BWR

Boiling water reactor (BWR) is a type of light‑water nuclear reactor in which the fission heat boils water inside the reactor vessel, producing steam that directly drives a turbine generator. In a BWR, there is no separate steam generator; the same water that cools the fuel also becomes the steam that powers the turbine.

Operation: The core boils water to generate saturated steam. Steam separators and dryers remove remaining droplets before the steam enters the high‑pressure turbine. After expansion, the steam is condensed and the condensate is returned as feedwater. The reactor operates at about 7 MPa, keeping the water in the primary loop mostly liquid outside the core while boiling occurs in the core.

Control: Reactivity is adjusted by changing the core recirculation flow (via jet pumps or recirculation pumps) and by inserting control rods from above. Some designs also use soluble boron in the feedwater.

Safety and design: BWRs employ a containment and multiple safety systems, including emergency core cooling. Because steam from the reactor is sent directly to the turbine, turbine components and piping are exposed to irradiation and must be designed to manage radioactive corrosion products and water chemistry.

History and variants: Developed by General Electric in the 1950s, BWR designs have evolved through Mark I–III containments to modern ABWR (Advanced BWR) and ESBWR variants. Typical electrical outputs range from a few hundred megawatts to over 1,000 MWe.