αβγ decay
Decay Series
Chain Reaction
Nuclear Energy
Nuclear reactors

Nuclear Reactors use fission to release energy.

Uranium is the main nuclear fuel.

A controlled chain reaction is needed.

France has a significant part of its energy requirements met by nuclear power plants.

Nuclear reactors


Nuclear reactors function by controlling a chain reaction in which energy is released by the fission of Uranium nuclei.

The component parts of a reactor that convert nuclear energy to electrical are shown here.

Four important features of the core of the reactor are:

  • fuel rods
  • moderator
  • control rods
  • coolant

The fuel rods contain Uranium.

The moderator slows down the neutrons released by fission to the sort of speeds at which they are more likely to cause further fission. (e.g. Graphite and heavy water, i.e. water formed with Deuterium rather than hydrogen).

The control rods absorb unwanted neutrons. The rods may be lowered into or raised out of the core to decrease or increase the rate at which fission happens. (e.g. Cadmium or Boron).

The coolant removes energy to a heat exchanger, where steam is generated to turn turbines as in a conventional power station. (e.g. water or carbon dioxide).

A 1000 megawatt pressurized water reactor would usually have about 200 fuel rods. One third of these might be replaced each year because so many of the uranium-235 nuclei in them would have undergone fission. These fuel rods are still very radioactive long after they have ceased to be useful. These wasted fuel rods are placed in water storage tanks at the power station site for a year or more. After they have cooled completely they are put in sealed containers and brought by ship to permanent storage facilities or to a chemical reprocessing plant. Reprocessing allows useful radioactive material to be extracted and waste to be made more compact.
When a nuclear reactor is in normal operation, a small amount of radioactive effluent is released. For people living nearby, this extra exposure is only a few percent of the natural background radiation that we are all exposed to. However, the levels of exposure that might result from a nuclear accident are on a far greater scale altogether.

Do you think you could control a nuclear reactor. Test your skill using the demonstration opposite.