Jump to content

Uranium hexafluoride: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
Deano8216 (talk | contribs)
70 edits
m rearranged pictures
Deano8216 (talk | contribs)
70 edits
m minor picture alteration
Line 76: Line 76:


== Application in the nuclear fuel cycle ==
== Application in the nuclear fuel cycle ==
[[Image:Uranium hexafluoride phase diagram.gif|thumb|left|300px|[[Phase diagram]] of UF<sub>6</sub>.]]
[[Image:Uranium hexafluoride phase diagram.gif|thumb|left|250px|[[Phase diagram]] of UF<sub>6</sub>.]]
<!-- please explain why its triple point makes it useful in these methods. -->UF<sub>6</sub> is used in both of the main uranium enrichment methods, [[gaseous diffusion]] and the [[gas centrifuge]] method, because it has a [[triple point]] at 64.05 °C (147 °F, 337 K) and slightly higher than normal atmospheric pressure. [[Fluorine]] has only a single stable naturally occurring isotope, so [[isotopologue]]s of UF<sub>6</sub> 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 | accessdate = 2007-09-24}}</ref>
<!-- please explain why its triple point makes it useful in these methods. -->UF<sub>6</sub> is used in both of the main uranium enrichment methods, [[gaseous diffusion]] and the [[gas centrifuge]] method, because it has a [[triple point]] at 64.05 °C (147 °F, 337 K) and slightly higher than normal atmospheric pressure. [[Fluorine]] has only a single stable naturally occurring isotope, so [[isotopologue]]s of UF<sub>6</sub> 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 | accessdate = 2007-09-24}}</ref>


Line 84: Line 84:


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, used [[oxide]] [[nuclear fuel]] is treated with fluorine gas to form a mixture of fluorides. This is then distilled to separate the different classes of material.
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, used [[oxide]] [[nuclear fuel]] is treated with fluorine gas to form a mixture of fluorides. This is then distilled to separate the different classes of material.






Line 91: Line 89:


== Storage in gas cylinders ==
== Storage in gas cylinders ==
[[Image:DUF6PH38.jpg|255px|thumb|left|UF<sub>6</sub>-cylinder]]
[[Image:DUF6PH38.jpg|250px|thumb|left|UF<sub>6</sub>-cylinder]]
⚫
[[Image:UF6_cylinder_rupture_bw.png|250px|left|thumb|Ruptured 14-ton UF<sub>6</sub> shipping cylinder. 1 fatality, dozens injured. ~29500 lbs of material released. 1986]]
About 95% of the [[depleted uranium]] produced to date is stored as uranium hexafluoride, DUF<sub>6</sub>, in steel cylinders in open air yards close to enrichment plants. Each cylinder contains up to 12.7 tonnes (or 14 US tons) of solid UF<sub>6</sub>. In the U.S. alone, 560,000 tonnes of depleted UF<sub>6</sub> had accumulated by 1993. In 2005, 686,500 tonnes in 57,122 storage cylinders were located near Portsmouth, Ohio, Oak Ridge, Tennessee, and 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 = http://web.ead.anl.gov/uranium/faq/health/faq16.cfm | publisher = [[Argonne National Laboratory]]}}</ref><ref>[http://web.ead.anl.gov/uranium/documents/index.cfm Documents<!-- Bot generated title -->]</ref> The long-term storage of DUF<sub>6</sub> presents environmental, health, and safety risks because of its chemical instability. When UF<sub>6</sub> is exposed to moist air, it reacts with the water in the air to produce UO<sub>2</sub>F<sub>2</sub> ([[uranyl fluoride]]) and HF ([[hydrogen fluoride]]) both of which are highly soluble and toxic. Storage cylinders must be regularly inspected for signs of corrosion and leaks. The estimated life time of the steel cylinders is measured in decades.<ref>{{cite web | publisher = Institute for Energy and Environmental Research | date = December 1997 | 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 | date = 2007-09-24}}</ref>
About 95% of the [[depleted uranium]] produced to date is stored as uranium hexafluoride, DUF<sub>6</sub>, in steel cylinders in open air yards close to enrichment plants. Each cylinder contains up to 12.7 tonnes (or 14 US tons) of solid UF<sub>6</sub>. In the U.S. alone, 560,000 tonnes of depleted UF<sub>6</sub> had accumulated by 1993. In 2005, 686,500 tonnes in 57,122 storage cylinders were located near Portsmouth, Ohio, Oak Ridge, Tennessee, and 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 = http://web.ead.anl.gov/uranium/faq/health/faq16.cfm | publisher = [[Argonne National Laboratory]]}}</ref><ref>[http://web.ead.anl.gov/uranium/documents/index.cfm Documents<!-- Bot generated title -->]</ref> The long-term storage of DUF<sub>6</sub> presents environmental, health, and safety risks because of its chemical instability. When UF<sub>6</sub> is exposed to moist air, it reacts with the water in the air to produce UO<sub>2</sub>F<sub>2</sub> ([[uranyl fluoride]]) and HF ([[hydrogen fluoride]]) both of which are highly soluble and toxic. Storage cylinders must be regularly inspected for signs of corrosion and leaks. The estimated life time of the steel cylinders is measured in decades.<ref>{{cite web | publisher = Institute for Energy and Environmental Research | date = December 1997 | 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 | date = 2007-09-24}}</ref>


