Plutonium Processing at Los Alamos
The element plutonium occupies a unique place in the history of science, technology, and international relations. After the initial discovery of only a few atoms, it is now generated by transmutation of uranium in nuclear reactors on a large scale and has been separated in ton quantities in large industrial facilities. The intense interest in plutonium has always centered on the nexus between nuclear weapons and domestic nuclear power—drawing energy from an atomic nucleus that can be tapped for a multiplication factor of millions in energy output relative to chemical energy sources.
Historically, plutonium was first produced in production reactors; extracted, concentrated, and converted to either an oxide or fluoride; and then reduced to metal. The resulting metal was used for fabrication of various parts and components. The fabrication process itself generates major quantities of waste and scrap plutonium that must then be recovered and recycled.
In modern times, the feed material for preparing and refining metallic plutonium and its important compounds now includes recovered and recycled residues and scrap material. This in turn drives the current technology selection for processing, preparing, and refining. In addition, the technology selection must take nuclear material safeguards, accountability, criticality safety, radiation exposure, and environmental protection into consideration.
In 2008, more than 2200 metric tons of plutonium exists throughout the world in the form of spent nuclear fuel, nuclear weapons components, various nuclear inventories, legacy materials, and wastes. Regardless of your views on how this situation came to be, it is clear that these large plutonium inventories must be prudently managed for many centuries. We will have to stabilize and store excess plutonium, secure it against theft and diversion, and research modern reactor concepts to reduce plutonium inventories. To succeed, we will have to improve our understanding of plutonium by continuing to work at the frontiers of science, and continuing to attract and retain the best and the brightest talent of the next generation.
Under NNSA’s proposed preferred alternative, Los Alamos will maintain its role as the center of excellence for nuclear weapons design and engineering, and plutonium research, development, and manufacturing. As the nuclear weapons program becomes smaller as part of the NNSA weapons complex transformation, Los Alamos’ Stockpile Manufacturing and Support (SMS) Directorate must maintain the breadth of capabilities that support stockpile stewardship and nuclear deterrence while also producing innovative discoveries that will lead to new missions in plutonium science and engineering. Plutonium processing will be a key component of the Los Alamos mission for the foreseeable future.
Virtually all plutonium operations at Los Alamos occur within the Plutonium Facility at Technical Area 55. It is the nation’s most modern plutonium facility, consisting of a 75,000-square-foot building that is built to withstand 200-mile-per-hour tornadic winds and any credible seismic event. TA-55, as the facility is commonly called, opened in 1978.
The work at TA-55 supports a wide range of national programs, such as stockpile stewardship, nuclear materials stabilization, materials disposition, nuclear forensics, nuclear counter-terrorism, and nuclear energy. Each of these programs revolves around plutonium. In stockpile stewardship, for example, pure plutonium metal is used to manufacture nuclear-weapon pits or to conduct experiments related to maintenance of the nation’s nuclear stockpile. The materials disposition program recovers plutonium from decommissioned weapons and processes it for eventual disposal or for burning as mixed oxide (MOX) fuel.
Almost all the plutonium at TA-55 has been recycled, having been recovered from previous TA-55 operations or from operations at other sites. But plutonium continually undergoes radioactive decay, and trace amounts of uranium, neptunium, and americium impurities accumulate in aged metal. These impurities must be removed before the material can be reused. In addition, the plutonium used for an experiment may have been alloyed, become oxidized, or been formed into a chemical compound; it too must be purified before reuse.
Thus, a significant portion of the work done at TA-55 involves chemical processing to produce pure plutonium metal or compounds such as the oxide (PuO2). Anion exchange, solvent extraction, and pyrochemical processing are the three production-scale techniques that are used extensively. Nitric and hydrochloric acid processing produces purified plutonium dioxide, which is then further processed by pyrochemical operations to produce very pure plutonium metal.
Nitric acid processing has been used over the last 30 years to process literally tons of plutonium. Hydrochloric acid processing has been used for the last 15 years, allowing for processing of a wider variety of plutonium materials. Pyrochemical processing was used extensively at the Rocky Flats Plant in Colorado and is still used to purify plutonium at TA-55. While all three processes are efficient and robust, they produce a prodigious stream of low-level and trans-uranic (TRU) waste. There are various repositories around the country for low-level waste, including one at Los Alamos. The Waste Isolation Pilot Plant (WIPP) in New Mexico is the nation’s repository for defense-related TRU waste. Several R&D successes at Los Alamos, however, have dramatically reduced the waste volume that results from these processes.
David L. Clark and Gordon Jarvinen of the Seaborg Institute and Cynthia Kowalczyk, Jim Rubin, and Mary Ann Stroud of Plutonium Manufacturing and Technology Division contributed to this issue.