Efficiency of severe accident management options for in-vessel core melt retention in a large power reactor

A simple probabilistic analysis method has been proposed to estimate efficiency of external reactor vessel cooling and late in-vessel injection as Severe Accident Management (SAM) actions for retention of molten core inside the reactor vessel (In-Vessel Retention, IVR) under hypothetical core-melting severe accidents. This method defines fractional core damage frequency where molten core can be retained inside the vessel with severe accident management actions of primary system depressurization, external reactor vessel cooling and/or late in-vessel injection. The method applied to the Korean Next Generation Reactor (KNGR), a large evolutionary pressurized water reactor shows that inclusion of external reactor vessel cooling strategy significantly increases the frequency of in-vessel retention even with conservative assumptions of system availability and conditional probabilities