MICROSTRUCTURE AND DENSITY CHANGES OF LI2O DURING IRRADIATION IN BEATRIX-II, PHASE-I AND PHASE-II

BEATRIX-II Phase I and II were in-situ tritium recovery experiments to characterize the behavior of ceramic breeders irradiated to high bum- up using the fast flux test facility (FFTF). A thin-walled, Li2O-sinte red ring specimen and single crystals specimen were irradiated to tota l lithium bum-ups of about 5 at%. Scanning electron microscopy of the ring specimen in Phase II revealed a substantial increase of open poro sity and platelet-shaped grains and a decrease in grain size for most parts of the specimens. At the top end of the specimen hexagonal-shape d bubbles were observed in addition to the increase of porosity and th e decrease of grain size. The increase of open porosity and the decrea se of grain size were considered to arise from a significant link-up o f the bubbles. Such increase of open porosity led to volumetric swelli ng in the order of 20%. Fracture surfaces of the single crystals exhib ited morphological changes resembling blisters.