Nuclear Power
A nuclear plant is a thermal power plant whose heat comes from splitting atoms rather than burning fuel. Everything downstream of the reactor — steam, turbine, generator — is conventional engineering.
~90%
capacity factor across the US nuclear fleet, the highest of any resource
2M×
the energy released by fissioning a uranium atom versus burning a carbon atom
How does fission produce electricity?
When a neutron strikes a uranium-235 nucleus, the nucleus splits. The fragments fly apart with enormous kinetic energy, which becomes heat as they collide with surrounding material, and two or three fresh neutrons are released. If enough of those neutrons go on to split further nuclei, the reaction sustains itself. A reactor is the apparatus that holds that chain reaction at exactly break-even, neither growing nor dying, for months at a time.
Control comes from three places. Control rods made of neutron-absorbing material are raised or lowered to set the reaction rate. A moderator, usually water, slows fast neutrons to the speed at which they are most likely to cause fission. And the coolant carries heat away to the steam cycle, which is also what keeps the fuel intact. From there the plant behaves like any thermal station: heat raises steam, steam turns a turbine, the turbine spins a generator.
From atom to kilowatt-hour
Fission
A neutron splits a U-235 nucleus, releasing heat and more neutrons
Heat transfer
Coolant carries heat out of the core to a steam generator or directly to the turbine
Steam cycle
Steam expands through the turbine, condenses, and returns as water
Generation
The shaft drives a generator, stepped up to transmission voltage on site
What kinds of reactors are there?
Almost every commercial reactor operating today is a light water reactor, cooled and moderated by ordinary water under pressure. The designs under development differ mainly in what they use as coolant, because coolant choice sets the operating temperature, the pressure, and therefore the safety case.
| Design | Coolant | Outlet temperature | Status |
|---|---|---|---|
| Pressurized water (PWR) | Water at ~155 bar | ~320°C | The dominant commercial design worldwide |
| Boiling water (BWR) | Water, boiling in the core | ~285°C | Widely operating; simpler cycle, no separate steam generator |
| Heavy water (CANDU) | Heavy water | ~310°C | Operating in Canada and abroad; runs on natural uranium |
| High-temperature gas (HTGR) | Helium | 750–950°C | Gen IV; demonstration units operating in China, others in licensing |
| Sodium fast (SFR) | Liquid sodium | ~500–550°C | Gen IV; decades of prototype experience, first commercial units under construction |
| Molten salt (MSR) | Fluoride or chloride salts at atmospheric pressure | 700–800°C | Gen IV; proven at Oak Ridge in the 1960s, targeted for commercialization after 2030 |
The fuel cycle
Natural uranium is only about 0.7% U-235. Most reactors need it concentrated to between 3% and 5%, which is what enrichment does. The material then spends several years in a core, after which the spent fuel is intensely radioactive but small in volume: the entire output of the US commercial fleet since the 1950s would cover a single football field to a depth of about ten yards.
Step 1
Mine and mill
Ore becomes uranium oxide concentrate, then a gas for processing.
Step 2
Enrich
Centrifuges raise the U-235 share from 0.7% to a few percent.
Step 3
Fabricate
Pellets are sealed into rods and assembled into fuel bundles.
Step 4
Irradiate
Fuel runs 18 to 24 months per cycle, with a third of the core replaced at a time.
Step 5
Store or recycle
Pools then dry casks in the US; France and Russia reprocess to recover usable material.
Safety, waste and land
Safety record
Deaths per unit of energy
Counting the accidents at Chernobyl, Fukushima and Three Mile Island, nuclear’s fatality rate per terawatt-hour sits alongside wind and solar and far below coal, oil and gas.
Decay heat
The core stays hot after shutdown
Fission products keep generating heat for days. Every serious accident has been a failure to remove that heat, which is why newer designs cool passively without pumps or power.
Waste
Contained, not dispersed
Spent fuel is solid, tracked and stored on site in casks. Finland’s Onkalo is the first deep geological repository to reach operation; the US has no permanent site.
Footprint
Dense by area
Because the energy density of the fuel is so high, a gigawatt-scale plant occupies roughly a square mile including its buffer zone, and it runs about nine hours in ten.
What is being built now
The cost problem with nuclear in the West is not the physics but the delivery model. Large one-off projects built by shifting teams to evolving designs have overrun badly, while the same reactor built repeatedly by a stable workforce, as in South Korea and increasingly in China, has not. That observation is what drives the current wave of smaller, factory-built designs: shrink the unit, repeat it often, and move the work from the field to a production line.
Small modular reactors put 50 to 300 megawatts in a shippable package. Advanced designs go further, using gas, sodium or salt coolants to reach temperatures that serve industrial heat, hydrogen and desalination as well as electricity. Both routes face the same gating question: how quickly a regulator can license a design that has no operating precedent.