Molecular dynamic study of the local structure and transport properties of LiF-NaF molten salt

Abstract

LiF-NaF molten salts have received extensive attention due to their excellent heat transfer performance in molten salt reactors. However, their structural and thermodynamic properties have not been systematically studied. In this study, molecular dynamic simulations were performed using polarized force fields to investigate the local structures of cations and thermodynamic properties of mixed salts in a temperature range of 873 K to 1273 K and at all concentration components. Furthermore, a linear relationship between density and LiF concentration at different temperatures was fitted. Regarding local structure, an increase in LiF concentration gradually increased the coordination numbers of Li and Na ions, but the strength of Li–F and Na–F ionic bonds gradually weakened. Regarding the thermodynamic properties, an increase in the LiF concentration linearly increased the self-diffusion coefficients of all ionic species, while the viscosity of the system approximately decreases exponentially. The ionic conductivities were calculated using the Green–Kubo and Nernst–Einstein relationships, and the results reflect that the Nernst–Einstein approximation is not suitable for describing molten salt systems.