Pressurised Water Reactor (PWR): what is the specific function of the pressuriser and primary-side pressure control?

Introduction / Context:
In a Pressurised Water Reactor, the primary circuit carries heat from the core to steam generators. Boiling in the primary side must be avoided to maintain stable heat transfer and fuel cladding margins. The pressuriser is a dedicated vessel connected to the primary loop to control pressure.

Given Data / Assumptions:

• Closed primary loop with reactor vessel, pumps, and steam generators.
• Dedicated pressuriser provides a steam-water cushion.
• Load changes disturb temperature and volume in the loop.

Concept / Approach:
The pressuriser maintains the primary pressure at a high setpoint so that the coolant remains subcooled (no bulk boiling) throughout normal operation. Electric heaters and spray systems inside the pressuriser add or remove energy to adjust the steam-water inventory and, hence, the loop pressure.

Step-by-Step Solution:
1) Set a pressure high enough that core outlet remains below saturation temperature.2) Use heaters to increase pressure when it tends to drop; use sprays to condense steam and reduce pressure when it tends to rise.3) Keep the primary loop single-phase liquid to ensure predictable heat transfer and pump performance.

Verification / Alternative check:
Plant schematics show the pressuriser connected to the hot leg; control logic references primary pressure, not secondary steam superheat (which is produced on the secondary side).

Why Other Options Are Wrong:
Maintaining “constant” pressure is a control outcome, but the core purpose is to keep the primary coolant pressurised to prevent boiling.Superheating steam occurs on the secondary side in some designs, not via the pressuriser.Hence “None of these” is incorrect.

Common Pitfalls:
Confusing primary and secondary systems; assuming the pressuriser affects turbine steam conditions directly.

Final Answer:
Pressurise the primary coolant water to prevent boiling