Hydrogen Distribution and Explosion in Containment Building

Abstract

The hydrogen risk should be considered in severe accident strategies in nuclear power plants. This paper describes the analytical result of the hydrogen distribution and explosion after the failure takes place in a containment building. Hydrogen is accumulated on the top of the containment during the hydrogen release period. After the period, the released steam pushes down the hydrogen, and some amount of hydrogen is trapped among the compartments in the lower part of the containment. Long time after the accident the hydrogen slowly rises up to the top of the containment with temperature cooling down. During the process, there are many chances for hydrogen explosion. At the containment top, the hydrogen increases up to 55 vol.% and air is 45 vol.% at 15 hours after the accident, which is the most dangerous state of hydrogen explosion. The hydrogen flame is developed slowly until 4 second after ignition, then the detonation is begun. The maximum explosion pressure reaches 75 bar which is the dangerous impact pressure which may destroy a containment building. At the containment bottom, the gas composition is 33 vol.% of hydrogen, 30 vol.% of steam and 35vol.% of air at 4 hours after the accident, which is the most dangerous state among the compartments at the bottom. The flame develops much faster than that at the top area, but the peak impact pressure is much lower than at the containment top.