BWRreaktorer

BWRreaktorer, or boiling water reactors (BWR), are a class of light‑water nuclear reactors in which the reactor coolant directly boils to generate steam that drives the turbine. Developed in the 1950s by General Electric, BWRs became a widely used reactor type in North America, Japan and elsewhere, with many units still operating worldwide.

In a BWR, fuel assemblies generate heat in the core, which boils the surrounding light water. The steam formed in the reactor vessel drives a turbine directly, while the remaining liquid water remains in the closed loop to be reheated and recycled. The reactor water also serves as the neutron moderator.

BWRs use jet pumps or recirculation pumps to control coolant flow and the level of boiling in the core. Unlike some other designs, there is no separate steam generator: steam is produced inside the reactor vessel and sent to the turbine houses. Control rods are inserted from above to adjust reactivity.

Safety systems combine active and passive features, including emergency core cooling, containment structures, and hydrogen management after losses of coolant. Notable design families include the early Mark I and Mark II, the more capable ABWR (Advanced Boiling Water Reactor), and ESBWR variants with passive safety.

Boiling water reactors remain in operation in several countries, notably the United States, Japan and parts of Europe. They are valued for a compact plant layout and a single-water cycle, but require careful management of corrosion, radiological exposure, and hydrogen risk. Ongoing evolution focuses on safety, efficiency and extended fuel cycles.