Irradiation effects on Charpy impact and tensile properties of low upper-shelf welds, HSSI series 2 and 3

When reactor pressure vessel steels exhibit Charpy V-notch impact upper-shelf energy levels of less than 68 J (50 ft-lb), the requirements of Title 10, Code of Federal Regulations, Part 50, Appendix G, are not met. The regulations require, as an option, that a fracture mechanics analysis be performed that conservatively demonstrates adequate safety margins for continued operation. Under conditions where large prefracture crack-tip plastic zones are present, linear-elastic fracture mechanics concepts are not applicable, and the use of elastic-plastic fracture mechanics concepts has been recommended by the US Nuclear Regulatory Commission. A number of Babcock and Wilcox Company-fabricated reactor vessels in commercial pressurized water reactor plants include welds with both relatively low initial Charpy upper-shelf energies and high copper concentrations, which make them highly sensitive to neutron irradiation. As a result, the Charpy upper-shelf energies of many welds are expected to fall below 68 J (50 ft-lb) prior to reaching design life. The Heavy-Section Steel Irradiation Program conducted the Second and Third Irradiation Series to investigate the effects of irradiation on the ductile fracture toughness of seven commercially fabricated, low upper-shelf welds. This report represents analyses of the Charpy impact and tensile test data, including adjustments for irradiation temperature andmore » fluence normalization, which make possible comparison of the irradiation sensitivity the different welds.« less