Nuclear Fission and Fusion

• Nuclear fission


  The splitting of large, unstable nuclei to form smaller more stable nuclei (+the emission of spare neutrons)
• Fissionable isotope


  • Uranium - 235
• Inducing fission


  1. The unstable nuclei must absorb a neutron

  2. Spontaneous fission (where no neutron absorption occurs) is rare
• Products of fission reaction

  • Two smaller nuclei
  • Two or three neutrons
  • Gamma rays
  • Energy
• Form of energy of fission products

  Kinetic energy
• Chain reaction in a nuclear reactor

  1. An unstable nucleus absorbs a neutron

  2. The nucleus undergoes fission and releases 2 or 3 further neutrons

  3. These induce more fission, which results in a chain reaction
• Uncontrolled chain reaction


  The rate of fission events becomes too high and results in the production of too much energy, which can lead to a nuclear explosion
• Main components of a nuclear reactor core

  • Fuel rods
  • Control rods
  • Moderator
• Role of the moderator

  To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission
• Controlling the chain reaction

  1. Control rods are positioned in between the fuel rods

  2. The rate of fission is controlled by moving these rods up and down

  3. The lower the rods are inserted, the slower the rate of fission
• Fissile nuclei


  Nuclei in which fission can be induced through the absorption of slow neutrons
• Nuclear fusion


  The joining of two light nuclei to produce a heavier nuclei and release energy
• Isotopes of hydrogen used in nuclear fusion

  • Deuterium and Tritium
• Nuclear fusion releases more energy than nuclear fission
• Difficulty of generating energy through nuclear fusion

  • Fusion requires very high temperatures which in itself requires large quantities of energy and also requires casing which can withstand them
• Nuclear fusion is currently not a viable way to produce energy on Earth as the energy required is greater than the energy produced, resulting in a net energy loss