⚫
[[Image:UF6_cylinder_rupture_bw.png|255px|left|thumb|Ruptured 14-ton UF<sub>6</sub> shipping cylinder. 1 fatality, dozens injured. ~29500 lbs of material released. 1986]]
There have been several accidents involving uranium hexafluoride in the United States.<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]]}}</ref><ref>{{cite web | title = Uranium Hexafluoride (UF<sub>6</sub>) Tailings: Characteristics, Transport and Storage at the Siberian Chemical Combine (Sibkhimkombinat) Tomsk | format = briefing note | publisher = Large and Associates | date = 5 November 2005 | url = http://www.largeassociates.com/R3139-a1%20frontispiece.pdf | accessdate = 2007-09-24}}</ref> The U.S. government has been converting DUF<sub>6</sub> 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 = http://web.ead.anl.gov/uranium/faq/health/faq22.cfm | publisher = [[Argonne National Laboratory]]}}</ref> Such disposal of the entire DUF<sub>6</sub> inventory could cost anywhere from [[United States dollar|$]]15 million to $450 million.<ref>{{cite web | work = Depleted UF<sub>6</sub> FAQs | title = Are there any currently-operating disposal facilities that can accept all of the depleted uranium oxide that would be generated from conversion of DOE's depleted UF6 inventory?| url = http://web.ead.anl.gov/uranium/faq/health/faq27.cfm | publisher = [[Argonne National Laboratory]]}}</ref>
There have been several accidents involving uranium hexafluoride in the United States.<ref>{{cite web | work = Depleted UF<sub>6</sub> FAQs | title = Have there been accidents involving uranium hexafluoride? | url = http://web.ead.anl.gov/uranium/faq/health/faq30.cfm | publisher = [[Argonne National Laboratory]]}}</ref><ref>{{cite web | title = Uranium Hexafluoride (UF<sub>6</sub>) Tailings: Characteristics, Transport and Storage at the Siberian Chemical Combine (Sibkhimkombinat) Tomsk | format = briefing note | publisher = Large and Associates | date = 5 November 2005 | url = http://www.largeassociates.com/R3139-a1%20frontispiece.pdf | accessdate = 2007-09-24}}</ref> The U.S. government has been converting DUF<sub>6</sub> to solid uranium oxides for disposal.<ref>{{cite web | work = Depleted UF<sub>6</sub> FAQs | title = What is going to happen to the uranium hexafluoride stored in the United States? | url = http://web.ead.anl.gov/uranium/faq/health/faq22.cfm | publisher = [[Argonne National Laboratory]]}}</ref> Such disposal of the entire DUF<sub>6</sub> inventory could cost anywhere from [[United States dollar|$]]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 UF6 inventory?| url = http://web.ead.anl.gov/uranium/faq/health/faq27.cfm | publisher = [[Argonne National Laboratory]]}}</ref>
{{-}}
{{-}}

