The passive debris cooling system provides a means to stably hold and cool the molten core (debris) dropped from the reactor vessel by the heat resistant material laid on the bottom of the containment vessel. As a heat resistant material, high melting point and highly corrosion-resistant oxide is laid on the pedestal and water is injected afterwards to suppress MCCI by the molten core. In the past research, although knowledge about molten core and concrete has been acquired, knowledge about interaction between molten core and heat resistant material is insufficient. Therefore, element tests on heat resistant materials were conducted, various heat resistant materials were screened, and molten core - heat resistant material interaction model was constructed using the obtained findings. Using the constructed model, we evaluated the erosion / heat transfer behavior of the heat resistant material assuming the bottom of the BWR / Mark - II type containment vessel at the time of severe accident and confirmed the MCCI suppression effect by the passive debris cooling system.