In a pressurized water reactor (PWR), pressurized light water in the primary circuit performs which role(s)? Choose the statement that best captures its function.

Introduction / Context:
Pressurized water reactors (PWRs) dominate the global fleet of light-water reactors. Understanding which role the primary-circuit water plays clears up frequent confusion between “coolant,” “moderator,” and the secondary steam cycle that drives the turbine.

Given Data / Assumptions:

• Standard PWR design with a closed, high-pressure primary loop.
• Separate secondary loop where steam drives the turbine.
• No graphite or heavy-water moderation in a conventional PWR.

Concept / Approach:
In a PWR, light water (H2O) at high pressure circulates through the reactor core, removing fission heat (coolant function) and slowing down fast neutrons to thermal energies (moderator function). It is kept under pressure to avoid boiling in the primary loop. Heat is transferred to the secondary side via steam generators to produce steam for the turbine, keeping radioactive primary water out of the turbine system.

Step-by-Step Solution:
Identify primary-loop functions: heat removal + moderation.Confirm turbine working fluid: secondary-side steam, not primary water.Exclude graphite/heavy water: those are design features of other reactor types.Hence, the correct role is “both coolant and moderator.”

Verification / Alternative check:
Reactor schematics universally show primary pressurized water through core and steam generators, with moderation achieved by the same water in-core. The turbine loop is separate and non-radioactive (under normal operation).

Why Other Options Are Wrong:
Primary coolant only with graphite: incorrect for PWRs; graphite is used in other designs.Working fluid in turbine: wrong; that is secondary steam.Neither coolant nor moderator: contradicts PWR fundamentals.Emergency-only use: primary water is continuously used, not only in emergencies.

Common Pitfalls:
Confusing PWR with BWR (where water boils in the core).Assuming the same loop drives the turbine in all LWRs.

Final Answer:
It serves as both the coolant and the neutron moderator in the primary circuit