Plutonium

Description

Plutonium is a gray metal, relatively soft, very heavy (density: 19,84), solid with room temperature but at very low point melting (640°C).

It is synthesized during the nuclear explosions (In 1952, the explosion of the American thermonuclear bomb most powerful thus produced two Radioélément S then still unknown; plutonium-244 (Pu 244) and plutonium-246 (Pu 246).
Le plutonium is also a waste or by-product of operation of civil nuclear plants, with various Actinide S.
Il is also voluntarily produced by neutron capture of the Uranium in the nuclear reactors.
For example, isotope 239 is formed in three stages:

captures neutron uranium 238 to form uranium 239;
decrease β- of the Uranium 239 (1/2 life: 23 minutes) in Neptunium 239;
decrease β- of neptunium 239 (1/2 life: 2,3 days) out of plutonium 239.

The heaviest isotopes of plutonium are mainly formed by neutron capture of plutonium 239.

Plutonium is a metal silver plated very radioactive (according to the isotopic composition, isotopes 238 and 241 being by far more radioactifs : to very see toxic table), and (one milligram of plutonium can be enough to induce a Cancer). It reacts with the Oxygène, the steam and the acids. It does not react with the bases. It is Radiotoxique. Its period of Demi-vie is of 24 000 years for isotope 239.

There are fifteen Isotope S known. The isotopes most produced out of engines are isotopes 238,239,240,241,242. All are radioactive. The isotopes of odd atomic number (239 and 241) are fissile in thermal spectrum (engines currently in production).

Legal status

Plutonium answers the allowed definitions of “Polluant” When it is produced in the civil engines; is regarded Déchet by certain countries and as matter which may undergo beneficiation by others (of which France). Indeed, the worn fuel discharged from the engines can be reprocessed in order to isolate from it the plutonium, which is then mixed with Uranium impoverished (resulting from the initial stage of enrichment) to form Combustible MOX. In small quantities, plutonium is used in the thermo-electric generating with radioisotope.

Plutonium is also produced with fine soldiers in dedicated installations or generating engines according to the countries. It is then used to manufacture nuclear weapons. Approximately 5 is needed; kg of plutonium to obtain a bends. As an element useful for the manufacture of Weapon of massive destruction, it is followed by various texts and international conventions

See also: Control of the nuclear matters

Plutonium 239

Production

The irradiation of uranium 238 in the nuclear reactors generates plutonium 239. When the fuel undergoes increasingly long periods of irradiation, the higher isotopes accumulate because of the neutron absorption by plutonium 239 and its products. It is thus formed isotopes ²⁴⁰Pu, ²⁴¹Pu, ²⁴²Pu. In parallel, of plutonium 238 is formed by the chain of transformation starting with Uranium 235.

Thus, when one uses a specific engine for the manufacture of military plutonium, fuel used for the production of plutonium as well as the targets and the cover if there is, are extracted after a short stay (a few weeks) in the engine in order to have the assurance which plutonium 239 is as pure as possible. A short irradiation, however, does not extract all the energy which the fuel can produce. One thus removes fuel of the generating engines only after one stay much longer (three or four years).

Once the fuel, the targets and the cover removed of the engine in which they were irradiated, they undergo a chemical treatment, which is called the reprocessing of irradiated fuel, in a factory or a workshop to separate plutonium.

Reprocessing

The two larger world installations recycling plutonium are based with La Hague and Sellafield

Plutonium 238

Plutonium 238, of a half-life of 86,41 years, is a very powerful transmitter of radiation α (helium cores). Because of its specific activity alpha and gamma raised, it is used like neutron source (by reaction alpha with light elements), like source of heat and electric energy source (by the conversion of heat into electricity). The uses of Pu 238 to produce electricity are confined with the cardiac pacemakers and the space uses.

One prepares plutonium 238 starting from the irradiation of neptunium 237, a minor actinide recovered during the reprocessing or starting from the irradiation of americium, out of engine. In both cases, to extract plutonium 238 from the targets, one subjects them to a chemical treatment, comprising a nitric dissolution.

There are only approximately 700 g/t neptunium 237 in fuel of the ordinary water reactors man exposed to atomic radiation during three years, and it should be extracted selectively.

Plutonium dioxide

The plutonium dioxide (PuO₂) is for the radiochimists the ideal form to handle the dangerous element. Discovered in 1940 by the American chemists left on the way the atomic bomb, one finds it for the recycling of nuclear fuels, the clothes industry of the warheads or the storage of the radioactive waste. It is about a crystal yellow-greens powder.

He was regarded a long time as stainless. A long time the trioxyde of plutonium (PuO₃) required but anybody was forever succeeded in manufacturing some. However in 2000, the laboratory of Los Alamos (New Mexico) showed that the Pu dioxide can in makes react simply with water, at a temperature going of 25 with 350°C, to form a stable compound more oxidized: the proportion between oxygen and plutonium can go up to 2,27. Moreover, this reaction releases from the Dihydrogène, a flammable gas.

This is problematic because water would be the principal potential vector of radioactive dissemination during the storage of in-depth waste. A fraction of new formed oxide could dissolve in water and be disseminated slowly in the neighborhoods.

In France, the plutonium dioxide is stored on the surface, in limp tight, to be then re-used in ordinary power stations, while using the composition of the Combustible MOX (MiXed Oxyde).

Precautions

Control nuclear matters

Plutonium is a nuclear matter whose detention is regulated (R1333-1 Article of the code of defense).

