Cyclic Voltammetry on Zirconium Redox Reactions in LiCl-KCl-ZrCl₄at 500°C for Electrorefining Contaminated Zircaloy-4 Cladding

Abstract

This study examines zirconium electrochemical redox behaviors in LiCl-KCl-ZrCl 4 at 500 • C. Cyclic voltammetries are conducted with tungsten working and counter electrode. Four oxidation peaks and three reduction peaks are observed and redox reactions which could contribute to each peak are determined based on electrolysis results and peak height changes of cyclic voltammogram according to scan rates and ranges. Zr(IV) could be reduced into ZrCl when cathode potential is more negative than −1.1 V (vs. 1 wt% Ag/AgCl) and ZrCl would be reduced into Zr metal if cathode potential become more negative than −1.2 V. ZrCl and Zr metal could be oxidized into mainly Zr(IV) in LiCl-KCl-ZrCl 4 (1 wt%). Zr(II) could exist in the molten salt but the concentration might be small because heights of cyclic voltammogram peaks related to redox reactions of Zr(II) are relatively small. Based on cyclic voltammetry results, suggestions for the electrorefining of irradiated Zircaloy-4 cladding are proposed. High cathodic current density is preferred to recover zirconium as a metal state and low anodic current density is required to prevent dissolution of elements which are more reductive than zirconium.

Investigation on the reaction progress of zirconium and cuprous chloride in the LiCl–KCl melt

“…Their corresponding anodic peaks C and E are found at around À0.85 and À0.78 V, respectively. The electrochemical behavior of Zr(IV) in LiCl-KCl melt has been studied by several investigators [2,5,7,9,23]. Sakamura [7] assumed that the reduction peaks E 0 , C 0 , D 0 are corresponding to the reactions given in equations (2),(3), (4) and (6), respectively.…”

“…The chosen of the liquid alloy anode can not only reduce the operating temperature, but also expect to provide a low cost and semi-continuous process for production nuclear grade zirconium. The electrorefining and electrochemical process of Zr has been studied in various molten salt systems, including all-chloride baths such as LiCl-KCl-ZrCl 4 [2,[5][6][7], KCl-ZrCl 4 [8,9], all-fluoride baths such as LiF-NaF-KF-ZrF 4 and K 2 ZrF 6 [10,11], LiF-KF-ZrF 4 [3], LiF-CaF 2 -ZrF 4 [12] and chloridefluoride-mixed baths such as KCl-NaCl-ZrF 4 [13], KCl-NaCl-K 2 ZrF 6 [8,13,14], and LiCl-KCl-K 2 ZrF 6 [15] at temperature ranges of 450 C to 750 C. However, the operating temperature of the all-fluoride baths is 100 C $ 200 C higher, and the corrosion issue is more severe compared to those of all-chloride baths. In consideration of the melting point of liquid alloy anode and a moderate experimental condition, the Zr electrorefining process is proposed in LiCl-KCl-ZrCl 4 molten salt at 500 C in the initial stage of research.…”

“…In consideration of the melting point of liquid alloy anode and a moderate experimental condition, the Zr electrorefining process is proposed in LiCl-KCl-ZrCl 4 molten salt at 500 C in the initial stage of research. However, the starting zirconium compound, ZrCl 4 , usually sublimates at 331 C [1,5], and some will be lost if it is directly introduced into the salt. Thus, the preparation of the molten salt with the content of ZrCl 4 has become one of the most challenges in the research of electrorefining zirconium in the molten salt.…”

Anodic behaviour of Cu, Zr and Cu–Zr alloy in molten LiCl–KCl eutectic

“…Zr alloys, which are widely used as cladding hull materials for light water reactors, contain approximately 98% of Zr with other alloying elements such as Sn, Fe and Cr for zircaloy-4 and Sn, Nb and Fe for Zirlo [3]. However, after being used for a certain number of years, Zr alloys would achieve its service life due to wear, corrosion and other causes, resulting in a large amount of scrap Zr alloy [4]. Depending on its radioactivity and the pollution to the environment, scrap Zr alloy would be disposed of as intermediate or low-level waste, causing serious problems for storage and handling.…”

Investigation of the reaction progress between stannous chloride and zirconium in molten LiCl–KCl

“…2 The electrochemical rening of molten chlorides with ZrCl 4 has been developed as a promising option for zirconium rening from impure zirconium metal, alloy or spent metal fuels. However, there is a big challenge for preparation of the molten LiCl-KCl-ZrCl 4 as an electrolyte, if ZrCl 4 is directly introduced into the salt since it is easy to be atomized due to its low boiling point of 331 C. 3,6,7 Several investigators 7-10 have attempted to prepare the molten chlorides by the oxidation of metal with CdCl 2 in the LiCl-KCl melt, and this method also can eliminate any gasication of the metal chloride with low boiling point because the chloride will preferably dissolve in the melt rather than gasify into the air. 5 The method would not only reduce the operating temperature, but also provide a low cost and semi-continuous process for the production of the nuclear grade zirconium.…”