Boiling Water Reactor (BWR)

The boiling water reactor (BWR) is the second most common type of nuclear reactor. There are about 94 operating BWRs in the world, which is 21% of all reactors.

Cofrentes is a typical Spanish picturesque village with a dominant castle and a nuclear power plant in the background. (Source: © h368k742 / stock.adobe.com)

Cofrentes is a typical Spanish picturesque village with a dominant castle and a nuclear power plant in the background.

The fuel is very similar to the fuel of the PWR. Ceramic pellets are made of uranium enriched to 2.1%—2.6%. They are inserted into fuel rods that are assembled into fuel bundles 4 meters long. Each assembly resides in its own channel that rectifies the water coolant flow. The reactor is actually a steel pressure vessel about 10 meters high and the reactor core is 3.5 meters high and 4.5 meters in diameter. This reactor is refueled once a year during reactor shutdown when one-quarter to one-third of the  fuel bundles is replaced.

Ordinary water is used as both the moderator and the coolant. The water boils directly inside the reactor. The design of the reactor core allows operation even if approximately 12%—15% of its top portion is filled with steam (however, with lower efficiency). Boiling water is also used for control purposes because steam bubbles are not a very good moderator compared to water and thus the fission reaction is attenuated. The water pressure is 7 MPa and its temperature is about 280 °C. The steam generated inside the reactor is dried and supplied directly to a turbine. This is a single-circuit power plant.

BWR schematic diagram.

BWR schematic diagram.

On the coast of Lake Erie In between the American cities of Detroit and Toledo, there is a nuclear power plant named after the Italian scientist Enrico Fermi. There is a single operating boiling water reactor (1,122 MW); an older 94 MW fast reactor is being decommissioned. (Source: © spiritofamerica / stock.adobe.com)

On the coast of Lake Erie In between the American cities of Detroit and Toledo, there is a nuclear power plant named after the Italian scientist Enrico Fermi. There is a single operating boiling water reactor (1,122 MW); an older 94 MW fast reactor is being decommissioned.

This cooling tower is part of the Leibstadt nuclear power plant located in the north of Switzerland. There is a single nuclear block with a boiling water reactor with electric power output of 1,220 MW and it generates about 8.5 TWh of electric energy, annually. (Source: © UrbanExplorer / stock.adobe.com)

This cooling tower is part of the Leibstadt nuclear power plant located in the north of Switzerland. There is a single nuclear block with a boiling water reactor with electric power output of 1,220 MW and it generates about 8.5 TWh of electric energy, annually.

More than half (32 out of 55) of the Japanese reactors are BWRs.

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