Edge Rewrite
everything Source code View original
// HTMLRewriter · presentation

This page was redesigned at the edge.

Cloudflare fetched the original article and streamed it through HTMLRewriter to apply an entirely new visual system without rebuilding the source page.

// request.cf · coarse context

A page that knows where it met you.

Only coarse request metadata is shown. This demo does not display or persist visitor IP addresses.

Country
US
Cloudflare location
CMH
Connection
HTTP/2
Language
Not provided

Ray ID: a221ff18b860122e

Jump to content

Separation of isotopes by laser excitation

From Wikipedia, the free encyclopedia
(Redirected from SILEX)

Separation of isotopes by laser excitation (SILEX) is an experimental process for producing enriched uranium. It is strongly suspected that SILEX utilizes laser condensation repression to excite a vibrational mode of the 235
Uranium isotope in uranium hexafluoride (UF6), allowing this lighter molecule to move more rapidly to the outer rim of a gaseous jet and resist condensing compared to heavier, unexcited 238UF6.[1] This differs from previous laser enrichment methods: one using atomic uranium (atomic vapor laser isotope separation (AVLIS)) and another molecular method that uses lasers to dissociate a fluorine atom from 235UF6 (molecular laser isotope separation (MLIS)), allowing the enriched product to precipitate.[1]

While Australian company Silex Systems Limited is the most prominent developer of this technology (as part of the Global Laser Enrichment consortium), the acronym SILEX refers to a physical separation concept utilizing condensation repression.[2] Slight variations in operating parameters, equipment arrangements, lasers and their capabilities, may exist from one SILEX-type process to the next (under a different name), but the physical separation concept remains the same if condensation repression is utilized, especially when compared to that used by AVLIS or MLIS.[3][1]

History

[edit]

Development of various molecular laser isotope separation (MLIS) variants began in the 1970s. The key technology is an infrared laser, which vibrationally excites only one isotope in gaseous uranium hexafluoride. This requires a wavelength near 16 μm. Traditional MLIS continued to excite the molecules unto dissociation, at which point they crystallized as uranium-235 pentafluoride.

After initial euphoria, laser isotope separation research was mostly abandoned during the 1990s, mainly because it still required extensive and uncertain research and development work, while gas centrifuges had reached technological maturity.[4] However, Australia continued SILEX research.

In November 1996, Silex Systems Limited licensed its technology exclusively to United States Enrichment Corporation (USEC).[5] In 1999, the United States and Australia signed an international treaty for SILEX R&D.[6] However, in 2003 USEC left the project.[original research?]

Silex Systems concluded the second stage of testing in 2005 and began its Test Loop Program. In 2007, the company signed an exclusive commercialization and licensing agreement with General Electric Corporation (GE), transferring their test loop to GE's facility in Wilmington, North Carolina. That year, GE Hitachi Nuclear Energy (GEH) signed letters of intent for uranium enrichment services with Exelon and Entergy - the US' two largest nuclear utilities.[7][original research?]

In 2008, GEH spun off Global Laser Enrichment (GLE) and announced the first potential commercial SILEX facility. The Nuclear Regulatory Commission (NRC) approved a license amendment allowing GLE to operate the Test Loop. Also in 2008, Cameco Corporation, Canada, the world's largest uranium producer, joined GE and Hitachi as a part owner of GLE.[8]

In 2010, concerns were raised that the SILEX process poses a threat to global nuclear security.[9]

Between 2011 and 2012, GLE applied for and received a permit to build a commercial plant at Wilmington.[10][11] The plant would enrich to 8% 235U, the upper end of low-enriched uranium.[12]

In 2014, both GLE and Silex Systems restructured, with Silex halving its workforce.[13] In 2016 GEH withdrew from GLE, writing off their investment.[13][14]

In 2016, the United States Department of Energy (DOE) agreed to sell about 300,000 tonnes of depleted uranium hexafluoride to GLE for re-enrichment (from 0.35 to 0.7 % 235U) over 40 years at a proposed Paducah, Kentucky site.[15]

In 2018, Silex Systems abandoned plans for GLE, intending to repatriate the SILEX technology to Australia.[16]

In 2021, Silex Systems took majority ownership (51%) of GLE, with Cameco (49%) as minority owner. Under an agreement between GLE and DOE, GLE agreed to re-enrich to natural levels several hundred kilotons of depleted uranium tailings from the last enrichment plant to use gaseous diffusion. That plant operated until 2013.[17][18]

Process

[edit]
Infrared absorption spectra of the two UF6 isotopes at 300 and 80 K.
Scheme of Silex laser isotope enrichment
Schematic of a stage of an isotope separation plant for uranium enrichment with laser. An infrared laser with a wavelength of approx. 16 μm radiates at a high repetition rate onto a UF6 carrier gas mixture, which flows supersonically out of a laval nozzle. The excited component moves away from the axis of the molecular beam faster than the unexcited tailings stream which is separated at a skimmer.

