Electrochemical Properties and Analyses of CeCl₃in LiCl-KCl Eutectic Salt

Abstract

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...

Measurement and Analysis of Exchange Current Density for U/U3+ Reaction in LiCl-KCl Eutectic Salt via Various Electrochemical Techniques

“…Then, a charge transfer feature can be measured via impedance spectra. This 155 minimum overpotential method was used in previous study [12], in which i 0 for Ce/Ce 3+ in LiCl-…”

Electrochemical and Thermodynamic Properties of CeCl3on Liquid Cadmium Cathode (LCC) in LiCl-KCl Eutectic Salt

“…The diffusion coefficients of Ce ranged from 2.9 × 10 −6 cm 2 s −1 to 5.1 × 10 −6 cm 2 s −1 at temperatures from 723 to 798 K. Figure 5 shows the diffusion coefficients of CeCl 3 on the LCC versus 1000/T, which are superimposed on the diffusion coefficients of CeCl 3 on tungsten electrode measured by Yoon and Phongikaroon. 14 The diffusion coefficients on the LCC were almost half of the values of the diffusion coefficients on the tungsten electrode. Gha-Young and co-workers 22 also had a similar trend with uranium chloride.…”

“…The value of the diffusion coefficient of Ce on the LCC was found to range from 2.9 × 10 −6 cm 2 s −1 to 5.1 × 10 −6 cm 2 s −1 , which is almost half compared with those on the tungsten solid electrode. 14 The slow diffusion rate of Ce on the LCC may result from the special structure of the LCC. In the cyclic voltammogram of LiCl-KCl-CeCl 3 -CdCl 2 , the Ce-Cd intermetallic compound formations were verified by obtaining the different anodic peaks.…”

Numerical analysis and experimental validation of planar electrorefiner for spent nuclear fuel treatment using a tertiary model

“…In this calculation, the U dendrite density selected was 2000 kg m −3 , and this value was assumed to be independent from the current density. The value of the parameters used in this calculation are as follows: anodic transfer coefficient, 0.5 [21]; cathodic transfer coefficient, −0.5 [21]; diffusion coefficient of U 3+ in molten salt, 1.03e−9 m 2 s −1 at 500°C [25]; electrical mobility, −4.64e−8 m 2 (Vs) −1 (calculated value based on the Nernst-Einstein relation [26]); and exchange current density, 60 mA cm −2 [27,28]. Also, in order to create an efficient grid from the cathode shape, a tetrahedral mesh was used for the rod cathode and mapped mesh was used for the flat-plate cathode, as shown in Figure 2(a) and 2(b), respectively.…”