The containment cooling system (see Fig. II-6) includes design features for circulation and cooling of the RB atmosphere both during normal operation and following an accident.

During normal operation local air coolers (LACs) operate to remove heat from the RB atmosphere. Two fuelling machine vaults and steam generator enclosures are atmospherically isolated from the rest of the RB.

Following an accident large airflow paths are established by, interconnecting the fuelling machine vaults and steam generator enclosures with the rest of the RB, permitting natural circulation flows to mix the RB atmosphere, without the need for fans or other active components (i. e. LACs), .This feature allows hydrogen dispersion/dilution throughout the larger RB volume and prevents formation of regions of locally high temperature. Hydrogen control design features are provided to restrict the concentration of hydrogen to below the limit for deflagration or detonation.

If needed, post-accident pressure and temperature suppression is performed by a containment cooling spray system supplied from the RWS.

A combination of passive and active features are provided in the ACR-1000 for atmospheric hydrogen control; passive auto catalytic recombiners, and active igniters (or ‘glow plugs’) that limit the concentration of hydrogen in the RB atmosphere to below the threshold limit at which deflagration or detonation could occur.