Metal Foil Pump performance aspects in view of the implementation of Direct Internal Recycling for future fusion fuel cycles

The current design baseline for the EU DEMO implements the KALPUREX process for the tritium fuel cycle. This process aims to reduce the tritium inventory of the fuel cycle by separating hydrogen from other gases within the tokamak building and feeding it back to the matter injection system (Direct Internal Recycling). Thus, systems with high tritium inventory are close to the torus and have small residence time. The best candidate for the hydrogen separation unit close to the torus is a metal foil pump that relies on the effect of superpermeation. This effect is studied at a dedicated setup at KIT. In the theoretical part of this paper the impact of Direct Internal Recycling on the fuel cycle of a fusion device is quantified. This is done by introducing dimensionless numbers for the tritium stream reduction, the tritium conversion rate improvement and the mean tritium processing time. A major improvement for future fusion fuel cycles in terms of the size of the tritium plant as well as its tritium inventory could be shown. In the experimental part of this paper, results showing hydrogen permeation on an iron foil are presented. Superpermeability and surface limited permeation are demonstrated with an iron foil.