Effects of thickness and catalysts on metal foil pump technology

One of the most critical challenges facing a viable fusion reactor is to avoid excessive tritium inventories. The direct internal recycling concept utilizes a metal foil pump (MFP) to filter tritium from a stream of gases via superpermeation. This technology has the potential of pumping hydrogen isotopes against moderate (0.1 MPa) pressure gradients, however, concerns regarding hydride formation and embrittlement of the metal foil remain. Moreover, the effectivity of catalysts for superpermeation is not well understood. Superpermeation works only in the surface-limited regime, for which H thermodynamics determine the main characteristics of the pump. In this work, H solubility is studied for a MFP composed of several group V transition metals, Pd, Nb, Ta, V, and W. The solution energy of H at interstitial positions and the interactions of H at Pd/Nb interfaces. The results show that Nb has the lowest H solution energy, whereas the other transition metals generally have lower H solution energies as compared to Pd. These findings indicate the importance of the fabrication of a MFP with superpermeation using a thermodynamically constrained diffusion barrier, such as a Pd/Nb interface.