Thermodynamic efficiency comparison at the same temperature and pressure limits: which reactor/coolant system is generally most efficient?

Introduction / Context:
Thermal efficiency for power cycles is primarily governed by the temperature at which heat is added and rejected. Reactor systems that permit higher coolant and steam temperatures (for a given pressure constraint and material limits) can reach higher Rankine-cycle efficiencies.

Given Data / Assumptions:

• Operating between comparable overall temperature and pressure limits for the core/steam cycle.
• Focus on thermodynamic potential, not licensing or economic factors.
• Heat-exchanger and materials performance are adequate for the stated limits.

Concept / Approach:
Liquid-metal coolants like sodium feature excellent thermal conductivity, low pumping power, and allow high core outlet temperatures at relatively low pressures, enabling higher steam temperatures and better thermal efficiencies. Water-cooled systems (PWR, BWR) operate at high pressures to prevent boiling (PWR) or at saturation conditions (BWR), which constrain peak steam temperatures. Gas-cooled systems can also achieve good temperatures, but pressure and heat-transfer limitations often reduce practical efficiencies compared with liquid-metal systems under the same constraints.

Step-by-Step Solution:
Recall efficiency trends: higher heat-addition temperature increases ideal Rankine efficiency.Identify coolant classes that safely support higher outlet temperatures.Recognise sodium-cooled reactors typically allow higher temperature operation.Select molten sodium cooled reactor as most efficient under the stated comparison.

Verification / Alternative check:
Fast sodium-cooled reactor concepts frequently target higher steam-generator outlet temperatures than light-water designs, improving cycle efficiency for similar pressure limits. This qualitative industry pattern supports the selection.

Why Other Options Are Wrong:

• CO2 gas-cooled: Reasonable performance but generally less than liquid-metal systems for the same limits.
• PWR: High pressure but relatively lower steam temperature versus sodium-cooled potential.
• BWR: Saturation-temperature constraints limit main steam temperature.
• Heavy-water moderated, light-water cooled: Similar water constraints apply.

Common Pitfalls:
Equating pressure capability with efficiency; overlooking the role of achievable main steam temperature and heat-transfer characteristics.

Final Answer:
Molten sodium cooled reactor