1 Notable characteristics

When refined, uranium is a silvery white, weakly radioactive metal, which is slightly softer than steel. It is malleable, ductile, and slightly paramagnetic. Uranium metal has very high density, 65% more dense than lead. When finely divided, it can react with cold water; in air, uranium metal becomes coated with uranium oxide. Uranium in ores can be extracted and chemically converted into uranium dioxide or other chemical forms usable in industry.

Uranium metal has three allotropic forms:

• alpha (orthorhombic) stable up to 667.7°C
• beta (tetragonal) stable from 667.7 C to 774.8°C
• gamma (body-centered cubic) from 774.8°C to melting point - this is the most malleable and ductile state.

Its two principal isotopes are ²³⁵U and ²³⁸U. Naturally-occurring uranium also contains a small amount of the ²³⁴U isotope, which is a decay product of ²³⁸U. The isotope ²³⁵U is important for both nuclear reactors and nuclear weapons because it is the only isotope existing in nature to any appreciable extent that is fissile, that is, fissionable by thermal neutrons. The isotope ²³⁸U is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope ²³⁹Pu ( plutonium), which also is fissile.

The artificial ²³³U isotope is also fissile and is made from ²³² thorium by neutron bombardment.

Uranium was the first element that was found to be fissile, i.e. upon bombardment with slow neutrons, its ²³⁵U isotope becomes the very short lived ²³⁶U, that immediately divides into two smaller nuclei, liberating energy and more neutrons. If these neutrons are absorbed by other ²³⁵U nuclei, a nuclear chain reaction occurs, and if there is nothing to absorb some neutrons and slow the reaction, it is explosive. The first atomic bomb worked by this principle ( nuclear fission). A more accurate name for both this and the hydrogen bomb ( nuclear fusion) would be "nuclear weapon", because only the nuclei participate.

2 Applications

Uranium metal is very dense and heavy. Depleted uranium (almost pure U-238 with less than 0.2% U-235) is used by some militaries as shielding to protect tanks, and also in parts of bullets and missiles, as it is extremely dense. The military also uses enriched uranium (more than natural levels of U-235) to power nuclear propelled navy ships and submarines, and in nuclear weapons. Fuel used for United States Navy reactors is typically highly enriched in U-235 (the exact values are classified information). In nuclear weapons uranium is also highly enriched, usually over 90% (again, the exact values are classified information).

The main use of uranium in the civilian sector is to fuel commercial nuclear power plants, where fuel is typically enriched in U-235 to 2-3%. However, the Canadian Candu reactors use natural unenriched uranium as fuel. Depleted uranium is used in helicopters and airplanes as counterweights on certain wing parts. Other uses include;

• Ceramic glazes where small amounts of natural uranium (that is, not having gone through the enrichment process) may be added for color.
• Addition of uranium makes fluorescent yellow or green colored glass.
• The long half-life of the isotope uranium-238 (4.51 × 10⁹) make it well-suited for use in estimating the age of the earliest igneous rocks.
• U-238 is converted into plutonium in breeder reactors. Plutonium can be used in reactors, or in nuclear weapons.
• Uranyl acetate , UO₂(CH₃COO)₂ is used in analytical chemistry. It forms an insoluble salt with sodium.
• Some lighting fixture s utilize uranium, as do some photographic chemicals (esp. uranium nitrate ).
• Phosphate fertilizers often contain high amounts of natural uranium, because the mineral material from which they are made is typically high in uranium.
• Uranium metal is used for X-ray targets in making of high-energy X-rays.
• The element has found use in inertial guidance devices and in gyroscopic compasses.

3 History

The use of uranium, in its natural oxide form, dates back to at least 79 AD, when it was used to add a yellow color to ceramic glazes (yellow glass with 1% uranium oxide was found near Naples, Italy).

The discovery of the element is credited to the German chemist Martin Heinrich Klaproth who in 1789 found uranium as part of the mineral called pitchblende. It was named after the planet Uranus, which had been discovered eight years earlier. It was first isolated as a metal in 1841 by Eugene-Melchior Peligot . Uranium was found to be radioactive by French physicist Henri Becquerel in 1896, who first discovered the process of radioactivity with uranium minerals.

During the Manhattan Project, the wartime Allied program to develop the first atomic bombs during World War II, uranium gained new importance on the world political scene. Before the discovery of plutonium, only uranium was considered for the development of an atomic bomb, though the process of enriching it to applicable levels required gargantuan facilities (see Oak Ridge National Laboratory). Eventually enough uranium was enriched for one atomic bomb, which was dropped on Hiroshima, Japan in 1945. The other nuclear weapons developed during the war used plutonium as their fissionable material, which itself requires uranium to produce. Initially it was believed that uranium was relatively rare, though within a decade large deposits of it were discovered in many places around the world.

