The AP1000 Design Control Document (DCD) Tier 2, Section 5.1, “Reactor Coolant Systemپ and Connected Systems,” provides a summary description of the AP1000 reactor coolant system (RCS) and connected systems, as well as their design bases. DCD Tier 2, Sections 5.2 through 5.4 provide detailed design descriptions of reactor coolant pressure boundary integrity, reactor vessel (RV), and component and system design, respectively. Following is an overview of the AP1000 RCS and connected systems. Sections 5.2 through 5.4 of this report provide the staff’s evaluation of these systems. DCD Tier 2, Figures 5.1-1 through 5.1-3 show the schematic and layout of the AP1000 RCS and its principal auxiliary systems. The RCS consists of two heat transfer circuits (loops), each with a U-tube steam generator (SG), two reactor coolant pumps (RCPs), a single hot leg pipe, and two cold leg pipes for circulation of reactor coolant. The RCS also includes the pressurizer, interconnecting piping, valves, and instrumentation for operational control, actuation, and monitoring of plant safety systems. All RCS equipment is located in the reactor containment. The reactor coolant pressure boundary (RCPB) provides a barrier against the release of radioactivity generated within the reactor. It is designed to provide a high degree of integrity throughout operation of the plant.