Question

What are moderators in a nuclear reactor?

Answer 1

The moderator, which is of importance in thermal reactors, is used to moderate, that is, to slow down, neutrons from fission to thermal energies. ... Commonly usedmoderators include regular (light) water (roughly 75% of the world'sreactors), solid graphite (20% ofreactors) and heavy water (5% ofreactors

Answer 2

$\bold\red{\underline{\underline{Moderator:-}}}$

→The most efficient fission reactions occur with slow neutrons. Thus, the fast neutrons ejected during fission must be slowed down by collisions with atoms of comparable mass that do not absorb them. Such materials are called moderators.

→The most commonly used moderators are ordinary water and graphite.

→The most efficient moderator is helium.

→The next most efficient one is heavy water (D20) but this is so expensive that it has been used only in research reactors.

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@swigy