Revision as of 15:36, 9 November 2010

Uranium fluoride
Names
IUPAC names
Uranium hexafluoride
Uranium(VI) fluoride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.116 Edit this at Wikidata
RTECS number
  • YR4720000
UN number 2978 (<1% 235U)
2977 (>1% 235U)
  • InChI=1/6FH.U/h6*1H;/q;;;;;;+6/p-6/rF6U/c1-7(2,3,4,5)6
    Key: SANRKQGLYCLAFE-IIYYNVFAAT
  • F[U](F)(F)(F)(F)F
Properties
UF6
Molar mass 352.02 g/mol
Appearance colorless solid
Density 5.09 g/cm3, solid
Melting point 64.05 °C (triple point)
Boiling point 56.5 °C (sublimes)
reacts
Solubility soluble in chloroform, CCl4, liquid chlorine and bromine
dissolves in nitrobenzene
Structure
Orthorhombic, oP28
Pnma, No. 62
octahedral (Oh)
0
Thermochemistry
– solid: −430,4 ± 1,5 J·K−1·mol−1[1]

– gaseous: −280,4 ± 1,5 J·K−1·mol−1[1]

– solid: −(2197,7 ± 1,8) kJ·mol−1[1]

– gaseous: −(2148,1 ± 1,8) kJ·mol−1[1]

Hazards
Flash point Non-flammable
Related compounds
Other anions
 Uranium hexachloride
Other cations
 Neptunium hexafluoride
Plutonium hexafluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Uranium hexafluoride (UF6), referred to as "hex" in the nuclear industry, is a compound used in the uranium enrichment process that produces fuel for nuclear reactors and nuclear weapons. It forms solid grey crystals at standard temperature and pressure (STP), is highly toxic, reacts violently with water and is corrosive to most metals. It reacts mildly with aluminium, forming a thin surface layer of AlF3 that resists further reaction.

Preparation

Milled uranium ore—U3O8 or "yellowcake"—is dissolved in nitric acid, yielding a solution of uranyl nitrate UO2(NO3)2. Pure uranyl nitrate is obtained by solvent extraction, then treated with ammonia to produce ammonium diuranate ("ADU", (NH4)2U2O7). Reduction with hydrogen gives UO2, which is converted with hydrofluoric acid (HF) to uranium tetrafluoride, UF4. Oxidation with fluorine yields UF6.

Properties

UF6 in a glass ampoule.

Physical Properties

At room pressure, it sublimes at 56.5 °C.[2] The triple point is at 64.05 °C and 1.5 bar.[3]

The solid state structure was determined by neutron diffraction at 77 K an 293 K.[4][5]

  • This is a simple mononuclear molecule
    This is a simple mononuclear molecule
  • The crystal structure of uranium hexafluoride
    The crystal structure of uranium hexafluoride

Chemical Properties

It has been shown that uranium hexafluoride is an oxidant[6] and a Lewis acid which is able to bind to fluoride, for instance the reaction of copper fluoride with uranium hexafluoride in acetonitrile is reported to form copper(II) heptafluorouranate(VI), F7Cu3U.[7]

Polymeric uranium(VI) fluorides containing organic cations have been isolated and characterised by X-ray diffraction.[8]

Application in the nuclear fuel cycle

Phase diagram of UF6.

UF6 is used in both of the main uranium enrichment methods, gaseous diffusion and the gas centrifuge method, because it has a triple point at 64.05 °C (147 °F, 337 K) and slightly higher than normal atmospheric pressure. Fluorine has only a single stable naturally occurring isotope, so isotopologues of UF6 differ in their molecular weight based solely on the uranium isotope present.[9]

All the other uranium fluorides are involatile solids which are coordination polymers.

