An Approach to Numerical Simulation and Analysis of Molten Corium Coolability in a Bwr Lower Head

The paper discusses an application of the Computational Fluid Dynamics (CFD) method to support the development and validation of a computationally-affordable method named Effective Convectivity Model (ECM) for simulation of turbulent natural convection heat transfer and phase changes in a decay-heated corium pool in the Boiling Water Reactor (BWR) lower head. The CFD method simulations enable detailed study of separate-effect phenomena of corium flows. Insights gained from the CFD simulations, e.g. the heat flux profile along the vertical wall and the locally enhanced downward heat flux in the vicinity of the Control Rod Guide Tube (CRGT), are implemented in the ECM model and its extension, the PECM, for phase changes. The paper reports validation of the PECM model against experimental data, including SIMECO and LIVE experiments. Assessment of thermal loading on BWR vessel structures during severe accident progression using the PECM is performed and safety-relevant aspects are discussed.