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A multistage extraction model based on the distribution of actinides and rare earths between two phases of lithium activated bismuth and molten LiF-BeF 2 (66 mole % LiF) has been developed. The model shows that the distribution across the cascade is affected by the concentration of Li in the metal phase, system temperature, flow rates of each phase, and the presence and concentration of other elements in the molten salt phase. Based on the model, it is predicted that an online molten salt coolant purification system could be used to separate both rare earths and actinides from the primary salt coolant in fluoride salt-cooled hightemperature reactors (FHRs). Additionally, the results provide sufficient evidence that this extraction method can separate primarily actinides prior to extraction of other rare earth elements, which would allow for fission products and other reactor poisons to be discarded, while fuel materials (U and Pu) can be recycled back into a reactor system.

Pyroprocessing technology is a promising tool for recycling nuclear fuel and producing high purity gadolinium for industrial applications. An efficient implementation of pyroprocessing entails a careful characterization of the electrochemical and transport properties of lanthanides in high temperature molten salts. In this work, the cyclic voltammetry signals of Gd in molten LiCl-KCl salt were recorded for a combination of three temperatures (723 K, 773 K, and 823 K) and three concentration levels (3 wt. %, 6 wt. %, and 9 wt. %) including concentration levels higher than previously reported and relevant for a realistic application of pyroprocessing for molten salt recycle, and the concentration effects were investigated. Four scan rates (200 mV/s to 500 mV/s) were used for each condition, and the signals were examined using conventional Cyclic Voltammetry (CV) analysis equations and by utilizing a two-plate Brunauer, Emmett, and Teller (BET) model accounting for mass diffusion, kinetics, adsorption, and the evolution of electrode morphology via a nonlinear least squares procedure for fitting the model to the experimental signals. It was determined that the redox process is quasi-reversible for the scan rates being used. Furthermore, the applicability of the conventional equations for CV analysis was shown to be problematic for the conditions used, and this is thought to be due to the fact that these equations were derived under the assumption of reversible conditions. The model-derived values for diffusivity are consistent with the literature and are shown to decrease with increasing concentration. This may be due to increased interactions at higher concentration levels. It was also shown that the formal redox potential increased with a concentration and was slightly more positive on the covered electrode.