4.4.1 Nuclear Fission

• What is nuclear fission?

  The splitting of a large and unstable nucleus (e.g uranium or plutonium).
• Is spontaneous fission common or rare?

  Rare.
• For fission to occur what must usually happen?

  The unstable nucleus must first absorb a neutron.
• What does the nucleus undergoing fission split into and emit?


  It splits into two smaller nuclei (roughly equal in size) and emits two or three neutrons plus gamma rays. Energy is also released by the fission reaction.
• All products created by nuclear fission also produce what type of energy?

  Kinetic energy.
• What may the neutrons emitted during nuclear fission go on to start?

  A chain reaction.
• Where is a chain reaction controlled and why?

  A nuclear reactor to control the energy released.
• What is the explosion caused by a nuclear weapon caused by?

  A uncontrolled chain reaction.
• Fission can occur by an atom's nucleus absorbing a neutron and becoming even more unstable. The neutron helps to split the nucleus.
• Steps for a nuclear fission chain reaction:

  1. It starts with an unstable nucleus like uranium-235.
  2. A neutron is then fired at the unstable nucleus and causes it to split apart.
  3. The unstable nucleus splits into two 'daughter' nuclei and two or three neutrons, while also emitting lots of energy in the form of gamma radiation.
  4. The two or three neutrons that were released are then absorbed by other unstable nuclei and this repeats the process from step 3.
  5. This process then occurs over and over again in what we call a chain reaction.

  
• How nuclear power stations generate electricity:

  1. Whenever unstable nuclei split apart they release lots of radiation.
  2. This gamma radiation is then used to heat liquid into steam.
  3. As the steam rises it turns turbines, and the kinetic energy of those turbines is converted into electricity by a generator.
• It is very important that the chain reaction of nuclear reactors is kept under control to avoid a nuclear meltdown.  To help keep the reaction stable, we can lower control rods into the nuclear reactor which absorb neutrons and slow down the chain reaction.
• What are the main pros of nuclear power?

  • Nuclear power plants can produce large and steady electric power
  • Nuclear fuel such as uranium or plutonium is relatively cheap
  • Nuclear power does not produce any greenhouse gas
• State three cons of nuclear power:

  • They are very expensive to build
  • The waste is radioactive and very expensive to get to store
  • There is a risk of a nuclear meltdown