Table of Contents
Moderators
This page goes hand in hand with the learnings from the fission page!
Learning about fission first will aid in understanding what a moderator is and how it helps run our nuclear reactors.
What is a Moderator?
The power generation in a nuclear reactor begins with the fuel undergoing fission. This is the chain reaction that releases the energy we need. For successful fission reactions to take place, the fast neutrons released by the fuel need to be slowed down. Fast neutrons are less effective at causing fission reactions so need to be moderated to increase their chances of leading to more reactions. The moderator in a nuclear reactor slows down these neutrons.
How do they work?
So why don’t fast neutrons cause more fission reactions? This is similar to what happens in putting when the golf ball moves towards the hole but is moving too quickly to drop in, it will jump straight over or maybe run around the rim.
Moderators slow down the neutrons (golf balls) so they can effectively cause another reaction (drop in the hole) and not just fly straight past another fissionable molecule.
The neutrons will collide with atoms within the moderator at high speeds, and pass some of their energy onto that atom. When the neutron passes some of its energy away, it slows down.
Examples
Bethan Fox
NSAN – GAIN Exam Material
US Department of Energy Office of Scientific and Technical Information, Analysis of essential nuclear reactor materials – Graphite Introduction and History.
United States Nuclear Regulatory Commission https://www.nrc.gov/reading-rm/basic-ref/glossary/moderator.html
WNA – Nuclear Power Reactors https://world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-power-reactors/nuclear-power-reactors.aspx
Graphite: World Nuclear Association, https://world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-power-reactors/nuclear-power-reactors.aspx
Golf: Wikipedia Commons, https://commons.wikimedia.org/wiki/File:Golf_ball_2015.JPG – Licence CC BY 4.0 DEED
PWR: Wikipedia Commons, https://commons.wikimedia.org/wiki/File:Pressurized_Water_Reactor_01.svg – Licence CC BY 4.0 DEED
