Uranium (chemical symbol U) is a naturally-occurring radioactive
element, with atomic number 92. Uranium is commonly found in very
small amounts in rocks, soil, water, plants, and animals (including
humans). Uranium is weakly radioactive and contributes to low
levels of natural background radiation in the environment.
Who discovered uranium?
The use of uranium, in its natural oxide form, dates back to
at least 79 A.D., when it was used to add color to ceramic glazes.
The German chemist Martin Klaproth is credited with discovering
uranium in samples of the mineral pitchblende in 1789. It was
first isolated as a metal in 1841 by Eugene-Melchior Peligot.
Uranium was discovered to be radioactive in 1896 by French physicist
Henri Becquerel. Through his work with uranium metals, he was
the first to discover the process of radioactivity.
Where does uranium come from?
Uranium is a naturally-occurring element found at low levels
in virtually all rock, soil, and water. Significant concentrations
of uranium occur in some substances such as phosphate rock deposits,
and minerals such as uraninite in uranium-rich ores. Because uranium
has such a long radioactive half-life (4.47x109 years for U-238),
the total amount of it on earth stays almost the same.
What are the properties of uranium?
When refined, uranium is a silvery white, weakly radioactive
metal. Uranium metal has very high density, 65% more dense than
lead. Uranium in ores can be extracted and chemically converted
into uranium dioxide or other chemical forms usable in industry.
Uranium found naturally has 3 different isotopes, U-238, U-235,
and U-234. Other isotopes can be synthesized. All uranium isotopes
are radioactive. The table below shows the percentage of natural
abundance of each natural uranium isotope, and their respective
half-lives.
Relative Abundance of Uranium
Isotopes
Isotope
U-238
U-235
U-234
Natural Abundance (%)
99.27
0.72
0.0055
Half-life (years)
4.47 billion
700 million
246,000
Uranium isotopes can be separated to increase the concentration
of one isotope relative to another. This process is called "enrichment."
The enriched fraction has increased U-235. Uranium-235 is better
for nuclear power reactors, and for making nuclear weapons. The
process produces huge quantities of uranium that are depleted
in U-235, but are almost pure U-238, called depleted
uranium, or DU.
What is uranium used for?
Uranium metal is very dense and heavy. When it is depleted (DU),
uranium is used by the military as shielding to protect Army tanks,
and also in parts of bullets and missiles. The military also uses
enriched uranium to power nuclear propelled Navy ships and submarines,
and in nuclear weapons. Fuel used for Naval reactors is typically
highly enriched in U-235 (the exact values are classified information).
In nuclear weapons uranium is also highly enriched, usually over
90% (again, the exact values are classified information).
The main use of uranium in the civilian sector is to fuel commercial
nuclear power plants, where fuel is typically enriched in U-235
to 2-3%. Depleted uranium is used in helicopters and airplanes
as counter weights on certain wing parts. Other uses include ceramic
glazes where small amounts of natural uranium (that is, not having
gone through the enrichment process) may be added for color. Some
lighting fixtures utilize uranium, as do some photographic chemicals.
Phosphate fertilizers often contain high amounts of natural uranium,
because the mineral material from which they are made is typically
high in uranium. Also, people who collect rocks and minerals may
have specimens of uranium minerals in their collection such as
pitchblende, uraninite, autunite, uranophane, or coffinite.
Uranium is present naturally in virtually all soil, rock and
water. Uranium in soil and rocks is distributed throughout the
environment by wind, rain and geologic processes. Rocks weather
and break down to form soil, and soil can be washed by water and
blown by wind, moving uranium into streams and lakes, and ultimately
settling out and reforming as rock. Uranium can also be removed
and concentrated by people through mining and refining. These
mining and refining processes produce wastes such as mill tailings
which may be introduced back into the environment by wind and
water if they are not properly controlled. Manufacturing of nuclear
fuel, and other human activities also release uranium to the environment.
How does uranium change in the environment?
