Density and Thermal Conductivity of Some Molten Mixtures in FLiNaK–NdF3 System

Abstract

Currently, the properties of molten lithium, sodium and potassium fluoride eutectic mixtures with different additions are immensely important for the development of molten salt nuclear reactors. In the present work, the density of molten FLiNaK mixtures with additions of neodymium fluoride was studied by the Archimedean method. The neodymium fluoride addition increased the density of the 46.5 mol% LiF–11.5 mol % NaF–42.0 mol % KF (FLiNaK) and FLiNaK + 25 mol% NdF₃ mixture from 2.00 g⋅cm⁻³ to 3.25 g⋅cm⁻³, respectively. Thermal diffusivity was measured by the laser flash method. It was found to decrease abruptly as the NdF₃ concentration increased. Thermal conductivity of the FLiNaK–NdF₃ system, which was calculated using thermal diffusivity, density and heat capacity values, was lower than that of molten FLiNaK at the same temperature. The composition with 25 mol % NdF₃ (0.69 W⋅m⁻¹⋅K⁻¹) had a lower value of thermal conductivity than molten FLiNaK without additions (0.74 W⋅m⁻¹⋅K⁻¹) at the same temperature of at 973 K. It can be concluded that neodymium fluoride additions resulted in the density growth and decrease in the thermal diffusivity, heat capacity and thermal conductivity of molten FLiNaK. The change in the neodymium fluoride concentration can affect the technological process in nuclear reactor.