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.

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What is a gas centrifuge?

A gas centrifuge (diagrams below) comprises an evacuated casing containing a cylindrical rotor which rotates at high speed in an almost friction-free environment. The uranium is fed into the rotor as gaseous uranium hexafluoride (UF6)² which also rotates.

The centrifugal forces push the heavier uranium 238 (U-238) closer to the wall of the rotor than the lighter U-235. The gas closer to the wall becomes depleted in U-235 whereas the gas nearer the rotor axis is enriched in U-235.

The arrows in the first illustration depict the gas flowing within the rotor. The gas flow can be produced by a temperature gradient over the length of the centrifuge. UF6 depleted in U-235 flows upwards adjacent to the rotor wall, while UF6 enriched in U-235 flows downwards close to the axis. The two gas streams are removed through small scooped pipes, called "scoops."

The enrichment effect of a single centrifuge is small, so they are linked together by pipes into cascades. Passing through the successive centrifuges of a cascade, the U-235 is gradually enriched to the required level. For civil applications, natural uranium containing about 0.7 percent U-235 is enriched to about 3-5 percent U-235 and the depleted uranium contains typically about 0.2-0.3 percent U-235. For military applications, highly enriched uranium (HEU) containing greater than 20 percent U-235 is usually produced.

Once started, a modern centrifuge runs for more than 10 years with no maintenance. An advantage of the centrifuge process is its low energy consumption.

Click on any of the above images to see a larger display

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¹Source: www.urenco.com

² Uranium hexafluoride (UF6) is a solid white material at room temperature, which evaporates into gaseous material at elevated temperatures.

THE IRANIAN GAS CENTRIFUGE URANIUM ENRICHMENT PLANT

DRAWING FROM COMMERCIAL SATELLITE IMAGES

DAVID ALBRIGHT AND COREY HINDERSTEIN

THE INSTITUTE FOR SCIENCE AND INTERNATIONAL SECURITY (ISIS)

March 14, 2003

Figure 1	Figure 2	Figure 3	Figure 4

Iran is building a high security uranium enrichment facility using gas centrifuges near Natanz. This site is about 40 kilometers southeast of Kashan and about 150 kilometers north of Isfahan. The IAEA has characterized the centrifuges at this site as sophisticated and the culmination of a large, expensive effort.

Iran has demonstrated a capability possessed by only about ten countries. Because of the characteristics of gas centrifuges, the Iranian facility could be used for the production of low enriched uranium for civil purposes or highly enriched uranium for nuclear weapons, depending on the decision of the Iranian government.

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Urenco Power

Urenco is short for Uranium Enrichment Company. Three countries – Germany, the Netherlands and the United Kingdom – signed the Treaty of Alemlo (Netherlands) on March 4, 1970 as a way to collaborate in developing centrifuge technology for uranium enrichment. In 1971, three industrial partners – British Nuclear Fuels plc (BNFL), Ultra-Centrifuge Nederland N.V. (UCN) and Uranit GmbH – founded Urenco Ltd.

The Louisiana Energy Services partnership plans on building the National Enrichment Facility (NEF) about five miles east of Eunice, New Mexico. The NEF plans on providing a sustainable domestic supply of slightly enriched uranium, also called ‘low enriched uranium’ or LEU, using Urenco’s gas centrifuge technology. Currently, USEC is the other uranium enrichment facility, using the more expensive gaseous diffusion technology. USEC is a publicly traded company, created under the Clinton-Gore Administration for the purposes of the Russia-US ‘swords for plowshares’ HEU deal. Under the HEU agreement, Russia’s counterpart supplied USEC with uranium from decommissioned Russian nuclear weapons. This uranium now supplies U.S. utilities with about 50 percent of the uranium used to power domestic nuclear power plants.

In 2001, the domestic uranium industry only produced 12 percent of its required supply of enriched uranium, while Russia exported 55 percent to the United States. Urenco supplied 16 percent of the U.S. demand. Urenco plans to increase its percentage of enriched uranium to about one-quarter of U.S. enrichment demand, once the plant is running at full capacity. This amounts to annual production of 3 million Separative Work Units (SWUs). A Separative Work Unit is the unit used to express the effort necessary to separate U-235 and U-238. The capacity of enrichment plants is measured in tons SW per year. For example, a large nuclear power station with a net electrical capacity of 1300 MW requires an annual amount of 25 tons SW (enriched uranium) to operate (with a concentration of 3.5 percent U-235).

The National Enrichment Facility will become Urenco’s North American debut of the company’s gas centrifuge technology, which the company boasts is the ‘world’s most advanced, energy-efficient and cost-effective uranium enrichment technology.’ It has reportedly been used for more than thirty years.

Rattehalli Rare Materials Plant (RMP)

posted Friday September 9, 2005 under india by jeffrey

The Institute for Science and International Security has published the first ever satellite photograph of India’s

Rattehalli Rare Materials Plant (RMP)—a gas centrifuge facility with several hundred subcritical centrifuge rotor assemblies operating at less 3 SWU/year per machine—located near Mysore in Karnataka state.

The facility has reportedly been upgraded at least once since that estimate. Albright and Hinderstein will release an analysis of India’s program in the coming weeks.

The best reports about Rattehalli are available from the nuclear trade press:

• Mark Hibbs, “India to Equip Centrifuge Plant with Improved Rotor Assemblies,” Nuclear Fuel 22:24 (1 December 1997) 7

• Mark Hibbs, “India and Pakistan Fail To Include New SWU Plants on Exchanged Lists,” Nuclear Fuel 17:7 (30 March 1992) 6.

• Mark Hibbs, “Second Indian Enrichment Facility Using Centrifuges is Operational,” Nucleonics Week 33:13 (26 March 1992) 9.