United States Nuclear Regulatory Commission - Protecting People and the Environment

Evaluations of Structural Failure Probabilities and Candidate Inservice Inspection Programs (NUREG/CR-6986)

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Publication Information

Manuscript Completed: November 2008
Date Published: May 2009

Prepared by:
M.A. Khaleel and F.A. Simonen

Pacific Northwest National Laboratory
P.O. Box 999
Richland, WA 99352

D.A. Jackson and W.E. Norris, NRC Project Managers

Prepared for:
Office of Nuclear Regulatory Research
US Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code N6398

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Abstract

The work described in this report applies probabilistic structural mechanics models to predict the reliability of nuclear pressure boundary components. These same models are then applied to evaluate the effectiveness of alternative programs for inservice inspection to reduce these failure probabilities. Results of the calculations would support the development and implementation of risk-informed inservice inspection of piping and vessels. Studies have specifically addressed the potential benefits of ultrasonic inspections to reduce failure probabilities associated with fatigue crack growth and stress-corrosion cracking. Parametric calculations were performed with the computer code pc-PRAISE to generate an extensive set of plots to cover a wide range of pipe-wall thicknesses, cyclic operating stresses, and inspection strategies. The studies have also addressed critical inputs to fracture mechanics calculations such as the parameters that characterize the number and sizes of fabrication flaws in piping welds. Other calculations quantify uncertainties associated with the inputs to the calculations, the uncertainties in the fracture mechanics models, and the uncertainties in the resulting calculated failure probabilities. A final set of calculations address the effects of flaw-sizing errors on the effectiveness of inservice inspection programs.

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