View source for Fertile material

{{Short description|Substance that can be converted into material for use in nuclear fission}}
{{Mcn|date=May 2024}}
[[File:Sasahara.svg|thumb|375px|Transmutation flow between <sup>238</sup>U and <sup>245</sup>Cm in [[light water reactor|LWR]].<ref>{{cite journal|title=Neutron and Gamma Ray Source Evaluation of LWR High Burn-up UO2 and MOX Spent Fuels |journal=Journal of Nuclear Science and Technology |volume=41 |issue=4 |pages=448–456 |date=April 2004 |doi=10.3327/jnst.41.448 |author=Sasahara, Akihiro |last2=Matsumura |first2=Tetsuo |last3=Nicolaou |first3=Giorgos |last4=Papaioannou |first4=Dimitri |doi-access=free }}</ref> Speed of transmutation varies greatly by nuclide, and percentages are relative to total transmutation and decay. After removal of fuel from reactor, decay will predominate for shorter-lived isotopes such as <sup>238</sup>Pu, <sup>241</sup>Pu, <sup>242–244</sup>Cm; but <sup>245–248</sup>Cm are all long-lived.]]
'''Fertile material''' is a material that, although not [[nuclear fission|fissile]] itself, can be converted into a [[fissile material]] by [[neutron absorption]].

==Naturally occurring fertile materials==
Naturally occurring fertile materials that can be converted into a fissile material by irradiation in a reactor include:
*[[thorium-232]] which converts into [[uranium-233]]
*[[uranium-234]] which converts into [[uranium-235]]
*[[uranium-238]] which converts into [[plutonium-239]]
Artificial isotopes formed in the reactor which can be converted into [[fissile material]] by one neutron capture include:
*[[plutonium-238]] which converts into [[plutonium-239]]
*[[plutonium-240]] which converts into [[plutonium-241]]
Some other [[actinides]] need more than one neutron capture before arriving at an isotope which is both fissile and long-lived enough to probably be able to capture another neutron and fission instead of decaying.
*[[plutonium-242]] to [[americium]]-243 to [[curium]]-244 to [[curium]]-245
*[[uranium-236]] to [[neptunium]]-237 to [[plutonium-238]] to [[plutonium-239]]
*[[americium]]-241 to [[curium]]-242 to [[curium]]-243 (or, more likely, curium-242 decays to plutonium-238, which also requires one additional neutron to reach a fissile nuclide)

Since these require a total of 3 or 4 thermal neutrons to eventually fission, and a thermal neutron fission generates only about 2 to 3 neutrons, these nuclides represent a net loss of neutrons. A [[subcritical reactor]] operating in the thermal neutron spectrum would have to adjust the strength of the external [[neutron source]] in accordance with the build-up or consumption of such materials. In a [[fast reactor]], those nuclides may require fewer neutrons to achieve fission, as well as producing more neutrons when they do fission. However, there is also the chance of (n,2n) or even (n,3n) "knockout" reactions (an incident fast neutron hits a nucleus and more than one neutron leaves) with fast neutrons which are not possible with thermal neutrons.

==Fissile materials from fertile materials==
A [[fast-neutron reactor]], meaning one with little or no [[neutron moderator]] and hence utilising [[fast neutron]]s, can be configured as a [[breeder reactor]], producing more fissile material than it consumes, using fertile material in a blanket around the core, or contained in special [[fuel rod]]s. Since [[plutonium-238]], [[plutonium-240]] and [[plutonium-242]] are fertile, accumulation of these and other nonfissile isotopes is less of a problem than in [[thermal reactor]]s, which cannot burn them efficiently.  Breeder reactors using thermal-spectrum neutrons are only practical if the [[thorium fuel cycle]] is used, as [[uranium-233]] fissions far more reliably with thermal neutrons than plutonium-239. A [[subcritical reactor]] —regardless of neutron spectrum— can also "breed" fissile nuclides from fertile material, allowing in principle the consumption of very low grade actinides (e.g. Spent [[MOX fuel]] whose plutonium-240 content is too high for use in current critical thermal reactors) without the need for highly enriched material as used in a [[fast breeder reactor]].

==Applications==
Proposed applications for fertile material includes a space-based facility for the manufacture of fissile material for [[spacecraft]] [[nuclear propulsion]]. The facility would notionally transport fertile materials from Earth, safely through the [[atmosphere of Earth|atmosphere]], and locate them at a space facility at the [[Lagrangian point#L1|Earth–Moon L1 Lagrangian]] point where manufacture of fissile material would occur, eliminating the safety risk of transport of fissile materials from Earth.<ref name=dodd2012>{{cite book |doi=10.2514/6.2012-5329 |chapter=SNAP-X: The Space Nuclear Activation Plant |title=AIAA SPACE 2012 Conference & Exposition |year=2012 |last1=Dodd |first1=Jake |last2=Thangavelu |first2=Madhu |isbn=978-1-60086-940-2 }}</ref> While uranium and thorium are [[Lunar habitation#Nuclear power| present on the moon]], they seem to be in more limited supply than on earth, especially near the surface. If [[in situ resource utilization]] is desired to fuel nuclear power plants on the moon, converting fertile material to fissile material could be a way to make the resources last longer and to reduce the need for [[uranium enrichment]] which requires the chemically aggressive volatile [[fluorine]] to prepare [[uranium hexafluoride]] as used in the current enrichment technology.

== References ==

{{Reflist}}

{{Nuclear Technology}}

[[Category:Fertile materials| ]]