ANS:A - electromagnetic

Circulation of liquid metal, such as molten sodium, in a liquid metal-cooled nuclear reactor is typically done by an electromagnetic pump. Explanation:

• Liquid metal-cooled nuclear reactors, such as sodium-cooled fast reactors (SFRs), use a liquid metal, usually sodium or a sodium-potassium alloy, as the coolant.
• Electromagnetic pumps, also known as magnetohydrodynamic (MHD) pumps, are commonly employed to circulate the liquid metal coolant in these reactors.
• Electromagnetic pumps work based on the principle of magnetohydrodynamics, where the motion of electrically conducting fluids (such as liquid metals) can be controlled or induced using magnetic fields.
• In an electromagnetic pump, a magnetic field is applied to the liquid metal coolant, inducing an electric current in the fluid. This electric current interacts with the magnetic field to produce a Lorentz force, which pushes the liquid metal through the pump and circulates it through the reactor's coolant loop.
• Electromagnetic pumps offer several advantages, including simplicity, reliability, and the absence of moving mechanical parts in contact with the corrosive liquid metal coolant.

While other types of pumps, such as axial flow pumps, may also be used in certain reactor designs, electromagnetic pumps are particularly well-suited for liquid metal-cooled nuclear reactors due to their compatibility with the conductive nature of the coolant and their ability to operate in high-temperature, high-radiation environments.