IMPACT OF SURFACE PHENOMENA IN METALS ON HYDROGEN ISOTOPE PERMEATION

The ion and gas driven deuterium permeation behavior in niobium (Nb) w as investigated. The GDP (gas driven permeation) rate (flux) was measu red to be proportional to the D-2 gas pressure and to increase with th e temperature, whereas the IDP (ion driven permeation) rate (flux) was 0.2-0.3 times the incident ion flux and was almost independent of the temperature. Based on the diffusion-recombination limited hydrogen tr ansport model, the ''phenomenological'' recombination rate coefficient , k(R), was calculated for both upstream-side and downstream-side from the IDP experiment and the obtained result agreed well with the GDP r esult. Furthermore, in-situ surface analysis by Auger electron spectro scopy (AES) revealed that the presence of carbon suppressed the GDP ra te to a larger extent than that of oxygen. These newly obtained result s on Nb enable comparison of the hydrogen transport characteristics of various metals which are of interest for fusion applications in terms of the so-called ''recycling constant'', D/2k(R) (D is the diffusivit y). It is shown that Nb, together with vanadium, has larger values of D/2k(R).