ROUGH ESTIMATES OF SEVERE ACCIDENT CONTAINMENT LOADS ACCOMPANYING VESSEL BREACH IN BOILING WATER-REACTORS

Several probabilistic risk assessments (PRAs) have identified containm ent loads accompanying reactor vessel failure as a major contributor t o the probability of early containment failure during severe accidents . Two significant contributors to these loads are phenomena referred t o as ''steam spike'' and ''direct containment heating.'' To date, dire ct application of experimental and analytical studies of these phenome na to boiling water reactors (BWRs) are constrained by two limitations : (a) they are based on applications of large, complex containment res ponse analysis computer codes, for which values of many major input pa rameters are highly uncertain, or (b) they only address pressurized wa ter reactor containment designs. Relatively simple, parametric models are developed which allow a PRA analyst to evaluate the range of condi tions under which steam spike or direct containment heating may be imp ortant contributors to containment loads for postulated severe acciden ts in BWRs. The models have been applied to a representative BWR/4 Mar k I containment design to illustrate calculated results.