Plutonium is a chemical element used as nuclear fuel in the manufacture of nuclear weapons. Although traces can be found in nature, all plutonium isotopes are of artificial origin.
The first time that significant quantities of plutonium were produced was during World War II within the Manhattan Project. The purpose of this project was to manufacture a sufficient quantity of material to use nuclear energy to develop a nuclear bomb.
What is plutonium like?
Plutonium is a radioactive metal that is silvery-gray in its pure state, although it oxidizes rapidly on contact with air, taking on yellow or brown hues. It is a very dense and heavy element, with a density close to 19.8 g/cm³, similar to that of uranium.
Furthermore, it has a complex crystalline structure and can exist in various allotropic forms, making its mechanical and thermal behavior unusual.
Chemically, plutonium is highly reactive and can form various oxides and hydrides. It dissolves in strong acids and can generate heat due to radioactive decay, making it a hazardous material.
Its best-known isotope, plutonium-239, is used in nuclear weapons and reactors as fuel, as it can easily undergo nuclear fission. Due to its radioactivity and toxicity, its handling requires strict safety measures.
How is plutonium obtained?
Plutonium is obtained primarily as a by-product of nuclear fission in conventional nuclear reactors.
During reactor operation, uranium-238 absorbs neutrons and is converted to uranium-239, which in turn decays into neptunium-239 and finally plutonium-239, a fissile isotope key to nuclear energy and weapons production.
Spent fuel from nuclear reactors is composed primarily of uranium (approximately 96%) and a small fraction of plutonium (less than 1%), as well as other fission products and transuranium elements. Depending on the management strategy adopted, this spent fuel may be considered waste or may be recycled for reuse.
Spent fuel management
There are two main approaches to managing plutonium and other materials present in used nuclear fuel:
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Open cycle (final disposal)
In this approach, spent fuel is considered highly radioactive waste and is stored in long-term safe facilities such as cooling ponds or deep geological repositories. No attempt is made to recover plutonium or uranium present in the irradiated material. -
Closed-loop (reprocessing and reuse)
In the closed-loop, spent fuel undergoes a mechanical-chemical reprocessing process, which allows plutonium and uranium to be separated from fission products and other radioactive elements. The recovered plutonium can be used to manufacture new nuclear fuel, such as MOX (a mixture of uranium and plutonium oxides), thus optimising the use of nuclear resources and reducing the amount of high-level waste.
This approach extends the life of nuclear fuel and reduces the need for new uranium mining, but poses challenges in terms of cost, safety and nuclear non-proliferation.
Where is it found in nature?
Plutonium is an extremely rare element in nature due to the short half-lives of its isotopes compared to the age of the Earth. However, traces have been found in uranium minerals, such as uraninite, where uranium-238 can capture neutrons and transform into plutonium-239 through natural nuclear reactions.
A notable example of natural plutonium production occurred at the Oklo reactor in Gabon, where 2 billion years ago conditions existed for spontaneous fission reactions to occur in uranium deposits.
In addition, small amounts of plutonium can be formed by the interaction of cosmic rays with heavy elements in the Earth's atmosphere or crust.
However, much of the plutonium detected in the environment today comes from nuclear tests conducted in the 20th century, which released isotopes such as plutonium-239 and plutonium-240 into the biosphere.
Currently, plutonium is mainly obtained from nuclear reactors, since its occurrence in nature is negligible.
The plutonium atom on the periodic table
Plutonium (symbol Pu) is element 93 on the periodic table, meaning its atomic number is 94.
Plutonium is a chemical element belonging to the actinide series of elements. Plutonium has 16 isotopes, all of which are radioactive. Physically, plutonium is a silvery metal and has 5 different crystalline structures.
Chemically, it is a very active material that can form compounds with all non-metallic elements except the noble gases. The metal dissolves in acids and reacts with water, although moderately compared to acids.
|
Atomic mass |
244 u |
|
Ordinary state |
Solid |
|
Density |
19816 kg/m3 |
|
Melting point |
912.5 K (639 °C) |
|
Boiling point |
3505 K (3232 °C) |
Plutonium-239 and other isotopes
Plutonium-239 is a fissile isotope of plutonium that is composed of 145 protons and 54 neutrons. It is the isotope primarily used to manufacture nuclear weapons, but is also used as nuclear fuel in power reactors and in research projects.
Another important isotope is plutonium-238, which is used in heat sources for space applications, thermoelectric heat generators, and has been used in cardiac pacemakers.
Uses and applications of plutonium
The main uses of plutonium are the following:
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Nuclear fuel for nuclear power plants.
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Radioisotope thermoelectric generators . A thermoelectric generator is a device that converts heat into electricity. This technology is not practical on a large scale but is useful in certain applications such as artificial pacemakers, space probes and space vehicles. Plutonium-238 is used in this application because the radiation it emits does not pose a threat to human health.
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Manufacturing of atomic bombs. The isotope used for this purpose is plutonium-239. It is used because it will undergo nuclear fission. Very few isotopes will undergo nuclear fission.
Management of plutonium recovered from nuclear reactors
As plutonium is generated inside the fuel of nuclear reactors, it also fissions, collaborating with uranium in the production of energy.
About 7 to 8 kilograms per ton of unburned plutonium remain in spent fuel. This plutonium, recovered during reprocessing, can be used to replace uranium-235 in nuclear fuel by making mixed uranium oxide-plutonium oxide pellets (MOX fuel).
MOX fuel can replace enriched uranium fuel in light water nuclear reactors.
Health effects of plutonium
Plutonium is a toxic and radioactive chemical element. The main type of radiation it emits is alpha radiation, which cannot penetrate the skin.
Plutonium is dangerous because of its radiotoxicity. Ingested or inhaled alpha particles can cause lung cancer or other types of cancer. In large quantities, they can cause acute radiation poisoning or even death.
Once plutonium has entered the body it remains for a long time.
The probability of people being exposed to plutonium is very low. If this happens, it is usually due to handling.