Thermodynamic description of the constitutive binaries of the NaCl-KCl-UCl₃-PuCl₃ system

Thermodynamic assessment of the constitutive binaries of the NaCl-KCl-UCl₃-PuCl₃ system was carried out by CALPHAD (CALculation of PHase Diagrams) approach. The liquid phase was described by the substitutional solution model, and the intermediate compounds were treated as stoichiometric phases. The thermodynamic parameters of the binary systems were obtained based on experimental phase equilibria data available in the literature and theoretical prediction data by first-principles calculations and empirical equations. A set of self-consistent thermodynamic parameters for each of the binary system was finally obtained. Some representative liquidus surface projections, isothermal sections and pseudo-binary phase diagram for the sub-ternary and quaternary systems were calculated by model extrapolation. The influence of KCl on the thermodynamic behavior of NaCl-UCl₃-PuCl₃ matrix salt was analyzed. The extrapolated results indicated that KCl can be used as a candidate additive component of NaCl-UCl₃-PuCl₃ matrix salt from the point of view of thermodynamics. This study provided a comprehensive understanding for the thermodynamic behavior of a candidate molten salt fast reactor nuclear fuel and a fundament for the design of nuclear fuel.