Which coolant is commonly used in fast reactors?

Which coolant is commonly used in fast reactors?

• A. Light water
• B. Gas coolant
• C. Liquid metal coolant
• D. Molten salt coolant

Answer: (C)

Fast reactors keep neutrons moving fast to sustain the intended spectrum, so the coolant must remove heat without slowing down or absorbing too many neutrons. Liquid metal coolants fit this requirement well: they conduct heat extremely well, have low neutron absorption, and interact weakly with the fast neutrons, so the fast spectrum remains intact while heat is efficiently carried away. Light water would act as a strong neutron moderator and absorber, which would slow the neutrons and shift the reactor away from a fast-spectrum design. A gas coolant, while possible in some designs, has much lower heat capacity and makes heat removal more challenging at reactor scales. Molten salt coolants are used in other reactor concepts and bring different neutron and chemical behaviors that aren’t aligned with maintaining a fast spectrum. So, the commonly used coolant in fast reactors is a liquid metal coolant.

Fast reactors keep neutrons moving fast to sustain the intended spectrum, so the coolant must remove heat without slowing down or absorbing too many neutrons. Liquid metal coolants fit this requirement well: they conduct heat extremely well, have low neutron absorption, and interact weakly with the fast neutrons, so the fast spectrum remains intact while heat is efficiently carried away. Light water would act as a strong neutron moderator and absorber, which would slow the neutrons and shift the reactor away from a fast-spectrum design. A gas coolant, while possible in some designs, has much lower heat capacity and makes heat removal more challenging at reactor scales. Molten salt coolants are used in other reactor concepts and bring different neutron and chemical behaviors that aren’t aligned with maintaining a fast spectrum. So, the commonly used coolant in fast reactors is a liquid metal coolant.