Void swelling in ferritic steels

Ferritic steels are highly resistant to void swelling, and are therefore good candidate materials for fast and fusion reactor core components. The program of irradiations described has provided much needed experimental information about the individual characteristics of ferritic alloys which influence swelling. The ferritic materials studied were two high purity alloys, iron and iron-10% chrome, and a 10% chrome commercial steel, FV448. An austenitic Type 316 stainless steel was also included. Samples of these were bombarded with neutrons, heavy ions and electrons in four irradiation facilities: a High Voltage Electron Microscope, the Variable Energy Cyclotron at Harwell, the Van der Graaff Accelerator at Oak Ridge and the EBR-II fast reactor. The resulting microstructural damage was examined by transmission electron microscopy, and quantitative measurements were made of the size and density of voids and dislocation loops in each specimen. The experiments covered a range of doses and temperatures, and different alloys were mounted on the same targets so that their behaviour under identical conditions could be compared. A computer model based on the rate theory of swelling was written to calculate loop and void growth rates as a function of dose, and by fitting the predicted curves to the observed values the interstitial bias of the dislocations was determined. As a result of this project the main factors responsible for the suppression of void growth in these materials have now been established. (author)