The function of a moderator is to?

What is Nuclear Reactor? 

It operates on the controlled chain reaction theory and gives off energy steadily. The moderator’s job is to slow down the fission-generated secondary neutrons, which are created quickly. The moderator should be made of a light substance that does not absorb neutrons. Typical moderators include heavy water, graphite, deuterium, paraffin, and others. Protons are abundant in these moderators. Rapidly travelling neutrons are slowed down when they come into direct contact with the protons of materials that act as moderators. These neutrons are referred to be thermal neutrons because they trigger the fuel’s U235 to fission.

Heat generation

The reactor core generates heat in numerous ways:

• The fission product’s kinetic energy is transformed to thermal energy when the nuclei collide with atoms nearby.
• The reactor absorbs the gamma rays which are produced during fission and transforms their energy to heat.
• By radioactive decay of fission products, heat is produced, and materials are activated by neutron absorption. This decay heat source will stay for a little time after the reactor is shut down.

Summary:

The function of a moderator is to? (A) Slow down the neutrons (B) Extract the heat (C) Reflect back some of the neutrons (D) Start the reactor

A moderator’s job is to slow down the neutrons. It functions as a system for initiating, sustaining, and managing nuclear reactions. All these activities are related to the the Nuclear Reactors.