Mitigating Hydrogen Risks in Light-Water Nuclear Reactors: A CFD Simulation of the Distribution and Concentration

During severe accidents in light-water nuclear reactors, the release of hydrogen poses significant risks to the integrity of the containment and the surrounding infrastructure. To address this, passive autocatalytic re-combiners (PARs) have been adopted in several countries. However, it remains challenging to eliminate the production of flammable combinations and the potential for local flame explosions, even with PARs installed. Understanding the distribution and concentration of generated hydrogen, particularly in 100% fuel-clad coolant reactions, is therefore crucial. In this study, numerical investigations using ANSYS CFX, a commercially available code, are conducted to analyze the hydrogen generation and distribution in a 1000 MWe nuclear power plant. The results show the effectiveness of PARs through a comparative evaluation of reactors with PARs and without PARs installed. The simulated scenario involved the release of hydrogen from the reactor pressure vessel, resulting in a reduction in the maximum hydrogen concentration released from 17.85% in the containment model without PARs to 9.72% in the containment model with PARs installed after 22,000 s. These findings highlight the importance of understanding and controlling the hydrogen distribution in light-water nuclear reactors during severe accidents. This study is useful in informing the mitigation risks strategy for hydrogen release in light-water nuclear reactors.