Uranium hexafluoride: Difference between revisions

Latest revision as of 12:07, 28 June 2025

Uranium hexafluoride, sometimes called hex, is the inorganic compound with the formula Template:Chem2. Uranium hexafluoride is a volatile, white solid that is used in enriching uranium for nuclear reactors and nuclear weapons.^[1]

Preparation

Uranium dioxide is converted with hydrofluoric acid (HF) to uranium tetrafluoride:^[1]

Template:Chem2

The resulting Template:Chem2 is subsequently oxidized with fluorine to give the hexafluoride:

Template:Chem2

In samples contaminated with uranium trioxide, uranyl fluoride, an oxyfluoride compound is produced in the HF step:

Template:Chem2

which can be fluorinated to produce the same product, uranium hexafluoride.

Template:Chem2

The fluorination step in both reactions above are highly exothermic.

Properties

Physical properties

At atmospheric pressure, Template:Chem2 sublimes at 56.5 °C.^[2]

The solid-state structure was determined by neutron diffraction at 77 K and 293 K.^[3]^[4]^[5]

File:Uranium-hexafluoride-unit-cell-3D-balls.png

Packing of UF₆ in its unit cell.^[6]

Chemical properties

UF₆ reacts with water, releasing hydrofluoric acid. The compound reacts with aluminium, forming a surface layer of [[aluminium fluoride|Template:Chem2]] that resists any further reaction from the compound.

Uranium hexafluoride is a mild oxidant.^[7] It is a Lewis acid as evidenced by its binding to form heptafluorouranate(VI), Template:Chem2.^[8]

Polymeric uranium(VI) fluorides containing organic cations have been isolated and characterized by X-ray diffraction.^[9]

Application in the fuel cycle

File:Uranium hexafluoride phase diagram.gif

Phase diagram of Template:Chem2

As one of the most volatile compounds of uranium, uranium hexafluoride is relatively convenient to process and is used in both of the main uranium enrichment methods, namely gaseous diffusion and the gas centrifuge method. Since the triple point of Template:Chem2; 64 °C(147 °F; 337 K) and 152 kPa (22 psi; 1.5 atm);^[10] is close to ambient conditions, phase transitions can be achieved with little thermodynamic work.

Fluorine has only a single naturally occurring stable isotope, so isotopologues of Template:Chem2 differ in their molecular weight based solely on the uranium isotope present.^[11] This difference is the basis for the physical separation of isotopes in enrichment.

All the other uranium fluorides are nonvolatile solids that are coordination polymers.

The conversion factor for the Template:Chem2 isotopologue of Template:Chem2 ("hex") to "U mass" is 0.676.^[12]

Gaseous diffusion requires about 60 times as much energy as the gas centrifuge process: gaseous diffusion-produced nuclear fuel produces 25 times more energy than is used in the diffusion process, while centrifuge-produced fuel produces 1,500 times more energy than is used in the centrifuge process.

In addition to its use in enrichment, uranium hexafluoride has been used in an advanced reprocessing method (fluoride volatility), which was developed in the Czech Republic. In this process, spent nuclear fuel is treated with fluorine gas to transform the oxides or elemental metals into a mixture of fluorides. This mixture is then distilled to separate the different classes of material. Some fission products form nonvolatile fluorides which remain as solids and can then either be prepared for storage as nuclear waste or further processed either by solvation-based methods or electrochemically.

Uranium enrichment produces large quantities of depleted uranium hexafluoride (DTemplate:Chem2 or D-Template:Chem2) as a waste product. The long-term storage of D-Template:Chem2 presents environmental, health, and safety risks because of its chemical instability. When Template:Chem2 is exposed to moist air, it reacts with the water in the air to produce Template:Chem2 (uranyl fluoride) and HF (hydrogen fluoride) both of which are highly corrosive and toxic. In 2005, about 686,000 tonnes of D-Template:Chem2 was housed in 57,122 storage cylinders located near Portsmouth, Ohio; Oak Ridge, Tennessee; and Paducah, Kentucky.^[13]^[14] Storage cylinders must be regularly inspected for signs of corrosion and leaks. The estimated lifetime of the steel cylinders is measured in decades.^[15]

Accidents and disposal

There have been several accidents involving uranium hexafluoride in the US, including a cylinder-filling accident and material release at the Sequoyah Fuels Corporation in 1986 where an estimated 29,500 pounds of gaseous Template:Chem2 escaped.^[16]^[17] The US government has been converting DTemplate:Chem2 to solid uranium oxides for disposal.^[18] Such disposal of the entire DTemplate:Chem2 stockpile could cost anywhere from $15 million to $450 million.^[19] Script error: No such module "Gallery".

