Bounding analysis of the containment of high-pressure melt ejection in advanced light water reactors

The loadings on containment due to direct containment heating (DCH) as a result of high-pressure melt ejection (HPME) in advanced pressurized water reactors meeting the recommendations of the Electric Power Research Institute Advanced Light Water Reactor (ALWR) Requirements Document were assessed by the U.S. Department of Energy (DOE) Advanced Reactor Severe Accident Program. Advanced light water reactors will have at least five features that tend to mitigate the effects of HPME: (1) a large, strong containment; (2) a reactor cavity configuration that limits the amount of debris that can transfer thermal and chemical energy rapidly to gases in the containment; (3) a means of reactor cavity flooding; (4) an in-containment refueling water storage tank (IRWST) that assures a large supply of water and also serves as a quench tank; and (5) a depressurization system to reduce reactor coolant system (RCS) pressure prior to reactor vessel melt-through to prevent HPME. The results indicate that the reactor cavity configuration need only inhibit ∼40% of the energy entering it from the HPME [(0.75 to 0.45)/0.75, assuming a 75% maximum possible core ejection] from heating and pressurizing the upper containment atmosphere. If the cavity is preflooded with IRWST water, the containment is unchallenged for even 100% core ejection. Since these analyses were based on conservative assumptions, they provide an upper bound on the effect of HPME and DCH on ALWR containment pressure