Uranium oxide, formation

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. 

For many years the corrosion of uranium has been of major interest in atomic energy programmes. The environments of importance are mainly those which could come into contact with the metal at high temperatures during the malfunction of reactors, viz. water, carbon dioxide, carbon monoxide, air and steam. In all instances the corrosion is favoured by large free energy and heat terms for the formation of uranium oxides. The major use of the metal in reactors cooled by carbon dioxide has resulted in considerable emphasis on the behaviour in this gas and to a lesser extent in carbon monoxide and air. 

Fluidized bed reactors were first employed on a large scale for the catalytic cracking of petroleum fractions, but in recent years they have been employed for an increasingly large variety of reactions, both catalytic and non-catalytic. The catalytic reactions include the partial oxidation of naphthalene to phthalic anhydride and the formation of acrylonitrile from propylene, ammonia, and air. The noncatalytic applications include the roasting of ores and Tie fluorination of uranium oxide. 

The aim of this work is to further characterize the different generations of uranium oxide from three basement-hosted deposits the Miiiennium, Eagie Point, and P-Patch with muitipie micro-scaie anaiysis techniques. The resuits wiii be compared to those previousiy obtained on uranium oxides from deposits iocated in the vicinity of the unconformity to evaiuate the previousiy proposed ore formation modeis. 

Uranium(VI) dioxydichloride, 5 148 Uranium (VI) hydrogen dioxyortho-phosphate 4-hydrate, 6 150 analysis of, 5 151 Uranium(IV) oxalate, 3 166 Uranium (IV) oxide, formation of, by uranyl chloride, 6 149 Uranium (IV) (VI) oxide, U3Oa, formation of, by uranyl chloride, 5 149... 

The ionic defects characteristic of the fluorite lattice are interstitial anions and anion vacancies, and the actinide dioxides provide examples. Thermodynamic data for the uranium oxides show wide ranges of nonstoichiometry at high temperatures and the formation of ordered compounds at low temperatures. Analogous ordered structures are found in the Pa-O system, but not in the Np-O or Pu-O systems. Nonstoichiometric compounds exist between Pu02 and Pu016 at high temperatures, but no intermediate compounds exist at room temperature. The interaction of defects with each other and with metallic ions in the lattice is discussed. 

Reaction of uranium oxide with nitric acid results in the formation of nitrates U02(N03)2.x H2O (x = 2, 3, 6) the value of x depends upon the acid concentration. All contain [U02(N03)2(H20)2] molecules the nitrate groups are bidentate, so that uranium is 8 coordinate (Figure 11.5). Its most important property lies in its high solubility in a range of organic solvents in addition to water (Table 11.4), which is an important factor in the processing of nuclear waste. 

Among the transition metals from chromium through zinc, iron remains the only element for which no double oxide formation with uranium oxide has been reported. Both the l.T and 1 3 compounds of mainganese, cobalt, and copper have been prepared, while only the 1 1 compound of chromium, and the 1 3 compound of nickel and zinc are known. 

Sealed Tube Method. No evidence for compound formation was observed when mixtures of iron and uranium oxides were heated in air to temperatures as high as 1200°C. Substituting ferric and uranyl nitrates for the oxides as starting materials also proved unsuccessful. Ferric oxide and UO2.64 were the only product phases, thus giving an empirical formula of FeU04.i4 in the 1 1 mixture, and FeU309.42 in the 1 3 mixture. Unlike the situation encountered in the other double oxide systems, the iron uranates do not appear to have sufficient thermodynamic stability to be synthesized at ambient oxygen pressure. 

Madhavaram H, Idriss H (1997) Temperature programmed desorption of ethylene and acetaldehyde on uranium oxides. Evidence of furan formation from ethylene. Stud Surf Sci Catal 110 265... 

Temperature Programmed Desorption of Ethylene and Acetaldehyde on Uranium Oxides. Evidence of Furan Formation from Ethylene. 

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