Modelling synergistic isotope effects of the permeation of multiple hydrogen isotopes through metals

Tritium permeation into the structural materials of the fusion devices is an important safety issues. Various mathematical models and experiments related to tritium permeation through key components of the fusion devices have been carried out. However, there are still unresolved issues related to modelling of synergistic isotope effects (the mutual influence among isotopes) in multi-isotope permeation of hydrogen through metals. Therefore, to further explore such issues, a research project has been started at National R&D Institute for Cryogenics and Isotopic Technologies, Romania. The aim of the project activities is to develop a simulation tool that eventually will be benchmarked against the experimental results. Some controversial issues among other previous steady-state works have led us to set up a non-steady-state model for multi-isotope permeation in surface limited regime. The mathematical model and the results obtained by numerical simulation are presented in this paper. The main conclusion is that, in contrast to previous steady-state approaches, the permeation flux of an isotope is not reduced by the presence of another isotope, but on the contrary it is increased. A versatile installation will be realized within the project to experimentally investigate these effects, and some of its design features are briefly mentioned here.