Extraction of uranium

The industry of extraction of the Uranium is a mining Industrie which goes from the initial prospection to the transportable product (the Yellowcake). It belongs to the Cycle of nuclear fuel (together of operations aiming at providing fuel to the nuclear plants) and is necessary for the manufacture of a bends with uranium enriched. It includes/understands the following successive operations:

the Prospection of new layers,
preparation of a site for the exploitation of a layer (authorizations, design and installation of the equipment, possible construction of the works of access),
the extraction of the ore, extract alone or as a Co or by-product of the extraction of Gold, Copper or Phosphate.
concentration of transportable uranium in the form of Yellowcake, and the sale of uranium
the Dismantling of the sites when the layer is exhausted.

History

The first systematic radioactive ore exploitation is carried out with Jáchymov (in German, Joachimsthal), a mining city located in what is now the Czech Republic. Marie Curie uses Pechblende coming from Jáchymov to insulate the Radium, a radioactive descendant of uranium. Thereafter, and until the Second world war, mining aims mainly radium. This element is used as component paintings Phosphorescent are for faces of watches or other instruments, as for medical applications (certain applications are now regarded as dangerous for health). Uranium is then a derivative product of these applications, mainly used like yellow pigment.

A specific demand for uranium appears during the Second world war. The Project Manhattan, studying the military applications of atomic energy, seeks to acquire uranium stocks in sufficiently large quantity. The historical layer of Jáchymov, under German occupation, not being accessible, American uses ores coming from the Belgian Congo, provided by the Mining Union of High Katanga, as well as Canada. Pursuant to a policy of self-sufficiency, they also recover uranium present in exploitations of Vanadium, present in the south-west of the USA, but of contents much lower. The Soviet Union, which does not have uranium stock at the beginning of its program of atomic weapons, has a similar step.

Geology of uranium

Mineralogy

Uranium is relatively widespread in the Earth's crust, that it is in the grounds granitic S or Sédimentaire S. the uranium concentration in these rocks is about 3 g/tonne. As example, a square garden of 20 m on side contains thus, on a depth of 10 m, approximately 24 kg of uranium.

Natural uranium is also present in water. 3 is found; mg/d' uranium per cubic meter of sea water, is thousand times less than in the rocks. The the Rhone carts some indeed close to 100 tons each year. This uranium comes from the streaming of the rains on the the Alps. From the prospective point of view, the recovery of the uranium dissolved in sea water is studied with the Japan without however being able to conclude on the industrial feasibility of the process.

The natural uranium ore is the Pechblende, which can appear in the form of Filon S metalliferous. In the majority of the layers however, uranium is present only at the state of traces.

According to the layers, the ore considered as exploitable has a content of about 1 to 200 kg of uranium per ton of ore, that is to say at least thousand times the average natural concentration of the ground. The exploitable concentration very strongly varies according to the conditions of operating and the course of the ore.

Prospection

The propection of uranium uses all the traditional geological tools. Its principal originality is to use moreover techniques of Prospection Radiologique: the passage of a few tens of shocks a second to a few thousands indicates the proximity of a Affleurement presenting a potentially interesting concentration.

Uranium is a metal relatively running in the Earth's crust, whose most remarkable characteristic is the Radioactivité: it contributes mainly to the radiometric background noise. Historically, the tool for detection employed was the Geiger counter, of which first transportable models (about 25 kg…) appeared in the years 1930. The Geiger counter was replaced since by the use of Scintillation counter.

The idea of a radiological air prospection was put forward in 1943, by G.C. Ridland, working geophysicist with Port Radium (Canada). It is now the technique most employed for the initial prospection of uranium. The extension of the layer is then specified by more traditional means: samplings, then prospective drillings.

Layers under discordance

The uranium-bearing Minéralisation S of type Discordance were discovered for the first time at the end of the years 1960 in the basins of the Athabasca (Canada) and of Mc Arthur (Australia). Their richness is exceptional.

The uranium deposits are located at the interface between a base of age Archéen with lower Protérozoïque and a powerful sandstone cover of the protérozoïque means. They are generally associated with faults with graphite and are surrounded by halations of argillaceous deteriorations of high temperature. Mineralizations are not clearly dated but are more recent than the sedimentary covers.

The commonly allowed model for the genesis of these layers is hydrothermal Diagénétique, i.e. the deposit takes place during the Diagenèse with the favor of circulations of fluids. A percole Brine very concentrated and oxidizing in the base and grows rich out of calcium, magnesium and uranium by dissolution of Monazite, is impoverished in quartz and increases its Température. In contact with a Face redox with the discordance, this brine dissolves quartz and precipitates uranium in released space. Successive deteriorations, re-mobilizations and precipitations probably take place later on.

