How a nuclear energy reactor works
At the centre of a nuclear plant is the reactor core, where the chain reaction takes place
Nuclear power plants generate electricity using heat from a process called nuclear fission.
This happens when atoms of uranium-235 split after being hit by a neutron. The split releases heat and more neutrons, which go on to split other atoms. This creates a steady chain reaction inside the reactor, according to the US Department of Energy.
What is inside a reactor?
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At the centre of a nuclear plant is the reactor core, where the chain reaction takes place.
- Fuel rods: Uranium is formed into small ceramic pellets and placed in long metal tubes called rods. Many rods are grouped together into fuel assemblies, which make up the reactor core.
- Water (coolant and moderator): The core is surrounded by water. This water removes heat from the reactor and also slows down neutrons so the chain reaction can continue.
- Control rods: These rods can be moved in and out of the core. They absorb neutrons and help control how fast the reaction happens, or stop it completely if needed.
How electricity is produced
Nuclear power plants turn heat into electricity in several steps:
- Heating water: The heat from fission raises the temperature of water in the reactor. In some designs, this water is kept under high pressure so it does not boil.
- Making steam: The hot water is used to produce steam, either in a separate system or directly inside the reactor.
- Spinning turbines: The steam pushes large turbines, causing them to spin.
- Generating power: The turbines are connected to a generator, which produces electricity.
- Cooling and reuse: After passing through the turbine, the steam is cooled back into water in a condenser and reused in the system.
Different reactor designs
Nuclear reactors are mainly classified by how they use water:
- Pressurised Water Reactors (PWR): These are the most common. Water in the reactor is kept under high pressure so it does not boil. Heat is transferred to a second system to create steam.
- Boiling Water Reactors (BWR): In these reactors, water boils inside the reactor, and the steam goes directly to the turbine.
- Advanced designs: Newer models, such as the European Pressurised Reactor, aim to produce more power, last longer, and reduce waste. Other technologies include small modular reactors and fast neutron reactors.
Cooling systems and visible emissions
After electricity is generated, the system must cool down. Power plants use water from rivers, the sea, or cooling towers to remove heat. The white clouds often seen rising from these towers are water vapour, not smoke.
Environmental impact and safety
Nuclear energy produces electricity without releasing carbon dioxide or air pollutants during operation. Modern reactor designs include improved safety systems and are built to reduce the risk of accidents compared to older plants.
Overall, nuclear reactors work by controlling a chain reaction to produce heat, which is then used to generate electricity in a reliable and continuous way.
