|
|
| Line 1: |
Line 1: |
| '''Gaseous diffusion''' is a technology used to produce [[enriched uranium]] by forcing gaseous [[uranium hexafluoride]] (UF<sub>6</sub>) through [[semipermeable membrane]]s. This produces a slight separation between the molecules containing [[uranium-235]] (<sup>235</sup>U) and [[uranium-238]] (<sup>238</sup>U). By use of a large [[cascade (chemical engineering)|cascade]] of many stages, high separations can be achieved. It was the first process to be developed that was capable of producing enriched uranium in industrially useful quantities.
| | Nice to meet you, my name is Refugia. For a while I've been in South Dakota and my parents live close by. What I adore doing is to gather badges but I've been using on new issues recently. In her professional lifestyle she is a payroll clerk but she's always wanted her personal company.<br><br>Also visit my blog :: [http://tinyurl.com/k7cuceb http://tinyurl.com] |
| | |
| Gaseous diffusion was devised by [[Francis Simon]] and [[Nicholas Kurti]] at the [[Clarendon Laboratory]] in 1940, tasked by the [[MAUD Committee]] with finding a method for separating uranium-235 from uranium-238 in order to produce a bomb for the British [[Tube Alloys]] project. The prototype gaseous diffusion equipment itself was manufactured by [[Metropolitan-Vickers]] (MetroVick) at [[Trafford Park]], Manchester, at a cost of £150,000 for four units. This work was later transferred to the United States when the Tube Alloys project became subsumed by the later [[Manhattan Project]].<ref>{{Cite web |title=The Tube Alloys Project |author=Colin Barber |publisher=Rhydymwyn Valley History Society |url=http://www.rhydymwynvalleyhistory.co.uk/}}</ref>
| |
| | |
| ==Background==
| |
| Of the 33 known [[Primordial_nuclide#List_of_radioactive_primordial_nuclides_with_measured_half_lives|radioactive primordial nuclides]], two (<sup>235</sup>U and <sup>238</sup>U) are [[isotopes of uranium]]. These two [[isotope]]s are similar in many ways, except that only <sup>235</sup>U is [[fissile]] (capable of sustaining a [[Chain_reaction#Nuclear_chain_reactions|nuclear chain reaction]] of [[nuclear fission]] with [[Neutron_temperature#Thermal_neutrons|thermal neutrons]]). In fact, <sup>235</sup>U is the only naturally occurring fissile nucleus.<ref name=Cotton2006/> Because [[natural uranium]] is only about 0.72% <sup>235</sup>U by weight, it must be enriched to a concentration of 2–5% to be able to support a continuous nuclear chain reaction<ref name=USNRC/> when normal water is used as the moderator. The product of this enrichment process is called enriched uranium.
| |
| | |
| ==Technology==
| |
| ;Scientific basis
| |
| Gaseous diffusion is based on [[Graham's law]], which states that the rate of [[effusion]] of a gas is inversely proportional to the square root of its [[molecular mass]]. For example, in a box with a semi-permeable membrane containing a mixture of two gases, the lighter molecules will pass out of the container more rapidly than the heavier molecules. The gas leaving the container is somewhat enriched in the lighter molecules, while the residual gas is somewhat depleted. A single container wherein the enrichment process takes place through gaseous diffusion is called a [[Diffuser (thermodynamics)|diffuser]].
| |
| | |
| ;Uranium hexafluoride
| |
| UF<sub>6</sub> is the only compound of uranium sufficiently [[Volatility (chemistry)|volatile]] to be used in the gaseous diffusion process. Fortunately, [[fluorine]] consists of only a single isotope <sup>19</sup>F, so that the 1% difference in molecular weights between <sup>235</sup>UF<sub>6</sub> and <sup>238</sup>UF<sub>6</sub> is due only to the difference in weights of the uranium isotopes. For these reasons, UF<sub>6</sub> is the only choice as a [[Raw material|feedstock]] for the gaseous diffusion process.<ref name=Beaton1962/> UF<sub>6</sub>, a solid at room temperature, [[Sublimation (phase transition)|sublimes]] at 56.5 °C (133 °F) at 1 atmosphere.<ref>http://nuclearweaponarchive.org/Library/Glossary</ref> The triple point is at 64.05 °C and 1.5 bar.<ref>[http://web.ead.anl.gov/uranium/guide/ucompound/propertiesu/hexafluoride.cfm Uranium Hexafluoride: Source: Appendix A of the PEIS (DOE/EIS-0269): Physical Properties]</ref> Applying Graham's Law to uranium hexafluoride:
| |
| | |
| :<math>{\mbox{Rate}_1 \over \mbox{Rate}_2}=\sqrt{M_2 \over M_1}=\sqrt{352.041206 \over 349.034348}=1.004298...</math>
| |
| | |
| where:
| |
| :''Rate<sub>1</sub>'' is the rate of effusion of <sup>235</sup>UF<sub>6</sub>.