The shortest-wavelength fundamental vibration of gaseous UF6 is ~16 μm. At room temperature its width (around 20 cm−1) is much larger than the isotopic shift (0.6 cm−1). The broadening is due to thermally populated excited vibrational and rotational states. To allow for selective excitation, UF6, diluted about 100x by a carrier gas (argon or nitrogen), is cooled to about 80 K by adiabatic expansion through a nozzle into vacuum. Initially, collisions occur (which are necessary for cooling). But after traveling about 10 nozzle diameters, due to the expansion, they are so rare that condensation no longer takes place. Avoiding collisions is necessary to suppress collisional transfer of energy between the isotopes. Such a molecular beam method is used where spectral narrowing is needed for selective excitation.

With SILEX, the pressure and nozzle diameter are large enough to provide a sufficient number of collisions immediately after the nozzle, to allow for formation of clusters (UF6•G) with carrier gas G. (UF6•UF6 clusters are practically not formed due to the much lower density of UF6 compared to G.) If 235UF6 is selectively excited at 628.3 cm−1, this molecule does not aggregate with G, whereas the nonexcited heavier 238UF6 does. Due to their higher thermal velocity, the free molecules leave the axis of the molecular beam faster than the clusters. The latter are therefore enriched in the part transmitted by a skimmer nozzle downstream, while the non-transmitted fraction is enriched in the 235UF6. The enrichment factor is better, the larger the transmitted fraction (i.e. the smaller the depletion and the smaller the cut). SILEX uses a separation nozzle, modified by a laser and profiting from selective repression of cluster formation ("condensation").

For that, the CO2 laser needs at least 20 MW. With a Raman shift of 354.3 cm−1 and a CO2 laser wavenumber of 982.1 cm−1 (10R30 line), one receives 627.8 cm−1. This is close to the Q-branch of 235UF6 (center at 628.3 cm−1, width 0.01 cm−1 [19]) and is closer to the Q-branch of 238UF6. GLE does not publish how they accomplish the necessary fine tuning. High-pressure CO2 lasers would cause additional problems with the pulse repetition rate. With common (atmospheric-pressure) CO2 lasers and with the stimulated Raman shifter, the state of technology is 2–4 kHz.[20] In order not to leave large parts of the molecular beam unirradiated, one needs at least 20 kHz (according to Urenco several tens of kHz[21]), unless pulsed nozzles are used. The nozzles must have slit form, in order to provide enough absorption length.

GLE states that they reach separation factors of 2–20. The higher values are likely coupled to poorer depletion (which is not explained). This is sufficient for enrichment from natural uranium (0.72 % 235U) to reactor grade (> 3% 235U). The pioneer works of the van den Bergh group obtained much smaller enrichments with SF6.[22]

Using lasers with suitable wavelengths, SILEX can enrich elements such as chlorine, molybdenum, carbon and silicon.

Proliferation concerns

[edit]

Compared to alternative enrichment technologies, SILEX achieves higher enrichment levels. Fewer stages are necessary to reach weapons-grade uranium (> 90% 235U). According to GLE, each stage requires as little as 25% of the space of centrifuge methods. It could enable rogue governments to more easily conceal enrichment facilities.[9] The appeal is further enhanced by claims from GLE that a SILEX plant is faster and cheaper to build and consumes less energy. Scientists have therefore repeatedly expressed their concerns that SILEX could create an easy path towards a nuclear weapon.[1][23]

Security classification

[edit]

In June 2001, DOE classified "certain privately generated information concerning an innovative isotope separation process for enriching uranium". Under the Atomic Energy Act, all information not specifically declassified is classified as Restricted Data, whether it is privately or publicly held. This is in marked distinction to the national security classification executive order, which states that classification can only be assigned to information "owned by, produced by or for, or is under the control of the United States Government". This is the only known case in which the Atomic Energy Act is used in such a manner.[24][25]

[edit]

The 2014 Australian Broadcasting Corporation drama The Code uses "Laser Uranium Enrichment" as a plot device. Protagonist Sophie Walsh states that the technology will be smaller, less energy-intensive, and more difficult to control once it becomes a viable alternative. Walsh also states that development has been protracted, and that significant governmental interests work to maintain the classified status of the technology.

