Submerged-arc weld material has been exposed to accelerated irradiation at ~180°C to a nominal total fast neutron dose of ~5 × 10¹⁷ neutrons (n)/cm² (E > 1 MeV). The effect of this irradiation on the fracture toughness has been measured using both precracked Charpy and 25-mm compact tension specimens.

Results show that upper-shelf fracture toughness values, though within the scatter-band on unirradiated control data, appear to be reduced by irradiation. No change in fracture toughness transition temperature is induced by the accelerated irradiation exposure. Comparison of the accelerated irradiation data with that obtained from much lower dose rate irradiations indicates the importance of irradiation exposure time. The effect of exposure time is explained in terms of the precipitation of small copper-rich complexes. This proposal is supported by preliminary small-angle neutron scattering data.