NUCLEAR WASTE CONTAINER
by
Stephen C. Dexter
Assistant Professor
of Ocean Engineering
and Materials Science
College of Marine Studies
University of Delaware
August 1979
This report was prepared as an account of
work sponsored by the United States
Environmental Protection Agency
Under Contract No. WA-6-99-2767-J
Project Officer
Robert S. Dyer
Radiation Source Analysis Branch
Technology Assessment Division
Office of Radiation Programs
U.S. Environmental Protection Agency
Washington, D.C. 20460
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EPA REVIEW NOTICE
This report has been reviewed by the Office of Radiation Programs, U.S.
Environmental Protection Agency (EPA) and approved for publication. Approval
does not signify that the contents necessarily reflect the views and policies
of the EPA. Neither the United States nor the EPA makes any warranty,
expressed or implied, or assumes any legal liability or responsibility for any
information, apparatus, product or process disclosed, or represents that its
use would not infringe privately owned rights.
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EPA TECHNICAL PUBLICATIONS
Publications of the Environmental Protection Agency's (EPA) Office of
Radiation Programs (ORP) are available in paper copy, as long as the EPA/ORP
supply is available, or from the National Technical Information Service
(NTIS), Springfield, VA 22161.
The following reports are part of the EPA/ORP 1976 Ocean Disposal Report
Series:
ORP/TAD-79-1 Materials for Containment of Low-Level Nuclear Waste in the Deep
Ocean
ORP/TAD-79-2 On Board Corrosion Analysis of a Recovered Drum from the
Atlantic 2800 Meter Radioactive Waste Disposal Site
ORP/TAD-79-3 Analysis and Evaluation of a Radioactive Waste Package Retrieved
from the Atlantic 2800 Meter Disposal Site
ORP/TAD-79-1* Reports of Infaunal Analyses Conducted on Biota Collected at the
Atlantic 2800 Meter Radioactive Waste Disposal Site
ORP/TAD-79-5 Geologic Observations of the Atlantic 2800 Meter Radioactive
Waste Dumpsite
ORP/TAD-79-6 Sediment Geochemistry of the 2800 Meter Atlantic Radioactive
Waste Disposal Site
ORP/TAD-79-7 Ocean Current Measurements at the Atlantic 2800 Meter
Radioactive Waste Disposal Site
ORP/TAD-79-8 Survey Coordination and Operations -Report - EPA Atlantic 2800
Meter Radioactive Waste Disposal Site Survey
ORP/TAD-79-9 1976 Site Specific Survey of the Atlantic 2800 Meter Deepwater
Radioactive Waste Dumpsite: Radiochemistry
ORP/TAD-79-10 Sediment Characteristics of the 2800 Meter Atlantic Nuclear
Waste Disposal Site
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FOREWORD
The Environmental Protection Agency, (EPA), was given a Congressional
mandate to develop criteria, standards, and regulations governing the ocean
disposal of all forms of wastes pursuant to Public Law 92-532, the Marine
Protection, Research and Sanctuaries Act of 1972. Within this Congressional
mandate, EPA has initiated a specific program to develop regulations and
criteria to control the ocean disposal of radioactive wastes.
EPA has taken an active role both domestically and within the
international nuclear regulatory arena to develop the effective controls
necessary to protect the health and safety of man and the marine environment.
The EPA Office of Radiation Programs (ORP) initiated feasibility studies to
determine whether current technologies could be applied toward determining the
fate of radioactive wastes dumped in the past. After successfully locating
actual radioactive waste containers in three of the primary radioactive waste
disposal sites used by the United States in the past, ORP developed an
intensive program of dumpsite characterization studies to investigate the
following: (a) the biological, chemical and physical parameters, (b) the
presence and distribution of radionuclides within these sites, and (c) the
performance of past packaging techniques and materials.
These studies have provided needed information and data on the past and
present nuclear waste disposal activities concomitant with the growing
national and international concern for the long-term effects of this low-level
waste disposal option.
ORP has now completed the fifth in a series of Pacific and Atlantic Ocean
dumpsite surveys which began in 197^. This survey of the Atlantic 2800 meter
deep-sea radioactive waste disposal site, which is centered at coordinates
38030'N, 72°06'W and located approximately 120 miles east of the
Maryland-Delaware coast, was conducted in June 1976.
