In a BWR, where does boiling primarily occur?

• A. In the upper region of the core.
• B. In the steam generator.
• C. In the cold leg of the primary loop.
• D. In the feedwater heater.

Answer: (A)

Boiling in a BWR happens inside the reactor vessel as the coolant is heated by the fuel to near the saturation temperature. The water rises as a two-phase mixture, and most of the vapor forms in the upper portion of the core where voids develop and steam can be readily separated from liquid. That steam is then carried to the turbine directly from the core.

There is no separate steam generator in a BWR, since boiling occurs in the core itself. The cold leg concept and feedwater heaters belong to other parts of reactor designs or the feedwater loop and are not where core boiling primarily occurs.