Integrated MELPROG/TRAC analyses of a PWR station blackout

A complete, coupled, mechanistic analysis of the entire reactor coolant system during a station blackout accident (TMLB') has been completed using the MELPROG/TRAC code. The analysis includes the failure of the seal on all coolant pumps at 100 min into the accident; in all other respects the case is identical to a previous station blackout calculation. Both cases started at accident initiation and continued through boiloff of the water, failure of the control and fuel rods, oxidation of the zircaloy and the formation of U-Zr-O eutectics, failure of the vessel internal structures due to melting and loading, massive core disruption, and subsequent vessel failure. The two cases reached significantly different end conditions. The basic TMLB' resulted in a high pressure (15 MPa) vessel failure approximately 4 h after accident initiation. The addition of a 12.5-mm hole in each pump seal caused the water in the loop seal to clear and resulted in a significantly lower pressure (0.27 MPa) at vessel failure, which occurred almost 10 h after accident initiation. Therefore, high pressure melt ejection (HPME) and the potential for subsequent direct containment heating (DCH) were predicted not to occur in the TMLB' accident scenario with pump seal failure. (orig.)