To develop an electrochemical reduction technique for the reprocessing of nuclear fuels, the reduction behavior of UO2 at the cathode and the anode reactions were investigated in both CaCl2 and LiCl salt baths. In the CaCl2 at about 800 degrees C, UO2 was reduced into metal over the potential range < 0.6 V vs the Ca2+/Ca. The reduced uranium metal cohered due to the high temperature and a dense metal skin covered the surface of the UO2 disk sample. It prevented the transportation of oxygen from the inside to the bulk salt and the reduction often stopped with UO2 remaining inside. A significant underpotential deposition of calcium metal was observed. In the LiCl at 650 degrees C, UO2 was reduced into metal over the potential range < 0.15 V vs the Li+/Li. The UO2 disk sample was satisfactorily reduced because the LiCl melt could permeate into the sample. The current efficiency of UO2 reduction in the LiCl was much better than in the CaCl2. The anodic currents for oxygen and carbon oxide gas evolutions were verified in cyclic voltammograms of the platinum and glassy carbon electrodes. At the platinum surface, Pt3O4 and Li2PtO3 yielded in the CaCl2 and LiCl, respectively. (c) 2006 The Electrochemical Society.