Preliminary Study of Optimization of Normal Pulse Voltammetry for Actinide Measurement in Molten Salt Electrorefiners Using LiCl-KCl-UCl3-MgCl2 as a Surrogate Salt

Abstract

Normal pulse voltammetry has been applied and optimized to develop correlations between diffusional current and concentration for UCl3 and MgCl2 in molten eutectic LiCl-KCl. This method was selected to mitigate working electrode area growth in concentrated molten salt mixtures in which a fairly wide potential range is needed to analyze all actinides. MgCl2 has been selected as a surrogate for PuCl3 based on similar standard reduction potential. Diffusional current plateaus were successfully attained by adjusting the step size to 0.03 V. Relaxation time of 15 seconds was found to be sufficient to recover after each pulse. A matrix of mixtures were prepared and tested with UCl3 concentration varying between 1 to 9 wt% and MgCl2 concentration varying between 0.3 and 1.5 wt%. The measured diffusional currents correlated well with concentration and matched a model that includes both diffusion and migration from the bulk molten salt to the working electrode surface. Concentrations of MgCl2 do not appear to affect the UCl3 diffusional current and vice versa. This is, thus, a promising method for simultaneous analysis of UCl3 and PuCl3 in molten salt electrolytes used for spent nuclear fuel electrorefining.