Theoretical calculations and multiscale molecular simulations are applied to the study of solute behavior in pyroprocessing of spent fuels, including classic molecular dynamics (MD) and first principles molecular dynamics (FPMD) simulations of structural, energetic and transport properties of actinide elements in molten salts, first principles calculations of redox potentials of metal ions in molten salts, and first principles calculations in combination of recursive fitting of force field parameters for actinide molten salts and liquid actinide alloy. The radial distribution functions, probability distribution of coordination numbers, dynamic fluctuation of coordination structure, self-diffusion coefficients and ionic conductivity in actinide molten mixtures are evaluated and compared with experimental and other simulation results. In addition, polarizable force field model and embedded atom model are developed, respectively, for actinide molten mixtures and liquid U-Zr alloy. The MD and FPMD simulations reveal that the 6-fold coordination structure of U3+ dominates in molten LiCl-KCl-UCl3 mixture and high temperature is conducive to the formation of low coordinated structure. Besides, a computational strategy for the evaluation of redox potentials of solute elements in molten salts is developed based on ensemble average of FPMD simulations, and the calculated redox potentials agree satisfactorily with experimental values (Figure 1). For liquid U-Zr alloy, the mixed volume of U and Zr increases compared to the component elements, and the mixing of U and Zr is energetically unfavorable with positive mixing enthalpy. These achievements are essentially important for the development of pyroprocessing techniques of spent fuels by providing fundamental physical chemistry data.

Pyroprocessing of spent nuclear fuels: Theoretical calculations and multiscale molecular simulations of solute behavior in molten salts

253rd National Meeting (2017)

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