Liquid Bi pool is a candidate electrode for an electrometallurgical process in the molten LiCl-KCl eutectic to treat the spent nuclear fuels from nuclear power plants. The electrochemical behavior of Bi3+ ions and the electrode reaction on liquid Bi pool were investigated with the cyclic voltammetry in an environment with or without BiCl3 in the molten LiCl-KCl eutectic. Experimental results showed that two redox reactions of Bi3+ on inert W electrode and the shift of cathodic peak potentials of Li+ and Bi3+ on liquid Bi pool electrode in molten LiCl-KCl eutectic. It is confirmed that the redox reaction of lithium with respect to the liquid Bi pool electrode would occur in a wide range of potentials in molten LiCl-KCl eutectic. The obtained data will be used to design the electrometallurgical process for treating actinide and lanthanide from the spent nuclear fuels and to understand the electrochemical reactions of actinide and lanthanide at liquid Bi pool electrode in the molten LiCl-KCl eutectic.

Molten salt solutions consisting of eutectic LiCl-KCl and concentrations of samarium chloride (0.5 to 3.0 wt%) at 500℃ were analyzed using both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CV technique gave the average diffusion coefficient for Sm3+ over the concentration range. Equipped with Sm3+ diffusion coefficient, the Randles-Sevcik equation predicted Sm3+ concentration values that agree with the given experimental values. From CV measurements; the anodic, cathodic, and half-peak potentials were identified and subsequently used as a parameter to acquire EIS spectra. A six-element Voigt model was used to model the EIS data in terms of resistance-time constant pairs. The lowest resistances were observed at the half-peak potential with the associated resistance-time constant pairs characterizing the reversible reaction between Sm3+ and Sm2+. By extrapolation, the Voigt model estimated the polarization resistance and established a polarization resistance-concentration relationship.

LiCl-KCl 용융염에서 광학적으로 투명한 텅스텐 망으로 제작된 작업전극에 대해 사마륨의 전기화학적 거동을 Cyclic voltammetry와 Potential step chronoabsorptometry의 전기화학적 및 분광전기화학적 방법으로 조사하였다. Cyclic voltammogram 으로 결정된 Sm3+/Sm2+의 산화환원 반응의 가역성을 기반으로 형식전위와 확산계수를 계산하여 각각 –1.99 V vs. Cl2/Cl- 와 2.53×10-6 cm2·s-1를 얻었다. 작업 전극에 –1.5 V vs. Ag/AgCl (wt%)로 전압을 인가하여 측정한 Chronoabsorptometry 를 통해 사마륨 이온의 특성 파장으로 Sm3+에 대해 408.08 nm, Sm2+에 대해 545.62 nm를 확인하였다. Voltammogram에서 얻은 환원 피크 전압과 산화 피크 전압을 이용하여 Potential step chronoabsorptometry를 수행하였다. 545.63 nm의 흡광 피크 값을 분석하여 2.15×10-6 cm2·s-1의 확산계수를 얻었으며 이 값은 동일한 온도에서 Cyclic voltammtry 분석으로 얻은 값과 큰 차이를 보이지 않았다. 실험결과로부터 고온 용융염에서 광학적으로 투명한 작업전극을 이용한 분광전기화학적 방 법이 용융염에 용해된 이온의 종류를 확인하며 전기화학적 거동을 조사하는데 유용한 도구로 활용될 수 있음을 확인하였다.

Densities of molten salt mixtures of eutectic LiCl-KCl with UCl3, CeCl3, or LaCl3 at various concentrations (up to 13 wt%) were measured using a liquid surface displacement probe. Linear relationships between the mixture density and the concentration of the added salt were observed. For LaCl3 and CeCl3, the measured densities were significantly higher than those previously reported from Archimedes’ method. In the case of LiCl-KCl-UCl3, the data fit the ideal mixture density model very well. For the other salts, the measured densities exceeded the ideal model prediction by about 2%.