A major objective of this 1976 Atlantic survey was the first recovery of
a steel and concrete container from any deep-sea dumpsite. In conjunction
with the survey, EPA/ORP initiated a contract study to evaluate, prior to
extensive laboratory analysis, the chemical, biological and corrosion status
of the exterior of the container immediately upon recovery. The following
report presents this evaluation.
Readers of this report are encouraged to inform the Director, Technology
Assessment Division (ANR-459), Office of Radiation Programs, U.S.
Environmental Protection Agency, Washington, D.C. 20460, of any errors,
omissions, or other comments.
David S. Smith
Director, Technology Assessment Division
Office of Radiation Programs (ANR-^59)
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Abstract
During the 1976 Atlantic 2800m radioactive waste dumpsite survey, an
80-gallon low-level radioactive waste container was recovered. Within the two
hour interval between the time the container first emerged from the ocean
until it was encapsulated, the exterior condition of the drum, including the
appearance of corrosion product films and attached biological growths, was
extensively documented photographically. In this report, representative
photographs, as well as the results of limited chemical and biological
analyses performed by University of Delaware personnel during the above two
hour interval, are presented. These results are discussed in light of
previously published deep ocean corrosion data, and recommendations on
improving shipboard sampling and analytical procedures are given.
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1.0 INTRODUCTION
On July 31i 1976, an 80-gallon nuclear waste container was recovered by
the Environmental Protection Agency from a depth of 2?83 meters in the
Northwestern Atlantic Ocean at a point approximately 120 miles east of the
Delaware-Maryland border. The container was hoisted aboard the research
vessel, Cape Henlopen, where it was photographed, and samples were immediately
taken of corrosion products and attached biological growths. The container
was then encapsulated in a jet engine shipping container which was flushed
thoroughly with argon to minimize any further corrosion. The elapsed time
from when the container first broke the surface of the water to the start of
the argon flushing process was two hours.
The purpose of this report is to describe the photographic, chemical, and
biological analyses performed on board the ship by University of Delaware
personnel during those two hours and to present the results of those analyses.
2.0 EXPERIMENTAL METHODS
Both the surface condition of the container as it came on board the ship,
and the recovery operation itself, were documented photographically.
Thirty-five mm color slides of the container were taken as soon as it broke
the surface in order to record the volume and distribution of corrosion
products before any changes due to decreasing pressure and increasing
temperature took place. After the container was secured to the deck of the
ship, photographs were taken in a systematic way so that they could be related
to the correct position on the exterior of the drum upon subsequent laboratory
examination.
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2
Close-up photographs were taken of all interesting features including
biological growths. Close-up photographs were located with respect to the
container by taking photo pairs. First, an overall picture was taken of the
container with a cut-out cardboard frame held over the feature of interest.
The camera was then repositioned and a close-up photograph was taken of the
area within the frame. The photographs presented in this report were printed
from color plates made from selected original color slides.
The pH of the corrosion products and the mud layer, where it was still
clinging to the drum, was spot checked at several locations while the drum
surface was still wet. Readings were taken with pH indicator papers and
recorded for each location.
Samples of the corrosion product were taken both from the outer layers
(reddish orange) and from the layer immediately adjacent to the bare metal
surface (greenish black) at a location just above the mudline on the
cylindrical surface near the metal end and were examined for bacterial
activity. The examination was done both immediately on board the ship as well
as subsequently ashore in the laboratory. A Unitron BPH phase contrast
microscope was used for all observations. The samples observed on board were
examined directly at 600X by spreading the moist sample on a glass slide.
These observations were very difficult due to ship roll and vibration. The
samples to be observed in the laboratory were diluted with seawater that had
been passed through a 0.22 urn membrane filter (Millipore) and encapsulated in
glass vials to prevent them from drying. In the laboratory, these samples
were spread between a glass slide and coverslip and examined in phase contrast
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3
at 1500X using an oil immersion lens. No special measures were taken to avoid
bacterial contamination of the sample nor were aseptic techniques used in
preparing the filtered seawater.
