Characterisation of molten salts for their application to Molten Salt Reactors

Abstract

Molten Salt Reactors (MSRs) are one of the six Gen (IV) reactor designs chosen by the Generation IV International Forum for further development. A key area of concern for MSRs is the selection of molten salt composition. Parameters such as heat capacity, thermal conductivity, and viscosity are essential to consider when selecting a salt mixture for use as a coolant in an MSR. In this meta-study, the thermodynamic properties of a range of halide, carbonate and nitrate salts are compared. Using this data, an estimate is made for the usable energy density of each salt. This value in combination with the raw data is used to assess the viability of each salt for use in an MSR. It was found that fluoride salts are the most suitable. They tend to have high heat capacities and large thermal conductivities in relation to the other salts in this study. The 50-50 concentration of LiF-BeF2 had by far the highest usable energy density at 2.21 J/cm3K, however its extremely high viscosity, of 22.2 mPa.s, makes it unsuitable for use as a circulating coolant. LiF-NaF-BeF2 had the next highest usable energy density at 1.82 Jcm-3K-1. Without considering factors beyond thermodynamic properties, it was concluded that LiF-NaF-BeF2, would be the most suitable of the studied salts for use as an MSR coolant. Much of the experimental data in this field was obtained over 40 years ago, it is often of poor quality, lacking standardisation and with large error margins. An attempt has been made in this paper to compile this data and to standardise it to such a degree that salts can be reasonable compared. Keywords: Molten Salt Reactor; FLiBe; FLiNaK; Heat Capacity; Carnot Efficiency