Uranium dioxide

Last updated
Uranium dioxide
UO2lattice.jpg
Names
IUPAC names
Uranium dioxide
Uranium(IV) oxide
Other names
Urania
Uranous oxide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.014.273 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 215-700-3
PubChem CID
RTECS number
  • YR4705000
UNII
  • InChI=1S/2O.U
    Key: FCTBKIHDJGHPPO-UHFFFAOYSA-N
  • O=[U]=O
Properties
UO2
Molar mass 270.03 g/mol
Appearanceblack powder
Density 10.97 g/cm3
Melting point 2,865 °C (5,189 °F; 3,138 K)
insoluble
Structure
Fluorite (cubic), cF12
Fm3m, No. 225
a = 547.1 pm [1]
Tetrahedral (O2−); cubic (UIV)
Thermochemistry
Std molar
entropy (S⦵298)
78 J·mol−1·K−1 [2]
−1084 kJ·mol−1 [2]
Hazards
GHS labelling:
GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg
Danger
H300, H330, H373, H410
P260, P264, P270, P271, P273, P284, P301+P310, P304+P340, P310, P314, P320, P321, P330, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazard RA: Radioactive. E.g. plutonium
4
0
0
Radiation warning symbol 3.svg
Flash point N/A
Safety data sheet (SDS) ICSC 1251
Related compounds
Other anions
Uranium(IV) sulfide
Uranium(IV) selenide
Other cations
Protactinium(IV) oxide
Neptunium(IV) oxide
Related uranium oxides
Triuranium octoxide
Uranium trioxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Uranium dioxide or uranium(IV) oxide (UO2), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear reactors. A mixture of uranium and plutonium dioxides is used as MOX fuel. It has been used as an orange, yellow, green, and black color in ceramic glazes and glass.

Contents

Production

Uranium dioxide is produced by reducing uranium trioxide with hydrogen. This reaction often creates triuranium octoxide as an intermediate. [3] [4] [5]

UO3 + H2 → UO2 + H2O at 700 °C (973 K)

This reaction plays an important part in the creation of nuclear fuel through nuclear reprocessing and uranium enrichment. [5]

Chemistry

Structure

The solid is isostructural with (has the same structure as) fluorite (calcium fluoride), where each U is surrounded by eight O nearest neighbors in a cubic arrangement. In addition, the dioxides of cerium, thorium, and the transuranic elements from neptunium through californium have the same structures. [6] No other elemental dioxides have the fluorite structure. Upon melting, the measured average U-O coordination reduces from 8 in the crystalline solid (UO8 cubes), down to 6.7±0.5 (at 3270 K) in the melt. [7] Models consistent with these measurements show the melt to consist mainly of UO6 and UO7 polyhedral units, where roughly 2⁄3 of the connections between polyhedra are corner sharing and 1⁄3 are edge sharing. [7]

Oxidation

Uranium dioxide is oxidized in contact with oxygen to form triuranium octoxide: [8]

3 UO2 + O2 → U3O8 at 250 °C (523 K)

The electrochemistry of uranium dioxide has been investigated in detail as the galvanic corrosion of uranium dioxide controls the rate at which used nuclear fuel dissolves.[ clarification needed ] See spent nuclear fuel for further details. Water increases the oxidation rate of plutonium and uranium metals. [9]

Reaction with carbon

Uranium dioxide reacts with carbon at high temperatures, forming uranium carbide and carbon monoxide. [10]

UO2 + 4 C → UC2 + 2 CO

This process must be done under an inert gas as uranium carbide is easily oxidized back into uranium oxide.

