Influence of transmutation products on the thermophysical properties of eutectic NaCl-UCl3 fuel salt in a fast-spectrum molten salt reactor

During the operation of fast-spectrum liquid-fueled molten salt reactors (MSRs), the salt composition of the fuel salt changes due to the generation of transmutation products (TPs) with the depletion of fuel, which can influence the thermophysical properties of the salt. Here, we evaluate changes in thermophysical properties of NaCl-UCl₃, such as density, viscosity, heat capacity, and thermal conductivity, due to generation of TPs after a representative burn-up of 180 MWd/Kg-HM. Concentration of TPs was determined from Monte Carlo simulations. Thermophysical properties were evaluated using semi-empirical models with input from experiments, ab initio molecular dynamics, and machine learning potentials. Our analysis predicts that although the aforementioned properties of the salt mixture are altered after the burn-up period, the concentration of TPs is small enough so that the overall changes in these properties in the fuel salt are likely not significant for nuclear applications.