Uranium

What is Uranium?

CAS#: 007440-61-1

Uranium is a common naturally occurring and radioactive substance. It is a normal part of rocks, soil, air, and water, and it occurs in nature in the form of minerals - but never as a metal. Uranium metal is silver-colored with a gray surface and is nearly as strong as steel. Natural uranium is a mixture of three types or isotopes called U-234 (²³⁴U), U-235 (²³⁵U), and U-238 (²³⁸U). All three are the same chemical, but they have different radioactive properties.

Typical concentrations in soil are a few parts per million (ppm). Some rocks contain high enough mineral concentrations of uranium to be mined. The rocks are taken to a chemical plant where the uranium is taken out and made into uranium chemicals or metal. The remaining sand is called mill tailings. Tailings are rich in the chemicals and radioactive materials that were not removed, such as radium and thorium.

One of the radioactive properties of uranium is half-life, or the time it takes for half of the isotope to give off its radiation and change into another substance. The half-lives are very long (around 200,000 years for ²³⁴U, 700 million years for ²³⁵U, and 5 billion years for ²³⁸U. This is why uranium still exists in nature and has not all decayed away.

The isotope ²³⁵U is useful as a fuel in power plants and weapons. To make fuel, natural uranium is separated into two portions. The fuel portion has more ²³⁵U than normal and is called enriched uranium. The leftover portion with less ²³⁵U than normal is called depleted uranium, or DU. Natural, depleted, and enriched uranium are chemically identical. DU is the least radioactive and enriched uranium the most.

Related Resources for Uranium

• CERCLA Priority List of Hazardous Substances
  Prioritization of substances based on a combination of their frequency, toxicity, and potential for human exposure at National Priorities List (NPL) sites.
• Interaction Profile
  Succintly characterizes the toxicologic and adverse health effects information for mixtures of hazardous substances.
• Minimal Risk Levels (MRL)
  The MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse, non-cancer health effects over a specified duration of exposure. The information in this MRL serves as a screening tool to help public health professionals decide where to look more closely to evaluate possible risk of adverse health effects from human exposure.
  
• National Report on Human Exposure to Environmental Chemicals
  Provides an ongoing assessment of the exposure of the U.S. population to environmental chemicals using biomonitoring.
  
  • Results by Chemical Group
• NCEH Fact Sheets

Quick reference guide providing information such as chemical and physical properties, sources of exposure, routes of exposure, minimal risk levels, children's health, and health effects for a substance.

• Fallon Nevada Cancer Study- Frequently Asked Questions about Uranium
• Public Health Statement
  Summary about a hazardous substance taken from Chapter One of its respective ATSDR Toxicological Profile.
  
• ToxFAQ
  Fact sheet that answers the most frequently asked questions about a contaminant and its health effects.
  
• Toxicological Profile
  Succinctly characterizes the toxicologic and adverse health effects information for a hazardous substance.