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Electrochemical impedance spectroscopy (EIS), linear polarization (LP), Tafel and cyclic voltammetry (CV) were performed to investigate the exchange current density (i 0) of U/U 3+ reaction in LiCl-KCl eutectic salt under different UCl 3 concentrations (0.5 wt%-4 wt%) and temperature conditions (723 K-798 K). The EIS spectra were measured by applying minimum overpotential from equilibrium potential and fitted to the proposed equivalent circuit. From the EIS experiments, the calculated values of i 0 were ranging from 0.0054 A cm-2 to 0.102 A cm-2. For the LP and Tafel methods, i 0 values were determined from the linear fitting at small and large overpotential ranges of the current-potential curves. The measurement for i 0 via CV was done analogously to the LP method. All i 0 values have the linear trend with the change of concentration and temperature; however, these values measured by LP, Tafel, and CV methods are greatly influenced by the change in electrode surface area. Overall, i 0 agreed within 33% relative error range with the EIS method being the most consistent and accurate in comparison to reported literature values. Dimensionless analysis was done on the EIS data sets providing insightful correlations for prediction of i 0 under various experimental conditions.

Thermodynamic and electrochemical properties of cerium in LiCl-KCl eutectic salt have been measured and studied at different concentrations (0.5 -4 wt%) and temperatures (698 K -798 K) via both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques as a part of developing a fundamental understanding and methodology in materials detection and accountability for pyroprocessing technology. CV experiments were performed to determine the diffusion coefficient and apparent standard potential of CeCl 3 on the tungsten working electrode. The diffusion coefficient was calculated by using Delahay equation, and raging from 0.48 × 10 −5 to 1.01 × 10 −5 cm 2 s −1 . Results reveal that the calculated diffusion coefficient of CeCl 3 in the salt follows the Arrhenius temperature relationship and it is weakly affected by the changes in concentration of CeCl 3 . The apparent standard potentials were calculated from peak potentials showing linear relationship with temperature. Exchange current density values of Ce 3+ /Ce couple in the salt were obtained from EIS experiments, ranging from 0. Pyroprocessing technology has been proposed as another promising method for the recovery and recycle of uranium and actinide elements from the used nuclear fuel. An essential step in this technology is the electrorefining process in which uranium is selectively recovered by using solid cathodes in chloride-based molten salt at high temperature.1 Then, co-recovery of uranium and transuranic elements can be accomplished by replacing the solid cathodes with a liquid cadmium cathode because the reduction potentials of the elements become close when the liquid cadmium is used as a cathode electrode.2,3 Since uranium is the major element in most nuclear fuel cycle paths as well as pyroprocessing technology, the assessment of accurate thermochemical data for the element in the molten salt is extremely important. 4Many studies on the thermochemical properties of uranium have been done in LiCl-KCl molten eutectic salt in different temperature ranges. Masset et al. 5,6 investigated diffusion coefficients of actinides and lanthanides in LiCl-KCl via cyclic voltammetry (CV) and chronopotentiometry (CP). Kuznetsov et al. 7,8 studied the electrochemical behaviors of actinides and rare-earth metals in LiCl-KCl salt. They performed CP and chronoamperometry (CA), and linear sweep voltammetry to determine the diffusion coefficients. Hoover et al. in 2014 9 extended the uranium concentration in LiCl-KCl molten salt up to 10 wt% and observed the electrochemical and thermodynamic behaviors of uranium using CV, CP, and anodic stripping voltammetry. These data are valuable to a development of kinetic models, which can be useful for understanding the main features of actinide deposition at the electrode surface, and also for prediction of material distribution in an electrorefiner of a safeguarding aspect. Zhang 10 developed a kinetic model for electrorefining system showing that the model is capable of predicting the kinetic features and...

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In the pyrochemical separation of used nuclear fuel (UNF), fission product, rare earth, and actinide chlorides accumulate in the molten salt electrolyte over time. Measuring this salt composition in near real-time is advantageous for operational efficiency, material accountability, and nuclear safeguards. Laser-induced breakdown spectroscopy (LIBS) has been proposed and demonstrated as a potential analytical approach for molten LiCl-KCl salts. However, all the studies conducted to date have used a static surface approach which can lead to issues with splashing, low repeatability, and poor sample homogeneity. In this initial study, a novel molten salt aerosol approach has been developed and explored to measure the composition of the salt via LIBS. The functionality of the system has been demonstrated as well as a basic optimization of the laser energy and nebulizer gas pressure used. Initial results have shown that this molten salt aerosol-LIBS system has a great potential as an analytical technique for measuring the molten salt electrolyte used in this UNF reprocessing technology.

In this current study, the molten salt aerosol-laser-induced breakdown spectroscopy (LIBS) system was used to measure the uranium (U) content in a ternary UCl-LiCl-KCl salt to investigate and assess a near real-time analytical approach for material safeguards and accountability. Experiments were conducted using five different U concentrations to determine the analytical figures of merit for the system with respect to U. In the analysis, three U lines were used to develop univariate calibration curves at the 367.01 nm, 385.96 nm, and 387.10 nm lines. The 367.01 nm line had the lowest limit of detection (LOD) of 0.065 wt% U. The 385.96 nm line had the best root mean square error of cross-validation (RMSECV) of 0.20 wt% U. In addition to the univariate calibration approach, a multivariate partial least squares (PLS) model was developed to further analyze the data. Using partial least squares (PLS) modeling, an RMSECV of 0.085 wt% U was determined. The RMSECV from the multivariate approach was significantly better than the univariate case and the PLS model is recommended for future LIBS analysis. Overall, the aerosol-LIBS system performed well in monitoring the U concentration and it is expected that the system could be used to quantitatively determine the U compositions within the normal operational concentrations of U in pyroprocessing molten salts.