Hydrogen combustion in a flat semi-confined layer with respect to the Fukushima Daiichi accident

Abstract

Hydrogen accumulations at the top of a containment or reactor building may occur due to the interaction of molten corium and water followed by a severe accident of a nuclear reactor (TMI, Chernobyl, Fukushima Daiichi). The hydrogen that is released from the reactor accumulates usually as a stratified semi-confined layer of hydrogen–air mixture. A series of large scale experiments on hydrogen combustion and explosion in a semi-confined layer of uniform and non-uniform hydrogen–air mixtures in the presence of obstructions or without them was performed at the Karlsruhe Institute of Technology (KIT). Different flame propagation regimes from slow subsonic to relatively fast sonic flames and then to detonations were experimentally investigated in different geometries and then simulated with COM3D code with respect to evaluate the amount of hydrogen that was involved in the Fukushima Daiichi Accident (FDA).The experiments were performed in a horizontal semi-confined layer with the dimensions 9×3×0.6m with/without obstacles opened from below. The hydrogen concentration in the mixtures with air was varied in the range of 10–34vol.% without or with a gradient of 20–60vol.%H2/m. Effects of hydrogen concentration gradient, layer thickness, obstruction geometry, average and maximum hydrogen concentration on the flame propagation regimes were investigated with respect to evaluate the maximum pressure loads on internal structures. Blast wave strength and dynamics of propagation after the explosion of the hydrogen–air mixture layer were numerically simulated to reproduce the hydrogen explosion process during the Fukushima Daiichi Accident (Unit 1).