Concentration and solvent effects on structural and thermodynamic properties of uranium (Ⅳ) fluoride by molecular dynamic simulation

The structural and thermodynamic properties of UF4-LiF, UF4-NaF and UF4-KF molten salts were systematically investigated by using molecular dynamic simulation with a polarizable force field, and the effects of UF4 concentration and solvent were discussed. The reliability of molecular dynamic simulation was verified by the reasonable agreements between the calculated and experimental density values of the molten salts. The calculated diffusion coefficients of U4+, Li+, Na+, K+ and F‒ in various systems all followed the form of Arrhenius equation. A linear relationship between the logarithm of viscosity and the reciprocal of temperature was observed. The association between U4+ and F‒ in UF4-KF was strongest, followed by UF4-NaF and UF4-LiF. A transition percentage of 0.3–0.4 for UF4 in mix salts should be paid attention to, which is generally used in nuclear fuel design. The enthalpy of mixing, diffusion coefficient, the radial distribution function and coordination number all showed some transition behaviors at such UF4 transition percentage.