How It Works
Nuclear Power Plant Fuel
Nuclear power plants do not burn any fuel. Instead, they use uranium fuel, consisting of solid ceramic pellets, to produce electricity through a process called fission.
Processing Uranium to Make Fuel
Boiling water reactors and pressurized water reactors use essentially the same uranium fuel.Before its use in a reactor, uranium must undergo four processing steps to convert it from an ore to solid ceramic fuel pellets. These processes are: mining and milling, conversion, enrichment and fabrication.
Uranium miners use several techniques to obtain uranium: surface (open pit), underground and in-situ leach mining. Uranium also is a byproduct of other mineral processing operations.
Solvents remove the uranium from mined ore or in-situ leaching, and the resulting uranium oxide—called yellowcake—undergoes filtering and drying.
The yellowcake then goes to a conversion plant, where chemical processes convert it to uranium hexafluoride. The uranium hexafluoride is heated to become a gas and loaded into cylinders. When it cools, it condenses into a solid.
Low Concentration of Uranium
Uranium hexafluoride contains two types of uranium, U-238 and U-235. The percentage of U-235, which is the type of uranium that fissions easily, is less than 1 percent. To make the uranium usable as a fuel, its U-235 content is increased to between 3 percent and 5 percent. This process is called enrichment. The concentration of U-235 is so low in enriched uranium that an explosion is impossible.
After the uranium hexafluoride is enriched, a fuel fabricator converts it into uranium dioxide powder and presses the powder into fuel pellets. The fabricator loads the ceramic pellets into long tubes made of a noncorrosive material, usually a zirconium alloy. Once grouped together into a bundle, these tubes form a fuel assembly.
Size of Nuclear Fuel Assemblies
A single fuel assembly for a boiling water reactor (BWR) is approximately 14.5 feet high and weighs approximately 704 pounds. A single fuel assembly for a pressurized water reactor (PWR) is approximately 13 feet high and weighs approximately 1,450 pounds. The PWR fuel assembly weighs more because it contains 264 fuel tubes, while the BWR fuel assembly contains 63.
Abundant Supplies of Uranium
Uranium is one of the world’s most abundant metals and can provide fuel for the world’s commercial nuclear plants for generations to come. The price of uranium has increased significantly since 2000, spurring uranium exploration and mining.The Organization for Economic Cooperation and Development (OECD) and the International Atomic Energy Agency (IAEA) issued a report on uranium resources in 2005. The report, based on projections from 43 uranium-producing countries and studies by the OECD and IAEA, concluded that uranium supplies are adequate to meet the needs of existing and future nuclear plants worldwide for the foreseeable future.
The utility industry is confident that the fuel supply industry will respond to increasing demand. In addition to ongoing exploration for new uranium deposits, some existing deposits now are economic to produce given the higher price of uranium in the market.
In 2005, the major foreign supplier of uranium to the United States was Canada, followed by Russia and Australia. Other major suppliers were Namibia, Uzbekistan and Kazakhstan. The United States supplied approximately 20 percent of all uranium purchased by U.S. nuclear plant owners.
'Megatons to Megawatts' Program
A U.S.-Russian program to eradicate weapons provides the uranium to generate 10 percent of America’s electricity.
The “Megatons to Megawatts” program involves the conversion, dilution and recycling of highly enriched uranium fuel from former Soviet nuclear warheads into low-enriched fuel for nuclear power plants. USEC Inc. purchases the uranium and then markets the fuel to its electric industry customers.
The program implements a 1993 agreement between the United States and Russia calling for Russia to recycle 500 metric tons of weapons-grade uranium from dismantled warheads. USEC reported that as of June 2006, the program had recycled 275 metric tons of highly enriched uranium into 8,102 metric tons of low-enriched uranium fuel.
Viewpoints on Nuclear Energy
Integrated Used Fuel Management
Under an integrated management approach, used nuclear fuel will remain stored at nuclear power plants in the near term. Eventually, the government will recycle it and place the unusable end product in a repository at Yucca Mountain, Nev.
