Thermodynamic assessment of the Li, Na, K, Cs | F, I reciprocal salt for MSR applications

Gibbs energy models necessary to describe the thermochemical behavior of cesium and iodine in molten FLiNaK (46.5LiF-11.5NaF-42KF mol%), a proposed molten salt reactor coolant and fuel solvent, have been developed as they are of concern due to their high radiotoxicity and volatility. The six constituent pseudo-binary systems LiI-CsI, LiI-KI, LiI-NaI, NaI-KI, KI-CsI and NaI-CsI were evaluated using available phase equilibria and mixing enthalpy measurements. The models for the ternary reciprocal salt systems Li,Cs|F,I, Li,K|F,I, Li,Na|F,I, Na,K|F,I, Na,Cs|F,I and K,Cs|F,I were obtained by interpolation of the optimized pseudo-binary systems and parameters fit as necessary based on observed behavior. The additive (common cation) pseudo-ternary system representations were obtained by interpolation of the optimized pseudo-binary systems, and parameters for those as well modified as necessary to best fit observations. Together, the evaluated systems contain the necessary thermochemical models to generate quaternary and higher order reciprocal salt system descriptions, with the representations of the Li,Na,Cs|F,I, Li,K,Cs|F,I and Na,K,Cs|F,I quaternary reciprocal salt systems largely well-reproducing reported behavior. These salt system representations have subsequently been incorporated in the Molten Salt Thermal Properties Database – Thermochemical (MSTDB-TC).