A Quantitative Comparison of Solidification Analysis for Single-Component and Mixed-Oxide Fuels

An important question to the liquid-metal fast breeder reactor safety program is a description of molten fuel dynamics, or, more specifically, whether fuel will freeze locally on structural material within the reactor core, preventing dispersal and nuclear shutdown, or in the extremeties of the fuel assembly. In this Note, a comparison is made between the solidification processes for single-component (i.e., UO₂) and mixed-oxide fuel [i.e., (U, Pu)O₂] by solving a Stefan-type problem for both pure and binary alloy solidification. Analytic calculations indicate that the freezing rate of the mixed fuel is not significantly different from that for the single-component system; thus, single-front analysis may be used for such mixed-oxide fuels in assessing safety questions associated with solidifacation phenomena.