THE FLEET
Nine still generating
The UK government's 2026 safety report counts nine operating reactors: twin gas-cooled reactors at four sites and one pressurised water reactor at Sizewell B.
Meet the fleetA nuclear power station is, at heart, a very hot kettle.
Splitting atoms gives off heat. That heat makes steam, the steam spins a turbine, and the turbine drives a generator. This independent guide explains the UK's reactors in plain English, from official energy statistics and the safety regulator's reports.
- Fission makes heat
- Heat makes steam
- Steam makes power
- From split atoms to the grid
THE SHORT ANSWER
Split atoms,
boil water.
The reactor is new; the rest is a power station.
Three things worth knowing.
HOW IT WORKS
Steam turns the turbine
The US Energy Information Administration explains that reactors use heat from fission to make steam, which spins turbines that drive generators.
Step by step
THE GRID
About one unit in eight
Nuclear made 12.2 per cent of UK electricity in 2025, down from 2024 because of outages at the remaining stations, DUKES says.
See the numbers
FROM ATOM TO SOCKET
Four steps
to the plug.
Reactor designs differ, but the journey from fuel to electricity follows the same broad path, as the US Energy Information Administration and the UK safety report describe it.
Split the atoms
In fission, a neutron strikes a large atom such as uranium and splits it, releasing energy and more neutrons that can keep a chain reaction going.
Carry the heat away
A coolant takes heat from the fuel. In the UK's AGRs it is carbon dioxide gas; in a pressurised water reactor like Sizewell B it is water.
Make steam
The heat boils water into pressurised steam. In the AGRs the boilers sit inside the concrete reactor vessel.
Spin the turbine
Steam spins large turbine blades that drive generators, and the electricity goes out to the grid.
TWO NUMBERS WORTH KNOWING
A smaller share,
still steady.
One figure for nuclear's share of UK electricity,
one for how hard the stations work.
12.2%
Nuclear share of UK generation, 2025
Nuclear generated 35.9 TWh in 2025, down 12 per cent on 2024 and the lowest since the 1980s, because of refuelling and maintenance outages.
SHARE · DUKES 2026
64.0%
Share of time producing, 2025
Load factors show how much of the time a plant is producing electricity. Among major power producers, nuclear stations had the highest load factor in 2025.
LOAD FACTOR · DUKES 2026
DUKES counts nuclear with renewables as low carbon generation: together they made 64.3 per cent of UK electricity in 2025, just below the 2024 record.
MEET THE FLEET
Is it making
electricity now?
Pick a kind of UK reactor to see where it stands. The bar shows how much it is generating today: none, winding down, or running.
Based on the UK's Tenth National Report on the Convention on Nuclear Safety (DESNZ, 2026).
WHO KEEPS IT SAFE
Licensed,
inspected, reported.
The Office for Nuclear Regulation is the UK's independent statutory regulator for nuclear safety and civil nuclear security. Companies need a nuclear site licence from ONR to build and run a station, and the licence alone is not permission to start nuclear construction.
Licence holders carry the main legal responsibility for safety. The Environment Agency in England and SEPA in Scotland also regulate, and the UK reports on its nuclear safety to an international peer review under the Convention on Nuclear Safety.
In conversation
Questions people ask
How many nuclear reactors does the UK have?
The UK's 2026 safety report counts nine operating reactors: twin AGRs at Hartlepool, Heysham 1, Heysham 2 and Torness, and a single PWR at Sizewell B. Three more twin-reactor AGR sites have stopped generating.
How much UK electricity comes from nuclear?
DUKES 2026 says nuclear made 12.2 per cent of UK electricity in 2025, down 2.0 percentage points on 2024 because of outages at the remaining stations.
How does a nuclear power station make electricity?
Heat from splitting atoms is used to make steam. The steam spins turbines that drive magnetic generators to produce electricity, the US Energy Information Administration explains.
What happens when a station closes?
It stops generating, the fuel is removed (defuelling) and it moves towards decommissioning. Hunterston B was declared fuel-free in April 2025.
Who regulates nuclear power stations?
The Office for Nuclear Regulation, the UK's independent statutory regulator for nuclear safety, licenses and inspects them, alongside the Environment Agency and SEPA for environmental permits.
Sources
Each figure on this page comes from the sources below.
- GOV.UK (DESNZ/ONR): UK Tenth National Report on the Convention on Nuclear Safety, 2026
- GOV.UK: Digest of UK Energy Statistics (DUKES) 2026, Chapter 5 Electricity
- US Energy Information Administration: Nuclear explained, nuclear power plants
- Office for Nuclear Regulation: About ONR
- Office for Nuclear Regulation: Licensing of new reactors