Modeling of hydrogen permeation behavior through tungsten deposition layer growing on nickel substrate by hydrogen plasma sputtering

Tungsten (W) is a candidate material of plasma-facing walls for fusion reactors. When a W redeposition layer is formed on the plasma-facing wall by sputtering, the behavior of tritium in the in-vessel components is possible to be affected. Therefore, it is necessary to understand the tritium permeation behavior through the W deposition layer as well as W bulk. In the previous study, the hydrogen permeating through the W deposition layer growing on a nickel substrate was measured experimentally. In this work, the TMAP simulation code was used to analyze the time variation in the measured hydrogen permeation flux and mass transfer parameters were obtained. The results suggested that the permeation flux initially increased with increasing temperature but decreased when the thickness of the W deposition layer was greater than the hydrogen injection range. The obtained recombination coefficient was several orders of magnitude larger than that reported for W bulk. The obtained values were used to predict hydrogen isotope permeation through the plasma-facing wall in the DEMO reactor. The results suggested that the W deposition formed on the plasma-facing wall of the DEMO reactor significantly reduces tritium permeation rate.