Nuclear reactor types
Reactors are classified by what cools them and what slows their neutrons. Those two choices determine almost everything else: what enrichment the fuel needs, whether the plant can refuel while running, and how hot it can run. Of 419 operating units worldwide, 311 are pressurised water reactors — roughly 74% of the fleet.
| Type | Coolant | Moderator | Operating | GW gross | Building | All units |
|---|---|---|---|---|---|---|
| Pressurised water reactor PWR | Light water | Light water | 311 | 317.7 | 70 | 948 |
| Boiling water reactor BWR | Light water | Light water | 45 | 48.3 | 4 | 197 |
| Pressurised heavy water reactor PHWR | Heavy water | Heavy water | 44 | 24.8 | 3 | 96 |
| Gas-cooled reactor GCR | Carbon dioxide | Graphite | 9 | 5.3 | 1 | 58 |
| Light water graphite reactor LWGR | Light water | Graphite | 7 | 7.0 | — | 34 |
| Fast reactor FBR | Liquid sodium or lead | None | 2 | 1.5 | 3 | 44 |
| High-temperature gas reactor HTGR | Helium | Graphite | 1 | 0.2 | — | 41 |
| Molten salt reactor MSR | Molten fluoride or chloride salt | Graphite, or none in fast-spectrum designs | — | — | — | 4 |
| Fusion Fusion | Varies by design | None | — | — | — | 2 |
Units with no type stated
Global Energy Monitor classifies some units only by size, not by coolant and moderator. Those units appear here rather than being assigned a family we would be guessing at.
- 193 units recorded as type unknown with no coolant or moderator stated
- 24 units recorded as microreactors with no coolant or moderator stated
- 184 units recorded as small modular reactors with no coolant or moderator stated
Sources
- Global Nuclear Power Tracker, Global Energy Monitor, August 2026 release — CC BY 4.0 · retrieved 2026-09-06