Uranium hexafluoride

Uranium hexafluoride
Names
	IUPAC names Uranium hexafluoride; Uranium(VI) fluoride
Identifiers
CAS Number	7783-81-5;
3D model (JSmol)	Interactive image;
Abbreviations	hex
ChEBI	CHEBI:30235;
ChemSpider	22966;
ECHA InfoCard	100.029.116
EC Number	232-028-6;
Gmelin Reference	2923
PubChemCID	24560;
RTECS number	YR4720000;
UNII	N06GJ1D94J;
UN number	2978 (<1%235U); 2977 (>1%235U)
CompTox Dashboard(EPA)	DTXSID4074566;
	InChI InChI=1S/6FH.U/h61H;/q;;;;;;+6/p-6 Key: SANRKQGLYCLAFE-UHFFFAOYSA-H; InChI=1/6FH.U/h61H;/q;;;;;;+6/p-6/rF6U/c1-7(2,3,4,5)6 Key: SANRKQGLYCLAFE-IIYYNVFAAT;
	SMILES F[U](F)(F)(F)(F)F;
Properties
Chemical formula	UF6
Molar mass	352.02 g/mol
Appearance	Colorless solid
Density	5.09g/cm3,solid
Boiling point	56.5 °C (133.7 °F; 329.6 K) (sublimes, at atmospheric pressure)
Solubility in water	Hydrolyzes
Solubility	Soluble inchloroform,CCl4,liquidchlorine,andbromine; Dissolves innitrobenzene; 151kPa;
Structure
Crystal structure	Orthorhombic,oP28
Space group	Pnma, No. 62
Coordination geometry	Octahedral (Oh)
Dipole moment	0
Thermochemistry
Std molar; entropy(S⦵298)	Solid, 227.8±1.3J·K−1·mol−1; Gaseous, 377.8±1.3J·K−1·mol−1;
Std enthalpy of; formation(ΔfH⦵298)	Solid, −2197.7±1.8kJ·mol−1; Gaseous, −2148.1±1.8kJ·mol−1;
Hazards
	Occupational safety and health(OHS/OSH):
Main hazards	Toxic, corrosive, radioactive
	GHSlabelling:
Pictograms
Signal word	Danger
Hazard statements	H300,H330,H373,H411
NFPA 704(fire diamond)	4 0 2 W; OX
Flash point	Non-flammable
Safety data sheet(SDS)	ICSC 1250
Related compounds
Otheranions	Uranium hexachloride
Othercations	Neptunium hexafluoride; Plutonium hexafluoride; Americium hexafluoride; Curium hexafluoride; Tungsten hexafluoride;
Related uranium fluorides	Uranium(III) fluoride; Uranium(IV) fluoride; Uranium(V) fluoride;
	Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa). verify(what is?) Infobox references

Uranium hexafluoride,sometimes calledhex,is aninorganic compoundwith the formulaU F₆.Uranium hexafluoride is a volatile and toxic white solid thatreacts with water,releasing corrosivehydrofluoric acid.The compound reacts mildly withaluminium,forming a thin surface layer ofAlF₃that resists any further reaction from the compound.UF₆is used in the process ofenriching uranium,which produces fuel fornuclear reactorsandnuclear weapons.

Preparation[edit]

Milled uranium ore—U₃O₈or "yellowcake"—is dissolved innitric acid,yielding a solution ofuranyl nitrateUO₂(NO₃)₂.Pure uranyl nitrate is obtained bysolvent extraction,then treated withammoniato produceammonium diuranate( "ADU",[NH₄]₂U₂O₇). Reduction withhydrogengivesUO₂,which is converted withhydrofluoric acid(HF) touranium tetrafluoride,UF₄.Oxidation withfluorineyieldsUF₆.

TheHoneywell Uranium Hexafluoride Processing Facilityuses a different process.

