The Research Of Probabilistic Fracture Mechanics Analysis Of Reactor Pressure Vessel With Defects Under The Pressurized Thermal Shock Transient

Reactor pressure vessel (RPV) is an important component in nuclear power plants, the crack-like defects may exist in RPV during the whole operation life of nuclear power plants as a result of the manufacturing process or the operation condition. During the Pressurized Thermal Shock (PTS) transient, a higher stress is applied on the RPV crack face under the combined effects of system's high pressure and the thermal stress produced by cooling water, at the same time the fracture toughness is reduced with RPV cooled by the cooling water. So the safety of the RPV would undergo a greater challenge, it is necessary to assess the structural integrity of RPV under PTS transient. Many parameters have statistical distribution characteristics in the structural integrity of RPV, and it's difficult to evaluate the influence of the relevant parameters'uncertainty on the safety of RPV by deterministic fracture mechanics analysis. So it is needed to conduct probabilistic fracture mechanics (PFM) assessment of RPV to analysis the RPV's reliability under PTS transient more comprehensively. We haven't found any domestic research on this field, the following aspects of the PFM analysis of RPV under PTS transient has been studied and discussed in this paper.(1) The analyzed method of crack initiation, crack arrest and the plastic failure of RPV are established according to the failure model of RPV under PTS transient and the special nature of the relevant parameters during the PTS transient. We choose flaw size, chemical composition, fracture toughness and fast neutron irradiation flux as the parameter that has statistical distribution characteristics, and we focus on the analysis of fracture toughness's statistical distribution model, the three-parameter Weibull distribution model of initiation toughness and the log-normal distribution model of arrest toughness are established by the statistical analysis of fracture toughness data. In addition, the choice of fast neutron irradiation embrittlement prediction model is determined by the comparison and analysis of the different model and the probabilistic fracture model is established according to the content of fracture mechanics analysis and reliability analysis method.(2) The Monte Carlo simulation method is used to calculate the relevant probability and it is realized by compute programming in Visual C++ 2010. The Qinshan 2# RPV-600 is analyzed by the PFM analysis program. The results show that:the probability of crack penetrates through wall is less than 1.0×10-6 at the beginng of RPV life, and the probability of crack penetrates through wall increases gradually with the growth of fast neutron irradiation flux, the probability of crack penetrates through wall is less than 1.0×10-5 at the end of RPV life.