Introduction to Uranium
(October 25, 2007)
A typical pellet of uranium weighs about 7 grams (0.24 ounces). It can generate as much energy as 3.5 barrels of oil, 17,000 cubic feet of natural gas, or 1,780 pounds of coal.
What is uranium?
In its pure form, uranium is a silvery white metal of very high density
-- even denser, than lead. Uranium can take many chemical forms, but in
nature it is generally found as an oxide (in combination with oxygen).
Triuranium octoxide (U
3O8) is the most stable form of uranium oxide and
is the form most commonly found in nature.
Uranium has the highest atomic weight of the naturally occurring
elements. In the actinide series of the periodic table it has the symbol
U and atomic number 92. It has 92 protons, 92 electrons and either 145
or 146 neutrons. Uranium atoms that contain 146 protons are referred to
as the "uranium 238 isotope" (238U) and constitute 99.3% of naturally
occurring uranium. Uranium atoms that contain 145 neutrons are
referred to as the "uranium 235 isotope" (235U) and are weakly
radioactive. The 235U isotope makes up the balance (0.71%) of naturally
occurring uranium. Its nucleus can be made to split (or fission)
inside a nuclear reactor with the release of great quantities of energy
which can be used to generate electricity.
Uranium decays slowly by emitting an alpha particle. The half-life of
uranium-238 is about 4.47 billion years and that of uranium-235 is 704
million years, making them useful in dating the age of the Earth.
The 1789 discovery of uranium in the mineral pitchblende is credited to
Martin Heinrich Klaproth, who named the new element after the planet
Uranus. Eugène-Melchior Péligot was the first person to isolate the
metal, and its radioactive properties were uncovered in 1896 by Antoine
In 1993 the USA and Russia entered into the so-called
"Megatons-to-Megawatts" agreement whereby each country would dismantle a
significant fraction of its nuclear weapons and recycle the contained
Highly Enriched Uranium (approximately 90% 235U) to Low Enriched Uranium
(4-5% 235U) for use as fuel in nuclear power reactors. To date this
program has converted the uranium in approximately 11,000 nuclear
warheads into reactor fuel.
Where is uranium found?
Uranium is one of the most abundant elements found in the Earth's crust.
It can be found almost everywhere in soil, rock, rivers and oceans.
Traces of uranium are even found in food and human tissue.
It is 500 times more abundant than gold and it is as common in the
earth's crust, often in association with tin, tungsten and molybdenum
and is commercially extracted from uranium-bearing minerals such as
The concentrations of uranium vary according to the substances with
which it is mixed and where it is found. For example, granite, which
covers 60% of the Earth's crust, contains approximately four parts of
uranium per million, i.e. 999,996 parts of granite and four parts of
uranium. When uranium is present at concentrations exceeding
approximately 500 parts per million (0.05%) it can be economically
recovered at today's market prices.
Whether uranium can be mined is a function of many factors including
geological setting, extraction method, market prices and social and
Supply of uranium
World uranium production is dominated by Canada and Australia which,
together, produce about 51% of annual mine supply. These two countries
are followed by Kazakhstan, Niger, Russia and Namibia. These six leading
producers account for approximately 84% of worldwide mine production.
In 2006, world production of uranium was 40,000 tonnes U.
Canada, Australia and Kazakhstan are estimated to account for over half
of the world's resources of uranium, which are estimated to total
approximately 4.74 million tonnes. Australia has approximately 30% of
World resources, Kazakhstan 17% and Canada 12%.
Demand for uranium
Many industrialized nations are heavily dependent on nuclear power
generation, with nuclear electricity representing a major component in
such countries as the United States (20%), Germany (30%), Japan (34%),
Hungary (36%), Sweden (46%), and particularly France (78%) and Lithuania
(80%). Worldwide, there are 443 nuclear power reactors operating in 31
countries with total installed capacity of 370,000 MWe. The scale of the
world's nuclear industry is considerable and growing.
Primary uranium production filled only about 62% of world reactor
requirements during 2006. The balance was made up by secondary supplies
including: re-enriched depleted uranium; reprocessed used fuel; and
blended down highly enriched uranium (HEU).
