Analysis of molten pool physico-chemical interactions and interpretation of the Phebus FP tests observations

The new 2D model for non-equilibrium U–Zr–O melt oxidation is developed on the base of the previously developed 1D model and extended to consideration of the general case of simultaneous UO₂ dissolution and melt oxidation accompanied with growth of the peripheral ceramic layer (crust) and bulk ceramic precipitates. The model is validated against isothermal crucible tests where precipitation of ceramic phase during molten Zr interactions with ceramic crucible walls along with oxide growth on non-oxidised surface of the melt were observed. In order to analyse melt oxidation under transient temperature conditions of the Phebus FP tests, the new physico-chemical model was tightly coupled with the heat exchange model and applied to interpretation of the post-test microstructure observations of the molten pool in the FP bundles.