Analysis of a LBLOCA with FLEX actuations in a PWR-W

Abstract

After the Fukushima-Daiichi accident, different methods, strategies and guidelines were developed to improve the Severe Accident Management Guidelines (SAMG). One of these additions, named the FLEX strategies, relies on portable equipment to obtain power or water to restore key safety functions in the reactor.In the present study, the FLEX strategies are studied under an in-vessel molten core retention scenario; these actions will try to avoid the reactor pressure vessel failure when the core is in a degraded or molten state. In order to analyze this sequence, a large break LOCA is simulated in a three loops PWR-W using the MELCOR 2.2 code.During the simulated sequences different configurations are assessed; the water injection by the ECCS during the recirculation phase is supposed to fail at different times, and the water injection with portable equipment subsequently occurs also at different times after the ECCS failure. Additionally, different water injection rates are also analyzed to compare different portable pumps capabilities.The obtained results agree with previous literature, i.e. the reactor vessel failure could be precluded if the water injection with portable equipment starts before there is a large amount of corium in the lower head. No significant differences are found between different water injection rates (20-60 kg/s) to prevent vessel failure, but it does have an impact on the containment pressure and hydrogen generated.