Thermodynamic assessment of lithium halide reciprocal salt systems for energy applications.

• Thermochemical properties of lithium halide pseudobinary systems are assessed based on reported experimental data. • LiF-LiI system is essential for understanding fission product iodine behavior, thus developing source terms for accident analysis of fluoride-based MSRs. • The calculated vapor pressures of LiI and LiF endmembers are verified using available experimental partial pressures. • For example, vapor pressures are computed by our assessed models for LiF-70 mol% LiI and compared to reported experimental vapor pressures. • Extrapolations to the pseudoternary and pseudoquaternary systems have been performed. Lithium halides are of interest because of their unique applications as fuel or coolants in molten salt reactors (MSRs) and electrolytes in thermally activated batteries. Because iodine is an important fission product for MSRs, the Molten Salt Thermal Properties Database-Thermochemical (MSTDB-TC) is being expanded to include relevant iodide reciprocal salt systems. In this work, we assess the thermochemical properties of lithium halide pseudobinary systems based on reported experimental phase diagrams, eutectic temperatures, and enthalpies of mixing. Within the framework of the modified quasi-chemical model in the quadruplet approximation (MQMQA), extrapolations to the related pseudoternary and pseudoquaternary systems have been performed. The pseudoquaternary representations of phase equilibria, enthalpy, entropy, and heat capacity are represented in the resultant models. Of interest for generating source terms for accident analysis is the ability to compute the vapor pressures of the dominant iodide species for the systems at any composition. An example of such calculations is provided for the LiF-LiI system at x LiI = 0.01 and x LiI = 0.70, in this case indicating that the LiI vapor species are predominant. [ABSTRACT FROM AUTHOR]