Fluoride salt coolant properties for nuclear reactor applications: A review

Fluoride salts are crucial to achieving the benefits of Fluoride-salt-cooled High-temperature Reactors (FHRs). Intensive studies and modeling are being performed in different countries aimed at FHR technology development. Better understanding of liquid fluoride salt coolant properties and their uncertainties are needed for design and analysis of nuclear facilities. The main objective of the present study is to perform a literature survey of the experimental data, numerical studies, reports, and other review compilations for the main thermophysical properties of liquid fluoride salts. The review recommends density, heat capacity, thermal conductivity, and viscosity properties for potential primary coolants LiF-BeF₂ (flibe) and NaF-ZrF₄ (nafzirf) and secondary coolant LiF-NaF-KF (flinak). It is found that there is a dearth of experimental data. Thus recommended property uncertainties are included, which range from 2 to 20%, complete with a discussion on the recommended definition of the uncertainties. The recommended properties and their uncertainties provide a reference point for incorporating uncertainty in modeling to understand its impacts and for code benchmarking and validation. Keywords: FHR; Fluoride salt; Thermophysical properties; Flibe; Nafzirf; Flinak