Plutonium (chemical symbol Pu) is a radioactive metal with Atomic
Number 94. Plutonium is considered a man-made element, although
scientists have found trace amounts of naturally occurring plutonium
produced under highly unusual geologic circumstances. The most
common radioisotopes of plutonium are plutonium-238, plutonium-239,
and plutonium-240.
Who discovered plutonium?
Plutonium was discovered by nuclear chemist Glenn T. Seaborg
and his colleagues Joseph W. Kennedy, Edwin M. McMillan, and Arthur
C. Wahl, in 1941 at the University of California - Berkeley. However,
wartime secrecy prevented them from announcing the discovery until
1948.
Where does plutonium come from?
Plutonium is created from uranium in nuclear reactors. When uranium-238
absorbs a neutron, it becomes uranium-239 which ultimately decays
to plutonium-239. Different isotopes of uranium and different
combinations of neutron absorptions and radioactive decay, create
different isotopes of plutonium.
Some plutonium is created as a by-product in commercial nuclear
power reactors. The normal operating conditions of these reactors
provide conditions for making some plutonium . The plutonium burns
(fissions) in the fuel rods along with uranium and helps produce
electricity. Some plutonium remains even when the nuclear fuel
is spent.
The majority of plutonium was produced for nuclear weapons in
several government reactors designed to maximize the production
of plutonium. Between 1944 and 1988, the U.S. built and operated
these ‘production reactors' at high-security government facilities.
In all, the U.S. produced about 100 metric tons of plutonium.
The reactors made plutonium by bombarding special fuel rods containing
uranium with neutrons. Once the maximum amount of plutonium was
produced, workers removed the fuel rods (now called ‘spent
fuel') from the reactor. The spent fuel rods were extremely radioactive,
and the process for recovering the plutonium used only remote-controlled
equipment.
First workers used strong acid to dissolve the fuel rods. Then
they treated the mixture with chemicals to precipitate the plutonium
so that it would settle out. The process was very expensive and
at the time made plutonium about the most expensive material on
earth. This processing also left behind over 100 million gallons
of exceedingly hazardous mixed wastes of acids and radioactive
fission products. Part of our legacy of nuclear weapons production
is dealing with these high-level wastes.
In extremely rare cases, rocks with a high localized concentration
of uranium can provide the right conditions for making small amounts
of plutonium naturally. This natural process is called spontaneous
fission. Only very small (trace) amounts of natural plutonium
have ever been found in nature.
What are the properties of plutonium?
Plutonium is a silvery-grey metal that becomes yellowish when
exposed to air. It is solid under normal conditions, and is chemically
reactive.
Plutonium has at least 15 different isotopes, all of which are
radioactive. The most common ones are Pu-238, Pu-239, and Pu-240.
Pu-238 has a half-life of 87.7 years. Plutonium-239 has a half-life
of 24,100, and Pu-240 has a half-life 6,560 years. The isotope
Pu-238 gives off useable heat, because of its radioactivity.
What is plutonium used for?
Plutonium-239 is used to make nuclear weapons. For example, the
bomb dropped on Nagasaki, Japan, in 1945, contained Pu-239. The
plutonium in the bomb undergoes fission
in an arrangement that assures enormous energy generation and
destructive potential.
The isotope, plutonium-238, is not useful for nuclear weapons.
However it generates significant heat through its decay process,
which make it useful as a power source. Using a thermocouple,
a device that converts heat into electric power, satellites rely
on plutonium as a power source. Tiny amounts also provide power
to heart pacemakers.
Some foreign countries mix isotopes of plutonium and uranium
to manufacture special reactor fuel called mixed-oxide fuel, for
commercial nuclear power reactors. The plutonium increases the
power output. The U.S. does not currently manufacture mixed-oxide
fuel, but is funding research in this type of reactor fuel as
a means of dealing with excess plutonium in stockpile.
Plutonium was dispersed world wide from atmospheric testing of
nuclear weapons conducted during the 1950s and ‘60s. The
fallout from these tests left very low concentrations of plutonium
in soils around the world.
Nuclear weapons production and testing facilities (Hanford, WA,
Savannah River, GA, Rocky Flats, CO, and The Nevada Test Site,
in the United States, and Mayak in the former Soviet Union), also
released small amounts. The releases occurred in accidents with
nuclear weapons, the reentry of satellites that used Pu-238, and
by the Chernobyl nuclear reactor accident.
How does plutonium change in the environment?
All isotopes of plutonium undergo radioactive decay. As plutonium
decays, it releases radiation and forms other radioactive isotopes.
For example, Pu-238 emits an alpha particle and becomes uranium-234;
Pu-239 emits an alpha particle and becomes uranium-235.
This process happens slowly since the half-lives of plutonium
isotopes tend to be relatively long: Pu-238 has a half-life of
87.7 years; Pu-239 has a half-life is 24,100 years, and Pu-240
has a half-life of 6,560 years. The decay process continues until
a stable, non-radioactive element is formed.
