Preliminary Analysis of Hydrogen Distribution during Severe Accident induced by Loss of Coolant Accident

During hypothetical severe accidents in nuclear power plants, a large amount of hydrogen is generated rapidly as a result of Zirconium-Steam reaction and released into the containment. Hydrogen mixes with air and may come into combustion or detonation under proper conditions, which threatens the integrity of containment. Therefore, getting detailed hydrogen flow and distribution in various physical mechanisms is a key issue to resolve the hydrogen risk in containment and compartments. To study local hydrogen distribution in the containment of advanced passive PWR, an analysis model is built by 3-dimensional CFD code. Computational domain is divided by structured grid which contains over 100,000 cells. the shape and surface area of walls and obstacles of steel shell and internal structure, which have great impact on gas flow and heat transfer, are included. Hydrogen distribution in containment simulating with different turbulence models is studied, the result shows that during large amount of hydrogen release stage. In hydrogen distribution result simulating with algebraic model, hydrogen is all gathered in the dome and the peak concentration reaches 17%. When k-epsilon model is adopted, the peak concentration in the dome is 8%, hydrogen stratification is established in whole large space. Besides, hydrogen distribution near source also shows algebraic model cannot simulate turbulence diffusion in local compartment. It is more reasonable choosing k-epsilon model to study hydrogen behavior in containment. Based on adopted k-epsilon model, the effect of steam on hydrogen distribution is investigated. With steam injection, the hydrogen distribution is more homogeneous in upper space and average concentration is lower. In local compartalent, due to diffusion enhanced by steam, the hydrogen concentration is higher in the bottom.