Uranium, as it is mined from the ground, is not directly useable for power generation. Much processing must be carried out before uranium can be used efficiently to generate electricity. Uranium's transformation from ore in the ground into nuclear fuel and ultimately the handling of waste products is described as the nuclear fuel cycle.
After a successful exploration program, uranium ore undergoes:
- mining and milling to produce uranium concentrate known as yellowcake
- conversion of the concentrated uranium into either uranium dioxide (UO2) for heavy water reactors or gaseous uranium hexafluoride (UF6) for light water reactors
- enrichment, which increases the proportion of the rarer 'fissile' form of uranium, U-235, which is the essential component of nuclear fuel
- fuel fabrication, where the uranium is manufactured into fuel pellets
- electricity generation where nuclear fuel is loaded into a reactor and allows nuclear reactions to generate electricity. After fuel is consumed, it is removed from the reactor and stored on-site for a number of years while its radioactivity and heat subside.
- optional chemical reprocessing, after a period of storage, recover from the spent fuel elements any residual uranium or byproduct plutonium, both of which are still useful sources of energy - and at the same time to separate and package the highly radioactive residues produced while the fuel was in the reactor; or alternatively storage, without chemical treatment, for up to fifty years to allow the radioactivity to diminish; (while its radioactivity and heat subside).
- and finally disposal where, depending on the design of the disposal facility, the nuclear fuel may be recovered if needed again, or else remain permanently stored. At some point in the future the spent fuel will be encapsulated in sturdy, leach-resistant containers and permanently placed deep underground where it originated, thus completing the cycle.
Steps one to four are known as the front end of the fuel cycle; steps six and seven, the back end, refers to what happens after the fuel comes out of the reactor.
How do you find uranium deposits?
Today's exploration activities are much more complex than in the past since the deposits that were close to the surface were found first because they were easier to discover. With the highest-grade deposits buried in deep rock formations, advanced technologies like satellite imagery, geophysical surveys, multi-element geochemical analysis and computer processing are required to locate and confirm the deposits.
Once geologists locate a prospective deposit, detailed geological and economic evaluation of the grade and characteristics of the orebody must be completed. Then mining engineers develop a mining plan to extract the ore. If the project looks promising, environmental impact assessments and the public consultation process begin so that applications can be made for regulatory approvals of project development. When permits and licences are in place, mine development and construction of surface facilities can begin. The timeline from discovery of an orebody to electricity production can span decades. Cameco's McArthur River mine was fast-tracked and still took 12 years to bring to commercial production.
At Cameco, uranium exploration has focused in recent years on targets in northern Saskatchewan's Athabasca Basin and in Arnhem Land in the Northern Territory of Australia.
How is uranium mined?
Uranium ore is removed from the ground in one of three ways depending on the characteristics of the deposit. Uranium deposits close to the surface can be recovered using the open pit mining method, and underground mining methods are used for deep deposits. In some circumstances the ore may be mined by in situ recovery, a process that dissolves the uranium while still underground and then pumps a uranium-bearing solution to the surface.
Open pit mining
When uranium ore is found near the surface, generally less than 100 metres deep, it is typically extracted by the open pit mining method. Open pit mining begins by removing overburden (soil) and waste rock on top of the orebody to expose the hard rock. Then a pit is excavated to access the ore. The walls of the pit are mined in a series of benches to prevent them from collapsing. To mine each bench, holes are drilled into the rock and loaded with explosives, which are detonated to break up the rock. The resulting broken rock is then hauled to the surface in large trucks that carry up to 200 tonnes of material at a time.
Underground mining
When an orebody is located more than 100 metres below the surface, underground mining methods are necessary since it is uneconomic to mine by open pit. For example, Cameco's McArthur River orebody is located more than 500 metres below the surface and so is it mined using an underground mining method.
The first step in underground mining is to access the ore. Entry into underground mines is gained by digging vertical shafts to the depth of the orebody. Then a number of tunnels are cut around the deposit. A series of horizontal tunnels, called drifts, offer access directly to the ore and provide ventilation pathways. All underground mines are ventilated, but in uranium mines, extra care is taken with ventilation to minimize the amount of radiation exposure and dust inhalation.
In most underground mines the ore is blasted and hoisted to the surface for milling. At McArthur River, due to the potential for radiation exposure from the high-grade ore, processing systems must ensure worker safety. As a result, the ore is processed underground to the consistency of fine sand, diluted with water and pumped to the surface as slurry or mud. The slurry is trucked to the Key Lake site for milling.
does uranium become nuclear fuel?How do you find uranium deposits?
How is uranium mined?
What happens to the ore during milling?
What is refining and conversion?
What is enrichment?
What is fuel fabrication?
How does a nuclear reactor work?
Can nuclear fuel be reused?
How are nuclear fuel wastes handled?
Source:http://www.cameco.com/uranium_101/fact.php#two
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