This paper studies the mitigation strategies for combustible gases in a NPP. Based on the PSA results and engineering experiences, one typical case and one bounding case are chosen for the study of the control systems for the combustible gases. The combustible gases control strategies for AP1000 and EPR are also discussed. The studies find that, the combustible gases control system should be designed along with containment heat removal systems. The containment heat removal system will cool the containment and condense the vapor in the containment, which will facilitate the effectiveness of the igniters. The advantage of the passive recombiners system is the ability to eliminate hydrogen beyond the flammability limit. But the recombination rate is slow, and at the early stage of the accidents, the hydrogen will still be at a high level. In this condition, the operation of the containment heat removal systems should be designed carefully to eliminate the negative hydrogen risks.

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