Moderators in Nuclear Reactors

Moderators are materials that are used in nuclear reactors to slow down the speed of neutrons. This is important because neutrons that are moving too quickly are less likely to interact with atoms in the reactor, and if they do interact, they are more likely to cause fission without producing additional neutrons. The goal of a nuclear reactor is to sustain a chain reaction, in which each fission event produces additional neutrons that can cause further fission. Slowing down the neutrons increases the likelihood of interaction and increases the number of neutrons produced, keeping the chain reaction going.

Two Common Moderators

There are several materials that can be used as moderators in a nuclear reactor, but two of the most common are graphite and heavy water.

- Graphite: Graphite is a form of carbon that is commonly used as a moderator in nuclear reactors. It is an excellent moderator because it slows down neutrons without absorbing them, which means that the neutrons can continue to cause fission in the reactor.
- Heavy Water: Heavy water is a form of water in which the hydrogen atoms are replaced with deuterium, a heavier isotope of hydrogen. Heavy water is also an excellent moderator because it slows down neutrons without absorbing them. In addition, heavy water is a good coolant, which means it can help remove heat from the reactor.

Function of the Moderator

The function of the moderator is to slow down neutrons so that they are more likely to interact with atoms in the reactor and cause fission. The moderator does not absorb neutrons or cool the reactor, although some moderators may also have cooling properties. By slowing down neutrons, the moderator helps to sustain the chain reaction in the reactor, which is necessary for the production of nuclear energy.