Modelling of the MCCI phenomena with the presence of a water layer

If a severe reactor accident progresses to the point that the core melt breaches the reactor pressure vessel, the core is deposited onto the containment concrete basemat. Termination of the accident and attainment of a stable state where core cooling is assured requires the presence of a water layer which carries away nuclear decay heat. This paper discusses the possible set of conditions necessary for the attainment of this state and presents a simple thermal-structural model that predicts the transition of the molten core-concrete interaction from one state to the other. Such a model provides a semi-quantitative picture of how the interaction may proceed and how it scales from tests to prototypic reactor scale. All quantitative predictions are tentative pending more exact core-concrete properties. (orig.)