Introduction

Uranium occurs naturally in the earth's crust. In the United States, it is found most abundantly in the western states [EPA 2006a, b, c; Lide 1994; USGS 2009b]. Enrichment of uranium for nuclear weapons began in the 1940s and for energy production in the 1950s. Gaseous diffusion was developed by the War Department [precursor to the Atomic Energy Commission and the Department of Energy (DOE)] as a way to enrich uranium. Uranium is currently used to fuel nuclear power plants, create medical isotopes, and for industrial and defense purposes. Detailed information on where uranium is found in the United States is available using the National Geologic Map Database [USGS 2008].

The Natural Environment

Uranium is naturally present in the world's environment. It is commonly found in

• plants,
• rock,
• soil,
• water, and
• animals in small quantities.

Uranium is present in the earth at approximately 3 parts per million (ppm). The most important uranium ores for commercial production include

• autunite,
• carnotite,
• coffinite,
• pitchblend,
• tobernite,
• tyuyamunite, and
• uraninite,

The majority of the uranium deposits in the United States are found in the western states of

• Arizona,
• Colorado,
• Nebraska,
• New Mexico,
• Texas,
• Utah, and
• Wyoming.

Uranium is radioactive and contributes to the natural background radiation levels in the environment [EPA 2009b]. For information on the location of uranium deposits in other areas of the United States, please visit U.S. Geological Surveys website on Uranium Resources and Environmental Issues [USGS 2009a].

Uranium is redistributed on the Earth through various natural and anthropogenic processes. Volcanic eruptions, wind and water erosion, and other weathering processes can mobilize uranium into the atmosphere and redeposit it into other media.

Industrial Processes

Some industrial processes also contribute to the movement of uranium, including

• extraction of phosphorus from phosphate ores to produce phosphate fertilizers,
• uranium enrichment,
• uranium mine tailings disposal, and
• uranium mining and milling to produce uranium oxides.

DOE and Civilian Reactor Sites

Uranium processing (enrichment and reprocessing) occurred at a number of DOE sites beginning in 1943 and continues to the present day. DOE sites also store uranium and uranium wastes. Spent fuel rods are stored at civilian reactor sites. For information on the location of uranium sites in the United States, please visit the U.S. Geological Survey website Uranium Resources-Uranium Information System [USGS 2009b].

Progress Check