Fuel Cycle Facts

Uranium is a naturally occurring, very hard, heavy, silvery, radioactive metallic element (atomic number 92). It was discovered in 1789 by Martin Klaproth, a German chemist, who isolated an oxide of uranium while analyzing pitchblende samples from the Joachimsal silver mines in the former Kingdom of Bohemia, located in the present day Czech Republic. He named his discovery ‘uran' after the planet Uranus. Uranium is referred to as a ‘special radioactive element' because it is capable of undergoing fission.


For many years, uranium was used primarily as a colorant for ceramic glazes and for tinting in early photography. Its radioactive properties were not recognized until 1866, and its potential for use as an energy source was not manifested until the mid-20th century. Now it is used to power nuclear reactors that produce electricity and for isotopes used for medical, industrial, and defense purposes around the world.

Nuclear Fuel Cycle

Uranium ore can be mined from open pits or underground excavations and crushed and treated at a mill to separate the valuable uranium from the ore, or uranium may be dissolved directly from the ore deposits in the ground (in-situ leaching) and pumped to the surface. Uranium mined from the earth is stored, handled, and sold as uranium oxide concentrate (U₃O₈).

Physical Properties of Uranium

• Concentration - uranium ranks 48th among the most abundant elements found in natural crustal rock.
  
• Density - uranium is very dense. At about 19 grams per cubic centimeter, it is 1.6 times more dense than lead. Density increases weight. For example, while a gallon of milk weighs about 8 pounds, a gallon container of uranium would weigh about 150 pounds.
  
• Melting Point - uranium boils at about 3,818 degrees Celsius (about 6,904 degrees Fahrenheit).

Types of Uranium

• Natural Uranium - contains a ²³⁸U concentration of 99.3 percent and ²³⁵U concentration of 0.7 percent.
  
• Low Enriched Uranium – contains a ²³⁵U concentration between 0.7 percent and 20 percent ²³⁵U. Most commercial reactor fuel used low enriched uranium (LEU) enriched to between 3 and 5 percent ²³⁵U.
  
• Highly Enriched Uranium – contains a ²³⁵U concentration greater than 20 percent. Highly enriched uranium (HEU) is used in research reactors, naval propulsion reactors, and weapons.
  
• Depleted Uranium – contains a ²³⁵U concentration of 0.7 percent or less.

What is Uranium Enrichment?

Uranium enrichment is a critical step in transforming natural uranium into nuclear fuel to produce energy. Uranium is a naturally occurring element containing ²³⁵U and ²³⁸U isotopes. Only the ²³⁵U isotope is fissionable. Enrichment is the process of increasing the concentration of ²³⁵U while decreasing the concentration of ²³⁸U. The stream with the greater ²³⁵U concentration is referred to as enriched uranium, while the stream that is reduced in its concentration of ²³⁵U is referred to as depleted uranium.

Uranium is enriched commercially using either (1) gaseous diffusion technology or (2) gas centrifuge technology. In both processes the compound uranium hexafluoride (UF₆) is heated and converted from a solid to a gas. At a gaseous diffusion plant, the UF₆ gas is forced through a series of compressors and converters that contain porous barriers. Because ²³⁵U has a slightly lighter isotopic mass than ²³⁸U, it filters through the barriers at a slightly higher rate than the ²³⁸U. The operation of this equipment consumes a significant amount of electricity. The gaseous diffusion process for enriching uranium was first developed on a large scale at the DOE plant in Oak Ridge, Tennessee. Two additional plants were subsequently constructed in Kentucky and Ohio. Presently, the publicly-owned U.S. Enrichment Corporation (USEC) leases the only operating government-owned gaseous diffusion plant in Paducah, Kentucky, and is the only domestic supplier of enriched uranium services.

In the gas centrifuge process the UF₆ gas is rapidly spun in cylinders. The difference in isotopic masses allow centrifugal forces to separate the ²³⁵U and ²³⁸U isotopes; concentrating the slightly heavier ²³⁸U closer to the cylinder wall. The gas centrifuge technology consumes only about five percent as much electricity as the gaseous diffusion technology. Presently, two private sector projects plan to build new gas centrifuge capacity in the United States: the USEC American Centrifuge Plant in Ohio and Louisiana Energy Services’ (LES) National Enrichment Facility in New Mexico. USEC will use its own advanced design based on DOE technology (the Department’s centrifuge research and development program ended in 1985), while LES will use the Urenco centrifuge technology. The Nuclear Regulatory Commission (NRC) is reviewing construction applications submitted by both companies, each of which will need to find private capital of $1.0 - $1.5 billion.

Fast Facts

• One ton of natural uranium can produce more than 40 million kilowatt-hours of electricity. This is equivalent to burning 16,000 tons of coal or 80,000 barrels of oil.
• There are currently 103 operating nuclear power plants in the United States that produce about 20 percent of the nation’s electricity.
• Worldwide, there are more than 440 nuclear power plants operating in 31 countries that supply about 16 percent of the world's electricity.
• World uranium production in 2004 was 104.6 million pounds of U3O8.
• The price of natural uranium was approximately $36 per pound U3O8 at end of 2005.