First-principles investigation on diffusion and permeation behaviors of hydrogen isotopes in molybdenum

We have investigated diffusion and permeation behaviors of hydrogen (H), deuterium (D), and tritium (T) in bulk molybdenum (Mo) by a first-principles calculations combined with simplified models. The H diffusion energy barrier with quantum correction is shown to be 0.12 eV, in good agreement with the value of 0.11 eV obtained from experiment. According to the diffusion theory presented by Wert and Zener, the diffusion coefficients of H, D and T are estimated, respectively. The H diffusion coefficient is found to be D=1.27×10-7exp(-0.12eV/kT)m2s-1, which is also basically consistent with the experiment. Permeability Φ can be approximately evaluated in terms of Φ = SD, where S and D are the solubility and the H diffusion coefficient, respectively. We found that H has the low solubility in bulk Mo, consistent with the results at the temperature from 900 K to 1500 K in the earlier experiment. The permeability of H isotopes are calculated to be one order of magnitude larger than those of the experimental values. Such discrepancy should stem from that the “defect-free” Mo in the present calculations is considered. The permeation flux of H isotopes are finally examined. At the temperature of 1200 K, the fluxes of H, D, and T are calculated to be 1.27 × 10−6 mol m−2 s−1, 8.95 × 10−7 mol m−2 s−1, and 7.30 × 10−7 mol m−2 s−1, respectively.

► Mo and Mo-alloy are considered as the promising plasma facing material.
► Hydrogen isotopes (H, D, T) have large effect on the properties of Mo.
► Diffusion and permeation of H isotopes is very important in Mo.
► Especially, permeation of T in Mo is a great concern of safety.