[en] For the safety issue of fusion reactor, it is important to understand the tritium behavior in each component of a fusion reactor, especially in the blanket system, where tritium will be bred and processed under higher temperature and higher flux of neutrons with higher energy than ever. In the blanket which is designed to apply solid tritium breeding materials, it is one of the most important issue to reveal the tritium permeation behavior from purge gas for recover the bred tritium in solid tritium breeding materials to coolant of which aim is recover the heat energy generated by nuclear fusion. From these viewpoints, some studies have been performed to reveal the tritium permeation behavior in F82H, one of low-activation ferritic-martensitic steels. These studies, however, were performed with the use of pure hydrogen isotope gas as source of permeant and vacuum for outlet side (named [pure-hydrogenisotope-gas/vacuum] experiments), although the purge gas could not consist of only tritium gas or hydrogen isotope gas and outlet side is not vacuum but coolant. Moreover, it is reported that the chemical states of tritium released from solid tritium breeding materials would not be hydrogen molecule but water. From these viewpoints, it is predicted that the tritium permeation behavior in F82H in blanket is different from that in reported experimental condition. Therefore in the present study, it is subjected to reveal the tritium permeation from feed gas composed from tritiated water vapor diluted by helium to purge gas composed from helium, as a simulation of helium cooled solid breeder (HCSB) blanket. Tritium permeation experiments were performed with use of tritiated water vapor diluted by helium as inlet side source and helium as outlet side purge gas. In the present study, two series of experiments were performed: (1) temperature dependence experiment, of which temperature range is from 573 to 873 K, and (2) tritiated water vapor partial pressure dependence experiment. As the results of experiments, tritium permeation looked limited by diffusion, and the activation energies of diffusion and permeation were comparable to reference data which had been estimated from [pure-hydrogen-isotope-gas/vacuum] experiments, while the pre-exponential factors of them were clearly different. Especially, the permeability and the pre-exponential factor of permeation estimated from the present study were almost three magnitudes smaller than those reference data. Therefore, it is implied that the surface reactions, such as adsorption, desorption, dissociation, recombination and dissolution, would be different, while the tritium behavior in the bulk is comparable, and the difference in surface reaction on inlet side between the present study and reference could result from the deference of permeants of water vapor and hydrogen gas. It is also implied that the existence of water could result in the formation of oxide layer which can work as tritium permeation barrier. On the other hand, there is a possibility that the surface reaction could be different on the outlet surface as well resulting in having an effect on tritium permeation behavior, because the chemical states of permeated tritium were the mixture of water vapor and hydrogen molecule. For the blanket system in fusion reactor, it was suggested from the present study that F82H ferritic steel could form the oxide layer which can work as tritium permeation barrier in certain condition and/or with pretreatment. (author)