Probabilistic Safety Analysis For ATWS Of AP1000

Probabilistic Safety Analysis can provide a comprehensive analysis for the nuclear reactor accident process, and can be quantified for the potential accident. In the nuclear reactor safety analysis, PSA that is a supplement to deterministic safety analysis can identify the weak points of the plant design or operation. In order to assess the safety performance of the AP1000 advanced passive plant in the ATWS accident, PSA for the ATWS accident of AP1000 has been researched in this study. The main contents and results are as follows:The ATWS have been classified into three categories: ATWS without main feed water,ATWS with SI and ATWS transients with main feed water. The ATWS accident process and security function have been analyzed. On this basis, the three event tree models of the ATWS have been established.The fault trees of the AP1000 system for mitigating of ATWS accident have been established, the uncertainty and human reliability about the fault trees have been analyzed in detail, and the common cause failure(CCF) analysis has been researched deeply. Common cause failure model have been given, including the parameter estimators of Alpha, Beta factor model and MGL model under staggered testing scheme and nonstaggered testing scheme. The effects of the three models on system failure unavailability have been evaluated.The Risk Spectrum software has been used to finish the quantitative and qualitative analysis of the system fault trees and accident sequences. The result shows that the core damage frequency(CDF) of the ATWS accident is 5.35E-10 per reactor year. The lower(5%)and upper(95%) limit of confidence interval are 3.70E-12 per reactor year and 1.55E-09 per reactor year. The minimal cut sets of the system fault trees and accident sequences have been obtained, and it's probabilities have been calculated. The importance measures of core damage have been analyzed to identify the important risk and security basic events. In addition, in a sensitivity case, the CDF of ATWS has been evaluated to be 2.52E-06 per reactor year, after setting human error failure probabilities by 1.It's increase in 4710 times. It is evident that human actuations are very important for the mitigation of ATWS accident. The CDF increased in 10.7 times after the PRHR is not available,PRHR is the most important of passive safety systems.