Insights on the microstructural correlations of density and specific heat capacity for halophilic fission products and NaF-BeF2 molten mixtures

A comprehensive study by integrating first principles molecular dynamic (FPMD) simulations and differential scanning calorimetry (DSC) experiments on the physicochemical properties of multiple halophilic fission products (MFn = RbF, SrF2, YF3, and ZrF4) and molten NaF-BeF2 (FNaBe) mixed salts is reported. The effect mechanism of product type on density and specific heat capacity has been discussed from the interionic distance and its stability, coordination number and its distribution, as well as the neighbor cluster structure and its orientation. It is concluded that volume increments of molten FNaBe+MFn are primarily caused by Na-Na and M-F interactions, while the highest specific heat capacities (cp) of molten FNaBe+ZrF4 is closely related to the stability of Zr-F bonds and its coordination structures. Furthermore, the DSC results assisted by quantitative analysis of elements indicate that the additive concentration of YF3 is positively correlated with cp of molten FNaBe+YF3 in a certain range.