Thermophysical properties of molten NaF-LaF3 mixture. Experiment and simulation

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Abstract
Fluoride molten salts are the most promising media for molten salt reactors utilizing highly active actinides as the products of the spent nuclear fuel reprocessing. Knowledge of the thermophysical properties of molten mixtures is a crucial key point for the reactor operation. Using an experimental approach and simulation techniques, the heat capacity and thermal conductivity of molten NaF-LaF3 system were studied in the temperature (1100 K ≤ T ≤ 1800 K) and concentration (15–100 mol. % of LaF3) ranges. The experimental setup provided the determination of the molten salt properties up to temperatures of 1200 K at LaF3 concentrations up to 35 mol. %. The molecular dynamics method made it possible to extend this range to temperatures up to 1800 K and LaF3 concentrations up to 100 mol. %. The solidus and liquidus temperatures of the NaF-LaF3 system, as well as the temperature dependences of the isobaric heat capacity and thermal diffusivity, were experimentally determined. In addition, the heat capacity and thermal conductivity of liquid LaF3 were calculated at T = 1800 K. The approximation line slopes of the experimental and calculated data coincide. The discrepancies obtained between the experimental and computational data were 25 % for heat capacity and 15 % for thermal conductivity. The developed model may be used to supplement the experimental data under conditions that are challenging for measuring equipment and to obtain the thermophysical properties of the fluorides of refractory elements.

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