A nuclear power plant (NPP) is a thermal power station in which the heat source is one or more nuclear reactors generating nuclear power.
Nuclear power plants are base load stations, which work best when the power output is constant (although boiling water reactors can come down to half power at night). Their units range in power from about 40 MWe to almost 2000 MWe. New units under construction in 2005 are typically in the range 600-1200 MWe.
As of 2005 there are 443 licensed nuclear power reactors in the world [1], of which 441 are currently operational [2]. Together they produce about 17% of the world's electric power.
A nuclear power station. The nuclear reactors are inside the cylindrical
containment buildings to the right - left is a cooling tower venting water vapor (literally a
cloud).
History
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 that generated electricity for commercial use was officially connected to the Soviet power grid at Obninsk, Kaluga Oblast, Russia.
- For more history, see nuclear reactor and nuclear power.
- For information on the Chernobyl accident, see that subject and RBMK and nuclear power.
Types of nuclear power plants
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. In addition, some of the plant-types below in the future may have passively safe features.
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 rate of production of fast neutrons 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 feasibility studies had been conducted.
Thermal reactor classes
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. Because most fast reactors have historically been used for plutonium production, they are associated with nuclear proliferation concerns.
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, 0.2 MWe, USA, 1951-1964.
- Dounreay Fast Reactor, 14 MWe, UK, 1958-1977.
- Enrico Fermi Nuclear Generating Station Unit 1, 94 MWe, USA, 1963-1972.
- EBR-II, 20 MWe, USA, 1963-1994.
- Phénix, 250 MWe, France, 1973-present.
- BN-350, 150 MWe plus desalination, USSR/Kazakhstan, 1973-2000.
- Prototype Fast Reactor, 250 MWe, UK, 1974-1994.
- BN-600, 600 MWe, USSR/Russia, 1980-present.
- Superphénix, 1200 MWe, France, 1985-1996.
- FBTR, 13.2 MWe, India, 1985-present.
- Monju, 300 MWe, Japan, 1994-present.
- PFBR, 500 MWe, 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.)
Fusion reactors
- Main article: fusion power
Nuclear fusion offers the possibility of the release of very large amounts of energy with a minimal production of radioactive waste and improved safety. However, there remain considerable scientific, technical, and economic obstacles to the generation of commercial electric power using nuclear fusion. It is therefore an active area of research, with very large-scale facilities such as JET, ITER, and the Z machine.
Advantages and disadvantages
Advantages of NPPs are:
- No greenhouse gas emissions during normal operation (greenhouse gases are emitted only when the Emergency Diesel Generators are tested) (the processes of uranium mining and of building and decommissioning power stations produce some greenhouse gas emissions, while enrichment of uranium is powered by Tennessee Valley Authority which has six nuclear reactors of its own)
- Does not produce air pollutants such as carbon monoxide, sulfur dioxide, mercury, nitrogen oxides or particulates
- The quantity of waste produced is small
- Small number of major accidents - only one (Three Mile Island) in types of plants in common use
- Low fuel costs
- Large fuel reserves
- Ease of transport and stockpiling of fuel
- Future designs may be small and modular (SSTAR, etc.)
Disadvantages are:
- Consequences of an accident have in the past been projected to possibly be disastrous (see NUREG-1150)
- Nuclear waste produced is dangerous for thousands of years (unless reprocessed)
- Risk of nuclear proliferation associated with some designs
- High capital costs (cost to build the plant)
- In the past long construction periods (largely due to regulatory delays), imposing large finance costs and delaying return on investment
- High maintenance costs
- High cost of decommissioning plants
- Designs of current plants are all large-scale
Nuclear power is highly controversial, enough so that the building of new nuclear power stations has ceased in Europe (except in Finland and the Ukraine). Almost all the advantages and disadvantages are disputed in some degree by the advocates for and against nuclear power.
The cost benefits of nuclear power are also in dispute. It is generally agreed that the capital costs of nuclear power are high and the cost of the necessary fuel is low compared to other fuel sources. Proponents claim that nuclear power has low running costs, opponents claim that the numerous safety systems required significantly increase running costs.
Disposal of spent fuel and other nuclear waste is claimed by some 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.
Accident indemnification
The Vienna Convention on Civil Liability for Nuclear Damage puts in place an international framework for nuclear liability [3]. However states with a majority of the world's nuclear power plants, including the U.S., Russia, China and Japan, are not party to any 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.
In the UK, the Nuclear Installations Act of 1965 governs liability 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). [4]
See also
External links
The content of this page is retrieved from http://en.wikipedia.org/wiki/Nuclear_power_plant under GFDL
