Key Issues
Nuclear Fuel Production: A Four-Step Process
Enrichment: Boosting the Fuel’s Potency
Natural uranium contains two different forms, or isotopes, of uranium; one (U-238) is heavier than the other (U-235). The lighter U-235 is “fissionable” and makes up less than 1 percent of uranium by weight. U-238 accounts for more than 99 percent of uranium by weight.
To make uranium usable as a fuel, its U-235 content must increase to between 3 percent and 5 percent by weight through a process called enrichment.
Utilities can buy uranium and have it converted and enriched, or they can buy uranium already enriched. Uranium producers sell enrichment services in “separative work units,” or SWUs. An SWU is a measure of the amount of energy needed to raise the concentration of U-235 to a specified level.
There are three ways to enrich uranium: gaseous diffusion, gas centrifuge and laser enrichment. The gaseous diffusion enrichment process is the only method now used in the United States.
USEC Inc. currently is the only U.S. provider of enrichment services. The Energy Policy Act of 1992 established the United States Enrichment Corp., a government-owned corporation, to take over the U.S. Department of Energy’s uranium enrichment services business. The corporation was privatized as USEC Inc. in 1998.
USEC supplies approximately 50 percent of U.S. market needs. The company also serves as the U.S. executive agent for the U.S.-Russian High-Enriched Uranium Agreement, also known as “Megatons to Megawatts.” Under this program, uranium from Russian weapons is converted for sale and use in commercial reactors. The weapons material represents slightly more than 100 million SWUs of enrichment services and will be available through 2013.
Three companies—USEC, Louisiana Energy Services (LES) and AREVA—are building or plan to build new gas centrifuge enrichment facilities in the United States. The LES facility will be based in New Mexico, the AREVA facility is planned for Idaho, and USEC’s new facility will be located in Ohio. USEC’s existing facility is based in Kentucky.
LES is owned by Urenco, a British-Dutch-German consortium that enriches uranium in Europe. AREVA is based in France.
A fourth company, GE Hitachi Nuclear Energy, plans to build a facility in Wilmington, N.C., that will use a laser process for enrichment.
Three other major commercial enrichment service producers operate facilities in France, Germany, the Netherlands, Russia and the U.K.
Fabrication: Precisely Tailoring Uranium Fuel
After enrichment, a fuel fabricator converts enriched uranium hexafluoride into uranium dioxide powder and presses it into fuel pellets. The fabricator loads the ceramic pellets into long tubes, or “fuel rods,” made of a noncorrosive material, usually a zirconium alloy. Once grouped together into a bundle, these fuel rods form a fuel assembly.
Fuel assemblies, though similar, are designed to meet the specific requirements of each nuclear reactor. To ensure that each assembly performs to design criteria over its lifetime, fuel fabricators employ stringent quality-control measures throughout the production process.
Although nuclear reactors differ somewhat from one utility to another, a typical large pressurized water reactor contains 193 fuel assemblies composed of about 51,000 fuel rods containing more than 18 million uranium dioxide fuel pellets.
A fuel assembly’s life in a reactor is 36 to 54 months, after which the majority of the U-235 has fissioned and there is an inadequate amount to support the chain reaction. Operators then remove the fuel from the reactor through refueling, which normally replaces about one-quarter to one-third of the fuel assemblies with new fuel every 18 to 24 months.
Three U.S. companies offer fabrication services: AREVA NP Inc., which operates facilities in Lynchburg, Va., and Richland, Wash.; GE Hitachi Nuclear Energy in Wilmington, N.C.; and Westinghouse Electric in Columbia, S.C. These companies essentially meet all U.S. fabrication demand.
