Recent numerical simulations and experiments on coolability of debris beds during severe accidents of light water reactors

•Investigation on coolability of three-dimensional debris beds has been performed.•Computer code MEWA (Melt Water) is introduced and described briefly.•Validation experiments have been carried out in DEBRIS facility.•Comparison of MEWA simulations and DEBRIS experiments show good agreement.•Example simulation on reactor scale was performed to explain the analysis method.

In the course of a severe accident in light water reactors with core degradation, so-called debris beds can be formed inside the reactor pressure vessel or in the reactor cavity. The strategy to analyse the coolability of such debris beds with both experiments and numerical simulations is discussed. The numerical simulations are carried out with MEWA (MElt WAter) code, being developed at the institute for the prediction of the thermal-hydraulic conditions inside a debris bed, including the prediction of dryout heat flux. The simulations show good agreement with experimental data of the DEBRIS experiments.