Nuclear Power Plant Condensate-Feedwater Systems

Condensate-Feedwater Systems

Function

The Condensate-Feedwater Systems have two major functions:

Supply adequate high quality water to the steam generator (or reactor, if a BWR)
Heat the water from about 90F to about 450F.

The Condensate-Feedwater System is the light blue colored portion in the diagram. Water comes from condenser (represented by 3 pipes) to a Condensate pump (actually 3-4), then to Low Pressure Feedwater Heaters (usually 2 sets of 3-5 heaters), then to a Feedwater pump (usually 2-3), then to the High Pressure Feedwater Heaters (usually 2 sets of 1-2), then to the steam generators (for all types except BWR). In that case the water is supplied to the reactor.

Between the Condenser and Feedwater Pump, the water is called condensate; between the Feedwater Pump and the Steam Generator (or Reactor if a BWR), the water is called Feedwater.

Graphic courtesy NEK

Major Components

Condensate Pump

Raises pressure from almost vacuum levels to about 350 pounds per square inch.

Low Pressure Feedwater Heaters

Heat condensate water flowing through the tubes with steam exhausted from turbine. Temperature is raised from about 90F to about 350F

Feedwater Pump

Photo by J.A. Gonyeau

The Feedwater Pump increases the water pressure from about 350 pounds per square inch (psi) to about 1200 pounds per square inch. Each unit typically will have 2 or 3 Feedwater pumps.

The feedpumps may be electrically or turbine-driven. For the pump shown, a large electric motor is located at the back.Water is being supplied by the large right hand pipe in the foreground, and leaves by the large left hand pipe.

Feedpumps usually rotate at about 5000 revolutions per minute and have an oil lubricating system. Typical flowrates are 5000 to 10000 gallons per minute.

The Feedwater Pumps take a suction from both the Condensate and Heater Drains Systems. Condensate is routed from the condenser, where the steam from the low pressure turbine is condensed to water in a vacuum. Condensate pumps raise the pressure to over 350 psi. Typically the Condensate water passes through 4 to 6 stages of heater drain coolers and feedwater heaters which recover heat from steam exhausted from the various turbine stages and heat the Condensate water temperature from 90F to approximately 350F. The condensate passes on the inside of tubes in the feedwater heaters; the heater drains pass on the outside of the tubes (shell side) of the heat exchangers.

The Feedwater pumps then raise the pressure to about 1100 psi. The water then passes typically through 1 stage of High Pressure Feedwater heater. After passing through the HP Feedwater heater, the water is at about 425F and then passes to through regulating, or control, valves and then to the steam generator in the PWR, VVER, CANDU, and RBMK designs. In the case of the BWR, the water is supplied to the reactor.

High Pressure Feedwater Heaters

Raises temperature of the feedwater passing through tubes from about 350F to about 450F using steam exhausted from the turbine passing on the outside of the tubes.