In a PWR, reactor coolant temperature is controlled by what?

• A. Turbine load
• B. Boron concentration
• C. Recirculation flow
• D. Decay heat removal system

Answer: (B)

In a PWR, the temperature of the reactor coolant is set by the power level of the core, since the coolant temperature rises with higher heat generation. The primary way to control that power continuously during operation is by adjusting the boron concentration in the primary coolant. Boron acts as a soluble neutron absorber; increasing boron concentration lowers reactivity, reduces core power, and thus lowers the heat being dumped into the coolant. Decreasing boron raises reactivity, increases power, and raises coolant temperature. The other mechanisms don’t serve as the normal control lever for core temperature: turbine load affects steam flow and electrical output rather than directly setting core temperature; recirculation flow is a reactor type feature more associated with BWRs; and the decay heat removal system is used after shutdown, not for steady-state temperature control.