Thermodynamic Simulation of UCl3 Oxidation with Lead Chloride and UCl4 Reduction with Metallic Uranium in the Molten LiCl–KCl Eutectic

The equilibrium composition of the system (LiCl–KCl)eut + 1 mol E_Pb^2 + / . -0emPb^* and E_U^4 + / . -0emU^3 + ^* is only about 0.2 V. Therefore, PbCl2 is a weak oxidizing agent in this case. The difference between the E_Pb^2 + / . -0emPb^* and E_U^4 + / . -0emU^3 + ^* potentials increases with the temperature. Therefore, the equilibrium fraction of UCl4 increases with the temperature and excess PbCl2. For example, at 773 K and a threefold PbCl2 excess over stoichiometry, the average uranium valence is n = 3.27. At 973 K and the same PbCl2 excess, the average valence of uranium increases to n = 3.36. In addition, the reduction of UCl4 to UCl3 with metallic uranium in the molten LiCl–KCl eutectic is simulated taking into account the activity coefficients of the components. In the temperature range from 773 to 973 K, the reduction has no thermodynamic difficulties and proceeds completely. The HSC-9.9 software was used for the thermodynamic calculations.