A new methodology for measuring the enthalpies of mixing and heat capacities of molten chloride salts using high temperature drop calorimetry

Molten salt reactors (MSRs) are a promising alternative to conventional nuclear reactors as they may offer more efficient fuel utilization, lower waste generation, and improved safety. The state of knowledge of the properties of liquid salts is far from complete. In order to develop the MSR concept, it is essential to develop a fundamental understanding of the thermodynamic properties, including the heat capacities (C-p) and enthalpies of mixing (Delta H-mix), of molten salts at MSR operating conditions. Historically, the C-p values of molten salts were determined by drop-calorimetry or differential scanning calorimetry, whereas their Delta H-mix values were typically measured using specialized high temperature calorimeters. In this work, a new methodology for measuring both the C-p and the Delta H-mix of molten chloride salts was developed. This novel method involves sealing a chloride salt sample in a nickel capsule and performing conventional transposed temperature drop calorimetry using a commercially available Setaram AlexSYS-800 Tian-Calvet twin microcalorimeter. This methodology may be applied to calorimetric measurements of more complex salt mixtures, especially mixtures containing actinides and fission products.