Uranium hydride

Uranium hydride, also called uranium trihydride (UH3), is an inorganic compound and a hydride of uranium.

This article is about UH3. For the low temperature molecular compound, see Uranium(IV) hydride.
Uranium hydride
Names
Other names
Uranium(III) hydride[1]
Uranium trihydride[2][3]
Hypouranous hydride
Identifiers
3D model (JSmol)
ChemSpider
Properties
UH
3
Molar mass 241.05273 g mol−1
Density 10.95 g cm−3
Reacts
Structure
Cubic, cP32
Pm3n, No. 223
a = 664.3 pm[4]
Hazards
Safety data sheet ibilabs.com
Flash point Pyrophoric
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Properties

Uranium hydride is a highly toxic, brownish grey to brownish black pyrophoric powder or brittle solid. Its density at 20 °C is 10.95 g cm−3, much lower than that of uranium (19.1 g cm−3). It has a metallic conductivity, is slightly soluble in hydrochloric acid and decomposes in nitric acid.

Two crystal modifications of uranium hydride exist, both cubic: an α form that is obtained at low temperatures and a β form that is grown when the formation temperature is above 250 °C.[5] After growth, both forms are metastable at room temperature and below, but the α form slowly converts to the β form upon heating to 100 °C.[3] Both α- and β-UH3 are ferromagnetic at temperatures below ~180 K. Above 180 K, they are paramagnetic.[6]

Formation in uranium metal

Hydrogen gas reaction

Exposure of uranium metal to hydrogen leads to hydrogen embrittlement. Hydrogen diffuses through metal and forms a network of brittle hydride over the grain boundaries. Hydrogen can be removed and ductility renewed by annealing in vacuum.[7]

Uranium metal heated to 250 to 300 °C (482 to 572 °F) reacts with hydrogen to form uranium hydride. Further heating to about 500 °C will reversibly remove the hydrogen. This property makes uranium hydrides convenient starting materials to create reactive uranium powder along with various uranium carbide, nitride, and halide compounds.[5] The reversible reaction proceeds as follows:[2]

2 U + 3 H2 ⇌ 2 UH3

Uranium hydride is not an interstitial compound, causing the metal to expand upon hydride formation. In its lattice, each uranium atom is surrounded by 6 other uranium atoms and 12 atoms of hydrogen; each hydrogen atom occupies a large tetrahedral hole in the lattice.[8] The density of hydrogen in uranium hydride is approximately the same as in liquid water or in liquid hydrogen.[9] The U-H-U linkage through a hydrogen atom is present in the structure.[10]

Water reaction

Uranium hydride forms when uranium metal (e.g. in Magnox fuel with corroded cladding) becomes exposed to water; the reaction proceeds as follows:

7 U + 6 H2O → 3 UO2 + 4 UH3

The resulting uranium hydride is pyrophoric; if the metal (e.g. a damaged fuel rod) is exposed to air afterwards, excessive heat may be generated and the bulk uranium metal itself can ignite.[11] Hydride-contaminated uranium can be passivated by exposition to a gaseous mixture of 98% helium with 2% oxygen.[12] Condensed moisture on uranium metal promotes formation of hydrogen and uranium hydride; a pyrophoric surface may be formed in absence of oxygen.[13] This poses a problem with underwater storage of spent nuclear fuel in spent fuel ponds. Depending on the size and distribution on the hydride particles, self-ignition can occur after an indeterminate length of exposure to air.[14] Such exposure poses risk of self-ignition of fuel debris in radioactive waste storage vaults.[15]

Uranium metal exposed to steam produces a mixture of uranium hydride and uranium dioxide.[8]

Uranium hydride exposed to water evolves hydrogen. In contact with strong oxidizers this may cause fire and explosions. Contact with halocarbons may cause a violent reaction.[16]

Other chemical reactions

Polystyrene-impregnated uranium hydride powder is non-pyrophoric and can be pressed, however its hydrogen-carbon ratio is unfavorable. Hydrogenated polystyrene was introduced in 1944 instead.[17]

Uranium deuteride is said to be usable for design of some types of neutron initiators.

Uranium hydride enriched to about 5% uranium-235 is proposed as a combined nuclear fuel/neutron moderator for the Hydrogen Moderated Self-regulating Nuclear Power Module. According to the aforementioned patent application, the reactor design in question begins producing power when hydrogen gas at a sufficient temperature and pressure is admitted to the core (made up of granulated uranium metal) and reacts with the uranium metal to form uranium hydride.[18] Uranium hydride is both a nuclear fuel and a neutron moderator; apparently it, like other neutron moderators, will slow neutrons sufficiently to allow for fission reactions to take place; the uranium-235 atoms within the hydride also serve as the nuclear fuel. Once the nuclear reaction has started, it will continue until it reaches a certain temperature, approximately 800 °C (1,500 °F), where, due to the chemical properties of uranium hydride, it chemically decomposes and turns into hydrogen gas and uranium metal. The loss of neutron moderation due to the chemical decomposition of the uranium hydride will consequently slow — and eventually halt — the reaction. When temperature returns to an acceptable level, the hydrogen will again combine with the uranium metal, forming uranium hydride, restoring moderation and the nuclear reaction will start again.[18]

Uranium zirconium hydride (UZrH), a combination of uranium hydride and zirconium(II) hydride, is used as a fuel/moderator in the TRIGA-class reactors.