Gaseous diffusion requires about 60 times as much energy as the gas centrifuge process; even so, this is just 4% of the energy that can be produced by the resulting enriched uranium.

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, used oxide nuclear fuel is treated with fluorine gas to form a mixture of fluorides. This is then distilled to separate the different classes of material.



Storage in gas cylinders

UF6-cylinder
Ruptured 14-ton UF6 shipping cylinder. 1 fatality, dozens injured. ~29500 lbs of material released. 1986

About 95% of the depleted uranium produced to date is stored as uranium hexafluoride, DUF6, in steel cylinders in open air yards close to enrichment plants. Each cylinder contains up to 12.7 tonnes (or 14 US tons) of solid UF6. In the U.S. alone, 560,000 tonnes of depleted UF6 had accumulated by 1993. In 2005, 686,500 tonnes in 57,122 storage cylinders were located near Portsmouth, Ohio, Oak Ridge, Tennessee, and Paducah, Kentucky.[10][11] The long-term storage of DUF6 presents environmental, health, and safety risks because of its chemical instability. When UF6 is exposed to moist air, it reacts with the water in the air to produce UO2F2 (uranyl fluoride) and HF (hydrogen fluoride) both of which are highly soluble and toxic. Storage cylinders must be regularly inspected for signs of corrosion and leaks. The estimated life time of the steel cylinders is measured in decades.[12]

There have been several accidents involving uranium hexafluoride in the United States.[13][14] The U.S. government has been converting DUF6 to solid uranium oxides for disposal.[15] Such disposal of the entire DUF6 inventory could cost anywhere from $15 million to $450 million.[16]

References

  1. ^ a b c d Gerald K. Johnson: "The Enthalpy of Formation of Uranium Hexafluoride", The Journal of Chemical Thermodynamics, 1979, 11 (5), p. 483–490; doi:10.1016/0021-9614(79)90126-5.
  2. ^ http://nuclearweaponarchive.org/Library/Glossary
  3. ^ Uranium Hexafluoride: Source: Appendix A of the PEIS (DOE/EIS-0269): Physical Properties
  4. ^ 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.: 219–224. doi:10.1039/DT9760000219.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ J. H. Levy, J. C. Taylor and A. B. Waugh (1983). "Neutron Powder Structural Studies of UF6, MoF6 and WF6 at 77 K". Journal of Fluorine Chemistry. 23: 29–36. doi:10.1016/S0022-1139(00)81276-2.
  6. ^ 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.
  7. ^ 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.: 272–274. doi:10.1039/DT9760000272.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. ^ 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. ^ "Uranium Enrichment and the Gaseous Diffusion Process". USEC Inc. Retrieved 2007-09-24.
  10. ^ "How much depleted uranium hexafluoride is stored in the United States?". Depleted UF6 FAQs. Argonne National Laboratory.
  11. ^ Documents
  12. ^ "What is DUF6? Is it dangerous and what should we do with it?". Institute for Energy and Environmental Research. 2007-09-24.
  13. ^ "Have there been accidents involving uranium hexafluoride?". Depleted UF6 FAQs. Argonne National Laboratory.
  14. ^ "Uranium Hexafluoride (UF6) Tailings: Characteristics, Transport and Storage at the Siberian Chemical Combine (Sibkhimkombinat) Tomsk" (briefing note). Large and Associates. 5 November 2005. Retrieved 2007-09-24.
  15. ^ "What is going to happen to the uranium hexafluoride stored in the United States?". Depleted UF6 FAQs. Argonne National Laboratory.
  16. ^ "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 UF6 inventory?". Depleted UF6 FAQs. Argonne National Laboratory.

Further reading

Retrieved from "https://en.wikipedia.org/w/index.php?title=Uranium_hexafluoride&oldid=395755998"