Insights into the structural dynamics, thermophysical properties, and thermodynamics of the NaCl-ThCl4 and NaCl-UCl4 systems

The structural, thermochemical, and thermophysical properties of the AnCl 4 , and NaCl-AnCl 4 (An = Th, U) melts were investigated using molecular dynamics (MD) simulations based on the Polarizable Ion Model (PIM). New force fields were proposed that were used to compute key properties including density, thermal expansion, enthalpy of mixing, heat capacity, as well as the local structure and chemical speciation in the molten (Na,An)Cl x (An = Th, U) salts. Thermodynamic models were then developed based on the CALPHAD method, using both PIM-MD and experimental data as input. Employing the modified quasichemical formalism in the quadruplet approximation for the liquid solution, the models account for the chemical speciation in the melt as calculated by MD simulations, and reproduce well phase equilibria in those systems. In particular, the models included monomeric and dimeric species to represent the physical nature of the ionic melt, that shows progressive oligomerisation with increasing AnCl 4 fraction. Our studies confirm that the melt becomes highly volatile at high AnCl 4 fractions, which is discussed in light of the results obtained herein. • New polarisable ion model (PIM-MD) force fields were developed for ThCl 4 and UCl 4 . • Structural and thermophysical properties of molten ThCl 4 and UCl 4 were elucidated. • NaCl-AnCl 4 (An = Th,U) mixtures were investigated using PIM-MD. • Thermodynamic models of NaCl-AnCl 4 (An = Th, U) are reported. • The models couple MD-derived chemical speciation with phase equilibria.