Concerns over the global oil supply and global warming have renewed
interest in nuclear energy as it is a carbon-free source of electricity
with no CO
2 emissions. Other factors that are In addition, improved
reactor performance, extended fuel cycles, increased generating capacity
and reduced operating costs are also contributing to a revival in
As of January 2006, there were 24 reactors under construction, 41
planned (approved and funded) and another 113 proposed (intended but not
approved or funded). New construction is currently concentrated in Asia
with China and India in the forefront.
Power uprates have been granted for reactors in many countries,
including Belgium, Sweden, Germany, Switzerland, Spain and the United
States. In the USA such uprates have added 3,000 MW of new generating
capacity which is equivalent to the output of three new reactors. Many
reactors are having their operating licenses extended by an additional
20 years; over three-quarters of USA nuclear plants have received
20-year license renewals or are in the process of having their
As secondary supplies of uranium decrease and as new reactors under
construction come on stream, the demand for primary uranium will rise
appreciably and temporary shortages may result. Although known world
resources of uranium are more than adequate to fuel the world's reactors
for several decades, the licensing, construction and commissioning of
new uranium mines is a lengthy process (5-10 years), making it essential
that exploration and mine development now proceed expeditiously.
Where are uranium deposits located?
Uranium deposits are found all over the world. The largest deposits of
uranium are found in Australia, Kazakhstan and Canada. High-grade
deposits (>20% U3O8) are only found in Canada.
What is Uranium used for?
The principal use for uranium is in nuclear fuel for power generation.
Approximately 16% of the world's electricity is generated from nuclear
reactors, and it is growing in popularity given declining fossil fuel
supplies and increased pressure to use cheaper, cleaner (i.e.
low-carbon) forms of energy.
By the time it is completely fissioned, one kilogram of uranium can
theoretically produce about 20 trillion joules of energy (20×10
12 joules), or as much electricity that 1,500 tonnes of coal could yield.
Commercial nuclear power plants generally use uranium whose 235U isotope has been enriched to around 4-5%. CANDU heavy water reactor, however, have traditionally used natural uranium whose 235U
isotope concentration is 0.71%. Fuelling of heavy water reactors with
uranium that has been slightly enriched to approximately 0.85% is now
underway and significantly reduces fuel costs. Fuel used in nuclear
submarine reactors is typically highly enriched to 90-95%
235U. In a breeder reactor, uranium-238 can also be converted into plutonium through the following reaction: 238U (n, gamma) -> 239U - (beta) -> 239Np - (beta) -> 239Pu.
How do you find uranium deposits?
Today's exploration activities are much more complex than in the past,
for the surficial, easily-discovered deposits have, for the most part,
been located. With the highest-grade deposits buried in deep rock
formations, advanced technologies like satellite imagery, geophysical
surveys, multi-element geochemical analysis and computer processing must
be employed. Once geologists locate a prospective deposit, detailed
geological and economic evaluation of the grade and characteristics of
the ore body must be completed.
Once a deposit with sufficient reserves is discovered 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
and necessary licenses. When permits and licenses are in place, mine
development and construction of surface facilities, including mills to
extract the uranium, access roads, utilities and worker facilities, can
begin. The timeline from discovery of an ore body to electricity
production can span many decades.
How is uranium mined?
Uranium ore is removed from the ground in one of three ways depending on
the characteristics of the deposit and the value of the uranium (as the
price of uranium rises, formerly uneconomic deposits may become
economic). Uranium deposits close to the surface can be recovered using
the open pit mining method, while underground mining methods are used
for deep deposits. Given the right hydrology and geology, the ore may be
mined by in situ recovery (ISR) leaching; a process that dissolves the
uranium by circulating oxygenated solutions through the uranium-bearing
rock formations. In 2006 worldwide production of uranium came from
underground (41%), open pit (24%) and ISR mines (26%). As mentioned
earlier, uranium frequently occurs as a trace element in other mineral
deposits such as copper, gold or phosphates. Approximately 9% of the
2006 worldwide uranium production originated from such by-product
Open pit mining
When uranium ore is present within 100-200m of the surface, it is
typically extracted with open pit mining techniques. Open pit mining
begins by removing overburden (soil) and waste rock that overlies the
ore body to expose the uranium mineralization. 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.
