Criteria for successful core reflood under severe accident conditions

In present German nuclear power plants, safety is enhanced by prescription of preemptive measures and accident mitigation measures. If preemptive measures (e.g. backfitting, improved safety procedures) should fail, mitigative procedures are foreseen to take credit of all safety-related systems available on site. As usual in daily life, no guarantee of complete success of accident management measures can be given, because the success of a core reflood depends essentially on the actual core state and its history, system pressure, and the injection rate of the activated reflood system. In the present work, available experimental data on core reflood are reviewed to define characteristic regimes and dependencies as well as identifying areas where experimental data are lacking, e.g. reflooding of large in-core debris/pool configurations. A reflood map is proposed based on core state and reflood mass flow rate. Common features of the behavior are deduced on the assumption that non-prototypic facility-based effects can be excluded. (authors)