(489c) Speciation of Fuel and Fission Products in Molten Salt Solutions from Ab Initio Molecular Dynamics

Impurities including fuel, fission products, and corrosion products are formed and consumed within molten salt reactors. These dissolved impurities will likely affect salt structure and thermophysical properties as they interact with each other and the solvent environment, and understanding these effects is crucial to the safe and effective design of reactors and the economical production of clean energy. We use first principles molecular dynamics to examine solute-solute interactions within molten fluoride and chloride salts. Simulated density and structure are compared to experimentally-determined values for validation. Our simulations find that solute-solute interactions have a significant effect on solute speciation, with—for example—uranium forming diverse complexes with multiple formal oxidation states at process-relevant concentrations. Molybdenum, another solute expected to be generated in the molten salt as both a fission and corrosion product, is found to form polynuclear molybdenum halide anions in solution, with possibly profound implications for the stability of molybdenum in the salt. Water is introduced, representing contamination of the salt, and is found to have significant effects on anion stability. Extensive charge analysis is used to analyze solute-solute and solute-solvent interactions. The applications of these results to thermophysical property prediction and fission product separation is discussed.