Uranium

Uranium is a heavy, naturally radioactive (it doesn't have stable isotopes), metallic element, in the periodic table uranium has the symbol U and atomic number 92. Its melting point is 1132°C

Uranium 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 principally occurring isotopes are ²³⁵U and ²³⁸U. The isotope ²³⁵U is indispensable for both nuclear reactors and nuclear weapons because it is the only isotope existing in nature to any appreciable extent 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 fissionable by thermal neutrons.

Uranium was the first element that was found to be fissionable, 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 neutron are absorbed by other ²³⁵U nuclei, a nuclear chain reaction occurs, and if there isn't anything to absorb some neutrons and slow the reaction, it is explosive. The first atomic bomb worked with 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.

Types of Uranium

Yellowcake (ammonium diuranate) is a natural uranium concentrate that takes its name from its color and texture. Yellowcake typically contains 70 to 90 percent uranium oxide (U₃O₈) by weight. It is used as feedstock for uranium fuel enrichment and fuel pellet fabrication.

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).

Uranium hexafluoride (UF₆) is a white solid obtained by chemical treatment of uranium oxide which forms a vapor at temperatures above 56 degrees Centigrade. UF₆) is the form of uranium required for the enrichment process.

Enriched uranium is uranium in which the ²³⁵U isotope concentration has been increased to greater than the 0.711 percent ²³⁵U (by weight) present in natural uranium.

Historical Background (at least the US version)

Uranium was discovered in 1789 by the German chemist Martin Heinrich Klaproth as part of the mineral called pitchblende. It was named after the planet Uranus, which had been discovered eight years earlier.

In the Manhattan Project the names tuballoy and oralloy were used to refer to natural uranium and enriched uranium respectively. These names are still used occasionally to refer to natural or enriched uranium.

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. Uranium became important for defense purposes during World War II. In 1943, the Union Mines Development Corporation operated mills in Colorado to process uranium ore for the Manhattan Project, which applied atomic power to military use. To ensure adequate supplies of uranium for national defense, Congress passed the U.S. Atomic Energy Act of 1946, creating the Atomic Energy Commission. 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.

Statistics:

Owners and operators of U.S. civilian nuclear power reactors purchased from U.S. and foreign suppliers a total of 51.8 million pounds of uranium oxide (equivalent) of deliveries during 2000. The average price paid was $11.04 per pound of uranium oxide equivalent, a decrease of 14 percent compared with the 1997 price.

In year 2000, the U.S. produced 3,123 thousand pounds of uranium oxide from 10 mining perations all of which are west of the Mississippi River.

Australia has extensive uranium deposits making up approximately 30% of the world's known uranium reserves.

External Links:

Los Alamos National Laboratory's Chemistry Division: Periodic Table - Uranium http://pearl1.lanl.gov/periodic/elements/92.html
The US government provides lots of statistics and information relevant to the energy industry at http://www.eia.doe.gov/fuelnuclear.html
The Uranium Information Centre also has lots of information on uranium - http://www.uic.com.au