Experimental setup and pre-experiment issues for multi-component hydrogen isotopes permeation through metals, in non-steady-state

The permeation of hydrogen isotopes (especially tritium) through the structural materials of the fusion reactors is an important issue. The isotope effects have to be taken into account in the permeation assessments because both deuterium and tritium are fuel constituents. However, there still are some controversies regarding the mutual influence among isotope species in the multi-isotope permeation; some authors state that the lighter isotope reduces the permeation flux of the heavier one, while others state the contrary. In a previous work, using a non-steady-state model for multi-isotope hydrogen permeation in surface-limited regime, it was shown that the presence of hydrogen leads to an increase in the permeation of deuterium. In order to highlight experimentally the small differences between single-and multi-isotope permeation, carefully designed experimental techniques are required. A review of the most important techniques is presented in this paper, outlining their advantages and drawbacks that were considered in the design of the experimental setup also presented here in detail. Three measuring methods of the permeation rates were implemented within; one of them is a new (sequential) version of the gas accumulation method. The measuring methods are also described in the paper, along with operating procedures.