Evaluation of WF-70 Weld Metal From the Midland Unit 1 Reactor Vessel (NUREG/CR-5736)

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Publication Information

Manuscript Completed: February 1998
Date Published: November 2000

Prepared by:
D. E. McCabe, R. K. Nanstad, S. K. Iskander,
D. W. Heatherly, R. L. Swain

Oak Ridge National Laboratory
Managed by Lockheed Martin Energy Research Corporation

Oak Ridge National Laboratory
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

Low upper-shelf (LUS) weld metal was sampled from the Midland Unit 1 reactor vessel. The weld metal was designated to be WF-70 by Babcock and Wilcox Company code. The sampling was taken from both the nozzle course and beltline girth welds. The as-received materials characterization using Charpy curves, drop-weight nil-ductility transition, tensile tests, and chemical analysis surveys indicated that the materials from the two locations were essentially the same except for the copper content. The expected nominal copper contents were 0.40 and 0.26 wt % for the nozzle course and beltline welds, respectively. Because the experiment involved detailed evaluations of both unirradiated and irradiated (1 x 10¹⁹ n/cm²) conditions, the two weld metals were evaluated separately.

Fracture mechanics data were obtained for both the unirradiated and irradiated conditions; two methods of evaluating the transition temperatures were (1) the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, augmented with the American Society for Testing and Materials (ASTM) MethodE 185, and (2) the relatively new master curve method. The ASME method uses a reference temperature determination (RT_NDT) from nonfracture mechanics test practices; the master curve method uses a transition temperature, T_o, obtained from fracture mechanics-based data. The deficiencies of the ASME method as applied to LUS materials were evident. The master curve method, supplemented with fracture mechanics-based R-curve data, proved to have sufficient sensitivity to show differences between the nozzle course and beltline materials. The ASME-recommended methods failed to detect differences, thereby revealing the lower sensitivity of the empirical methods associated with RT_NDT.