On heating with diborane, uranium hydride produces uranium boride.[19] With bromine at 300 °C, uranium(IV) bromide is produced. With chlorine at 250 °C, uranium(IV) chloride is produced. Hydrogen fluoride at 20 °C produces uranium(IV) fluoride. Hydrogen chloride at 300 °C produces uranium(III) chloride. Hydrogen bromide at 300 °C produces uranium(III) bromide. Hydrogen iodide at 300 °C produces uranium(III) iodide. Ammonia at 250 °C produces uranium(III) nitride. Hydrogen sulfide at 400 °C produces uranium(IV) sulfide. Oxygen at 20 °C produces triuranium octoxide. Water at 350 °C produces uranium dioxide.[20]

Uranium hydride ion may interfere with some mass spectrometry measurements, appearing as a peak at mass 239, creating false increase of signal for plutonium-239.[21]

History

Uranium hydride slugs were used in the "tickling the dragon's tail" series of experiments to determine the critical mass of uranium.[22]

Uranium hydride and uranium deuteride were suggested as a fissile material for a uranium hydride bomb. The tests with uranium hydride and uranium deuteride during Operation Upshot–Knothole were disappointing, however. During the early phases of the Manhattan Project, in 1943, uranium hydride was investigated as a promising bomb material; it was abandoned by early 1944 as it turned out that such a design would be inefficient.[23]

Applications

Hydrogen, deuterium, and tritium can be purified by reacting with uranium, then thermally decomposing the resulting hydride/deuteride/tritide.[24] Extremely pure hydrogen has been prepared from beds of uranium hydride for decades.[25] Heating uranium hydride is a convenient way to introduce hydrogen into a vacuum system.[26]

The swelling and pulverization at uranium hydride synthesis can be used for preparation of very fine uranium metal, if the powdered hydride is thermally decomposed.

Uranium hydride can be used for isotope separation of hydrogen, preparing uranium metal powder, and as a reducing agent.

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References
  1. Carl L. Yaws (2008). Thermophysical properties of chemicals and hydrocarbons. William Andrew. pp. 307–. ISBN 978-0-8155-1596-8. Retrieved 11 October 2011.
  2. Egon Wiberg; Nils Wiberg; Arnold Frederick Holleman (2001). Inorganic chemistry. Academic Press. pp. 239–. ISBN 978-0-12-352651-9. Retrieved 11 October 2011.
  3. Gerd Meyer; Lester R. Morss (1991). Synthesis of lanthanide and actinide compounds. Springer. pp. 44–. ISBN 978-0-7923-1018-1. Retrieved 11 October 2011.
  4. Bartscher W., Boeuf A., Caciuffo R., Fournier J.M., Kuhs W.F., Rebizant J., Rustichelli F (1985). "Neutron diffraction study of b-UD3 AND b-UH3". Solid State Commun. 53: 423–426. doi:10.1016/0038-1098(85)91000-2.CS1 maint: uses authors parameter (link)
  5. Seaborg, Glenn T. (1968). "Uranium". The Encyclopedia of the Chemical Elements. Skokie, Illinois: Reinhold Book Corporation. p. 782. LCCCN 68-29938.
  6. K. H. J. Buschow (2005). Concise encyclopedia of magnetic and superconducting materials. Elsevier. pp. 901–. ISBN 978-0-08-044586-1. Retrieved 11 October 2011.
  7. I. N. Toumanov (2003). Plasma and high frequency processes for obtaining and processing materials in the nuclear fuel cycle. Nova Publishers. p. 232. ISBN 1-59033-009-9. Retrieved 2010-02-07.
  8. Amit Arora (2005). Text Book Of Inorganic Chemistry. Discovery Publishing House. p. 789. ISBN 81-8356-013-X. Retrieved 2010-02-07.
  9. Peter Gevorkian (2009). Alternative Energy Systems in Building Design (GreenSource Books). McGraw Hill Professional. p. 393. ISBN 978-0-07-162147-2. Retrieved 2010-02-07.
  10. G. Singh (2007). Environmental Pollution. Discovery Publishing House. ISBN 978-81-8356-241-6. Retrieved 2010-02-07.
  11. "Rust never sleeps". Bulletin of the Atomic Scientists. 50 (5): 49. 1994. Retrieved 2010-02-07.
  12. "EMSP". Teton.if.uidaho.edu. Archived from the original on 2009-09-30. Retrieved 2010-02-07.
  13. OECD Nuclear Energy Agency (2006). Advanced nuclear fuel cycles and radioactive waste management. OECD Publishing. p. 176. ISBN 92-64-02485-9. Retrieved 2010-02-07.
  14. Abir Al-Tabbaa; J. A. Stegemann (2005). Stabilisation/Solidification Treatment and Remediation: Proceedings of the International Conference on Stabilisation/Solidification Treatment and Remediation, 12–13 April 2005, Cambridge, UK. Taylor & Francis. p. 197. ISBN 0-415-37460-X. Retrieved 2010-02-07.
  15. International Conference on Nuclear Decom 2001: ensuring safe, secure and successful decommissioning : 16–18 October 2001 Commonwealth Conference and Events Centre, London UK, Issue 8. John Wiley and Sons. 2001. p. 278. ISBN 1-86058-329-6. Retrieved 2010-02-07.
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  18. Peterson, Otis G. (2008-03-20). "Patent Application 11/804450: Self-regulating nuclear power module". United States Patent Application Publication. United States Patent and Trademark Office, Federal Government of the United States, Washington, DC, USA. Retrieved 2009-09-05.
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