Postirradiation heat treatment (annealing) is being investigated as a possible method for the periodic relief of radiation embrittlement to reactor vessel steels. This report describes a study of the Charpy-V (C_V) notch ductility of two representative A533-B weld deposits under two full annealing and reirradiation cycles. The welds were specially chosen for their high sensitivity to radiation effects and for their difference in as-fabricated C_V upper-shelf energy levels. Notch ductility properties were determined at each phase in the irradiation-annealing sequence. Heat-treatment temperatures were selected to represent two heat-treatment options open for vessel annealing.

The results demonstrate that a 399°C (750°F), 168-h heat treatment is highly effective for reducing radiation embrittlement accrual in service; in contrast, a 343°C (650°F), 168-h heat treatment is shown to be of little benefit for the fluence conditions investigated. A greater rate of radiation embrittlement was observed for the heat-treated material (both conditions) compared with nonheat-treated material. The investigations also revealed a significant difference between upper-shelf energy and transition temperature response to heat treatment.