The features of the AP600 passive safety systems include passive safety injection, passive residual heat removal, passive containment cooling, and passive main control room habitability maintenance. All of these passive systems have been designed to meet the NRC single failure criteria, and probabilistic risk analyses have also been used to verify their reliability. These passive systems employ natural forces and stored energy to operate. They are highly reliable because in the unlikely event of an accident, with an assumed unavailability of non-safety systems, they do not require the starting of motors, pumps, or diesel generators. These passive systems have also been designed to satisfy additional NRC criteria, including Three Mile Island lessons learned, Standard Review Plan, Regulatory Guides, and unresolved and generic safety issues.

Several aspects of the passive safety systems have been used in existing nuclear plants. The accumulators are a part of most PWR designs, so their use is well understood. Several early boiling water reactors (BWRs), like Dresden in the U.S., used isolation condensers as natural circulation closed-loop heat removal systems. The AP600 passive residual heat removal heat exchanger was designed with the benefit of this experience. BWRs have used automatic depressurization systems (ADS) and spargers for many years. Use of slow opening valves is a result of understanding the air clearing loads discovered in BWR operation. The AP600 ADS incorporates spargers to allow depressurization of the RCS to the in-containment refueling water storage tank (IRWST) in lieu of the containment atmosphere to minimize the containment cleanup following an ADS actuation. The sparger design incorporates BWR design and operating experience.