The effect of hydrogen isotopes and helium on tritium diffusion and extraction from candidate fusion breeder blanket ceramics

In the fusion power stations of the future, the radioactive fuel tritium will be produced (bred) in a region surrounding the fusion core (the breeder blanket), with both solid and liquid tritium breeder designs being developed around the world. The tritium breeding material will comprise the element lithium, which can absorb fusion neutrons and transform into tritium and helium (transmutation). At the University of Sheffield, solid breeder materials are being developed and tested in fusion-relevant environments. Most solid breeders are poly-crystalline ceramics, specifically lithium-containing ceramics such as lithium metatitanate (Li2TiO3), through which the gaseous tritium will diffuse and be extracted. Previous work has found direct correlations between ceramic grain size and efficient tritium diffusion and extraction, as well as the ceramics ability to resist/recover from fusion neutron irradiation induced damage. In our previous work we found that Li2TiO3 contains small vacancy-type defects which grow at fusion relevant temperatures. These vacancy-type defects and the helium generated transmutation have the potential to trap tritium as it diffuses through the material, and the extent of this trapping must be determined if Li2TiO3 is to be a serious contender for a breeder blanket material. Therefore, the focus of this PhD project is to determine how defects, intrinsic to candidate Li-containing ceramics, as well as helium, impact radiation damage resistance and tritium diffusion and extraction.