Investigation on the Influence of Pressure and Temperature on the Ignition Limits of Hydrogen Inside Recombiners

Abstract

Passive Auto-catalytic Recombiners (PARs) are used to avoid excessive hydrogen accumulation inside the reactor containment in case of severe accident. Their behavior is based on the exothermic recombination of hydrogen into steam in presence of oxygen. This surface mechanism leads to an overheating of the catalytic plates and activates natural convection-driven circulation of gases in contact with the catalyst. The heat source induced by the PAR activity can then create local conditions for hydrogen gaseous combustion, as igniters do.This paper deals with the numerical simulation of the impact of thermal-hydraulic conditions on PAR hydrogen ignition limits. The separated effects of three main parameters (steam, pressure and temperature) are analyzed. Calculations using an IRSN dedicated CFD code, reveal that hydrogen ignition inside recombiners can be significantly accelerated or delayed according to the reactor containment atmosphere.