Fuel debris which is removed from the Fukushima Dai-ichi Nuclear Power Plant is packed to the radioactive waste long-term storage containers. When the fuel debris includes water, hydrogen and oxygen are gener-ated by decomposition of water by radiation from the fuel debris. Since hydrogen is flammable gas, it has a high risk of combustion and explosion. Therefore, it is important to clarify the hydrogen behavior in the radioactive waste long-term storage container under the conditions that the fuel debris containing water is accumulated. As for former studies of hydrogen behavior in the sealed container, experimental and analyt-ical studies on hydrogen behavior under the various conditions of the fuel debris have not been conducted sufficiently. Then, the influence of hydrogen flow rate, temperature, porosity, etc. upon the hydrogen be-havior was investigated experimentally and numerically. Moreover, reduction of hydrogen concentration by the passive autocatalytic recombiner which is installed in the storage container was studied. The present study shows the controlling factors on hydrogen behavior in the storage container and the results on reduc-tion of the hydrogen concentration by PARs.