Effect of neutron flux on irradiation-induced microstructure and hardening of reactor pressure vessel steel

Existing knowledge about the effect of neutron irradiation on the mechanical properties of reac-tor pressure vessel steels under reactor service conditions relies to a large extent on accelerated irradiations realized by exposing steel samples to a higher neutron flux. A deep understanding of flux effects is, therefore, vital for gaining service-relevant insight on the mechanical property degradation. Existing studies on flux effects often suffer from incomplete descriptions of the ir-radiation-induced microstructure. Our study aims at giving a detailed picture of irradia-tion-induced nanofeatures by applying complementary methods using atom probe tomography, positron annihilation, small-angle neutron scattering and transmission electron microscopy. The characteristics of the irradiation-induced nanofeatures and the dominant factors responsible for the observed increase of Vickers hardness are identified. The results rationalize why pronounced flux effects on the nanofeatures, in particular on solute atom clusters, only give rise to small or moderate flux effects on hardening.