Mohsen Salehi - Young Researchers and Elites club, Science and Research Branch, Islamic Azad University, Tehran, Iran
Mohsen Shayesteh - Physics Department, Imam Hossein University, Tehran, Iran

‎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.

‎SBLOCA, ‎LBLOCA, ‎SBO, ‎Creep rupture, ‎In-vessel cooling