Use of Phébus results for EDF severe accidents studies

Abstract

In France, severe accident analysis has been incorporated into the safety cases and operation strategies of the current power plants and is required for the design of new plants (EPR). The assessment of fission products release in the environment is of primary concern in the frame of severe accident studies. They consist of:•For current plants, assessing radiation doses in the environment to determine their compatibility with the radiological objectives.•For EPR, verifying compliance of radiological objectives with the design provisions.The radiological consequences of core melt sequences are based on a bounding reference source term, calculated with reasonably conservative and simplified bounding assumptions, independent of the initiator event but which relate to the core melt sequence. These bounding assumptions relate to fission product behaviour and to the behaviour of the plant (containment leakage, filter efficiency, etc).Three phases are distinguished in the behaviour of fission products:•the release of fission products and other radioactive materials from the fuel matrix during core degradation,•the behaviour of fission products in the reactor coolant system,•the behaviour of fission products in the containment and in the plant environment.The research program Phébus FP has provided a comprehensive database to improve our understanding of the various phenomena leading to fission product behaviour and has been used to determine, in combination with other experiments, bounding assumptions for each phase described above. Furthermore, Phébus experiments are the most representative integral cases, in such a way that this program has formed an interesting validation database for the EDF version of the MAAP integral scenario code. The aim of this paper is to present this two last points.