Thermodynamic assessment of the LiF-BaF2-ZrF4 system

Lithium-based fluoride salts are one of the leading options as fuel matrix in Molten Salt Reactors. The understanding of their thermodynamic behavior, e.g. chemical stability, activity, as well as heat transfer properties, in the reactor’s environment is crucial for the safety assessment. In this work, the chemical equilibria of lithium fluoride with two important fission products dissolved in the salt matrix, namely barium fluoride and zirconium fluoride, are considered. The phase diagrams of the binary systems LiF-BaF2, LiF-ZrF4 and BaF2-ZrF4, as well as the ternary system LiF-BaF2-ZrF4 are assessed by the CALPHAD (CALculation of PHase Diagram) method using the quasichemical model in the quadruplet approximation for the liquid solution. These models are based on literature and new experimental data, and provide a good overview of the stability of intermediate compounds formed in the various systems and of the liquid solution.