How does the generated energy compare to the energy required in both types of nuclear reactions (nuclear fission and nuclear fusion) and why does nuclear fusion ultimately produce free energy?

Answer

Dear Ivo,

When free protons and neutrons are bound together to form a nucleus under the influence of the strong nuclear forces, a certain amount of energy is released, the binding energy. For example, each nucleus has its own binding energy, which is the difference between the energy of the protons and neutrons separately and the energy of the nucleus formed by these so-called nucleons. It is therefore this binding energy that is needed if you want to separate all the particles from the nucleus. A nucleus with a high binding energy (such as iron, Fe for example) is therefore more stable than a nucleus with a small binding energy (such as deuterium for example: heavy hydrogen: 1 proton and 1 neutron)

When you plot the binding energy per nucleon as a function of the number of nucleons, you get a curve that first rises sharply before rising less and reaching a maximum at Fe. When the number of nucleons in the nucleus increases, the binding energy per nucleon decreases again. This means that you can increase the binding energy per nucleon by either merging a number of small nuclei (nuclear fusion) or splitting a large nucleus into two smaller ones (nuclear fission). If you do that then extra energy is released, namely the difference between the binding energies per nucleon multiplied by the number of nucleons. It is this energy that can then be converted into electricity.

Nuclear fusion first requires a very high temperature for fusion to continue, but not actually for nuclear fission. A simple neutron with not too much kinetic energy is sufficient for this).

The problem with nuclear fusion lies in achieving and maintaining a sufficiently high temperature in a controlled manner. After all, there are no ‘recipients’ that can withstand these extreme temperatures, so an attempt is made to have these reactions take place in a magnetic field that is ‘built’ in such a way that it traps the extremely warm nuclei. But once a solution has been found, nuclear fusion will indeed offer a huge opportunity to produce energy relatively cheaply. After all, the ‘ingredients’ of nuclear fusion are small nuclei such as hydrogen, which are massively present on our planet. This is in contrast to the raw materials for nuclear fission (uranium, plutonium) which are available in a relatively limited way and even then at a limited number of locations in the world.

regards,

Lieven