In nuclear reactor engineering, an ideal coolant should enable efficient heat removal while remaining chemically compatible with materials: which property best captures this requirement?

Introduction / Context:
An ideal nuclear reactor coolant must remove fission heat safely and efficiently without undermining the neutron economy or damaging plant materials. Besides thermal performance, chemical stability and radiation tolerance are crucial because coolants are exposed to intense neutron and gamma fields and contact structural alloys, fuel cladding, and seals for long periods.

Given Data / Assumptions:

• We are considering generic reactor-coolant requirements, not a specific design.
• Key concerns include neutron absorption, thermal capacity, heat-transfer coefficient, viscosity, corrosion, and radiation stability.
• “Ideal” emphasises safety and compatibility as well as performance.

Concept / Approach:
A practical coolant should have low neutron absorption (to preserve reactivity), high specific heat and good thermal conductivity (to carry heat effectively), low viscosity (to limit pumping power), a high boiling point or high allowable temperature (to widen the operating window), and—critically—chemical compatibility with structural materials and resistance to radiolysis and radiation-induced degradation. Among competing statements, the property that most universally safeguards integrity and availability is freedom from radiation damage and non-corrosiveness.

Step-by-Step Solution:
Identify essential coolant traits: thermal efficiency, neutronic benignity, chemical compatibility, radiation stability.Evaluate each option against these traits.Select the option that is always beneficial and broadly necessary across reactor types.Conclude that “free from radiation damage and non-corrosive” is the best overarching requirement.

Verification / Alternative check:
Water (light or heavy) is favoured for many designs due to chemical manageability, while liquid metals (e.g., sodium) are selected for high-temperature performance; in all cases, corrosion control and radiation stability define maintenance cycles, component life, and safety margins. Thus, compatibility is a universal criterion.

Why Other Options Are Wrong:

• Be a good absorber of neutrons: High absorption is undesirable; it poisons the neutron economy.
• Attain high temperature only when highly pressurised: Pressure dependence is a system design constraint, not an “ideal” coolant property.
• Have very high density but a low heat-transfer coefficient: Low heat-transfer coefficient is detrimental to heat removal.
• Exhibit high viscosity: Increases pumping power and reduces heat-transfer coefficients.

Common Pitfalls:
Overrating thermal metrics while ignoring long-term material compatibility; assuming any one property (e.g., density) dominates overall performance; neglecting radiolysis and corrosion product transport.

Final Answer:
Be free from radiation damage and be non-corrosive