Thermodynamic assessment of the LiF-NiF₂, NaF-NiF₂ and KF-NiF₂ systems

Abstract

Using the modified quasi-chemical model in the quadruplet approximation, three new thermodynamic assessments of binary systems useful for the detailed operational design of the Molten Salt Reactor are presented: AF-NiF₂ (A = Li, Na, K). These systems are particularly relevant for the study of the molten salt-structural materials interaction, as the salt containment is made of a Ni-based alloy. Using powder X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC), new experimental data were gathered for two of these systems, LiF-NiF₂ and KF-NiF₂, and compared to previous experimental assessments. Our data have confirmed the formation of a (Li_1-2xNi_x)F solid solution. The three thermodynamic models show a very good agreement with the experimental data. The melting point of NiF₂ was measured for the first time to be T = (1629 ± 5) K, and the thermal expansion coefficient for Li₂NiF₄ was found to be α=27.6·10^-6K^-1 in the temperature range T = (298–773) K.