Evaluation of the Maine Yankee Reactor Beltline Materials

Abstract

Tension and Charpy V-notch specimens of the base metal, heat-affected zone metal, and weld metal from the beltline region of the Maine Yankee pressure vessel (Type A533B-1 steel) were irradiated in an accelerated surveillance capsule. The specimens were exposed to a fluence of 1.3 × 1019 neutrons (n)/cm2 (>1 MeV) at 550 °F (288 °C). Charpy V-notch specimens of a standard reference material (SRM) were also irradiated in the surveillance capsule as a correlation monitor for dosimetry. Irradiation increased the yield and ultimate strength and decreased the ductility of all of the Maine Yankee materials. The yield strength increased 50 percent for the weld metal and 35 percent for the base and heat-affected zone materials. Radiation-induced shifts in the Charpy V-notch curves at the 30 ft∙lb, 50 ft∙lb, and 35-mil levels were measured. The decrease in the Charpy upper shelf energy was also measured. The largest temperature shift occured at the 35-mil level for all materials, and this shift was used to determine the adjusted reference temperature. The increase in reference temperature ranged from 140°F (60°C) for the base metal to 345°F (174°C) for the weld metal. The weld metal also showed the largest drop in the Charpy upper-shelf energy (44 percent) versus 23 to 31 percent for the other materials. The critical beltline material for determining the new operating limit curves for the reactor was the weld metal, with an adjusted reference temperature of 315°F (157°C) and a Charpy upper-shelf value of 57 ft∙lb. The high copper and phosphorus content of the weld (0.36 percent copper, 0.015 percent phosphorus) caused the irradiated Charpy data to fall above the general trend curve for Type A533B steel. A trend curve for the weld metal was constructed using independently generated irradiation data on the same weld metal.