Transient and long-term heat removal from the cerium mass following a severe accident

Significant research efforts have been spent in the direction of safety for the nuclear power plants of the next generation and, in particular, new measures against the cerium attack to the safety barriers are under study for limiting significantly the radiological consequences in the case of core meltdown accident. Theoretical and experimental investigations are carried out to evaluate the possibility of confining the cerium, and then most of fission products radioactivity, within a properly cooled structure. In the case of traditional reactor cavity concepts, the possibility of inclusion in the containment layout of a protective barrier, able to avoid the contact between cerium and concrete basemat, is investigated. Also, taking into account the typical features of advanced LWR containment designs, attention is paid to the possibility to directly retain and cool the cerium within the reactor vessel. An overview of the heat transfer phenomena which are dominant in the corium-structure-coolant systems is made and the typical responses given by a dynamic simulation tool developed for their thermal analysis are illustrated.