Dose-rate effects on irradiation embrittlement and composition and temperature effects on annealing/reirradiation sensitivity

Recent MEA investigations on the effect of neutron flux level on radiation-induced embrittlement accrual and the contributions of metallurgical variables to postirradiation annealing and reirradiation behavior are reviewed. Studies of dose-rate effects involved experiments in the UBR test reactor and separately, radiation sensitivity determinations for the decommissioned Gundremmingen (KRB-A) vessel material. Annealing-reirradiation studies employed 3990C and 4540C heat treatments. Material composition is shown to play a major role in postirradiation annealing recovery. Results illustrate effects of variable copper and variable nickel contents on recovery for steel plate having low phosphorus levels. Composition effects on recovery were also observed for prototypic welds depicting high/low copper and high/low nickel contents and three flux types. The welds, in addition, indicate major differences in re-irradiation sensitivity. The UBR investigations revealed a significant difference in flux level sensitivity between the ASTM A 302-B reference plate and a submerged-arc (S/A) Linde 80 weld, based on C/sub v/ tests and quasi-static fracture toughness (J-R curve) tests. Studies of the Gundremmingen reactor vessel, representing a joint USA-FRG-UK undertaking, revealed an anomaly in strong vs. weak test orientation radiation sensitivity