Influence of the Salt-Solvent Composition on the Thermodynamic Characteristics of the U–Ga Alloy in the Liquid Metal–Molten Salt System

The equilibrium potentials of the U(III)/U couple and liquid metal U–Ga alloy in molten salt media of the LiCl–KCl, LiCl–KCl–CsCl, and NaCl–CsCl eutectics in a temperature range of 673–873 K are measured by open-circuit potentiometry. Experiments are carried out under a purified inert gas atmosphere. Reagents containing no impurities of moisture, oxygen, and their compounds are used in experiments. All the main procedures are conducted in a dry glove box. The working melts are prepared in two stages: the chlorination of metallic uranium by gaseous chlorine in the molten salts followed by the storage of the formed electrolyte with uranium for several hours to have a uranium trichloride-containing solution. Uranium alloys with gallium are prepared prior to experiment by the electrolysis of the melt. The electrolysis time corresponds to the conditions of single-phase region formation. The emf of the galvanic cells W(U) | melt, UCl3 || melt | C(s), Cl2(g) and U(Ga)alloy | melt, UCl3 || melt | C(s), Cl2(g) are measured to study the influence of the salt-solvent composition on the equilibrium potentials of the U(III)/U couple and U–Ga alloy. The temperature dependences of the apparent standard potentials, which are approximated by straight lines, are calculated from the results obtained. An increase in the effective radius of the salt-solvent cations is found to result in the shift of the potentials toward more electronegative values. The activity coefficients of γ-uranium in liquid gallium are measured, and their dependences on the temperature and electrolyte composition are determined. The excess partial Gibbs free energy change in the molten salt media at different temperatures are calculated.