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Abstract Electrochemical methods have been developed to measure metal ion concentrations in spent nuclear fuel electrorefiner by correlating concentration with current response. Analytes UCl 3 and GdCl 3 were studied in LiCl-KCl eutectic solvent at 773 K. A mixture matrix, which consisted of varying concentrations of UCl 3 and GdCl 3 from 1 to 10 wt% and from 1 to 3 wt%, respectively, was tested. Optimized normal pulse voltammetry (NPV) measurements were made on this mixture matrix and used for the concentration correlations. The accuracy of the prediction was improved by including solution resistance compensation and minimizing the working electrode surface area. The presence of GdCl 3 showed no effect on the U3+ NPV reduction current, but high U concentrations affected the Gd3+ NPV reduction current. This is speculated to be due to increased migrational current in the molten salt mixture. The average relative measurement errors obtained were 1.6% and 2.7% for UCl 3 and GdCl 3 respectively. [ABSTRACT FROM AUTHOR]

One of the major sources of error for electroanalytical measurements in high-temperature molten salts is from the measurement of the working electrode (WE) area. A glass sealed working electrode (GSWE) was developed in order to set the exposed area of tungsten and reduce the error associated with WE area. The insulating property of the glass while in contact with molten salt was verified by observing the independence of electrochemical signals with adjustments in the WE position. The integrity of the glass coating was also confirmed by observing the stability of electrochemical signals (±1.9%) over several hours. Cyclic voltammetry (CV) and normal pulse voltammetry (NPV) were applied at 10 different concentrations of UCl 3 . Above 0.17 mol dm −3 UCl 3 , the electrochemical signals from CV and NPV deviate significantly from linearity with concentration, but in opposite directions. A shift from reversible to quasi-reversible behavior and migration are theorized to cause the non-linearity for CV and NPV, respectively. A model is proposed to account for migration in NPV resulting in a significant error reduction in the electrochemical concentration measurement. [ABSTRACT FROM AUTHOR]

Abstract Direct electrolytic reduction (DER) of UO 2 utilizes a molten LiCl-Li 2 O electrolyte operating at 650 °C.Productive processes at the cathode are UO 2 and Li 2 O reduction (followed by metallothermic reduction of UO 2 by Li metal). Non-productive reduction current has been observed that could be attributed to impurities produced from interaction of the salt with water. Cyclic voltammetry (CV) scans of molten mixtures of LiCl containing Li 2 O, LiOH, and/or Li 2 O 2 indicate that LiOH is the primary cause of reduction current preceding UO 2 and Li 2 O reduction. LiOH reduction appears as a broad soluble-soluble transition and forms a pre-reduction plateau characteristic of micro-electrode reactions. Electrochemical response to LiOH in the salt is reduced with addition of Li0, providing a practical approach to eliminating LiOH from LiCl-Li 2 O salt before the DER process. Generation of H 2 gas was detected while heating Li0 with LiCl-Li 2 O-LiOH, consistent with a reaction mechanism where LiOH reduction causes formation of Li 2 O and H 2. [ABSTRACT FROM AUTHOR]

Rare earth oxides in spent oxide fuel from nuclear plants have poor reducibility in the electrochemical reduction process due to their high oxygen affinity and thermodynamic stability. Here, we demonstrate that the extent of their reduction can be enhanced via co-reduction of NiO in a Li 2 O–LiCl electrolyte for the electrochemical reduction of a simulated oxide fuel (simfuel). First, the electrochemical behaviors of Nd 2 O 3 , NiO, and Nd 2 O 3 –NiO were studied by cyclic voltammetry and voltage control electrolysis. Then, the electrochemical reduction of the simfuel containing UO 2 and rare earth oxides (Nd 2 O 3 , La 2 O 3 , and CeO 2 ) was conducted in molten LiCl salt with 1 wt.% Li 2 O via the co-reduction of NiO. The extent of reduction of the rare earth oxides was found to be significantly improved. [ABSTRACT FROM AUTHOR]

Understanding the electrochemical properties of rare earth elements is important for developing efficient techniques for separating rare earth elements from actinides recovered during the electrodeposition process. In this study the cyclic voltammetry for lanthanum in molten LiClKCl eutectic was recorded at 773 K for different scan rates and different bulk concentrations. A model accounting for mass transport, kinetics and adsorption was applied to analyze the experimental data via performing a nonlinear least squares fit. The results of the simulation are compared against the results of a conventional analysis of the cyclic voltammograms and against the existing literature. At the scan rates used, the reduction/oxidation process is quasi-reversible. The values of diffusivities derived from simulation were larger than the ones derived commonly using equations for diffusion-limited processes. However, those equations were derived based on an assumption of reversibility. This simulation-based approach may provide a more accurate option for analyzing systems that do not exhibit reversibility. [ABSTRACT FROM AUTHOR]