A Reassessment of Fracture-Safe Operating Criteria for Reactor Vessel Steels Based on Charpy-V Performance

Fracture-safe operating criteria for commercial nuclear pressure vessels based on fracture analysis diagram procedures and Charpy-V energy trends are reappraised with respect to the effects of thick section mechanical constraint and low Charpy - V shelf energies resulting from neutron irradiation. Comparisons of the Charpy-V test with the more definitive dynamic tear test procedures indicate the former to be an acceptable means of assessing the fracture toughness of A533-B steel. The mechanical constraint associated with 12-in. thicknesses of this steel suggests the addition of 70 F (39 C) to the existing criterion requiring vessel operation above NDT + 60 F (33 C). Ratio analysis diagram procedures are shown to be useful in interpreting Charpy-V shelf level data obtained from vessel surveillance programs in terms of critical toughness levels relating to brittle fracture.