In a PWR, reactor power is controlled primarily by what?

• A. Turbine load
• B. Rods
• C. Boron concentration
• D. Recirculation flow

Answer: (A)

In a PWR, reactor power is controlled by adjusting the neutron economy, i.e., reactivity, rather than by the electrical load of the turbine. The primary tools are control rods and soluble boron in the coolant. Control rods, made of neutron-absorbing material, are inserted or withdrawn to change how many neutrons are captured; inserting rods lowers reactivity and power, withdrawing them raises reactivity and power. Soluble boron acts as a chemical shim: increasing boron concentration absorbs more neutrons and reduces reactivity, while decreasing boron increases reactivity. This boron adjustment provides a long-term, fine-tuning mechanism to compensate for fuel burnup and operating conditions.

Turbine load, while important for matching electricity output and slightly affecting plant operating conditions, does not set the reactor’s reactivity and thus does not determine the core power in steady operation. Recirculation flow is a mechanism associated with other reactor types when discussing power control, not the primary method in a PWR. So the key concept is that power is controlled primarily by altering reactivity through control rods and boron concentration.