Electrochemical studies and analysis of 1–10 wt% UCl3 concentrations in molten LiCl–KCl eutectic

Abstract

Three electrochemical methods – cyclic voltammetry (CV), chronopotentiometry (CP), and anodic stripping voltammetry (ASV) – were applied to solutions of up to 10wt% UCl3 in the molten LiCl–KCl eutectic salt at 500°C to determine electrochemical properties and behaviors and to help provide a scientific basis for the development of an in situ electrochemical probe for determining the concentration of uranium in a used nuclear fuel electrorefiner. Diffusion coefficients of UCl4 and UCl3 were calculated to be (6.72±0.360)×10−6cm2/s and (1.04±0.17)×10−5cm2/s, respectively. Apparent standard reduction potentials were determined to be (−0.381±0.013) V and (−1.502±0.076) V vs. 5mol% Ag/AgCl or (−1.448±0.013) V and (−2.568±0.076) V vs. Cl2/Cl− for the U(IV)/U(III) and U(III)/U redox couples, respectively. In comparing this data with supercooled thermodynamic data to determine activity coefficients, the thermodynamic database used was important with resulting activity coefficients ranging from 2.34×10−3 to 1.08×10−2 for UCl4 and 4.94×10−5 to 4.50×10−4 for UCl3. Of anodic stripping voltammetry and cyclic voltammetry anodic or cathodic peaks, the CV cathodic peak height divided by square root of scan rate was shown to be the most reliable method of determining UCl3 concentration in the molten salt.