REEVALUATION OF STATION BLACKOUT RISK OF OPR-1000 NUCLEAR POWER PLANT APPLYING COMBINED APPROACH OF DETERMINISTIC AND PROBABILISTIC METHOD

摘要

Station blackout (SBO) is a typical beyond design basis accident (BDBA) and significant contributor to overall plant risk. The risk analysis of SBO provides an important basis for rulemaking, accident mitigation strategy, etc. The SBO risk can be reevaluated when (1) the loss of offsite power (LOOP) frequency is updated reflecting the latest operating experience database, (2) the availability of component/systems involved in the accident scenario is changed, (3) the system design is modified such as the improvement of direct current (DC) battery capacity, or (4) the methodology of thermal-hydraulic analysis used in probabilistic risk assessment (PRA) is changed. Recently a procedure for combining deterministic and probabilistic methods was proposed, where the conditional exceedance probability (CEP) acts as go-between deterministic and probabilistic methods. The combined approach is accompanied by a best estimate plus uncertainty (BEPU) method, and results in more reliable values of core damage frequency (CDF) and conditional core damage probability (CCDP). This study intends to reevaluate the SBO risk in the reference OPR-1000 nuclear power plant by applying the combined approach. Meanwhile, the current PRA results indicate that the time to offsite power restoration is the most important contributor to the SBO risk of the plant, where it has been determined by conservative thermal hydraulic analysis with MAAP code. In this study the uncertainty parameters affecting SBO transient were preliminarily identified and quantified by determining their distributions, then the CEPs were calculated with various values of offsite restoration time. The combined approach can extend the offsite power restoration time for no core damage more than the PRA. Then use of offsite restoration time, obtained from operating experience analysis, decreases the SBO risk.