Separation of Zr from Zr-2.5Nb by Electrorefining in LiCl-KCl for Volumetric Decontamination of CANDU Pressure Tube

Abstract

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.

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

“…Some studies reported that pure Zr metal could be electrochemically deposited on inert electrodes by a constant-potential method. [18][19][20] However, the adhesion strength of deposits in their studies was also poor. Thus, detached precipitates in the molten salt should be collected by the catch crucible or the desalting process.…”

“…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.…”

“…Currently, reliable strategies are limited to indirect approaches, such as depositing an intermetallic compound with other metals 10,16,22,[34][35][36] using active metal electrodes, or the ZrCl 20 instead. These strategies may improve the adhesion strength of the deposit, but have the disadvantage of requiring additional chemical processes to convert to Zr metal.…”

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 Zralloy cladding is an electrometallurgical process that uses molten LiCl-KCl salt as a medium. [7][8][9][10][11][12][13][14][15][16][17][18][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.…”

“…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.…”