Assessment of ex-vessel steam pressure spikes in BWR Mark 2 containments

If a postulated severe light water reactor accident results in molten corium discharge into water, the potential exists for rapid steam production and an associated pressure spike or steam explosion. The magnitude of such an event depends on the rate of thermal energy transfer and the water dynamic response. A simplified thermal-hydraulic methodology is presented in this study which displays the effect of various parameters on containment pressure loads. The methodology is applied to a postulated severe accident in a representative BWR Mark 2 containment. Results show that for a state-of-the-art corium discharge calculation, steam explosion impact loads would not occur, and pressure spikes would be substantially less than containment design values