:Depleted uranium hexafluoride

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.{{Cite web|language=en|url=https://www.sciencehistory.org/historical-profile/otto-hahn-lise-meitner-and-fritz-strassmann|title=Otto Hahn, Lise Meitner, and Fritz Strassmann|website=Science History Institute|date=2016-06-01|access-date=2020-12-26}}{{Cite web|language=en|url=https://www.britannica.com/biography/Fritz-Strassmann|title=Fritz Strassmann {{!}} German chemist|website=Encyclopedia Britannica|access-date=2020-12-26}}{{Cite book|last=Amaldi|first=Edoardo|title=The Adventurous Life of Friedrich Georg Houtermans, Physicist (1903-1966) |chapter=An Outline of the Early Development of Applied Nuclear Energy in Germany |series=SpringerBriefs in Physics |publisher=Springer|year=2013|isbn=978-3-642-32854-1|location=Berlin, Heidelberg|pages=83–93|doi=10.1007/978-3-642-32855-8_16}} This discovery marked the beginning of the peaceful and military use of the nuclear energy of uranium.{{Cite journal|first=David|last=Holloway|title=Entering the Nuclear Arms Race: The Soviet Decision to Build the Atomic Bomb, 1939-45|year=1981|language=en|journal=Social Studies of Science|volume=11|issue=2|pages=159–197|doi=10.1177/030631278101100201|jstor=284865|s2cid=145715873|issn=0306-3127}} A year later, Yulii Khariton and Yakov Zeldovich were the first to prove theoretically that with an enrichment of ²³⁵U in natural uranium, a chain reaction could be sustained.{{Cite book|last=Pondrom|first=Lee G|title=The Soviet Atomic Project: How the Soviet Union Obtained the Atomic Bomb|publisher=World Scientific|year=2018|isbn=978-981-3235-55-7|location=Wisconsin, USA|pages=|doi=10.1142/10865|s2cid=158496106}} This nuclear chain reaction requires on average that at least one neutron, released by the fission of an atom of ²³⁵U, will be captured by another atom of ²³⁵U and will cause it also to fission. The probability of a neutron being captured by a fissile nucleus should be high enough to sustain the reaction. To increase this probability, an increase in the proportion of ²³⁵U is necessary, which in natural uranium constitutes only 0.72%, along with 99.27% ²³⁸U and 0.0055% ²³⁴U.

By the mid-1960s, the United States had a monopoly on the supply of uranium fuel for Western nuclear power plants.{{Cite book |title=Uranium enrichment and nuclear weapon proliferation|date=1983|publisher=International Publications Service, Taylor & Francis|author=Krass, Allan S. |author2=Stockholm International Peace Research Institute |isbn=0-85066-219-2|location=New York|oclc=9489089}} In 1968, the USSR declared its readiness to accept orders for uranium enrichment.{{Cite journal|author=Bukharin|first=Oleg|title=Understanding Russia's Uranium Enrichment Complex|url=http://fissilematerials.org/library/sgs12bukharin.pdf |journal=Science & Global Security|year=2004|volume=12|issue=3|pages=193–214|language=en|doi=10.1080/08929880490521546|bibcode=2004S&GS...12..193B|s2cid=122263881|issn=0892-9882}} As a result, a competitive market formed in the world, and commercial enrichment companies began to appear (e.g., URENCO and Eurodif). In 1971, the first Soviet contract was signed with the French Alternative Energies and Atomic Energy Commission, where nuclear power plants were actively built. In 1973, roughly 10 long-term contracts were signed with power companies from Italy, Germany, Great Britain, Spain, Sweden, Finland, Belgium and Switzerland.{{Cite web|language=ru|url=https://tenex.ru/media-center/coverage/tenex-50-let-na-yadernom-rynke/index.php|title=TENEX: 50 years on the nuclear market|author=|website=Stock company «Techsnabexport»|date=|publisher=|access-date=2020-12-26}} By 2017, large commercial enrichment plants have been operating in France, Germany, the Netherlands, Great Britain, the United States, Russia and China.{{Cite web|url=https://ec.europa.eu/euratom/observatory_segments_e.html|title=Nuclear Observatory Segments|website=ec.europa.eu|access-date=2020-12-26}} The development of the enrichment market has led to the accumulation of over 2 million tons of DUHF in the world during this period.{{Cite web|language=en|url=https://bellona.org/news/nuclear-issues/2020-08-the-adventures-of-depleted-uranium-hexafluoride-in-russia|title=The adventures of depleted uranium hexafluoride|author=|website=Bellona.org|date=2020-08-06|publisher=|access-date=2020-12-26}}

