Many of the active safety-related systems in existing and evolutionary pressurized water reactor designs are retained in the AP1000® but are designated as non safety-related. Active, non safety-related systems support normal operations and are also the first line of defense in the event of transients or plant upsets. While these systems are not credited in the safety analysis evaluation, they provide additional defense-in-depth by adding a layer of redundancy and diversity. In addition to contributing to the very low CDF, the non safety-related active systems require fewer in-service inspections, less testing and maintenance and are not included in the Technical Specifications.

Examples of these systems include:
  • Chemical and volume control system
  • Normal residual heat removal system
  • Startup (auxillary) feedwater system
These systems utilize non-safety support systems such as the standby diesel generators, the component cooling water system and the service water system.

Additionally, the AP1000 includes other active non safety-related systems such as the heating, ventilation and air-conditioning (HVAC) system, which removes heat from the instrumentation and control cabinet rooms as well as the main control room. These are all familiar systems used in past and current reactors that act as a simplified first line of defense for the AP1000. They are all backed up by the ultimate defense: the passive safety-grade systems.

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