Uranium hexafluoride isotope separation using

One of the most important examples of the fluorination of oxides is the fluorination of uranium dioxide. Uranium tetrafluoride (UF4) is the intermediate compound which is reduced to uranium metal. The gaseous higher fluoride, uranium hexafluoride (UF6) is used for the separation of uranium isotopes to obtain enriched uranium (i.e., uranium containing a higher proportion of the isotope, U235, than natural uranium). 

Uranium hexafluoride, UFg, is used in the gaseous diffusion process for separating uranium isotopes since not all uranium isotopes can be undergo chain reaction, a requirement for use in reactors and nuclear weapons. How many kilograms of elementary uranium can be converted to UFg per kilogram of combined fluorine ... 

Uranium hexafluoride (the gas used in the gaseous diffusion separation of uranium isotopes) has a molecular weight of 352. Assuming that for it k — 1.2, calculate its speed of sound at 200°F. 

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. 

Our discussion concentrates on the uranium-235 isotope. It makes up only about 0.7% of naturally occurring uranium. The more abundant isotope, uranium-238, does not undergo fission. The first process used to separate these isotopes, and until recently the only one available, was that of gaseous effusion (Chapter 5). The volatile compound uranium hexafluoride, UF6, which sublimes at 56°C, is used for this purpose. 

The enrichment procedure uses the small mass difference between the hexafluorides of uranium-235 and uranium-238 to separate them. The first procedure to be developed converts the uranium into uranium hexafluoride, UFfl, which can be vaporized readily. The different effusion rates of the two isotopic fluorides are then used to separate them. From Graham s law of effusion (rare of effusion l/(molar mass)1/2 Section 4.9), the rates of effusion of 235UFfe (molar mass, 349.0 g-mol ) and 238UF6 (molar mass, 352.1 g-mol ) should be in the ratio... 

Uranium hexafluoride, UF6, shown here, is a relatively volatile molecular compound that is used in the separation of the naturally occurring isotopes uranium-235 and uranium-236. There is only one naturally occurring isotope of fluorine, so any difference in the molar mass of the molecule is due to the uranium. 

Assume that you have a sample of uranium hexafluoride with the natural abundance (0.7%) of 235U, and that you want to use gaseous effusion to separate the isotopes. 

Uranium hexafluoride is the most important fluoride and is made on a large scale, since it is the compound used in gas diffusion plants for the separation of uranium isotopes. It is made by the reactions... 

Fluorine is combined either directly or indirectly with other elements to form compounds such as hydrofluoric acid, fluoropolymers and is used in the synthesis of organic fluorine compounds such as fluorides as in the manufacture of Freon (i.e., dichlo-rodifluoromethane, CCI2F2), which is used as a refrigerant. Fluorine is used in the manufacture of uranium hexafluoride that is necessary for the separation of the isotopes of uranium in centrifuges in the production of nuclear weapons. Fluorine and its compounds are used in producing more than 100... 

Uranium hexafluoride has a molecular formula of UF. It is a colorless, volatile crystal that sublimes and reacts vigorously with water. It is highly corrosive and is a radiation risk. The four-digit UN identification number for fissile material containing more than 1% of uranium 235 is 2977 for lower specific activity, the number is 2978. Uranium hexafluoride is used in a gaseous diffusion process for separating isotopes of uranium. 

One of the most important inorganic fluorides is uranium hexafluoride, UFg, which is essential to the gaseous diffusion process for separating isotopes of uranium (U-235 and U-238). Industrially, fluorine is used to produce polytetrafluoroethylene, a polymer better known as Teflon ... 

In natural uranium ores, the fraction of the atoms of the fissile isotope is about 0.72%. For many commercial applications, like production of fuel for light water reactors or several types of research reactors and other nuclear functions, its fraction must be increased, that is, isotope enrichment is carried ont. The main isotope separation methods, or isotope enrichment processes, ntilize the small differences in between the mass of U-235 and U-238. The two major commercial methods that have supplied most of the enriched uranium to date, gaseous diffusion and gas centrifuges, use the only gaseous compound of nraninm, nranium hexafluoride (UFg), as the feed material. Both methods utilize the difference between the mass of UFg (349 Da) and UFg (352 Da) where the mass ratio difference that is 0.86%. The product and tails of the enrichment process are also with the same chemical form, but the isotope composition of the material is altered in the enrichment process. Schematic diagrams of the principle of operation of these methods can be found on the web and in many textbooks, so will not be shown here. 

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