Pressurised Water Reactor (PWR) primary circuit: the reactor coolant in the primary loop is maintained as high-pressure __________ to prevent bulk boiling in the core.

Introduction / Context:In a PWR, the primary circuit removes fission heat from the core while avoiding boiling to maintain stable heat transfer and prevent departure from nucleate boiling margins. The thermal-hydraulic state of the primary coolant is central to safe operation.

Given Data / Assumptions:

• PWR design with pressuriser maintaining high pressure.
• Boiling is purposely suppressed in the primary loop.
• Steam is generated only in the secondary side (steam generator).

Concept / Approach:By keeping the primary coolant at high pressure (typically ~15–16 MPa), its saturation temperature is raised well above core outlet temperature, ensuring the fluid remains a single-phase liquid (subcooled). This avoids void formation in the core and keeps neutron moderation and heat transfer predictable.

Step-by-Step Solution:Identify PWR goal: no bulk boiling in primary.High pressure elevates saturation temperature.Operating temperatures are kept below saturation, hence liquid is subcooled.Steam forms only on the secondary side of steam generators.

Verification / Alternative check:Basic PWR schematics show pressuriser and steam generators, with primary water circulating through the reactor vessel and remaining in liquid state throughout normal operation.

Why Other Options Are Wrong:

• Saturated water/steam or two-phase mixture contradicts the PWR primary objective.
• Superheated steam exists only in the secondary/tertiary cycles, not in the primary circuit.

Common Pitfalls:Confusing BWR and PWR designs; in BWRs, boiling occurs in the core and steam goes directly to the turbine.

Final Answer:sub cooled water