I-26. The pressurized containment system (Fig. I-8) used in pressurized heavy water reactors for single unit plant designs typically consists of the following subsystems:

(a) A containment envelope comprising a prestressed, post-tensioned concrete reactor building and its extensions;

(b) An energy suppression system that consists of a dousing tank and a spray system that suppress the initial peak pressure;

(c) A reactor building cooling system to depressurize the containment in the longer term;

(d) A filtered air discharge system to help to maintain subatmospheric pressure within the containment envelope in the long term after an
accident, and an atmospheric control system to aid in cleanup operations for the containment.

I-27. Upon the detection of radioactivity or high pressure in the reactor building, the isolation system closes the appropriate penetrations of the containment envelope.

_v

FIG. I-8. Schematic diagram of a pressurized containment system for a pressurized heavy water reactor: 1, containment; 2, dousing tank and spray system; 3, filtered air discharge system; 4, emergency core cooling system.

I—28. When high pressure is detected in the reactor building, the dousing system is also activated. The initial peak pressure following a LOCA is suppressed by the condensation of steam through the dousing spray system. Long term energy management is provided by the atmosphere control system (building air coolers) and by the heat exchangers in the recirculation system of the emergency core cooling system. Radionuclide management is accom­plished by plate-out on the internal surfaces of the containment envelope, by washout afforded by the dousing spray system, by the leaktightness of the containment envelope and, in some plants, by pH control buffers in the sump.