3-0 RESULTS
3.1 Photographic Analysis
Figure 1 is a schematic diagram of the container showing the locations
from which each of the photographs in Figures 2 through 9 were taken. Figures
2 through 9 show the general condition of the container immediately upon
recovery. Note that the container as it sat on the deck was upside down
compared to its position on the sea floor.
Figure 2a shows the concrete end of the drum seconds after it first broke
the surface of the water. The identifying markings on the concrete end are
legible in Figure 2b and include such information as the package number (28),
the volume of the waste-matrix mixture (9.0 cubic feet), the weight of the
package (1682 pounds), the most hazardous isotope present in the package
(cobalt-60) and the dose rate at the surface of the drum at the time of
packaging (3 millirads/hour). Information not clearly visible in Figure 2(b)
indicated that the radioactive waste package was prepared in 1961. Prior to
the start of recovery operations the drum sat partially embedded in the bottom
sediments. The sediment line is clearly visible in Figure 2, the black
portion of the concrete end having been in the mud.
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4
Figures 3a and 3b show the surface condition of the container after
hoisting out of the water but before securing on deck. There was a
10 to 15 minute interlude here while the radioactivity level of the drum was
being measured. As seen in the photographs, the container is in remarkably
good condition after 14-15 years of immersion. The mud line can again be seen
in Figure 3b between the two arrows. Note that the upper half of the drum,
which was below the mud line, is less corroded than the lower half which was
exposed to the water column. The view in Figure 3a, for instance, shows most
of the area that was in the mud, and there is very little corrosion visible.
Identical areas on the drum surface are labeled "A" and "B" on Figures 3a and
3b. On seventy-five percent of the metallic surface area of the drum (and on
considerably more of the area below the mud line) the original black enamel
finish was still intact.
Several of the more interesting areas of the container surface were
photographed in detail after the container was secured on deck. These are
shown in Figures 4 through 9. Figure 4 shows the surface above and below the
mud line on the left portion of the cylindrical surface of the drum as seen in
Figure 3b. The large area of bare metal surface showing there as well as the
bare metal showing on the raised ribs of the drum in Figures 3a and 3b were
probably scraped clean as the drum was dragged along the bottom during the
initial part of the hoist precedure. There is little doubt that this
happened, as the track of the drum where it was dragged along was clearly
visible from the deep submersible, Alvin, upon subsequent inspection of the
site.
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5
Figure 5 shows the heavy concentration of corrosion products just to the
lower right of the letter "A" in Figure 3b. By the time this picture was
taken, some of the corrosion product had been scraped off into sample
bottles. Other portions of it had rubbed off against the nylon webbing,
visible in Figure 5, which had been installed as an additional aid to handling
shortly after the picture in Figure 3b was taken. There was no attempt made
at this time to scrape all the way through the corrosion product layer to
determine the condition of the underlying metal as this was planned for
subsequent laboratory operations.
The outer steel container was in the worst condition around the rim at
the concrete end as shown in Figure 6. There was no marked difference in the
condition of the rim above as opposed to below the mud line. A sample of the
corroded edge of the metal was clipped off with metal shears for later
examination at the Brookhaven National Laboratory.
When the container first arrived at the surface, it was apparent that
there was a perforation in the metal drum as a stream of seawater was observed
coming out as if under pressure. The stream can be seen just below the letter
"B" in both Figures 3a and 3b. The area from which the stream came was below
the mud line and is shown close up in Figure 7. By the time this photograph
was taken, the pressure had nearly equalized and the remaining liquid was
seeping out as shown. Some of this liquid was collected by the EPA Project
Officer for subsequent laboratory analysis. Upon further examination with a
probe, it became apparent that the perforation was not due to corrosion but
was a recent puncture. It is suspected that this occurred as the drum was
being dragged along the bottom as related above.
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Figures 8a and 8b show the condition of the metallic end of the drum.
The mud line runs between the two arrows from upper right to lower left of
Figure 8a, the portion to the upper left having been buried in the bottom
sediments. The corroded area in the center of the metallic end is shown in
Figure 8b. This appearance is typical of a painted steel surface in the early
stages of seawater corrosion. The small white streaks near the lower rim of
the metallic end as seen in Figure 8a were the only macroscopic biological
growths that were found attached to the drum. They were sampled and
identified as polychaete tubes under separate contract by Dr. Donald Reish of
California State University.
