Molecular dynamics simulations of structures and transport properties of UCl3-NaCl molten salts

We have used classical molecular dynamics to investigate the molten salt system UCl3-NaCl at various concentrations of U³⁺. From the radial distribution functions, we see that high UCl3 concentration brings in the change of the second peak of gU-Cl(r) and the first peaks of gU-U(r) and gCl-Cl(r), suggesting the change of sharing modes of U-Cl-U bridges. The diffusivities of all the ion species decrease with x[UCl3]. Especially, the movement of the anions is strongly coupled with U³⁺ as these cations become dominant in the mixture. The viscosity of UCl3-NaCl increase with x[UCl3] in contrast. Although PIM calculation predicts a steeper ascent of this trend compared to experimental data, the calculated values are still much lower compared to the fluoride molten salts. These findings will be helpful to fill the gap of understanding the fuel behavior of UCl3 in molten chlorides.