Condensate-Feedwater System
Add a quick list of factual stuff about nuclear energy.Explain
diagram. PWRs keep water under pressure so that it heats, but does
not boil. Water from the reactor and the water in the steam
generator that is turned into steam never mix. In this way, most of
the radioactivity stays in the reactor area.
In a typical commercial pressurized light-water reactor (1) the
reactor core creates heat, (2) pressurized-water in the primary
coolant loop carries the heat to the steam generator, and (3) the
steam generator vaporizes the water in a secondary loop to drive
the turbine, which produces electricity.
Know where it starts and where the steam goes. Some steam
condenses down from the turbine causing the cycle to repeat
itself.
Explain diagram.Boiling Water Reactors This design uses lower
pressure (1500 pounds per square inch) piping nominally 1.5 to 3
feet (0.5 to 1 meter) in diameter. The BWR design allows bulk
boiling in the reactor. The BWR recirculation loop allows water to
be removed from the reactor for cooling down from the hot (~550 F)
condition to the cold or refueling (~100-200 F) condition. Water
can also be diverted to remove chemical impurities and unwanted
radioactive materials. Each loop has a single recirculation pump.
This pump is used to regulate the power in the reactor. As recirc
pump speed is increased, the power is raised.
Another type of PWR with three turbines. As the steam goes to
the right, turbines pressure change from high to low.
Pressurized Water Reactors-includes PWR, VVER, and CANDU This
design uses high pressure (1500 to 3000 pounds per square inch)
piping nominally 1.5 to 3 feet (0.5 to 1 meter) in diameter. Two
figures of the Reactor Coolant System are linked. One (267K) shows
the relative positions of Reactor, Pressurizer, Steam Generator,
and Reactor Coolant Pumps for a typical 4 Loop plant. The other
(191K) illustrates the flow path for a typical Reactor Cooling
System.Major components in this design are: Hot Leg between the
Reactor and Steam generator Steam Generator (link to 248K
illustration) to transfer the heat from the reactor cooling system
to a secondary system Intermediate Leg between the steam generator
and reactor coolant pump Reactor Cooling Pump (link to 71K or 264K
illustration) to pump the water through the entire system Cold Leg
between the reactor coolant pump and the reactor Pressurizer (link
to 271K illustration) to maintain the pressure within an allowed
range Pressurizer safety valves that open automatically to prevent
overpressurizing the reactor coolant pipe. Note-The illustrations
in the links above in this section were provided courtesy
Westinghouse Electric Corporation.In addition, there are usually
automatic air or motor operated valves that would open below the
setpoint of the Pressurizer safety valves to provide added
protection from overpressurization. These are usually referred to
as the Pressurizer Power Operated Relief Valves (or PORVs).It
should be noted that a single loop may have vertical or horizontal
steam generators. See the Steam generator. page for more
information on this. CANDU and VVER designs use the horizontal
steam generators. PWR designs use vertical steam generators. A
single loop may use 1 or 2 reactor coolant pumps per loop.
Combustion Engineering plants use 2 pumps per loop; the other
manufacturers usually use 1 pump per loop. CANDU, B&W, and
ABB-CE designs use 2 loops, Westinghouse -2, 3, or 4 loops.Some
designs (e.g. VVER) have motor operated isolation valves in the
reactor cooling loops on both the hot and cold leg sections of
pipe. This feature allows isolation of one loop and reduces the
likelihood of losing water from the reactor if there is a major
loss of coolant.
In a typical boiling water reactor the reactor core creates heat
and a single loop both delivers steam to the turbine and returns
water to the reactor core to cool it. The cooling water is
force-circulated by electrically powered pumps. Emergency cooling
water is supplied by other pumps, which can be powered by onsite
diesel generators. Other safety systems, such as the containment
building air coolers, also need electric power.
This design uses lower pressure (1500 pounds per square inch)
piping nominally 1.5 to 3 feet (0.5 to 1 meter) in diameter. The
BWR design allows bulk boiling in the reactor. The BWR
recirculation loop allows water to be removed from the reactor for
cooling down from the hot (~550 F) condition to the cold or
refueling (~100-200 F) condition. Water can also be diverted to
remove chemical impurities and unwanted radioactive materials. Each
loop has a single recirculation pump. This pump is used to regulate
the power in the reactor. As recirc pump speed is increased, the
power is raised.The NRC's Monticello Nuclear Plant diagram provides
a good illustration of a recirc system with the various connections
to supporting systems.
This is a bigger picture of the reactor coolant system.The main
steam system together with the feedwater system, turbine and
condenser, are connectedto form a closed flow circuit. This circuit
contains ordinary water and steam.. These systems carry heat from
the Heat Transport circuit to the turbine operating on a
Rankinecycle. This cycle transforms heat energy to rotational
energy in the turbine shaft. About 30% ofthe heat energy is changed
to rotational energy, and the rest is rejected to the condenser
coolingwater.. Several valves are connected to the main steam
pipes. The most important of these are the steamsafety relief
valves, which protect against overpressure in the vessels. These
valves also areequipped with actuators which can open the valves to
reduce pressure (and therefore temperature)in the steam generators.
This action cools and reduces pressure in the HT circuit in the
event ofan accident --- this is the same function as performed by
the automatic depressurization system(ADS) in a PWR. In a CANDU,
this important safety function can be done without opening theHT
circuit piping, as must be done in a PWR.. Main steam isolation
valves are needed in case one or more tubes start to leak in a
steamgenerator. Using one of these valves and one feedwater
isolation valve, a steam generator can becompletely isolated from
the circuit.. Atmospheric steam discharge valves have a capacity of
10% main steam flow are used to controlsteam pressure during
transients following rapid turbine power reduction.. Condenser
steam discharge valves can transfer up to 100% steam flow,
bypassing the turbine.This capability can be used to keep the
reactor at 60% power or more to limit Xenon buildup andconsequent
reactor poison shutdown.. Turbine stop valves are used to prevent
transfer of liquid water from the steam generator to theturbine --
which might seriously damage the turbine.. Flow is measured in both
the feedwater and steam piping. Large and small control valves
ensurethat the water level in each steam generator is correct.
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.
Major ComponentsCondensate 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 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.