Material Influence on Steam Explosion Efficiency: State of Understanding and Modelling Capabilities

Summary Steam explosions as explosive melt-water interactions may happen in the course of a severe reactor accident with core melting. It is to be analyzed whether such explosions could lead to severe consequences, e.g. jeopardizing the lower head in in-vessel events or especially the containment integrity in ex-vessel events. Major mechanisms limiting the strength of explosions have been identified and elaborated in the past, recently in the OECD-SERENA Phase 1 project. Continued analyses are being performed in SARNET. Void buildup in premixtures has been considered as a major limitation, reducing by compressibility the potential of mixtures of being triggered and of yielding strong pressure escalations. Material influences are under discussion. Exclusion of strong explosions with corium has been concluded from experiences with KROTOS experiments, in comparison with explosions obtained with alumina melts. Spontaneous and triggered explosions with corium have been obtained in TROI experiments, but not spontaneously and with less strength under triggering for non-eutectic corium. In the present paper, the status of knowledge about the material influences is analyzed, as well as possible consequences to be drawn. In general, the effects limiting the strength of explosions are discussed and demonstrated by applications to an in-vessel scenario. Conclusions are drawn on the status of modelling and guidelines for further resolution of remaining problems and uncertainties are proposed.