New Oxygen-Evolving Inert Anode Made of Nickel Metal Applicable to Electrolytic Reduction of UO2 in LiCl-Li2O Melt

The development of an O-2-evolving inert anode is of crucial importance for the electrolytic reduction process of oxide nuclear fuels using LiCl-Li2O melts at 923 K. As scaled-up anodes for practical use, metallic anodes are preferable. In this study, Fe, Ni, and Fe-Ni metals were electrochemically examined and the results indicate that Ni metal coated with NiO is a promising anode material. Ni metal is easily dissolved in LiCl in the form of Ni2+ ions over the potential range >2.3 V (vs Li+/Li). However, in LiCl-Li2O, after NiO was formed at the surface of Ni metal, the dissolution of Ni2+ ions was inhibited and O-2 evolution occurred over the potential range >2.6 V at a high current density. Oxygen gas was stably evolved during current-controlled electrolysis at currents up to 0.6 A (0.94 A cm(-2)) performed using a Ni rod anode of 3 mm diameter, which was heat-treated in air and covered with a MgO protective tube at around the interface between the melt and the cover gas. Moreover, it was demonstrated that about 100 g of UO2 was completely reduced to the metallic form in 8.7 h using a Ni plate anode.