Void swelling of ferritic steel during 1 MeV electron irradiation

FV448 ferritic-martensitic stainless steel is irradiated with 1 MeV electrons to damage levels up to 40 displacements per atom (dpa) at temperatures in the range 350 to 500 0C. The microstructures after irradiation are evaluated and compared with those produced by fast reactor irradiations to similar dose levels. Electron irradiation induces spatially homogeneous dislocation substructures and a uniform high density (<= 8 x 1022 m-3) of small (approximately 5 to 10 nm) slow-growing voids, giving low swelling rates (approximately 0.07% per dpa) at a peak swelling temperature of approximately 425 to 450 0C. The microstructural evolution is in marked contrast to the heterogeneous dislocation substructures and near swelling immunity observed after fast reactor irradiations. The results are discussed in terms of void nucleation events, simplified rate theory, and a previously proposed model for swelling resistance of ferritic steels based on a duplex system of interstitial dislocation loop geometries. The implications of the observed microstructures on the maintenance of long-term swelling resistance of ferritic steels in both fast and fusion reactor environments are briefly considered. (author)