The safety improvement of VVER-1000 NPP against SBO accident using portable air-cooled diesel generator

Abstract

The Fukushima accident demonstrated that the safety design of nuclear power plants should be assessed by installing additional backup sources of electrical power and cooling to cope with extreme natural events. It is supposed that both off-site and on-site AC power supply sources are lost during the station blackout accident (SBO). The probabilistic safety analysis (PSA) of VVER-1000/V-446 nuclear reactor shows that the core damage frequency (CDF) due to SBO is a dominant contributor to the total CDF of NPP. In this study, the installation of portable air-cooled diesel generator (PDG) is proposed to prevent severe core damage and maintain the safety functions during SBO accident in NPP. The scenarios to remove the residual heat of the core through primary and secondary cooling systems by deploying PDG are determined. The list of loads and sequence connection of safety systems are specified for each scenario. The capacity, type, and characteristics of PDG are determined based on the identified electrical loads and weather condition of the NPP site. The conceptual plans for connections of PDG into the electrical distribution of NPP to feed safety systems are represented as well. The suggested scenarios are justified by thermal balance method and assessment of reported thermal-hydraulic calculation of NPP. The PSA analysis is performed by SAPHIRE code as a reliability and risk assessment software to investigate safety improvement of NPP against SBO accident with considering PDG. The results show that the CDF due to SBO is reduced from 3.61E−06 (1/year) to 9.897E−009 (1/year).