The AP600 is a 600 MWe PWR utilizing passive safeguard systems and extensive plant simplifications to enhance the construction, operation, and maintenance of the plant. The plant design utilizes proven technology which builds on over 40 years of operating PWR experience. PWRs represent 76 percent of the light water reactors around the world; 67 percent of the PWRs are based on Westinghouse PWR technology.

The AP600 nuclear steam supply system (NSSS) design is based on the standard two-loop Westinghouse PWR designs that have collectively logged more than 100 reactor years of operation and shown capacity factors in excess of 85 percent (as compared to an overall industry-wide capacity factor of approximately 74 percent). The U.S. plants of this design include Ginna, Prairie Island, Kewaunee, and Point Beach. Their operating record is the best among any group of plants in the U.S. Internationally, Korea's Kori-2 plant, which became operational in 1983, is a Westinghouse two-loop PWR that has been among the best performers in the world, and it is this plant design which is the basis, or reference, for the AP600 NSSS design.

Westinghouse's two-loop plant designs are both robust and simple. These two features are primarily responsible for the excellent reliability of this class of plants. The AP600 NSSS is based on the same robust and simplified design approach. In addition, the same control and feedback mechanisms (e.g., steam generator level, pressurizer pressure), successfully demonstrated in the operation of the existing two-loop plants, are used in the AP600 design. As a result, the AP600 plant response to system transients is well understood and can be reliably predicted based on the proven performance of the existing two-loop plants.