Technical reliability of tritium confinement shall be elevated taking hypothetic extraordinary situations occurred in a nuclear fusion facility such as events of fire and loss of electric power fully into consideration in order to enhance public acceptance of a nuclear fusion reactor. Considerable attention has been paid to the research of passive tritium conversion in the research field of detritiation system. Demonstration of detritiation to grasp the dynamic behavior is practically important to enhance the tritium confinement. In this study, passive detritiation of a 12 [m3] container was demonstrated with hydrophobic catalyst packed in a catalytic reactor. Initial tritium concentration in the container was 1.0 [GBq/m3]. The volume of hydrophobic catalyst packed in the passive catalytic reactor was 1000 [cm3]. The flow rate was set to 2.4 [Nm3/h] which is equivalent to atmosphere exchange rate of 5 times per day. The tritium concentration in the container successfully decreased two order magnitude after 23 hours processing. The conversion rate of tritium by passive catalytic reactor was initially 99.1 [%] and it decreased gradually with an increase in processing time. The rate fell to 70.7 [%] after 23 hours processing due mainly to the effect of hydrogen concentration on conversion efficiency. Unreacted amount of tritium passed through the passive catalytic reactor was less than 4.8 [%] of initial tritium amount. We have confirmed that the passive tritium oxidation is feasible with the hydrophobic platinum catalyst even in the presence of moisture.