Thermodynamic optimization of the constitutive binaries of the LiCl/RbCl/CaCl2-NaCl-UCl3-PuCl3 systems

This study is aiming at building a set of self-consistent thermodynamic database of the constitutive binaries of the LiCl/RbCl/CaCl2-NaCl-UCl3-PuCl3 systems, and evaluating whether LiCl, RbCl or CaCl2 is an appropriate additive of NaCl-UCl3-PuCl3 matrix fuel of Molten Salt Reactor in terms of CALculation of PHAse Diagrams (CALPHAD) method. Substitutional solution model was adopted to describe the liquid phase and solid solution phase, while compound energy formalism was used to depict the intermediate phases. The model parameters were optimized based on the experimental data and theoretical predicted values. The thermodynamic parameters for describing the constitutive binaries of LiCl/RbCl/CaCl2-NaCl-UCl3-PuCl3 were ultimately obtained. Phase diagram information such as liquidus surface projections, isothermal sections and vertical sections of the LiCl/RbCl/CaCl2-NaCl-UCl3-PuCl3 system were predicted from the models with the optimized parameters. The effect of LiCl, RbCl and CaCl2 on the isothermal sections and melting temperature of NaCl-UCl3-PuCl3 matrix fuel was also investigated. The results show that RbCl is suitable as the candidate additive component of NaCl-UCl3-PuCl3 matrix fuel from the thermodynamic viewpoint, while LiCl and CaCl2 not. This work not only enriches the thermodynamic databases of NaCl-UCl3-PuCl3 matrix fuel, but also provides a direct guidance for the design and preparation of nuclear fuel in the Molten Salt Reactor.