Diablo Canyon Nuclear Power Plant: The WikiBook/orphaned pages/NPP BasicsNuclear power plant

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A nuclear power plant (NPP) is a thermal power station in which the heat source is one or more nuclear reactors.

Nuclear power plants are base load stations, which work best when the power output is constant (although boiling water reactors (BWRs) can come down to half power at night).[citation needed]


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

Electricity was generated for the first time by a nuclear reactor on December 20, 1951 at 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 operations at Obninsk, USSR [1]. The world's first commercial scale power station, Calder Hall in England opened in October 17, 1956. [2].


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BWR schematic.
Pressurised water reactor
This section has recently been translated from the German Wikipedia.

The conversion to electrical energy takes place indirectly, as in conventional thermal power plants: The heat is produced by fission in a nuclear reactor (in a coal power plant it would correspond 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. The pressurized steam is then usually fed to a multi-stage steam turbine. Steam turbines in Western nuclear power plants are among the largest steam turbines ever. After the steam turbine has expanded and partially condensed the steam, the remaining vapor is condensed in a condenser. The condenser is a heat exchanger which is connected to secondary side such as a river or a cooling tower. The water then pumped back into the nuclear reactor and the cycle begins again. The water-steam cycle corresponds to the Rankine cycle.

Nuclear reactors

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

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

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 reactor against external impacts.

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

Steam turbine

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The object of the steam turbine is to convert the heat contained in steam into rotational energy. To the turbine shaft, the shaft of the generator is coupled. In nuclear power plants are mostly Saturated steam turbine Application. The turbine has a high-pressure part, and usually two or three low pressure stages. Due to the high moisture vapor after the high pressure part of the steam is dried before entering the low pressure part of means of steam heating and high-speed deposition. At the end of the last blade row of the low pressure part of the steam has a moisture content of about 15%. The expansion into the wet steam region leads to a high working efficiency, but with the disadvantages associated with wet steam.

If the generator to hand over by a disturbance generated electrical energy can, he takes little analogy to mechanical energy. In response to this Load drop would be the Speed the turbine to increase the allowable operating limit by the threat of self-destruction too high Centrifugal. To avoid this process, are close to the turbine inlet valves in the steam pipe installed. If this quick-closing valves activated, they direct the steam bypassing the turbine directly into the Capacitor. In parallel, the reactor is shut down because of the full reactor power capacitor can absorb only a limited time.

The engine house with the steam turbine is usually structurally separated from the main reactor building. It is oriented to fly from the destruction of a turbine in operation as no debris in the direction of the reactor.

In the case of a pressurized water reactor, the steam turbine hermetically separated from the nuclear system. To detect a leak in the steam generator and thus the passage of radioactive water at an early stage is the outlet steam of the steam generator mounted an activity meter. In contrast, boiling water reactors and the steam turbine with radioactive water applied and therefore part of the control area of ​​the nuclear power plant.


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The generator converts kinetic energy supplied by the turbine into electrical energy. Low-pole AC synchronous generators of high rated power are used. The Olkiluoto nuclear power plant was the largest synchronous generator (as of 2010) made. It has a rated power 1992 MW.

Main coolant pump (PWR) and forced circulation pump (BWR)

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The reactor coolant pump in the case of the DWR has the task to circulate the coolant between the reactor and steam generators. In western nuclear power plants, the nuclear reactor is fed with four redundant pumps (loops), each separated by Redundancy structurally accommodated in the reactor building. The design of the pump corresponds to a Centrifugal with a one-piece forged body. The throughput is up to 10,000 l / s at a pressure of 175 bar and a maximum allowable temperature of 350 ° C.[13] The increase in pressure through the main coolant pump when DWR indicates pressure loss in the reactor, steam generators and piping system. Even after the failure of the main coolant pumps (RESA is the result of) the circulation and thus the heat dissipation is by so-called Natural circulation guaranteed.

In the case of boiling water reactor are the reactor pressure vessel forced circulation pumps to avoid core wings attached to their interpretation is approximately equal to those in a PWR. You are responsible for the safety of the plant is not absolutely necessary.

Besides these main coolant pump of a nuclear power plant has usually still have several emergency supplies at different pressure levels, the case of disturbances (see Design basis accident) Maintain the cooling of the reactor core.

Safety valves

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The pressure in the reactor pressure vessel at an incident, to limit upward, two independent safety valves are available. The pressure relief prevents bursting of pipes or reactor. The valves are in their capacity designed so that they can derive all of the supplied flow rates with little increase in pressure. In the case of the BWR, the steam is directed into the condensate chamber and condenses there. The chambers are on heat exchanger connected to the intermediate cooling circuit.

Should not close the safety valves, are very close again safety shut any, should, if necessary, prevent coolant accident. The non-closing of a safety valve led to a serious accident at Three Mile Island.

Feedwater pump

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The Feedwater pump have the task of the water from the feedwater tank to the vapor pressure in the reactor and the steam generator 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. Emergency power supply [Edit]

The Emergency 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, the emergency power supply allows the safe descent down the nuclear reactor. Less important auxiliary systems such as, for example, heat tracing of pipelines are not receiving it. The majority of the required power is used to supply the feed pumps and Notspeisepumpen order to shut down the nuclear reactor, the Decay heat even with a Failure of the power system, A Blackout permanently dissipate.

People in a nuclear power plant

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Nuclear power plants typically employ just under a thousand people per reactor (including security guards and engineers associated with the plant but possibly working elsewhere).[citation needed]

In the United States and Canada, workers except for management, professional (such as engineers) and security personnel are likely to be members of either the International Brotherhood of Electrical Workers (IBEW) or the Utility Workers Union of America (UWUA).


