What is Uranium?
Uranium is a slightly radioactive, very dense metal that occurs throughout the earth's crust. It is about 500 times more abundant than gold and about as common as tin. It is present in most rocks and soils as well as in many rivers and in sea water.
It was discovered in 1789 by Martin Klaproth, a German chemist, in the mineral called pitchblende. It was named after the planet Uranus, which had been discovered eight years earlier.
It is found in concentrations of about four parts per million (ppm) in granite, which makes up 60% of the Earth's crust. In fertilisers, uranium concentration can be as high as 400 ppm (0.04%), and some coal deposits contain uranium at concentrations greater than 100 ppm (0.01%). Most of the radioactivity associated with uranium in nature is in fact due to other minerals derived from it by radioactive decay processes, and which are left behind in mining and milling.
There are a number of areas around the world where the concentration of uranium in the ground is sufficiently high that extraction of it for use as nuclear fuel is economically feasible. Such concentrations are called “ore”.
About 72 percent of the world's production of uranium from mines is from Kazakhstan, Canada, Australia and Namibia.
Uranium was discovered in the Namib Desert in 1928, but it was not until the mid-seventies that uranium was produced from Rio Tinto’s Rössing mine. Namibia currently produces approximately 9% of world production from the Rössing and Langer Heinrich mines.
What is uranium used for?
Uranium’s primary use is as fuel for nuclear power plants. Energy from uranium is used directly to power nuclear power plants as well as some sea-going vessels such as military ships, submarines and icebreakers.
How does Uranium become Nuclear Fuel?
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
- refining and 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 manufacture, where the uranium is manufactured into fuel pellets
- electricity generation where nuclear fuel is loaded into a reactor and nuclear reactions 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, residual uranium or by-product plutonium, both of which are still useful sources of energy, are recovered from the spent fuel elements and reprocessed. Alternatively, the spent fuel is stored 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.
Who uses nuclear power?
Over 16% of the world's electricity is generated from uranium in nuclear reactors. This amounts to about 2400 billion kWh each year, as much as from all sources of electricity worldwide in 1960. In a current perspective, it is twelve times Australia's or South Africa's total electricity production, five times India's, twice China's and 500 times Kenya's total.
It comes from about 440 nuclear reactors with a total output capacity of about 370 000 megawatts (MWe) operating in 31 countries. About thirty more reactors are under construction and another 40 are planned.
Belgium, Bulgaria, Finland, France, Germany, Hungary, Japan, South Korea, Lithuania, Slovakia, Slovenia, Sweden, Switzerland and Ukraine all get 30% or more of their electricity from nuclear reactors. The USA has more than 100 reactors operating, with capacity of almost three times Australia's total, and supplying 20% of its electricity. The UK gets almost a quarter of its electricity from uranium.
Nuclear Energy and Greenhouse Gas Emissions
If the electricity produced worldwide by nuclear reactors were generated instead by burning coal, an additional 2600 million tonnes of carbon dioxide would be released into the atmosphere each year. This can be compared with the target of a 5% reduction (600 million tonnes per year) in carbon dioxide emissions by the year 2010, as agreed in 1997 at Kyoto just for the developed countries.
Every 22 tonnes of uranium used avoids the emission of one million tonnes of carbon dioxide, relative to coal. When the electricity comes from coal, every kilowatt hour of it results in about a kilogram of carbon dioxide being emitted.
