Gas-cooled reactor GCR
A gas-cooled reactor (GCR) uses carbon dioxide as coolant and graphite as moderator. 9 are operating worldwide, totalling 5.3 GW gross, out of 58 units of this type on record.
Operating
9
5.3 GW gross
Under construction
1
Planned
0
Retired
44
Carbon dioxide circulates through a graphite core at temperatures high enough to give these plants better thermal efficiency than any water-cooled reactor. Britain built the family in two generations — Magnox, running on natural uranium metal, and the Advanced Gas-cooled Reactor, running on enriched oxide in stainless steel cladding. Both use a graphite structure whose slow degradation, rather than the fuel or the vessel, sets the fleet's retirement date.
Advantages
- Highest thermal efficiency of any commercial reactor fleet, around 40%, because gas runs hotter than water
- CO₂ at low pressure relative to water reactors, and the coolant cannot boil away
- Graphite core has large thermal inertia, so temperature changes are slow
- On-load refuelling in the Magnox design
Drawbacks
- Very large core for the power produced, so the buildings are big and expensive
- Graphite ageing, not the fuel or the vessel, determines when the plant must close
- Fuel is bespoke, with a single supplier for a single fleet
- No new units have been ordered anywhere since the 1980s
Design basis
| Coolant | Carbon dioxide |
|---|---|
| Moderator | Graphite |
| Fuel form | Uranium metal (Magnox) or uranium dioxide (AGR) |
| Typical enrichment | Natural uranium to 2.5–3.5% U-235 |
Where they operate
| United Kingdom | 8 |
|---|---|
| North Korea | 1 |
Model lines
| Model | Operating | Units on record |
|---|---|---|
| MAGNOX | 1 | 30 |
| AGR | 8 | 15 |
| Uranium Naturel Graphite Gaz | — | 6 |
| STGR20 | — | 1 |
| MMR | — | 1 |
Operating GCR units
| Unit | Country | Gross MW | Online |
|---|---|---|---|
| Torness nuclear power plant 1 | United Kingdom | 682 | 1988 |
| Torness nuclear power plant 2 | United Kingdom | 682 | 1989 |
| Heysham nuclear power plant B1 | United Kingdom | 680 | 1989 |
| Heysham nuclear power plant B2 | United Kingdom | 680 | 1989 |
| Hartlepool nuclear power plant A1 | United Kingdom | 655 | 1989 |
| Hartlepool nuclear power plant A2 | United Kingdom | 655 | 1989 |
| Heysham nuclear power plant A1 | United Kingdom | 625 | 1989 |
| Heysham nuclear power plant A2 | United Kingdom | 625 | 1989 |
| Nyongbyon nuclear power plant 1 | North Korea | 5 | 1985 |
Sources
- Global Nuclear Power Tracker, Global Energy Monitor, August 2026 release — CC BY 4.0 · retrieved 2026-09-06