The atomic vapor laser isotope separation (AVLIS) process is based on the fact that 235 U atoms and 238 U atoms absorb light of different frequencies (or colors). Although the absorption frequencies of these two isotopes differ only by a very small amount (about one part in a million), the dye lasers used in AVLIS can be tuned so that only the 235 U atoms absorb the laser light. As the 235 U atom absorbs the laser light, its electrons are excited to a higher energy state. With the absorption of sufficient energy, a 235 U atom will eject an electron and become a positively charged ion. The 235 U ions may then be deflected by an electrostatic field to a product collector. The 238 U atoms remain neutral and pass through the product collector section and are deposited on a tails collector.
The AVLIS process consists of a laser system and a separation system. The separator system contains a vaporizer and a collector. In the vaporizer, metallic uranium is melted and vaporized to form an atomic vapor stream. The vapor stream flows through the collector, where it is illuminated by the precisely tuned laser light. The AVLIS laser system is a pumped laser system comprised of one laser used to optically pump a separate dye laser, which produces the light used in the separation process. Dye master oscillator lasers provide precise laser beam frequency, timing, and quality control. The laser light emerging from the dye master oscillator laser is increased in power by passage through a dye laser amplifier. A total of three colors are used to ionize the 235 U atoms.
Many countries are pursuing some level of AVLIS research and/or development, and major programs exist in the United States, France, Japan, and probably Russia. Principal advantages of the AVLIS process include a high separation factor, low energy consumption (approximately the same as the centrifuge process), and a small volume of generated waste. However, no country has yet deployed an AVLIS process, although several have demonstrated the capability to enrich uranium with the process.
Lawrence Livermore National Laboratory was responsible for the development of the Atomic Vapor Laser Isotope Separation process for enriching uranium and transfer of the technology to the U.S. Enrichment Corporation (USEC). The Atomic Vapor Laser Isotope Separation process was operated in 1985 at the Former K-25 Site at the East Tennessee Technology Park. DOE spent more than $1.7 billion developing the technology. USEC announced in June 1999 that it was suspending further In July 1994, the USEC Board of Directors authorized their management to begin taking necessary steps to commercialize AVLIS technology. In April 1995, USEC and DOE entered into an agreement that provided for the transfer of intellectual and physical property pertaining to AVLIS enrichment technology to USEC. USEC expected to operate AVLIS commercially in 2004. The U.S. Enrichment Corporation came to the conclusion that AVLIS would never be profitable. In June 1999, USEC announced that it was discontinuing its development of the AVLIS process. While USEC owns the AVLIS technology, the Department retains the right to utilize the intellectual property for government purposes. When USEC terminated development of the AVLIS technology, it argued that the rates of return were not sufficient to outweigh the risks and ongoing capital expenditures necessary to develop and construct an AVLIS production plant. USEC had spent about 100 million in development of the technology since the corporation was privatized in July 1998. The estimated cost to develop AVLIS is $659 million.
The suspension left USEC without a complete plan to replace its existing gaseous diffusion enrichment technology, which is nearly 50 years old and very costly when compared with its competitors’ centrifuge enrichment technology. USEC is evaluating both centrifuge technology and another laser-based technology called SILEX as a replacement for its gaseous diffusion technology. One advanced enrichment technology being evaluated is the laser-based technology developed by Silex Systems Ltd. of Australia. In 2001, the third-generation Silex /USEC Inc. project moved into the pilot engineering study phase, which includes the construction and testing of prototype equipment.
While conceptually simple, the actual implementation of the process is likely to be difficult and expensive, especially for countries with limited technical resources. The AVLIS process requires much sophisticated hardware constructed of specialized materials that must be capable of reliable operation for extended periods of time in a harsh environment.