Figure V-6 presents a schematic of the AP600/AP1000 containment. It consists of a large steel vessel that houses the nuclear steam supply system (NSSS) and all of the passive safety injection systems. The steel containment vessel resides inside of a concrete structure with ducts that allows cool outside air to come in contact with the outside surface of the containment vessel. When steam is vented into containment via a primary system break or ADS-4 valve actuation, it rises to the containment dome where it is condensed into liquid. The energy of the steam is transferred to the air on the outside of containment via conduction through the containment wall and natural convection to the air. As the air is heated, it rises through the ducts creating a natural circulation flow path that draws cool air in from the inlet duct and vents hot air out the top of the concrete structure. The condensate inside containment is directed back into the IRWST and the containment sump where it becomes a source of cool water in the sump recirculation process. In a LOCA, cold water is sprayed by gravity draining onto the containment vessel head to enhance containment cooling. A large tank of water, located at the top of the containment structure, serves as the source of water for this operation.

FIG. V — 6. Containment and passive containment cooling system (PCCS).