When an ore body is located more than 100 metres below the surface,
underground mining methods are necessary as the costs to remove the
overlying rocks (overburden) would be prohibitive. For example, Cameco's
McArthur River ore body is located more than 500 metres below the
surface and is 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 (or inclined) shafts to the depth of the
ore body. 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 radon 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 a slurry or mud.
The slurry is trucked to the Key Lake site for milling.
In situ Recovery
In certain sandstone deposits geological and hydrological conditions
allow uranium to be dissolved directly by pumping an oxygenated
lixiviant underground where it dissolves the uranium, pumping it back to
the surface, extracting the dissolved uranium in ion exchange columns
and recycling the barren solution back underground to repeat the
process. With this in situ recovery (ISR) process there is limited
surface environmental disturbance. Leaching is another word for
dissolving and 'in situ' means in the original position or place. A
majority of the uranium produced in the USA, Kazakhstan and in Western
Australia is produced by this environmentally benign and comparatively
After being in a nuclear reactor for approximately 18 months, a portion
of the nuclear fuel must be replaced with new fuel. The used (spent)
fuel contains upwards of 95% of the 235U that was in the fresh fuel,
plutonium (created when 238U absorbs a neutron) and actinide wastes from
the fission process. Reprocessing is the chemical separation of spent
fuel into these three components. The 235U can again become reactor
fuel. The plutonium can be blended with natural UO2 to create mixed
oxide fuel (MOX), a fuel used in some reactors in Belgium, Germany,
France and Switzerland. The actinide waste is placed in secure storage
for eventual permanent disposal in an underground repository.
While the costs of reprocessing outweigh its benefits at the present
time, Russia and some European countries reprocess used fuel for
environmental reasons or as a result of political policy. As well,
countries like Japan are turning to reprocessing because they lack
domestic fuel sources and wish to be energy independent.
How is nuclear fuel waste handled?
Radioactive waste is generally divided into three categories depending
on its level of radioactivity: low, intermediate and high-level waste.
Low-level waste includes slightly contaminated clothing and items that
come from nuclear medicine wards in hospitals, research laboratories and
nuclear plants. Low-level waste contains only small amounts of
radioactivity that decays away in hours or days. After the radioactivity
has decayed, low-level waste can be treated like ordinary garbage.
Intermediate-level wastes mostly come from the nuclear industry. They
include used reactor components and contaminated materials from reactor
decommissioning. Typically these wastes are embedded in concrete for
disposal and buried in licensed landfills.
High-level waste primarily generally describes used fuel from nuclear
reactors. Used nuclear fuel assemblies are removed from a reactor and
placed into large water-filled pools for 10-20 years. The water provides
shielding from the radiation and cooling to remove the heat, which
continues to be generated by the radioactive material. When the
radioactivity and its associated heat have diminished, the fuel is
transferred to canisters for above-ground, medium-term, dry storage. The
nuclear industry and government authorities are evaluating long-term
storage of high-level waste. While spent fuel is safely stored at
nuclear plant sites today, the storage facilities were never intended
for permanent storage. Countries operating nuclear power reactors are
conducting extensive studies on how high-level wastes should be
disposed. Research indicates the ideal permanent storage disposal is in
deep underground caverns (or repositories) in stable geological
At present, no country has constructed a repository, although
considerable research is underway on a variety of different geologies.
Belgium, for example is studying permanent disposal in a clay formation.
The US is investigating the suitability of the volcanic tuffs of Yucca
Mountain in Nevada. The site received government approval in 2002 and is
now in the multi-year process of licensing application. Finland is the
closest to implementing disposal of high-level
World Nuclear Association
National Atomic Energy Commission, Argentina
UxC Global Nuclear Fuel Cycle Markets information