The story behind nuclear power
Nuclear power has been in the news a lot this year.
The Fukushima Daiichi disaster, where reactors melted down and released radioactivity, made many people question the future of nuclear power.
This year also marked the 25th anniversary of the Chernobyl disaster in Russia, when an explosion released a huge amount of radiation into the air.
These massive accidents suggest we should stop using nuclear power.
But on the other side of the argument is the fact that nuclear power is also a very clean alternative to traditional coal burning.
It generates electricity without creating harmful greenhouse gases.
1895 - ionising radiation is discovered by German physicist Wilhelm R?ntgen. He develops X-rays using this discovery.
1896 - French scientist Henri Becquerel discovers a rock that contains uranium makes a photographic plate turn dark.
1896 - French scientists Marie and Pierre Curie call this occurrence 'radioactivity'.
1902 - British scientist Ernest Rutherford shows radiation is a spontaneous event. He went on to discover more about the structure of atoms.
1932 - British physicist James Chadwick discovers the neutron.
1938 - German scientists Otto Hahn and Fritz Strassmann conduct experiments that prove atomic fission has occurred.
1939 - Germans Lise Meitner and Otto Frisch calculate the huge amount of energy released when an atom's nucleus is split.
1945 - America drops two nuclear bombs on Japan.
1954 - Obninsk Nuclear Power Plant in the Soviet Union becomes the first nuclear plant to generate electricity for public use.
How it works
Nuclear energy is stored in the nucleus, or central core, of atoms of chemicals like uranium and plutonium. This energy can be released in one of two ways: nuclear fusion or nuclear fission.
Nuclear fission is the method currently used to produce electricity. 'Fission' means splitting something, or breaking it into parts.
In this case, it means firing neutrons (a tiny particle within an atom) at the atoms of radioactive elements, and breaking them up to produce smaller atoms, as in the diagram above.
When the atom is split, it releases heat and energy. The process is a chain reaction: these smaller atoms then split other atoms, and so on.
In a nuclear plant, small lumps of uranium are packed into long tubes known as fuel rods.
Hundreds of these rods make up the core of the nuclear reactor.
The heat that is produced by the fission in the rods is used to boil water and turn it into steam.
This steam then turns a turbine, which spins a generator, producing electricity.
To prevent the system from overheating, control rods are included in the nuclear reactor.
These are made of a material that absorbs neutrons, so that fewer neutrons hit the radioactive material.
There is also a cooling system that uses water to keep temperatures at the desired level.
Some of the arguments for and against nuclear power
Unlike coal, producing nuclear power releases very little pollution into the atmosphere. That means it doesn't contribute to climate change, acid rain, air pollution and so on.
Nuclear reactor technology is already very advanced. Money doesn't have to be spent on researching ways to make it more efficient.
A single nuclear facility can produce electricity for many years.
If nuclear energy is used to produce electricity, we can use the rarer fossil fuels for other power needs, such as transport.
When radioactive atoms break down, they release radiation, or radioactivity. Nuclear radiation can interact with matter - for example, the human body. When this happens, it can cause problems, such as genetic mutations which can lead to cancer.
Nuclear power can be used to make powerful weapons. A small nuclear bomb can destroy a city within seconds. But the radioactive dust created when the bomb explodes, is very dangerous. It may kill straight away, or make people gradually ill over many years.
Nuclear reactors are at risk of melting down, as we saw in Fukushima Daiichi in March. This is when the reactor's core melts. The radioactive fuel can leak into the cooling pool, and possibly out into the environment.
Fuel rods are no longer useful after a certain time. They must be thrown away. But they are still radioactive, so must be stored until they are no longer radioactive. But if the storage is not secure, radioactivity could leak out.
Uranium is a fairly common, naturally occurring metal found in rocks all over the world.
However, the kind used in nuclear plants, U-235, is relatively rare.