Which statement best describes a Boiling Water Reactor (BWR)?

• A. The reactor water boils directly inside the reactor to create steam that drives turbines.
• B. The reactor uses a separate steam generator to produce steam from a primary coolant that never boils.
• C. The reactor uses a molten salt coolant that boils at high temperature.
• D. The reactor uses a gas coolant to drive turbines.

Answer: (A)

In a Boiling Water Reactor, the working fluid is the coolant that also becomes the steam that drives the turbine. Heat from the fuel heats the reactor water to near saturation, and the water boils directly inside the reactor vessel, producing steam that goes straight to the turbine. There’s no separate steam generator or secondary loop—the same loop supplies both cooling and steam generation. In practice, moisture separators may remove liquid water before the steam reaches the turbine, but the core concept remains direct boiling in the reactor.

Other designs use different approaches: some keep the primary coolant from boiling and generate steam in a separate steam generator, others use entirely different coolants such as molten salt or gas.