Fusion

• The formation of a heavier nuclide by the fusing of two light nuclides.
• In the sun, the following fusion reaction occurs:

• The first artificial fusion reaction was the hydrogen bomb which was tested in November, 1952.
• The theoretical d-t (deuterium-tritium) reaction that would occur in a fusion reactor is:

Where deuterium and tritium are isotopes of hydrogen.

• Fusion reactions are thermonuclear reactions which must occur at extremely high temperatures.
  • In order to fuse deuterium and tritium, the force of repulsion of these two positively charged particles must be overcome.
  • Each fusion reaction has a certain ignition temperature which must be passed before a reaction can occur.

    e.g.  The ignition temperature for the d-t reaction is above 10⁸ K.

  • An uncontrolled fusion reaction is much more easier to produce than a controlled one.  In the hydrogen bomb, for example, a fission reaction provided the initial energy to reach the ignition temperature, and the reaction sustained itself.
  • At such extremely high temperatures, any substance can only exist as a plasma - an ionized gas.
  • In order to successfully create a nuclear fusion reactor, we must be able to:
    1. Reach the required ignition temperature to start the reaction.
    2. Keep the plasma contained to collect the energy produced by the reaction.
    3. Produce more energy than is used to start the reaction and contain the plasma.
  • One thing that could contain a plasma is a magnetic field.
  • Another proposal is to target fuel pellets with laser beams to cause them to implode, producing enough energy to ignite the reaction.

Pros and Cons

• Pros
  1. The fuels that could be used are relatively inexpensive and readily available.
  2. The products of a fusion reaction are not radioactive, thus thee are no nuclear waste problems.
  3. Fusion is not a chain reaction, therefore it can be stopped at anytime and there is no threat of a meltdown.
  4. Fusion would be a virtually inexhaustible energy supply that could eliminate most of the world's dependence on other fuels.
• Cons
  1. Ignition temperature is extremely high.
  2. Any substance at these high temperature are in the plasma state which is very difficult to contain.
  3. Large-scale fusion reactions are very expensive.

Next:  "Radon"