Assessment of Reliability of Emergency Core Cooling System (ECCS) of Bushehr Nuclear Power Plant

Bushehr Nuclear Power Plant (BNPP) originally designed by German KWU and then modified by Russian companies is approaching commissioning. In this paper, the reliability of Emergency Core Cooling System (ECCS) of the new design is compared with the older one using both deterministic and probabilistic methods. The reliability of both systems is calculated in case of occurrence of Large Loss of Coolant Accident (Large LOCA). The new Russian design is based on the original KWU Convoy design and the applied modifications have improved its reliability. To perform the reliability analysis the event tree/fault tree method is used and the calculations are done by IAEA computer code PSAPACK. The results show that the applied modifications such as, increase of redundancy from 4 × 50% to 4 × 100%, change of cool down route, fuel storage pool cooling in all four trains have reduced the ECCS unavailability from 5.9 E−4 to 1.7 E−4. Furthermore, based on the results it is shown that both designs comply well with the IAEA recommendations on Probabilistic Safety Criteria (PSC) and INSAG-3 requirements.