Thermophysical properties of liquid UO₂, ZrO₂ and corium by molecular dynamics and predictive models

The analysis of such accidents (fate of the melt), requires accurate corium thermophysical properties data up to 5000 K. In addition, the initial corium melt superheat melt, determined from such properties, are key in predicting the fuel-coolant interactions (FCIs) and convection and retention of corium in accident scenarios, e.g., core-melt down corium discharge from reactor pressure vessels and spreading in external core-catcher. Due to the high temperatures, data on molten corium and its constituents are limited, so there are much data scatters and mostly extrapolations (even from solid state) have been used. Here we predict the thermophysical properties of molten UO₂ and ZrO₂ using classical molecular dynamics (MD) simulations (properties of corium are predicted using the mixture theories and UO₂ and ZrO₂ properties). The thermophysical properties (density, compressibility, heat capacity, viscosity and surface tension) of liquid UO₂ and ZrO₂ are predicted using classical molecular dynamics simulations, up to 5000 K. For atomic interactions, the CRG and the Teter potential models are found most appropriate. The liquid behavior is verified with the random motion of the constituent atoms and the pair-distribution functions, starting with the solid phase and raising the temperature to realize liquid phase. The viscosity and thermal conductivity are calculated with the Green-Kubo autocorrelation decay formulae and compared with the predictive models of Andrade and Bridgman. For liquid UO₂, the CRG model gives satisfactory MD predictions. For ZrO₂, the density is reliably predicted with the CRG potential model, while the compressibility and viscosity are more accurately predicted by the Teter model