Failure Probability Analysis of a Reactor Pressure Vessel Using a Deterministic Flaw Acceptance Criterion

Abstract

The accepted defective components using a deterministic approach in structural integrity assessment may still fail under the operation conditions used in the assessment. A probability analysis method is proposed in this paper to estimate the failure probability of the defective components corresponding to the critical conditions of the deterministic assessment method. The method not only can be used to validate the probabilistic requirement under the deterministic assessment criteria, but also guide to draft the safety factors in the deterministic assessment criteria based on the probabilistic requirement. Considering elastic fracture mechanics based flaw acceptance criteria given in ASME BPVC Section XI, a typical cooling down transient(normal operation) and a typical pressurized thermal shock transient(a fault condition) are analyzed using both the deterministic and probabilistic methods for a reactor pressure vessel(RPV) with defects. The critical crack sizes are calculated using the deterministic method with assigned safety factors and the corresponding failure probabilities are estimated. Then, the effect of the safety factor on the failure probabilities is discussed. The results of the case study show that the safety factors recommended by ASME Code may not be sufficient for the normal cooling down transient to satisfy the probabilistic requirement of nuclear safety.