When the Cold War ended in 1991, the Department of Energy (DOE) stopped its historic practice of producing plutonium for nuclear weapons. Facility missions were changed and budgets were dramatically reduced. Tons of plutonium destined for warheads were left in place, much of it in forms and facilities not suited for long-term storage. For the past three years and under the auspices of the Defense Nuclear Facility Safety Board (DNFSB) Recommendation 94-1, the DOE has been addressing the potential environmental, safety, and health hazards posed by this legacy nuclear material. The recommendation recognized the imminent safety concerns associated with stored nuclear materials whose condition, packaging, and storage situations may no longer meet current safety guidelines. It was especially focused on specific liquids and solids containing fissile and other radioactive materials in spent fuel storage pools, reactor basins, reprocessing canyons, processing lines, and the various buildings once used for chemical processing and weapons manufacture. In essence, the recommendation stated the following:
On a high-priority basis, a program plan will be formulated to convert high-vulnerability items to forms or conditions suitable for safe interim storage within two or three years. And within a reasonable period of time (such as eight years), all storage of metal and oxide will be in conformance with the DOE criteria for the safe storage of plutonium metal and oxides (DOE-STD-3013).
NMT-7 employees Davy Sparks and Charles Lehman cement evaporator
bottoms produced from a nitric acid evaporator. "At risk" materials are
stabilized by processing through aqueous recovery lines. The resulting
spent nitric acid
is processed through the evaporator and the cement process as part of
final acid disposition.
Throughout the history of the Los Alamos Plutonium Facility, the operational strategy has been to recycle both primary and secondary plutonium residues through aqueous recovery operations for actinide separation and recovery. With the mission of the 1980s to increase the amount of pure plutonium metal feed sent to the Rocky Flats weapons manufacturing program, it was simply not feasible to take the time to recover plutonium from lean process residues. In addition, research and development activities supporting technology transfer programs also produced numerous lean residues that were not slated for immediate plutonium recovery. As a result, when the Cold War ended, Los Alamos had a total transuranic inventory of some 9,300 residue packages containing a plutonium inventory of ~2,600 kg. Out of this total, about 8,600 residue items were subject to the stabilization requirements of Recommendation 94-1. Approximately 90% of the item count was plutonium, with the remainder consisting of plutonium-contaminated depleted and enriched uranium, uranium-233, curium, berkelium, californium, neptunium, and isotopes of americium.
The approach we have taken to respond to Recommendation 94-1 is to prioritize the legacy residue inventory based on real or perceived worker-safety risk and then utilize our actinide separation and processing capability to stabilize these materials, especially those "at-risk" material categories with demonstrated material instabilities or packaging defects. For us, stabilization is the separation and recovery of the nuclear material for either programmatic use or for packaging to meet the DOE long-term metal and oxide storage criteria, DOE-STD-3013. After separation the matrix material associated with the nuclear material in the residue is declared a waste and is packaged as transuranic waste for ultimate transfer to the Waste Isolation Pilot Plant.
For the past three years we have stabilized certain "at-risk" material categories, as well as other categories posing some risk to the worker, and we have packaged plutonium metal and oxide for either programmatic use or for long-term storage. Because the "at-risk" material categories have a history of demonstrated material instabilities or packaging defects, they take the majority of our stabilization emphasis.
Materials stored in the vault, such as these cans of residue, are
sampled on a regular basis to assess the stability of the material and
the inner and outer containers. Such sampling provides a database for
analysis and modeling that can assess the reliability of storage
assumptions, methods, plans, and priorities.
To date, we have stabilized over 3000 items out of a legacy inventory of over 8500 items, we have prepared over 500 kg of plutonium metal and over 100 kg of plutonium oxide for long-term storage, we have prepared over 100 packages meeting the DOE-STD-3013 storage standard, and we have recovered over 200 kg of plutonium (as oxide) from residue sources (see figure at right). Because this is a long-term program, it became evident very early that understanding the aging phenomena of our inventory would become a very important tool in prioritizing material for stabilization and in being able to anticipate any safety risk to the worker when handling these materials in the vault or in other areas outside of glove box lines. We have taken advantage of ongoing programs, and we have initiated new programs to gather data to fill gaps in our knowledge about how packages age, to validate our processing priorities, and to continue increasing the margin of safety afforded our plutonium workers.
To gain relevant knowledge about the aging phenomena of our legacy inventory, we have instituted a sampling plan whereby on an annual (or more frequent) basis we randomly sample vault items for inspection as well as inspecting the package condition of the materials currently undergoing stabilization. The inspection consists of evaluating the condition of the inner package inside the container stored in our vault. We are primarily interested in failed "bagout" bags (contamination on the inside of the outer container) or some condition of the inner package that causes us to suspect that the item or that the entire material category is unsuitable for continued storage in the vault as is. To date, we have an inspection database of over 2500 items, and after analysis and modeling, we feel we have significantly reduced the uncertainty in our conclusions about worker- safety risk and also have used these data to validate or change our material stabilization and processing priorities. Since the overall response to the DNFSB Recommendation is long-term (eight years or longer), this continued inventory evaluation and any resultant schedule reprioritization is necessary to continually understand and improve the margin of safety afforded our plutonium workers.
Beginning in FY98, as a result of diminishing DOE budgets and expanding Departmental programmatic requirements, the formal response to Recommendation 94-1 underwent a dramatic change. It underwent an evolution from a program addressing only legacy inventories to one with a more integrated approach to managing the entire nuclear material inventory at the Laboratory-both the legacy and the newly generated residue inventories. Very recently, the DOE approached the DNFSB with this integrated plan for managing the nuclear materials inventory at the Laboratory. Because of our demonstrated success over the past three years in stabilizing residues and packaging metal and oxide, and because of our demonstrated success in understanding the worker-safety risk of our aging inventory, we were successful in obtaining a schedule extension from 2002 to 2005 for stabilizing the legacy materials.
This new schedule is important for several reasons: it allows us to increase staff at a manageable level, it allows us to perform much-needed maintenance and replacement of aqueous processing equipment and other elements of the project infrastructure, it allows us to focus resources on the selective processing of materials currently occupying premier vault storage locations, and it provides us the ability to support more effectively the other programs at TA-55 while still reducing to zero the worker-safety risk surrounding the legacy inventory. Most importantly, however, it allows the DOE Defense Programs Office to use our Plutonium Facility effectively for many of its programs that affect national security.
This article was contributed by Keith W. Fife, NMT-2.
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