Evaluation of ECCS passive part operability at severe accident conditions due to LBLOCA along with SBO using RELAP5/SCDAP3.4 code

In this paper, VVER-1000/V446 nuclear reactor is modeled using RELAP5/SCDAP3.4 code in order to its behavior investigation during severe accident conditions in a LBLOCA scenario along with station blackout (SBO) was carried out. The analyze was performed in two stages related to availability and unavailability of emergency core cooling systems passive part (Hydro Accumulators & KWU tanks). The initial core inventory is calculated using MCNPX 2.7 code and the primary & secondary systems was modeled in RELAP5/SCDAP3.4. The reactor core consists of 163 hexahedral fuel assemblies was divided into five groups based on average power peaking factors which were modeled in SCDAP code. For each group a corresponding channel was considered in relap5 code plus a bypass channel.Finally in order to investigation the phenomena of slumped core into lower plenum, input of couple code along with related geometric mesh was coupled to input of RELAP5/SCDAP3.4 code. Results of first stage analyze (availability of ECCS) was showed that the operators have ~3hr before core degradation and results of second stage analyze (unavalability of ECCS) was demonstrated that this time to ~15min was decreased. As for availability and unavalability ECCS, respectively 350 and 210 kg hydrogen in vessel was producted. Also Calculation of first stage analyze was showed that beginning of oxidation, release of FPs , creep rupture of vessel with conservative calculation and creep rupture with best estimat calculation respectively at times 9850, 10900 , 17700 and 31000 and respectively for second stage at times 580, 660, 4100 and 9700 second after beginning of transient condition was occurred.