Proposal of nuclear power plant piping maintenance method based on reliability evaluation
Crack evaluation Fitness-for-service Fracture probability Reliability Successive inspection
When cracks are found in nuclear power plant piping, the integrity during the evaluation period is secured using the Rules on Fitness-For-Service of the JSME (the Rules on FFS), and continuous operation is allowed while leaving cracks if satisfying the criteria. This paper focuses on the reliability of crack evaluation using the Rules on FFS and proposes inspection and evaluation methods to satisfy the target reliability. The sufficient reliability cannot be obtained by employing safety factor or limitation of crack depth due to variations in inspection and evaluation particularly when the pipe diameter is small or the crack angle is large. Prediction accuracy of the crack depth is very important to keep the sufficient reliability. Reliable crack evaluation is achieved by performing successive inspections defined by the rules on FFS and re-predicting the crack size to envelope the actual crack size based on the successive inspection results.