Consideration on hydrogen explosion scenario in APR 1400 containment building during small breakup loss of coolant accident

This paper describes the analytical result of the potential risk of hydrogen gas up to 15 h after the failure takes place. The major cause of the disaster occurred in Fukushima Daiichi nuclear reactor was the detonation of accumulated hydrogen in the containment by highly increased reactor core temperatures after the failure of the emergency cooling system. The hydrogen risk should be considered in severe accident strategies in current and future NPPs. A hydrogen explosion scenario is proposed. Hydrogen is accumulated on top of the dome during the hydrogen release period. At this point, there are no risk of explosion due to the steam that resides in upper part of the dome. As the hydrogen concentration increase, substantial amount of steams are released. Subsequently, hydrogen is forced into the lower part of the building with high air density-small explosion and dormant steam condensation phase are possible. The light hydrogen rises up slowly with air, gathering on top of the building with high air density. Massive hydrogen explosion is anticipated upon ignition at this stage.