World Mineral Production - NERC Open Research Archive - Natural ...

URANIUM
Characteristics
Uranium is a very dense, metallic element which is naturally
radioactive. It spontaneously decays, through a long series of
alpha or beta particle emissions, ultimately forming the stable
element lead.
It occurs in a variety of different geological environments. The
largest economic deposits are in sedimentary rocks, but
deposits are also found in hydrothermal, metamorphic,
surficial and igneous settings. Under oxidizing conditions it
exists in a highly soluble form and is therefore very mobile.
However, under reducing conditions ,where oxygen is
depleted, it converts to an insoluble form and is precipitated.
This is the process that usually results in concentrations of
uranium that are sufficient for economic extraction. The most
common uranium mineral is uraninite (uranium oxide), known
as pitchblende when in its massive form,. Lesser amounts of
the silicate brannerite and the uranium titanate, coffinite, also
occur in economic deposits, in association with uraninite. The
product shipped from all uranium mines is purified solid U3O 8,
known as ‘yellowcake’. This is produced by leaching either
crushed or in situ ore, followed by solvent extraction,
precipitation, and calcining.
Uranium occurs as several isotopes, of which the most
abundant are uranium-238 (about 99.3 per cent of natural
uranium) and uranium-235 (0.7 per cent of natural uranium).
In most nuclear power plants it is uranium-235 that is required
and hence uranium often undergoes enrichment prior to being
made into fuel.
Uses
Uranium’s main use comes from the energy that is released
when an atom of uranium is split by nuclear fission. This is
caused by the uranium atom being struck by, and absorbing,
an extra neutron. Each time an atom undergoes fission,
additional neutrons are also released and these can cause a
chain reaction to occur if they collide with other uranium
atoms.
Over 95 per cent of uranium is used in the production of
electricity in nuclear power stations. The remainder is used for
the propulsion of ships, research, desalination and military
ordnance.
Most nuclear power stations use the fission of uranium-235 as
a heat source for converting water into steam. The steam is
then used to propel turbines, which generate electricity, in the
same way that fossil fuels are used in conventional power
stations. The main contrast is that one kilogram of uranium-
235 produces approximately three million times more energy
than a similar weight of coal.
The International Energy Agency (IEA) estimates that 18 235
TWh of electricity were produced around the world in 2005.
Of this, 15.2 per cent was produced by nuclear power,
compared to 40.3 per cent produced by coal (IEA, 2007).
However, some countries are far more reliant on nuclear
power to generate their electricity than this overall figure
would suggest. For example, in 2005, France produced 79 per
cent of its electricity requirements from nuclear power,
compared to 20 per cent in the UK. In China, the figure was
only two per cent, but significant growth in nuclear power is
anticipated due to the number of new reactors under
construction or planned.
94
In November 2007, there was a total of 439 nuclear reactors
generating electricity in the world, with another 33 under
construction. This includes seven in Russia, six in India and
five in China. A further 94 reactors were ‘on order or
planned’, including 30 in China, and 222 reactors were
‘proposed’ of which 86 were in China (WNA, 2007).
In addition to nuclear reactors for electricity production, there
are currently around 280 reactors used for research purposes in
56 countries. These are used to create neutron beams suitable
for studying the structure and dynamics of materials at atomic
level. They are also used to produce radioisotopes for medical
applications such as cancer treatment.
Nuclear reactors have also been used to propel ships since the
1950s. They are particularly useful in submarines and ships
operating in arctic conditions where they provide considerably
more power than other fuels, and enable long periods at sea
without the need to refuel. Eleven of the USA’s aircraft
carriers are also propelled in this way.
Desalination is an energy intensive process and in this context
nuclear power is often cost-competitive with other sources of
power. In several countries desalination takes place alongside
electricity generation and there is potential for this combined
method to increase.
Uranium has long been a sensitive political topic because
highly enriched uranium (which contains over 90 per cent of
uranium-235) can be used in weapons. No uranium used in
power stations is capable of use in a weapon because it
contains either natural or low-enriched uranium (generally a
maximum of 5 per cent of uranium-235). However, lowenriched
uranium can be converted into highly enriched
uranium with further enrichment.
To prevent the spread of nuclear weapons, the International
Atomic Energy Authority (IAEA) has operated a series of
safeguards since 1970 under the Nuclear Non-Proliferation
Treaty. A large number of nations have signed the Treaty,
including the five countries who have officially declared that
they have nuclear weapons: USA, Russia, China, UK and
France. Three other countries are known to hold them: India,
Pakistan and Israel, but these countries have not signed the
Treaty. North Korea withdrew from the Treaty in 2003 and
claimed to have tested a nuclear weapon in 2006. Subsequent
negotiations resulted in the closure of their nuclear facilities in
2007. Another country causing concern is Iran. It is a
signatory of the Treaty and insists that the construction of
facilities in the country is for peaceful purposes. The work of
the IAEA in attempting to enforce safeguards under the Treaty
is often difficult and politically sensitive.
World production in 2006
The total mined production of uranium (metal content) fell
slightly in 2006 compared to 2005, reversing an upward trend
of recent years. This was largely as a result of production
difficulties encountered by the two largest-producing
countries, Canada and Australia.
Canada continued to be the largest producer of mined
uranium, with 25 per cent of the world’s total, despite a fall in
production from more than 11 000 tonnes to less than 10 000
tonnes. Australia was again in second place, with 19 per cent
of the world total, despite a fall from over 9 000 tonnes to less
than 8 000 tonnes. Kazakhstan remained in third place, with
14 per cent of the world total, and continued their steady