As a measure to prevent the generation of combustible hydrogen/oxygen gases expected in an ABWR accident, a flammability control system (FCS) needs to be installed. The autocatalytic FCS, which has been introduced mainly in Europe and the US, is composed of multiple passive autocatalytic recombiners (PARs) and is capable of recombining hydrogen and oxygen at room temperature (low activation energy) by catalysis. Unlike conventional forced-circulation and heating FCS, the autocatalytic FCS is a passive system that does not need operator startup; it also has a simple structure, without components requiring power supplies, such as blowers and heaters. Thus, it is superior in terms of reliability and operability. This system is considerably smaller than a conventional FCS, and can be installed in portions within the pressure containment vessel (PCV); conventional FCSs are installed inside the reactor building (outside the PCV). So autocatalytic FCS makes it possible to reduce the size of the building, and construction costs as well. Though multiple tests have been performed in Europe and the US on the autocatalytic FCS for product development and to check performance[1],[2],[3],[4], before introducing this FCS to a new ABWR plants, some additional tests have been performed with consideration for Japanese BWR accident conditions like PCV spray, influence of low oxygen condition and reaction inhibition in the collaborative research by Japanese electric power companies. These include examining the influences of low-oxygen conditions and reaction inhibitors. This paper presents the details of additional studies made after considering results of the additional tests performed in Japan to install the autocatalytic FCS instead of the thermo-reactive FCS.

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