Experimental research on hydrogen deflagration in multi-compartment geometry and application to nuclear reactor conditions

In the course of a severe accident maintaining containment integrity is of fundamental importance to avoid fission product release to the environment as becomes obvious by a comparison of the severe accidents in Three Mile Island (TMI), Chernobyl and Fukushima. Since containment integrity is mainly impaired by hydrogen combustion in the early and intermediate phase of a severe accident with core degradation, research on hydrogen behaviour was and is in the focus of international research. This paper provides an overview about hydrogen combustion experiments with premixed and stratified atmosphere in multi-compartment facilities, both for vented combustion and combustion in closed facilities. The influence of scale is discussed and a threshold for facility size has been identified above which a further increase of peak pressure and peak temperature is not to be expected. Effects typical for multi-compartment deflagration like jet ignition, displacement of unburnt mixture and interacting flame fronts are assessed. The influence of certain engineered safety measures like spray systems and filtered containment venting systems on hydrogen combustion is discussed. Source-term relevant phenomena related to hydrogen combustion like fission product resuspension and fission product decomposition which may occur during a deflagration or in a standing flame are dealt with by discussion of the respective experimental work. Based on the state-of-the-art review, knowledge gaps and open issues on hydrogen combustion are being identified which require further research work using sufficiently large experimental facilities in order to ease application of the results to reactor containments.