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NUCLEAR POWER
 Nuclear power relies on nuclear fission.
 What's nuclear fission?
Some types of heavy atoms have a nucleus that is unstable and will split apart automatically all by itself. This is called nuclear fission or 'splitting the atom'. One such heavy atom is uranium-236 (236 refers to the number of particles in its nucleus). Uranium-236 is formed when an extra neutron joins the nucleus of an atom of uranium-235. The extra neutron makes the nucleus unstable and makes it likely to split into two or more smaller nuclei.
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Chain reaction
When uranium-236 breaks apart (fission) it forms two other atoms, releases a lot of energy and spits out 3 neutrons. There is a chance that these neutrons will hit nearby nuclei of uranium-235, which will in turn split up. If there is enough uranium-235 around there will be a chain reaction as each atom which splits will send out another two or three neutrons which splits more uranium-235 and so on.
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What are the products?
It's impossible to predict what the products will be. However, they will tend to be radioactive themselves - they will give out alpha or beta radiation which can be harmful to humans and cause damage to electrical circuitry. Therefore, they have to be kept away from people and shielded from the surroundings. Alpha radiation has a short range in air - and is stopped by just a thin layer of paper. Beta radiation has a range of several centimetres in air and is stopped by a thin sheet of aluminium. Gamma radiation travels several metres and is only stopped by a thick layer of lead.
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How is the energy harnessed?
Fission of uranium-236 releases lots of energy in the form of heat which can be converted into electricity. In a nuclear power station, this heat is used to boil water which then drives a turbine. The turbine is connected to a generator, which produces electricity.
Are there other ways of generating electricity from nuclear power?
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There are more compact ways of generating electricity from the heat produced by fission. NASA's Galileo Probe which reached Jupiter in 1995 was designed to take pictures of the planet and perform a range of scientific tests in Jupiter's atmosphere. Unfortunately, because Jupiter is so far from the sun, powering the equipment on board using solar energy would have been impossible. So, NASA came up with another solution. They designed a special self contained power source called a Radioisotope Thermoelectric Generator. The heat produced by the fission in the Generator generates electricity thanks to the Seebeck effect - which was discovered in 1822. When two different metals or semiconductors are joined together and heated up, a voltage is produced from the diffusion of electrons across the joint. The Generator was able to generate 570 watts of electric power - enough to power all of the scientific instruments, radio transmitters and cameras on board.
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Image courtesy of NASA/JPL/Caltech
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| POWER batteries petrol nuclear energy |
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