References

Template:Reflist

External links

Template:Subject bar

Simon Cotton (Uppingham School, Rutland, UK): Uranium Hexafluoride.
Uranium Hexafluoride (UF₆) – Physical and chemical properties of UF₆, and its use in uranium processing – Uranium Hexafluoride and Its Properties
Uranium Hexafluoride at WebElements
Import of Western depleted uranium hexafluoride (uranium tails) to Russia [dead link 30 June 2017]

Template:Hexafluorides Template:Uranium compounds Template:Fluorides Template:Actinide halides

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↑ J. C. Taylor, P. W. Wilson, J. W. Kelly: „The structures of fluorides. I. Deviations from ideal symmetry in the structure of crystalline UF₆: a neutron diffraction analysis", Acta Crystallogr., 1973, B29, p. 7–12; Script error: No such module "doi"..
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[UF6_1973-5] J. C. Taylor, P. W. Wilson, J. W. Kelly: „The structures of fluorides. I. Deviations from ideal symmetry in the structure of crystalline UF₆: a neutron diffraction analysis", Acta Crystallogr., 1973, B29, p. 7–12; Script error: No such module "doi"..

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@@ Line 12: / Line 12: @@
 |ImageClass2 = bg-transparent
 |ImageSize2 = 150px
-|IUPACName = Uranium hexafluoride<br>Uranium(VI) fluoride
+|IUPACName = Uranium hexafluoride<br/>Uranium(VI) fluoride
 |Section1={{Chembox Identifiers
 |Abbreviations = hex
@@ Line 34: / Line 34: @@
 |UNII = N06GJ1D94J
 |RTECS = YR4720000
-|UNNumber = 2978 (<1% {{chem2|^{235}U}})<br>2977 (>1% {{chem2|^{235}U}})
+|UNNumber = 2978 (<1% {{chem2|^{235}U}})<br/>2977 (>1% {{chem2|^{235}U}})}}
-}}
 |Section2={{Chembox Properties
 |Formula = {{chem2|UF6}}
@@ Line 78: / Line 77: @@
 |OtherFunction = {{ubl|[[Uranium(III) fluoride]]|[[Uranium(IV) fluoride]]|[[Uranium(V) fluoride]]}}
 |OtherFunction_label = uranium fluorides
- }}
+}}
 }}
-'''Uranium hexafluoride''', sometimes called '''hex''', is the [[inorganic compound]] with the formula {{chem2|UF6|auto=1}}. Uranium hexafluoride is a volatile, white solid that is used in enriching uranium for [[nuclear reactor]]s and [[nuclear weapon]]s.<ref name=Ull/>
+'''Uranium hexafluoride''', sometimes called '''hex''', is the [[inorganic compound]] with the formula {{chem2|UF6|auto=1}}. Uranium hexafluoride is a volatile, white solid that is used in [[uranium enrichment|enriching uranium]] for [[nuclear reactor]]s and [[nuclear weapon]]s.<ref name=Ull />
 ==Preparation==
@@ Line 92: / Line 91: @@
 which can be fluorinated to produce the same product, uranium hexafluoride.
 :{{chem2|UO2F2  + 5 F2  ->  UF6  +  O2}}
-The fluorination step in both reactions above are highly exothermic.
+The fluorination step in both reactions above are highly [[exothermic]].
 ==Properties==
@@ Line 112: / Line 111: @@
 ==Application in the fuel cycle==
 [[File:Uranium hexafluoride phase diagram.gif|thumb|left|250px|[[Phase diagram]] of {{chem2|UF6}}]]
-As one of the most [[volatility (chemistry)|volatile]] compounds of uranium, uranium hexafluoride is relatively convenient to process and is used in both of the main uranium [[nuclear enrichment|enrichment]] methods, namely [[gaseous diffusion]] and the [[gas centrifuge]] method. Since the [[triple point]] of {{chem2|UF6}}; 64 °C(147 °F; 337 K) and 152 kPa (22 psi; 1.5 atm);<ref>{{cite web |title=Uranium Hexafluoride: Source: Appendix A of the PEIS (DOE/EIS-0269): Physical Properties |url=https://web.evs.anl.gov/uranium/guide/ucompound/propertiesu/hexafluoride.cfm |access-date=2022-08-18 |website=web.evs.anl.gov}}</ref> is close to ambient conditions, phase transitions can be achieved with little [[work (thermodynamics)|thermodynamic work]].
