Short-term programme for seismic safety of Units 3 and 4 of Kozloduy NPP

According to experts' opinion and experimental results the safety level of the units WWER-440/230 in Kozloduy NPP is vulnerable both to internal (accidents) and external (seismic) events. Two short-term programmes for overcoming this risk are launched almost simultaneously by the Kozloduy NPP and Excellent Quality Engineering (EQE) - Bulgaria: 1) for technological improvements aiming diminution of internal risk in Units 1 and 2; 2) for antiseismic modification of the Units 3 and 4. The antiseismic improvements have been done on unit 3 and partially on unit 4. A comparative seismic probabilistic analysis was performed before and after the implementation of the projects of EQE-Bulgaria for the Unit 4. For optimizing the safety-related investments in Kozloduy NPP, EQE-Bulgaria suggests to perform a total seismic PSA and to combine the antiseismic improvements with appropriate changes in the safety systems. (author)