Molecular dynamics investigation on the local structures and transport properties of uranium ion in LiCl-KCl molten salt

Abstract

The effects of temperature and composition on the structures and transport properties of UCl3-LiCl-KCl salts were systematically investigated by using molecular dynamics simulation with a polarizable force field. In the molten salt of pure UCl3, there exist networks of [UCln] (n = 6, 7, 8, …) clusters, dominated by corner-sharing, Cl-linked [UCl8]5−. The networks became sparser with the UCl3 concentration decreasing. The local structures of U3+ complexes in LiCl-KCl salts were also compared with that of typical fission products such as Sc3+, Y3+, La3+ and Tb3+. It is found that the local structures of the U3+ complexes in LiCl-KCl were very similar to that of La3+, while the U-Cl coordination bonds were less stable than that of Y-Cl, Sc-Cl, and Tb-Cl complexes. Finally, two basic transport properties, diffusion coefficient and viscosity of UCl3-LiCl-KCl were predicted to a broader range than the previous reported data. These results help to understand the underlying mechanisms related to the pyrochemical processing for separation of trivalent uranium ions from other fission product ions in LiCl-KCl salts.