Hydrogen distribution and Passive Autocatalytic Recombiner (PAR) mitigation in a PWR-KWU containment type

The PAR configuration offered an improvement in the chosen accidental scenario, decreasing the possibility of hydrogen combustion in all the containment compartments at the end of the transient. The analyses showed that this PAR configuration could lead to a reduction between 30-45% of the final hydrogen concentration. The hydrogen combustion risk is decreased with final hydrogen concentration values below the flammability limit (hydrogen concentration below 7%). Nonetheless, the analysis showed the inability of the PARs to recombine in the early stage of the fast release (the first 1-2 min in this sequence), due to their inertia and occurrence of oxygen starvation conditions.