Uses

Nuclear fuel

UO2 is used mainly as nuclear fuel, specifically as UO2 or as a mixture of UO2 and PuO2 (plutonium dioxide) called a mixed oxide (MOX fuel), in the form of fuel rods in nuclear reactors. [11]

The thermal conductivity of uranium dioxide is very low when compared with elemental uranium, uranium nitride, uranium carbide and zircaloy cladding material as well as most uranium-based alloys. [12] [13] [14] This low thermal conductivity can result in localised overheating in the centres of fuel pellets. [15]

The graph below shows the different temperature gradients in different fuel compounds. For these fuels, the thermal power density is the same and the diameter of all the pellets are the same.[ citation needed ]

The thermal conductivity of zirconium metal and uranium dioxide as a function of temperature ZrUthermalcond.png
The thermal conductivity of zirconium metal and uranium dioxide as a function of temperature

Color for glass ceramic glaze

Geiger counter (kit without housing) audibly reacting to an orange Fiestaware shard.

Uranium oxide (urania) was used to color glass and ceramics prior to World War II, and until the applications of radioactivity were discovered this was its main use. In 1958 the military in both the US and Europe allowed its commercial use again as depleted uranium, and its use began again on a more limited scale. Urania-based ceramic glazes are dark green or black when fired in a reduction or when UO2 is used; more commonly it is used in oxidation to produce bright yellow, orange and red glazes. [16] Orange-colored Fiestaware is a well-known example of a product with a urania-colored glaze. [17] Uranium glass is pale green to yellow and often has strong fluorescent properties. [18] Urania has also been used in formulations of enamel and porcelain. [19] It is possible to determine with a Geiger counter if a glaze or glass produced before 1958 contains urania.

Other uses

Prior to the realisation of the harmfulness of radiation, uranium was included in false teeth and dentures, as its slight fluorescence made the dentures appear more like real teeth in a variety of lighting conditions. [20]

Depleted UO2 (DUO2) can be used as a material for radiation shielding. For example, DUCRETE is a "heavy concrete" material where gravel is replaced with uranium dioxide aggregate; this material is investigated for use for casks for radioactive waste. [21] Casks can be also made of DUO2-steel cermet, a composite material made of an aggregate of uranium dioxide serving as radiation shielding, graphite and/or silicon carbide serving as neutron radiation absorber and moderator, and steel as the matrix, whose high thermal conductivity allows easy removal of decay heat. [22]

Depleted uranium dioxide can be also used as a catalyst, e.g. for degradation of volatile organic compounds in gaseous phase, oxidation of methane to methanol, and removal of sulfur from petroleum. It has high efficiency and long-term stability when used to destroy VOCs when compared with some of the commercial catalysts, such as precious metals, TiO2, and Co3O4 catalysts. Much research is being done in this area, DU being favoured for the uranium component due to its low radioactivity. [23]

The use of uranium dioxide as a material for rechargeable batteries is being investigated. [24] The batteries could have a high power density and a reduction potential of -4.7 V per cell. [25] Another investigated application is in photoelectrochemical cells for solar-assisted hydrogen production where UO2 is used as a photoanode. In earlier times, uranium dioxide was also used as heat conductor for current limitation (URDOX-resistor), which was the first use of its semiconductor properties.[ citation needed ]

Uranium dioxide displays strong piezomagnetism in the antiferromagnetic state, observed at cryogenic temperatures below 30 kelvins. Accordingly, the linear magnetostriction found in UO2 changes sign with the applied magnetic field and exhibits magnetoelastic memory switching phenomena at record high switch-fields of 180,000 Oe. [26] The microscopic origin of the material magnetic properties lays in the face-centered-cubic crystal lattice symmetry of uranium atoms, and its response to applied magnetic fields. [27]

Semiconductor properties

The band gap of uranium dioxide is comparable to those of silicon and gallium arsenide, near the optimum for efficiency vs band gap curve for absorption of solar radiation, suggesting its possible use for very efficient solar cells based on Schottky diode structure; it also absorbs at five different wavelengths, including infrared, further enhancing its efficiency. Its intrinsic conductivity at room temperature is about the same as of single crystal silicon. [28]

The dielectric constant of uranium dioxide is about 21.5, [29] which is almost twice as high as of silicon (11.7) [30] and GaAs (12.4). [31] This is an advantage over Si and GaAs in the construction of integrated circuits, as it may allow higher density integration with higher breakdown voltages and with lower susceptibility to the CMOS tunnelling breakdown.

