United States Nuclear Regulatory Commission - Protecting People and the Environment

Comparison of Irradiation-Induced Shifts of KJc and Charpy Impact Toughness for Reactor Pressure Vessel Steels (NUREG/CR-6609)

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Publication Information

Manuscript Completed: February 1999
Date Published: November 2000

Prepared by:
M. A. Sokolov, R. K. Nanstad

Oak Ridge National Laboratory
Managed by Lockheed Martin Energy Research Co.
Oak Ridge, TN 37831-6151

C. J. Fairbanks, NRC Project Manager

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

NRC Job Code W6953

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Abstract

The current provisions for determination of the upward temperature shift of the lower-bound static fracture toughness curve due to irradiation of reactor pressure vessel steels are based on the assumption that they are the same as for the Charpy 41 -J shifts as a consequence of irradiation. The objective of this report by the Heavy-Section Steel Irradiation Program is to evaluate this assumption relative to data reported in open literature. Depending on the specific source, different sizes of fracture toughness specimens, procedures for the determination of KJc, and fitting functions were used. It was anticipated that data scatter might be reduced by using a consistent approach to analyze the published data. A method employing Weibull statistics was applied to analyze original fracture toughness data of unirradiated and irradiated pressure vessel steels. The master curve concept was used to determine shifts of fracture toughness transition curves. A hyperbolic tangent function was used to fit Charpy absorbed energy data. The fracture toughness shifts were compared with Charpy impact shifts evaluated with various criteria. Linear regression analysis showed that for weld metals, on average, the fracture toughness shift is the same as the Charpy 41 -J temperature shift, while for base metals, on average, the fracture toughness shift at 41 J is 16% greater than the shift of the Charpy 41 -J transition temperature, with both correlations having relatively large (95%) confidence intervals of ±26°C and ±36°C, respectively.

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