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In some nuclear reactors, under accidental conditions, core debris forms a molten pool, which is later located in a core catcher. The core catcher proposed by the authors uses special refractory material to absorb enthalpy of corium so that temperatures are within 1500 K, which is possible to cool with side cooling and top flooding. Since performing a full-scale prototypic experiment is extremely challenging and complex because of the involvement of very high temperatures and the presence of radioactive materials, it is important to develop a Computational Fluid Dynamics (CFD) model capable of simulating coolability of the melt pool with the above cooling strategy. In the present work, a CFD model was developed for the above purpose and was benchmarked with experiments conducted under simulated conditions by the authors. The experiment involved the melting of about 25 L of sodium borosilicate glass at about 1473 K and cooling it in a scaled-down core catcher model. In the presence of decay heat inside the melt pool, turbulent natural convection plays an important role in the temperature distribution inside the melt pool and on the vessel walls. For this, we used different turbulence models. Comparisons among the Standard k-ε, Shear Stress Transport (SST) k-ω, and two-dimensional (2D) Large Eddy Simulation (LES) turbulence models show that SST k-ω and 2D LES turbulences are found to be in good agreement with the experimental results for the temperature distribution in the melt pool, and SST k-ω is found to be computationally less expensive than 2D LES. In general, the CFD model is capable of simulating heat transfer with phase changes inside the heat-generating melt pool. In view of this, the model can be further extended to include cooling of the melt pool in the prototype core catcher. The evolution of crust formation has been investigated in detail using a CFD model. [ABSTRACT FROM AUTHOR]

To mitigate severe accidents in nuclear reactors, the present research sheds light on the melt-coolability behavior of corium with hypothetical experiments that have been performed at two different nozzle diameters under bottom flooding conditions. In this research, a simulant material CaO-Fe2O3 powder mixture was melted and poured into the test section that was embedded in the test facility (using a bottom pouring furnace instead of a tiltable furnace). Then, from the bottom of the melt pool, water was flooded through a nozzle at a pressure of 0.70 bar and a water flow rate of 12 liters per minute. Because of the interaction between the water and melt, the melt quenched and converted into fine porous debris, and the temperature history was recorded using 12 K-type thermocouples connected to a data acquisition system. The average quenching time and porosity of the debris were affected by variations in the nozzle diameter. This research will help in understanding real core-melt accidents that generally occur in nuclear power plants. [ABSTRACT FROM AUTHOR]