Mitigation of severe accidents in AREVA's Gen 3+ nuclear power plants

The current AREVA Gen 3+ PWR designs (EPR™ and ATMEA1) are based on the proven defense-in-depth safety concepts inherited from their predecessors, the French “N4” and the German “Konvoi” reactors. Complemented by specific enhancements, including higher redundancy and diversity as well as the use of passive systems, this leads to very low values of the core damage frequency (CDF). Notwithstanding this very low probability, dedicated design measures have been implemented to improve the response of the plant in case of a postulated severe accident (SA) with core melting. This way not only the frequency of large-early-releases (LERF) but also the related radiological consequences are drastically reduced. Situations that potentially lead to high loads that can challenge the short-term integrity of the containment, like RPV melt-through under high pressure, energetic hydrogen/steam explosions, as well as long-term containment failure caused by internal over-pressure are avoided by a combination of preventive measures and dedicated systems. At the example of the EPRTM, the paper gives an overview of the severe accident mitigation strategy and the related measures and systems of AREVAs current Gen 3+ reactors, with special focus on the function of the core melt stabilization system.