Study on the impact of containment mesh refinement and PAR installation on hydrogen distribution during severe accidents

Abstract In response to the heightened global focus on hydrogen management following the Fukushima nuclear disaster, the Maanshan Nuclear Power Plant (NPP) in Taiwan has initiated safety enhancements by installing Passive Autocatalytic Recombiners (PARs) to reduce the risk of hydrogen explosions during severe accidents. This study utilizes the MAAP5 software to refine the containment model of Maanshan NPP, introducing updates in compartment divisions, flow paths, and heat sinks to simulate gas behavior, specifically hydrogen and carbon monoxide distribution, under accident conditions. A small break loss-of-coolant accident (LOCA) scenario was modeled to evaluate the containment’s performance before and after these updates, as well as after PAR installation. The results demonstrate that the updated model improves gas transfer and diffusion simulations, while the PARs effectively reduce hydrogen and carbon monoxide concentrations below the flammability limit (<10 %), lowering the risk of detonation. Additionally, the Adiabatic Isochoric Complete Combustion (AICC) pressure remains within safety standards, which is below 8.48 bar. These findings confirm that the containment model enhancements and PAR installations significantly improve nuclear safety at Maanshan NPP.