CALPHAD analyses of molten chloride fast reactor fuels with U/Pu cycles

Abstract

In this study, a comprehensive Calculation of Phase Diagrams (CALPHAD) approach was undertaken to assess the effects of molten chloride fast reactor (MCFR) fuel chemistry on the initial and transient performance of MCFR fuel systems that utilize U/Pu fuel cycles. In this context, thermodynamic optimization of constitutive binary and ternary subsystems of the NaCl, KCl, MgCl2, CaCl2, UCl3, PuCl3, RbCl, CsCl, SrCl2, and BaCl2 containing system was performed and subsequently used to derive the phase behavior of high-order constitutive mixtures. The simulation results indicate that the appropriate modification of base salt compositions can significantly augment the heat transfer and melting properties of MCFR fuels, consequently leading to enhanced fuel performances, better compatibility with structural materials, and improved reactor economics. Moreover, it was discovered that the response of the fuel properties to shifts in fuel chemistry largely depends on solid phase interactions between the base salt and actinide content. The novel insights from this study bring forth several practical applications in various key facets of molten salt reactor design, such as fuel composition optimization, periodic optimization of fuel cleanup schemes, and structural material integrity assurance.