Question

Which materials are commonly used as a moderator in a nuclear reactor?

Hint:

These substances slow down fast neutrons so fission can continue in a controlled way.

Answer 1

The correct answer is heavy water and graphite.

A moderator in a nuclear reactor slows down fast neutrons released during fission so they can efficiently cause further fission in uranium or plutonium fuel. Heavy water (deuterium oxide) and graphite are both effective moderators because they slow neutrons without absorbing too many of them.

Heavy water is used in reactors like India's Pressurized Heavy Water Reactors (PHWRs), while graphite has been used in reactors like early British and Soviet designs.