Depleted uranium may exist in several chemical forms; in the form of DUHF, the most common form, with a density of 5.09 g/cm³, in the form of depleted triuranium octoxide (U₃O₈) with a density of 8.38 g/cm³, and in the form of depleted uranium metal with a density of 19.01 g/cm³.{{Cite web|author=UNITED STATES DEPARTMENT OF ENERGY|date=|title=Uranium Metal Reaction Behavior in Water, Sludge, and Grout Matrices|url=https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-17815.pdf|url-status=live|archive-url=https://web.archive.org/web/20210506230946/https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-17815.pdf |archive-date=2021-05-06 |website=pnnl.gov|publisher=|language=en}}

Since the various uranium isotopes share the same chemical properties, the chemical and physical properties of depleted, enriched, and unenriched UF₆ are identical, except for the degree of radioactivity. Like other forms of UF₆, under standard conditions, DUHF forms white crystals, with a density of 5.09 g/cm3. At pressures below 1.5 atm, the solid DUHF sublimes into gas when heated, with no liquid form. At 1 atm, the sublimation point is 56.5 °C. The critical temperature of DUHF is 230.2 °C, and the critical pressure is 4.61 MPa.

The radioactivity of DUHF is determined by the isotopic composition of uranium because the fluorine in the compound is stable. The radioactive decay rate of natural UF₆ (with 0.72% ²³⁵U) is 1.7×10⁴ Bq/g of which 97.6% is due to ²³⁸U and ²³⁴U.

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 specified by the content of ²³⁵U. The reduction of ²³⁴U, and to a slight degree ²³⁵U, content reduces the radioactivity below unenriched UF₆.

File:Uranium Hexafluoride Enrichment.svg

Low enriched uranium with enrichment of 2 to 5% ²³⁵U (with some exceptions when using 0.72% in natural composition, for example in Canadian CANDU reactors) is used for nuclear power, in contrast to weapons-grade highly enriched uranium with ²³⁵U content of over 20% and usually over 90%. Various methods of isotope separation are used to produce enriched uranium, mainly gas centrifugation and, in the past, the gaseous diffusion method. Most of them work with gaseous UF₆, which in turn is produced by fluorination of elemental uranium tetrafluoride (UF₄ + F₂ → UF₆) or uranium oxides (UO₂F₂ + 2 F₂ → UF₆ + O₂), both highly exothermic.

Since UF₆ is the only uranium compound that is gaseous at a relatively low temperature, it plays a key role in the nuclear fuel cycle as a substance suitable for separating ²³⁵U and ²³⁸U.{{Cite web|language=en|url=https://energyeducation.ca/encyclopedia/Uranium_hexafluoride|title=Uranium hexafluoride - Energy Education|website=energyeducation.ca|access-date=2020-12-26}} After obtaining enriched UF₆, the remainder (approximately 95% of the total mass) is transformed into depleted UF₆ , which consists mainly of ²³⁸U, because its ²³⁵U content is reduced by perhaps a factor of three, and its ²³⁴U content by a factor of six (depending on the degree of depletion). In 2020, nearly two million tons of depleted uranium was accumulated in the world. Most of it is stored in the form of DUHF in special steel tanks.{{Cite web|language=en|url=https://www.nrc.gov/materials/fuel-cycle-fac/ur-deconversion/faq-depleted-ur-decon.html|title=Frequently Asked Questions about Depleted Uranium Deconversion Facilities|author=|website=U.S. Nuclear Regulatory Commission|date=|publisher=|access-date=2020-12-26}}

