Future fusion power reactors such as the UK’s STEP reactor, due to begin construction in the next 10 years, will require the tritium fuel to be generated (bred), extracted, separated, and regenerated into new fueling (either pellets or gas) prior to (re-)introduction into the fusion core. With the target of STEP to be generating net power output by the 2040’s, it is no longer sufficient to only have qualitative or approximately quantitative understanding of the tritium fuel cycle; more detailed examinations and quantification are required.
A key scientific and technological challenge associated with the tritium fuel cycle, is the tritium migration and retention behaviour in both solids and liquids. At present, it is likely that the first net power generating fusion reactors will have a liquid Li based breeder and that the tritium that is generated within these regions will both interact with the structural components of the breeder blanket, and need to be removed from the liquid Li to be fed back into the fueling system [1]. As such, it is critical to develop an understanding of tritium mass transport. Hydrogen-isotope diffusivity and solubility in lithium are crucial parameters for the design of recovery system of tritium dissolved in Li. There is limited data available for tritium diffusivity, solubility, and permeability in lithium due to the difficulty associated with handling highly reactive Li metal and, as such, there are large discrepancies in the experimental literature. This proposed program will use atomistic scale modelling (density functional theory and molecular dynamics) to investigate and model the tritium behaviour and characteristics in two technologically important areas: 1) tritium dissociation and diffusivity within liquid Li; and 2) tritium trapping, desorption, and mass transport in and around the interface between the liquid Li and structural components.
This work will develop first-principles-based models to enable a better understanding of the diffusion and trapping processes by which tritium can be extracted from the liquid Li breeder and made available for refueling into the plasma. It also provides accurate prediction of the underlying physics to understand the mechanisms by which hydrogen isotopes may be trapped at the interface barrier between breeder and structural materials components such as P91 or Eurofer selected for the application (simplified in this case by assuming Fe is the structural material) in order to facilitate the development of mitigation strategies or material/barrier development. Furthermore, if sufficient progress is attained other systems based around PbLi or FLiBe liquids may also be explored.
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