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

Abstract

The electrochemical reduction of UO2 to U metal has been investigated in both Fluidized Cathode (FC) and Metallic Cavity Electrode (MCE) cell arrangements. Differences in the local concentration of O2− where the reduction takes place influnces the reduction potential. The fleeting contact of UO2 particle contact with the current collector in case of the FC results in much less O2− buildup compared to MCE. Consequently, UO2 reduction occurs over a range of potentials in the FC and may involve separate two 2-electron steps compared to one apparent 4-electron step in the MCE. It is proposed that there are three discrete periods during the FC reduction process. The first is an induction period during which reduced uranium particles gradually adhere to the tungsten current collector. The second is reduction associated with a rapid growth in electrode area and consequent increase in current. The third is a slower reduction of the remaining oxide in the melt. Complete reduction of metallic U is achieved at −2.2 V (vs. Ag/Ag+) with an estimated faradaic current efficiency of >92%.