nuclear energy

A pressurized water nuclear power station. Water at high pressure is circulated around the reactor vessel where it is heated. The hot water is pumped to the steam generator where it boils in a separate circuit; the steam drives the turbines coupled to the electricity generator. This is the most widely used type of reactor. More than 20 countries have pressurized water reactors.

Chapelcross nuclear power station, Dumfriesshire, Scotland, opened in 1959, and was built at the same time as the Calder Hall plant at Sellafield in West Cumbria, England. Its four carbon-dioxide-cooled reactors were once used to produce plutonium for nuclear weapons, and are currently used to produce tritium. Accidents in the handling of nuclear waste at Chapelcross, and concern about the transportation of nuclear waste in the UK, led to public protests at the plant in 1999.

Energy released from the inner core, or nucleus, of the atom. Energy produced by nuclear fission (the splitting of certain atomic nuclei) has been harnessed since the 1950s to generate electricity, and research continues into the possible controlled use of nuclear fusion (the fusing, or combining, of atomic nuclei).

In nuclear power stations, fission of radioactive substances (see radioactivity) takes place, releasing large amounts of heat energy. The heat is used to produce the steam that drives turbines and generators, producing electrical power.

Nuclear energy is produced from the transformation of matter into energy. The amount of energy can be calculated from Einstein's equation, E = mc², where E is the heat energy given out, m is the mass of radioactive substance, and c is the speed of light.

The Sun is an example of a natural nuclear reactor. In every second enormous numbers of nuclei of hydrogen fuse together to form nuclei of helium, generating a continuous supply of heat and light energy. This is called a fusion reaction. A hydrogen bomb obtains its energy from a fusion reaction.

Unlike fossil fuels, such as coal and oil, which must be burned in large quantities to produce energy, nuclear fuels are used in very small amounts and supplies are therefore unlikely to be exhausted in the foreseeable future. However, the use of nuclear energy has given rise to concern over safety. Anxiety has been heightened by accidents such as the one at Chernobyl, Ukraine, in 1986. There has also been mounting concern about the production and disposal of toxic nuclear waste, which may have an active life of several thousand years, and the cost of maintaining nuclear power stations and decommissioning them at the end of their lives. However, many experts claim that nuclear energy is an essential part of the drive to reduce carbon emissions to combat global warming.