Plasma- and Gas-Driven Hydrogen Isotope Permeation Through the First Wall of a Magnetic Fusion Power Reactor

The first wall of a magnetic fusion power reactor is defined essentially as the plasma-facing walls of blankets. For the high temperature operation of self-cooled breeder blankets, the first wall is often designed to be less than 1cm thick to reduce mechanical stresses and as a result will be subjected to bi-directional hydrogen permeation by two distinctive mechanisms; in one direction by edge plasma-driven and in the other direction by bred tritium gas-driven permeation. Using a laboratory-scale plasma device and a one-dimensional diffusion model, plasma-driven and gas-driven hydrogen permeation behavior has been investigated under some of the conditions relevant to FLiBe-employed blankets. For a 5mm F82H membrane, the plasma-driven permeation flux at ~500 eC and the gas-driven hydrogen permeation flux at ~350 CC have been measured to be of the orders of 10¹³ H-atoms/cm²/s and 10¹⁴ H-atoms/cm²/s, respectively. From these data one predicts that gas-driven permeation could dominate the hydrogen isotope transport through the first wall.