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

This paper summarizes the technical basis for using an integrated recombiner-igniter system, called the dual concept for combustible gas control 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 and self-feeding, even under cold and wet conditions, and without any power supply. It has been demonstrated by testing that the efficiency of the catalytic coating of the recombiner is resistant to impurities expected 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 types of igniters are capable of reliable ignition close to the upper and lower flammability limits. Based on experiments in realistic multi-compartment test facilities which investigate the combustion and recombination behavior in different accident situations, an efficient arrangement of the devices inside the containment is recommended to cover all possible scenarios. The dual concept causes only low loads which maintain the integrity of the containment.