The methods of handling depleted uranium in different countries depends on their nuclear fuel cycle strategy. The International Atomic Energy Agency (IAEA) recognizes that policy determination is the prerogative of the government (para. VII of the Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management).{{Cite web|language=en|url=https://www.iaea.org/publications/7452/joint-convention-on-the-safety-of-spent-fuel-management-and-on-the-safety-of-radioactive-waste-management|title=Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management|website=www.iaea.org|date=2017-10-16|access-date=2020-12-26}} Given the technological capabilities and concepts of the nuclear fuel cycle in each country, with access to separation facilities, DUHF may be considered as a valuable raw material on one hand or low-level radioactive waste on the other. Therefore, there is no unified legal and regulatory status for DUHF in the world. The IAEA expert report {{ISBN|92-64-195254}}, 2001 and the joint report of the OECD, NEA and IAEA Management of Depleted Uranium, 2001 recognize DUHF as a valuable raw material.{{Cite web|author=|first=|date=|title=DEPLETED URANIUM HEXAFLUORIDE|url=https://network.bellona.org/content/uploads/sites/3/2020/08/Depleted-Uranium-Hexafluoride.pdf|url-status=live|archive-url=https://web.archive.org/web/20200810102620/https://network.bellona.org/content/uploads/sites/3/2020/08/Depleted-Uranium-Hexafluoride.pdf |archive-date=2020-08-10 |website=network.bellona.org|publisher=Bellona Foundation Environmental Protection NGO 'Ecopravo' Expert and Legal Center|language=en}}{{Cite web|language=en|url=https://www.oecd-nea.org/jcms/pl_13470/management-of-depleted-uranium?details=true|title=Management of Depleted Uranium|website=Nuclear Energy Agency (NEA)|access-date=2020-12-26}}

As a result of chemical conversion of DUHF, anhydrous hydrogen fluoride and/or its aqueous solution (i.e. hydrofluoric acid) are obtained, which have a certain demand in non-nuclear energy markets, such as the aluminum industry, in production of refrigerants, herbicides, pharmaceuticals, high-octane gasoline, plastics, etc.{{Cite web|author=|date=|title=Processing of an aqueous solution of hydrogen fluoride|url=http://newchem-products.ru/en/processing-aqueous-solution-of-hydrogen-fluoride/|access-date=2020-12-26|website=NCP — New chemical products {{!}} resident of Skolkovo|publisher=|language=en}} It is also applied in the reuse of hydrogen fluoride in the production of UF₆ via the conversion of U₃O₈ into uranium tetrafluoride (UF₄), before further fluorination into UF₆.{{Cite web|author=PubChem|title=Hydrofluoric acid|url=https://pubchem.ncbi.nlm.nih.gov/compound/14917|access-date=2020-12-26|website=pubchem.ncbi.nlm.nih.gov|language=en}}

There are multiple directions in the world practice of DUHF reprocessing. Some of them have been tested in a semi-industrial setting, while others have been and are being operated on an industrial scale with an effort to reduce the reserves of uranium tailings and provide the chemical industry with hydrofluoric acid and industrial organofluorine products.{{Cite web|title=Radioactive Waste Management {{!}} Nuclear Waste Disposal - World Nuclear Association|url=https://www.world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-wastes/radioactive-waste-management.aspx|access-date=2020-12-26|website=www.world-nuclear.org}}{{Cite web|author=IAEA|date=|title=Status and Trends in Spent Fuel and Radioactive Waste Management|url=https://www-pub.iaea.org/MTCD/publications/PDF/P1799_web.pdf|website=pub.iaea.org|publisher=|language=en}}

Depending on nuclear fuel cycle strategy, technological capabilities, international conventions and programs, such as the Sustainable Development Goals (SDG) and the UN Global Compact, each country approaches the issue of the use of accumulated depleted uranium individually.{{Cite web|language=en|url=https://www.un.org/en/un-chronicle/un-global-compact-finding-solutions-global-challenges|title=The UN Global Compact: Finding Solutions to Global Challenges|author=United Nations|website=United Nations|access-date=2020-12-26}}{{Cite web|language=en|url=https://www.undp.org/content/undp/en/home/sustainable-development-goals.html|title=Sustainable Development Goals|website=UNDP|access-date=2020-12-26}} The United States has adopted a number of long-term programs for the safe storage and reprocessing of DUHF stocks prior to their final disposal.{{Cite web|language=en|url=https://www.energy.gov/pppo/pppo-services/pppo-cleanup-projects-portsmouth-paducah-duf6/duf6-conversion-project|title=DUF6 Conversion Project|website=Energy.gov|access-date=2020-12-26}}{{Cite web|url=https://www.fluor.com/projects/operations-uranium-hexafluoride-facilities|title=Depleted Uranium Hexafluoride Conversion Operations - Fluor|website=www.fluor.com|access-date=2020-12-26}}{{Cite web|date=|title=URANIUM From exploration to remediation|url=https://www.iaea.org/sites/default/files/bull592june2018corr.pdf|url-status=live|archive-url=https://web.archive.org/web/20210122052011/https://www.iaea.org/sites/default/files/bull592june2018corr.pdf |archive-date=2021-01-22 |website=|publisher=International Atomic Energy Agency|language=en}}

