Boiling water reactor BWR
A boiling water reactor (BWR) uses light water as coolant and light water as moderator. 45 are operating worldwide, totalling 48.3 GW gross, out of 197 units of this type on record.
Operating
45
48.3 GW gross
Under construction
4
Planned
13
Retired
55
Water boils directly in the core and the steam drives the turbine without an intermediate loop. Removing the steam generator makes the plant simpler and thermally more efficient, at the cost of routing mildly radioactive steam through the turbine hall. Power is trimmed by varying recirculation flow as well as by control rods, which enter from below because the top of the vessel is full of steam separators. The family includes the ABWR, the first Generation III design to actually enter service.
Advantages
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- Higher thermal efficiency than a PWR because there is no intermediate heat exchange step
- Operates at about half the pressure of a PWR
- Power can be adjusted with recirculation flow as well as control rods, which helps load-following
Drawbacks
- Steam from the core drives the turbine, so the turbine hall is mildly radioactive and harder to maintain
- Control rods must enter from below, so gravity does not assist a shutdown
- Larger containment volume needed for the same power because of the steam
- Same enrichment dependency and refuelling outages as a PWR
Design basis
| Coolant | Light water |
|---|---|
| Moderator | Light water |
| Fuel form | Uranium dioxide pellets in zirconium-alloy cladding |
| Typical enrichment | 3–5% U-235 |
Where they operate
| United States | 31 |
|---|---|
| Sweden | 4 |
| Japan | 3 |
| Mexico | 2 |
| Finland | 2 |
| India | 1 |
| Spain | 1 |
| Switzerland | 1 |
Model lines
| Model | Operating | Units on record |
|---|---|---|
| BWR-5 | 4 | 20 |
| BWR-4 (Mark 1) | 13 | 18 |
| BWRX-300 | — | 11 |
| ABWR | 1 | 11 |
| BWR-4 | — | 8 |
| BWR-6 (Mark 3) | 5 | 6 |
| BWR-3 (Mark 1) | 5 | 6 |
| BWR-6 | 1 | 5 |
| BWR-5 (Mark 2) | 4 | 5 |
| BWR-4 (Mark 2) | 4 | 5 |
| BWR-69 | — | 4 |
| AA-III, BWR-2500 | 4 | 4 |
Operating BWR units
Sources
- Global Nuclear Power Tracker, Global Energy Monitor, August 2026 release — CC BY 4.0 · retrieved 2026-09-06