Evolution of the radiation-induced defect structure in 316 type stainless steel after post-irradiation annealing

The thermal stability of Frank loops, black dots, cavities and gamma' precipitates in an irradiated 316 stainless steel was studied by transmission electron microscopy. The samples were retrieved from a thimble tube irradiated at around 320 degrees C up to 80 dpa in a commercial nuclear power reactor, and thermally annealed, varying both annealing temperature and time. With increasing annealing temperature the density of all defects gradually decreased, resulting in the complete removal of Frank loops at 550 degrees C. In contrast to other defects, the density of the gamma' precipitates sharply decreased with increasing annealing time, which indicates that the dissolution of the gamma' precipitates is governed by the iron diffusion length. (C) 2014 Elsevier B. V. All rights reserved.