Reduction of ZrO2 during SNF Pyrochemical Reprocessing

Abstract

Reduction of ZrO2 by lithium during electrolysis of LiCl-KCl-Li2O melt at 650 °C was studied using a set of physicochemical methods of analysis. Influence of ZrO2 in the space near a molybdenum cathode on the kinetics of the cathode process was established. Possible variations of the electrode reaction associated with the zirconium reduction were proposed. The appearance of ZrO2 in the cathode space resulted in consumption of reduced lithium and in increase in the potential relaxation time of the molybdenum cathode after cathode polarization. Long-term galvanic impulse electrolysis of LiCl-KCl-Li2O melt at 650 °C was carried out using the molybdenum cathode which was immersed into the ZrO2 powder. According to the X-ray fluorescence analysis as well as the method of nuclear reactions the reduction product was presented by the ZrO2, Li2ZrO3, Zr3O phases. Additionally, by alloying the reduction product with tin, the ZrO2 reduction degree to metallic zirconium was estimated, which was close to zero. It was assumed that the main pathway for the appearance of the metallic zirconium in the ZrO2 reduction product during electrolysis of the LiCl-KCl-Li2O melt was direct electroreduction of dissolved zirconium in the melt.