Characterization of ion irradiated microstructure and cavity swelling evolution up to high doses in austenitic stainless steels representative of PWR internals

Abstract : Ion irradiations have been performed at 450 °C on 304 and 304L austenitic stainless steels representative of PWR internals structure up to high doses (close to 100 dpa). TEM and APT have been carried out on irradiated samples. Depending on the dose, Frank loops, dislocation network, cavities, precipitates and segregations have been observed in both 304 steels grades. Their evolution with dose, and in particular for cavities and corresponding swelling, is described and potential microstructural differences between materials are highlighted. It appears that swelling is limited even up to high doses in both materials due to only slight evolution of cavity density and size from intermediate to high doses. As the irradiation temperature has been chosen to simulate PWR microstructure taking into account a temperature/flux shift effect, the microstructural results are discussed and compared with those of PWR.