Spent nuclear fuel pool

Plutonium

Plutonium

Plutonium is a chemical element, usually of artificial origin, that is used as a nuclear fuel in the manufacture of nuclear weapons.

The symbol of this chemical element is Pu and its atomic number is 94. It is an element that belongs to the series of actinide elements. Plutonium has 16 isotopes, all of them radioactive. The element is a silver metal and has 5 different crystalline structures.

Chemically plutonium is a very active material. It can form compounds with all non-metallic elements, except noble gases. The metal dissolves in acids and reacts with water, although moderately compared to acids.

Although traces can be found in nature, all plutonium isotopes are of artificial origin.

Plutonium Isotopes

The isotope with the highest chemical interest is plutonium-239. It is formed in nuclear reactors. It is a fissile isotope but can also capture neutrons to form superior isotopes. In the field of nuclear energy, plutionio-239 is used as a nuclear fuel in the production of radioactive isotopes for research and as a fissile agent in nuclear weapons.

Plutonium-238 is used in heat sources for space applications, thermoelectric heat generators and has been used in cardiac pacemakers.

An important characteristic of many of the isotopes of plutonium is that they exhibit the phenomenon of spontaneous fission, in which the atomic nucleus can be divided spontaneously without the need to be bombarded by any neutron.

Origin and obtaining

Plutonium is obtained by burning nuclear fuel is burned in conventional nuclear reactors. The irradiated fuel from nuclear reactors is mainly made up of uranium (with a percentage of approximately 96%) and plutonium (with a percentage somewhat less than 1%).

The spent fuel can be managed in two different ways in the long term:

  • Open cycle management. In the open cycle, spent fuel is considered to be a radioactive waste of high activity from the moment of discharge from the reactor and is stored permanently.
  • Closed cycle management. The closed cycle consists in subjecting the spent fuel to a mechanical-chemical process, known as reprocessing or reprocessing, which allows the separation of uranium and plutonium that still contain fission and transuranic products. The recovered uranium and plutonium are used to make new fuel and fission and transuranic products constitute the high-activity nuclear waste.

Uses of Plutonium

The most important uses of plutonium depend on two of its properties. First, the emitted radiation generates a lot of heat, thermal energy. In fact, plutonium emits so much heat that the metal feels warm when touched. If a large piece of plutonium is placed in the water, the heat released can make the water boil.

Plutonium provides electrical energy in space probes and space vehicles.

The ability of plutonium to generate heat makes it an ideal material for use in thermoelectric generator applications. A thermoelectric generator is a device that converts heat into electricity. Generating electricity through such a generator is not practical on a large scale. Anyway, they are very interesting in certain conditions. These thermoelectric generators have been used in artificial pacemakers for people with heart conditions. The most used isotope for this application is plutonium-238 because the radiation it emits does not pose a threat to people's health.

Plutonium is also used as fuel in nuclear power plants and in the manufacture of nuclear weapons ("atomic bombs"). The isotope used for this purpose is plutonium-239. It is used because it will suffer nuclear fission. Very few isotopes will suffer nuclear fission.

Role of plutonium in nuclear reactors

As plutonium is generated inside the fuel of nuclear reactors, it also fission, collaborating with uranium in energy production. During the process, other isotopes also originate; some are neutron absorbers and others are fissile isotopes.

Depending on the irradiation time or the degree or degree of burning at which the proportion of these isotopes of plutonium in the fuel is reached. At reduced burns the proportion of fissile isotopes is very high, while at high burns this proportion is reduced.

In commercial nuclear reactors, the combustible elements remain in the reactor for a long time until the accumulation of fission products and the consumption of fissile material cancel their contribution to the operation of the reactor.

Management of recovered plutonium in nuclear reactors

In spent fuel, between 7 and 8 kilograms per ton of unburned plutonium remain. This plutonium, recovered at reprocessing, can be used to replace uranium-235 in nuclear fuel, making mixed uranium oxide and plutonium oxide pellets, (MOX fuel).

MOX fuel can replace enriched uranium fuel in light water nuclear reactors.

Health Hazard

Plutonium is radioactive and toxic. But, although sometimes it has been described in the media as the most toxic substance known to humans there are substances that are much more. The radius of natural occurrence is about 200 times more radiotoxic, and some organic toxins such as botulinum toxin are billions of times more toxic.

The main type of radiation emitted (alpha radiation) does not pass through a sheet of paper, that is, a thin layer of a material can stop the radiation. It cannot cross the skin.

What makes plutonium really dangerous is its radiotoxicity. The radiation emitted (alpha radiation) when ingested or inhaled, can cause lung cancer or cancers of other types depending on where it is deposited in the body. In considerably larger quantities they can cause acute radiation poisoning and death if ingested or inhaled.

This material has been used for the manufacture of nuclear and explosive weapons for a long time. At atmospheric tests of atomic bombs, large amounts of radioactive material have been released that subsequently fall and settle on the ground.

Humans are not likely to be exposed to plutonium, but sometimes it occurs as a result of accidental leaks during use, transportation or dumping.

When breathing, plutonium can remain in the lungs or move to the bones or other organs. It generally remains in the body for a long time and exposes the body's tissues continuously to radiation. After a few years this could result in the development of cancer.

Plutonium can affect the ability to resist disease and its radioactivity can cause reproductive failure.

Environmental effects

Plutonium is naturally present in very small quantities. However, the element has other routes of entry into the environment through leaks of nuclear reactors, atomic weapons production plants, and research facilities. Especially in nuclear weapons testing.

Plutonium can enter surface waters by accidental leaks and spills of radioactive waste. The soil can become contaminated with radioactive material through radioactive rain during nuclear weapons testing. The material moves slowly down the ground, to the groundwater. Plants absorb low levels of this material, but these levels are not high enough to cause biomagnification of plutonium in the food chain, or accumulation in animal bodies. 

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References

Yosoynuclear - Preguntas y respuestas sobre el plutonio

Lenntech - Plutonio - Pu

Last review: August 1, 2019