Use of Molten Core Concrete Interactions in the Melt Stabilization Strategy of the EPR

The EPR is equipped with a core melt stabilization system to prevent basemat attack and melt through in a severe accident with core melting. The basic conceptual idea behind this system is to spread the core melt on a large area located lateral to the reactor pit and to cool it from all sides. Spreading transforms the melt into a coolable configuration by significantly increasing the melt surface/volume ratio. A fundamental precursor for successful spreading and thus long-term melt stabilization is temporary melt retention in the reactor pit. The purpose of this retention is to decouple the long-term stabilisation from the uncertainties involved in in-vessel processes, RPV failure mode and corresponding melt discharge sequence. Its specific objectives are (i) to accumulate the melt in cases of sequential melt releases and (ii) to unify and to condition the spectrum of in-vessel melt characteristics at the time of and for spreading. Temporary melt retention is based on molten core concrete interactions (MCCI) with sacrificial concrete. The present paper highlights the inherent advantages of using MCCI to achieve the goals of the temporary melt retention and also discusses the corresponding verification with the MCCI code COSACO. (authors)