What is the primary coolant in a PWR?

• A. The cooling water that flows through the core.
• B. The steam used to drive the turbine.
• C. The water in the cooling tower.
• D. The gas used for cooling.

Answer: (A)

In a PWR, the primary coolant is the liquid water in the primary loop that flows through the reactor core to remove the fission heat. It stays in the liquid phase because the loop is kept at high pressure, then transfers its heat to the steam generators where it heats the secondary loop to make steam for the turbine. The other options aren’t the primary coolant: the steam driving the turbine is on the secondary side, the water in the cooling tower is part of the secondary/ultimate heat-sink system, and gas cooling isn’t used in a PWR.