URANIUM ENRICHMENT
Coming Full Circle

The resurrection of gas centrifuge technology for uranium enrichment—a dream come true for many Oak Ridge researchers—has brought the largest CRADA ever to ORNL.

From neckties to popular music, numerous trends and ideas identified with the 1970s are finding their way back into the American mainstream more than two decades later. The phenomenon extends to the world of technology, where the gas centrifuge method for making fuel for nuclear power plants, after a 20-year hiatus, is once again on center stage.

The uranium enrichment technology using spinning rotors was largely developed in Oak Ridge; highlights were the successful operation of the first cascade of 35 centrifuges in 1961 and the startup of the Centrifuge Test Facility in 1975. Centrifuge technology was shelved in 1985 by the Department of Energy in favor of the now-abandoned atomic vapor laser isotope separation (AVLIS) technology. At the time, fiberglass centrifuges were being built for a DOE-sponsored centrifuge enrichment plant at Portsmouth, Ohio. The plant closed in 2000. Research on AVLIS continued at DOE's Lawrence Livermore National Laboratory.

Multiple gas centrifuge cascades were constructed at the Portsmouth Gaseous Diffusion Plant in Ohio and successfully operated until the program was discontinued in 1985.

"The uranium enrichment market was nonexistent in the mid1980s because nuclear power was not seen as the energy source of the future," says John Shaffer of ORNL's Nuclear Science and Technology Division. "Interest in centrifuge technology for uranium enrichment in the United States lay dormant until 1999."

By then, DOE had turned over the agency's enrichment facili-ties—two gaseous diffusion plants—to a new private company, the United States Enrichment Corporation (USEC). USEC, which has one-third of the world's enriched uranium market, obtains one-half its product from down-blended Russian weapons material and half from the gaseous diffusion plant in Paducah, Kentucky.

Because a gas centrifuge plant uses only 5% as much electricity as is consumed by a diffusion plant, USEC determined that the best chance to remain competitive with URENCO—a British, Dutch, and German consortium that uses centrifuge plants—was to resurrect the centrifuge technology. USEC turned to the "priesthood" of American centrifuge technology, Oak Ridge researchers and retirees.

Since July 2002 ORNL researchers have been working on the centrifuge program as part of a five-year, $125-million cooperative research and development agreement (CRADA) with USEC. Some $28.5 million worth of centrifuge research in Oak Ridge is directly funded by USEC as part of the CRADA, the largest in ORNL history.

Materials, Motors, Modeling

Since the mid-1980s, advances in materials, motors, controls, and modeling have made possible the improvement of technology developed in the 1960s and 1970s in Oak Ridge. The advances are enabling the development of centrifuges that can be manufactured more economically and produce nuclear fuel with greater efficiency.

A group led by Shaffer developed carbon-fiber composites to replace the fiberglass used for the 1985 rotor. "Our new centrifuge material is lighter and stronger, so the rotor can spin faster without falling apart," Shaffer says. "As a result, more enriched uranium can be produced by each machine for a longer time."

While the centrifuge program lay dormant in the 1980s and 1990s, carbon-fiber composite technology moved from a laboratory curiosity to a mature technology. "These materials are being used anywhere high strength and light weight are needed," Shaffer says. "They are found in racing cars, rocket motors, submarine hulls, missiles, bridges, space satellites, telephone poles, and sewer pipes."

A group led by Don Adams of ORNL's Engineering Science and Technology Division has developed small motors operated by power electronics for the centrifuges. "The new motors are smaller and cheaper than the 1985 motors and the use of power electronics will simplify the control of the centrifuge motors," Shaffer says. In recent years, Adams and his colleagues have been adapting the technology for use in American automakers' development of hybrid gasoline-electric cars.

More than 15 years ago, Oak Ridge researchers developed computer models to optimize the centrifuge design. The design's geometry had to be precise to balance the high-speed rotating equipment. The speed had to be increased to improve the flow of uranium hexafluoride (UF 6 ) gas. The goal is to locate the most fissionable uranium-235 into the middle and out the top of the rapidly spinning centrifuge as it separates from the heavier and much more abundant uranium-238, which migrates toward the rotor wall.

"In the 1980s we needed weeks or even months to do these tricky, intensive calculations on the CRAY supercomputer," says Doug Craig, who leads the ORNL effort in the CRADA. "Now, running fluid dynamics and other codes can be done in a few days on a desktop computer."

The question now becomes, "Can ORNL help USEC reduce the cost of manufacturing a centrifuge from $100,000 to $50,000?"

Cutting Costs

"ORNL is working out the techniques for making more economic centrifuges using carbon-fiber composites." Craig says. "Shaffer is helping USEC employees learn how to fabricate the components at the Boeing facility USEC is leasing in Oak Ridge. Shaffer's group is leading the manufacturing of test centrifuges for a demonstration program at Building K-1600 at the East Tennessee Technology Park in Oak Ridge. The project, which will involve the experimental operation of centrifuges using UF 6 , is funded by USEC and overseen by DOE."

"The CRADA allows us to refresh and reinvigorate the enrichment technology base with new people," Craig says. "The younger folks can get hands-on experience with the technology that hasn't been used in Oak Ridge since 1985. It's great to have an opportunity to train a new generation of centrifuge researchers and transfer the technology to USEC."

Former ORNL employees who worked in the centrifuge program are coming out of retirement to lend their expertise to USEC, which now has approximately 100 employees in Oak Ridge. The retirees are helping USEC build 200 test centrifuges for a lead cascade plant in Portsmouth. The centrifuges will be installed and operating by 2005 under the watchful eye of the Nuclear Regulatory Commission. USEC's longer-range plans include construction of a modern commercial centrifuge enrichment plant by 2012.

Not surprisingly, USEC's chief scientist for the centrifuge project is a former ORNL employee, Dean Waters, who received an E. O. Lawrence Award from DOE, largely for his centrifuge innovations. Like Shaffer and his ORNL colleagues, Waters is helping transfer the centrifuge technology he developed during much of his career. Former and present ORNL researchers are excited. As they bring their old ties out of the closet after two decades, they also are making an invaluable contribution that will help sustain America's uranium enrichment program.

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