The AP600 uses passive safety systems to enhance the safety of the plant and to satisfy NRC safety criteria. These systems use only natural forces, such as gravity, natural circulation, and compressed gas. No pumps, fans, diesels, chillers, or other rotating machinery are used in the passive safety sub-systems. A few simple valves are used to align the passive safety systems when they are automatically actuated. In most cases these valves are "fail safe" (i.e., they require power to stay in their normal, closed position; loss of that power causes them to open to their safety alignment. This power is normally supplied by class lE uninterruptible power supplies). These passive safety systems are significantly simpler than typical PWR safety systems.

In addition to being simpler, the passive safety systems do not require the large network of safety support systems needed in typical nuclear plants, such as AC power, HVAC (heating, ventilating, air conditioning) and cooling water systems and seismic buildings to house these components. This simplification includes eliminating the safety-grade emergency diesel generators and their network of support systems, air start, fuel storage tanks and transfer pumps, and the air intake/exhaust system. As a result, support systems no longer need to be safety grade and can be simplified or eliminated.

The features of the AP600 passive safety systems include passive safety injection, passive residual heat removal, and passive containment cooling. All these passive systems have been designed to meet the NRC single-failure criteria and its recent criteria, including TMI lessons-learned and unresolved and generic safety issues. PRAs have also been used to quantify the safety of the design.