Nuclear fuel oxides

Other forms of carbon-carbon composites have been or are being developed for space shutde leading edges, nuclear fuel containers for sateUites, aircraft engine adjustable exhaust nozzles, and the main stmcture for the proposed National Aerospace plane (34). For reusable appHcations, a siHcon carbide [409-21 -2] based coating is added to retard oxidation (35,36), with a boron [7440-42-8] h Lsed sublayer to seal any cracks that may form in the coating. 

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. 

Oxides. Owing to the importance as nuclear fuel material, actinide oxides have been intensively investigated. These are very compHcated compounds because of the formation of non stoichiometric or polymorphic materials. Actinide oxides are very heat-resistant and Th02 is the highest... 

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). 

Uranium and mixed uranium—plutonium nitrides have a potential use as nuclear fuels for lead cooled fast reactors (136—139). Reactors of this type have been proposed for use ia deep-sea research vehicles (136). However, similar to the oxides, ia order for these materials to be useful as fuels, the nitrides must have an appropriate size and shape, ie, spheres. Microspheres of uranium nitrides have been fabricated by internal gelation and carbothermic reduction (140,141). Another use for uranium nitrides is as a catalyst for the cracking of NH at 550°C, which results ia high yields of H2 (142). 

Hafnium-free zirconium is particularly weU-suited for these appHcations because of its ductiHty, excellent oxidation resistance in pure water at 300°C, low thermal neutron absorption, and low susceptibiHty to radiation. Nuclear fuel cladding and reactor core stmctural components are the principal uses for zirconium metal. 

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... 

In addition to these are studies prepared before President Carter stopped the GESMO (Generic Environmental Statement for Mixed Oxide) that addressed the chemical processing of fissionable material for the nuclear fuel cycle. Some references are Cohen (1975), Schneider (1982), Erdmann (1979), Fuliwood (1980), and Fullwood (1983). 

Oxides of the actinides are refractory materials and, in fact, Th02 has the highest mp (3390°C) of any oxide. They have been extensively studied because of their importance as nuclear fuels. However, they are exceedingly complicated because of the prevalence of polymorphism, nonstoichiometry and intermediate phases. The simple stoichiometries quoted in Table 31.5 should therefore be regarded as idealized compositions. 

Uranium is used as the primai-y source of nuclear energy in a nuclear reactor, although one-third to one-half of the power will be produced from plutonium before the power plant is refueled. Plutonium is created during the uranium fission cycle, and after being created will also fission, contributing heat to make steam in the nuclear power plant. These two nuclear fuels are discussed separately in order to explore their similarities and differences. Mixed oxide fuel, a combination of uranium and recovered plutonium, also has limited application in nuclear fuel, and will be briefly discussed. 

Now that much of the world has agreed to nuclear disarmament, scientists and world leaders are searching for uses for the surplus weapons-grade plutonium. Instead of pursuing disposal options, one option is the use of mixed-oxide (MOX) nuclear fuel. 

Reported plant applications of a.c. impedance and electrochemical noise are rare, but include stainless steels in terephthalic acid (TA) plant oxidation liquors , nuclear fuel reprocessing , and fluegas desulphurisation (FGD) scrubber systems . 

Ceric Oxide (Cerium Dioxide, Cerium Oxide, Ceria). CeOj, mw 172.13, white powd, mp ca 2600°, d 7.132g/cc at 23°. Sol in coned sulfuric and nitric acids, insol in dil acids and w. Prepn is by dissolving CeCOj in 16N HNOa contg 3% H202 and then evapg off the nitrate soln followed by thermal decompn. The yield is 97.6% of 99.8% pure Ce02, The oxide is used in optics, electronics, as a diluent in nuclear fuels (as... 

Uranium. tetrathiocyanatotetrakis[tris-(dimethylamino)phosphine oxide]-structure, 1.87 Uranium carbide nuclear fuels dissolution, 6, 928 Uranium complexes, 3,1131-1215 carbamic acid... 

The possible application of aqueous plutonium photochemistry to nuclear fuel reprocessing probably has been the best-received justification for investigating this subject. The necessary controls of and changes in Pu oxidation states could possibly be improved by plutonium photochemical reactions that were comparable to the uranyl photochemistry. 

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