Study on the hydrogen risk in venturi scrubber filter of filtered containment venting system under PWR severe accident

As the third barrier to prevent radioactive material from leaking into the environment, containment vessel plays an important role in nuclear safety of the Nuclear Power Plant (NPP). Severe accident may result in massive production of hydrogen in the vessel, and vessel pressure may increase rapidly. That may further threat the integrity of the containment vessel. Based on this phenomenon, the Filtered Containment Venting System (FCVS) has been proposed by researchers, which is very essential to protect the integrity of the containment vessel and remove contaminated particles from exhausting gaseous stream under PWR severe accident. The key equipment in FCVS is venturi scrubber filter. When the system is activated under severe accident, the hydrogen produced in the containment vessel will flow into the filtering equipment, which may lead to high hydrogen concentration in some regions of it. High hydrogen concentration may result in combustion, deflagration, and endanger the whole system. In the present study, the temperature and velocity distribution of gaseous mixture in the filtering equipment was simulated on the basis of CFD technology, and high hydrogen concentration region was recognized according to the simulation results of gas concentration distribution. Meanwhile, in order to mitigate the consequence of hydrogen aggregation, the nitrogen injection condition was taken into consideration in simulation process, and the effects of different injection conditions on hydrogen inerting performance was also analyzed in detail. The present study is significant for hydrogen risk management and further design of FCVS under PWR severe accident.