A time-dependent gas-phase absorption-desorption technique has been used to evaluate the isotope effect on the diffusive transport parameters of hydrogen isotopes in polycrystalline tungsten and the reduced activation ferritic-martensitic steel OPTIFER-IVb.

Experiments have been run with both protium and deuterium obtaining their respective transport parameters of diffusivity (D), Sieverts' constant (Ks), the trap site density (Nt) and the trapping activation energy (Et). Isotope effects on these transport parameters are analysed and modelled. Because the classical isotope relation for diffusivity has not been fulfilled, quantum-statistical vibration theory has been applied to model the isotopic relation. The hydrogen vibration properties description in a metallic-host lattice allows deriving more accurate tritium transport parameters. A congruent isotopic variation of diffusion parameters related to the type of crystal structure, bcc, has been confirmed.