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

ABSTRACT

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)O${}_2$ to accurately reproduce density and heat capacity of molten UO${}_2$ and ZrO${}_2$ 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 ZrO${}_2$ (d=0.070 atoms/Å${}^3$ at T=2900 K). The proposed fitted potential shows good agreement during validation with experimental data when applied at high temperatures.

KEYWORDS:

• Nuclear fuel
• corium
• molecular dynamics

Acknowledgements

High-performance resources from Grand Equipement National de Calcul Intensif (GENCI) [Centre Commun de Recherche et de Technologie (CCRT)] were used for the calculations.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 Some points were reported below the melting point (2973 K) for Kondo and Kohara. Such results are common for ADL experiments, as the system is completely isolated from its surrounding besides the stream of gas: the molten droplet can therefore maintain a ‘supercooled state’, where the liquid phase can exist below the melting point (or liquidus, as levitation was reported to prevent nucleation).