Revise: Nuclear radiationNuclear power stations

The main nuclear fuels are uranium and plutonium. In a nuclear power station nuclear fuel undergoes a controlled chain reaction in the reactor to produce heat - nuclear to heat energy. The chain reaction is controlled by Boron control rods. Boron is a non-fissile material. This means it will not undergo a fission reaction when bombarded with neutrons. When the Boron absorbs the neutrons then the chain reaction will slow down due to lack of neutrons producing reactions.

In times of high energy demand, control rods are raised allowing more reactions to take place. In times of low demand, control rods are lowered to absorb neutrons and hence decrease the number of reactions; less reactions = less heat energy produced.

• Heat from the nuclear reaction is used to change water into steam in the boiler. (The water in the boiler NEVER actually comes into contact with the same coolant that is used in the reactor but is transferred from the reactor to the external water by using a HEAT EXCHANGER.)
• The steam drives the turbine (heat to kinetic energy – the same as a conventional power station).
• This drives the generator to produce electricity - kinetic to electrical energy.

Important points

• The fuel rods: source of enriched Uranium fuel that undergoes fission reactions.
• The moderator: the fuel rods are encased in the moderator (graphite is sometimes used) and help the fission reaction to proceed efficiently.
• The control rods: normally made of Boron, these help control the fission reaction.
• The coolant: This is a liquid or gas that transfers energy from reactor to the heat exchanger. Also used to cool the reactor.
• The containment vessel: This is a thick concrete shield that absorbs neutrons and ionising radiation. In practice this can be 5.5m thick.

Advantages of nuclear fuels

• Unlike fossil fuels, nuclear fuels do not produce carbon dioxide or sulphur dioxide.
• In terms of energy produced: 1kg of nuclear fuel = 2,900,000 kg of coal
• Since comparatively small volumes of fuel are used, this can be easily transported by road or rail.
• Waste product produced in small volumes.

Disadvantages of nuclear fuels

• Like fossil fuels, nuclear fuels are non-renewable energy resources.
• If there is an accident, large amounts of radioactive material could be released into the environment. Modern reactor designs are extremely safe and this very rarely happens.
• Nuclear waste remains radioactive and is hazardous to health for thousands of years. It must be stored safely. Storing nuclear waste is another hotly debated issue.