Nuclear power gives us about 17% of the world's electricity. Some countries produce more nuclear power than others. France, for example, gets about 75% of its energy from nuclear power plants, the USA only 15%. Many countries, like Austria, don't have any nuclear energy at all.
Nuclear energy comes from the energy inside each atom. Atoms are made up of a nucleus with protons and neutrons—and electrons which revolve around the nucleus like the earth goes around the sun.
An atom's nucleus can be split apart. When this is done, a lot of energy is released. Albert Einstein, the world's most famous scientist, said that you can get a lot of energy out of a small number of atoms. When it is let out slowly, you can use this energy to produce electricity, but if you let it out all at once, it can cause a great explosion—like in an atomic bomb.
In a nuclear power station uranium atoms are split apart to create energy. Uranium can be found in rocks on earth, but only a special form of uranium—U 235—can be used to make energy. A pound of uranium has the same energy as about 250 000 litres of petrol.
In a nuclear reactor free neutrons hit a uranium atom and split it. New neutrons are set free and when they run into other uranium atoms they split them again. When this continues over and over again, you call it a chain reaction.
Control rods are put into the reactor so that the chain reaction doesn't go on so fast. The chain reaction also gives off heat energy. This heat is used to make water hot and produce steam. The steam turns a turbine to generate electricity.
When parts of atoms hit each other they also become radioactive, which is very dangerous if it doesn't stay in the reactor.
A nuclear power plant must be safe, otherwise radiation could get into the air. They have a containment - a building around it that is made of concrete and steel. In the core of the reactor uranium is formed into long rods which are put into water. This water cools the rods when they get too hot.
Control rods are also put into the core. They take up the neutrons and control the chain reaction. They can be raised or lowered into the core. If you raise them the chain reaction goes on quicker, the core gets hotter and more energy is produced. If you lower them they absorb free neutrons and the chain reaction is slowed down.
Nuclear power plants have advantages because they produce electricity in a clean way. But there are also many problems:
• Natural uranium cannot be used in power plants. You have to enrich it. This costs a lot of money and is not good for our environment.
• There is the danger of nuclear explosions. The explosion at Chernobyl in 1986 blew up the rector's containment and tons of radioactive dust were blown into the atmosphere. Many people were killed and millions around the power station had to leave their homes.
• Used uranium stays radioactive for thousands of years. There is no way to store it safely.
• Transporting uranium is very dangerous.
Fusion is the opposite of fission. The nuclei of small atoms are joined to make one bigger atom. The sun uses nuclear fusion of hydrogen atoms to produce light and heat.
Fusion is better than fission because it doesn’t create that much radiation and you can use water as fuel.
When the uranium in the core of a reactor is used up, you have to take it out. In some cases uranium can be recycled and used again. If you reprocess uranium you can make another dangerous product—plutonium, which is used to make atomic bombs.
But even though uranium can be used again it finally has to be stored safely. Nuclear waste remains radioactive for thousands of years. Even putting it deep into a mountain would not be completely safe.
In the 1950s and 60s we thought that nuclear power was a clean and cheap form of energy. The energy companies thought that nuclear energy would replace coal, oil and gas.
But as time went on and disasters in Three Mile Island and in Chernobyl happened, people around the world saw nuclear energy as a danger. Some countries have already stopped their reactors completely and other are shutting them down in the near future.
On 26th April 1986 the world's worst nuclear disaster took place at the Chernobyl nuclear power station in the northern Ukraine. One of the four reactors exploded because the operators were very careless about safety during a routine test. The explosion blasted a large hole through the roof of the building. Tons of radioactive material were blown up to a height of about 1km. There was also a big fire in the station.
About 100 million curies of radiation escaped from the station into the atmosphere. Most of it fell on the farmland of Belarus and the Ukraine. A lot of fallout also drifted westwards to northern and central Europe.
The people of Chernobyl were exposed to radiation about 100 times greater than from the bomb that was dropped on Hiroshima. Since the accident, many hundred thousand people have become ill, a lot of them have died of cancer or other diseases.
Over 400,000 people had to leave their homes as a result of the explosion. The area around Chernobyl today is a radioactive desert and nobody is allowed to live there.
The population of the Ukraine and Belarus is living in constant danger because the water is still poisoned and the ground on which they plant crops is still radioactive. The children are not allowed to walk in forests, play in parks or pick wild flowers.