Study of hydrogen mitigation for safe storage of spent cesium adsorption vessels

Hydrogen mitigation is one of the important issues for safe storage of spent cesium adsorption vessels that were used in the contaminated-water treatment facility at the Fukushima Daiichi Nuclear Power Station because the production and accumulation of hydrogen is induced by the radiolysis of residual water in the vessel. In the present study, an experimental examination was performed using a miniature acrylic vessel to simulate an upper section of the vessel using particle image velocimetry to clarify the internal flow of hydrogen-mixed gas and to verify the analytical results by the ANSYS Fluent code. As a result, weak upflow and circulating flow at the stepped section were successfully visualized, and the validity of the analytical results was confirmed by the flow patterns. Additionally, the practicality of a recombination catalyst for hydrogen and oxygen was considered as a passive autocatalytic recombiner in hydrogen mitigation. A catalytic reaction test was conducted to evaluate its effectiveness. The results showed that the catalyst retains activity under the humid condition assumed in the real vessel.