Structure Investigations on Russian Reactor Pressure Vessel Steels by Small Angle Neutron Scattering

The effect of radiation embrittlement has high safety significance for Russian VVER reactor pressure vessel steels. Heats of base and weld metal of the as received state, irradiated state and post-irradiation annealed state were investigated by SANS to get insights about the microstructural features caused by neutron irradiation.
The SANS intensities increase in the momentum transfer range between 0.8 and 3 nm-1 for all material compositions in the irradiated states. The size distribution function of the irradiation-induced defects has a pronounced maximum at 1 nm in radius. Their volume content varies between 0.1 and 0.7 vol.% dependent on material composition and increase with the neutron fluence. The comparison of nuclear and magnetic scattering indicate that the defects differ in their composition. Thermal annealing reduces volume fraction of irradiation defects.