It is this process, in effect 'burning' uranium, which occurs in a nuclear reactor. When this happens over and over again, many millions of times, a very large amount of heat is produced from a relatively small amount of uranium. If enough of these expelled neutrons split the nuclei of other U-235 atoms, releasing further neutrons, a chain reaction can be achieved.
When the nucleus of a U-235 atom is split in two by a neutron c, some energy is released in the form of heat, and two or three additional neutrons are thrown off. The nucleus of the U-235 isotope comprises 92 protons and 143 neutrons (92 + 143 = 235). b In decay it generates 0.1 watts/tonne and this is enough to warm the Earth's mantle. Uranium-238 has a specific radioactivity of 12.4 kBq/g, and U-235 80 kBq/g, but the smaller amount of U-234 is very active (231 MBq/g) so the specific radioactivity of natural uranium (25 kBq/g) is about double that of U-238 despite it consisting of over 99% U-238. This means that it is barely radioactive, less so than many other radioisotopes in rocks and sand. U-238 decays very slowly, its half-life a being about the same as the age of the Earth. Meanwhile, like all radioactive isotopes, it decays. The isotope U-235 is important because under certain conditions it can readily be split, yielding a lot of energy. Natural uranium (Unat) as found in the Earth's crust is a mixture of three isotopes: uranium-238 (U-238), accounting for 99.275% U-235 – 0.720% and traces of U-234 – 0.005%. These isotopes differ from each other in the number of neutron particles in the nucleus. Like other elements, uranium occurs in slightly differing forms known as isotopes. Uranium is one of the heaviest of all the naturally-occurring elements and has a specific gravity of 18.7. And small nuclear reactors are important for making radioisotopes. It is also used for marine propulsion (mostly naval). While nuclear power is the predominant use of uranium, heat from nuclear fission can be used for industrial processes. Uranium-235 is the only naturally-occurring material which can sustain a fission chain reaction, releasing large amounts of energy. Today the only substantial use for uranium is as fuel in nuclear reactors, mostly for electricity generation. This element was used in luminous paint, particularly on the dials of watches and aircraft instruments up to the 1950s, and in medicine for the treatment of disease.įor many years from the 1940s, virtually all of the uranium that was mined was used in the production of nuclear weapons, but this ceased to be the case in the 1970s. In the past, uranium was also used to colour glass (from as early as 79 AD) and deposits were once mined in order to obtain its decay product, radium. Natural uranium is a mixture of isotopes, including a small proportion of one that is fissile – readily able to fission (split) to yield vastly more energy than any combustion process.
When mined, it yields a mixed uranium oxide product, U 3O 8. Uraninite, or pitchblende, is the most common uranium mineral. There are a number of locations in different parts of the world where it occurs in economically-recoverable concentrations. Being relatively soluble (in contrast to thorium), it is also found in the oceans, at an average concentration of 3 parts per billion. It occurs in most rocks in concentrations of 2 to 4 parts per million and is as common in the Earth's crust as tin, tungsten and molybdenum and about 40 times as common as silver. Uranium was discovered by Martin Klaproth, a German chemist, in 1789 in the mineral pitchblende, and was named after the planet Uranus.
As decay proceeds, the final product, lead, increases in relative abundance. Its radioactive decay provides the main source of heat inside the Earth, causing convection and continental drift. The Earth's uranium (chemical symbol U) was apparently formed in supernovae up to about 6.6 billion years ago (see information page on The Cosmic Origins of Uranium). The health hazards associated with uranium are much the same as those for lead.Most of the uranium used in nuclear reactors can be recycled.Depleted uranium is a by-product from enriching natural uranium to use in nuclear power reactors.Uranium occurs naturally in the Earth's crust and is mildly radioactive. It is the only element with a naturally-occurring fissile isotope.The basic fuel for a nuclear power reactor is uranium – a heavy metal able to release abundant concentrated energy.