High-Entropy Li-Na-K Fluoride-Chloride Melts for MSRs

D Zakiryanov and N Tkachev, JOURNAL OF PHYSICAL CHEMISTRY B, 129, 12276-12284 (2025).

DOI: 10.1021/acs.jpcb.5c05076

This study theoretically evaluates the thermophysical properties of high-entropy molten salt mixtures composed of lithium, sodium, and potassium fluorides and chlorides, exhibiting enhanced thermodynamic stability as a result of the high configurational entropy. The equimolar mixture, L i 1 / 6 N a 1 / 6 K 1 / 6 F 1 / 4 C l 1 / 4 , maximizes configurational entropy. This mixture's configurational entropy ( 1 2 R ln 24 approximate to 1.59 R = 13.21 J mol-1 K-1) approaches the high- entropy threshold of Rln5 (13.38 J mol-1 K-1). These high-entropy mixtures, with entropy significantly exceeding that of FLiNaK (6.9 J mol-1 K-1), are promising coolants for molten salt reactors due to improved thermodynamic stability. Two eutectic compositions with reduced lithium content, derived from the phase diagram (melting points 606 and 630 degrees C), are also analyzed. Density, heat capacity, thermal conductivity, and viscosity are calculated from liquidus to 1000 degrees C using phenomenological superposition-extrapolation, thermodynamic perturbation theory (TPT), and molecular dynamics with machine learning interatomic potentials (MLIPs).

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