Diffusion-Based Kinetic Model for the Electroreduction of UO2 in LiCl-Li2O Melt

Abstract

The reduction of UO2 in molten salt can be achieved either by lithium or by electrolysis, but its rate-determining step remains ambiguous. In this study, the use of non-conductive porous magnesia filter as cathode basket has been proved to be crucial in distinguishing the diffusion of solvated lithium and O2− ions. Kinetic models based on diffusion with three typical geometries are derived, and the validity of the obtained equations has been checked. The obtained DC0 of each model is compared directly, and it demonstrates that the diffusion of O2− ions from loaded oxides in cathode to the bulk molten salt determines the reduction rate during electrolysis, despite the occurrence of Li deposition. With the DC0 constant, the time at which complete conversion of UO2 in molten LiCl occurs under a number of conditions (oxides porosity, loading size, cathode geometries, and etc.) can be estimated.