| |
| :''Rate<sub>2</sub>'' is the rate of effusion of <sup>238</sup>UF<sub>6</sub>.
| |
| :''M<sub>1</sub>'' is the [[molar mass]] of <sup>235</sup>UF<sub>6</sub> = 235.043930 + 6 × 18.998403 = 349.034348 g·mol<sup>−1</sup>
| |
| :''M<sub>2</sub>'' is the molar mass of <sup>238</sup>UF<sub>6</sub> = 238.050788 + 6 × 18.998403 = 352.041206 g·mol<sup>−1</sup>
| |
| | |
| This explains the 0.4% difference in the average velocities of <sup>235</sup>UF<sub>6</sub> molecules over that of <sup>238</sup>UF<sub>6</sub> molecules.<ref>{{cite web|url = http://www.globalsecurity.org/wmd/intro/u-gaseous.htm|title = Gaseous Diffusion Uranium Enrichment|date = April 27, 2005|accessdate = November 21, 2010|publisher = GlobalSecurity.org}}</ref>
| |
| | |
| UF<sub>6</sub> is a highly [[corrosive substance]]. It is an [[oxidant]]<ref name=Olah1978/> and a [[Lewis acids and bases|Lewis acid]] which is able to bind to [[fluoride]], for instance the [[Reactivity (chemistry)|reaction]] of [[copper(II) fluoride]] with uranium hexafluoride in [[acetonitrile]] is reported to form copper(II) heptafluorouranate(VI), Cu(UF<sub>7</sub>)<sub>2</sub>.<ref name=Berry1976/> It reacts with water to form a solid compound, and is very difficult to handle on an industrial scale.<ref name=Beaton1962/> As a consequence, internal gaseous pathways must be fabricated from [[austenitic stainless steel]] and other [[Austempering|heat-stabilized]] metals. Non-reactive [[fluoropolymer]]s such as [[Polytetrafluoroethylene|Teflon]] must be applied as a [[coating]] to all [[valve]]s and [[Seal (mechanical)|seals]] in the system.
| |
| | |
| ;Barrier materials
| |
| Gaseous diffusion plants typically use aggregate barriers (porous membranes) constructed of [[Sintering|sintered]] nickel or [[Aluminium|aluminum]], with a pore size of 10–25 [[Nanometre|nanometers]] (this is less than one-tenth the [[mean free path]] of the UF<sub>6</sub> molecule).<ref name=Cotton2006/><ref name=Beaton1962/> They may also use film-type barriers, which are made by boring pores through an initially nonporous medium. One way this can be done is by removing one constituent in an alloy, for instance using [[hydrogen chloride]] to remove the [[zinc]] from silver-zinc (Ag-Zn).
