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In this paper, the thermodynamic activity of two lanthanide chlorides (CeCl 3 and NdCl 3 ) in molten LiCl-KCl eutectic salt measured using open circuit potentiometry has been reported. Activity coefficient of CeCl 3 was found to be strongly dependent on the concentration of CeCl 3 in a concentration window of up to 4.66 mol % CeCl 3 . The activity coefficient of NdCl 3 could not be measured due to the uncertainty in NdCl 3/ NdCl 2 molar ratio in the salt, however the thermodynamic activity was measured relative to a 5 mol% Ag∣AgCl reference electrode. The concurrent analysis of data presented in this paper along with previously published activity data for LaCl 3 and GdCl 3 demonstrates that the departure from ideal solution behavior shown by the rare earths chlorides correlates with ionic size of underlying rare earth element. The smaller the ionic size of the species under consideration, the greater its departure from ideal solution behavior. Further, using the activity data of all four rare earth chlorides, an ionic size dependent correlation was developed. Using this empirical correlation, it is possible to calculate the activity of all species from La(Z = 57) to Gd (Z = 64) for a concentration of up to 2.5 mol% rare earth chloride in LiCl-KCl molten salt at 773 K. [ABSTRACT FROM AUTHOR]

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]

Several electrochemical techniques, including cyclic voltammetry (CV), chronopotentiometry-open circuit potential (CP-OCP), chronoamperometry (CA) and normal pulse voltammetry (NPV) were applied to the eutectic LiCl-KCl melt containing LaCl 3 and ThCl 4 at 773K. The dependence of diffusion coefficient of La(III) on concentration of LaCl 3 was investigated by using CV, CP and CA. As the concentration of LaCl 3 increases, the D La(III) value obtained from CV gradually decreases, while the values derived from CA and CP exhibit a dome-shaped variation trend. In the LiCl-KCl-LaCl 3 -ThCl 4 system, the diffusion coefficients of La(III) and Th(IV) are both approximately constant regardless of changes in the composition of LaCl 3 and ThCl 4 . Concentration correlations were developed for LaCl 3 and ThCl 4 using the normalized CV peak heights in addition to the diffusion-limited relationships for CV, CA and NPV. NPV was found to be superior for the concentration prediction over the range studied in this work. [ABSTRACT FROM AUTHOR]

2D and 3D numerical models for electrorefining used in pyroprocessing have been developed by Seoul National University with the Korea Atomic Energy Research Institute and University of Idaho with the Idaho National Laboratory, respectively. To validate these models, numerical simulations are conducted on a rotating cylindrical Hull cell for copper deposition in a sulfuric acid solution. The primary current density distribution along the cathode is compared to an empirical equation of Madore. The 2D and 3D modeling results of the tertiary current density distribution along the cathode were compared. The numerical modeling results of the 2D and 3D models match each other well. In addition, the modeling results of the 3D model on the tertiary current density distributions according to the applied current densities are compared to the experimentally measured distributions. There are some discrepancies between the modeling results and experimental data. The discrepancies could be mainly explained by the hydrodynamic effect of Luggin probes used for measuring the overpotential distribution. At low Reynolds number, Luggin probes could act as a static mixer improving mass transfer near working electrode. In contrast, at high Reynolds number, Luggin probes could act as a flow obstacle dissipating flow kinetic energy. [ABSTRACT FROM AUTHOR]