Nuclear fission

• Nuclear fission - when a large unstable nucleus absorbs a extra neutron, which causes it to split into two smaller nuclei
• Products of nuclear fission:

  • high energy gamma rays
  • neutrons
• Example of nuclear fission (uranium):

  1. Extra neutron is absorbed by uranium-235, causing nucleus to split into to two smaller daughter nuclei
  2. Then, gamma decay is released and three neutrons
  3. These neutrons produced can collide with three uranium nuclei
  4. These will undergo further nuclear fission and release neutrons again (9 neutrons, 3 each)
  5. These 9 neutrons can collide with another 9 uranium nuclei, and undergo nuclear fission
  6. This is known as a chain reaction
• Nuclear fission can become a chain reaction
• Nuclear fission can occur in power reactors (controlled)
• Nuclear fission can occur in nuclear explosions (uncontrolled)
• Main components of the core in a nuclear reactor;

  • Fuel rods -
  • Control rods - controls chain reaction.
  • Moderator - slows down the neutrons, which are travelling at high speed which is needed for them to be absorbed by nuclei to cause fission.
• How is a chain reaction of nuclear fission kept under control?

  • Control rods are positioned in between the fuel rods.
  • The rate is controlled by moving the rods up and down.
  • So the lower the rods are then the slower the rate of reaction.