Electrochemical Reduction of UO2 to U in LiCl-KCl Molten Salt Eutectic Using the Fluidised Cathode Process

Abstract

The electrochemical reduction of UO2 to U metal using a fluidised cathode process [1] has been investigated. This has relevance for the pyroprocessing of mixed oxide spent fuel from certain types of nuclear power stations. Considering voltammetry alongside a predominance diagram for the system, the reaction path-way for both a fluidised cathode process and a packed metallic cavity electrode precursor was studied. The route the reduction process follows depends on pO2- and potential, which is highly influenced by the process used to reduce the metal oxide and its form. The main reduction potential using the fluidised cathode appeared to be -2.2 V (vs. Ag/Ag+). Faradaic current efficiency was found to be ~ 92 %. The reduction process is split into three stages; the first where a seeding process takes place at a low potential to allow for the reduced uranium particles to be deposited onto the tungsten current collector; the second where rapid reduction of UO2 particles occurs with a growth in electrode size accompanied by an increase in current being passed; and the third where diminishing current is associated with reduction of the residual oxides in the melt takes place.