Nuclear reactors
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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. |
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Four important features of the core of the reactor are:
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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. |
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