Process modeling of plutonium conversion and mixed-oxide fuel fabrication for plutonium disposition

In an effort to reduce the global stockpile of nuclear explosive devices, s imilar to 50 tonnes of weapons-grade plutonium have been declared surplus t o national security needs by the United States. This surplus, located at si x sites within the U.S. Department of Energy complex (the Hanford Site, Ida ho National Engineering and Environmental Laboratory, Los Alamos National L aboratory the Pantex Plant, the Rocy Flats Environmental Technology Site, a nd the Savannah River Site) must now be rendered unattractive for use in nu clear weapons. The goal is that this drive will be concurrent with similar activities in Russia. One method currently under investigation is the conve rsion of the plutonium metal into mixed-oxide (MOX) reactor fuel. Approxima tely 35 tonnes of the surplus plutonium is in a form suitable for fabricati on into MOX fuel. This fuel would be used in currently operating reactors f or power production. Two processes are currently under consideration for the disposition of the 35 tonnes of surplus plutonium through its conversion into fuel for power p roduction. These processes are the Advanced Recovery and Integrated Extract ion System (ARIES) process, by which Plutonium metal is converted into a po wdered oxide form, and MOX fuel fabrication, where the oxide powder is comb ined with uranium oxide powder to form ceramic fuel. Because it is envision ed that plutonium disposition will occur concurrently in the United States and Russia, the timely disposition of the plutonium is deemed important to national security. However, the need for quick disposition must be tempered by cost considerations and constraints on the reactors that will ultimatel y use the fuel. This study was undertaken to determine the optimal size for both the pit conversion and MOX fabrication facilities, whereby the 35 ton nes of plutonium metal will be converted into fuel and burned for power. Pr oper sizing of the facilities will help avoid unnecessary delays and excess ive costs and thus is important in the success of the disposition mission. The bounding conditions used were a plutonium concentration of 3 to 7%, a b urnup of 20 000 to 40 000 MWd/tonnes HM, a core fraction of 0.1 to 0.4, and the number of reactors ranging from 2 to 6. Using these boundary condition s, the optimal plutonium concentration was found to be 7%. This resulted in an optimal throughput ranging from 2000 to 5000 kg/yr of plutonium. The da ta showed minimal costs (based solely on facility size and required manpowe r) resulting from throughputs in this range, at 3840, 2779, and 3497 kg/yr of plutonium, which resulted in a facility lifetime of 9.1, 12.6, and 10.0 yr, respectively.