How do people come in contact with plutonium?
Residual plutonium from atmospheric nuclear weapons testing is
dispersed widely in the environment. As a result, virtually everyone
comes into contact with extremely small amounts of plutonium.
People who live near nuclear weapons production or testing sites
may have increased exposure to plutonium, primarily through particles
in the air, but possibly from water as well. Plants growing in
contaminated soil can absorb small amounts of plutonium.
How does plutonium get into the body?
People may inhale plutonium as a contaminant in dust. It can
also be ingested with food or water. Most people have extremely
low ingestion and inhalation of plutonium. However, people who
live near government weapons production or testing facilities
may have increased exposure. Plutonium exposure external to the
body poses very little health risk.
What does plutonium do once it gets into the body?
The stomach does not absorb plutonium very well, and most plutonium
swallowed with food or water passes from the body through the
feces. When inhaled, plutonium can remain in the lungs depending
upon its particle size and how well the particular chemical form
dissolves. The chemical forms that dissolve less easily may lodge
in the lungs or move out with phlegm, and either be swallowed
or spit out. But, the lungs may absorb chemical forms that dissolve
more easily and pass them into the bloodstream.
Once in the bloodstream, plutonium moves throughout the body
and into the bones, liver, or other body organs. Plutonium that
reaches body organs generally stays in the body for decades and
continues to expose the surrounding tissue to radiation.
External exposure to plutonium poses very little health risk,
since plutonium isotopes emit alpha radiation, and almost no beta
or gamma radiation. In contrast, internal exposure to plutonium
is an extremely serious health hazard. It generally stays in the
body for decades, exposing organs and tissues to radiation, and
increasing the risk of cancer. Plutonium is also a toxic metal,
and may cause damage to the kidneys.
Is there a medical test to determine exposure to plutonium?
There are tests that can reliably measure the amount of plutonium
in a urine sample, even at very low levels. Using these measurements,
scientists can estimate the total amount of plutonium present
in the body. Other tests can measure plutonium in soft tissues
(such as body organs) and in feces, bones, and milk. However,
these tests are not routinely available in a doctor's office because
they require special laboratory equipment.
What can I do to protect myself and my family from plutonium?
Since plutonium levels in the environment are very low, they
pose little risk to most people. However, people who live near
government weapons production or testing sites may have higher
exposure.
Plutonium particles in dust are the greatest concern, because
they pose the greatest health risk. People living near government
weapons facilities can track radiation monitoring data made available
by site personnel. If radiation levels rise, they should follow
the radiation protection instructions given by site personnel.
How do I know if I'm near plutonium?
You must have special equipment to detect the presence of plutonium.
What is EPA doing to protect us from plutonium?
EPA sets health-based limits on radiation in air, soil, and water.
Federal government agencies are required to meet EPA standards
the same as commercial industries. Using its authority under the
Safe Drinking Water Act, EPA
limits the amount of radiation in community water systems by establishing
maximum contaminant levels. Maximum Contaminant Levels limit the
amount of activity from alpha emitters, like plutonium, to 15
picocuries per liter.
EPA also protects people against exposure from soil and ground
water from sites that have been contaminated with plutonium. We
set criteria that soil and ground water from the sites must meet
before releasing the sites for public use.
Rather than limiting the concentration of plutonium itself, the
criteria limit the cancer risk the sites pose. A person's added
risk of developing cancer is limited to no more than about 1-in-10,000
and if possible to 1-in-1,000,000, or less. Under the Clean
Air Act, EPA limits the dose to humans from radionuclides
to 10 millirem from emissions to air.
EPA sets standards for radioactive waste storage and disposal
facilities. We can't treat plutonium or other radioactive materials
to get rid of their radioactivity. We can only isolate and store
them until they decay. The extremely long half-lives of some plutonium
radioisotopes make the management of spent nuclear fuel, and wastes
from nuclear weapons facilities a difficult problem.
One of EPA's responsibilities has been to develop public health
and safety standards for the two major U.S. nuclear waste storage
and disposal facilities. The Waste
Isolation Pilot Plant in New Mexico stores transuranic wastes.
They range from slightly contaminated clothing to barrels of waste
so radioactive that it can only be handled with remote control
equipment. The proposed Yucca
Mountain repository is designed to store high-level radioactive
waste and spent nuclear fuel.
EPA also responds to radiation emergencies. Additionally, EPA
helps state and local governments during emergencies that involve
radioactive materials. We provide guidance on ways to protect
people from harmful exposure to radiation. We can also monitor
radiation levels in the environment and assess the threat to public
health. We also work with international radiation protection organizations
to prepare for large scale foreign emergencies such as Chernobyl.
EPA also works with law enforcement agencies to develop counter
terrorism plans.