| |
| | |
| ;Energy requirements
| |
| Because the molecular weights of <sup>235</sup>UF<sub>6</sub> and <sup>238</sup>UF<sub>6</sub> are nearly equal, very little separation of the <sup>235</sup>U and <sup>238</sup>U is effected by a single pass through a barrier, that is, in one diffuser. It is therefore necessary to connect a great many diffusers together in a sequence of stages, using the outputs of the preceding stage as the inputs for the next stage. Such a sequence of stages is called a ''cascade''. In practice, diffusion cascades require thousands of stages, depending on the desired level of enrichment.<ref name=Beaton1962/>
| |
| | |
| All components of a diffusion [[Chemical plant|plant]] must be maintained at an appropriate temperature and pressure to assure that the UF<sub>6</sub> remains in the gaseous phase. The gas must be compressed at each stage to make up for a loss in pressure across the diffuser. This leads to [[Adiabatic_process#Adiabatic_heating_and_cooling|compression heating]] of the gas, which then must be cooled before entering the diffuser. The requirements for pumping and cooling make diffusion plants enormous consumers of [[electric power]]. Because of this, gaseous diffusion is the most expensive method currently used for producing enriched uranium.<ref name=Silex2008/>
| |
| | |
| ==History==
| |
| Scientists working on the Manhattan Project in [[Oak Ridge, Tennessee]], developed several different methods for the [[isotope separation|separation of isotopes]] of uranium. Three of these methods were used sequentially at three different plants in Oak Ridge to produce the <sup>235</sup>U for "[[Little Boy]]" and other [[Gun-type fission weapon|early nuclear weapons]]. In the first step, the [[S-50 (Manhattan Project)|S-50]] uranium enrichment facility used the [[Enriched_uranium#Thermal_diffusion|thermal diffusion]] process to enrich the uranium from 0.7% up to nearly 2% <sup>235</sup>U. This product was then fed into the gaseous diffusion process at the [[K-25]] plant, the product of which was around 23% <sup>235</sup>U. Finally, this material was fed into [[calutron]]s at the [[Y-12 National Security Complex|Y-12]]. These machines (a type of [[particle accelerator]] or [[cyclotron]]) employed [[Enriched_uranium#Electromagnetic_isotope_separation|electromagnetic isotope separation]] to boost the final <sup>235</sup>U concentration to about 84%.
| |
| | |
| The preparation of UF<sub>6</sub> feedstock for the K-25 gaseous diffusion plant was the first ever application for commercially produced fluorine, and significant obstacles were encountered in the handling of both fluorine and UF<sub>6</sub>. For example, before the K-25 gaseous diffusion plant could be built, it was first necessary to develop non-reactive [[chemical compound]]s that could be used as coatings, [[lubricant]]s and [[gasket]]s for the surfaces that would come into contact with the UF<sub>6</sub> gas (a highly reactive and corrosive substance). Scientists of the Manhattan Project recruited [[William T. Miller]], a professor of [[organic chemistry]] at [[Cornell University]], to [[chemical synthesis|synthesize]] and develop such materials, because of his expertise in [[organofluorine chemistry]]. Miller and his team developed several novel non-reactive [[chlorofluorocarbon]] [[polymer]]s that were used in this application.<ref name=obituary/>
| |
| | |
| Calutrons were inefficient and expensive to build and operate. As soon as the engineering obstacles posed by the gaseous diffusion process had been overcome and the gaseous diffusion cascades began operating at Oak Ridge in 1945, all of the calutrons were shut down.<ref name=WND2001/> The gaseous diffusion technique then became the preferred technique for producing enriched uranium.<ref name=Cotton2006/>
| |
| | |
| At the time of their construction in the early 1940s, the gaseous diffusion plants were some of the largest buildings ever constructed.{{citation needed|date=November 2010}} Large gaseous diffusion plants were constructed by the United States, the [[Soviet Union]] (including a plant that is now in [[Kazakhstan]]), the [[United Kingdom]], [[France]], [[China]], and [[South Africa]]. Most of these have now closed or are expected to close, unable to compete economically with newer enrichment techniques. However some of the technology used in pumps and membranes still remains top secret, and some of the materials that were used remain subject to export controls, as a part of the continuing effort to control [[nuclear proliferation]].
