Modern physics

• Rutherford: '"The energy produced by an atom is a very poor kind of thing. Anyone who expects a source of power from the transformation of these atoms is talking moonshine."'
• Patrick Moore, former Director of Greenpeace International: '"We made the mistake of lumping nuclear energy in with nuclear weapons, as if all things nuclear were evil. I think that's as big a mistake as if you lumped nuclear medicine in with nuclear weapons."'
• Nuclear fission


  The splitting of a large nucleus into two smaller nuclei with the release of energy and neutrons

  
• Natural uranium is made up of two isotopes: 235U (0.7%), and 238U (99.3%). Only U-235 undergoes fission.

  
• Uranium 235 fission


  1. Bombarded with fast-moving or slow-moving neutrons

  2. More likely to occur if the neutrons are relatively slow moving

  
• The neutrons produced are fast moving and may trigger further fission

  
• Chain reaction


  A self-sustaining reaction where fission neutrons go on to produce further fission (giving more neutrons) etc.

  
• If the mass of the sample is above a certain critical mass, the process will become self-sustaining and a chain reaction will occur
• If the mass is below the critical mass the reaction will simply fizzle out
• This process also occurs in a nuclear reactor, but at a controlled rate
• E = mc2


  The total mass on the left-hand side is greater than the total mass on the right-hand side. The mass which has disappeared has been converted into (re-appeared as) the kinetic energy of the particles on the right

  
• Parts of a nuclear fission reactor

  • Fuel (natural uranium)
  • Moderator (graphite or heavy-water)
  • Control rods (absorb neutrons, usually made of boron)
  • Heat exchanger
  • Shielding

  
• Moderator


  Slows down the fast moving neutrons to enable further fission in 235U rather that being absorbed in 238U

  
• Control rods


  Lowering them over the fuel rods prevents the neutrons from one fuel rod reaching the next rod, and so they control the rate of the reaction. Lowering them completely causes the reaction to stop.
• Heat exchanger


  Allows heat from the hot radioactive coolant to pass to another series of pipes containing water without having to mix together
• Advantages of nuclear fission power

  • No harmful greenhouse gases
  • Massive amounts of efficient energy compared to fossil fuels and renewable energy
  • No shortage of nuclear fuel
  • Reduces need for fossil fuels
  • Very low accident rate compared to other energy sources
• Disadvantages of nuclear fission power

  • Radioactive waste has a long half-life and is expensive to store
  • Reprocessing of fuel is hazardous and expensive
  • If a major accident occurs, there can be a large-scale and long lasting health impact

  
• Nuclear fusion


  The combining of two small nuclei to form one large nucleus with the release of energy

  
• 1H2 = deuterium (one proton plus one neutron), 1H3 = tritium (one proton plus two neutrons)

  
• Both nuclei are hydrogen because it is the number of protons that determines the identity of the element, and both of these have one proton
• To overcome the Coulombic repulsion between the two positively charged particles, a large amount of energy must be supplied
• Why is a fission reactor a more viable source of energy than a fusion reactor?

  • Easier to initiate reaction
  • Fission can be more easily controlled

  
• Advantages of fusion over fission

  • Little to no radioactive waste
  • Releases significantly higher amount of energy than any current technology
  • Deuterium is readily available from the oceans (Cheap and plentiful fuel source)
  • No dangerous chain reactions

  
• There is, as of yet, no way to maintain and control the high temperatures required for fusion reactors

  
• The sun generates more energy in a second than has been used across the whole of human history
• 3 different forms of nuclear energy

  • Radiation from nuclei (alpha, beta and gamma radiation)
  • Nuclear fission (splitting of a large atom)
  • Nuclear Fusion (fusing of two smaller nuclei)

  
• E = mc2


  If the mass of the reactants is less than the products, energy is required. If the mass of the reactants is greater than the products, energy is liberated.
• The mass of certain atomic nuclei can be given in terms of their atomic mass unit (a.m.u). If this is the case use the conversion shown in the F&T booklet: 1 a.m.u = 1 u = 1.66 x 10-27 kg