ELECTROCONDUCTIVITY OF MOLTEN FLiNaK AND FLiNaK–CeF₃

Abstract

The eutectic mixture LiF–NaF–KF (FLiNaK) is promising as a carrier salt for molten-salt reactors. Cerium fluoride CeF3 can be considered as a simulant of plutonium fluoride PuF3. In this work, the temperature dependence of the electrical conductivity of the molten ternary eutectic LiF–KF–NaF containing from 0 to 25 mol % cerium fluoride in the temperature range 480–777°C. FliNaK–CeF3 mixtures containing up to 25 mol. % of cerium fluoride were prepared directly in the experimental cell, dropping the required amount of CeF3 into the melt and keeping mixtures of a given composition for 12 h at temperatures exceeding the liquidus temperatures of the studied compositions. The electrolyte resistance was determined from impedance hodographs, which were taken using the Z-1500J impedance meter. A two-electrode cell with Pt electrodes was used. Analysis of the experimental values of the electrical conductivity of double and triple fluoride melts KF–LiF available in the literature; KF–NaF; LiF–NaF–KF shows that our data on the electrical conductivity of the LiF–NaF–KF (FLiNaK) eutectic mixture are consistent with the general trend in electrical conductivity with increasing KF concentration in the melt. A significant decrease in the specific electrical conductivity of the molten system and a slight increase in the activation energy of electrical conductivity with an increase in the concentration of cerium fluoride are shown. The temperature dependences of the electrical conductivity of the molten system were approximated by second-order polynomials. The formation of the \({\text{CeF}}_{6}^{{3 - }}\) complex ion in the melt was confirmed by spectral studies. The Raman spectra of molten FLiNaK and FliNaK–CeF3 mixtures containing 8 and 15 mol. % of cerium fluoride were recorded. With an increase in the concentration of CeF3 in the melt, the amount of \({\text{CeF}}_{6}^{{3 - }}\) complex ions increases, which leads to an increase in the intensity of the observed vibrational bands.