Which component in a nuclear reactor is responsible for slowing down fast-moving neutrons?

The component responsible for slowing down fast-moving neutrons in a nuclear reactor is the moderator. The role of the moderator is crucial as it allows thermal neutrons to be produced, which are more likely to induce fission in nuclear fuel such as uranium-235 or plutonium-239.

When fast neutrons collide with the nuclei of the atoms in the moderator, they lose kinetic energy and slow down, making them more effective at causing fission reactions. Common materials used as moderators include water, heavy water, and graphite. The effectiveness of the moderator directly impacts the efficiency of the nuclear reaction and the overall operation of the reactor.

In contrast, control rods primarily serve to absorb neutrons and regulate the fission process by controlling the number of neutrons available for sustaining the chain reaction. Coolant is used to remove heat generated from the fission reaction to keep the reactor at safe operating temperatures, while fuel rods contain the fissile material that undergoes fission. Each of these components plays a specific role, but it is the moderator that specifically slows down the fast neutrons, making the thermally slowed neutrons capable of sustaining a controlled chain reaction.