International MCCI reactor benchmark

In the course of a severe accident with total and long-term loss of heat removal, formation of a corium melt would eventually lead to melt-through of the reactor pres-sure vessel and discharge of the corium melt into the reactor cavity. Subsequently the corium would interact, in current reactors, with the concrete in the reactor pit. This concrete layer is part of the third and last containment barrier. Molten Core-Concrete Interaction (MCCI) is characterized by the intense coupling of several phenomena: High temperature concrete behaviour, bubbling corium pool thermal hydraulics and heat transfer, and physical chemistry which describes the changes in material com-position in the corium melt by admixture of molten concrete, oxidation of metals, or onset of solidification. The codes that were developed are based on different approaches of this complex phenomenology. They are briefly presented and their pre-dictions for plant analysis are discussed. Finally, the uncertainties and remaining questions are discussed with respect to the safety analysis of nuclear plants. (orig.)