Under the UN SDG, nuclear power plays a significant role not only in providing access to affordable, reliable, sustainable and modern energy (Goal 7), but also in contributing to other goals, including supporting poverty, hunger and water scarcity elimination, economic growth and industry innovation.{{Cite web|language=en|url=https://www.un.org/en/chronicle/article/goal-7-ensure-access-affordable-reliable-sustainable-and-modern-energy-all|title=Goal 7—Ensure Access to Affordable, Reliable, Sustainable and Modern Energy for All|author=United Nations|website=United Nations|access-date=2020-12-26}}{{Cite web|author=|first=|date=February 15, 2019|title=The Role of Nuclear Energy in Sustainable Development: Entry Pathways|url=https://unece.org/fileadmin/DAM/energy/se/pdfs/egrm/egrm10_apr2019/ECE_ENERGY_GE.3_2019_6_e.pdf|url-status=live|archive-url=https://web.archive.org/web/20210122051923/https://unece.org/fileadmin/DAM/energy/se/pdfs/egrm/egrm10_apr2019/ECE_ENERGY_GE.3_2019_6_e.pdf |archive-date=2021-01-22 |website=UNECE|publisher=Committee on Sustainable Energy|location=Geneva|language=en}} Several countries, such as the United States, France, Russia, and China, through their leading nuclear power operators, have committed to achieving the Sustainable Development Goals.{{Cite web|language=en|url=https://www.iaea.org/sites/default/files/np-sustainable-development.pdf|title=Nuclear Power for Sustainable Development|author=IAEA|website=iaea.org|date=|publisher=}} To achieve these goals, various technologies are being applied both in the reprocessing of spent fuel and in the reprocessing of accumulated DUHF.{{Cite web|url=https://world-nuclear-news.org/Articles/First-serial-batch-of-MOX-fuel-loaded-into-BN-800|title=First serial batch of MOX fuel loaded into BN-800: Uranium & Fuel - World Nuclear News|website=world-nuclear-news.org|access-date=2020-12-26}}{{Cite web|url=https://www.world-nuclear.org/information-library/nuclear-fuel-cycle/fuel-recycling/processing-of-used-nuclear-fuel.aspx|title=Processing of Used Nuclear Fuel - World Nuclear Association|website=www.world-nuclear.org|access-date=2020-12-26}}{{Cite web|language=en|url=https://www.energy.gov/ne/articles/3-advanced-reactor-systems-watch-2030|title=3 Advanced Reactor Systems to Watch by 2030|website=Energy.gov|access-date=2020-12-26}}{{Cite web|language=en|url=https://www.sciencedaily.com/releases/2020/01/200110101025.htm|title=Unused stockpiles of nuclear waste could be more useful than we might think: Chemists have found a new use for the waste product of nuclear power|website=ScienceDaily|access-date=2020-12-26}}{{Cite web|language=en|url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/31/004/31004098.pdf?r=1&r=1|title=Recycle and reuse of materials and components from waste streams of nuclear fuel cycle facilities|author=IAEA|website=inis.iaea.org|date=|publisher=}}

International policies for transporting radioactive materials are regulated by the IAEA since 1961.{{Cite web|url=https://www.world-nuclear.org/information-library/nuclear-fuel-cycle/transport-of-nuclear-materials/transport-of-radioactive-materials.aspx|title=Transport of Radioactive Materials - World Nuclear Association|website=www.world-nuclear.org|access-date=2020-12-26}}{{Cite web|language=en|url=https://www-pub.iaea.org/MTCD/publications/PDF/Pub1570_web.pdf|title=Regulations for the Safe Transport of Radioactive Material 2012 Edition|author=IAEA|website=pub.iaea.org|date=|publisher=}} These regulations are implemented in the policies of the International Civil Aviation Organization, International Maritime Organization, and regional transport organizations.{{Cite web|url=https://web.evs.anl.gov/uranium/mgmtuses/transport/index.cfm|title=Transportation|website=web.evs.anl.gov|access-date=2020-12-26}}

