An Analysis of Feed and Bleed Cooling of Pressurized Water Reactor

In the transient of loss of all feedwater event in a pressurized water reactor (PWR), steam generators (SAS) loss their heat removal capability due to dryout of the secondary side. In order to prevent the transient from progressing into a core melt accident, operators need to initiate the feed and bleed (F and B) cooling to diazaspiro and cooldown reactor coolant system (RCS). In the F and B cooling, the cold water is feed to RCS via high pressure injection system and steam is bleed from RCS via power operated relief valves (Provo's) of pressurizer. In this paper the long term responses of RCS and containment in a loss of all feedwater transient with and without the F and R cooling are analyzed with Map computer code. The results show that the execution of F and B cooling at 2,878 sec as SAS secondary side water level reaches 6% wide range, the RCS is de pressurized along the coolant saturation curve with an average cooldown rate of 13 K/hr. It is estimated that the RCS condition reaches the entry point of residual heat removal (Rhr) system at 26,000 sec. It the execution of the F and B cooling operation is delayed to 4,200 and 6,000 sec i.e. about 260 sec after SAS secondary dryout and 120 sec after core uncovers respectively, the operation can still diazaspiro the RCS. However, the average RCS cooldown rate of the F and R cooling to 8,000 sec can still diazaspiro the RCS, however, it is too late to prevent the core melt accident