See for example the configuration illustrated in the article natural Nuclear reactor of Oklo.

The mechanisms of mineralization in Australia and to the Canada are rather similar but their forms and their sites different appreciably, which leads the scientists to speculate in different mechanisms of reduction for the two basins. The geologists however try to include/understand what they have jointly to find of new layers of this type. Lastly, the analogy between this type of layer and the current design of the Stockage of the radioactive waste in deep geological layer strongly interests the researchers.

Some remarkable sites

the natural Nuclear reactor of Oklo had reached concentrations allowing the starting of a chain reaction.
With the mine of Cigar Lake, with the Canada, is extracted a Minerai which contains up to 210 kilograms of uranium per ton of ore!
the mine of Shinkolobwe, in Democratic republic of Congo, today is officially closed. She provided as of 1939 uranium to the the United States of America which in particular used it during the Second world war for their nuclear program (Projet Manhattan).
the mines of Arlit to the Niger, exploited by Areva, provided since the Années 1970 the essence of French uranium.

; In France In France, the reserves are estimated at 12500 tons (either 0,5% of the world total). The majority of the layers are:

in the Vendée,
in the Massif Central: the department of the High-Vienna counted to about fifty mines in exploitation.

France does not present however mining resources out of uranium sufficiently profitable. The richest layers indeed count 1 to 5 kilograms of uranium per ton of ore, under conditions of difficult operating (underground mines).

Technique of extraction

The Minerai of Uranium is classically produced in mines of uranium to open sky (28%) or by underground mining work (43%). More recently, a technique by injection of acid or basic solutions (Leaching in situ) is used for the extraction of the layers of sandstone (15%). These techniques are known as conventional.

Other techniques the such lixivation in heaps (which make it possible to exploit secondarily Terril S) even the recovery of water of pumping out are also implemented and are qualified the nonconventional ones.

The layers under discordance are currently (in 2003) the only profitable uranium layers alone. In the other cases, the uranium ore is extracted as a Co or a by-product from the extraction from Or, Cuivre or Phosphate, profitable by itself.

To mitigate the presence of Radioactivity in the uranium mine, mining industry sets up special security measures: for example of the systems of watering and permanent ventilation to decrease the Irradiation and to reduce the concentrations of dust and Radon.

Concentration in Yellowcake

Weak the concentration out of uranium of the extracted ores make economically its transport nonprofitable, and impose a treatment of concentration on the spot. The concentrate of Yellowcake is prepared with the accesses of the mine by many methods of extraction and refining, depend on the type of ore. One typically extracts from a ton of this ore approximately 500 G of yellowcake .

Mining economy of uranium in the world

Production

The worldwide production of uranium reached 45103 tons in 2001, of which 34% comes from the Canada, the most important country as regards production of uranium.

The uranium ore is relatively well distributed geographically with many other producer countries. In 2006, the principal producer countries (for an aggregate output of about 40.000 tons of U) are:

the Canada (25% of the production - 9862 tons of U), with in particular the centers of Key Lake and McArthur To rivet,
the Australia (19% of the production - 7593 tons of U), with in particular Arranging and Olympic Prejudice,
the Kazakhstan (13% of the production - 5279 tons of U) has important reserves and affirms like a future large supplier,
the Niger (8% of the production - 3434 tons of U) with the mine of Arlit,
the Russia (8% of the production - 3400 tons of U),
the Namibia (7% of the production - 3077 tons of U).

The remainder of the production (less than 20%) divides between small producers the such in particular South Africa, the Ouzbékistan, the Ukraine, and the the United States.

One counts in France nearly 170 old sites of extraction and ore processing of uranium. All these sites represented a production of approximately 72 800 tons of uranium. The French mining activity, for the uranium extraction in any case, ended in May 2001 with the closing of the underground mine of Jouac /Le Bernardan, in High-Vienna, which was exploited by Cogéma. Certain French mines are useful today like sites of storage of the residues of treatment and the Radioactive waste imported.

World reserves

Proven uranium world reserves, i.e. the recoverable resources with less 80$/kg U, reach a world total of 2516 thousands of tons, except Chile and China (AIEA/OCDE 2001). The most important resources are in Australia (26%), with the Kazakhstan (17%), with the Canada (12%), in South Africa (9%), with the Brésil (6,4%), in Namibia (5,7%), in Russia (5,5%), with the the United States (4,1%), in Ouzbékistan (3,6%), in Mongolia (2,4%), in Ukraine (1,7%), with the Niger (1,2%) and in Algérie (1%).

