The AP600 passive core cooling system (PXS) performs two major functions:

• Safety Injection and Reactor Coolant Makeup for Inventory
• Passive Residual Heat Removal (Passive RHR)

Computer analyses demonstrate that the PXS provides effective core cooling for various break sizes and locations. These calculations show that the PXS prevents core damage for breaks as large as the 8-inch vessel injection lines and provides about 500 degF margin to the maximum peak clad temperature limit for the double-ended rupture of a main reactor coolant pipe.