Case Study on the Relationship between Safety Margin and Conditional Probability for the Integrity Analysis of Reactor Pressure Vessel under Pressurized Thermal Shock

Abstract

Both probabilistic and deterministic analysis methods are used in structural integrity assessment of the reactor pressure vessel (RPV) under pressurized thermal shock (PTS). In the deterministic analysis, the assessment of integrity according to the linear elastic fracture mechanics principle is carried out by comparing the stress intensity factor (SIF) KI with the fracture toughness KIc which is characterized by a reference transition temperature Tref. Then the safety margin ΔTm can be determined. In the probabilistic analysis, the conditional probability on the probabilistic fracture mechanics analysis can be obtained by Monte Carlo simulation, where some input parameters are regarded as random variables, such as fracture toughness, crack size, neutron fluence, etc. Then, the relationship between the conditional probability and the temperature margin is analyzed for some typical PTS transients. From the analysis, a good correlation between the conditional probability and the temperature margin is obtained.