Charpy impact and compact fracture specimens were tested to determine the response of actual reactor vessel weld metals to the in-situ annealing cycle (454°C for 168 h) suggested by the Electric Power Research Institute (EPRI). This annealing cycle was developed to recover fracture properties lost as a result of radiation damage. The Linde 80 submerged-arc weld metals from the Babcock and Wilcox (B&W) Owners Group Integrated Reactor Vessel Material Surveillance Program were irradiated in power reactors. Resultant data are compared with the data from the EPRI sponsored in-situ annealing program. Comparison of the power reactor and test reactor data show similar responses to annealing. One-hundred percent recovery of the upper shelf and transition temperature was achieved after annealing for both reactor types. The EPRI J-R data showed only partial recovery with annealing. However, the B&W submerged-arc weld metals exhibited four responses to annealing: 1) complete recovery, 2) partial recovery, 3) negligible effect of either irradiation or annealing on the J-R fracture toughness, and 4) an increase in J-R fracture toughness to greater than the unirradiated value.

These varied responses indicate that the mechanism(s) of annealing recovery may be more complex than heretofore believed. A qualitative rationale, based on a defect cluster mechanism and a copper precipitation mechanism, is employed to explain the various annealing responses.