A large amount of hydrogen is generated by the metal water-reaction in the Primary Containment Vessel (PCV) of Light Water Reactors in the severe accident. Then we have been developing the Hydrogen Treatment System to prevent excessive pressure without PCV vent. By focusing on the oxidation-reduction reaction of metal oxides with high reaction rate, we have been studying hydrogen treatment system using metal oxides as effective device under oxygen deficit conditions of PCV of Boiling Water Reactor (BWR).
We have been considering a hydrogen treatment unit with a lot of pipes in which metal oxides are filled. We have already investigated experimentally the basic trend of metal oxides temperature and gas concentration as well as hydrogen processing rate dependency on gas temperature and concentration in the absence of steam. However, the influence of steam on hydrogen processing characteristics has not been clarified yet.
The objective of the present research is to investigate how the steam, which is supposed to be a reaction-inhibiting-factor, affects hydrogen processing characteristics of the hydrogen treatment unit. We conducted experiments using a test section of one pipe simulating a part of the hydrogen treatment pipes. The granulated CuO, which is a candidate material for the actual system was used. The hydrogen concentration of 10 wt% at the inlet of the pipes was decreased to 0 wt% at the outlet even in high steam concentration conditions (30–50 wt%) when the gas temperature was 250 °C, therefore, it was confirmed that hydrogen was treated with high processing rate under steam circumstances. It was also found that cumulative amount of treated hydrogen was strongly correlated with temperature and relative humidity.
We have been developing the thermal-chemical model of hydrogen treatment unit. The prediction margin of error was decreased to 30 % from over 100 % by improving degradation model based on the experiment results, therefore, it reached the practical level.