The exploration and mining of radioactive ores in the United States began around the turn of the 20th century. Sources for radium (contained in uranium ore) were sought for use as luminous paint for watch dials and other instruments, as well as for health-related applications (some of which in retrospect were incredibly unhealthy). Because of the need for the element during World War II, the Manhattan Project contracted with numerous vanadium mining companies in the American Southwest, and also purchased uranium ore from the Belgian Congo. American uranium ores mined in Colorado were primarily mixes of vanadium and uranium, but because of wartime secrecy the Manhattan Project would only publicly admit to purchasing the vanadium, and did not pay the uranium miners for the uranium ore (in a much later lawsuit, many miners were able to reclaim lost profits from the U.S. government). American uranium ores did not have nearly as high uranium concentrations as the ore from the Belgian Congo, but they were pursued vigorously to ensure nuclear self-sufficiency. Similar efforts were undertaken in the Soviet Union, which did not have native stocks of uranium when it started developing its own weapons program.

In the beginning of the Cold War, to ensure adequate supplies of uranium for national defense, Congress passed the U.S. Atomic Energy Act of 1946 , creating the Atomic Energy Commission (AEC) which had the power to withdraw prospective uranium mining land from public purchase, and also to manipulate the price of uranium to meet national needs. By setting a high price for uranium ore, the AEC created a uranium "boom" in the early 1950s, which attracted many prospectors to the four corners region of the country. Moab, Utah became the Uranium-capital of the world, when geologist Charles Steen discovered such an ore in 1952. Military requirements declined in the 1960s, and the government completed its uranium procurement program by the end of 1970. Simultaneously, a new market emerged - commercial nuclear power plants.

Because uranium ores emit radon gas, and their harmful and highly radioactive daughter products, uranium mining is significantly more dangerous than other (already dangerous) hard rock mining, requiring adequate ventilation systems if the mines are not open pit. During the 1950s, a significant amount of American uranium miners were Navajo Indians, as many uranium deposits were discovered on Navajo reservations. An unusually high number of these miners later developed lung cancer. Some survivors and their descendants received compensation under the Radiation Exposure Compensation Act in 1990.

During the Manhattan Project, the names tuballoy and oralloy were used to refer to natural uranium and enriched uranium respectively, originally for purposes of secrecy. These names are still used occasionally to refer to natural or enriched uranium.

4 Compounds

Uranium tetrafluoride (UF₄) is known as "green salt" and is an intermediate product in the production of uranium hexafluoride.

Uranium hexafluoride (UF₆) is a white solid which forms a vapor at temperatures above 56 degrees Celsius. UF₆ is the compound of uranium used for the two most common enrichment processes, gaseous diffusion enrichment and gas centrifuge enrichment. It is simply called "hex" in the industry. Yellowcake is uranium concentrate. It takes its name from the color and texture of the concentrates produced by early mining operations, despite the fact that modern mills using higher calcining temperatures produce "yellowcake" that is dull green to almost black. Yellowcake typically contains 70 to 90 percent uranium oxide (U₃O₈) by weight.

Ammonium diuranate is an intermediate product in the production of yellowcake, and is bright yellow in colour. It is sometimes confusingly called "yellowcake" as well, but this is not a standard name.

5 Occurrence

Uranium is a naturally-occurring element found at low levels in virtually all rock, soil, and water. It is considered to be more plentiful than antimony, beryllium, cadmium, gold, mercury, silver, or tungsten and is about as abundant as arsenic or molybdenum. It is found in many minerals including pitchblende, uraninite (most common uranium ore), autunite, uranophane, torbernite, and coffinite. Significant concentrations of uranium occur in some substances such as phosphate rock deposits, and minerals such as lignite, and monazite sands in uranium-rich ores (it is recovered commercially from these sources). Because uranium has such a long radioactive half-life (4.47x10⁹ years for U-238), the total amount of it on Earth stays almost the same.

The decay of uranium and its nuclear reactions with thorium in the Earth's core is thought to be the source for much of the heat that keeps the outer core liquid, which in turn drives plate tectonics.

Uranium ore is rock containing uranium mineralization in concentrations that can be mined economically, typically 1 to 4 pounds of uranium oxide per ton or 0.05 to 0.20 percent uranium oxide.

6 Production and distribution

Commercial-grade uranium can be produced through the reduction of uranium halides with alkali or alkaline earth metals. Uranium metal can also be made through electrolysis of KU F₅ or UF₄, dissolved in a molten Ca Cl₂ and NaCl. Very pure uranium can be produced through the thermal decomposition of uranium halides on a hot filament.

Owners and operators of U.S. civilian nuclear power reactors purchased from U.S. and foreign suppliers a total of 21,300 tons of uranium deliveries during 2001. The average price paid was $26.39 per kilogram of uranium, a decrease of 16 percent compared with the 1998 price. In year 2001, the U.S. produced 1,018 tons of uranium from 7 mining operations, all of which are west of the Mississippi River.

