HYDROGEN REDUCTION FOLLOWING SEVERE ACCIDENTS USING THE DUAL RECOMBINER-IGNITER CONCEPT

This paper summarizes the technical basis for using an integrated reco mbiner-igniter system, called the dual concept for combustible gas con trol during severe accidents in non-inerted pressurized water reactor containments. The recombiners use catalytic coatings to turn molecular hydrogen and oxygen gases into water vapor. They are self-starting an d self-feeding, even under cold and wet conditions, and without any po wer supply. It has been demonstrated by testing that the efficiency of the catalytic coating of the recombiner is resistant to impurities ex pected to be present in the containment atmosphere following a severe accident. Catalytic and spark igniters have been developed for use in controlled hydrogen ignition without an external power supply. Both ty pes of igniters are capable of reliable ignition close to the upper an d lower flammability limits. Based on experiments in realistic multi-c ompartment test facilities which investigate the combustion and recomb ination behavior in different accident situations, an efficient arrang ement of the devices inside the containment is recommended to cover al l possible scenarios. The dual concept causes only low loads which mai ntain the integrity of the containment.