Modeling of low-temperature reduction of metal oxide in hydrogen treatment system for severe accidents in nuclear power plants

In the accident at the Fukushima Daiichi Nuclear Power Station, reaction of water vapor with hot zirconium led to the generation of hydrogen and a subsequent explosion in the reactor building. From the perspective of defense-in-depth, multiple hydrogen explosion prevention measures are desirable to improve the safety of nuclear power generation. In this research, we focus on a hydrogen treatment system that re-oxidizes hydrogen into water vapor using a fixed, packed bed of copper oxide pellets. The advantages of this method are that the hydrogen oxidation rate is rapid and no external source of oxygen is necessary. In this study, we conducted experiments and complementary numerical calculations for the hydrogen oxidation reaction using copper oxide pellets. The oxidation reaction of hydrogen by copper oxide is decomposed into five elementary reactions, the rate of each was determined experimentally. The resultant numerical calculation accurately modeled experimentally observed hydrogen oxidation rates and provides insights into the phenomena controlling the reaction progression. The results suggest that the commonly observed induction period is due to the presence of poorly adsorbing sites on the copper oxide surface. Moreover, when water vapor is present, competition between water vapor and hydrogen for adsorption sites further suppresses the hydrogen oxidation reactions.