+As one of the most [[volatility (chemistry)|volatile]] compounds of uranium, uranium hexafluoride is relatively convenient to process and is used in both of the main [[uranium enrichment]] methods, namely [[gaseous diffusion]] and the [[gas centrifuge]] method. Since the [[triple point]] of {{chem2|UF6}}; 64 °C(147 °F; 337 K) and 152 kPa (22 psi; 1.5 atm);<ref>{{cite web |title=Uranium Hexafluoride: Source: Appendix A of the PEIS (DOE/EIS-0269): Physical Properties |url=https://web.evs.anl.gov/uranium/guide/ucompound/propertiesu/hexafluoride.cfm |access-date=2022-08-18 |website=web.evs.anl.gov}}</ref> is close to ambient conditions, phase transitions can be achieved with little [[work (thermodynamics)|thermodynamic work]].
 Fluorine has only a single naturally occurring stable isotope, so [[isotopologue]]s of {{chem2|UF6}} differ in their molecular weight based solely on the uranium [[isotope]] present.<ref>{{cite web |title=Uranium Enrichment and the Gaseous Diffusion Process |publisher=USEC Inc |url=http://www.usec.com/v2001_02/HTML/Aboutusec_enrichment.asp |access-date=2007-09-24 |url-status=dead |archive-url=https://web.archive.org/web/20071019081831/http://www.usec.com/v2001_02/HTML/Aboutusec_enrichment.asp |archive-date=2007-10-19}}</ref> This difference is the basis for the physical separation of isotopes in enrichment.
@@ Line 131: / Line 130: @@
 In addition to its use in enrichment, uranium hexafluoride has been used in an advanced reprocessing method ([[fluoride volatility]]), which was developed in the [[Czech Republic]]. In this process, [[spent nuclear fuel]] is treated with fluorine gas to transform the oxides or elemental metals into a mixture of fluorides. This mixture is then distilled to separate the different classes of material. Some [[fission product]]s form nonvolatile fluorides which remain as solids and can then either be prepared for storage as nuclear waste or further processed either by [[solvation]]-based methods or [[electrochemistry|electrochemically]].
-Uranium enrichment produces large quantities of [[depleted uranium hexafluoride]] (D{{chem2|UF6}} or D-{{chem2|UF6}}) as a waste product. The long-term storage of D-{{chem2|UF6}} presents environmental, health, and safety risks because of its chemical instability. When {{chem2|UF6}} is exposed to moist air, it reacts with the water in the air to produce {{chem2|UO2F2}} ([[uranyl fluoride]]) and HF ([[hydrogen fluoride]]) both of which are highly corrosive and toxic. In 2005, 686,500 tonnes of D-{{chem2|UF6}} was housed in 57,122 storage cylinders located near [[Portsmouth, Ohio|Portsmouth]], Ohio; [[Oak Ridge, Tennessee|Oak Ridge]], Tennessee; and [[Paducah, Kentucky|Paducah]], Kentucky.<ref>{{cite web |work=Depleted UF<sub>6</sub> FAQs |title=How much depleted uranium hexafluoride is stored in the United States? |url=https://web.evs.anl.gov/uranium/faq/mgmt/faq23.cfm |publisher=[[Argonne National Laboratory]]}}</ref><ref>{{cite web |title=Depleted UF<sub>6</sub> Management Program Documents |url=https://web.evs.anl.gov/uranium/documents/ |access-date=2006-05-17 |url-status=live |archive-url=https://web.archive.org/web/20080216013118/http://web.ead.anl.gov/uranium/documents/index.cfm |archive-date=2008-02-16}}</ref> Storage cylinders must be regularly inspected for signs of corrosion and leaks. The estimated lifetime of the steel cylinders is measured in decades.<ref>{{cite web |publisher=Institute for Energy and Environmental Research |date=2007-09-24 |title=What is DUF<sub>6</sub>? Is it dangerous and what should we do with it? |url=http://www.ieer.org/sdafiles/vol_5/5-2/deararj.html| archive-url=https://web.archive.org/web/20071014065307/http://www.ieer.org/sdafiles/vol_5/5-2/deararj.html| archive-date = 14 October 2007}}</ref>
