A New Fuel Material for Once-Through Weapons Plutonium Burning

For the burning of plutonium derived from nuclear warheads, once-through type oxide fuels have been studied by considering their proliferation resistance and environmental safety as well as their technological backgrounds of fuel fabrication and reactors. From phase relations of ceramic materials and their chemical properties, it seems that a two-phase mixture of a fluorite-type phase and alumina has favorable characteristics as a once-through-type fuel of plutonium burning. It also seems that the fluorite-type phases such as thoria and fully stabilized zirconia are acceptable as host phases of plutonium because of high solid solubility of the actinide elements and fission products, irradiation stability, and chemical stability. The spent fuels finally obtained will become mineral-like waste forms, which could be buried under deep geological formations without further processing. From reactor burnup calculations with the use of the fuels, light water reactors (LWRs) with the larger volume ratio of moderator to fuel than 1.4, such as conventional LWRs, are considered to be suitable for the once-through plutonium burning. Furthermore, such LWRs can transmute nearly 99% of ²³⁹Pu and 85% of initial loaded weapons-grade plutonium. The quality of plutonium becomes completely poor in the spent fuels.