Reactor type 6 of 10
Sodium-cooled fast reactor
by Joe Miller
Sodium-cooled fast reactors use liquid sodium metal as the coolant and no moderator, so neutrons stay fast. Fast neutrons can burn the long-lived parts of spent fuel and can even breed more fuel than they use.
Plain-English explainer by Joe Miller, a nuclear engineer. Not investment advice. Figures are the latest public numbers we could find and change fast; sources are at the bottom of each page.
What it looks like
How the coolant circulates
- Primary pumps push sodium up through the core (about 500 to 550°C out).
- Hot sodium flows through the IHX inside the pool.
- The intermediate sodium loop carries heat out to the steam generator (or salt storage in Natrium).
- Steam drives the turbine; cooled intermediate sodium returns to the IHX.
The main components
| Component | What it does |
|---|---|
| Reactor pool | A large tank of liquid sodium at near-atmospheric pressure holding the core, pumps and heat exchangers. |
| Core | Metal or oxide fuel pins, more highly enriched than water-reactor fuel (HALEU, up to about 20%), packed tightly with no moderator. |
| Primary pumps | Circulate sodium through the core inside the pool. |
| Intermediate heat exchanger (IHX) | Transfers heat to a separate, non-radioactive sodium loop so radioactive sodium never reaches the steam generators. |
| Steam generator | Intermediate sodium boils water; it is designed carefully because sodium reacts violently with water. |
| Cover gas | Argon blankets the sodium surface to keep air away. |
| Molten-salt heat storage (Natrium) | Hot salt tanks store heat so the plant can boost output from 345 to 500 MW for several hours. |
Key details
| Item | Detail |
|---|---|
| Coolant | Liquid sodium |
| Moderator | None (fast spectrum) |
| Fuel | Metal or oxide, HALEU up to about 20% |
| Pressure | Near atmospheric |
| Temperature | About 500 to 550°C |
| Efficiency | About 40% |
| Refueling | Every 1 to 2 years |
How it is maintained
- Opaque coolant: you cannot see through sodium, so inspections use ultrasonic viewing tools.
- Sodium handling: parts must be cleaned of sodium before maintenance, and the cover gas is watched for leaks.
- Steam generator leak detection (hydrogen meters) to catch any sodium-water reaction early.
- Refueling under the sodium with rotating plugs and in-vessel handling machines.
Where it runs
Russia's BN-600 and BN-800 at Beloyarsk (running); India's prototype fast breeder at Kalpakkam; China's CFR-600; TerraPower's Natrium at Kemmerer, Wyoming (NRC construction permit March 2026, aiming for about 2030; Meta has signed for up to eight units); Oklo's Aurora.
Who's writing this? I'm Joe Miller, a nuclear engineer since 1974 and an ASME Fellow. I've run safety analyses for PWRs and BWRs, directed nuclear engineering at a working BWR, and reviewed new reactor designs for the NRC. This site explains every kind of reactor in plain English. My background and papers.