Nuclear power plants generate electricity by using heat from nuclear fission to make steam. The steam turns a turbine, the turbine drives a generator, and transformers send the resulting electricity into the transmission grid. The fission process supplies heat; the turbine-generator performs the mechanical-to-electrical conversion used in many power stations.
How does a nuclear power plant generate electricity?
The process is a sequence of heat, motion and electrical conversion:
- Fuel and reactor core: Uranium fuel is formed into ceramic pellets, sealed inside metal rods, and assembled in the reactor core. In U.S. light-water reactors, water cools the fuel and slows neutrons; control rods help regulate the fission reaction. The U.S. Department of Energy explains the reactor and fuel basics.
- Fission releases heat: Uranium atoms split in a controlled chain reaction, releasing heat in the core.
- Heat makes steam: The reactor system transfers heat to water. Depending on reactor design, water boils in the reactor vessel or in a separate steam generator.
- Steam turns a turbine: High-pressure steam flows across turbine blades, turning the turbine shaft.
- The generator produces electricity: The turbine shaft turns a generator, which converts mechanical energy into electrical energy.
- Plant equipment connects output to the grid: Electricity passes through the plant switchyard and a step-up transformer before entering high-voltage transmission lines.
After passing through the turbine, steam is cooled in a condenser and returned as water for reuse. The exact arrangement of the steam and coolant circuits depends on the reactor type.
How do boiling-water and pressurized-water reactors differ?
The two designs use the same basic turbine-generator principle. Their key difference is where water boils and how reactor heat reaches the turbine.
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| Feature | Boiling-water reactor (BWR) | Pressurized-water reactor (PWR) |
|---|---|---|
| Where water boils | In the reactor vessel, where water absorbs heat from the core. | In a separate steam generator, not in the reactor core’s primary coolant circuit. |
| Steam route to turbine | Steam from the reactor vessel travels directly to the turbine. | Heat passes from pressurized primary coolant through steam-generator tubes to a separate water supply; that secondary water makes turbine steam. |
| Water circuits | The water boiled in the reactor vessel supplies steam to the turbine and is condensed and reused. | Primary coolant stays under pressure and circulates between the core and steam generator; secondary water becomes steam for the turbine. |
The U.S. Energy Information Administration describes these reactor types and their operating differences. The Department of Energy says all U.S. commercial reactors are light-water reactors; more than 65% are PWRs and roughly one-third are BWRs, according to its May 19, 2025 explainer. That mix describes the U.S. fleet, not the global fleet.
How does electricity from a nuclear plant get to homes?
A plant supplies electricity to an interconnected grid; it does not send a dedicated stream of electrons from one particular reactor to one particular home. Grid operators balance electricity from multiple generators with changing demand, while power flows through the connected network.
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- Switchyard and step-up transformer: Generator output is at relatively low voltage. The plant switchyard connects it to the grid, and a step-up transformer raises the voltage for transmission.
- High-voltage transmission: Transmission lines move electricity over long distances. Higher voltage allows the same power to travel at lower current, reducing resistive heating in the lines.
- Substations: Substations connect transmission to local distribution systems and lower voltage for that next stage.
- Distribution transformers: Transformers along distribution networks reduce voltage further to levels suitable for homes and other customers.
Within an interconnected AC network, generators operate in coordination at the grid’s frequency. The International Atomic Energy Agency’s overview of nuclear plants and grid interfaces discusses that synchronization. Its 2009 report gives around 7% as a typical transmission and distribution loss for the UK and USA; that older, general-network estimate is not a current loss rate for a nuclear plant.
What is the difference between generating capacity and electricity generation?
Capacity is a power rating: the maximum output a generator can produce under the stated capacity measure. It is usually expressed in watts, such as megawatts. Generation is the amount of electrical energy produced over time, commonly measured in megawatt-hours.
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For example, the U.S. Energy Information Administration says a 100-megawatt generator running continuously at that capacity for 24 hours would generate 2,400 megawatt-hours. Actual generation depends on how much power the generator produces and for how long. See the EIA explanation of how much electricity a power plant generates.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How steadily do nuclear plants operate?
U.S. nuclear plants typically run at or near generating capacity for much of the year, but they reduce output or shut down for maintenance and refueling. Refueling is typically needed every 18 to 24 months, and many U.S. refueling outages take place in spring and fall when electricity demand is lower. These are typical patterns, not a schedule that applies identically to every reactor.
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The EIA reports a 91% average annual capacity factor for U.S. nuclear power plants in 2025. Capacity factor compares actual generation over a period with the amount the plants could have generated by operating continuously at full capacity during that period. It is an annual fleet average, not a claim that every reactor runs at 91% output at each moment. The EIA’s U.S. nuclear industry overview reports that figure and a fleet count of 96 reactors at 57 plants in 28 states as of March 2026, with 98,441 megawatts of net summer capacity.
For context, nuclear power accounted for 18.2% of U.S. utility-scale net electricity generation in 2022, based on final EIA-923 data. That is a dated U.S. share, not a current global percentage. The EIA’s electricity-generation explainer was last updated October 31, 2023 and reports the 2022 figure.
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