+Uranium enrichment produces large quantities of [[depleted uranium hexafluoride]] (D{{chem2|UF6}} or D-{{chem2|UF6}}) as a waste product. The long-term storage of D-{{chem2|UF6}} presents environmental, health, and safety risks because of its chemical instability. When {{chem2|UF6}} is exposed to moist air, it reacts with the water in the air to produce {{chem2|UO2F2}} ([[uranyl fluoride]]) and HF ([[hydrogen fluoride]]) both of which are highly corrosive and toxic. In 2005, about 686,000 tonnes of D-{{chem2|UF6}} was housed in 57,122 storage cylinders located near [[Portsmouth, Ohio|Portsmouth]], Ohio; [[Oak Ridge, Tennessee|Oak Ridge]], Tennessee; and [[Paducah, Kentucky|Paducah]], Kentucky.<ref>{{cite web |work=Depleted UF<sub>6</sub> FAQs |title=How much depleted uranium hexafluoride is stored in the United States? |url=https://web.evs.anl.gov/uranium/faq/mgmt/faq23.cfm |publisher=[[Argonne National Laboratory]]}}</ref><ref>{{cite web |title=Depleted UF<sub>6</sub> Management Program Documents |url=https://web.evs.anl.gov/uranium/documents/ |access-date=2006-05-17 |url-status=live |archive-url=https://web.archive.org/web/20080216013118/http://web.ead.anl.gov/uranium/documents/index.cfm |archive-date=2008-02-16}}</ref> Storage cylinders must be regularly inspected for signs of corrosion and leaks. The estimated lifetime of the steel cylinders is measured in decades.<ref>{{cite web |publisher=Institute for Energy and Environmental Research |date=2007-09-24 |title=What is DUF<sub>6</sub>? Is it dangerous and what should we do with it? |url=http://www.ieer.org/sdafiles/vol_5/5-2/deararj.html| archive-url=https://web.archive.org/web/20071014065307/http://www.ieer.org/sdafiles/vol_5/5-2/deararj.html| archive-date = 14 October 2007}}</ref>
 == Accidents and disposal ==
-There have been several accidents involving uranium hexafluoride in the US, including a cylinder-filling accident and material release at the [[Sequoyah Fuels Corporation]] in 1986 where an estimated 29 500 pounds of gaseous {{chem2|UF6}} escaped.<ref>{{cite journal | pmc=1963288 | date=2007 | last1=Brugge | first1=D. | last2=Delemos | first2=J. L. | last3=Bui | first3=C. | title=The Sequoyah Corporation Fuels Release and the Church Rock Spill: Unpublicized Nuclear Releases in American Indian Communities | journal=American Journal of Public Health | volume=97 | issue=9 | pages=1595–1600 | doi=10.2105/AJPH.2006.103044 | pmid=17666688 }}</ref><ref>{{cite web |work=Depleted UF<sub>6</sub> FAQs |title=Have there been accidents involving uranium hexafluoride? |url=http://web.ead.anl.gov/uranium/faq/health/faq30.cfm |publisher=Argonne National Laboratory |archive-url=https://web.archive.org/web/20170609171651/http://web.ead.anl.gov/uranium/faq/health/faq30.cfm |archive-date=2017-06-09}}</ref>  The US government has been converting D{{chem2|UF6}} to solid [[uranium oxides]] for disposal.