This study presents an experimental investigation on Zr separation from Zr-2.5Nb by anode potentiostatic electrorefining in LiCl-KCl-ZrCl4 0.5 wt. % at 773 K for irradiated CANDU pressure tube decontamination. By the ORIGEN-2 code calculation, radioactive characteristics were investigated to show that Nb-94 was the most significant radionuclide with an aspect of waste level reduction by electrorefining. Three electrorefining tests were performed by fixing the applied potential as −0.9 V (vs. Ag/AgCl 1 wt. %) at the anode to dissolve only Zr. A cathode basket was installed to collect detached deposits from the cathode. Electrorefining results showed Zr was deposited on the cathode with a small amount of Nb and other alloying elements. The chemical form of the cathode deposits was shown to be only Zr metal or a mixture of Zr metal and ZrCl, depending on the experimental conditions related to the surface area ratio of the cathode to the anode. It was determined that the Zr metal reduction at the cathode was attributed to the two-step reduction reaction of Zr4+/ZrCl and ZrCl/Zr.

Summary 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 Cl2/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.

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