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The economics of new nuclear power plants is a controversial subject, since there are diverging views on this topic, and multi-billion dollar investments ride on the choice of an energy source. Nuclear power plants typically have high capital costs for building the plant, but low direct fuel costs (with much of the costs of fuel extraction, processing, use and long term storage externalized). Therefore, comparison with other power generation methods is strongly dependent on assumptions about construction timescales and capital financing for nuclear plants. Cost estimates also need to take into account plant decommissioning and nuclear waste storage costs. On the other hand measures to mitigate global warming, such as a carbon tax or carbon emissions trading, may favor the economics of nuclear power.


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The nuclear power debate is about the controversy[3][4][5][6] which has surrounded the deployment and use of nuclear fission reactors to generate electricity from nuclear fuel for civilian purposes. The debate about nuclear power peaked during the 1970s and 1980s, when it "reached an intensity unprecedented in the history of technology controversies", in some countries.[7][8]


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Reprocessing of spent nuclear fuel can extend the usefulness of mined uranium. However, it is generally conceded that reprocessed fuel is more expensive than fuel from mined uranium (providing that adequate disposal space is available)[citation needed]. Such processing of civilian fuel has long been employed in Europe (at the COGEMA La Hague site) and briefly at the West Valley Reprocessing Plant in the U.S.

Reprocessing of spent fuel to obtain plutonium for nuclear weapons has been done in a number of countries: however these programs are typically separate from civilian activities[citation needed], and usually classified.

Use of breeder reactors combined with reprocessing could extend the usefulness of mined uranium by more than 60 times. [9] However, breeder reactors, not yet well developed, are currently significantly more difficult to operate.

Accident indemnification

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The Vienna Convention on Civil Liability for Nuclear Damage puts in place an international framework for nuclear liability [10]. However states with a majority of the world's nuclear power plants, including the U.S., Russia, China and Japan, are not party to international nuclear liability conventions.

In the U.S., insurance for nuclear or radiological incidents is covered (for facilities licensed through 2025) by the Price-Anderson Nuclear Industries Indemnity Act.

Under the Energy policy of the United Kingdom through its Nuclear Installations Act of 1965, liability is governed for nuclear damage for which a UK nuclear licensee is responsible. The Act requires compensation to be paid for damage up to a limit of £150 million by the liable operator for ten years after the incident. Between ten and thirty years afterwards, the Government meets this obligation. The Government is also liable for additional limited cross-border liability (about £300 million) under international conventions (Paris Convention on Third Party Liability in the Field of Nuclear Energy and Brussels Convention supplementary to the Paris Convention). [11]


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Nuclear decommissioning is the dismantling of a nuclear power plant and decontamination of the site to a state no longer requiring protection from radiation for the general public. The main difference from the dismantling of other power plants is the presence of radioactive material that requires special precautions.

Generally speaking, nuclear plants were designed for a life of about 30 years. Newer plants are designed for a 40 to 60-year operating life.

Decommissioning involves many administrative and technical actions. It includes all clean-up of radioactivity and progressive demolition of the plant. Once a facility is decommissioned, there should no longer be any danger of a radioactive accident or to any persons visiting it. After a facility has been completely decommissioned it is released from regulatory control, and the licensee of the plant no longer has responsibility for its nuclear safety.

Future power plants

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The 1600 MWe European Pressurized Reactor reactor is being built in Olkiluoto, Finland. A joint effort of French AREVA and German Siemens AG, it will be the largest reactor in the world. In December 2006 construction was about 18 months behind schedule so completion was expected 2010-2011.[12][13]

As of March, 2007, there are seven nuclear power plants under construction in India, and five in China. [14]

Russia has begun building the world’s first floating nuclear power plant. The £100 million vessel, the Lomonosov, is the first of seven plants that Moscow says will bring vital energy resources to remote Russian regions.[15]

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  1. World Nuclear Association, Nuclear Power in Russia, June 2006
  2. 1956: Queen switches on nuclear power, BBC, 17/10/2005
  3. MacKenzie, James J. (December 1977). "Review of The Nuclear Power Controversy] by Arthur W. Murphy". The Quarterly Review of Biology. 52 (4): 467–8. doi:10.1086/410301. JSTOR 2823429.
  4. Walker, J. Samuel (10 January 2006). Three Mile Island: A Nuclear Crisis in Historical Perspective. University of California Press. pp. 10–11. ISBN 9780520246836.
  5. In February 2010 the nuclear power debate played out on the pages of the New York Times, see A Reasonable Bet on Nuclear Power and Revisiting Nuclear Power: A Debate and A Comeback for Nuclear Power?
  6. In July 2010 the nuclear power debate again played out on the pages of the New York Times, see We’re Not Ready Nuclear Energy: The Safety Issues
  7. Kitschelt, Herbert P. (1986). "Political Opportunity and Political Protest: Anti-Nuclear Movements in Four Democracies" (PDF). British Journal of Political Science. 16 (1): 57. doi:10.1017/S000712340000380X.
  8. Jim Falk (1982). Global Fission: The Battle Over Nuclear Power, Oxford University Press.
  9. [1]
  10. Vienna Convention on Civil Liability for Nuclear Damage, IAEA, 12/11/1977
  11. Nuclear section of the UK Department of Trade & Industry's website
  12. Finland nuclear reactor delayed again, Business Week, 4 December 2006
  13. Areva to take 500 mln eur charge for Finnish reactor delay, Forbes, 5 December 2006
  14. http://www.npr.org/templates/story/story.php?storyId=9125556
  15. Floating nuclear power stations raise spectre of Chernobyl at sea
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