Cyclic Voltammetry on Zirconium Redox Reactions in LiCl-KCl-ZrCl₄at 500°C for Electrorefining Contaminated Zircaloy-4 Cladding

This study examines zirconium electrochemical redox behaviors in LiCl-KCl-ZrCl 4 at 500°C. Cyclic voltammetries are conducted with tungsten working and counter electrode. Four oxidation peaks and three reduction peaks are observed and redox reactions which could contribute to each peak are determined based on electrolysis results and peak height changes of cyclic voltammogram according to scan rates and ranges. Zr(IV) could be reduced into ZrCl when cathode potential is more negative than −1.1 V (vs. 1 wt% Ag/AgCl) and ZrCl would be reduced into Zr metal if cathode potential become more negative than −1.2 V. ZrCl and Zr metal could be oxidized into mainly Zr(IV) in LiCl-KCl-ZrCl 4 (1 wt%). Zr(II) could exist in the molten salt but the concentration might be small because heights of cyclic voltammogram peaks related to redox reactions of Zr(II) are relatively small. Based on cyclic voltammetry results, suggestions for the electrorefining of irradiated Zircaloy-4 cladding are proposed. High cathodic current density is preferred to recover zirconium as a metal state and low anodic current density is required to prevent dissolution of elements which are more reductive than zirconium.