Deuterium permeation through metals under hydrogen counter flow

Experiments on counter-permeation of deuterium (D) and hydrogen (H) through a nickel membrane were performed under diffusion limited condition, and transient between surface limited and diffusion limited condition. Deuterium permeation rates were measured as a function of upstream D-2 pressure, with hydrogen being permeated in the opposite direction by supplying H-2 gas at the downstream side of the membrane with respect to the D permeation. The deuterium permeation rate was found to decrease with increasing the counter H permeation. Significant deuterium permeation remained to be observed even when the deuterium upstream pressure was much lower than the downstream hydrogen pressure. These results are very similar to those observed for palladium (Pd) which showed surface limited permeation. The deuterium permeation rate under counter H permeation was reasonably well explained by a simple model based on surface limited permeation in which the ratios of the deuterium permeation rates with and without counter H permeation are proportional to the fractional concentration of deuterium in the surface layers. This implies that adsorption (absorption) of D-2 from the gas phase is inhibited, and also surface recombination of deuterium is blocked by hydrogen. This model can be extended from the surface limited permeation to diffusion limited one. The present model may be applied for energetic tritium (T) impinging case. Tritium permeation rate to the cooling channel can be estimated, when the surface concentration of the impinging tritium and hydrogen uptake at the cooling side are determined. (C) 1999 Elsevier Science B.V. All rights reserved.