<ref>{{cite web |work=Depleted UF<sub>6</sub> FAQs |title=What is going to happen to the uranium hexafluoride stored in the United States? |url=https://web.evs.anl.gov/uranium/faq/storage/faq22.cfm |publisher=Argonne National Laboratory}}</ref> Such disposal of the entire D{{chem2|UF6}} stockpile could cost anywhere from $15 million to $450 million.<ref>{{cite web |work=Depleted UF<sub>6</sub> FAQs |title=Are there any currently-operating disposal facilities that can accept all of the depleted uranium oxide that would be generated from conversion of DOE's depleted UF<sub>6</sub> inventory? |url=http://web.evs.anl.gov/uranium/faq/mgmt/faq27.cfm |publisher=Argonne National Laboratory}}</ref>
+There have been several accidents involving uranium hexafluoride in the US, including a cylinder-filling accident and material release at the [[Sequoyah Fuels Corporation]] in 1986 where an estimated 29,500 pounds of gaseous {{chem2|UF6}} escaped.<ref>{{cite journal | pmc=1963288 | date=2007 | last1=Brugge | first1=D. | last2=Delemos | first2=J. L. | last3=Bui | first3=C. | title=The Sequoyah Corporation Fuels Release and the Church Rock Spill: Unpublicized Nuclear Releases in American Indian Communities | journal=American Journal of Public Health | volume=97 | issue=9 | pages=1595–1600 | doi=10.2105/AJPH.2006.103044 | pmid=17666688 }}</ref><ref>{{cite web |work=Depleted UF<sub>6</sub> FAQs |title=Have there been accidents involving uranium hexafluoride? |url=http://web.ead.anl.gov/uranium/faq/health/faq30.cfm |publisher=Argonne National Laboratory |archive-url=https://web.archive.org/web/20170609171651/http://web.ead.anl.gov/uranium/faq/health/faq30.cfm |archive-date=2017-06-09}}</ref>  The US government has been converting D{{chem2|UF6}} to solid [[uranium oxides]] for disposal.<ref>{{cite web |work=Depleted UF<sub>6</sub> FAQs |title=What is going to happen to the uranium hexafluoride stored in the United States? |url=https://web.evs.anl.gov/uranium/faq/storage/faq22.cfm |publisher=Argonne National Laboratory}}</ref> Such disposal of the entire D{{chem2|UF6}} stockpile could cost anywhere from $15 million to $450 million.<ref>{{cite web |work=Depleted UF<sub>6</sub> FAQs |title=Are there any currently-operating disposal facilities that can accept all of the depleted uranium oxide that would be generated from conversion of DOE's depleted UF<sub>6</sub> inventory? |url=http://web.evs.anl.gov/uranium/faq/mgmt/faq27.cfm |publisher=Argonne National Laboratory}}</ref>
 {{Gallery
 |width=250
 |height=180
 |File:UF6 cylinder rupture bw.png
-|Ruptured 14-ton {{chem2|UF6}} shipping cylinder. 1 fatality, dozens injured. ~29500&nbsp;lbs of material released. Sequoyah Fuels Corporation 1986.
+|Ruptured 14-ton {{chem2|UF6}} shipping cylinder. 1 fatality, dozens injured. ~29500&nbsp;lb of material released. Sequoyah Fuels Corporation 1986.
 |File:DUF6 storage yard far.jpg
 |D{{chem2|UF6}} storage yard from afar

Uranium hexafluoride: Difference between revisions

Latest revision as of 12:07, 28 June 2025

Contents

Preparation

Properties

Physical properties

Chemical properties

Application in the fuel cycle

Accidents and disposal

See also

References

Further reading

External links

Navigation menu

Uranium hexafluoride: Difference between revisions

Latest revision as of 12:07, 28 June 2025

Preparation

Properties

Physical properties

Chemical properties

Application in the fuel cycle

Accidents and disposal

See also

References

Further reading

External links

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