Small Angle Neutron Scattering Investigations of the Microstructure of VVER 440-type Reactor Pressure Vessel Steel after Irradiation at 60 °C

The formation of point defects and precipitates after neutron irradiation of VVER-440-type reactor pressure vessel steel was investigated by small angle neutron scattering experiments. Irradiation at 60 °C increased the number of point defects, decreased the precipitates, which already exist in the unirradiated state, and formed a new typ of fine-scaled precipitates. Post-irradiation annealing near the operational temperature of the nuclear power plants (270 °C) provoked a slight decrease of the content of point defects and of the irradiation-induced precipitates. The content of these precipitates which are also present in the unirradiated state did not change by annealing.