I-1. This annex presents short descriptions of several concepts for containment systems now in use or in an advanced stage of design. The descrip­tions are not comprehensive but are intended to provide a general overview of how certain containment subsystems have been combined to carry out the containment functions.

FULL PRESSURE DRY CONTAINMENT IN PRESSURIZED WATER REACTORS

I-2. In this concept (Fig. I-1), the primary containment envelope is a steel shell or a concrete building (cylindrical or spherical) with a steel liner that surrounds the nuclear steam supply system. The containment encompasses all components of the reactor coolant system under primary pressure. It is designed as a full pressure containment; i. e. it is able to withstand the increases in pressure and temperature that occur in the event of any design basis accident, especially a LOCA. The atmospheric pressure in the containment envelope is usually maintained at a substantial negative gauge pressure during normal operations by means of a filtered air discharge system (i. e. a fan and HEPA filter).

I-3. Energy management in the building can be accomplished by an air cooler system or by a water spray system. In addition, the free volume of the containment and the structural heat sinks (the containment envelope and the structures within it) are used to limit peak pressures and temperatures in postulated conditions for pipe rupture accidents. The initial supply of water for the spray system and for the emergency core cooling system is held in a large tank. When this water has been used, suction for both the spray system and the emergency core cooling system is switched to the containment building sump. Water that is recirculated to the reactor vessel is sometimes cooled by means of heat exchangers. In most designs the recirculation water for the spray headers — which is also used to limit contamination of the containment atmosphere — is cooled by means of heat exchangers. When pipes rupture in systems other than the reactor coolant system, only the spray system is operated in the recircu­lation mode.

(T) Pump

Blower, fan

FIG. I-1. Schematic diagram of a full pressure dry containment system for a pressurized water reactor: 1, containment; 2, containment spray system; 3, filtered air discharge system; 4, liner.