The fundamentally new concept for accident control incorporated into the SWR 1000 includes equipment which, in the event of failure of the active safety equipment, will bring the plant to a safe condition without the need for any instrumentation and control signals or external power. This passive safety equipment (Figures XI-1 and XI-2) includes the following:

Emergency condensers

The function of the emergency condenser system is to remove, in the event of an accident, the decay heat still being generated in the core as well as any sensible heat stored in the reactor pressure vessel
to the core flooding pools, without any coolant inventory being lost from the reactor pressure vessel. The system thus replaces the high pressure coolant injection systems used in existing BWR plants. The emergency condenser system also provides a means for reactor pressure relief that is diverse with respect to the safety-relief valves.

Containment cooling condensers

The function of the four containment cooling condensers is to remove — by entirely passive means — decay heat from the containment following accidents that result in the release of steam into the drywell, and in this way to limit the increase of containment pressure. They provide redundancy and diversity with respect to the residual heat removal system.

Core flooding system

The core flooding system is a passive low pressure flooding system for controlling the effects of loss — of-coolant accidents. It is installed at an elevation which ensures that, following automatic depressurization of the reactor, it can passively flood the reactor core by means of gravity flow. The system provides redundancy and diversity with respect to the core flooding function of the residual heat removal system.

Drywell flooding system

A postulated severe accident involving core melt is controlled such that the molten core is retained inside the reactor pressure vessel. For this purpose the section of the drywell surrounding the reactor pressure vessel is flooded with water in order to cool the exterior of the reactor pressure vessel and thus remove heat from the reactor.

Passive pressure pulse transmitters

The passive pressure pulse transmitter is a completely passive switching device which is used to directly initiate the following safety functions (as a minimum), without the need for instrumentation and control equipment: reactor scram, containment isolation at the main steam line penetrations, and automatic depressurization of the reactor pressure vessel. The passive pressure pulse transmitter comes into action as a result of a drop or increase in reactor water level as well as an increase in reactor pressure. For activating the various safety functions, passive pressure pulse transmitters of redundant design are installed at two elevations. The upper passive pressure pulse transmitters, situated at an elevation beneath that of the normal water level of the reactor pressure vessel, are responsible for initiating reactor scram. The lower passive pressure pulse transmitters, arranged at a lower elevation, activate automatic depressurization of the reactor as well as closure of the main steam containment isolation valves. Further passive pressure pulse transmitters installed at appropriate locations respond to a rise in reactor water level above the main steam nozzles and likewise activate containment isolation at the main steam line penetrations.