Depleted UF₆ is transported and stored under standard conditions in solid form and in sealed metal containers with wall thickness of about 1 cm (0.39 in), designed for extreme mechanical and corrosive impacts.{{Cite web|language=en|url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/28/030/28030673.pdf|title=Manual on safe production, transport, handling and storage of uranium hexafluoride|author=IAEA|website=inis.iaea.org|date=|publisher=}} For example, the most common "48Y" containers for transportation and storage contain up to 12.5 tons of DUHF in solid form.{{Cite web|language=en|url=https://www.wnti.co.uk/media/87140/WNTI%20STANDARD%20-%20UF6%20Cylinder%20Identification%20-%20Version%20--%20Final%20-%202017.pdf|title=UF6 Cylinder Identification|author=World nuclear transport institute|website=wnti.co.uk|date=|publisher=|access-date=2021-01-17|archive-date=2021-02-02|archive-url=https://web.archive.org/web/20210202192242/https://www.wnti.co.uk/media/87140/WNTI%20STANDARD%20-%20UF6%20Cylinder%20Identification%20-%20Version%20--%20Final%20-%202017.pdf|url-status=dead}}{{Cite tech report |language=en |title=Uranium hexafluoride: A manual of good handling practices. Revision 7 |year=1995 |publisher=U.S. Enrichment Corp |location=Bethesda, MA |osti=205924 |osti-access=free}} DUHF is loaded and unloaded from these containers under factory conditions when heated, in liquid form and via special autoclaves.{{Cite book |title=Affordable Cleanup?: Opportunities for Cost Reduction in the Decontamination and Decommissioning of the Nation's Uranium Enrichment Facilities |publisher=National Academy Press |year=1996 |isbn=978-0-309-05438-6|location=|page=157|language=en|doi=10.17226/5114 |doi-access=free}}

Due to its low radioactivity, the main health hazards of DUHF are connected to its chemical effects on bodily functions. Chemical exposure is a major hazard at facilities associated with the processing of DUHF. Uranium and fluoride compounds such as hydrogen fluoride (HF) are toxic at low levels of chemical exposure. When DUHF comes in contact with air moisture, it reacts to form HF and gaseous uranyl fluoride. HF is a corrosive acid that can be extremely dangerous if inhaled; it is one of the major work hazards in such industries.

In many countries, current occupational exposure limits for soluble uranium compounds are related to a maximum concentration of 3 μg of uranium per gram of kidney tissue. Any effects caused by exposure to these levels on the kidneys are considered minor and temporary. Current practices based on these limits provide adequate protection for workers in the uranium industry. To ensure that these kidney concentrations are not exceeded, legislation limits long-term (8 hours) concentrations of soluble uranium in workplace air to 0.2 mg per cubic meter and short-term (15 minutes) to 0.6 mg per cubic meter

In August 1984, the freighter MS Mont Louis sank in the English Channel with 18 containers of slightly depleted (0.67% ²³⁸U) uranium hexafluoride on board, along with enriched and natural UF₆. The 30 containers (type 48Y) of UF₆ were recovered, as well as 16 of the 22 empty containers (type 30B). Examination of the 30 containers revealed, in one case, a small leak in the shutoff valve. There were 217 samples taken, subjected to 752 different analyses and 146 measurements of dose levels on the containers. There was no evidence of leakage of either radioactive (natural or recycled uranium) or hazardous chemical substances (fluorine or hydrofluoric acid).{{Cite web|language=en|url=https://www.iaea.org/sites/default/files/publications/magazines/bulletin/bull27-1/27104592832.pdf|pages=28–31|title=The sinking of the Mont-Louis and nuclear safety|author=Bernard Augustin|website=iaea.org|date=|publisher=}}{{Cite web|url=https://inis.iaea.org/search/searchsinglerecord.aspx?recordsFor=SingleRecord&RN=18023280|title=INIS Repository Search - Single Result|website=inis.iaea.org|access-date=2020-12-26}} According to The Washington Post, this incident was not hazardous because the uranium cargo was in its natural state, with an isotope ²³⁵U content of 0.72% or less, and only some of it was enriched to 0.9%.{{Cite web|language=en|url=https://www.washingtonpost.com/gdpr-consent/?next_url=https%3a%2f%2fwww.washingtonpost.com%2farchive%2fpolitics%2f1984%2f09%2f01%2fa-cargo-of-uranium%2f7d9716f2-22a3-4012-a580-92a4abd8b96c%2f|title=A Cargo of Uranium|author=The Washington Post|website=washingtonpost.com|date=|publisher=}}

• Traveling wave reactor - a reactor concept that uses depleted uranium for fuel

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Category:Element toxicology

Uranium, Depleted

Category:Uranium