Electrorefining of HANA-4 Cladding Scrap in LiCl-KCl Salts for Volumetric Decontamination of Irradiated Cladding Containing Nb-94

Abstract

Nb-94, an activation product in irradiated cladding, is a major concern in geological disposal. As the Nb-94 is distributed throughout the cladding, volumetric decontamination should be applied to separate between Zr and Nb. In this study, the radiological characteristics of irradiated HANA-4 cladding were investigated using the ORIGEN-ARP code to derive a decontamination factor for Nb-94, 11. The electrochemical behavior of Nb was evaluated by cyclic voltammetry using low NbCl5 concentrations (0.15 and 0.5 wt. %) in LiCl-KCl at 773 K. Nb has a complex redox behavior but it was found the nobler tendency could be utilized for Zr electrorefining. Two electrorefining tests were performed by applying constant potentials of -0.85 V and -1.2 V (vs. Ag/AgCl 1 wt. %) at the anode and cathode, respectively. From the anodic test, Zr metal was obtained at the bottom of the salt, by two-step reactions among Zr4+ ,Zr2+, and Zr. Meanwhile, ZrCl and Zr were co-recovered as deposits in the cathodic test. The results revealed good separation performance between Zr and Nb. The Nb concentrations were 2.1 and 20.3 ppm in the product from the anodic and cathodic test, respectively, supporting feasibility of satisfying the radioactivity concentration limits of Gyeongju Disposal Facility.