Patent Number: 046541900
Section: summary

FIELD OF THE INVENTION The present invention relates to an emergency feedwater system to provide emergency feedwater to the steam generators of a pressurized water reactor so as to cool the reactor in the event of a failure of a main feedwater system to a steam generator. BACKGROUND OF THE INVENTION In pressurized water reactors for the nuclear production of power, a pressurized fluid is passed through the reactor core and, after being heated in the core, is passed through heat transfer tubes that are positioned in a secondary side of a steam generator. In the secondary side of the steam generator, the heat transfer tubes transfer heat to a secondary fluid to produce steam that is then used to operate a turbine for production of electrical power. The provision of emergency feedwater systems for the secondary side of the steam generators of a pressurized water reactor is made in order to supply feedwater to the steam generators following an accident or transient conditions when the main feedwater system is not available, thereby maintaining the capability of the steam generators to remove plant stored heat and reactor core decay heat by converting the emergency feedwater to steam which may then either be discharged to the condensor or to the atmosphere. Such emergency feedwater systems generally comprise a source of emergency feedwater, such as a supply of water contained in a storage tank, and associated lines, pumps and valving systems to direct the emergency feedwater, when necessary, to the steam condensors. In order to assure operation of the system under various adverse conditions, means must be provided to effect operation of the emergency feedwater system for example in the event of loss of electrical power, or in the event of a passive failure such as a pipe rupture or an active failure such as a failure of a valve to respond to a signal to open or close. In addition, provision should be made to address even remote possibilities of interruption of an emergency feedwater system, such as fires or other external events, such as air craft impacts, explosions, or the like, which might impair the operability of the system. SUMMARY OF THE INVENTION An emergency feedwater system for the steam generators of a pressurized water nuclear reactor power plant contains two separately located subsystems. Each subsystem comprises an emergency feedwater supply tank, and a pair of emergency feedwater lines for discharge of water from the tank to the inlet line of a steam generator. An electrically operated motor driven pump is located in one of said pair of emergency feedwater lines, and a steam driven turbine pump is located in the other of said pair of emergency feedwater lines. A cavitating venturi is provided in the emergency feedwater line between the pumps and the inlet line to a steam generator. In the embodiment for a four loop system, a cavitating venturi is provided in each of the emergency feedwater lines, with one feedwater line provided for each of four steam generators, and connecting lines are provided between each pair of emergency feedwater lines. In the embodiment for a three loop system, one of each of said pair of emergency feedwater lines of a subsystem charges emergency feedwater to separate first and second steam generators, while the other of each of said pair of emergency feedwater lines combine to form a common discharge line to a third steam generator. A cavitating venturi is provided in each of said feedwater lines to the first and second steam generators and a further cavitating venturi is provided in the common discharge line. In the embodiment for a two loop system, each pair of emergency feedwater lines of a subsystem combine to form a common discharge line to separate ones of the two steam generators, and a cavitating venturi is provided in each of the two common discharge lines.