Analysis shows that during severe accidents the AP1000 containment remains intact. As a result, the plant has a
significantly reduced frequency of release of large amounts of radioactivity following core damage in an accident. The PCS
cooling capability is very reliable with its 3 way redundant (and diverse) water drain valves. In addition, even with failure of
water drain, air-only cooling is capable of maintaining the containment below the predicted failure pressure. Other
contributing factors include improved containment isolation and reduced potential containment bypass sequences including
steam generator tube ruptures (SGTR). This enhanced containment performance supports the technical basis for
simplification of offsite emergency planning.