Figure 1. A sample of uranium-238, a fertile material.[1]

Fertile is a term used to describe an isotope that is not itself fissile (it cannot simply undergo fission by thermal neutrons), but can be converted into a fissile material through irradiation in a nuclear reactor. After this, the fission of this isotope could undergo radioactive decay.[2] Uranium-238 and thorium-232 are known as fertile materials, and the production of fissile materials from them after capturing a neutron is known as breeding.[3] When these fertile materials capture neutrons, they are converted into fissile plutonium-239 and uranium-233, respectively.[4]

Generally, larger nuclei with even atomic masses (such as thorium-232, plutonium-238, and uranium-238) are fertile materials. When the nuclei absorb a neutron, it induces an odd atomic mass—making it a fissile material.[5] Generally, this absorption results in an energetically unstable product and thus this product undergoes a radioactive decay fairly quickly until it reaches a fissile product that can be used as a nuclear fuel.[5]

Breeder Reactors

There is a special type of reactor that makes use of fertile isotopes to create nuclear fuel. These reactors are known as breeder reactors as they irradiate a fertile isotope inside of the reactor, causing the isotope to absorb a neutron and decay to a fissile isotope. In these reactors, fissile plutonium-239 is generally created by bombarding uranium-238 with neutrons. These reactors create fissile material more quickly than they could use a different fissile material (such as uranium-235) as fuel.[6]

For Further Reading


  1. Wikimedia Commons. (July 6, 2015). Uranium238 [Online]. Available:https://commons.wikimedia.org/wiki/File:Uranium238.jpg#/media/File:Uranium238.jpg
  2. World Nuclear Association. (June 16, 2015). Glossary [Online]. Available: http://www.world-nuclear.org/Nuclear-Basics/Glossary/#F
  3. IEER. (June 16, 2015). Fertile Materials [Online]. Available: http://ieer.org/resource/factsheets/basics-nuclear-physics-fission/
  4. NRC Glossary. (July 6, 2015). Fertile Material [Online]. Available: http://www.nrc.gov/reading-rm/basic-ref/glossary/fertile-material.html
  5. 5.0 5.1 C.Ferguson. Nuclear Energy: What Everyone Needs to Know, 1st ed. Cary, NC, USA: Oxford University Press, USA, 2011.
  6. Hyperphysics. (July 6, 2015). Fast Breeder Reactors [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/fasbre.html

Authors and Editors

Kailyn Stenhouse, Jordan Hanania, Bethel Afework, Jason Donev
Last updated: September 3, 2018
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