Nuclear power is based on the huge amounts of energy that bind together the nucleus of every atom in the Universe. It is an incredibly concentrated form of energy.
Nuclear energy is released by splitting the nuclei of atoms in a process called nuclear fission. One day scientists hope to release energy by nuclear fusion – by fusing nuclei together as in the Sun.
Most nuclear reactors use uranium-235. These are special atoms, or isotopes, of uranium with 235 protons and neutrons in their nucleus rather than the normal 238.
The fuel usually consists of tiny pellets of uranium dioxide in thin tubes, separated by sheets called spacers.
Three kilograms of uranium fuel provide enough energy for a city of one million people for one day.
The earliest reactors, called N-reactors, were designed to make plutonium for bombs. Magnox reactors make both plutonium and electricity.
Pressurized water reactors (PWRs), originally used in submarines, are now the most common kind. They are built in factories, unlike Advanced Gas Reactors (AGRs).
Fast-breeder reactors actually create more fuel than they burn, but the new fuel is highly radioactive.
Every stage of the nuclear process creates dangerous radioactive waste. The radioactivity may take 80,000 years to fade. All but the most radioactive liquid waste is pumped out to sea. Gaseous waste is vented into the air. Solid waste is mostly stockpiled underground. Scientists debate fiercely about what to do with radioactive waste.