Uranium conversion into nuclear fuel

Uranium hexafluoride [7783-81-5], UF, is an extremely corrosive, colorless, crystalline soHd, which sublimes with ease at room temperature and atmospheric pressure. The complex can be obtained by multiple routes, ie, fluorination of UF [10049-14-6] with F2, oxidation of UF with O2, or fluorination of UO [1344-58-7] by F2. The hexafluoride is monomeric in nature having an octahedral geometry. UF is soluble in H2O, CCl and other chlorinated hydrocarbons, is insoluble in CS2, and decomposes in alcohols and ethers. The importance of UF in isotopic enrichment and the subsequent apphcations of uranium metal cannot be overstated. The U.S. government has approximately 500,000 t of UF stockpiled for enrichment or quick conversion into nuclear weapons had the need arisen (57). With the change in pohtical tides and the downsizing of the nation s nuclear arsenal, debates over releasing the stockpiles for use in the production of fuel for civiUan nuclear reactors continue. 

In nuclear power stations electrical current is produced from nuclear energy. Efficient operation requires provision of the nuclear power station with fuel elements and the disposal of spent materials. These operations are brought together in the nuclear fuel cycle, which embraces on the provision side the extraction and dressing of uranium ores to uranium concentrates, their conversion to uranium(VI) fluoride, enrichment of the uranium isotope from 0.7% in natural uranium to ca. 3%, the conversion of uranium(VI) fluoride into nuclear fuel and the production of fuel elements. 

Uranium oxide [1344-57-6] from mills is converted into uranium hexafluoride [7783-81-5] FJF, for use in gaseous diffusion isotope separation plants (see Diffusion separation methods). The wastes from these operations are only slightly radioactive. Both uranium-235 and uranium-238 have long half-Hves, 7.08 x 10 and 4.46 x 10 yr, respectively. Uranium enriched to around 3 wt % is shipped to a reactor fuel fabrication plant (see Nuclear REACTORS, NUCLEAR FUEL reserves). There conversion to uranium dioxide is foUowed by peUet formation, sintering, and placement in tubes to form fuel rods. The rods are put in bundles to form fuel assembHes. Despite active recycling (qv), some low activity wastes are produced. 

Development efforts in the nuclear industry are focusing on the fuel cycle (Figure 6.12). The front end of the cycle includes mining, milling, and conversion of ore to uranium hexafluoride enrichment of the uranium-235 isotope conversion of the enriched product to uranium oxides and fabrication into reactor fuel elements. Because there is at present a moratorium on reprocessing spent fuel, the back end of the cycle consists only of management and disposal of spent fuel. 

The major use of C1F3 is in the nuclear industry which converts unclean spent fuel reprocessing, uranium metal into gaseous uranium hexafluoride. Other applications are low temperature etchant for single crystalline silicon [63,64], It is also used as a fluorinating reagent and in the synthesis of GIF and conversion of metals to metal fluorides such as tantalum and niobium metals to tantalum pentafluoride and niobium pentafluoride, respectively. 

The most important fuel for currently operated nuclear power stations (mainly light-water reactors) is - U-enriched uranium(IV) oxide. Also of importance are metallic uranium for the Magnox reactors and a few research reactors and uranium-plutonium mixed oxides for light-water reactors. Fuel production comprises extraction and dressing of uranium ores to uranium concentrates, conversion into UF, the uranium compound used for enrichment of the BSy.jjjotope, enrichment of and production of fuel from enriched UF5 (reconversion). 

Since UO2 is the most common uranium oxide found in nuclear fuels, uranium extraction from UO2 is indispensable in the nuclear fuel reprocessing and uranium waste treatment. From solid UO2, however, uranium extraction is not possible with this method because TTA nor TBP form complexes with UO2 directly. If we introduce acid homogeneously in SF-CO2, we can expect UO2 dissolution and conversion into U02, which can be complexed with TBP by the charge neutralization as TBP2U02(N03)2. For example, concentrated nitric acid is widely used to dissolve UO2 in aqueous solution forming U02(N03)2. 

In Chapter 2, we take a more detailed look at the analytical chemistry pertaining to key commercial activities, that is, uranium mining and its utilization in the nuclear fuel cycle (NFC) first, in the milling process, uranium-containing deposits are processed to form uranium ore concentrates (UOC) that are then shipped to uranium conversion facilities (UCF), where the uranium is transformed into high-purity nuclear grade compounds. These can serve as fuel for nuclear power plants or as feed material for isotope enrichment. Then we discuss the analytical aspects of compliance with the strict specifications of the materials used in enrichment plants and in fuel fabrication facilities. Finally, we deal with the analytical procedures to characterize irradiated fuel and waste disposal of spent fuel. 

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