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

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, Li1/6Na1/6K1/6F1/4Cl1/4, maximizes configurational entropy. This mixture's configurational entropy (12Rln⁡24≈1.59R = 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 °C), are also analyzed. Density, heat capacity, thermal conductivity, and viscosity are calculated from liquidus to 1000 °C using phenomenological superposition-extrapolation, thermodynamic perturbation theory (TPT), and molecular dynamics with machine learning interatomic potentials (MLIPs).