Experimental results of deuterium/hydrogen co-current permeation through Nickel membrane, in non-steady-state surface limited regime

Abstract

A better understanding of mutual influence among hydrogen isotope species in multi-isotope permeation is important for accurate assessments and predictions on tritium permeation through structural materials of fusion reactors. Moreover, this is important as the injection of H2 gas into the helium coolant of HCPB breeding blanket is proposed for mitigation of the permeation flux of tritium from the purge gas into the coolant. Although various modeling and experimental works have been carried out so far on this topic of multi-isotope permeation, unresolved issues or even controversies still persist. This work presents the results of some experimental tests of co-current permeation of deuterium with hydrogen through a very thin (0.075 mm) nickel membrane, performed in non-steady-state and surface limited regime (SLR), with the purposes to observe the effect of hydrogen on the permeation effective flux of deuterium, as well as to verify experimentally the predictions of a previous theoretical work. Thus, two deuterium/hydrogen gas mixtures of different ratios, as well as pure deuterium gas, were alternately introduced into the high-pressure side of the membrane by keeping the effective partial pressure of deuterium as close as possible to the same value (0.1 Pa), so that the comparison between multi- and mono-isotope permeation be relevant. The results indicate that the presence of (co-permeation) hydrogen does not lead to the decrease of deuterium permeation, but, on the contrary, to its increase. This effect is clearer revealed well before steady state is reached, where the effective permeation flux of deuterium has a constantly higher rise-rate when (co-permeation) hydrogen is present, and this rise-rate is even higher when the effective hydrogen pressure is higher. Also, a quite good consistency between experimental results and the theoretical predictions has been obtained, as well as a good repeatability of the results.