Depleted uranium hexafluoride: Difference between revisions
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Depleted uranium hexafluoride (DUHF; also referred to as depleted uranium tails or DUF6) is a byproduct of the processing of uranium hexafluoride into enriched uranium.[1][2] It is one of the chemical forms of depleted uranium (up to 73-75%), along with depleted triuranium octoxide (up to 25%) and depleted uranium metal (up to 2%).[3][4][5][6] DUHF is 1.7 times less radioactive than uranium hexafluoride and natural uranium.[4]
History
The concept of depleted and enriched uranium emerged nearly 150 years after the discovery of uranium by Martin Klaproth in 1789. In 1938, two German physicists Otto Hahn and Fritz Strassmann had made the discovery of the fission of the atomic nucleus of the 235U isotope, which was theoretically substantiated by Lise Meitner, Otto Robert Frisch and in parallel with them Gottfried von Droste and Siegfried Flügge.[7][8][9] This discovery marked the beginning of the peaceful and military use of the intra-atomic energy of uranium.[10] A year later, Yulii Khariton and Yakov Zeldovich were the first to prove theoretically that with an insignificant enrichment of natural uranium in the 235U isotope, it is possible to give the process a chain character, creating the necessary conditions for the continuous fission of atomic nuclei.[11] The principle of a nuclear chain reaction implies that at least one neutron, during the decay of an atom of the isotope 235U, will be captured by another atom of 235U and, accordingly, will also cause its decay. In this process, the probability of such a “capture” plays a significant role. To increase this probability, a fractional increase in the 235U isotope is necessary, which in natural uranium constitutes only 0.72%, along with the primary 238U, which takes up 99.27% and 234U - 0.0055%, respectively. A small fraction of the 235U isotope content in natural uranium, when used as a primary fissile material in most areas of nuclear technology, necessitated enrichment of natural uranium in this isotope.
Over time, in the process of improving nuclear technologies, optimal technological and economic solutions were identified, requiring an increase in the 235U fraction, that is, uranium enrichment and, as a consequence of these processes, the appearance of an equivalent amount of depleted uranium with a 235U isotope content of less than 0.72%.[12] The content of 235U in the depleted uranium formed during the enrichment process depends on the purpose of the enrichment.[13]
Physical properties
The key distinction between uranium hexafluoride and DUHF, besides the isotopic composition, are the differences in their origin, as well as their further purpose and application. Uranium hexafluoride is an intermediate product that is artificially created by fluorination of uranium tetrafluoride with fluorine in the amounts necessary to produce enriched uranium.[14] Whereas DUHF is a residual product of conversion of uranium hexafluoride into enriched uranium. At the end of the 235U enrichment process, the initial uranium hexafluoride, with its natural isotopic composition (due to the natural uranium isotope ratio), is converted into two other products (with new isotope ratios of 235U, 238U and 234U) - enriched uranium and DUHF.
Due to the same chemical properties of various uranium isotopes, the chemical and physical properties of depleted uranium hexafluoride and naturally occurring uranium hexafluoride substances, as well as enriched uranium, are identical, except for the degree of radioactivity. Depleted uranium hexafluoride, as the primary form of depleted uranium, can be converted to other forms of DU with a different density. Under standard conditions, DU appears as transparent or light gray crystals, with a density of 5.09 g/cm3. At temperatures below 64.1 °C and a pressure of 1.5 atm, the solid DUHF converts to a gaseous form and bypasses the liquid phase. The critical temperature of DUHF is 230.2 °C, and the critical pressure is 4.61 MPa.
