United States Nuclear Regulatory Commission - Protecting People and the Environment

Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials (NUREG/CR-6909) - Final Report

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Publication Information

Manuscript Completed: November 2006
Date Published:
February 2007

Prepared by:
O. K. Chopra and W. J. Shack

Argonne National Laboratory
9700 South Cass Avenue
Argonne, IL 60439

H. J. Gonzalez, NRC Project Manager

Prepared for:
Division of Fuel, Engineering and Radiological Research
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code N6187

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Abstract

The ASME Boiler and Pressure Vessel Code provides rules for the design of Class 1 components ofnuclear power plants. Figures I–9.1 through I–9.6 of Appendix I to Section III of the Code specify design curves for applicable structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. The existing fatigue strain–vs.–life (ε–N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. Under certain environmental and loading conditions, fatigue lives in water relative to those in air can be a factor of ≈12 lower for austenitic stainless steels, ≈3 lower for Ni-Cr-Fe alloys, and ≈17 lower for carbon and low-alloy steels. This report summarizes the work performed at Argonne National Laboratory on the fatigue of piping and pressure vessel steels in LWR environments. The existing fatigue ε–N data have been evaluated to identify the various material, environmental, and loading parameters that influence fatigue crack initiation, and to establish the effects of key parameters on the fatigue life of these steels. Fatigue life models are presented for estimating fatigue life as a function of material, loading, and environmental conditions. The environmental fatigue correction factor for incorporating the effects of LWR environments into ASME Section III fatigue evaluations is described. The report also presents a critical review of the ASME Code fatigue design margins of 2 on stress (or strain) and 20 on life and assesses the possible conservatism in the current choice of design margins.

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