The Seebeck coefficient of uranium dioxide at room temperature is about 750 μV/K, a value significantly higher than the 270 μV/K of thallium tin telluride (Tl2SnTe5) and thallium germanium telluride (Tl2GeTe5) and of bismuth-tellurium alloys, other materials promising for thermoelectric power generation applications and Peltier elements.

The radioactive decay impact of the 235U and 238U on its semiconducting properties was not measured as of 2005. Due to the slow decay rate of these isotopes, it should not meaningfully influence the properties of uranium dioxide solar cells and thermoelectric devices, but it may become an important factor for VLSI chips. Use of depleted uranium oxide is necessary for this reason. The capture of alpha particles emitted during radioactive decay as helium atoms in the crystal lattice may also cause gradual long-term changes in its properties.[ citation needed ]

The stoichiometry of the material dramatically influences its electrical properties. For example, the electrical conductivity of UO1.994 is orders of magnitude lower at higher temperatures than the conductivity of UO2.001[ citation needed ].

Uranium dioxide, like U3O8, is a ceramic material capable of withstanding high temperatures (about 2300 °C, in comparison with at most 200 °C for silicon or GaAs), making it suitable for high-temperature applications like thermophotovoltaic devices.

Uranium dioxide is also resistant to radiation damage, making it useful for rad-hard devices for special military and aerospace applications.

A Schottky diode of U3O8 and a p-n-p transistor of UO2 were successfully manufactured in a laboratory. [32]

Toxicity

Uranium dioxide is known to be absorbed by phagocytosis in the lungs. [33]

