Some welds made with Linde 80 flux and containing a high copper impurity level have exhibited postirradiation Charpy upper-shelf energy levels below 68 J (50 ft · lb). The J-R curve behavior of seven such low upper-shelf welds has been characterized in the ductile upper-shelf regime in both the preirradiation and the postirradiation conditions with fluences of ~1 × 1019 neutrons (n)/cm2 (E > 1 MeV). With the single specimen compliance (SSC) technique, these J-R curves were determined from compact toughness (CT) specimens ranging from 12.7 to 101.6-mm thick, over a temperature range of 75°C to 288°C.
For these reactor vessel steels exhibiting low upper-shelf energy levels, the J-R curves were shown to follow a power-law relationship for small crack extensions, that is, less than 2 mm. In some cases, a possible size dependence of the J-R curve has been seen, but the results are inconclusive on this point.
Correlations between J-R curve parameters (JIc and average value of tearing modulus, Tavg) and Cv upper-shelf energy have been suggested at 200°C. These findings could enhance the significance of Cv reactor surveillance data with respect to structural integrity. However, JIc and Tavg have demonstrated an inverse relationship with temperature that is not reflected by the Cv upper-shelf trend. Therefore, correlations between Cv energy and J-R curve must be adjusted to account for temperature.
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 (CV) 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 CV 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.
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