Analysis of Simultaneous H and D Permeation through Lithium-Lead

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Clarification of tritium transfer in blanket is an important issue for realizing fusion reactor. We perform an experiment of simultaneous H and D permeation through Li17Pb83 by means of an unsteady permeation method in order to clarify the interactions and isotope effects between H and D atoms. The experimentis conducted under the condition where the Sieverts law holds. As a result, it is found that (i) H and D atoms permeate independently regardless of the H/D component ratio in the upstream gas and (ii) diffusion process is the rate-determining step in the overall permeation process. The diffusivity of H is around 1.4 times larger than that of D. The solubility of H is close to that of D. We estimate two vibration modes at an absorption site and a saddle point of H in Li17Pb83 based on the ratio of isotope effect. It is considered that the zero-point vibration energy of H at the absorption site in Li17Pb83 is around 0.173 eV and that at the saddle point is around 0.235 eV. The ratio of isotope effect is almost in proportion to the square root of mass ratio of D to H. The diffusivity of T can be estimated as 1/1.7 times of H.
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