A nuclear reactor is driven by the splitting of atoms, a process called fission, where a particle (a neutron) is fired at an atom, which then fissions into two smaller atoms and some additional neutrons. Some of the neutrons that are released then hit other atoms, causing them to fission too and release more neutrons. This is called a chain reaction.
Atomic fission in a chain reaction also releases large amounts of energy as heat. The heat generated is removed from the reactor by a circulating fluid, usually water. This heat can then be used to generate turbine-powered steam for power generation.
To ensure that the nuclear reaction takes place at the correct speed, the reactor has systems that accelerate, slow down, or shut down the nuclear reaction and the heat it produces. This is usually done with control rods, which are usually made of neutron absorbing materials such as silver and boron.
Nuclear fission Two examples of uranium-235 fission, the most commonly used fuel in nuclear reactors. Nuclear reactors come in a variety of shapes and sizes - some use water to cool their core and others use gas or liquid metal. More than 90% of the world's reactors use water, the most common type of water-based reactants. Further information on the different types of reactors around the world can be found in the Nuclear Power Reactors section of the Library.
Nuclear reactors are very reliable at generating electricity, capable of running for 24 hours a day for many months, if not years, without interruption, whatever the weather or season. Additionally, most nuclear reactors can operate for very long periods of time – over 60 years in many cases. In 2019, units 3&4 at the Turkey Point plant in Florida were the first reactors in the world to be licensed for 80 years of operation.
What fules a reactor?
A number of different materials can be used to fuel a reactor, but most commonly uranium is used. Uranium is abundant, and can be found in many places around the world, including in the oceans. Other fuels, such as plutonium and thorium, can also be used.
Most of today’s reactors contain several hundred fuel assemblies, each having thousands of small pellets of uranium fuel. A single pellet contains as much energy as there is in one tonne of coal. A typical reactor requires about 27 tonnes of fresh fuel each year. In contrast, a coal power station of a similar size would require more than two-and-a-half million tonnes of coal to produce as much electricity.
How about the waste?
Like any industry, the nuclear industry generates waste. However, unlike many industries, nuclear power generates very little of it – and fully contains and manages what it does produce. The vast majority of the waste from nuclear power plants is not very radioactive and for many decades has been responsibly managed and disposed of. If nuclear power was used to supply a person’s electricity needs for an entire year, only about 5 grams of highly-radioactive waste would be produced, which is the same weight as a sheet of paper.
The used fuel which comes out of the reactor can be managed in different ways, including recycling for energy production or direct disposal. As a matter of fact, many countries have been using recycled fuel for decades to partially fuel their reactors.