Uranium

Article

October 28, 2021

Uranium is the chemical element with atomic number 92, symbol U. It is part of the actinide family. Uranium is the 48th most abundant natural element in the earth's crust, its abundance is greater than that of silver, comparable to that of molybdenum or arsenic, but four times less than that of thorium. It is found everywhere in traces, including in seawater. It is a radioactive heavy metal (alpha emitter) with a very long half-life (~ 4.468 8 billion years for uranium 238 and ~ 703.8 million for uranium 235). Its radioactivity, added to that of its descendants in its decay chain, develops a power of 0.082 watts per tonne of uranium, which in fact, with thorium 232 (four times more abundant, but three times less radioactive) and the potassium 40, the main source of heat which tends to maintain the high temperatures of the Earth's mantle, greatly slowing its cooling. The 235U isotope is the only naturally occurring fissile isotope. Its fission releases an energy of around 202.8 MeV per fissioned atom, including 9.6 MeV of unrecoverable energy, communicated to the neutrinos produced during fission. Recoverable energy is more than a million times greater than that of fossil fuels for an equivalent mass. As a result, uranium has become the main raw material used by the nuclear industry. World uranium production amounted to 54,742 tonnes in 2019, mainly split between Kazakhstan (41.7%), Canada (12.7%), Australia (12.1%) , Namibia (10%), Uzbekistan (6.4%), Niger (5.4%), Russia (5.3%) and China (3.4%). In 2020, production fell to 47,731 tonnes. For its use in nuclear reactors, the resources recoverable at a cost of less than 130 dollars / kg of uranium were estimated in 2019 by the IAEA at 6.15 million tonnes worldwide, distributed mainly between Australia (28 %), Kazakhstan (15%), Canada (9%), Russia (8%) and Namibia (7%).

Natural uranium

The uranium ore that has been mined on Earth has a uranium content that can vary from 0.1% to 20%. Uranium is said to be natural when it consists of isotopes in their original proportion (identical for all uranium ores): i.e. 99.2743% uranium 238 accompanied by 0.7202% uranium 235 and a minute amount of isotope 234 (0.0055%).

Discovery

Uranium was discovered in 1789 by the Prussian chemist Martin Heinrich Klaproth from the analysis of a piece of rock that had been brought to it from the Saint Joachimsthal mine. This rock was pitchblende, a uranium ore that mainly contains U3O8. Klaproth managed by heating it to extract a metallic gray body. In his communication of September 24, 1789 to the Royal Prussian Academy of Sciences and entitled "Ueber den Uranit, ein neues Halbmetall", he proposed the name of "urane" or "uranite" to the compound he had just identified ( an oxide of uranium and not the pure body), in reference to the discovery of the planet Uranus made by William Herschel in 1781. This oxide, renamed uranium in 1790, had the property of giving a fine fluorescence to the glasses and a yellow color greenish with enamels, so that pitchblende was extracted from the Joachimsthal mine and tin mines in Cornwall and from the alkaline uranates (ammonium and sodium diuranate) used by Bohemian glassmakers and Saxon ceramists. It was not until 1841 that the French chemist Eugène-Melchior Péligot was able to isolate it in a state of purity by reducing uranium tetrachloride (UCl4) with potassium. He established that uranium was composed of two atoms of oxygen and a metal which he isolated. Uranium entered the nomenclature of chemi

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