Duringnuclear reprocessing,uranium is reacted withchlorine trifluorideto giveUF₆:

U + 2 ClF₃→ UF₆+ Cl₂

Properties[edit]

Physical properties[edit]

Atatmospheric pressure,UF₆sublimesat 56.5 °C.^[4]

The solid-state structure was determined byneutron diffractionat 77 K and 293 K.^[5]^[6]

Ball-and-stick modelof the unit cell of uranium hexafluoride^[7]
Bond lengths and angles of gaseous uranium hexafluoride^[8]

Chemical properties[edit]

It has been shown that uranium hexafluoride is anoxidant^[9]and aLewis acidthat is able to bind tofluoride;for instance, the reaction ofcopper(II) fluoridewith uranium hexafluoride inacetonitrileis reported to form copper(II) heptafluorouranate(VI),Cu²⁺[UF−7]₂.^[10]

Polymericuranium(VI) fluorides containing organic cations have been isolated and characterized by X-ray diffraction.^[11]

Application in the fuel cycle[edit]

As one of the mostvolatilecompounds of uranium, uranium hexafluoride is relatively convenient to process and is used in both of the main uraniumenrichmentmethods, namelygaseous diffusionand thegas centrifugemethod. Since thetriple pointofUF₆;64 °C(147 °F; 337 K) and 152 kPa (22 psi; 1.5 atm);^[12]is close to ambient conditions, phase transitions can be achieved with littlethermodynamic work.

Fluorine has only a single naturally occurring stable isotope, soisotopologuesofUF₆differ in their molecular weight based solely on the uraniumisotopepresent.^[13]This difference is the basis for the physical separation of isotopes in enrichment.

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

The conversion factor for the²³⁸Uisotopologue ofUF₆( "hex" ) to "U mass" is 0.676.^[14]

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 theCzech Republic.In this process,spent nuclear fuelis 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. Somefission productsform nonvolatile fluorides which remain as solids and can then either be prepared for storage as nuclear waste or further processed either bysolvation-based methods orelectrochemically.

Uranium enrichment produces large quantities ofdepleted uranium hexafluoride(DUF₆or D-UF₆) as a waste product. The long-term storage of D-UF₆presents environmental, health, and safety risks because of its chemical instability. WhenUF₆is exposed to moist air, it reacts with the water in the air to produceUO₂F₂(uranyl fluoride) and HF (hydrogen fluoride) both of which are highly corrosive and toxic. In 2005, 686,500 tonnes of D-UF₆was housed in 57,122 storage cylinders located nearPortsmouth, Ohio;Oak Ridge, Tennessee;andPaducah, Kentucky.^[15]^[16]Storage cylinders must be regularly inspected for signs of corrosion and leaks. The estimated lifetime of the steel cylinders is measured in decades.^[17]

Accidents and disposal[edit]

There have been several accidents involving uranium hexafluoride in the US, including a cylinder-filling accident and material release at theSequoyah Fuels Corporationin 1986 where an estimated 29 500 pounds of gaseousUF₆escaped.^[18]^[19]The U.S. government has been converting DUF₆to soliduranium oxidesfor disposal.^[20]Such disposal of the entire DUF₆stockpile could cost anywhere from $15 million to $450 million.^[21]

Ruptured 14-tonUF₆shipping cylinder. 1 fatality, dozens injured. ~29500 lbs of material released. Sequoyah Fuels Corporation 1986.
DUF₆storage yard from afar
DUF₆cylinders: painted (left) and corroded (right)

References[edit]