Uranium is distributed worldwide, especially by the French. Generally, large countries produce more uranium than smaller ones because the worldwide distribution of uranium is very roughly uniform. Canada is the world's largest producer of uranium, with the world's richest deposits in Saskatchewan. Saskatchewan through three large mines produces over a quarter of the world's uranium. Because of this production, extra capacity, and the close government control of the industry the provincial government plays a central role in setting international uranium prices. Australia also has extensive uranium deposits making up approximately 30% of the world's known uranium reserves. The world's largest single uranium deposit is located at the Olympic Dam mine in South Australia. [1] [2]

7 Isotopes

Naturally occurring uranium is composed of 3 major isotopes, U-238, U-235, and U-234, with U-238 being the most abundant (99.3% natural abundance). These 3 isotopes are radioactive, creating radioisotopes, with the most abundant and stable being U-238 with a half-life of 4.5 × 10⁹ years, U-235 with a half-life of 7 × 10⁸ years, and U-234 with a half-life of 2.5 × 10⁵ years.

Uranium isotopes can be separated to increase the concentration of one isotope relative to another. This process is called "enrichment" (see enriched uranium). To be considered to be 'enriched' the U-235 fraction has to be increased to significantly greater than the 0.711% (by weight) (eg typically to levels from 3% to 7%). Uranium-235 is typically the main fissile material for nuclear power reactors. Either U235 or Pu239 are used for making nuclear weapons. The process produces huge quantities of uranium that is depleted of U-235 and with a correspondingly increased fraction of U-238, called depleted uranium or "DU". To be considered to be 'depleted', the U-235 isotope concentration has to have been decreased to significantly less than 0.711% (by weight). Typically the amount of U235 left in depleted uranium is 0.2% to 0.3%. This represents anywhere from 28% to 42% of the original fraction of U235.

Given that the half life of U235 is considerably shorter than U238, the "depleted" uranium is still significantly radioactive as is the natural uranium after refining.

Another way to look at this is as follows: Candu style reactors burn natural uranium (0.71% fissile material). From a PWR reactors of typical design (most USA reactors are PWR) we note the fuel goes in with about 4% U235 and 96% U238 and comes out with about 1% U235, 1% PU239 and 95%U238. If the PU239 were removed (fuel reprocessing is not allowed in the USA) and this were added to the "depleted uranium" then we would have 1.2% fissile material in the reprocessed "depleted uranium" and at the same time have 1% fissile material in the left over "spent" fuel. Both of these would be considered "enriched" fuels for a CANDU style reactor.

8 Precautions

All isotopes and compounds of uranium are toxic and radioactive. Toxicity can be lethal. In less than lethal doses toxicity is limited primarily to recoverable kidney damage. Radiological effects are systemic. Uranium compounds in general are poorly absorbed by the lining in the lungs and may remain a radiological hazard indefinitely. Finely-divided uranium metal presents a fire hazard.

A person can be exposed to uranium by inhaling dust in air, or ingesting water and food. The general population is exposed to uranium primarily through food and water. The average daily intake of uranium from food ranges from 0.07 to 1.1 micrograms per day. The amount of uranium in air is usually very small. People who live near government facilities that made or tested nuclear weapons, or facilities that mine or process uranium ore or enrich uranium for reactor fuel, may have increased exposure to uranium.

Uranium can enter the body when it is inhaled or swallowed, or under rare circumstances it may enter through cuts in the skin. Uranium does not absorb through the skin, and alpha particles released by uranium cannot penetrate the skin, so uranium that is outside the body is much less harmful than it would be if it were inhaled or swallowed. When uranium enters the body it can lead to cancer or kidney damage.

Uranium mining carries the danger of airborne radioactive dust and the release of radioactive Radon gas and its daughter products (an added danger to the already dangerous activity of all hard rock mining). As a result, without proper ventilation, uranium miners have a dramatically increased risk of later development of lung cancer and other pulmonary diseases. There is also the possible danger of groundwater contamination with the toxic chemicals used in the separation of the uranium ore.

9 See also

• nuclear physics
• nuclear weapon
• nuclear reactor
• nuclear engineering
• Depleted uranium

10 References

• Los Alamos National Laboratory's Chemistry Division: Periodic Table - Uranium
• U.S. EPA: Radiation Information for Uranium (some adapted public domain text)

11 External links

• WebElements.com - Uranium (also used as a reference)
• EnvironmentalChemistry.com - Uranium (also used as a reference)
• It's Elemental - Uranium
• The US government provides lots of statistics and information relevant to the energy industry at
• The Uranium Information Centre also has lots of information on uranium

Actinides Chemical elements Fuels

<Hide>