Effect of tungsten deposition thickness on hydrogen isotope permeation through RAFM steel

Deuterium (D) plasma-driven permeation (PDP) experiments through reduced activation ferritic/martensitic (RAFM) steel with and without tungsten (W) deposition layer have been performed. The results confirm that W deposition does not always work as D permeation barrier, but enhances D permeation flux through the structural material under certain conditions. The steady state PDP fluxes through RAFM steel with a thin (~30 nm) W deposition layer have been found to be larger than those of bare RAFM steel, whereas the RAFM steel membrane with a thick (6.0 μm) W deposition layer exhibits lower permeation fluxes than those of bare steel sample. Tritium Migration Analysis Program (TMAP) calculation indicates that the steady state permeation flux is determined by the D concentration accumulated at the interface between W layer and RAFM steel, which is highly relevant to the W deposition thickness. Only when the W thickness is larger than ~2 μm, the steady state permeation flux will be controlled by diffusion in W deposition layer.