See also

References

  1. ↑ Leinders, Gregory; Cardinaels, Thomas; Binnemans, Koen; Verwerft, Marc (2015). "Accurate lattice parameter measurements of stoichiometric uranium dioxide". Journal of Nuclear Materials. 459: 135–42. Bibcode:2015JNuM..459..135L. doi:10.1016/j.jnucmat.2015.01.029. S2CID   97183844.
  2. 1 2 Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN   978-0-618-94690-7.
  3. ↑ A.H. Le Page; A.G. Fane (1974). "The kinetics of hydrogen reduction of UO3 and U3O8 derived from ammonium diuranate". Journal of Inorganic and Nuclear Chemistry. 36 (1): 87–92. doi:10.1016/0022-1902(74)80663-9.
  4. ↑ Notz, K.J.; Huntington, C.W.; Burkhardt, W. (1 July 1962). "Hydrogen Reduction of Uranium Oxides. A Phase Study by Means of a Controlled-Atmosphere Diffractometer Hot Stage". Industrial & Engineering Chemistry Process Design and Development. 1 (3): 213–217. doi:10.1021/i260003a010.
  5. 1 2 "Conversion and Deconversion". World Nuclear Association. 20 Nov 2024. Retrieved 18 Mar 2025.
  6. ↑ Petit, L.; Svane, A.; Szotek, Z.; Temmerman, W. M.; Stocks, G. M. (2010-01-07). "Electronic structure and ionicity of actinide oxides from first principles". Physical Review B. 81 (4): 045108. arXiv: 0908.1806 . Bibcode:2010PhRvB..81d5108P. doi:10.1103/PhysRevB.81.045108. S2CID   118365366.
  7. 1 2 Skinner, L. B.; Benmore, C. J.; Weber, J. K. R.; Williamson, M. A.; Tamalonis, A.; Hebden, A.; Wiencek, T.; Alderman, O. L. G.; Guthrie, M.; Leibowitz, L.; Parise, J. B. (2014). "Molten uranium dioxide structure and dynamics". Science. 346 (6212): 984–7. Bibcode:2014Sci...346..984S. doi:10.1126/science.1259709. OSTI   1174101. PMID   25414311. S2CID   206561628.
  8. ↑ G. Rousseau; L. Desgranges; F. Charlot; N. Millot; J.C. Nièpce; M. Pijolat; F. Valdivieso; G. Baldinozzi; J.F. Bérar (2006). "A detailed study of UO2 to U3O8 oxidation phases and the associated rate-limiting steps". Journal of Nuclear Materials. 355 (1–3): 10–20. doi:10.1016/j.jnucmat.2006.03.015.
  9. ↑ Haschke, John M; Allen, Thomas H; Morales, Luis A (2001). "Reactions of plutonium dioxide with water and hydrogen–oxygen mixtures: Mechanisms for corrosion of uranium and plutonium". Journal of Alloys and Compounds. 314 (1–2): 78–91. doi:10.1016/S0925-8388(00)01222-6.
  10. ↑ Buchel, Gerald L. (1963). Equilibrium studies of the uranium dioxide - carbon and neodymium sesquioxide - carbon systems (M.S. thesis). Michigan State University.
  11. ↑ "Mixed Oxide (MOX) Fuel". World Nuclear Association. 10 Oct 2017. Retrieved 11 Mar 2025.
  12. ↑ Peakman, Aiden; Rossiter, Glyn (2024). "Incorporation of uranium nitride fuel capability into the ENIGMA fuel performance code: Model development and validation". Nuclear Engineering and Design. 429: 113604}. Bibcode:2024NuEnD.42913604P. doi:10.1016/j.nucengdes.2024.113604. ISSN   0029-5493.
  13. ↑ Dr. Celine Hin. "Thermal Conductivity of Metallic Uranium". U.S. Department of Energy Office of Scientific and Technical Information. Retrieved 18 Mar 2025.
  14. ↑ R. R. Hammer (September 1967). "Zircaloy-4, Uranium Dioxide, and Materials Formed by their Interaction: A Literature Review with Extrapolation of Physical Properties to High Temperatures". U.S. Department of Energy Office of Scientific and Technical Information. Idaho Nuclear Corporation. Retrieved 18 Mar 2025.
  15. ↑ "Thermal Conductivity of Uranium Dioxide". Nuclear Power. Retrieved 18 Mar 2025.
  16. ↑ Örtel, Stefan. Uran in der Keramik. Geschichte - Technik - Hersteller.
  17. ↑ Radon, Health and Natural Hazards, Editors: G.K. Gillmore, F.E. Perrier, R.G.M. Crockett, pp. 50-52, 2018, Geological Society of London, ISBN   1786203081, 9781786203083, Google Books
  18. ↑ Amber Davis (22 Jan 2025). "A 'glowing' review of uranium glass". ORAU: Then & Now. Oak Ridge Associated Universities.
