nuclear fission and fusion

• nuclear fission


  a nuclear reaction in which a heavy, unstable nucleus splits spontaneously or on impact with another particle, with the release of energy
• nuclear fission results in the transfer of energy to ... energy stores

  kinetic and heat
• which isotope goes through fission?

  uranium-235

  plutonium-239
• how often does spontaneous fission happen?

  rarely, so the nucleus has to absorb a neutron a neutron before it splits
• when the atom splits and forms two new lighter elements...

  they are roughly the same size and have some energy in their kinetic energy stores
• how many neutrons are released during nuclear fission?

  two or three; if any of these neutrons are moving slow enough to be absorbed by another nucleus, they can cause more fission to occur (a chain reaction).
• the energy released from fission is in the forms of...

  gamma radiation and kinetic energy
• the energy not transferred to the kinetic energy stores of the products during nuclear fission is carried away by...

  gamma rays
• what can energy carried away by gamma rays from nuclear fission be used for?

  heating water, making steam to turn turbines and generators
• how is the amount of energy produced by fission controlled by?

  by changing how quickly the chain reaction can occur
• how is a chain reaction set up in a nuclear reactor?

  a neutron is absorbed by a uranium 235 atom, causing the isotope to split into two smaller nuclei and release 2-3 neutrons, which go on to start other fissions - causing a chain reaction
• why do nuclear reactors need to be controlled?

  to prevent explosions
• nuclear reactor diagram

  
• nuclear reactor


  uses the energy from controlled nuclear reactions to generate electricity
• 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
• control rods


  absorb neutrons emitted to reduce the rate of reaction in the fuel.
• moderator


  slows down fast neutrons to increase the chance of more reactions (so they don't pass through the nuclei)
• coolant


  this is heated up by the energy released from the fission reactions to prevent a core meltdown and carry heat away to turn the turbines
• concrete shield


  used because the daughter products of the fission reaction are radioactive and can be a hazard
• heat exchanger


  transfers the heat from the coolant to heat water to steam, that in turn drives the turbine to generate electricity
• uncontrolled fission chain reactions can lead to...


  lots of energy being released as an explosion
• what happens in a nuclear reactor?

  1. split atoms to create heat (nuclear fission)

  2. use the heat to make steam

  3. use the steam to turn a turbine

  result: carbon-free electricity from nuclear
• nuclear fusion


  a nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus: some of the mass of the nuclei can be converted into energy, which is released as radiation