Radioactivity
The radioactivity of DUHF is determined by the isotopic composition of uranium and the ratio of its isotopes (234U, 235U and 238U), because the fluorine in the compound has only one stable isotope, 19F. The radioactive decay rate of natural uranium hexafluoride (with 0.72% of 235U) is 1.7×104 Bq/g and is determined by 238U and 234U isotopes by 97%.
| Uranium isotope | Mass fraction in natural uranium | Half-life, years | Activity of 1 mg of pure isotope | Contribution to the activity of natural uranium |
| 238U | 99,27% | 4,51×109 | 12,4 Bq | 48,8% |
| 235U | 0,72% | 7,04×108 | 80 Bq | 2,4% |
| 234U | 0,0055% | 2,45×105 | 231000 Bq | 48,8% |
When uranium is enriched, the content of light isotopes, 234U and 235U, increases. Although 234U*, despite its much lower mass fraction, contributes more to the activity, the target isotope for nuclear industry use is 235U. Therefore, the degree of uranium enrichment or depletion is determined by the content of 235U. Depending on the 235U content below the natural level of 0.72%, the activity of the DUHF can be significantly lower than that of natural uranium hexafluoride.
| Type of uranium hexafluoride | Degree of 235U content | Radioactive decay rate, Bq/g | Activity with respect to natural uranium hexafluoride |
| Natural
(with natural composition of uranium isotopes) |
0,72% | 1,7×104 | 100% |
| Depleted | 0,45% | 1,2×104 | 70% |
| 0,2% | 5,3×103 | 32% | |
| 0,1% | 2,7×103 | 16% |
*The values of radioactive decay rate include the activity of 234U, which is concentrated in the enrichment process, and do not include the contribution of daughter products.
References
- ^ "Uranium Enrichment Tails Upgrading (Re-enrichment)". www.wise-uranium.org. Retrieved 2020-12-26.
- ^ "Operation of Depleted Uranium Hexafluoride (DUF6) Conversion Facilities Project". www.emcbc.doe.gov. Retrieved 2020-12-26.
- ^ "Conversion - World Nuclear Association". www.world-nuclear.org. Retrieved 2020-12-26.
- ^ a b c "Depleted Uranium". International Atomic Energy Agency. 2016-11-08. Retrieved 2020-12-26.
{{cite web}}: CS1 maint: url-status (link) - ^ "Uranium Oxide - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2020-12-26.
- ^ "Reade Advanced Materials - Uranium Metal (U) & Depleted Uranium (DU)". www.reade.com. Retrieved 2020-12-26.
{{cite web}}: CS1 maint: url-status (link) - ^ "Otto Hahn, Lise Meitner, and Fritz Strassmann". Science History Institute. 2016-06-01. Retrieved 2020-12-26.
- ^ "Fritz Strassmann | German chemist". Encyclopedia Britannica. Retrieved 2020-12-26.
- ^ Amaldi, Edoardo (2013). An Outline of the Early Development of Applied Nuclear Energy in Germany. In: Braccini S., Ereditato A., Scampoli P. (eds) The Adventurous Life of Friedrich Georg Houtermans, Physicist (1903-1966). Berlin, Heidelberg: Springer. doi:10.1007/978-3-642-32855-8_16. ISBN 978-3-642-32854-1.
- ^ Holloway, David (1981). "Entering the Nuclear Arms Race: The Soviet Decision to Build the Atomic Bomb, 1939-45". Social Studies of Science. pp. 159–197. ISSN 0306-3127.
- ^ Pondrom, Lee G (2018). The Soviet Atomic Project: How the Soviet Union Obtained the Atomic Bomb. Wisconsin, USA: World Scientific. doi:10.1142/10865. ISBN 978-981-3235-55-7.
- ^ "Uranium enrichment technologies". English. Retrieved 2020-12-26.
- ^ "Use of Reprocessed Uranium: Challenges and Options" (PDF). pub.iaea.org. Vienna: INTERNATIONAL ATOMIC ENERGY AGENCY. ISBN 978-92-0-106409-7.
{{cite web}}: CS1 maint: url-status (link) - ^ "Fluorination and oxidation of uranium tetrafluoride to uranium hexafluoride by perchloryl fluoride". Retrieved 2020-12-26.
- ^ IAEA. "Interim guidance on the safe transport of uranium hexafluoride" (PDF). pub.iaea.org.