An Experiment-Oriented Analysis of a Non-Steady-State Model for the Permeation of Multicomponent Hydrogen Isotopes Through Metals

The control of tritium permeation through the structural materials of fusion reactors is an important safety issue, and because both deuterium and tritium are fuel constituents, the effects of isotopes have to be taken into account in permeation assessments. Although various mathematical models and experiments regarding hydrogen isotope permeation through metals have been carried out so far, there are still unresolved issues like those regarding synergistic isotope effects (by which an isotope influences the permeation of another isotope when multiple isotopes permeate simultaneously). Some controversial issues of other previous steady-state work have led us to set up a non-steady-state model for multi-isotope permeation in a surface-limited regime (SLR). The mathematical model and the results obtained by numerical simulation (which are published elsewhere) have shown that in contrast to some previous steady-state approaches, the permeation flux of a heavier isotope is not reduced by the presence of a lighter one; to the contrary, it is increased. This theoretical prediction has to be verified against experimental data, and this is the goal of future work. But, the differences between multi-isotope and single-isotope permeations are not so large, and some deviations of the experimental model from the assumptions of the theoretical model (like SLR, constant partial pressures in retentate, or vacuum on the permeate side) could affect the theoretical predictions or could lead to misinterpretations of the experimental data. Therefore, these kinds of deviations and their effects have been analyzed within this work with the aim of implementing, in the experimental model, appropriate measures to mitigate these undesirable effects. The conceptual design of the proposed experimental setup and a procedure for setting some key operating parameters (like flow rates and pressure of the purge gas) are also presented.