K.O. Bobrova, V. N. Dokytovich, P. N. Myshnikov.
ABSTRACT
The paper presents experimental data on the thermal conductivity of molten salt mixtures of the following compositions: 0.66LiF-0.34BeF2 and 0.73LiF-0.27BeF2, (0.73LiF-0.27BeF2) + 1 mol % UF4 and (0.73LiF-0.27BeF2) + 2 mol % UF4. The thermal conductivity of the last three mixtures was measured for the first time. Due to the hygroscopicity of beryllium fluoride, all work with salts, including the stages of remelting, filtration, crushing, etc., was carried out in a glove box in an inert argon atmosphere with a controlled level of oxygen and water vapor (no more than 1 ppm). The measurements were carried out by the stationary method of coaxial cylinders in a nickel device in the temperature range from 500 to 800°C. The thermal conductivity of the 0.66LiF-0.34 BeF2 melt is in good agreement with the experimental data described in the literature within the error of the method (± 5%). The thermal conductivity of all investigated molten mixtures increases with increasing temperature, the temperature dependences are approximated by linear equations. The maximum increase in thermal conductivity is 25% for a mixture of 0.73LiF-0.27 BeF2 + 2 mol % UF4 in the range of 560-800 °С. A change in the composition of FLiBe (LiF from 66 to 73 mol % and BeF2 from 34 to 27 mol %, respectively) leads to an insignificant change in thermal conductivity (by 5% on average, which lies within the experimental error). Adding 1 and 2 mol % UF4 (a strong complexing agent) leads to a more noticeable decrease in the thermal conductivity of the 0.73LiF-0.27BeF2 melt by 12% on average. Using our data on thermal conductivity, as well as the literature values of density and heat capacity, we calculated the thermal diffusivity of the studied molten mixtures at three temperatures: 600, 700, and 800°C. It is shown that the calculated values of the thermal diffusivity of the composition 0.66LiF-0.34 BeF2 are in good agreement with the literature data.
KEY WORDS: thermal conductivity, thermal diffusivity, molten salts, lithium fluoride, beryllium fluoride, uranium fluoride, coolant, fuel salt.
DOI: 10.31857/S0235010622050036