Plutonium Finishing Plant. Interim plutonium stabilization engineering study

Abstract

The Plutonium Finishing Plant (PFP), located at the Hanford Site in southeastern Washington, and operated by the Westinghouse Hanford Company (WHC) for the U.S. Department of Energy (DOE), contains plutonium-bearing material from 40+ years of processing plutonium for weapons production, research needs, and reactor fuel. In 1989 the plant was shut down, and DOE now wants to prepare these residues for storage. However, further processing will be required to stabilize many of these materials for interim storage (< 50 years).This engineering study was performed by the Pacific Northwest Laboratory (PNL) for WHC to evaluate the currently available and known technologies at Hanford and elsewhere for processing plutonium-bearing materials into a stable form. The inventory of plutonium-bearing materials stored in various vaults at the PFP was received from WHC in an unclassified form for use in this study. Table S. 1 summarizes that inventory. PNL staff conducted the study by compiling information on the technologies that would be considered, performing an initial screening, developing process descriptions, and subcontracting with an independent review team to evaluate and rank the processes. This independent review team consisted of representatives from the national laboratories and industry who are considered to be experts in the subject matter.Once PNL completed its analysis, the independent review team began a review of the technologies that passed the initial screening. Specifically, the goals of the independent review were to ensure that the appropriate set of technologies was considered, to identify any technologies that may have been overlooked by PNL, and to identify any significant issues relating to the technologies considered.The process for conducting the independent technical review involved the following activities: a presentation on specific technical information on each candidate technology by PNL staff to the independent review team a screening of the technologies that were initially identified to establish the applicable technologies a rating of the feasible alternatives against a predetermined set of criteria. These criteria consisted of technical feasibility, effluent and by-product disposition, worker safety, cost, and time required for implementing the technology and processing the plutonium. Note that the cost data are very, very preliminary and that a rigorous procedure for estimating costs was not applied in a consistent manner.Based upon its findings, the independent review team identified the preferred technologies for each waste stream (Le., liquid or solid effluents) as summarized in Table S.2. These technologies were, in general, preferred based on meeting the criteria of availability, flexibility, and technical maturity. 2. The preferred processes should be developed and finalized on an expedited basis. In addition, the development of the molten salt oxidation process followed by plutonium oxide recovery should be expedited. This process was the only technology identified that had multi-pu...

Stabilizing plutonium materials at Hanford: systems engineering for PFP transition project effort on DNFSB 94-1

“…the combustible material is introduced with oxygen under the surface of a molten salt bath consisting of a suitable mixture of carbonates, chlorides, or sulfates of sodium. potassium, lithium or calcium (Sevigny et al 1995). The molten salt is both the heat transfer medium and the reaction medium for the combustibles with oxygen to produce an off gas of carbon dioxide.…”

“…The acid gases produced by the pyrolysis of halogenated organic compounds react with the alkaline carbonates in the molten salt bath to form the corresponding salt. An ash consisting of dissolved solid and retained particulates builds up in the melt and is continuously removed to maintain an ash concentration of less than 20 wt% in the melt (Sevigny et al 1995). At an ash concentration of less than 20 wt% the fluidity of the melt necessary for contacting the feed material with oxygen, wetting the material and heat transfer to the material is maintained.…”

“…The molten salt oxidation process is operated at 800°C to IOOO' C and at atmospheric pressure with a residence time in the molten salt bath of hours (Sevigny et al 1995). Air is added in excess of 20% to 30% of that required for combustion.…”

“…There are 251 containers of polycubes (Sevigny et al 1995). Polycubes are small blocks of polystyrene containing dispersed plutonium or uranium oxide.…”

“…Polycubes heated above the softening point are fed to the molten salt oxidation unit using a pneumatic injector (Sevigny et al 1995). The rate of oxidation is controlled by regulating the oxygen supply to the molten salt bath.…”