Microstructures of T91 neturon irradiated in the BOR60 reactor at five temperatures between 376°C and 524°C to doses between 15.4 and 35.1 dpa were characterized using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and atom probe tomography (APT). Type a<100> dislocation loops were observed at 376-415°C and network dislocations dominated at 460°C and 524°C. Cavities appeared in a bimodal distribution with a high density of small bubbles less than 2 nm at irradiation temperatures between 376°C and 415°C. Small bubbles were also observed at 460°C and 524°C but cavities greater than 2 nm were absent. Enrichment of Cr, Ni, and Si at the grain boundary was observed at all irradiation temperatures. Radiation-induced segregation (RIS) of Cr, Ni and Si appeared to saturate at 17.1 dpa and 376°C. The temperature dependence of RIS of Cr, Ni and Si at the grain boundary, which showed a peak Cr enrichment temperature of 460°C and a lower peak Ni and Si enrichment temperature of ~400°C, was consistent with observations of RIS of Cr in proton irradiated T91, suggesting that the same RIS mechanism may also apply to BOR60 irradiated T91. G-phase and Cu-rich precipitates were observed at 376-415°C but were absent at 460°C and 524°C. The absence of G-phase at 524°C could be related to the minimal segregation of Ni and Si in that condition.

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