Question

what is moderator in nuclear reactor?

Answer 1

 a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235 or a similar fissile nuclide.

Answer 2

hey dear sweet friend here is your answer


In the fission of uranium-235 nuclei, on an average more than 2 neutrons are emitted. These neutrons are energetic. For fission to occur, the neutron needs to be absorbed in uranium-235 nucleus. The probability of absorption of a neutron is much more for thermal neutrons than fast neutrons. For the fission chain reaction to sustaisin, at least one of the neutron emitted in the preceding fission needs to cause further fission by being absorbed. So there is a need to slow down the neutrons emitted in fission. This is done by the moderator. The role of the moderator is to slow down theneutrons emitted in fission in a small number of collisions. Therefore, the moderator needs to a material of aomic weight near to atomic weight of the neutron. A second requirement is that the moderator should have a very low neutron absorption cross-section. Otherwise the neutrons available for fission will decrease. The second requirement rules out ordinary water as moderator. Heavy water fulfills both requirements. Graphite is another substance used as a moderator.


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