Enrichment of uranium

Uranium hexafluoride is used in the gaseous diffusion process for the separation and enrichment of uranium-235, which exists in low concentration in natural uranium. The enriched UF is converted back into an oxide and used as fuel for the nuclear power industry. 

A variety of nuclear reactor designs is possible using different combinations of components and process features for different purposes (see Nuclear REACTORS, reactor types). Two versions of the lightwater reactors were favored the pressurized water reactor (PWR) and the boiling water reactor (BWR). Each requites enrichment of uranium in U. To assure safety, careful control of coolant conditions is requited (see Nuclearreactors, water CHEMISTRY OF LIGHTWATER REACTORS NuCLEAR REACTORS, SAFETY IN NUCLEAR FACILITIES). 

Uranium-235 Enrichment. The enrichment of uranium is expressed as the weight percent of in uranium. For natural uranium the enrichment level is 0.72%. Many appHcations of uranium requite enrichment levels above 0.72%, such as nuclear reactor fuel (56,57). Normally for lightwater nuclear reactors (LWR), the 0.72% natural abundance of is enriched to 2—5% (9,58). There are special cases such as materials-testing reactors, high flux isotope reactors, compact naval reactors, or nuclear weapons where enrichment of 96—97% is used. 

The most important role of UO3 is in the production of UF4 [10049-14-6] and UF [7783-81-5], which are used in the isotopic enrichment of uranium for use in nuclear fuels (119—121). The trioxide also plays a part in the production of UO2 for fuel peUets (122). In addition to these important synthetic appHcations, microspheres of UO3 can themselves be used as nuclear fuel. Fabrication of UO3 microspheres has been accompHshed using sol-gel or internal gelation processes (19,123—125). FinaHy, UO3 is also a support for destmctive oxidation catalysts of organics (126,127). 

The most important industrial appHcation of the diffusion separation methods has been for the enrichment of uranium-235 [5117-96-17,... 

A vortex tube process has been developed in South Africa and is being used there for the enrichment of uranium (37). It appears that cascades of this type are characterized by an extremely high power consumption. 

Fluorine compounds from fluorite (fluorspar, CaF2) are used in water treatment (to suppress dental caries) and to make fluoropolymers (such as Teflon), lubricants, and refrigerants. Molten cryolite (Na3AlF6) is essential as a solvent for Al203 in the electrolytic production of aluminum metal, while the isotopic enrichment of uranium for nuclear power reactors is usually achieved by diffusion or gas centrifugation of volatile UF6. 

Fluorine is used in the nuclear industries of many countries to make uranium hexafluoride for enrichment of uranium in the fissile 235U isotope ... 

Uranium Enrichment. Enrichment of uranium-235, from 0.711 percent as present in natural uranium, is essential to the economical operation of light water reactors where the fuel life is a function of the enrichment. With approximately 4.95 percent U-235 fuel, the pressurized light water reactors... 

UFe and UCle are two remarkable substances, the former on account of its application in isotopic enrichment of uranium (Sections 9.4 and 10.4.5) the latter as the only actinide hexachloride. Colourless UFe can be made by a wide variety of routes, including ... 

Low enrichment of uranium concentration (D 10 see Table 50. An economically viable process for extracting uranium is achievable only with D > 10. ... 

The ore extracted by open cast or underground mines is coarsely ground in crushers and then finely ground, the thereby released radon being sucked off as a radiation prevention measure. The uranium content is extracted with the help of hydrometallurgical processes, in which the enrichment of uranium via ion exchange or extraction processes and a precipitation process follow the leaching step. 

This kind of enrichment of uranium is most pronounced where peat bogs or peaty soils lie in the path of surface water draining rocks from which uranium is being leached. Armands (1967) described a situation where water entering bogs in Northern Sweden averaged 0.1 pg U g . He found that peat in the bogs contained up to 3% uranium on a dry basis. Szalay (1958) has shown that peat, fully saturated with uranyl ion, can contain nearly 10% uranium on a dry basis. 

Szalay, A., 1958. The significance of humus in the geochemical enrichment of uranium. Geneva, Proc. Internat. Conf. Peaceful Uses Atom. Energy, 2nd, 2 182—186. 

The limit on the 1.00 wt % enrichment of uranium is valid only for the slurries in which the ratio of surface-to-volume of the particles is at least 80 cm. ... 

One of the first steps in the enrichment of uranium for use in nuclear power plants involves a displacement reaction between UO2 and aqueous HE ... 

Although other technologies are now coming into use for this purpose, gaseous diffusion has played an important role in the enrichment of uranium for use in nuclear reactors. Natural uranium is mostly 2, which cannot be fissioned to prodnce energy. It contains only about 0.7% of the fissionable nuclide IfU. For uranium to be useful as a nuclear fuel, the relative amount of IfU must be increased to abont 3%. In the gas diffusion enrichment process, the natnral nraninm (containing IfU and a small amount of 9iU) reacts with fluorine to form a mixtnre of and UFg. Because these... 

Chemistry used in the recovery of plutonium from irradiated fuel must provide a separation from all these elements, other fission and activation products, and the actinides (including a large amount of unburned uranium), and still provide a complete recovery of plutonium. The same issues apply to the recovery of uranium from spent thorium fuel. Most of the processes must be performed remotely due to the intense radiation field associated with the spent fuel. As in the enrichment of uranium, the batch size in the later steps of the reprocessing procedure, where the fissile product has become more concentrated, is limited by the constraints of criticality safety. There is a balance between maximizing the yield of the precious fissile product and minimizing the concentrations of contaminant species left in the final product These residual contaminants, which can be detected at very small concentrations using standard radiochemical techniques, provide a fingerprint of the industrial process used to recover the material. 

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