October 26, 2010

Laser Uranium Enrichment

IEEE Spectrum covers laser uranium enrichment. I have extracted the useful technical information and left out the IEEE Spectrum extra trash talking.

This site has covered the silex laser enrichment technology that is being commercialized by GE and its partners.

GE has called the laser method a "game-changing technology" and along with Hitachi and Cameco Corp., a Canadian nuclear fuel provider in Saskatoon, Sask., is devoting hundreds of millions of dollars to developing it and building the plant near Wilmington, N.C. The technology in question was licensed from Silex Systems, an Australian company that's been quietly conducting enrichment research at a small facility near Sydney for the last quarter century.





A laser facility would be both smaller in size and have much lower energy demands than existing enrichment plants.

A laser tuned to the precise vibrational frequency of a U-235 atom or a molecule containing U-235 can cause that isotope to behave differently from the heavier U-238.

Broadly, in the method that Silex explored, called molecular laser isotope separation, enrichment begins with uranium hexafluoride gas—in which each uranium atom is surrounded by six fluorine atoms—mixed with an inert gas that dilutes the uranium. The gas is cryogenically cooled and shot out of a nozzle at supersonic speeds. Rapid-fire pulses from an infrared laser penetrate the gas, increasing the vibrational energy in the U-235 molecules' chemical bonds.

That higher vibrational energy causes each U-235 molecule to react more quickly with a third substance in the gas stream, explains Garratt. In one version of the process, a new molecule forms around the U-235. The new molecule lasts for less than a microsecond before breaking apart, and the repelling force from that event pushes the U-235 to the edges of the stream, where it can then be siphoned off.

Though the precise mechanics of Silex's process may differ, the underlying logic is that illuminating a gas with a laser would require only a fraction of the energy needed by the two methods used now to enrich uranium—spinning the gas in a series of centrifuges or repeatedly forcing it through a porous membrane.

At least that's the theory. In practice, several obstacles have kept the technology in the lab. "These lasers are unlike any other in the world—basically, if you need a laser, you've got to go invent one," says Bruce Warner, a laser physicist who led Lawrence Livermore National Laboratory's enrichment program, in Livermore, Calif., until the program's demise in the late 1990s.

According to several laser enrichment experts, Silex's approach likely begins with a 10.8-micrometer carbon dioxide laser that pulses hundreds of times per second. The infrared pulses travel through elaborate optics that tune their wavelengths to the needed 16 µm. Each pulse must contain about one joule of energy and be repeated fast enough to expose as much gas as possible

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