Radiation damage in annealed type 304 stainless steel

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Abstract
The defect structures in irradiated type 304 stainless steel were characterized by transmission electron microscopy for irradiation temperatures between 370 and 840°C and for fluences ranging from 1018 to 1023 neutrons/cm2 (> 0.1 MeV). Below about 550°C the interstitial atoms produced by the irradiation precipitate as Frank sessile loops, which decrease in concentration and increase in size with increasing irradiation temperature. About 550°C the loops unfault and evidently glide and interact to form a loosely organized dislocation network, which becomes coarser with increasing irradiation temperature. The vacancies precipitate as voids, which also decrease in concentration and increase in size with increasing temperature. The damage appears to be first visible at a threshold fluence that increases with increasing irradiation temperature. At high fluences, void concentrations approach a saturation concentration that decreases with increasing irradiation temperature. Voids are often not homogeneously distributed but are preferentially associated with dislocations and precipitate particles. The void concentrations and size distributions are not strongly dependent on the fast neutron flux, at least over range encountered in fast reactors. These observations are discussed in terms of proposed mechanisms for void formation. It is concluded that most of the voids are probably nucleated on complexes of vacancies and helium atoms resulting from (n,α) transmutations.