^"Uranium Hexafluoride".Archived fromthe originalon 2013-09-16.Retrieved2013-08-08.
^^a ^b ^c ^dJohnson, Gerald K. (1979). "The Enthalpy of Formation of Uranium Hexafluoride".The Journal of Chemical Thermodynamics.11(5): 483–490.doi:10.1016/0021-9614(79)90126-5.
^Uranium(VI) fluoride
^Brickwedde, Ferdinand G.; Hoge, Harold J.; Scott, Russell B. (1948)."The Low Temperature Heat Capacities, Enthalpies, and Entropies of UF₄and UF₆".J. Chem. Phys.16(5): 429–436.Bibcode:1948JChPh..16..429B.doi:10.1063/1.1746914.
^J. H. Levy; John C. Taylor; Paul W. Wilson (1976). "Structure of Fluorides. Part XII. Single-Crystal Neutron Diffraction Study of Uranium Hexafluoride at 293 K".J. Chem. Soc., Dalton Trans.(3): 219–224.doi:10.1039/DT9760000219.
^J. H. Levy, J. C. Taylor and A. B. Waugh (1983). "Neutron Powder Structural Studies of UF₆,MoF₆and WF₆at 77 K ".Journal of Fluorine Chemistry.23:29–36.doi:10.1016/S0022-1139(00)81276-2.
^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;doi:10.1107/S0567740873001895.
^Kimura, Masao; Schomaker, Werner; Smith, Darwin W.; Bernard (1968)."Electron-Diffraction Investigation of the Hexafluorides of Tungsten, Osmium, Iridium, Uranium, Neptunium, and Plutonium".J. Chem. Phys.48(8): 4001–4012.Bibcode:1968JChPh..48.4001K.doi:10.1063/1.1669727.Archived fromthe originalon 2023-01-11.Retrieved2020-10-10.
^G. H. Olah; J. Welch (1978). "Synthetic methods and reactions. 46. Oxidation of organic compounds with uranium hexafluoride in haloalkane solutions".J. Am. Chem. Soc.100(17): 5396–5402.doi:10.1021/ja00485a024.
^J. A. Berry; R. T. Poole; A. Prescott; D. W. A. Sharp; J. M. Winfield (1976). "The oxidising and fluoride ion acceptor properties of uranium hexafluoride in acetonitrile".J. Chem. Soc., Dalton Trans.(3): 272–274.doi:10.1039/DT9760000272.
^S. M. Walker; P. S. Halasyamani; S. Allen; D. O'Hare (1999). "From Molecules to Frameworks: Variable Dimensionality in the UO₂(CH₃COO)₂·2H₂O/HF(aq)/Piperazine System. Syntheses, Structures, and Characterization of Zero-Dimensional (C₄N₂H₁₂)UO₂F₄·3H₂O, One-Dimensional (C₄N₂H₁₂)₂U₂F₁₂·H₂O, Two-Dimensional (C₄N₂H₁₂)₂(U₂O₄F₅)₄·11H₂O, and Three-Dimensional (C₄N₂H₁₂)U₂O₄F₆".J. Am. Chem. Soc.121(45): 10513–10521.doi:10.1021/ja992145f.
^"Uranium Hexafluoride: Source: Appendix A of the PEIS (DOE/EIS-0269): Physical Properties".web.evs.anl.gov.Retrieved2022-08-18.
^"Uranium Enrichment and the Gaseous Diffusion Process".USEC Inc. Archived fromthe originalon 2007-10-19.Retrieved2007-09-24.
^"Unit converter molar mass calculator".TranslatorsCafé.Mississauga, Ontario, Canada: ANVICA Software Development. 1 February 2021.
^"How much depleted uranium hexafluoride is stored in the United States?".Depleted UF₆FAQs.Argonne National Laboratory.
^"Depleted UF₆Management Program Documents ".Archivedfrom the original on 2008-02-16.Retrieved2006-05-17.
^"What is DUF₆?Is it dangerous and what should we do with it? ".Institute for Energy and Environmental Research. 2007-09-24.
^Brugge, D.; Delemos, J. L.; Bui, C. (2007)."The Sequoyah Corporation Fuels Release and the Church Rock Spill: Unpublicized Nuclear Releases in American Indian Communities".American Journal of Public Health.97(9): 1595–1600.doi:10.2105/AJPH.2006.103044.PMC1963288.PMID 17666688.
^ "Have there been accidents involving uranium hexafluoride?".Depleted UF₆FAQs.Argonne National Laboratory. Archived fromthe originalon 2017-06-09.
^"What is going to happen to the uranium hexafluoride stored in the United States?".Depleted UF₆FAQs.Argonne National Laboratory.
^"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 UF₆inventory? ".Depleted UF₆FAQs.Argonne National Laboratory.

External links[edit]

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 Hexafluorideat WebElements
Import of Western depleted uranium hexafluoride (uranium tails) to Russia[dead link 30 June 2017]

[1] "Uranium Hexafluoride".Archived fromthe originalon 2013-09-16.Retrieved2013-08-08.

[Enthalpie-2] Johnson, Gerald K. (1979). "The Enthalpy of Formation of Uranium Hexafluoride".The Journal of Chemical Thermodynamics.11(5): 483–490.doi:10.1016/0021-9614(79)90126-5.

[3] Uranium(VI) fluoride

[4] Brickwedde, Ferdinand G.; Hoge, Harold J.; Scott, Russell B. (1948)."The Low Temperature Heat Capacities, Enthalpies, and Entropies of UF₄and UF₆".J. Chem. Phys.16(5): 429–436.Bibcode:1948JChPh..16..429B.doi:10.1063/1.1746914.

