What is a coolant in a nuclear reactor?

• A. The medium used to remove heat from the reactor core and prevent overheating
• B. A device to control neutron speed
• C. A material used to slow down neutrons
• D. A substance used to generate steam directly in the core

Answer: (A)

The coolant is the fluid or gas that carries away the heat produced in the reactor core to prevent overheating. As fission heats the fuel, the coolant flows through the core, absorbs that energy, and transports it to a heat exchanger or steam generator. There, the heat is transferred to a secondary loop to generate steam and drive turbines. This keeps the fuel and cladding within safe temperatures. The coolant’s properties—high heat capacity, high operating temperature, chemical compatibility, and often low neutron absorption—are chosen to maximize efficient heat removal. In some designs, the same fluid also acts as a neutron moderator (like in light-water reactors), but its primary role is heat removal. The other descriptions refer to neutron-control devices, materials that slow neutrons, or direct in-core steam generation, which are not the coolant’s main function.