Uranium nuclear fuels

Uranium-235 is the most important uranium isotope for nuclear fuel. Uranium-238, although not fissionable itself, can be converted into the fissionable plutonium-239 in a breeder reactor by the following nuclear reaction ... 

Similarly, the nuclear fuel uranium-233 can be made when ordinary thorium. (Th-232) captures a neutron to produce thorium-233 the thorium-233 decays to produce uranium-233. 

B. Depleted Uranium (DU). During the enrichment process for nuclear fuel, Uranium-235 is removed from uranium ore. The by-product of this process is DEPLETED URANIUM (DU). The US Army and many other nations use DU in armor and munitions. As used by the US Army, DU is typically about 98.8% Uranium-238, 0.2% Uranium-235, and 0.0006% Uranium-234. The external radiation hazard from DU is roughly 40% less than an equal amount of natural uranium. 

The production of power from controlled nuclear fission of heavy elements is the most important technical application of nuclear reactions at the present time. This is so because the world s reserves of energy in the nuclear fuels uranium and thorium greatly exceed the energy reserves in all the coal, oil, and gas in the world [HI], because the energy of nuclear fuels is in a form far more intense and concentrated than in conventional fuels, and because in many parts of the world power can be produced as economically from nuclear fission as from the combustion of conventional fuels. 

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. 

The metal is a source of nuclear power. There is probably more energy available for use from thorium in the minerals of the earth s crust than from both uranium and fossil fuels. Any sizable demand from thorium as a nuclear fuel is still several years in the future. Work has been done in developing thorium cycle converter-reactor systems. Several prototypes, including the HTGR (high-temperature gas-cooled reactor) and MSRE (molten salt converter reactor experiment), have operated. While the HTGR reactors are efficient, they are not expected to become important commercially for many years because of certain operating difficulties. 

Uranium-235 can be concentrated by gaseous diffusion and other physical processes, if desired, and used directly as a nuclear fuel, instead of natural uranium, or used as an explosive. 

Chlorine ttifluoride is utilized in the processing of nuclear fuels to convert uranium to gaseous uranium hexafluoride. Chlorine ttifluoride has also been used as a low temperature etchant for single-crystalline siHcon (122,123). 

Neutron-rich lanthanide isotopes occur in the fission of uranium or plutonium and ate separated during the reprocessing of nuclear fuel wastes (see Nuclearreactors). Lanthanide isotopes can be produced by neutron bombardment, by radioactive decay of neighboring atoms, and by nuclear reactions in accelerators where the rate earths ate bombarded with charged particles. The rare-earth content of solid samples can be determined by neutron... 

Spent nuclear fuel has fission products, uranium, and transuranic elements. Plans call for permanent disposal in underground repositories. Geological studies are in progress at the Yucca Mountain site in Nevada. Until a repository is completed, spent fuel must be stored in water pools or in dry storage casks at nuclear plant sites. 

Predictions in the 1960s of the growth in nuclear power indicated the need for recycling (qv) of nuclear fuels. RadionucHdes involved are uranium-235, uranium-238 [24678-82-8] and plutonium-239. This last is produced by neutron absorption in the reactions ... 

The raw material for nuclear reactor fuel, uranium, exits the mining—milling sequence as uranium oxide. Because of its color, it is called yellow cake. The yellow cake is converted to uranium hexafluoride and enriched in 235u... 

AGNS Staff, Engineering Evaluations of alternativesfor Processing Uranium-Based Fuels, Studies and Research Concerning the Barnwell Nuclear Fuels Plant (BNFP), AGNS-1040-3.1-32, National Technical Information Service (NTlS), Springfield, Va., 1978. 

Several components are required in the practical appHcation of nuclear reactors (1 5). The first and most vital component of a nuclear reactor is the fuel, which is usually uranium slightly enriched in uranium-235 [15117-96-1] to approximately 3%, in contrast to natural uranium which has 0.72% Less commonly, reactors are fueled with plutonium produced by neutron absorption in uranium-238 [24678-82-8]. Even more rare are reactors fueled with uranium-233 [13968-55-3] produced by neutron absorption in thorium-232 (see Nuclear reactors, nuclear fuel reserves). The chemical form of the reactor fuel typically is uranium dioxide, UO2, but uranium metal and other compounds have been used, including sulfates, siUcides, nitrates, carbides, and molten salts. 

The determination of critical si2e or mass of nuclear fuel is important for safety reasons. In the design of the atom bombs at Los Alamos, it was cmcial to know the critical mass, ie, that amount of highly enriched uranium or plutonium that would permit a chain reaction. A variety of assembhes were constmcted. Eor example, a bare metal sphere was found to have a critical mass of approximately 50 kg, whereas a natural uranium reflected 235u sphere had a critical mass of only 16 kg. 

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. 

The main technological uses for UO2 are found in the nuclear fuel cycle as the principal component for light and heavy water reactor fuels. Uranium dioxide is also a starting material for the synthesis of UF [10049-14-6] 6 (both critical for the production of pure uranium metal and... 

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). 

Nitrides. Uranium nitrides are weU known and are used in the nuclear fuel cycle. There are three nitrides of exact stoichiometry, uranium nitride [2565843-9], UN U2N3 [12033-85-1/ and U4N2 [12266-20-5]. In addition to these, nonstoichiometric complexes, U2N3, where the N/U ratio ranges... 

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