Fission

• • Fission is the splitting of large, unstable nucleus
• • Spontaneous fission is rare
  • For fission to occur, unstable nucleus has to absorb neutron
• • Two or three neutrons and gamma rays are emitted
  • Energy is released
  • Neutrons may go on to cause chain reaction - neutrons can be absorbed by other nucleus
• • Energy not transferred to kinetic energy stored is carried by gamma rays
  • Energy carried by gamma rays and in kinetic energy stores of free neutrons can be used to heat water, making steam for turbines and generators
  • Amount of energy produced by fission is controlled by control rods that absorb neutrons
  • Uncontrolled chain reactions lead to lots of energy being released as explosion - how nuclear explosions work
• fission reactors:

  • nuclear fuel

  (the uranium isotope that will split when triggered by an incoming neutron) - the fuel is held in rods so that the neutrons released will fly out and cause nuclear fission in other rods

  • graphite core - graphite slows the neutrons down so that they are more likely to be absorbed into a nearby fuel rod
  • control rod - these are raised and lowered to stop neutrons from travelling between fuel rods and therefore change the speed of the chain reaction
• fission reactors

  • coolant - this is heated up by the energy released from the fission reactions and is used to boil water to drive turbines in the power station
  • concrete shield - the daughter products of the fission reaction are radioactive and can be a hazard