Thermodynamic Evaluation of NaF-MF n (M=Be, U, Th) Systems for Molten Salt Reactor

Abstract

The phase diagrams of NaF-BeF2, NaF-ThF4 and NaF-UF4 systems were assessed based on thermodynamic principles, and diverse thermodynamic models were adapted to different systems. Associate solution model (ASM) was used to describe the Gibbs energies of liquid phase of the NaF-BeF2 system, whereas other systems(NaF-ThF4 and NaF-UF4) were treated with the substitutional solution model(SSM) and intermediate compounds were described as stoichiometric compounds according to the Neumann-Kopp rule. All the thermodynamic model parameters were optimized by the least squares procedure until good coincidence was achieved between the calculated results and the experimental data. The derived thermodynamic parameters will be merged into the NaF-BeF2-ThF4-UF4 database to develop the thorium molten salt reactor(TMSR) project.