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FISSION: Is the basis of current atomic energy production. It involves the decay of certain large atomic nuclei such as uranium-235, which releases a large amount of energy. Commercial nuclear reactors started up in the 1950s and now about 440 reactors supply over 15% of global electricity. Despite its promise of clean and abundant fuel, the nuclear industry has struggled with its image and public perceptions as a result of accidents (eg Chernobyl) and the task of dealing with radioactive waste. However, with conventional fossil fuel prices rising as reserves dwindle and increased pressure to tackle climate change, some countries are looking again at expanding nuclear power capacity.

FUSION: Works on the principle that energy can be released by forcing together light atomic nuclei rather than by splitting heavy ones. It is the process which powers stars. Some think nuclear fusion will provide a relatively safe, green alternative to fossil fuels, enabling the production of vast amounts of energy from abundant sources (water and lithium) without producing carbon dioxide. But although a new, international experimental fusion reactor is on the horizon, there are many major scientific and engineering hurdles to overcome before the technology can become commercially viable. A commercial reactor is not expected before 2045 or 2050 - if at all.

Computer artwork of a nuclear fusion reaction
To produce fusion, very high temperatures are needed


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