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    Fracture Toughness Shifts and Bounds for Irradiated Reactor Pressure Vessel Materials

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    Transition temperature shift effects arising from neutron radiation embrittlement in ferritic nuclear pressure vessel materials are currently being evaluated using changes in the Charpy V-notch energy curve; typically, the temperature shift at the 41-J (30 ft-lb) energy level is used. Estimates of the 41 J (30 ft-lb) transition temperature are also projected based upon Nuclear Regulatory Commission Regulatory Guide 1.99, Revision 2. The estimated or measured Charpy shift is then applied to a lower-bound reference toughness KIR curve by moving the curve by the Charpy shift amount. Similarly, the flaw evaluation procedures in nonmandatory Appendix A of Section XI of the ASME Boiler and Pressure Vessel Code utilize the shifts in the equivalent of the KIR curve (termed the KIa curve for crack arrest) and a lower-bound static crack initiation toughness KIc curve. This study reviewed and tested this Code's approach, as well as the statistically based reference toughness method developed by W. Oldfield for estimating global tolerance bounds. Comparisons of actual, but limited, fracture toughness data and the predicted bounding curves indicate that the shifted KIR/KIc curves are generally very conservative. The Oldfield reference toughness approach for 95%-95% tolerance bounds is not as conservative, but may provide a better method. In terms of mean toughness shift behavior, the shifts predicted by Charpy V-notch results are not always a true indicator of the mean fracture toughness shift; however, the other margins included in Regulatory Guide 1.99, Revision 2 and those in the original unirradiated KIR/KIc curves appear to compensate for any nonconservatism in using the Charpy V-notch shift approach.


    reference toughness, fracture toughness, radiation embrittlement, Charpy energy, transition temperature shifts, pressure vessel steels

    Author Information:

    Server, William L.
    Senior project manager, TENERA, L. P., Berkeley, CA

    Griesbach, Timothy J.
    Senior project manager, TENERA, L. P., Berkeley, CA

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP49454S