Impact of surface phenomena in metals on hydrogen isotope permeation

The recycling of hydrogen isotopes (H, D and T) from the first wall material in a fusion device, as well as its tritium inventory and permeation characteristics will depend to a great deal on the surface properties of the material under consideration. Historically, the surface of the first wall was initially composed of such metals as stainless steel and nickel (Ni, the main constituent of Inconel) because of their good outgassing properties as vacuum vessel components. Then graphite and beryllium (Be) were favored due to their low Z properties. Presently, high Z refractory metals, molybdenum (Mo) and tungsten (W), are also being tested in the devices with the hope that control of the boundary plasma would reduce the incident energy low enough to prevent sputtering. Furthermore, vanadium (V) and its alloys are considered for DEMO reactors for their low activation. Or niobium (Nb) and tantalum (Ta) are potentially suitable for super-permeable membrane for separation and purification of hydrogen isotopes in the exhaust gas