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A nuclear power station. The nuclear reactor is containedinside the cylindrical containment buildings to the right -

left is a cooling tower venting water vapor from the non-radioactive side of the plant. A nuclear power plant (NPP ) i s a thermal powerstation in which the heat source is one or more nuclear

reactors .Nuclear power plants are base load stations, which workbest when the power output is constant.


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The control room at a U.S. nuclear power plant

Historyy E lectricity was generated for the first time ever in the

United States by a nuclear reactor on December

20, 1951at the EBR -I experimental station near Arco,Idaho in the United States . On June 27, 1954, the world's first nuclear power plant to generate electricity for a power grid started operationsat Obninsk ,USSR .[1] The world's first commercial scalepower station, Calder Hall in E ngland openedin October 17, 1956.[2]


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Systemsy The conversion to electrical energy takes place indirectly, as

in conventional thermal power plants: The heat is producedby fission in a nuclear reactor (in a coal power plant it wouldcorrespond to the boiler) and given to a heat transfer fluid -usually water (for a standard type light water reactor ).Directly or indirectly water vapor-steam is produced. Thepressurized steam is then usually fed to a multi-stage steamturbine. Steam turbines in Western nuclear power plants areamong the largest steam turbines ever. After the steamturbine has expanded and partially condensed the steam, theremaining vapor is condensed in a condenser. The condenseris a heat exchanger which is connected to secondary sidesuch as a river or a cooling tower. The water then pumpedback into the nuclear reactor and the cycle begins again. The water-steam cycle corresponds to the R ankine cycle


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Nuclear reactors

y A nuclear reactor is a device to initiate and control a sustained nuclearchain reaction . The most common use of nuclear reactors is forthe generation of electric energy and for the propulsion of ships .

y The nuclear reactor is the heart of the plant. In its central part, the reactorcore's heat is generated by controlled nuclear fission. With this heat, acoolant is heated as it is pumped through the reactor and thereby removesthe energy from the reactor. Heat from nuclear fission is used to raise steam, which runs through turbines , which in turn powers either ship's propellersor electrical generators.

y Since nuclear fission creates radioactivity, the reactor core is surrounded by a protective shield. This containment absorbs radiation and prevents

radioactive material from being released into the environment. In addition,many reactors are equipped with a dome of concrete to protect the reactoragainst external impacts.

y In nuclear power plants, different types of reactors, nuclear fuels, andcooling circuits and moderators are sometimes used.


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S team turbiney The object of the steam turbine is to convert the heat

contained in steam into rotational energy. The enginehouse with the steam turbine is usually structurally separated from the main reactor building. It is aligned to

prevent debris from the destruction of a turbine inoperation from flying towards the reactor.y In the case of a pressurized water reactor, the steam turbine

hermetically separated from the nuclear system. To detect aleak in the steam generator and thus the passage of

radioactive water at an early stage is the outlet steam of thesteam generator mounted an activity meter. In contrast,boiling water reactors and the steam turbine withradioactive water applied and therefore part of the controlarea of the nuclear power plant.


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G enerator

The generator converts kinetic

energy supplied by the turbineinto electrical energy. Low-pole AC synchronous generators of high rated power are used.


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S afety valvesy The pressure in the reactor pressure vessel at an incident,

to limit upward, two independent safety valves areavailable. The pressure relief prevents bursting of pipes orreactor. The valves are in their capacity designed so thatthey can derive all of the supplied flow rates with littleincrease in pressure. In the case of the B W R , the steam isdirected into the condensate chamber and condensesthere. The chambers are on heat exchanger connected tothe intermediate cooling circuit.

y Should not close the safety valves, are very close againsafety shut any, should, if necessary, prevent coolantaccident. The non-closing of a safety valve led to a seriousaccident at Three Mile Island.


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Feed water pumpy The Feed water pump have the task of the water from the feed

water tank to the vapor pressure in the reactor and the steamgenerator to bring and promote a water with approximately 2200 kg / s. The power required amounts here to about 20 MW per pump. About the feed water system, the water level in the

steam generator and nuclear reactor is controlled. E mergency power supply y The E mergency power supply a nuclear power plant is several

times redundant built up by diesel generators and battery buffers. The battery backup provides uninterrupted coupling of the diesel units in the network secure. If necessary, theemergency power supply allows the safe descent down thenuclear reactor. Less important auxiliary systems such as, forexample, heat tracing of pipelines are not receiving it. Themajority of the required power is used to supply the feedpumps and Not speisepumpen order to shut down the nuclearreactor, the Decay heat even with a Failure of the power system,

A B lackout permanently dissipate.


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People in a nuclear power plant

y Nuclear power plants typically employ just under a thousand peopleper reactor (including security guards and engineers associated withthe plant but possibly working elsewhere).

y Nuclearengineersy R eactor operatorsy Health physicistsy E mergency response team personnely Nuclear R egulatory Commission R esident Inspectors

y

In the United States and Canada, workers except for management,professional (such as engineers) and security personnel are likely to bemembers of either the International B rotherhood of E lectrical Workers (IBE W) or the Utility Workers Union of America (UWUA).


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Safetyy C omplexity y Nuclear power plants are some of the most sophisticated and complex

energy systems ever designed. Any complex system, no matter how well it isdesigned and engineered, cannot be deemed failure-proof. StephanieCooke has reported that:

y

The reactors themselves were enormously complex machines with anincalculable number of things that could go wrong. When that happenedat Three Mile Island in 1979, another fault line in the nuclear world wasexposed. One malfunction led to another, and then to a series of others,until the core of the reactor itself began to melt, and even the world's mosthighly trained nuclear engineers did not know how to respond. Theaccident revealed serious deficiencies in a system that was meant to protectpublic health and safety.

y A fundamental issue related to complexity is that nuclear power systemshave exceedingly long lifetimes. The timeframe involved from the start of construction of a commercial nuclear power station, through to the safedisposal of its last radioactive waste, may be 100 to 150 years.


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Failure modes of nuclear power plants

y There are concerns that a combination of human andmechanical error at a nuclear facility could result in

significant harm to people and the environment:y Operating nuclear reactors contain large amounts of

radioactive fission products which, if dispersed, canpose a direct radiation hazard, contaminate soil and

vegetation, and be ingested by humans and animals.Human exposure at high enough levels can cause bothshort-term illness and death and longer-term death by cancer and other diseases. [


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