Electrorefining of Zirconium from Zircaloy-4 Cladding Hulls in LiCl-KCl Molten Salts

Pyroprocessing is one of the options for the effective treatment and recycling of spent nuclear fuel (SNF) owing to its economic advantage, environmental safety, and proliferation resistance of the nuclear fuel cycle. [1, 2] The head-end process of the pyroprocessing under development at KAERI includes disassembly and oxidative decladding steps, where cladding hull wastes are generated from the fuel rods. The hull wastes are presumably categorized into high-level wastes (HLW) due to traces of SNF residue and fission products that are implemented into the inner surface of the hulls. Thus, the reduction of the amount of HLW will be one of the key issues for the waste management of the pyroprocess. This study demonstrates the electrorefining process, which is able to recover Zr, which is a major component of the hull wastes such as Zircaloy-4 or Zirlo. Electrochemical behaviors of Zr in LiCl-KCl molten salts are examined using cyclic voltammetries and chronoamperometries. An anhydrous LiCl-KCl eutectic (99.99 % purity, Sigma-Aldrich) was used as the electrolyte at 500 °C by adding 4 wt % ZrCl4 for Zr electrorefining. All the experiments were performed in an Ar-purging glove box, where the oxygen and moisture are controlled below 5 ppm. To examine the electrochemical behavior of Zr, cyclic voltammetries and chronoamperometries were performed using a pure Zr rod as an anode, a tungsten wire cathode, and a Ag/AgCl reference electrode. Subsequently, the Zr anode was replaced with Zircaloy-4 hulls to recover Zr by electrorefining. The Zr deposits were characterized by SEM-EDX, XRD, and ICP-AES. Figure 1 shows cyclic voltammograms of tungsten wire cathodes in LiCl-KCl molten salts at 500 °C. For Zr rod anodes in the absence of ZrCl4, the residual current was less than 0.4 mA with no apparent anodic and cathodic reactions associated with salt components within the potential range of-0.2 V to-1.4 V. However, in the presence of 4 wt % ZrCl4 (red dashed line), several peaks