Fission reactors

Cold coolant is injected at the bottom. It passes into reactor vessel and through gaps in graphite core which hold moveable control rods.  The now hot coolant is siphoned out.

A fission reactor contains a number of different parts:

  • Nuclear fuel - the uranium or plutonium isotope that will split when triggered by an incoming neutron. The fuel is held in rods so that the neutrons released will fly out and cause nuclear fission in other rods.
  • Moderator - graphite core - a graphite core, for example, slows the neutrons down so that they are more likely to be absorbed into a nearby fuel rod.
  • Control rods - these are raised and lowered to stop neutrons from travelling between fuel rods and therefore change the speed of the chain reaction.
  • Coolant - this is heated up by the energy released from the fission reactions and is used to boil water to drive turbines in the power station.
  • Concrete shield - the daughter products of the fission reaction are radioactive and can be a hazard.

Many of the features of the reactor are designed to control the speed of the reaction and the temperature inside the shielding. An uncontrolled fission reaction is the basis of an atomic bomb.

Advantages and disadvantages of nuclear power stations

Generating electricity using nuclear reactors carries high risk but offers large rewards. In operation, a very small amount of nuclear fuel will consistently generate a very large amount of electricity and generate very little polluting material. However, the financial costs of building and decommissioning a nuclear power station are very large, and the waste produced will remain radioactive - hazardous to humans and the environment - for thousands of years.

Produces no polluting gases. Waste is radioactive and safe disposal is very difficult and expensive.
Does not contribute to global warming.Local thermal pollution from wastewater affects marine life.
Very low fuel costs. Large-scale accidents can be catastrophic.
Low fuel quantity reduces mining and transportation effects on environment. Public perception of nuclear power is negative.
High technology research required benefits other industries.Costs of building and safely decommissioning are very high.
Power station has very long lifetime.Cannot react quickly to changes in electricity demand.