In a BWR, reactor power is controlled by what mechanisms?

• A. Turbine load only
• B. Rods and recirculation flow
• C. Boron concentration
• D. Pressure changes

Answer: (B)

Power in a BWR is controlled mainly by changing reactivity through two levers: moving the control rods to absorb or release neutrons, and adjusting the recirculation flow to change the core’s boiling and neutron economy. The control rods provide direct, rapid reactivity changes: inserting them lowers reactivity and power, withdrawing raises it. The recirculation system changes how much water is pumped through the core; increasing flow promotes more boiling and alters the voids in the core, which shifts how neutrons are moderated and thus changes reactivity to achieve the desired power level. Turbine load, boron concentration, or pressure changes aren’t used as the primary means of controlling reactor power in a BWR.