What is the function of a pressurizer in a PWR primary system?

• A. Maintains design pressure of the primary coolant.
• B. Controls turbine speed.
• C. Converts steam to water in the condenser.
• D. Shields the core from radiation.

Answer: (A)

In a PWR primary system, the crucial function of the pressurizer is to keep the primary coolant at its design pressure. Keeping the loop at this pressure ensures the coolant remains mostly liquid at high temperatures, which is essential for stable heat transfer and reactor safety. The pressurizer achieves this by using electric heaters to raise pressure (by generating more steam in the vapor space) and a spray system to lower pressure (condensing steam back into liquid). It also provides a flexible volume to absorb changes in coolant volume as the reactor heats up or cools down, preventing large pressure swings.

This is why it’s not used to control turbine speed, which is handled by the turbine-generator system; nor does it convert steam to water in the condenser, which is the condenser’s job; and it doesn’t shield the core from radiation, which is the role of shielding structures.