Zirconium Metal Recovery from Irradiated Radioactive Zirconium Alloy via Chloride-Based Electrorefining and Thermal Decomposition of ZrCl

Abstract

Chloride salt-based decontamination methods for neutron-irradiated radioactive zirconium alloys have been designed to directly recover metallic Zr. Previous studies have shown that ZrCl is co-deposited with Zr at a low current density on the cathode, while sparse and low-purity Zr is obtained with the application of a high current density. We propose a process to prepare high-purity Zr metal involving the electrochemical recovery of ZrCl and thermal decomposition of ZrCl to Zr. Electrodeposition of ZrCl in a LiCl-KCl-ZrCl4 system by controlling the cathode potential at -1.1 V (vs Ag/AgCl, -2.3 V vs Cl-2/Cl-) was performed at 723 K to produce ZrCl and confirm the morphology of deposition. Dense and layered depositions adhered to the cathode were introduced to a vacuum distillation furnace after washing with pyridine solvent. The optimized condition of the thermal decomposition process was deduced by experimental results using X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and inductively coupled plasma-optical emission spectrometry. Furthermore, the crystallographic phase transition of Zr into a face-centered cubic structure during the thermal decomposition was also observed by crystallographic analysis. Quantitative evaluation of electrodeposition of ZrCl and production Zr by thermal decomposition was discussed.