Zirconium metal recovery from irradiated radioactive zirconium alloy via chloride‐basedelectrorefining and thermal decomposition ofZrCl

Abstract

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.

Pulsed-Potential Electrodeposition of Zirconium in a Molten LiCl–KCl Salt: Improvements in the Selectivity and Adhesion Strength

“…48 According to the reference XRD data of the α-Zr metal, the intensities of the peaks corresponding to the crystal planes of ( 100) and ( 200) in the α-Zr metal are relatively weaker than the intensities of the nearby peaks. 15,45,49 The Zr peaks in the XRD pattern of R4-PPED generally follow this trend. However, the relative intensities of (100) and ( 200) for R3-PPED compared with those of the nearby peaks are definitely higher.…”

“…14 Accordingly, the electrodeposition and redox behavior of Zr in molten LiCl-KCl salt has been actively studied to develop a suitable process. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Until recently, there has been considerable progress in understanding the redox behavior of Zr in molten LiCl-KCl salt. On the other hand, the electrodeposition of Zr metal in molten LiCl-KCl salt is still a challenge since because of the co-deposition of insoluble zirconium monochloride (ZrCl) and the loss of deposits during retrieval from the molten salts.…”

“…On the other hand, the electrodeposition of Zr metal in molten LiCl-KCl salt is still a challenge since because of the co-deposition of insoluble zirconium monochloride (ZrCl) and the loss of deposits during retrieval from the molten salts. 14,15 Sakamura 16 attempted to deposit Zr metal on the Ta electrode, but ZrCl was co-produced during the process and the adhesion strength of deposits on the electrode was weak. Lee et al 17 reported similar results with the W electrode.…”

Optical monitoring of the anodic dissolution of zirconium and the agglomeration of potassium hexachlorozirconate during transpassive dissolution in molten LiCl–KCl salt

“…One promising methodology for recycling spent fuel Zr-alloy cladding is an electrometallurgical process that uses molten LiCl–KCl salt as a medium. 7–19 For such a process, the direct anodic dissolution of Zr-alloy cladding is the most straightforward strategy for administering Zr reactants into molten LiCl–KCl salts. 8,16 Since Zr-alloy cladding is generally composed of 97% or more of Zr; 8 it is essential to rigorously understand the anodic dissolution behavior of Zr in molten LiCl–KCl salt.…”