  19. ↑ Donna Strahan (19 Jul 2013). "Uranium in glass, glazes and enamels: history, identification and handling}". Studies in Conservation. 46 (3): 181–195. doi:10.1179/sic.2001.46.3.181.
  20. ↑ Toor, R. S. S.; Brar, G. S. (2012). "Uranium: A Dentist's perspective". Journal of International Society of Preventive and Community Dentistry. 2 (1): 1–7. doi: 10.4103/2231-0762.103447 . PMC   3894091 . PMID   24478959.
  21. ↑ Lessing, Paul A. (1 Mar 1995). Development of "DUCRETE" (Report). Idaho National Engineering Laboratory. doi:10.2172/366558. OSTI   366558.
  22. ↑ Forsberg, Charles W.; Swaney, Paul M.; Tiegs, Terry N. "Characteristics and Fabrication of Cermet Spent Nuclear Fuel Casks: Ceramic Particles Embedded in Steel" (Conference). 14th International Symposium on the Packaging and Transportation of Radioactive Materials (PATRAM 2004). https://www.osti.gov/etdeweb/servlets/purl/20773271
  23. ↑ Hutchings, Graham J.; Heneghan, Catherine S.; Hudson, Ian D.; Taylor, Stuart H. (1996). "Uranium-oxide-based catalysts for the destruction of volatile chloro-organic compounds". Nature. 384 (6607): 341–3. Bibcode:1996Natur.384..341H. doi:10.1038/384341a0. S2CID   4299921.
  24. ↑ Wu, Binbin; Yu, Jianguo (10 Jun 2013). "From Used Oxide Nuclear Fuel to Rechargeable Battery: A First-Principles Study". MRS Proceedings. 1541. doi:10.1557/opl.2013.732.
  25. ↑ Dunbar, Paul; Lee-Desautels, Rhonda. "Initial Development of a Depleted Uranium Battery". University of Kentucky.
  26. ↑ Jaime, Marcelo; Saul, Andres; Salamon, Myron B.; Zapf, Vivien; Harrison, Neil; Durakiewicz, Tomasz; Lashley, Jason C.; Andersson, David A.; Stanek, Christopher R.; Smith, James L.; Gofryk, Krysztof (2017). "Piezomagnetism and magnetoelastic memory in uranium dioxide". Nature Communications. 8 (1): 99. Bibcode:2017NatCo...8...99J. doi:10.1038/s41467-017-00096-4. PMC   5524652 . PMID   28740123.
  27. ↑ Antonio, Daniel J.; Weiss, Joel T.; Shanks, Katherine S.; Ruff, Jacob P.C.; Jaime, Marcelo; Saul, Andres; Swinburne, Thomas; Salamon, Myron B.; Lavina, Barbara; Koury, Daniel; Gruner, Sol M.; Andersson, David A.; Stanek, Christopher R.; Durakiewicz, Tomasz; Smith, James L.; Islam, Zahir; Gofryk, Krysztof (2021). "Piezomagnetic switching and complex phase equilibria in uranium dioxide". Communications Materials. 2 (1): 17. arXiv: 2104.06340 . Bibcode:2021CoMat...2...17A. doi:10.1038/s43246-021-00121-6. S2CID   231812027.
  28. ↑ An, Yong Q.; Taylor, Antoinette J.; Conradson, Steven D.; Trugman, Stuart A.; Durakiewicz, Tomasz; Rodriguez, George (2011). "Ultrafast Hopping Dynamics of 5f Electrons in the Mott Insulator UO2 Studied by Femtosecond Pump-Probe Spectroscopy". Physical Review Letters. 106 (20): 207402. Bibcode:2011PhRvL.106t7402A. doi:10.1103/PhysRevLett.106.207402. PMID   21668262.
  29. ↑ Hampton, R. N.; Saunders, G. A.; Harding, J. H.; Stoneham, A. M. (1 Sep 1987). "The pressure dependence of the dielectric constant and electrical conductivity of single crystal uranium dioxide". Journal of Nuclear Materials. 150 (1): 17–23. Bibcode:1987JNuM..150...17H. doi:10.1016/0022-3115(87)90089-4.
  30. ↑ Yang, Xiaofan; Liu, Xiaoming; Yu, Shuo; Gan, Lu; Zhou, Jun; Zeng, Yonghu (Aug 2019). "Permittivity of Undoped Silicon in the Millimeter Wave Range". Electronics. 8 (8): 886. doi: 10.3390/electronics8080886 .
  31. ↑ Fox, Mark (2010). Optical Properties of Solids (2 ed.). Oxford University Press. p. 283. ISBN   978-0199573370.
  32. ↑ Meek, Thomas T.; von Roedern, B. (2008). "Semiconductor devices fabricated from actinide oxides". Vacuum. 83 (1): 226–8. Bibcode:2008Vacuu..83..226M. doi:10.1016/j.vacuum.2008.04.005.
  33. ↑ Principles of Biochemical Toxicology. Timbrell, John. PA 2008 ISBN   0-8493-7302-6 [ page needed ]

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