Severe accidents in light-water reactors lead to core meltdown. Inadequate cooling can cause the melt to breach the reactor vessel and flow into the cavity below, which may be flooded with water. As the melt encounters water, new debris may form and some of the melt may interact with concrete, potentially releasing non-condensable gases. However, the primary focus in managing severe accidents is to ensure effective cooling of the debris bed. By modeling the flooding of the debris bed, we aim to predict the behavior and contribute to the understanding of the events.
In this thesis, we study experiments conducted at the experimental facility FLOAT at the University of Stuttgart, IKE Institute in Germany. The experiments simulated flooding of the debris bed from above at different initial temperatures of the debris. Some experiments also simulated the possibility of the release of non-condensable gases during the concrete-melt interaction.
To model the events, we first developed an analytical 1D model that partially describes the basic behavior and flooding rates. For a more complete and accurate description, the program MC3D (IRSN, France) was used to perform 2D modeling in cylindrical geometry. We considered the initial temperature profile of the debris bed, the air injection from below, and investigated the influence of the wall effect. The simulation results reasonably agree with the experimental data. We also studied the effects of cooling with and without air injection and the effects of different initial temperatures of the debris bed on the flooding process.
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