Deterministic safety analysis of SBO accident using FLEX strategies in VVER-1000

Following Fukushima Daiichi accident on March 2011, the nuclear power plants are requested to reassess the robustness NPPs in extreme natural events. Actually, the strong features, weakness and potential of NPP to cope with Station Black- Out (SBO) as a consequence of Fukushima accident should be identified. It is assumed that both the normal power supply sources and the emergency diesel generators (4100%) are lost during the SBO accident in VVER-1000 NPP as a case study. The diverse and flexible coping strategies (FLEX) including portable equipment are utilized in VVER-1000 in order to prevent the severe core damages and maintain residual heat removal due to SBO accident. The objective of this paper is deterministic safety analysis of SBO accident using FLEX strategies to manage accident in VVER-1000. Emergency operating procedures and deployment of portable equipment are considered in these strategies. The primary and secondary thermo-hydraulic parameters, critical times (time of steam generators emptying, time of fuel degradation, etc.) and procedure of portable equipment deployment are determined using the RELAP code. The effects of FLEX strategies on the behaviors of the core are analyzed during SBO accident. Obtained results show the delay of the severe core melting and subsequent reactor vessel failure for at least the extension time interval. The core integrity is also maintained by availability and operation of the portable equipment after SBO accident. It is revealed that the long-term core cooling is achieved by FLEX strategies to cope with SBO accident in VVER-1000.