Efficiency of selected methods of hydrogen removal from a nuclear reactor’s containment building

Abstract

The system of barriers is utilized to prevent a release of radioactive materials to the environment from a nuclear reactor's core. These barriers are the nuclear fuel structure, fuel cladding, walls of the primary cooling circuit and the containment building. Reliability of these barriers is very high and it is very unlikely to fail them all simultaneously. A one of crucial issues for containment integrity is the problem of hydrogen combustion and detonation. Gaseous hydrogen may be released into the containment building from overheated core region either during a loss-of-coolant accident by a break in the primary cooling circuit, or by a safety relieve valve (as in Fukushima Dai-ichi nuclear power plant). Mixing of hydrogen with the air in the internal atmosphere creates flammable mixtures. Taking this into account it is very important to avoid such situations and make possible removal of this gas.Five methods of hydrogen removal from the containment building can be distinguished:- intended ignition of hydrogen for its controlled combustion,- recombination of hydrogen by catalytic devices,- removal of oxygen by pre-inertisation,- dilution of the atmosphere by post-accidental injection of inert gas,- dilution of the atmosphere by increase of the containment volume.Efficiency of these methods has been assessed based on results of simulations realized by means of the in-door computer code HEPCAL. This is the lumped parameter code for analysis of a nuclear reactor containment transient response. Real systems utilizing the described hydrogen removal methods have been simulated in the first step applying design basis accident scenarios. As the results could not be directly compared, in the second step a virtual experiment has been simulated too.