Wiki
How nuclear power works
Three levels: the concepts you need to understand any reactor, an animated guide for each type, and an entry for each specific design, from the VVER to the ACR-300.
Fundamental concepts
- Concept
What nuclear fission is
A heavy nucleus splits in two, releasing energy and neutrons, and those neutrons split other nuclei. Everything else follows from that.
- Concept
What nuclear fusion is
Two light nuclei join into a heavier one and release even more energy per gram. It is what the Sun does and what no power plant does yet.
- Concept
Chain reaction, moderator and control
For a neutron to have a good chance of fissioning a nucleus it has to be slowed down. And to govern power, the surplus ones have to be absorbed.
- History
The first reactor
Chicago, December 2, 1942: a pile of graphite and uranium under a stadium grandstand goes critical. Twelve years later, Obninsk connects the first reactor to a grid.
- Concept
Fuel and enrichment
Natural uranium is 0.7% U-235. Depending on the reactor, it is used as is or concentrated up to 5%, and in the new designs up to 20%.
- Concept
Thermal power and electrical power
MWt is the heat the core produces; MWe is the electricity that reaches the grid. Two thirds are lost between one and the other, and that is physics, not bad engineering.
Reactor types
- PWRAnimated guide
Pressurized water →
Light water at 155 bar that never boils; steam is raised in a separate circuit.
≈ 300 operating
- BWRAnimated guide
Boiling water →
Water boils inside the vessel and the steam goes straight to the turbine.
≈ 40 operating
- PHWR · CANDUAnimated guide
Pressurized heavy water →
Natural uranium moderated by heavy water in pressure tubes; on-power refueling.
≈ 43 operating
- GCR / AGRAnimated guide
Gas-cooled →
Graphite moderator and CO₂ coolant at high temperature. A British design.
≈ 8 operating
- LWGR / RBMKAnimated guide
Graphite and light water →
Pressure tubes with boiling water and a graphite moderator. A Soviet design.
≈ 7 operating
- FBRAnimated guide
Fast breeder →
No moderator, sodium-cooled; produces more fissile material than it consumes.
≈ 3 operating
- HTGRAnimated guide
High-temperature gas →
TRISO particle fuel and helium above 700 °C. The HTR-PM.
≈ 2 operating
- SMRAnimated guide
Small modular reactor →
Factory-built modules under 300 MWe with passive safety. Families and status in 2026.
first units starting up