Toxicocinétique

In the event of ingestion by a healthy individual, only approximately 0,05% are absorbed by the digestive tract
Le plutonium crosses the cutaneous barrier badly (if the skin is in good state).
On the other hand, a big part of inhaled plutonium passes from the lungs to the blood which diffuses it towards other bodies, more or less quickly and well according to the size of the particles, and the nature and the solubility of the compound. In the animal of laboratory exposed tohigh rates plutonium , the target fabrics were the Poumon S, the lymphatic ganglia, the liver and the bones (with reduction of the lifespan, cancers and pathology pulmonary).

It is estimated that at the Man, 10% of the plutonium which crossed the intestinal or pulmonary barrier the body leaves (via the urine, and the excrements). The remainder after passage in blood is fixed for half in the Foie and for half in Squelette, where it remains very a long time and to some extent with life (the American DOE estimates that the half life in the body is respectively of 20 and 50 years for the liver and the bone, according to models simplified not taking account of intermediate redistributions (in the event of Fracture and/or of Ménopause (cf Décalcification) and during the normal recycling of the bone, etc). The DOE specifies that the rate accumulated in the liver and the skeleton also depends on the age of the individual (absorption in the liver increases with the age), and that in fact, plutonium is fixed initially on cortical surface and trabéculaire of the bones before being slowly redistributed in all osseous mineral volume.

Toxicity

All the isotopes and composed of plutonium are Toxique S and radioactive.
Ce metal is normally absent in nature on the surface of the sphere, but it was produced and diffused in significant and still measurable quantity in the Atmosphère and the Biosphère, in years 45 to 70 by the nuclear tests and shootings, with also of the repercussions (more local or regional) at the time of the accident of Tchernobyl.

Plutonium was sometimes described like the “substance more Toxique known by the man”, but for of its characteristics and many isotopes, it would be necessary to distinguish toxicity from short, average and long run, and the external cases of exposure and intern.
Although very few data are available in the public domain on the compared toxicity of its various isotopes, Some consider that this assertion is to be relativized for the following reasons;

It is a transmitter of radiation alpha, type of radiation easily stopped by the fine walls, including by the skin. However if it is inhaled or introduced, it directly irradiates the cells of the bodies which are in contact with him (or that it penetrated). It can then affect their core and DNA and to cause Cancer S. Its activity internal is all the more dangerous as a big part of the plutonium absorptive by the organization is fixed at it durably; its biological half-life is estimated to be 200 years.

the osseous cancer risk (or of blood) is highest because the Os easily fixes (Adsorption) plutonium, like it in the case of does it with the Plomb the Saturnisme.
the Foie can also accumulate it.
It is very slowly eliminated via the urine, but while passing by the Rein, which it can then damage.
the inhalation of Vapor, Microparticle S or Nanoparticule S of plutonium can cause a Lung cancer (one microgram inhaled is enough).

In strictly chemical term of toxicity acute; i.e. without taking account of the effects of its radioactivity (except in the event of exposure interns and it is not a question themselves of military plutonium of quality), plutonium never seems not to have caused a death documented by external exposure (Source?). It does not have acute toxicity (organic compounds such as the botulinic Toxine are much more quickly mortals, and with an amount of some nanogrammes that plutonium). Plutonium is nevertheless a powerful long-term carcinogen.
In term of radiotoxicity in the event of external exposure, the natural Radium is about 200 times more Radiotoxique that the least active plutonium, and of the elements such as the Carbon-14 or the Potassium 40 (transmitting beta) can cause cancers by simple contact what is not the case of plutonium when it is only one simple transmitting alphas. However the isotopes of plutonium have an activity (measured in curies) very variable. If one does not take account of possible differences in chemical toxicity, one can retain that the shorter them period of half-life is, the more they are active and dangerous. As example taken among the most current isotopes,

it Pu-242 has one period (half-life) 380.000 years, a specific activity of 0.0040 Ci/g and an emission α of 4.9 MeV (million electron volts), against only 0.0087 MeV in term of emission Beta (β) and 0.0014 MeV in term of emission Gamma (γ), which makes it much less dangerous than of other isotopes of Plutonium.

it Pu-241, although physically very near to preceding has to him one period (half-life) comparatively very short (14 years), but a specific activity much more important (100 Ci/g)! Moreover, it emits Beta particles and is transformed into Americium 241, a Actinide of which the period is 430 years, and who is much radiotoxique than the plutonium which generated it.

Plutonium is thus most dangerous when it is in the form of plutonium " of military quality " and when it is inhaled. It is it of course immediately when it is at the origin of a nuclear Explosion voluntary or of a Accident of criticality. It seems to be less dangerous in the event of internal exposure via Ingestion because then more easily eliminated via the excrements or the urine (According to the book from Eileen Welsome, when it is introduced, and if one does not take account of the risk of Cancer, plutonium would be chemically less harmful than substances like the Caféine or others which one can find in nature. It would be more harmful than of the pure ethanol, but less than the Tabac or certain drugs. Always only “chemical” point of view of (i.e. without taking account of its radioactivity), its Toxicité would be comparable with that of the Plomb or with others Heavy metals. Plutonium has a metal taste.

See too

Control of the nuclear matters
Nuclear energy
Radioactivity
the periodic Table of the elements

External bonds

Pu - table periodic of the elements (Faculty of chemistry of Split)
human experiments on plutonium in the United States (Los Alamos Science, 23,1995)

References

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