Two Factors Important to the Criticality Potential of Spent Fuel in Geologic Repositories

摘要

Two factors important to the criticality potential of spent fuel in geologic repositories are: the residual fissile content of the fuel, and the extent to which geochemical processes might somehow separate and accumulate plutonium from other spent fuel materials. This paper presents the results of two calculational surveys defining conditions required for criticality. In the first, homogeneous spherical mixtures of spent fuel actinide oxides and water with water reflection are analyzed. Graphs of minimum critical mass vs duration of in-reactor exposure are presented. Parametric variations from a base case are explored, including the effects of initial enrichment, post exposure radioactive decay and addition of rock materials to the mixture. In the second study, homogeneous spherical mixtures devoid of water, containing plutonium and a neutronically optimized rock material, with a thick rock neutron reflector are analyzed. Graphs of Pu critical mass are presented as a function of concentration over the range from 2 to 100 g Pu/l. Parametric variations from a base case are explored, including effects of rock composition, exp 240 Pu content and uranium contamination of the plutonium. (ERA citation 06:013458)