Exploratory Investigations of Cyclic Irradiation and Annealing Effects on Notch Ductility of A533-B Weld Deposits

Abstract

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.

Hardness tests on irradiated pressure vessel steel

“…The response to s ubsequent irra di a ti on af ter annea ling must also be taken into account . Both the annea ling response and the re-irr adiation respo nse are har d to predict because the mechanism f or the trace element e ff e c t is not well-known.Two annealing alternatives are presently bein g considered : anne aling at 343 de grees C (650 de grees F) or a t 399 degrees C (750 degrees F)(29). The 343 degrees Chea t treatment was selected as the maximum temperature a t which nuclear or pump h eating could be employed .…”

“…The 399 degrees C treatment was chosen as an achie vable temper atur e if auxi liary heaters are employed . This second al te rna t ive i s advan tageo us be cause greater pr operties recovery can t ake place by vi rtue of the higher temperature, bu t, it is disadvantageous because the co re internals , as well as the rea cto r coo lant , mus t be removed(29) .The r emoval o f the internals and the coolant wo uld add to the complexity of t he prob lem. The 343 degrees C treatment pro duced a high de gree of re covery (b etween 62 and 100%) in the USE but only l imited re covery in RTNDT (between 22 and 29%) after 168 hours a t tempera ture .…”