Actinide uranium

Carbides of the Actinides, Uranium, and Thorium. The carbides of uranium and thorium are used as nuclear fuels and breeder materials for gas-cooled, graphite-moderated reactors (see Nuclearreactors). The actinide carbides are prepared by the reaction of metal or metal hydride powders with carbon or preferably by the reduction of the oxides uranium dioxide [1344-57-6] UO2 tduranium octaoxide [1344-59-8], U Og, or thorium... 

The remaining exceptions concern the lanthanide series, where samarium at room temperature has a particular hexagonal structure and especially the lower actinides uranium, neptunium, and plutonium. Here the departure from simple symmetry is particularly pronounced. Comparing these three elements with other metals having partly filled inner shells (transition elements and lanthanides), U, Pu, Np have the lowest symmetry at room temperature, normal pressure. This particular crystallographic character is the reason why Pearson did not succeed to fit the alpha forms of U, Pu, and Np, as well as gamma-Pu into his comprehensive classification of metallic structures and treated them as idiosyncratic structures . Recent theoretical considerations reveal that the appearance of low symmetries in the actinide series is intimately linked to the behaviour of the 5f electrons. 

The seventh-period inner transition metals are called the actinides because they fall after actinium, Ac. They, too, all have similar properties and hence are not easily purified. The nuclear power industry faces this obstacle because it requires purified samples of two of the most publicized actinides uranium, U, and plutonium, Pu. Actinides heavier than uranium are not found in nature but are synthesized in the laboratory. 

After bum-up, the fuel elements are stored under water for radiation protection and cooling, for at least several months and generally for about one year. Afterwards, they may be either disposed of or reprocessed in order to separate the fuel into three fractions uranium, plutonium, and fission products including the rest of the actinides. Uranium and plutonium may be re-used as nuclear fuel, thus closing the U/Pu fuel cycle. The fission products and the rest of the actinides are converted into chemical forms that are suitable for long-temi storage. 

The pentavalent oxidation state is accessible for the early actinides uranium, protactinium, neptunium, and plutonium. Pentavalent species with neutral Group 16 bases can include either adducts of AnXg or complexes incorporating oxo-containing cations, AnO " or An02". ... 

It is frequently argued that a specific property of 5f g oup M(VI) nd M(V) is the formation of linear dioxo complexes, M022 and M02. Their most striking property is the coexistence of oxo and aquo ligands, which is exceedingly rare in the rest of the elements. There are characteristic differences found frequently between the oxo ions of the V- and VI-valent actinides, uranium through americium, and those of the d elements in the same valence states. 

Sb, 235.137cs. 205p, gjjj various actinides (uranium, neptunium, americium, and plutonium). They originate not only from the nuclear industry, but also from other industries and from medicine and research (Amiro, 1993 Ouzounian, 1996). 

The RWMC assigned a high priority to the critical review of relevant chemical thermodynamic data of inorganic species and compounds of the actinides uranium, neptunium, plutonium and americium, as well as the fission product technetium. The first four books in this series on the chemical thermodynamics of uranium, americium, neptunium and plutonium, and technetium originated from this initiative. 

The parent oxacalix[3]arenes show little ability to bind alkali metals, however, a range of quaternary ammonium cations are attracted to the symmetric cavity [4]. Deprotonation of the phenol moieties allows them to bind to transition metals (scandium, titanium, vanadium, rhodium, molybdenum, gold etc.) [5-7], lanthanides (lutetium, yttrium and lanthanum) [8,9] and actinides (uranium, as uranyl)... 

Of all the actinides, uranium is probably the most well known. Discovered in 1789, it plays a key part in the manufacture of nuclear weapons and reactors. Its radioactive properties were first identified and understood in the late 1800s. 

Some of the most active catalysts for the hydroamination of alkynes are based on lanthanides and actinides. The turnover frequencies for the additions are higher than those for lanthanide-catalyzed additions to alkenes by one or two orders of magnitude. Thus, intermolecular addition occurs with acceptable rates. Examples of both intermolecular and intramolecular reactions have been reported (Equations 16.87 and 16.88). Tandem processes initiated by hydroamination have also been reported. As shown in Equation 16.89, intramolecular hydroamination of an alk5me, followed by cyclization with the remaining olefin, generates a pyrrolizidine skeleton. Hydroaminations of aminoalkynes have also been conducted with the metallocenes of the actinides uranium and thorium. - These hydroaminations catalyzed by lanthanide and actinide complexes occur by insertion of the alkyne into a metal-amido intermediate. 

The operations and facilities include ore exploration (not included in NFCIS list), mining, ore processing, uranium recovery, chemical conversion to UO2, UO3, UF4, UFg, and uranium metal, isotope enrichment, reconversion of UF to UO2 (after enrichment), and fuel fabrication and assembly that are all part of the front end of the NFC. The central part of the NFC is the production of electric power in the nuclear reactor (fuel irradiation). The back end of the NFC includes facilities to deal with the spent nuclear fuel (SNF) after irradiation in a reactor and the disposal of the spent fuel (SF). The spent fuel first has to be stored for some period to allow decay of the short-lived fission products and activation products and then disposed at waste management facilities without, or after, reprocessing to separate the fission products from the useful actinides (uranium and plutonium). Note the relatively large number of facilities in Table 2.1 dedicated to dealing with the spent fuel. Also listed in Table 2.1 are related industrial activities that do not involve uranium, like heavy water (D2O) production, zirconium alloy manufacturing, and fabrication of fuel assembly components. 

Canberra, (n.d.). Actinide (uranium/plutonium) lung counter model 2270 http //www.canbeira.com/ ptoducts/hp radioprotection/model2270-lung-counter.asp (accessed August 3, 2014). 

Thorium is widely distributed in nature with an abundance in the Earth s crust of 12 mg/kg (i.e., ppm wt.), which is about four times greater than that of uranium and as abundant as lead and molybdenum. Owing to its chemical similarity with elements of group 1VB(4) such as zirconium, hafnium, and the other actinide uranium, thorium is usually associated in... 

The actinides uranium and thorium occur in nature as primordial matter. Actinium and protactinium occur in nature as daughters of thorium and uranium, while small amounts of neptunium and plutonium are present as a result of neutron-capture reactions of uranium. All other members of the series are man-made. Separation chemistry has been central to the isolation and purification of the actinides since their discovery. The formation of the transplutonium actinides was established only as a result of chemical-separation procedures developed specifically for that purpose. The continued application of separation science has resulted in the availability of weighable quantities of the actinides to fermium. Separation procedures are central to one-atom-at-a-time chemistry used to identify synthetic trans-actinide (superheavy) elements to element 107 and above (Report of a Workshop on Transactinium Science 1990). 

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