The proven reserves correspond to an about sixty years of production, which is a current order of magnitude as regards prospection for minerals; balance being made when the conditions do not justify an additional effort of prospection. This evaluation is very strongly dependant on the economic conditions.

Cours de l' uranium

The demand for uranium knew a historical peak as from the years 1950, with the beginning of the Arms race nuclear of the cold war. The military request attenuated in the years 1960, and at the end of the years 1970, the programs of acquisition were completed, a mutually assured level of destruction (MAD) being reached.

Years 1970 transfer a new request to emerge with the starting of the civil nuclear energy, and the construction of nuclear plants. This request crumbled with the beginning of the year 1980, on the one hand because constructions of power stations were completed, and on the other hand because the antinuclear pressure of opinion following the catastrophes of Three Mile Island and especially Tchernobyl involved in many countries a moratorium in fact on the construction of new power stations.

The price of uranium had reached 43 US$/lb U₃O₈ in 1978, and was of 32.90 US$/lb U₃O₈ in 1981. It reached a historical minimum of 7 US$/lb in 2001.

Since 2001, its price went back to 113 US$/lb in 2007, practically reaching the historical heights of 1977 after correction of inflation. This rise is due to many structural factors:

the moratorium on the nuclear plants tends to end, following the Protocole of Kyoto; the nuclear energy being not very producing of Gas to greenhouse effect.
worldwide consumption in fossil energies (gas and oil) draws the prices upwards, and accelerates the exhaustion of the reserves from them. The passage to an alternative energy is prepared as of now.
the price of nuclear kWh does not cease dropping, which makes a source increasingly gravitational of it economically.

The experts envisage the doubling of the number of power stations from here 2050, without counting the probable needs for an emergent Chinese industry. Stocks foreseeable in this term are insufficient to face the request, justifying a rise of the courses.

This increase of the courses gave a whiplash to the expansion of the current mines. In parallel, of new mines are open (or of old mines are réouvertes), and the prospection for minerals was started again. But it takes years to put a mine in production, and these economic adjustments will have effect only later on.

Environmental impact of a uranium mine

Uranium is an element slightly radioactive, which does not present a danger to the environment if it remains in its natural state. However, after the dismantling of a uranium mine, it remains more than 80% of the Radioisotope S in the cut hills. The wind diffuses radioactive particles in all the directions. Streaming water is contaminated and infiltrates in the ground water or the brooks.

A uranium mine in exploitation produces many waste:

of the stack disposals : the Radon and radioactive dusts. One of the most dangerous rejections of a uranium mine is the Radon, an invisible and odorless rare gas which is propagated since the installations of conditioning and the cut hills or the liquid tanks of waste. Radon involves a risk of Lung cancer.
of the liquid rejections : the water of pumping out created by drillings and the streaming inside the mine. Water can be pumped and it if necessary is treated before rejection.
of solid waste : muds and precipitates coming from the liquid liquid waste processing;
of the deads : the extracted rocks which contain only very little uranium and which, consequently are not treated. The quantity of the deads of uranium mines reaches hundreds of million tons. If the deads are not well covered and are not located, they reject radon and radioactive dusts in the air and by rainwater infiltration of the toxic and radioactive matters pass in subterranean water and surface.
of the raffs : the ores whose uranium content ranges between 0,03 and approximately 0,8%. They are not always treated. Stocks pose the same problems as the deads, worsened by the higher content uranium.

This waste exposes the environment to the Radioactivité of the Uranium, which can involve a radioactive Contamination the human ones, fauna and flora. Moreover, certain waste has not only one danger related to the radioactivity but also a risk related to the toxicity of the conventional chemicals such as the sulphuric acid and the heavy metals, used for the ore processing of uranium. Lastly, it is also necessary to consider the harmful effects of the mine due to:

the entire surface of ground occupied by the mine, which is higher for uranium than for the exploitation of other ores.
social impact for the natives residents on the exploitation site (examples in the USA, Canada, Africa, Australia…).

The CRIIRAD led in December 2003 an independent inspection to Arlit (Niger) where uranium mines worked by French nuclear industry are (Cogéma-Areva). Many irregularities were pointed in the final report, although the inspection was disturbed by the confiscation of the material and various obstructions on behalf of the authorities natives of Niger and of Cogéma.

According to the ecological Institute of Austria, the exploitation of the uranium mines and the operations of nuclear Retraitement are the stages of the Cycle of nuclear fuel which contribute more to the radiative amounts due to nuclear energy (by taking account of a normal functioning and “small” incidents, i.e. by excluding the Nuclear tests and the serious accidents such as the Catastrophe from Tchernobyl).

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