In the event of a severe nuclear accident, one important safety barrier to contain radioactive release to the environment is the containment. To ensure full functionality during an accident, venting of the gas inside may be necessary to avoid reaching critical pressures and accumulation of hydrogen, which both may result in damage to the containment integrity. One solution to mitigate either of these risks is via a filtered containment venting system (FCVS). Such a system is designed to remove different radioactive materials from the vented gas and potentially hydrogen. For the former, iodine is one of the most important fission products needing to be removed and it can exist as e.g., elemental and bound in different organics. In general, elemental iodine can be effectively removed via e.g., a wet scrubber. However, organic iodides are more difficult to retain. One possible solution is Ag-zeolites. After the accident at the Fukushima Daiichi Nuclear Power Plant, Japan installed silver zeolite-based organic iodine filters in all FCVS in order to strengthen mitigation measures against severe accidents. Several tests had already been conducted on the effect of silver zeolite retention of organic iodine, and the test results have been confirmed by the safety review of the Japanese Nuclear Regulatory Authority. In order to improve FCVS, attention should be paid to the reaction of hydrogen and oxygen in the containment vessel and in FCVS for the PWR. When FCVS is started, the scrubber pool water is cold, so the steam in the containment vessel is condensed and the concentration of hydrogen and oxygen increases.
In this study, two Ag-zeolites were experimentally investigated. AgX, which has a catalytic action for hydrogen, is foreseen to be installed in the containment vessel to reduce the hydrogen concentration, and AgR, which does not have a catalytic action for hydrogen, is foreseen to be used for the iodine filter in FCVS. The hydrogen catalysis effect of silver zeolites were compared by experiments.