STAR-CCM+ simulation of debris bed formation in the unheated DEFCON-S experiment

•The shape of debris bed is important for the coolability of molten corium in severe accident.•The debris bed formation in DEFCON-S experiment is analyzed with the STAR-CCM+ code.•Relevant CFD models are established for the interaction between particles and fluids.•The behavior of stainless-steel particles is simulated with the discrete element model (DEM).•The shape of the debris bed obtained in CFD simulation is consistent with the experiment. In a severe accident of light-water reactor, molten corium can be formed and discharged into the reactor cavity. If the resulting debris bed is not adequately cooled, it could threaten the containment integrity by causing a molten core-concrete interaction. This study analyzes a non-heating debris bed formation experiment of DEFCON-S using the STAR-CCM+ code. Relevant CFD models are established to reflect the interaction between particles and fluids to describe the particle behavior and flow of fluids. The shape and size of debris bed are predicted through the CFD calculation. The rolling resistance becomes an important parameter in this simulation. The prediction with the default values of STAR-CCM+ forms a spread shape of particle bed compared to the experimental result. The shape of debris bed obtained with modified rolling resistance coefficients gives consistency with the DEFCON-S experiment, having a deviation in diameter of 4.6 % and a deviation in height of 3.8 %.