Gas centrifuge versus laser uranium enrichment

General Electric has licenced and is commercializing a laser uranium enrichment process. The Silex laser uranium enrichment process has been indicated to be an order of magnitude more efficient than existing production techniques but again, the exact figure is classified.

Australian scientists Michael Goldsworth and Horst Struve developed the process, and from 1996 to 2002 received support from the United States Enrichment Corp. (Bethesda, MD); the two scientists have since formed a public corporation, Silex Systems (Lucas Heights, NSW, Australia). Last year they licensed the Silex process to General Electric. The process is based on selective excitation of uranium hexafluoride (UF6) molecules that contain U-235 by laser light at a narrow spectral line near 16 µm, but few details have been released (see figure). The Los Alamos National Laboratory (Los Alamos, NM) initially explored the concept three decades ago, but the U.S. Department of Energy later abandoned it in favor of atomic-vapor laser isotope enrichment.

The CO2 lasers can generate 1 J pulses, but only at a limited repetition rate, and only a fraction of the pulse is in the pump band. Unspecified “additional nonlinear optical tricks” are needed to convert the CO2 pump light to the correct wavelength to pump the Raman cell. The lasers are 1% efficient and the Raman conversion 25% efficient, so the overall efficiency is 0.25%.

With many details classified or proprietary, it is hard to quantify the processing. Lyman wrote that if a laser could illuminate a one-liter volume at an ideal repetition rate, it would take about 100 hours to produce one kilogram of U-235-assuming complete separation of the U-235 and U-238 isotopes. However, most processes require multiple stages of separation, and according to Lyman’s comments, a 5000 Hz laser would be needed to process all the feed stream (a mixture of UF6 and an unidentified diluting gas).

Solid state lasers able to be continuously tuned from the 0.2 to 10 micron range

Free electron lasers can operate 3 to 100 microns and in the 6-35 micron ranges

The US Navy has funded development of megawatt solid state free electron lasers for delivery in 2012

The new solid state lasers could be more efficient for the desired frequency and wavelengths.

The specific energy consumption is 2300-3000 kWh/SWU for Gaseous Diffusion, versus 100-300 kWh/SWU for gas centrifuge. The number of stages required to produce LEU is about 30 times larger in the diffusion plant than in the centrifuge plant.

A kilogram of LEU requires roughly 11 kilograms U as feedstock for the enrichment process and about 7 separative work units (SWUs) of enrichment services. To produce one kilogram of uranium enriched to 3.5% U-235 requires 4.3 SWU if the plant is operated at a tails assay 0.30%, or 4.8 SWU if the tails assay is 0.25% (thereby requiring only 7.0 kg instead of 7.8 kg of natural U feed).

Areva’s recently announced Idaho enrichment plant, estimated to cost $2 billion, is expected to supply 3 million SWU or half the capacity of the GE plant at full production. The full-scale GE plant, expected to supply 3.5-6.0 million SWU, will require additional investor commitments. The GE laser enrichment plant would start at 1 million SWU/year and then get expanded Close to one million kilograms/year of enriched uranium using 7 SWU per kg.

25 page powerpoint presentation made April 2008 on Silex

Silex is also examining Oxygen-18 (PET medical imaging) and Carbon-13 (medical diagnostic) laser separation.
Laser enrichment at Idaho Samizdat

Silex company site

Worldwide Uranium demand and Nuclear Reactor fuel requirements translate into a requirement for uranium enrichment separative work services in the range 35–38 million SWU/year over the next 10 years.

About 120,000 kg SWU are required to enrich the annual fuel loading for a typical large (1,000 MWe) nuclear reactor.

The Silex process is inefficient for highly enriched uranium at this time

The up to ten times greater enrichment efficiency improves the energy efficiency of nuclear power and the cost efficiency of nuclear fuel and operations.

Uranium: 8.9 kg U3O8 x $53 472
Conversion: 7.5 kg U x $12 90
Enrichment: 7.3 SWU x $135 985 [Silex could reduce this by 3-10 times]
Fuel fabrication: per kg 240
Total, approx: US$ 1787

About The Author