Editing Isotope separation (section)

===Diffusion===
[[File:Gaseous Diffusion (44021367082) (cropped).jpg|thumb|upright=1.2|Gaseous diffusion uses microporous membranes to enrich uranium]]
Often done with gases, but also with liquids, the [[diffusion]] method relies on the fact that in thermal equilibrium, two isotopes with the same energy will have different average velocities. The lighter atoms (or the molecules containing them) will travel more quickly through a membrane, whose pore diameters are not larger than the mean free path length ([[Free molecular flow|Knudsen flow]]). The speed ratio is equal to the inverse square root of the mass ratio, so the amount of separation is small. For example for <sup>235</sup>UF<sub>6</sub> versus <sup>238</sup>UF<sub>6</sub> it is 1.0043. Hence many cascaded stages are needed to obtain high purity. This method is expensive due to the work needed to push gas through a membrane and the many stages necessary, each requiring recompression of the gas.

The first large-scale separation of uranium isotopes was achieved by the United States in large [[gaseous diffusion]] separation plants at [[Clinton Engineering Works]], which were established as part of the [[Manhattan Project]]. These used [[uranium hexafluoride]] gas as the process fluid. Nickel powder and electro-deposited nickel mesh diffusion barriers were pioneered by Edward Adler and Edward Norris.<ref name="Rhodes1986">{{cite book |author=Richard Rhodes |title=The Making of the Atomic Bomb |url=https://archive.org/details/makingofatomicbo00rhod |url-access=registration |access-date=January 17, 2014 |year=1986 |publisher=Simon & Schuster |isbn=978-0-684-81378-3 |page=[https://archive.org/details/makingofatomicbo00rhod/page/494 494]}}</ref> Due to the high energy consumption, enrichment of uranium by diffusion was gradually replaced by more efficient methods. 

The last diffusion plant closed in 2013.<ref>World Nuclear Association, US Nuclear Fuel Cycle, (2015), http://www.world- 

nuclear.org/info/Country-Profiles/Countries-T-Z/USA--Nuclear-Fuel-Cycle/</ref> The [[Paducah Gaseous Diffusion Plant]] was a US government effort to generate highly enriched uranium to power military reactors and create nuclear bombs which led to the establishment of the facility in 1952. Paducah's enrichment was initially kept to low levels, and the facility operated as a "feed facility" for other defence facilities that processed the enriched uranium at [[Oak Ridge National Laboratory]] in [[Oak Ridge, Tennessee]], and [[Portsmouth Gaseous Diffusion Plant]] in [[Piketon, Ohio]]. The goal of Paducah and its sister facility in Piketon was adjusted in the 1960s when they started to enrich uranium for use in commercial nuclear reactors to produce energy.<ref>{{Cite web |title=Paducah |url=https://www.centrusenergy.com/who-we-are/history/gaseous-diffusion-plants/paducah/ |access-date=2023-04-30 |website=Centrus Energy Corp |language=en-US}}</ref>