investigation of molten material retention during the large and small breaks loca and station blackout accident

The analysis deals with the assessment of best estimate code relap5/scdap mod3.4 in the simulation of double-ended loss coolant accident as a lboca, 4 in break as a sbloca an sbo accident with considering except accumulator water where no core cooling water systems are available. the reference plant is surry nuclear power plant as a westinghouse three-loop nuclear power plant. in order to mitigation accident, the in-vessel retention strategy was investigated for the prevention of lower plenum failure. it has been concluded that during the sbloca, lbloca conditions bottom of active fuel is uncovered at 6340 s and 2160 s, respectively. it occurred for two times at 11650 s and 15608 s in sbo. at 6792 s and 57002 s in the lbloca and sbo due to reaching melting point and in the sbloca at 15215 s due to lower plenum creep rupture, failure of the reactor pressure vessel occurred. the results show that hydrogen production in the sbo is more than the other two cases. for the prevention of the lower plenum failure, the in-vessel molten material retention strategy is investigated as a passive system. the results show that lower plenum heat flux can be kept below the critical heat flux and its integrity is preserved in two cases of this analysis.