The tritium ( T or ³ H ) is a Isotope of the Hydrogène. It has 1 proton and 2 neutrons.
It is not stable. It is thus radioactive. It emits a radiation beta (β-) while being transformed into Helium-3 (³ He). Its period or Demi-vie is 12,32 years.
At the ordinary temperatures, the tritium is a gas (HT or T). In the presence of Oxygène, it produces tritiated water (HTO), if there are a source of heat or a spark. (Oxidation, just like the light isotope H). Into dry medium, the gas tritium is converted into tritiated water; approximately 1% of tritium are converted into 1 hour, and all the more quickly as the medium will be wet.
The tritium is formed naturally in the atmosphere by interaction of the cosmic radiation with the cores of Azote, Oxygène and Argon present in the high layers of the atmosphere. It arrives on the ground with rainwater.
The tritium is also produced by the man:
- the thermonuclear tests injected into the atmosphere a quantity of tritium approximately 100 times higher than the natural activity (source CRIIRAD).
- the nuclear reactors and the reprocessing of the nuclear waste produce toxic tritium, mainly dispersed today in the environment.
UseThe tritium is used in the nuclear bombs, by using the nuclear Fusion tritium-tritium or tritium Deutérium. This one is started by the extreme conditions of temperature and pressure during an explosive reaction of Nuclear fission of the Uranium 235 or Plutonium 239. The Neutron S released by the fusion of tritium support in their turn the fission of uranium or plutonium.
The tritium will be also one of the hydrogen isotope used for the operation of the future engine with nuclear fusion ITER.
ConstraintsThe irradiation beta emitted by tritium is weak. He nevertheless is recognized like carcinogen. He penetrates in the body by the aspiration, absorption through the skin or ingestion. Tritiated water mingles quickly with all water with the body. According to a study of IAEA, tritiated water is much more Radiotoxique (: 25000 times) that the gas form.
The Plant reprocessing of La Hague to the authorization to reject 37000 per annum TBq (Téra becquerel S) in liquid form and 2200 TBq per annum in gas form. For the year 2002, it rejected 11900 respectively of them TBq and 63.2 TBq (source Areva NC).
ProductionThe tritium can be produced in significant amounts by bombarding lithium by a neutron flux. It is the case for example in the Nuclear reactor of a nuclear plant. The light isotope ( 6 Li), present in natural lithium at a rate of 7.5%, captures the neutrons and gives tritium and helium cores following the reaction hereafter:
6 Li + N → 4 He + 3 H
In the future utilisaton of thermonuclear fusion for the energy production, lithium will be used in a peripheral zone known as of cover , wrapping the heart of the engine, in order to intercept a maximum of neutrons produced by the reactions of fusion. The tritium could thus be produced and consumed on the spot, by limiting the transport of radioactive material.
Tritium and drinking waterAccording to the CRIIRAD (1995), the rainwater polluted by the nuclear tests and natural tritium is likely to contaminate the ground water up to 4 Bq/l. Beyond that, one can suspecter that another source of tritium is in question, with certainty with the tops of 7 Bq/l.
Toxicology, ecotoxicologyThe tritium penetrates in the body by the Respiration, Ingestion or through the skin. The inhaled share is spread equitably in soft fabrics; and tritiated water mingles quickly with all water with the body. Tritiated water being very similar to ordinary water, it is much radiotoxique than the gas tritium; : 25,000 times more, according to a study of the IAEA, tritium trapped in the organic matter more dangerous because less quickly are still eliminated (550 days, during which it can irradiate the interior of the body (either 55 times more, which 10 days of stay of tritiated water).
Radioactivity of tritium is relatively weak, but if it were introduced, which is facilitated by its gas state or when it is present in the form of tritiated water, it can damage the cells which are exposed there. The tritium, as of many radioactive elements is preferentially fixed by certain bodies with which it has chemical affinities or which are charged to filter or detoxicate the organization, instead of being diluted in all the water of the body. Some studies let think that the tritium can be fixed in the core and on DNA even, where it can cause noxious genetic mutation.
Tritium and nuclear industryThe tritium is a nuclear matter whose detention is regulated (R1333-1 Article of the code of defense).
See also: Control of the nuclear matters
The nuclear reactors, the Nuclear industry, via in particular the reprocessing of the Nuclear waste produce tritium by Irradiation of Lithium 6 and during reactions of Fission or reprocessing. The tritium degasses “worn” fuel and is mainly released during the reprocessing of this fuel.
Christian Bataille, in his report/ratio on the management of the nuclear waste recalls that the tritium “ presents for the human health of the undeniable dangers which it is advisable never not to forget . ”
Difficulty of managementOne cannot - at reasonable costs - filter today, to isolate nor correctly to store tritium.
To separate it from the air or a gas mixture, one makes of it more toxic tritiated water, which can evaporate, be diluted in water and penetrate the Béton if it is not protected by a special layer. In the presence of Nitrogen (essential component of the Air), tritiated water generates nitric Acid which corrodes its container.
This atom being active and among smallest, it diffuses by the finest Porosité S, passing for example through rubber and diffusing in the majority of qualities of steel.
This is why the large tritium producers asked and obtained for standards allowing them to disperse and dilute tritium in the Environnement, but some ONG ( Crii-Rad, Greenpeace ,…) being based on scientific data propose the capacity of the organizations filterers Re-to concentrate certain poisons diluted in the environment (Bioconcentration; example: a mussel can concentrate: 700,000 times, even until approximately 1 million times the Iode which is so slightly distributed at sea that it is often not quantifiable in water).
The factories of production of Plutonium of La Hague or Sellafield have limits of rejections enabling them to reject at sea or in the air it quasi totality of the tritium which they produce or must manage. The reprocessing plants of La Hague can reject at sea: 1,400 times more tritium than what is authorized with the engine of the Nuclear plant of Gravelines also located in edge of the sea, also near great fishing zones, but in more urbanized zone and currents less strong.
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