Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!
Print

Science

Nuclear fission

Page:

  1. 1
  2. 2
  1. Next

Nuclear fission is the splitting of an atom's nucleus to release heat. Nuclear power stations use the fission of uranium-235 to heat water. Fossil fuel power stations burn their fuel (coal, oil or gas) to heat their water.

Dangerous radioactive waste is sealed in glass-like blocks and buried in rocks.

Nuclear fission

Nuclear power station

Calder Hall nuclear power station

Fission is the splitting of a large nucleus. When this happens energy is released in the form of heat. Nuclear reactors use the heat released by the fission of uranium. If 1kg of uranium-235 undergoes nuclear fission it can release about the same amount of energy as 2 million kg of coal.

The fission of uranium can set up a chain reaction that will keep on releasing energy as long as there are uranium nuclei present. If this chain reaction is allowed to get out of control, energy is released very quickly and the result is a nuclear bomb. Nuclear power stations are designed so that this cannot happen.

Higher tier only

Uranium-235 is a naturally occurring element which has a special property. When a neutron is absorbed by the nucleus, the new heavier nucleus becomes unstable. It is unable to hold itself together so splits into two smaller nuclei and gives out three neutrons and a burst of energy.

A uranium neutron hits a uranium nucleus, causing the nucleus to divide into smaller nuclei  and some more neutrons. These neutrons hit more uranium nuclei.

A chain reaction involving uranium-235

Page:

  1. 1
  2. 2
  1. Next

Back to Radiation for life index

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.