[5] J. H. Levy; John C. Taylor; Paul W. Wilson (1976). "Structure of Fluorides. Part XII. Single-Crystal Neutron Diffraction Study of Uranium Hexafluoride at 293 K".J. Chem. Soc., Dalton Trans.(3): 219–224.doi:10.1039/DT9760000219.

[6] J. H. Levy, J. C. Taylor and A. B. Waugh (1983). "Neutron Powder Structural Studies of UF₆,MoF₆and WF₆at 77 K ".Journal of Fluorine Chemistry.23:29–36.doi:10.1016/S0022-1139(00)81276-2.

[UF6_1973-7] 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;doi:10.1107/S0567740873001895.

[UF6_1968-8] Kimura, Masao; Schomaker, Werner; Smith, Darwin W.; Bernard (1968)."Electron-Diffraction Investigation of the Hexafluorides of Tungsten, Osmium, Iridium, Uranium, Neptunium, and Plutonium".J. Chem. Phys.48(8): 4001–4012.Bibcode:1968JChPh..48.4001K.doi:10.1063/1.1669727.Archived fromthe originalon 2023-01-11.Retrieved2020-10-10.

[9] G. H. Olah; J. Welch (1978). "Synthetic methods and reactions. 46. Oxidation of organic compounds with uranium hexafluoride in haloalkane solutions".J. Am. Chem. Soc.100(17): 5396–5402.doi:10.1021/ja00485a024.

[10] J. A. Berry; R. T. Poole; A. Prescott; D. W. A. Sharp; J. M. Winfield (1976). "The oxidising and fluoride ion acceptor properties of uranium hexafluoride in acetonitrile".J. Chem. Soc., Dalton Trans.(3): 272–274.doi:10.1039/DT9760000272.

[11] S. M. Walker; P. S. Halasyamani; S. Allen; D. O'Hare (1999). "From Molecules to Frameworks: Variable Dimensionality in the UO₂(CH₃COO)₂·2H₂O/HF(aq)/Piperazine System. Syntheses, Structures, and Characterization of Zero-Dimensional (C₄N₂H₁₂)UO₂F₄·3H₂O, One-Dimensional (C₄N₂H₁₂)₂U₂F₁₂·H₂O, Two-Dimensional (C₄N₂H₁₂)₂(U₂O₄F₅)₄·11H₂O, and Three-Dimensional (C₄N₂H₁₂)U₂O₄F₆".J. Am. Chem. Soc.121(45): 10513–10521.doi:10.1021/ja992145f.

[12] "Uranium Hexafluoride: Source: Appendix A of the PEIS (DOE/EIS-0269): Physical Properties".web.evs.anl.gov.Retrieved2022-08-18.

[13] "Uranium Enrichment and the Gaseous Diffusion Process".USEC Inc. Archived fromthe originalon 2007-10-19.Retrieved2007-09-24.

[14] "Unit converter molar mass calculator".TranslatorsCafé.Mississauga, Ontario, Canada: ANVICA Software Development. 1 February 2021.

[15] "How much depleted uranium hexafluoride is stored in the United States?".Depleted UF₆FAQs.Argonne National Laboratory.

[16] "Depleted UF₆Management Program Documents ".Archivedfrom the original on 2008-02-16.Retrieved2006-05-17.

[17] "What is DUF₆?Is it dangerous and what should we do with it? ".Institute for Energy and Environmental Research. 2007-09-24.

[18] Brugge, D.; Delemos, J. L.; Bui, C. (2007)."The Sequoyah Corporation Fuels Release and the Church Rock Spill: Unpublicized Nuclear Releases in American Indian Communities".American Journal of Public Health.97(9): 1595–1600.doi:10.2105/AJPH.2006.103044.PMC1963288.PMID 17666688.

[19] "Have there been accidents involving uranium hexafluoride?".Depleted UF₆FAQs.Argonne National Laboratory. Archived fromthe originalon 2017-06-09.

[20] "What is going to happen to the uranium hexafluoride stored in the United States?".Depleted UF₆FAQs.Argonne National Laboratory.

[21] "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 UF₆inventory? ".Depleted UF₆FAQs.Argonne National Laboratory.

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