Because hydrogen combustion is one of the major containment threats during severe accidents, different hydrogen mitigation measures have been implemented in nuclear power plants throughout the world. In German Konvoi plants passive autocatalytic recombiners have been selected for hydrogen risk reduction. This paper proposes a new further improved option by taking credit from both the recombiners for hydrogen releases on slow timescales and the large load-carrying capacity of the spherical steel containment for rapid releases. Therefore, the capacity of spherical steel containment shells is investigated in some detail. The hydrogen and steam distribution in the containment is simulated for a rather conservative accident scenario with a rapid hydrogen release; a large hydrogen detonation is assumed and the transient containment loads as well as the structural containment response are calculated. For all these analyses advanced methods with high time and space resolutions are applied.
Detailed evaluations of the structural results considering recent experimental findings suggest that the spherical steel containment can carry the detonation loads. For the final assessment additional accident scenarios must be considered and more plant specific finite element models for the structural response must be applied. Some very local integrity issues need further investigations.
