Nuclear power plant
From open-encyclopedia.com - the free encyclopedia.
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. Their units range in capacity from about 40Mwe to almost 2000Mwe, typical new units under construction in 2004 being in the range 600-1200Mwe.
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Types of nuclear power plant
Nuclear power plants are classified according to the type of reactor used. However some installations have several independent units, and these may use different classes of reactor.
Fission reactors
Fission power reactors generate heat by nuclear fission of fissile isotopes of uranium and plutonium.
They may be further divided into three classes:
- Thermal reactors use a neutron moderator to slow or moderate the fast neutrons produced by fission, to increase the probability that they will produce another fission and thus sustain the chain reaction.
- Fast reactors sustain the chain reaction without needing a neutron moderator.
- Subcritical reactors use an outside source of neutrons rather than a chain reaction to produce fission. As of 2004 this was a theoretical concept, and no prototype had been proposed or built to generate electric power by this means, although some laboratory demonstrations and several feasability studies had been conducted.
Thermal reactor classes
- light water reactor (LWR):
- pressurized water reactor (PWR)
- boiling water reactor (BWR)
- graphite-moderated:
- heavy water moderated:
- SGHWR.
- CANDU.
Fast reactors
Although some of the earliest nuclear power reactors were fast reactors, they have not as a class achieved the success of thermal reactors.
Fast reactors have the advantages that their fuel cycle can use all of the uranium in natural uranium, and also transmute the longer-lived radioisotopes in their waste to faster-decaying materials. For these reasons they are inherently more sustainable as an energy source than thermal reactors. See fast breeder reactor.
More than twenty prototype fast reactors have been built in the USA, UK, USSR, France, Germany, Japan, and India, and as of 2004 one was under construction in China. These include:
- EBR-I, 0.2MWe, USA, 1951-1964.
- Dounreay Fast Reactor, 14MWe, UK, 1958-1977.
- Enrico Fermi Power Station Unit 1, 94MWe, USA, 1963-1972.
- EBR-II, 20MWe, USA, 1963-1994.
- Phénix, 250MWe, France, 1973-present.
- BN-350, 150MWe plus desalination, USSR/Kazakhstan, 1973-2000.
- Prototype Fast Reactor, 250MWe, UK, 1974-1994.
- BN-600, 600MWe, USSR/Russia, 1980-?.
- Superphénix, 1200MWe, France, 1985-1996.
- FBTR, 13.2MWe, India, 1985-present.
- Monju, 300MWe, Japan, 1994-present.
- PFBR, 500MWe, India, 1998-present.
(Electric output shown is the highest output configuration where several were used, dates shown are first criticality, and last criticality in the case of a plant that is now decommissioned. It is not known whether BN-600 will return to use.)
Fusion reactors
See fusion power.
Advantages and disadvantages
Advantages of NPPs are:
- Lack of greenhouse gas emissions.
- Safety and reliability.
- Long-term cost of ownership.
- Ease of transport and stockpiling of fuel.
Disavantages are:
- Political opposition.
- Risks of nuclear proliferation associated with some designs.
- High capital costs.
- Currently available designs are all large-scale.
The question of the disposal of spent fuel and other nuclear waste is highly controversial. Some list this as an advantage of nuclear power, claiming that the waste is small in quantity compared to that generated by competing technologies, and the cost of disposal small compared to the value of the power produced. Others list it as a disadvantage, claiming that the environment cannot be adequately protected from the risk of future leakages from long-term storage.
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