How It Works
Nuclear Power Plant Fuel
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. Higher uranium prices have prompted a re-examination of existing deposits and exploration for new ones.
The Organization for Economic Cooperation and Development (OECD) and the International Atomic Energy Agency (IAEA) in 2008 jointly produced a report on uranium resources: “Uranium 2007: Resources, Production and Demand.” It says that uranium resources are adequate to meet nuclear energy needs for at least the next 100 years at present consumption levels. More efficient fast reactors could extend that period to more than 2,500 years.
The utility industry is confident that the fuel supply industry will respond to increasing demand. Bolstering confidence in future supply is the fact that some of the world’s richest deposits of uranium are in politically stable countries. Canada and Australia account for 44 percent of global uranium production; the United States accounts for 5 percent.
In 2007, uranium of U.S. origin accounted for eight percent of the material used by the owners and operators of U.S. nuclear power plants. The remainder (47 million pounds) came from other sources, according to the U.S. Energy Information Administration. The U.S. uranium production industry is working to increase domestic supplies. For example, 2007 expenditures for uranium exploration in the United States were up 116 percent from 2007.
Revitalization of the U.S. uranium production industry also brightens the job market. Although the industry remains comparatively small, employment rose 63 percent above the 2006 level.
'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 December 31, 2008, the program had recycled 352 metric tons of highly enriched uranium into 10,213 metric tons of low-enriched uranium—equivalent to 14,090 warheads eliminated. For more information, visit the USEC Inc. Web site.
