Deep potential molecular dynamics simulation of local structure and properties of LiCl-KCl-CsCl-LaCl3 molten salt

Abstract

LiCl-KCl-CsCl molten salt is regarded as an ideal electrolyte for the pyroprocessing of spent nuclear fuel due to the lower melting point compared to molten salts studied in the mainstream. In this work, the local structure and properties of LiCl-KCl-CsCl-LaCl₃ molten salts were systematically investigated over the temperature range of 573–813 K using deep potential molecular dynamics simulations. The short-range and intermediate-range ordering, along with the coordination environment of La³⁺ and their dependence on temperature and LaCl₃ concentration, were analyzed based on radial distribution functions and structure factors. La³⁺ predominantly exists as 6-coordinated clusters in the melt because of its low free energy. As temperature and LaCl₃ concentration rise, the short-range ordering of the melt decreases due to the weakened interactions between cations and Cl^-, whereas the intermediate-range ordering exhibits an increasing trend. The variation in intermediate-range ordering is determined by both the Cl^--decorated La³⁺ networks and the La-La networks. Moreover, a series of properties of LiCl-KCl-CsCl-LaCl₃ melts were evaluated, including the self-diffusion coefficient, viscosity, ionic conductivity, heat capacity, thermal expansion coefficient, and thermal conductivity. With the continuous La enrichment in the salt, LiCl-KCl-CsCl molten salt demonstrates excellent electrical conductivity and thermophysical properties, highlighting its advantages and potential as a superior alternative for LiCl-KCl molten salt in pyroprocessing.