Numerical Simulation of Flow with Volume Condensation in Presence of Non-condensable Gases in a PWR Containment - 14046

One severe accident scenario in a Pressurized Water Reactor (PWR) is a leak in the primary circuit of a reactor resulting in hydrogen and steam injection into the containment. The hydrogen-steam-air mixture could reach the conditions for deflagration of combustion or local detonations. Because of the influence of steam condensation on the gas mixing and hydrogen stratification in the containment, the wall and volume condensation phenomena are of interest for the safety considerations. The wall condensation model is available in the CFD code ANSYS CFX. This paper presents a newly developed volume condensation model in the presence of non-condensable gases with two-phase flow for the ANSYS CFX code. The two-fluid model with a continuous gas phase consisting of a steam-air-light gas mixture, and a dispersed liquid phase composed of water droplets in mechanical and thermal non-equilibrium is applied. Both phases are modeled with separate temperatures and velocities. The motion of the droplet due to gravitational force is considered. Volume condensation is modeled as a sink of mass and source of energy at the droplet interfaces. The newly developed volume condensation model is validated with a condensation experiment TH13, which was performed in the German THAI facility within the OECD/NEA International Standard Problem (ISP-47). Finally, in order to predict the local hydrogen behavior within a real containment during a severe accident, the containment flow was simulated at the time of accident in a 'Generic Containment', which was developed based on a German PWR. (authors)