Editing Fast-neutron reactor (section)

==Waste recycling==

Fast-neutron reactors can potentially reduce the radiotoxicity of nuclear waste. Each commercial scale reactor would have an annual waste output of a little more than a ton of fission products, plus trace amounts of transuranics if the most highly radioactive components could be recycled. The remaining waste should be stored for about 500 years.<ref name="Hannum">[http://www.nationalcenter.org/NuclearFastReactorsSA1205.pdf Smarter use of Nuclear Waste], by William H. Hannum, Gerald E. Marsh and George S. Stanford, Copyright Scientific American, Dec 2005.</ref>

With fast neutrons, the ratio between [[nuclear cross section|splitting]] and the [[neutron capture|capture]] of [[neutron cross-section|neutrons]] by [[plutonium]] and the [[minor actinide]]s is often larger than when the neutrons are slower, at thermal or near-thermal "epithermal" speeds. Simply put, fast neutrons have a smaller chance of being absorbed by plutonium or uranium, but when they are, they almost always cause a fission.
The transmuted even-numbered actinides (e.g. {{Chem|240|Pu}}, {{Chem|242|Pu}}) split nearly as easily as odd-numbered actinides in fast reactors. After they split, the [[actinide]]s become a pair of "[[nuclear fission product|fission products]]". These elements have less total radiotoxicity. 
Since disposal of the fission products is dominated by the most radiotoxic [[nuclear fission product|fission products]], [[strontium-90]], which has a half life of 28.8 years, and [[caesium-137]], which has a half life of 30.1 years,<ref name="Hannum"/> the result is the reduction of nuclear waste lifetimes from tens of millennia (from transuranic isotopes) to a few centuries. The processes are not perfect, but the remaining transuranics are reduced from a significant problem to a tiny percentage of the total waste, because most transuranics can be used as fuel.

Fast reactors technically solve the "fuel shortage" argument against uranium-fueled reactors without assuming undiscovered reserves, or extraction from dilute sources such as granite or seawater. They permit nuclear fuels to be bred from almost all the actinides, including known, abundant sources of depleted uranium and [[thorium]], and light-water reactor wastes. On average, more neutrons per fission are produced by fast neutrons than from [[thermal neutron]]s. This results in a larger surplus of neutrons beyond those required to sustain the chain reaction. These neutrons can be used to produce extra fuel, or to transmute long half-life waste to less troublesome isotopes, as was done at the [[Phénix]] reactor in [[Marcoule]], [[France]], or some can be used for each purpose. Though conventional [[thermal reactor]]s also produce excess neutrons, fast reactors can produce enough of them to breed more fuel than they consume. Such designs are known as [[fast breeder reactor]]s.<ref name="difference.minaprem.com"/>

In the spent fuel from water moderated reactors, several plutonium isotopes are present, along with the heavier, transuranic elements. [[Nuclear reprocessing]], a complex series of chemical extraction processes, mostly based on the [[PUREX]] process,  can be used to extract the unchanged uranium, the [[fission product]]s, the plutonium, and the heavier elements.<ref>{{cite web|url=https://www.world-nuclear.org/information-library/current-and-future-generation/fast-neutron-reactors.aspx|title=Fast Neutron Reactors |website=www.world-nuclear.org}}</ref> Such waste streams can be divided in categories; 
1) unchanged [[uranium-238]], which is the vast bulk of the material and has a very low radioactivity,
2) a collection of [[fission products]] and 
3) the [[transuranic element]]s.