By Nanashi
Nuclear reactors are giant steam engines
Let's follow the energy from one tiny atom to the plug in your wall
Splitting atoms makes heat
A tiny particle hits a uranium atom The atom splits and gives off heat It also shoots out new tiny particles Those particles split more atoms: a chain reaction
Fact sources: Idaho National Laboratory, 2025; MIT Nuclear Reactor Laboratory; U.S. NRC Student Corner
Tiny particle (neutron)
Uranium atom
New neutrons
Two smaller pieces
Heat
Tiny uranium pellets fuel the whole reactor
Fuel pellet
Uranium, about the size of a gummy bear
Fuel rod
Long metal tube filled with pellets
Fuel bundle
Over 200 rods tied together
Reactor core
Hundreds of bundles side by side
Fact sources: U.S. DOE Office of Nuclear Energy, 2025; Nuclear Energy Institute, 2026; Idaho National Laboratory, 2025
Water and control rods keep it steady
Water slows particles so atoms split more easily Control rods soak up particles like a sponge Rods down: less heat. Rods up: more heat Rods all the way down: the reaction stops
Fact sources: U.S. DOE Office of Nuclear Energy, 2025; World Nuclear Association; U.S. NRC Reactor Concepts Manual
Water
Reactor tank
Control rods
Fuel rods
Water carries the heat away in a loop
Reactor core
Water picks up heat from the fuel
Pressurizer
Squeezes the water so it can't boil
Steam generator
Passes the heat to other water
Pump
Pushes the water back to the core
Fact sources: U.S. NRC Reactor Concepts Manual (PWR Systems); Nuclear Energy Institute
Steam spins a turbine to make electricity
Heat boils a second batch of water into steam Steam spins the turbine like wind spins a pinwheel The turbine turns magnets inside the generator The condenser cools steam back into water
Fact sources: U.S. NRC, How Does a Nuclear Power Plant Make Electricity?; Nuclear Energy Institute
Reactor
Steam generator
Turbine
Generator
Condenser
Three walls and an off switch keep us safe
1. Metal tubes
The fuel pellets are sealed inside metal tubes. This is the first wall.
2. Steel tank
A thick steel tank holds the whole core. Its walls are about a foot thick.
3. Concrete dome
A huge building of concrete and steel covers everything. At Plant Vogtle it stands 226 feet tall.
Off switch
Control rods can drop all the way in to stop the reaction fast.
Fact sources: U.S. NRC, Backgrounder on Nuclear Reactor Risk; Southern Nuclear, 2021
We checked our facts with real experts
U.S. Energy Information Administration (EIA), 2026 U.S. Department of Energy and Idaho National Laboratory, 2025 U.S. Nuclear Regulatory Commission (NRC) MIT Nuclear Reactor Laboratory Nuclear Energy Institute (NEI), 2026
Nuclear makes about 18% of U.S. electricity. Tomorrow, share one question you still have.
Fact source: U.S. Energy Information Administration, 2026