Question
Heavy water is used as a moderator in a nuclear reactor. The function of the moderator is
A.
to control energy released in the reactor
B.
to absorb neutrons and stop chain reaction
C.
to cool the reactor
D.
to slow down the neutrons to thermal energies
Answer :
to slow down the neutrons to thermal energies
Solution :
The function of a moderator is to slow down the fast moving secondary neutrons produced during the fission as fission reaction can only be initiated by slow moving neutrons.
The material of moderator should be light and it should not absorb neutrons. Usually, heavy water, graphite, deuterium, paraffin etc. can act as moderators. These moderators are rich in protons.