Coolant circulation in liquid-metal fast systems: For recirculating molten sodium in a liquid-metal-cooled nuclear reactor, which pump type is most appropriate due to sodium’s high electrical conductivity and operating temperature?

Introduction / Context:
Liquid-metal-cooled reactors (especially fast reactors) often use sodium as a coolant because of its excellent thermal properties. Pumping liquid metals poses unique challenges: high temperature, reactivity, and the need to avoid moving seals and bearings in hot, reactive fluids. This question examines the pump technology best suited to such conditions.

Given Data / Assumptions:

• Coolant: molten sodium (electrically conductive, low viscosity, reactive with water/air).
• Continuous recirculation required in primary/secondary loops.
• High reliability and minimal leakage paths are desired.

Concept / Approach:
Electromagnetic pumps operate on the Lorentz force: a conductive fluid moving through a magnetic field experiences a body force that drives flow when an electric current is imposed. This design avoids rotating components in contact with the liquid metal, reducing mechanical wear and leakage risks at elevated temperatures. Conventional centrifugal or reciprocating pumps have shafts, seals, and bearings that become problematic in hot sodium service.

Step-by-Step Solution:
Assess sodium properties: conductive, hot, reactive.Match to pump principle: electromagnetic pumping provides contactless driving force.Conclude: choose an electromagnetic pump for molten sodium recirculation.

Verification / Alternative check:
Fast-reactor literature documents use of both electromagnetic and specially engineered mechanical pumps; however, electromagnetic pumps are particularly favored for leak-tight primary systems.

Why Other Options Are Wrong:
Reciprocating pumps: pulsating flow and seal complexity. Centrifugal/volute pumps: require shaft seals and bearings in hostile environments; used in some designs but not the typical best fit for sodium primary loops compared to electromagnetic options.

Common Pitfalls:

• Ignoring electrical conductivity; EM pumping relies on this property.
• Assuming room-temperature pump choices apply directly to liquid metals.

Final Answer:
Electromagnetic pump