Question

What makes the best moderators in nuclear power plant?

(a) Material with low atomic number

(b) Materials with low atomic mass

(c) Materials with high atomic number

(d) Materials with high mass number

The question was posed to me in my homework.

This intriguing question comes from Nuclear Reactor Components topic in portion Nuclear Power Plant of Energy Engineering

Answer 1

Correct answer is (a) Material with low atomic number

To explain: The moderator slows down the neutrons to thermal energies by collision with inert atoms (scattering). Speed of the neutrons is reduced within a small number of collisions as the moderator possesses a high scattering cross section. Materials with low atomic mass number make best moderators.