"Congress should promote research into the next generation of nuclear plants and encourage investment in existing nuclear plants to expand a clean and unlimited source of energy."

- President George W. Bush, Speech at Central Aluminum, Columbus, Ohio, Oct. 30, 2003

Nuclear Energy-the world's largest source of emission-free energy. nuclear power plants produce no controlled air pollutants, such as sulfur and particulates, or greenhouse gases. the use of nuclear energy in place of other energy sources helps to keep the air clean, preserve the Earth's climate, avoid ground-level ozone formation and prevent acid rain.

- Nuclear Energy Institute, November 2003, http://www.nei.org

Source: http://canteach.candu.org/

Pressurized Water Reactor DiagramSource: U.S. Nuclear Regulatory Commission

The Pressurized Water Reactor (PWR) AnimatedSource: U.S. Nuclear Regulatory Commission

Boiling Water Reactor DiagramSource: U.S. Nuclear Regulatory Commission

PWR Diagram w/ 3 Turbines

The Boiling Water Reactor (BWR) AnimatedSource: U.S. Nuclear Regulatory Commission

Reactor Coolant SystemThe system used to remove energy from the reactor core and transfer that energy either directly or indirectly to the steam turbine. Varies with what kind of reactor is used. PWR versus BWR

Main Steam SystemWorks with feedwater system, turbine and condenserCarries heat energy to be converted into rotational energy in turbine shaftValves are connected into the main steam pipes: safety relief valves (against overpressure in vessels)

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.