Thermophysical aspects of phase transformations of the cooled melt of high-temperature corium in nuclear power plants

   This study addresses three-dimensional modeling of the thermal interaction between the core melt and the melt localization device (trap) during a severe accident at a nuclear power plant. An optimized configuration for filling the localization device with sacrificial material is proposed. The calculations incorporate the Reynolds-averaged Navier–Stokes equations, numerical solutions of the heat conduction equation, and a two-fluid interface dynamics model, enabling simultaneous consideration of turbulent flow within the liquid phases, the moving boundary of the melting sacrificial material (Stefan problem), and stratification with inversion. The analysis proceeds in three consecutive stages. The first stage models the melting of the sacrificial material; the second simulates the stratification of layers; the third evaluates heat transfer after stratification. Based on the results, an optimal filling configuration for the trap is developed. The study presents detailed volumetric temperature distributions throughout all three stages, the heat flux distribution on the trap walls, and the maximum thickness of the melted shell caused by intense thermal interaction. Comparison between three-dimensional simulations and similar two-dimensional studies demonstrates that 3D modeling more accurately captures the characteristic timing of solidification and subsequent melting processes. The advantages of the proposed approach over existing methods are highlighted. Its applicability for designing and optimizing melt localization devices is shown, and prospects for future development are discussed, including incorporating chemical reactions and adapting the model to other reactor types. The data convincingly suggest that the adopted configuration has significant potential to extend the period during which effective mitigation of severe accident consequences at nuclear power plants can be maintained.

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