Numerical analysis of different break direction effect on hydrogen behavior in containment during a hypothetical LOCA

Abstract

Large amounts of hydrogen could be generated and released into the containment during the course of a severe accident in a Light Water Reactor nuclear power plant. Getting detail hydrogen distribution in containment is important for analysis of hydrogen risk. In this study, a three dimensional CFD analysis model is established to analyze hydrogen behavior during hypothesized severe accident induced by LOCA in advanced passive PWR containment. Hydrogen distribution in containment simulating with algebraic and k-ε turbulence models is studied, the result shows that when k-ε model is adopted, hydrogen stratification is established in whole upper space and the peak concentration in the dome is 8%. Then the effect of source injection direction with vertical and horizontal injection cases is investigated. In vertical injection case, the local high concentration of hydrogen reaches over 25% in source compartment. In horizontal injection case, it occurs in SG-2 and the channel connecting two steam generator compartment i.e. vertical compartment. In upper space, comparing with horizontal source direction, when source direction is vertically towards upper space, hydrogen flows into the dome driven by momentum and stratification can be established more possible. In long term, with hydrogen distribution tending to be uniform, the effect of direction is not obvious. Due to more steam transporting into local compartments (SG-2, vertical and CMT compartments) when direction is horizontal, hydrogen concentration in these compartment is lower. In addition, source direction change can also lead to the change of location where hydrogen combustion risk probably occurs. When direction is horizontal, combustion risk happens in SG-2, vertical or CMT compartments rather than source compartment.