Co-permeation of hydrogen isotopes in tungsten at high temperatures

The permeation behavior of hydrogen (H2)–deuterium (D2) mixtures with varying molar ratios through tungsten (W) was systematically investigated using the gas-driven permeation method. The deuterium permeability, diffusion coefficient, and solubility in W were determined under different hydrogen partial pressures. The impact of mixed-isotope permeation on the surface morphology of W was examined via scanning electron microscopy (SEM). Results indicate that the presence of hydrogen significantly suppresses deu terium permeability when the hydrogen molar fraction exceeds 30%. Specif ically, at a 50% H2 molar ratio, the deuterium permeability decreases by approximately 41% compared to pure D2 permeation, while the diffusion coefficient increases by a factor of seven. Consequently, the deuterium solu bility in W is reduced by about 95%. SEM analysis reveals that both grain boundaries and grain interiors exhibit pronounced damage after exposure to the H2–D2 mixture, with degradation more severe than that observed under pure D2 permeation. To gain deeper insight into the observed permeation behavior, numeri cal simulations were conducted using the established hydrogen isotope co permeation model. The simulated permeation fluxes were of the same order of magnitude as the experimental results. The reduction in deuterium permeation under co-permeation (H+D) conditions, compared to pure D expo sure, was also close to the experimental observations. However, simulations based on independent isotope diffusion inside the material failed to repro duce the unusual non-monotonic behavior—an initial increase followed by a decrease—observed in the experiments. This indicates that the inhibition of D permeation at high temperatures is not solely due to recombinative desorption of H and D at the upstream surface, but may also involve deeper inhibitory mechanisms within the tungsten bulk. Further investigation is needed to clarify these effects.