References

[edit]
  1. 1 2 3 4 Snyder, Ryan (2016-05-03). "A Proliferation Assessment of Third Generation Laser Uranium Enrichment Technology". Science & Global Security. 24 (2): 68–91. Bibcode:2016S&GS...24...68S. doi:10.1080/08929882.2016.1184528. ISSN 0892-9882.
  2. ↑ Snyder, Ryan (2021-05-18). "Proliferation Risks of Laser Enrichment of Uranium". National Academy of Sciences.
  3. ↑ W. Eberhardt (DESY), W. Fuss (MPQ), F. Lehner (DESY), and R. Snyder (IFSH) (2019-11-04). FELs and Laser Isotope Separation. Deutsches Elektronen-Synchrotron (DESY) and European XFEL.{{cite book}}: CS1 maint: multiple names: authors list (link)
  4. ↑ Schneider, K. R. (Mar 1995). LIS: The view from Urenco (PDF). 6th Int'l. Symp. on Adv. Nucl. Energy Research (Mito, Japan; 23–25 March 1994). Tokyo: Japan Atomic Energy Research Institute. pp. 280–289 – via INIS.
  5. ↑ "Silex Systems Ltd: New Laser Technology for Uranium Enrichment". Sustainable Energy & Anti-Uranium Service Inc. Archived from the original on 2007-05-14. Retrieved 2006-04-21.
  6. ↑ “Agreement for Cooperation between the Government of Australia and the Government of the United States of America concerning Technology for the Separation of Isotopes of Uranium by Laser Excitation (SILEX Agreement), Agreed Minute and Exchange of Notes (Washington, 28 October 1999). ATS 19 of 2000” Archived 16 April 2017 at the Wayback Machine. Australasian Legal Information Institute, Australian Treaties Library. Retrieved on 15 April 2017.
  7. ↑ "The Biggest Nuclear Operators In The United States". Investopedia US. 2011-03-28. Archived from the original on 2012-11-07. Retrieved 2012-08-28.
  8. ↑ "Cameco Joins GE Hitachi Enrichment Venture". Cameco. 2008-06-20. Archived from the original on 2012-08-09. Retrieved 2012-08-28.
  9. 1 2 McMurtrie, Craig (2010-04-13). "Australian laser 'threatens nuclear security'". ABC Online. Archived from the original on 2012-08-29. Retrieved 2012-08-28.
  10. ↑ Broad, William J. (2011-08-20). "Laser Advances in Nuclear Fuel Stir Terror Fear". The New York Times. Archived from the original on 2012-11-03. Retrieved 2012-08-28.
  11. ↑ Nuclear Regulatory Commission announcement |date=2012-09-19| http://pbadupws.nrc.gov/docs/ML1226/ML12263A046.pdf
  12. ↑ "Lasers point to the future of uranium enrichment". Gizmag.com. 6 November 2013. Retrieved 2013-11-06.
  13. 1 2 Patel, Sonal (1 June 2016). "GE-Hitachi Exits Nuclear Laser-Based Enrichment Venture". POWER. Retrieved 1 April 2017.
  14. ↑ Yasuhara, Akiko (31 March 2017). "Toshiba's U.S. unit bankruptcy dims Japan's nuclear ambitions". The Japan Times. Retrieved 1 April 2017.
  15. ↑ "US DOE sells depleted uranium for laser enrichment". World Nuclear News. 2016-11-11. Archived from the original on 2016-11-16. Retrieved 2025-04-22.
  16. ↑ "Silex Systems out of GLE restructure". World Nuclear News. 2018-06-13. Archived from the original on 2018-06-20. Retrieved 2025-04-22.
  17. ↑ Silex gets go ahead to enrich stockpiles to enrich uranium, AuManufacturing, 19 Jan 2021.
  18. ↑ "Global Laser Enrichment | Silex".
  19. ↑ Takami, Michio; Oyama, Toshiyuki; Watanabe, Tsunao; Namba, Susumu; Nakane, Ryohei (1984-02-01). "Cold Jet Infrared Absorption Spectroscopy: The ν 3 Band of UF 6". Japanese Journal of Applied Physics. 23 (2A): L88. doi:10.1143/JJAP.23.L88. ISSN 0021-4922. S2CID 93245695.
  20. ↑ Ronander, Einar; Rohwer, Erich G. (1993-05-04). Fotakis, Costas; Kalpouzos, Costas; Papazoglou, Theodore G. (eds.). "Multikilowatt TEA-CO2 laser system for molecular laser isotope separation". 9th International Symposium on Gas Flow and Chemical Lasers. 1810. Heraklion, Greece: 49–52. Bibcode:1993SPIE.1810...49R. doi:10.1117/12.144664. S2CID 94250559. {{cite journal}}: Cite journal requires |journal= (help)
  21. ↑ k. r., Schneider (1995). LIS: The view from Urenco. pp. 280–289.
  22. ↑ Zellweger, J. -M.; Philippoz, J. -M.; Melinon, P.; Monot, R.; van den Bergh, H. (1984-03-19). "Isotopically Selective Condensation and Infrared-Laser-Assisted Gas-Dynamic Isotope Separation". Physical Review Letters. 52 (12): 1055. Bibcode:1984PhRvL..52.1055Z. doi:10.1103/PhysRevLett.52.1055. ISSN 0031-9007.
  23. ↑ Boureston, Jack; Ferguson, Charles D. (2005-03-01). "Laser Enrichment: Separation anxiety". Bulletin of the Atomic Scientists. 61 (2): 14–18. doi:10.2968/061002005. ISSN 0096-3402.
  24. ↑ Steven Aftergood (26 June 2001). "DOE classifies privately held info". Secrecy News, Federation of American Scientists. Retrieved 2007-08-23.
  25. ↑ Steven Aftergood (23 August 2007). "A glimpse of the SILEX uranium enrichment process". Secrecy News, Federation of American Scientists. Retrieved 2007-08-23.
[edit]
Retrieved from "https://en.wikipedia.org/w/index.php?title=Separation_of_isotopes_by_laser_excitation&oldid=1366469096"