Assessment of thermal load at the stage of interaction between melted korium and the VVER reactor vessel during a severe accident

The paper considers heat transfer processes in the area of melting in the lower chamber of a nuclear reactor of the VVER reactor during a hypothetic severe accident. The distribution of the thermal flow from a heat releasing melted fuel to the reactor vessel is analysed. It is necessary to know this distribution to solve the problem of confining melted fuel in the vessel by its external cooling. Mechanisms, determining heat transfer in the melted material, are considered, not ignoring the existing uncertainties in estimating possible processes. The authors specially consider thermophysical aspects that may change the existing notion about processes in korium and modify methods of controlling severe accidents.