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How it works

A nuclear power station turns the nuclear energy in uranium atoms into electrical energy that can be used in homes and businesses.

The reactor pressure vessel (RPV) (1) is a tough steel capsule that houses the fuel rods: sealed metal cylinders containing pellets of uranium oxide. When a neutron – a neutrally charged subatomic particle – hits a uranium atom, the atom sometimes splits, releasing two or three more neutrons. This process converts the nuclear energy that binds the atom together into heat energy.

The fuel assemblies are arranged in such a way that when atoms in the fuel split, the neutrons they release are likely to hit other atoms and make them split as well. This chain reaction produces large quantities of heat.

Water flows through the RPV where the chain reaction heats it to around 340°C. The water needs to stay in liquid form for the power station to work, so the pressuriser (2) subjects it to around 155 times atmospheric pressure, which stops it boiling.

The reactor coolant pump (3) circulates the hot pressurised water from the RPV to the steam generator (4). Here the water flows through thousands of looped pipes before circulating back to the RPV. A second stream of water flows through the steam generator around the outside of the pipes. This water is under much less pressure, so the heat from the pipes turns it into steam.

The steam then passes through a series of turbines (5), causing them to spin and converting the heat energy produced in the reactor into mechanical energy. A shaft connects the turbines to a generator so when the turbines spin, so does the generator. The generator uses an electromagnetic field to convert this mechanical energy into electrical energy.

A transformer converts the electrical energy from the generator to a high voltage. The national grid uses high voltages to transmit electricity efficiently through the power lines (6) to the homes and businesses that need it (7). Here other transformers reduce the voltage to a usable level.

After passing through the turbines, the steam comes into contact with pipes full of cold water pumped in from the sea (8). The cold pipes cool the steam so that it condenses back into water. It is then piped back to the steam generator, where it can be heated up again, turned into steam, and keep the turbines spinning.