Thermal power vs electrical power
A reactor is fundamentally a heat source. Its thermal power (MWth) is how much heat the core produces. But a turbine and generator can only convert part of that heat into electricity — the rest is rejected as waste heat through the cooling towers. The electricity that reaches the grid is the electrical power (MWe).
Nuclear plants typically convert about a third of their heat to electricity, so a 3,000 MWth reactor delivers roughly 1,000 MWe. That's the same headline figure you see quoted for power stations.
Why annual generation is so large
The reason a single reactor powers so many homes isn't just its size — it's the capacity factor. Nuclear plants run near full power almost continuously, often 90% of the year, pausing only to refuel. Multiply a thousand megawatts by nearly every hour of the year and you get billions of kilowatt-hours — enough for millions of homes.
To see the fuel behind that output, try the fuel equivalence calculator; to understand the radioactive materials a reactor uses and produces, see the decay calculator.
Frequently asked questions
What's the difference between MWth and MWe?
MWth is the heat the reactor produces; MWe is the electricity delivered after the turbine and generator. MWe = MWth × efficiency, typically ~33% for nuclear.
How many homes can a reactor power?
A 1,000 MWe reactor generates roughly 8 billion kWh a year — enough for over two million average UK homes, depending on consumption and capacity factor.
What is a capacity factor?
The share of the year a plant generates at full power, accounting for refuelling and maintenance. Nuclear is often around 90%, which is why annual output is so high.