Recent developments for molten salt systems in Thermochimica

The modified quasi-chemical model in the quadruplet approximation has been implemented in the open-source equilibrium thermodynamics library Thermochimica, enabling single point equilibrium calculations and sophisticated multi-physics simulations of molten salt nuclear reactor systems. Here, the derivations necessary to obtain the chemical potentials of the quadruplet species required for Gibbs energy minimization are provided. The implementation is verified via code-to-code benchmarking against FactSage. A scheme to increase computational efficiency of multi-physics simulations including Thermochimica is described and its effectiveness for molten salt systems demonstrated. Finally, a multi-physics simulation of a molten salt nuclear fuel system is presented as a demonstration problem: ORIGEN-S is used to calculate the isotopic evolution of a fuel-loaded FLiBe mixture with fission and activation products as Thermochimica predicts the phase evolution and number of moles of Cs in various phases.