Dimension of the forced vessel water level based on subcooling margin of core outlet coolant in CPR1000 nuclear power plants

The core cooling and monitoring system (CCMS) supplies the sub-cooling margin (ΔTSAT) and the pressure vessel water level (L VSL) information for State Oriented Procedure (SOP) to identify the core cooling state in post-accident conditions, as some special accidents such as the rupture of the vessel vent line will lead to both train A and train B L VSL measurements failure, the forced L VSL values have to be designed and set in the CCMS to ensure the correct diagnosis of primary system state in these scenarios. Considering the inherent relationship between ∆TSAT and L VSL from the point of view of thermal-hydraulics, the forced L VSL values are dimensioned based on ∆TSAT while taking into consideration the presence of non-condensable gases in primary system and the operating state of reactor coolant pumps. These values have been practically applied in CPR1000 nuclear power plants.