Study on loss of normal feedwater accident of advanced third generation NPP AP1000

This paper studies the loss of normal feed water accident of advanced third generation NPP AP1000 from the aspects of overfilling of pressurizer and integrity of RCS's pressure boundary and fuel cladding. For each criterion, different initial conditions and assumptions of reactor control and protection system will be considered to get the most conservative results. Furthermore, the turbine trip may lead to disruption of the grid in the design of AP1000, thus a loss of offsite AC power will be considered due to turbine trip following reactor trip. The reactor coolant pump will coast down after the loss of offsite AC power, the capability of heat removal of primary side will decrease and the RCS's temperature and pressure will increase. However the loss of offsite AC power will also cause the isolation of Chemical and Volume Control System, which may reduce the risk of overfilling of pressurizer and overpressure of RCS. Therefore, for different limiting criterion, it is necessary to analyze availability of AC power. The results show that with the operation of PXS and the action of the operator, core residual heat could be removed effectively, pressurizer will not overfill and integrity of RCS's pressure boundary and fuel cladding will be maintained whether AC power is available or not. (authors)