Re-assessment of accumulators performance to identify VVER-1000 vulnerabilities against various break sizes of SB-LOCA along with SBO

摘要

After Fukushima Daiichi accident it is suggested to identify the vulnerabilities of nuclear power plants. In SB-LOCA along with SBO scenario, the passive safety systems can have a positive influence on the accident mitigation. This article aims to analyze the performance of passive accumulators (ACC) injection in the spectrum (10-100 mm break sizes) of SB-LOCA that simultaneously occurs with SBO in Bushehr Nuclear Power Plant (BNPP). The results showed that ACCs are not able to inject in the whole range of breaks, because the primary loop pressure is not decreased sufficiently in minimal breaks without operator intervention. Also, the Core Damage Times (CDT) have been calculated for this range of breaks based on 1204 degrees C of Peak Cladding Temperature (PCT) and Burst Pressure-Temperature Diagram (BPTD) to identify the vulnerable break size. Further, analysis showed that the range of smaller breaks has a shorter CDT (the 50 mm break is the most vulnerable break size) that can be improved by optimizing the set-points of accumulators.