| |
| | |
| ==Current status==
| |
| In 2008, gaseous diffusion plants in the United States and France still generated 33% of the world's enriched uranium.<ref name=Silex2008/> However the French one definitively closed in May 2012,<ref>[http://areva.com/EN/operations-887/tricastin-site-the-georges-besse-ii-enrichment-plant.html Aravea : Tricastin site: the Georges Besse II enrichment plant] ''Gaseous diffusion, which was used by AREVA at the Georges Besse plant until May 2012''</ref> and in 2013 the [[Paducah Gaseous Diffusion Plant]] in Kentucky, operated by the [[United States Enrichment Corporation]] (USEC) and currently the last fully functioning uranium enrichment facility in the United States to employ the gaseous diffusion process<ref name=USNRC/>{{ref|http://atomicinsights.com/2011/05/mcconnell-asks-doe-to-keep-using-60-year-old-enrichment-plant-to-save-jobs.html}}, is also planned to close in 2013.<ref>[http://epa.gov/region4/superfund/sites/fedfacs/pgasdifky.html U.S. DOE Gaseous Diffusion Plant] ''Operation of the GDP by USEC is slated to cease in or around 2013''</ref> The only other such facility in the United States, the [[Portsmouth Gaseous Diffusion Plant]] in Ohio, ceased enrichment activities in 2001.<ref name=USNRC/><ref name=USECOverview/><ref name=USECHistory/> Since 2010, the Ohio site is now used mainly by [[Areva|AREVA]], a French [[Conglomerate (company)|conglomerate]], for the conversion of depleted UF<sub>6</sub> to [[uranium oxide]].<ref name=NPN2010/><ref name=AREVA/>
| |
| | |
| As existing gaseous diffusion plants became obsolete, they were replaced by second generation [[gas centrifuge]] technology, which requires far less electric power to produce equivalent amounts of separated uranium. AREVA replaced its Georges Besse gaseous diffusion plant with the Georges Besse II centrifuge plant.{{ref|http://nuclearstreet.com/nuclear_power_industry_news/b/nuclear_power_news/archive/2010/12/15/areva_1920_s-georges-besse-ii-plant-starts-uranium-enrichment-process-121504.aspx}}
| |
| | |
| ==See also==
| |
| * [[Capenhurst]]
| |
| * [[Fick's laws of diffusion]]
| |
| * [[K-25]]
| |
| * [[Lanzhou]]
| |
| * [[Marcoule]]
| |
| * [[Molecular diffusion]]
| |
| * [[Nuclear fuel cycle]]
| |
| * [[Thomas Graham (chemist)]]
| |
| * [[Tomsk]]
| |
| | |
| ==References==
| |
| {{Reflist|colwidth=30em|refs=
| |
| | |
| <ref name=AREVA>{{cite web|title=DOE Gives AREVA Joint Venture Permission to Begin Operational Testing of New Ohio Facility|author=AREVA, Inc.|work=Press Release|publisher=AREVA, Inc.|location=Bethesda, Maryland|year=2010|url=http://us.areva.com/home/liblocal/docs/Press%20releases/2010/AREVA_DOE%20Grants%20Permission%20to%20AREVA_PR_6%2017%2010.pdf|accessdate=2010-11-20}}</ref>
| |
| | |
| <ref name=Beaton1962>{{cite journal|author=Beaton L|title=The slow-down in nuclear explosive production|journal=[[New Scientist]]|volume=16|issue=309|pages=141–3|year=1962|pmid=|doi=|url=http://books.google.com/?id=pp8mxf-9E_sC&pg=PA141&lpg=PA141&dq=%22The+slow-down+in+nuclear+explosive+production%22#v=onepage&q=%22The%20slow-down%20in%20nuclear%20explosive%20production%22&f=false|accessdate=2010-11-20}}</ref>
| |
| | |
| <ref name=Berry1976>{{cite journal|author=Berry JA, Poole RT, Prescott A, Sharp DWA, Winfield JM|title=The oxidising and fluoride ion acceptor properties of uranium hexafluoride in acetonitrile|journal=[[Dalton Transactions|Journal of the Chemical Society, Dalton transactions]]|volume=|issue=3|pages=272–4|year=1976|pmid=|doi=10.1039/DT9760000272}}</ref>
| |
| | |
