Evaluation of hydrogen permeation rate through zirconium pipe

To launch a fusion reactor stably, it is necessary to prepare sufficient amount of tritium by an external tritium source. Tritium production using nuclear reactions by neutron and Li in a high temperature gas-cooled reactor (HTGR) is an attractive method. An important issue is tritium confinement in high temperature conditions of HTGR. Covering Li compound by Al2O3 is a promising method because hydrogen permeability in Al2O3 is quite low. Furthermore, it is expected that inserting Zr between Li compound and Al2O3 suppresses tritium permeation because Zr has a large hydrogen absorption capacity. For example, a cylindrical multilayer structure consisted of Zr - Li compound - Zr - Al2O3 is a candidate structure to confine generated tritium. To evaluate hydrogen permeation rate through cylindrical Zr material, in this work, hydrogen permeation experiments were carried out for two samples of one-side sealed Zr pipe. Hydrogen permeation rate in one sample was proportional to as the square root of hydrogen pressure but that in another sample, which had retained a certain amount of hydrogen before the experiment, did not indicate an obvious pressure dependence regardless of almost the same experimental procedure except hydrogen permeation direction. Since observed hydrogen permeation rate in Zr was faster than that in Al2O3, under the multi confinement structure by Zr - Li compound - Zr - Al2O3, the generated tritium in Li compound diffuses promptly in whole Zr inside Al2O3 layer and it is expected tritium is stored stably in the structure.