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 of new units under construction in 2005 being in the range 600-1200MWe.

History

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. The Shippingport Reactor (Pennsylvania) was the first commercial nuclear generator to become operational in the United States.

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 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

• Light water reactor (LWR):
  • Pressurized water reactor (PWR)
  • Boiling water reactor (BWR)
• Graphite-moderated:
  • Magnox
  • Advanced gas-cooled reactor (AGR)
  • RBMK
  • Pebble bed reactor (PBMR)
• 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. 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, 0.2MWe, 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

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:

• Lack of greenhouse gas emissions
• The quantity of waste produced is small
• Small number of accidents
• Low fuel costs
• Large fuel reserves
• Ease of transport and stockpiling of fuel

Disadvantages are:

• The waste that is produced is dangerous.
• The accidents that have occurred have been serious.
• Risks of nuclear proliferation associated with some designs.
• High capital costs
• High maintenance costs
• High cost of decommissioning plants
• Currently available designs are all large-scale

Nuclear power is highly controversial, enough that the building of new nuclear power stations has ceased in the US and Europe. Almost all the advantages and disadvantages are disputed in some degree by the advocates for and against nuclear power.

Some disputes are simply disagreements due to different objectives. A government that wants to develop nuclear weapons will view the ability to create materials for military use an advantage. Those who wish to prevent the government in question acquiring this capability will consider it a disadvantage.

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.

Links

• Information about all NPP in the world
• SCK.CEN Belgian Nuclear Research Centre in Mol.