All uranium isotopes are radioactive. The three natural uranium
isotopes found in the environment, U-234, U-235, and U-238, undergo
radioactive decay by emission of an alpha particle accompanied
by weak gamma radiation. The dominant isotope, U-238, forms a
long series of decay products that includes the key radionuclides
radium-226, and radon-222. The decay process continues until a
stable, non-radioactive decay product is formed (see uranium decay
series). The release of radiation during the decay process raises
health concerns.
A person can be exposed to uranium by inhaling dust in air, or
ingesting water and food. The general population is exposed to
uranium primarily through food and water. The average daily intake
of uranium from food ranges from 0.07 to 1.1 micrograms per day.
The amount of uranium in air is usually very small. People who
live near federal government facilities that made or tested nuclear
weapons, or facilities that mine or process uranium ore or enrich
uranium for reactor fuel, may have increased exposure to uranium.
How does uranium get into the body?
Uranium can enter the body when it is inhaled or swallowed, or
under rare circumstances it may enter through cuts in the skin.
Uranium does not absorb through the skin, and alpha particles
released by uranium cannot penetrate the skin, so uranium that
is outside the body is much less harmful than it would be if it
where inhaled or swallowed. When uranium gets inside the body
it can lead to cancer or kidney damage.
What does uranium do once it gets into the body?
About 99 percent of the uranium ingested in food or water will
leave a person's body in the feces, and the remainder will enter
the blood. Most of this absorbed uranium will be removed by the
kidneys and excreted in the urine within a few days. A small amount
of the uranium in the bloodstream will deposit in a person's bones,
where it will remain for years.
The greatest health risk from large intakes of uranium is toxic
damage to the kidneys, because, in addition to being weakly radioactive,
uranium is a toxic metal. Uranium exposure also increases your
risk of getting cancer due to its radioactivity. Since uranium
tends to concentrate in specific locations in the body, risk of
cancer of the bone, liver cancer, and blood diseases (such as
leukemia) are increased. Inhaled uranium increases the risk of
lung cancer.
Is there a medical test to determine exposure to uranium?
Tests are available to measure the amount of uranium in a urine
or stool sample. Hospitals do not perform these tests routinely.
These tests are useful if a person is exposed to a large amount
of uranium, because most uranium leaves the body in the feces
within a few days after ingestion. Uranium can be found in the
urine for up to several months after exposure. However, the amount
of uranium in the urine and feces does not always accurately show
the level of uranium to which you may have been exposed. Since
uranium is known to cause kidney damage, special urine tests are
often used to determine whether kidney damage has occurred.
What can I do to protect myself and my family from uranium?
Most people are not exposed to dangerous levels of uranium. However,
people who live near uranium mining areas, or near government
weapons facilities or certain industrial facilities may have increased
exposure to uranium, especially if their water is from a private
well. Analytical laboratories can test water for uranium content.
Occasionally, household wares may be found with uranium in them,
such as some older ceramic dishes or plates in which uranium was
used in the glaze. These generally do not pose serious health
risks, but may nevertheless be retired from use as a prudent avoidance
measure. A radiation counter is required to confirm if ceramics
contain uranium.
How do I know I'm near uranium?
You need specialized equipment and training to detect uranium
in the environment.
What is EPA doing about uranium?
EPA standards under the Clean
Air Act limit uranium in the air. The maximum dose to an individual
from uranium in the air is 10 millirem. The cleanup of contaminated
sites to be released for public use, must meet EPA's risk-based
criteria for soil and ground water. EPA's site cleanup standards
limit a person's increased chance of developing cancer to between
1 in 10,000 to 1 in 1,000,000 from residual uranium on the ground.
Site-specific factors, cost, and community concerns are weighed
in establishing the actual clean up value.
Uranium in drinking water is covered under the Safe
Drinking Water Act. This law establishes Maximum Contaminant
Levels, or MCLs, for radionuclides and other contaminants in drinking
water. The uranium limit is 30 µg/l (micrograms per liter)
in drinking water.