Analysis of air ingression into the core region during hypothetical PWR shutdown accidents

An analysis is conducted of the thermal hydraulics during core uncovery of a typical pressurized water reactor (PWR) during shutdown accident conditions. The objective of the analysis is to identify the magnitude and mechanism of air ingression into the core region during the reactor accident. Shutdown accident scenarios are considered possible when a reactor has been shut down from normal operation, such as will occur during a refueling outage, and the plant is in an operational state where the reactor vessel is open to the containment atmosphere. Accident conditions are created when the ability to continue injecting water into the vessel is lost, thus leading to a boildown