Section 7 Radioactivity and particles

  • Neutrons are released as well as energy. This energy appears as kinetic energy of the neutrons and γ-radiation. The energy transfers into thermal energy when it is absorbed by the surrounding materials in the reactor.
  • Neutrons produced from one fission strike other uranium-235 nuclei, causing further fissions and releasing even more neutrons, and a chain reaction can develop. The chain reaction could cause an atomic explosion because of the huge amount of energy that is released.
  • The equation for this reaction can be expressed as:
  • In a nuclear reactor this chain reaction is controlled to release the energy at a steady rate and to stop the reaction from going too fast. Control rods and a moderator work together to control the reaction, but they have different functions.
  • The moderator keeps the reaction going and the control rods prevent the reaction going out of control.
  • The moderator, often made of graphite, slows down the neutrons released from the chain reaction so that they interact with the uranium fuel. If the neutrons are moving too fast, then they do not get captured by the nucleus of a uranium atom and the chain reaction stops. Ideally one neutron from each fission must go on to strike another nucleus for the process to keep going.
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