Nib asked
How does a nuclear reactor produce electricity?
A nuclear reactor never makes electricity itself: splitting atoms only makes heat, and that heat boils water into steam that spins a turbine and generator, like a steam power plant with a nuclear furnace.
7 steps, drawn by Nib. Read it here, or watch him draw it. Updated .
1just heat
A nuclear power plant is, at heart, a steam power plant. The reactor is the furnace: it makes heat and nothing else. Everything after that, boiling water, spinning a turbine and turning a generator, works much like a plant that burns coal or gas.
The reactor is a heat source; electricity comes later, from steam.
a common mix-upPeople picture a reactor as a bomb or an electricity machine. It is neither: its only product is steady, controlled heat.
2splitting atoms
When a neutron hits an atom of uranium-235, the atom splits in two. Each split frees two or three more neutrons, and the two fragments fly apart so fast that their motion becomes heat in the surrounding fuel.
Fission: a neutron splits uranium-235, freeing 2 or 3 neutrons and heat.
3the core
Fuel pellets are stacked in long metal rods. Each pellet is about a centimetre wide, yet releases about as much energy as a ton of coal. Between the fuel rods slide control rods made of neutron absorbers such as boron or cadmium. Pushing them in slows the chain reaction and pulling them out speeds it up, so the core sits at a steady power.
Fuel rods hold the pellets; control rods absorb neutrons to keep the chain reaction steady.
What do control rods do?
Show the answer
They soak up neutrons, so they hold the chain reaction steady.
4hot water
In the most common design, the pressurized water reactor, water flows through the core and heats to about 325 degrees Celsius. It is kept at roughly 150 times atmospheric pressure, so it stays liquid instead of boiling. This hot water is pumped to a steam generator, where it hands its heat on.
Pressurized water in the core reaches about 325 °C without boiling and carries the heat to the steam generator.
5steam
Inside the steam generator the hot primary water flows through thousands of tubes while a second, separate supply of water boils on the outside. The two never mix, so the radioactive water stays sealed in the reactor loop. The steam rushes to a turbine, a wheel of blades, and spins it.
The hot loop boils a second, separate loop of water; the steam spins the turbine.
6electricity
The turbine's shaft spins a generator: a magnet turning inside coils of copper wire, which pushes an electric current through the wire. That current is the electricity. The spent steam goes to a condenser, cools back into water, and is pumped to the steam generator to start again.
A generator turns the spinning into electricity; cooled steam returns as water.
Where in the plant does the electricity actually appear?
Show the answer
In the generator, where a spinning magnet turns inside coils of wire.
7the whole idea
The whole chain is: fission makes heat, the heat makes hot water, the hot water boils a second loop into steam, the steam spins a turbine, and a generator turns that spin into electricity. Light-water reactors turn roughly a third of the heat into electricity (33 to 37 percent is typical); the rest leaves as waste heat.
Fission heat boils water; steam spins a turbine and generator; roughly a third of the heat becomes electricity.
So a nuclear reactor is a heat source: it boils water, and the steam does the rest.