Thermophysical properties of liquid (U, Zr)O₂ by molecular dynamics

In-depth understanding of nuclear fuel behaviour under operation is critical to anticipate and prevent severe accidents. Loss-of-cooling events can lead to core meltdown, and formation of U–Zr–O liquids (the basic components of corium lavas), formed of molten fuel and cladding. To improve the knowledge on those liquid mixtures, we evaluate the ability of existing interatomic potentials (CRG and Yakub) for solid-phase (U, Zr)O₂ to accurately reproduce density and heat capacity of molten UO₂ and ZrO₂ and their binary mixes within molecular dynamics simulations. Facing their limits, we determine a new set of parameters for the CRG potential through optimisation on a single experimental density point for ZrO₂ (d=0.070 atoms/Å3 at T=2900 K). The proposed fitted potential shows good agreement during validation with experimental data when applied at high temperatures.