There was very little corrosion below the mud line. Where corrosion did
take place, it appeared to be highly localized as in Figure 9. Instead of
being spread uniformly over the surface, the corrosion took place in the form
of broad shallow pitting (see arrows). It is estimated that the depth of
attack was 0.2 to 0.5 mm. As there were no corrosion products associated with
these pits upon recovery of the drum, one can only assume that the products
were scraped off as the drum dragged along the bottom. This is a reasonable
assumption as this portion of the drum was below the mud line prior to
recovery.
3-2 Chemical Analysis
The pH of the corrosion products was measured with pH indicating paper at
several locations both above and below the mud line. The pH was generally
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7
found to be between 6 and 8. There was one notable exception. The pH of the
water bubbling from the puncture described in connection with Figures 3 and 7
was between 13.0 and 13.5.
3-3 Microbiological Analysis
Despite the fact that aseptic techniques were not used in sampling the
corrosion products, no microorganisms could be positively identified
microscopically as being present in the corrosion products. Both the
red-orange outer layer and the greenish-black inner layer adjacent to the bare
metal surface were examined. Since the shipboard observations were very
difficult due to vibration problems, observations were also made in the
laboratory. The same negative result was obtained.
4.0 DISCUSSION
The overall condition of the container that was recovered was much better
than might have been expected given the duration of exposure in the deep ocean
(probably in excess of 14 years). The often localized nature of the corrosion
that did take place was also somewhat surprising as one normally expects steel
structures to be corroded uniformly over the exposed surface. Before drawing
any conclusions about the significance of the good condition of the drum to
future ocean dumping, however, two things must be considered: first, this is
only a single data point; second, this single point is purposely biased. Many
of the containers observed by the submersible, Alvin, were in worse condition
than the one recovered. This particular drum was selected for recovery
because it appeared to be in good enough condition to survive the trip to the
surface and yet provide meaningful information on past packaging performance.
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The corrosion rate of uncoated plain carbon steel in aerated quiescent
seawater is normally as high as 0.25 to 0.40 mm/year (10 to 16 thousandths of
an inch per year fMPY]) for the first few months of immersion1' ^.
Gradually, as the fouling and corrosion product layer builds up, the above
rate decreases2 to 0.03 to 0.13 mm/year (1 to 5 MPY). In addition, this
rate depends directly on the concentration of dissolved oxygen present in the
seawater and on the pH of the seawater . Within the range of pH 4 to 10
the corrosion rate of steel is independent of pH and depends only on how
rapidly oxygen can be supplied to the steel surface. As the pH becomes more
basic than 10, however, steel becomes passive in seawater and the corrosion
rate drops rapidly to a negligible value^.
The well known corrosion behavior of steel in seawater described above
may partially account for the good condition of the recovered nuclear waste
container. Although dissolved oxygen measurements were not made at the drum
recovery site, it is generally found that the dissolved oxygen in the deep
ocean decreases rapidly with depth from 7 ppm at the surface to a minimum of
about 0.5 ppm at 750 meters, then rising again typically to 2 or 3 ppm at
great depth. Occasionally the dissolved oxygen at great depth may rise again
to a value as high as that at the surface or even higher.
Given the good condition of the recovered drum, it can be speculated that
the dissolved oxygen in both the water and the sediments at the drum recovery
site was low (perhaps 1 to 2 ppm). This, coupled with the low temperature to
be expected at great depth, would account for the relatively low corrosion
rates observed. In addition, the concrete inside the drum was saturated with
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9
seawater, and its pH was reported in the results section to be between 13 and
13.5. This is consistent with other measurements reported for the pH of
seawater in concrete . The corrosion rate of the steel on the inner surface
of the container should, therefore, have been negligible and corrosion should
have proceeded from the outside only. The difference that this can make is
illustrated by the fact that the steel container was in the worst condition
around the rim at the concrete end where the steel extending beyond the
concrete by about two centimeters was exposed to ambient pH seawater on both
sides. The perforated condition of the steel in that area was shown in
Figure 6.
