The Effect of Low Dose-Rate Irradiation on the Microstructure of 304 Stainless Steel*

Changes in mechanical and corrosion properties caused by the development of radiationinduced microstructure have relevance to the aging and lifetime extension of light water reactors (LWR’S). However, much of the current data related to microstructural development in irradiated metals are generated from studies carried out at much higher dose-rates than encountered in LWR’S. An opportunity exists to study the influence of low dose-rate irradiation on rnicrostructural development for a variety of structural and surveillance materials extracted from the experimental breeder reactor EBR-11. In thk study, irradiated 304 stainless steel hexagonal “hex” duct material is examined in order to compare microstructure in the dose-rate range of 10-710-g dpakec. The samples, taken from the reflector locations in EBR-11, experienced a total dose between 10 and 12 dpa at a temperature of -375”C. Transmission electron microscopy (TEM) results reveal that there is a moderate dose-rate effect on @crostructurzd development for samples irradiated in the range of 2 x 108 to 4 x 10-8dpakec, however a substantial dose rate-effect exists between dose-rates of 2 x 10-8and 1 x 10-9 dpak.ec Transmission electron microscopy (TEM) results will detail the development of the microstructure in terms of radiation-induced cavities, dislocations, and precipitates.