SWELLING AND DISLOCATION EVOLUTION IN SIMPLE FERRITIC ALLOYS IRRADIATED TO HIGH FLUENCE IN FFTF MOTA/

Microstructures of a series of Fe-Cr binary ferritic alloys were exami ned following neutron irradiation to 140 dpa at 698 K in FFTF/MOTA. Th e chromium concentration ranged from 3 to 18% in 3% increments and the irradiation temperature corresponded to the peak swelling condition f or this alloy class. The swelling varied from 0.4 to 2.9% depending on chromium concentration, and the highest swelling was found in the Fe- 9Cr alloy. The cavity microstructures corresponded to transient to ear ly steady-state swelling regime. Dislocations were composed of network s with both alpha[100] and (alpha/2)[111] Burgers vector and alpha[100 ] type interstitial loops. The dislocation density was negatively corr elated with swelling. Explanation for the observed chromium concentrat ion dependence of microstructural development and low swelling in the ferritic alloys will be studied in connection with the dislocation bia s efficiency and the theory of sink strength ratio.