| <ref name=Cotton2006>{{cite book|title=Lanthanide and actinide chemistry|edition=1st|chapter=Uranium hexafluoride and isotope separation|pages=163–5|author=Cotton S|publisher=John Wiley and Sons, Ltd.|location=Chichester, West Sussex, England|year=2006|isbn=978-0-470-01006-8|url=http://books.google.com/?id=SvAbtU6XvzgC&pg=PA164&lpg=PA164&dq=%22Graham's+law%22+%22uranium+enrichment%22#v=onepage&q=%22Graham's%20law%22%20%22uranium%20enrichment%22&f=false|accessdate=2010-11-20}}</ref>
| |
| | |
| <ref name=NPN2010>{{cite news|title=AREVA Starts Operations at the Portsmouth Facility|author=Tom Lamar|newspaper=Nuclear Power Industry News|publisher=Nuclear Street|location=Waynesboro, Virginia|date=September 10, 2010|url=http://nuclearstreet.com/nuclear_power_industry_news/b/nuclear_power_news/archive/2010/09/10/areva-starts-operations-at-the-portsmouth-facility.aspx|accessdate=2010-11-20}}</ref>
| |
| | |
| <ref name=obituary>{{cite web|author=Blaine P. Friedlander, Jr.|title=William T. Miller, Manhattan Project scientist and Cornell professor of chemistry, dies at 87|work=[[Cornell Chronicle|Cornell News]]|publisher=Cornell University|location=Ithaca, New York|date=3 December 1998|url=http://www.news.cornell.edu/releases/Nov98/Millerobit.bpf.html|accessdate=2010-11-20}}</ref>
| |
| | |
| <ref name=Olah1978>{{cite journal|author=Olah GH, Welch J|title=Synthetic methods and reactions. 46. Oxidation of organic compounds with uranium hexafluoride in haloalkane solutions|journal=[[Journal of the American Chemical Society]]|volume=100|issue=17|pages=5396–402|year=1978|pmid=|doi=10.1021/ja00485a024}}</ref>
| |
| | |
| <ref name=Silex2008>{{cite web|title=Lodge Partners Mid-Cap Conference|author=Michael Goldsworthy|publisher=Silex Ltd.|location=Lucas Heights, New South Wales, Australia|year=2008|url=http://www.asx.com.au/asxpdf/20080410/pdf/318j6y3ctrzwqf.pdf|accessdate=2010-11-20}}</ref>
| |
| | |
| <ref name=USECHistory>{{cite web|title=History: Paducah Gaseous Diffusion Plant|author=United States Enrichment Corporation|work=Gaseous Diffusion Plants|publisher=USEC, Inc.|location=Bethesda, Maryland|year=2009|url=http://www.usec.com/gaseousdiffusion_pad_history.htm|accessdate=2010-11-20}}</ref>
| |
| | |
| <ref name=USECOverview>{{cite web|title=Overview: Portsmouth Gaseous Diffusion Plant|author=United States Enrichment Corporation|authorlink=United States Enrichment Corporation|work=Gaseous Diffusion Plants|publisher=USEC, Inc.|location=Bethesda, Maryland|year=2009|url=http://www.usec.com/gaseousdiffusion_ports_overview.htm|accessdate=2010-11-20}}</ref>
| |
| | |
| <ref name=USNRC>{{cite web|title=Fact Sheet on Gaseous Diffusion|author=U.S. Nuclear Regulatory Commission|authorlink=Nuclear Regulatory Commission|publisher=U.S. Nuclear Regulatory Commission|location=Washington, DC|year=2009|url=http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/gaseous-diffusion.html|accessdate=2010-11-20}}</ref>
| |
| | |
| <ref name=WND2001>{{cite news|title=Get Saddam: any excuse will do|author=Gordon Prather|newspaper=[[WorldNetDaily]]|publisher=WorldNetDaily.com, Inc.|location=Washington, DC|date=2001-12-08|url=http://worldnetdaily.com/news/article.asp?ARTICLE_ID=25608|accessdate=2010-11-20}}</ref>
| |
| | |
| }}
| |
| | |
| ==External links==
| |
| * [http://alsos.wlu.edu/qsearch.aspx?browse=science/Gaseous+Diffusion Annotated references on gaseous diffusion from the Alsos Library]
| |
| | |
| {{DEFAULTSORT:Gaseous Diffusion}}
| |
| [[Category:Isotope separation]]
| |
| [[Category:Uranium]]
| |
| [[Category:Membrane technology]]
| |
Nice to meet you, my name is Refugia. For a while I've been in South Dakota and my parents live close by. What I adore doing is to gather badges but I've been using on new issues recently. In her professional lifestyle she is a payroll clerk but she's always wanted her personal company.
Also visit my blog :: http://tinyurl.com