Solution:

• A moderator is a material used in a nuclear reactor to slow down the neutrons produced from fission. By slowing the neutrons down the probability of a neutron interacting with Uranium-235 nuclei is greatly increased thereby maintaining the chain reaction.
• Other moderators include Heavy Water, Beryllium.
• Boron is used to absorb neutrons to control the chain reaction during nuclear fission. It is a control rod.Control rods are used in nuclear reactors to control the fission rate of uranium and plutonium.
• Fluid used to remove heat in a nuclear reactor- Coolant.