The corrosion rate of steel in seawater is not usually influenced
significantly by the presence (or absence) of microorganisms. The one
noticeable exception to this is in anaerobic bottom sediments where the
corrosion rate of steel normally is negligible. If sulfate reducing bacteria
are present, however, they allow the formation of a loosely adherent FeS scale
on the steel which is cathodic to the bare metal surface '. This produces
a galvanic couple which accelerates the corrosion of the steel and is
accompanied by hydrogen evolution. The excellent condition of the portions of
the recovered drum that were buried in the sediments testifies that sulfate
reducing bacteria were probably not active in sediments in the recovery iarea.
This view is also supported by the negative result of the microscopic
investigations reported in the results section. If sulfate reducing bacteria
had been active, we should have been able to detect them in the corrosion
products.
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5.0 RECOMMENDATIONS AND CONCLUSIONS
It is not possible based on the one container that was recovered to make
any definitive conclusions about the suitability, from a corrosion viewpoint,
of this method of packaging nuclear wastes for ocean disposal. It is possible
to say that at least one of the many containers dumped 16 to 20 years ago
survived its stay on the bottom with the exterior in reasonably good condition.
It is also possible to make recommendations for increasing the value of
future work of this type:
1. Determine the dissolved oxygen concentration both in the water column
within about ten meters of the bottom and in the upper one meter of the
sediments at the dumpsite. This should be done both several months before and
again several months after, as well as at the time of the survey (total of
three measurements with at least six months from the first to the last), in
order to detect if there is any variability. This type of data, which was not
available for the work reported here, would have allowed a more meaningful
corrosion analysis. The expected corrosion rate could have been estimated
more accurately and related directly to other published deep-sea corrosion
data.
2. Retain the services of a qualified marine microbiologist to test the
sediment samples for the presence of microorganisms. The sulfate reducing
bacteria are particularly important for evaluating the corrosion behavior.
Also have this person arrange to test the corrosion products for bacterial
activity by culturing techniques as well as by microscopy.
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The above recommendations should be extended to include not only research
on the effects of past dumping, but also research on sites that may be under
consideration for future dumping. In this way it will be possible to detect
and eliminate sites whose characteristics might accelerate deterioration of
the container by corrosion.
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6.0 REFERENCES
1. P.M. Reinhart "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.
2. F.W. Fink and W.K. Boyd, "The Corrosion of Metals in Marine
Environments," DMIC Report 245, May 1970, p. 9-22.
3- Marine Corrosion, F.L. LaQue, Wiley-Interscience, 1975, p.95.
4. Corrosion and Corrosion Control, H.H. Uhlig, second edition, John Wiley,
1971, p.92.
5. D.R. Lankard, "Cement and Concrete Technology for the Corrosion
Engineer," Materials Performance, 15, August 1976, p.24.
6. Microbial Aspects of Metallurgy, J.D.A. Miller, editor, American
Elsevier, 1970.
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PORT
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CONCRETE
END
2d & 2b
Figure 1. Schematic diagram of the recovered container showing the locations of
the photographs in Figures 2 through 9. The container as it sat on the deck,
and as pictured here is upside down compared to its position on the sea floor.
The shaded portion was embedded in the sediments.
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(a)
Figure 2. Nuclear waste container, a) a few seconds after
breaking surface of water, b) identification marks on con-
crete end.
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(a)
(b)
Figure 3. Nuclear waste container showing: a) portion of surface
that had been buried in the sediments, and b) the mud line between
arrows.
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Figure 4. Left end of cylindrical surface of nuclear waste
container as seen in Figure 3(b) after securing on deck.
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Figure 5. Heavily corroded portion of cylindrical surface
of container just to the lower right of letter "A" in
Figure 3(b).
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Figure 6. Corrosion around the rim of the concrete end of the
container.
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Figure 7. Water oozing out of perforation on cylindrical surface
of container. Location of the perforation is just below the letter
"B" in Figure 3(a) and (b).
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(a)
Figure 8. Metallic end of nuclear waste container: a) mud line is
shown between arrows, b) close up of corroded portion.
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,
Figure 9. Localized corrosive attack (see arrows) on cylindrical
surface below the sediment line.
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