Uranium oxide systems

The neptunium oxide system exhibits complexity similar to that found in the uranium oxide system. Thus, the important oxide is NpCL and there exists a range of compositions, depending upon conditions, up to Np30g. 

Criticality of Moderated and Undermoderated Low-Enriched Uranium Oxide Systems,... 

These critical experiments provide data on moderated and undermoderated low-enriched uranium oxide systems... 

G. TUCK and I. OH, "Benchmark Critical Experiments on Low-Enriched Uranium Oxide Systems with H/U = 0.77, NUREG/CR-0674, U.S. Nuclear Regulatory Commissimi (Aug. 1979). 

The HFBR core uses fully-enriched (93%) uranium oxide-aluminum cermet curved plates dad m aluminum. The core height is 0.58 m and the diameter is 0.48 m or a volume of 103.7 Itr. The U-235 weighs 9.83 kg supported by a grid plate on the vessel bottom. The coolant flow u downward. Iience. How reversal is necessary for natural circulation. It operating temperature and pressure are 60 ( and 195 psi. There are 8 main and 8 auxiliary control rod blades made of europium oxide (Lii A)o and dysprosium oxide (DyjO,), clad in stainless steel that operate in the reflector region. The scram system is the winch-clutch release type to drop the blades into the reflector region. Actuation of scram causes a setback for the auxiliary control rods which are driven upward by drive motors,... 

Fuel. The nuclear fuel cycle starts with mining of the uranium ore, chemical leaching to extract the uranium, and solvent extraction with tributyl phosphate to produce eventually pure uranium oxide. If enriched uranium is required, the uranium is converted to the gaseous uranitim hexafluoride for enrichment by gaseous diffusion or gas centrifuge techniques, after which it is reconverted to uranium oxide. Since the CANDU system uses natural uranium, I will say no more about uranium enrichment although, as I m sure you appreciate, it is a major chemical industry in its own right. 

Strangely enough, a combination similar to the ammonia catalyst, iron oxide plus alumina, yielded particularly good results (32). Together with Ch. Beck, the author found that other combinations such as iron oxide with chromium oxide, zinc oxide with chromium oxide, lead oxide with uranium oxide, copper oxide with zirconium oxide, manganese oxide with chromium oxide, and similar multicomponent systems were quite effective catalysts for the same reaction (33). 

Shortly after the introduction of the bismuth molybdate catalysts, SOHIO developed and commercialized an even more selective catalyst, the uranium antimonate system (4). At about the same time, Distillers Company, Ltd. developed an oxidation catalyst which was a combination of tin and antimony oxides (5). These earlier catalyst systems have essentially been replaced on a commercial scale by multicomponent catalysts which were introduced in 1970 by SOHIO. As their name implies, these catalysts contain a number of elements, the most commonly reported being nickel, cobalt, iron, bismuth, molybdenum, potassium, manganese, and silica (6-8). 

Hoekstra, H. R., ed., Uranium Dioxide, Properties and Nuclear Applications, Phase Relationships in Uranium-Oxygen and Binary Oxide Systems, Chap. 6, p. 251, U. S. Atomic Energy Commission, 1961. 

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. 

The aerosol by-products of exploded DU munitions are primarily the uranium oxides with varying dissolution rates. Uranium trioxide (UO3) is soluble like uranyl salts, and systemic absorption accounts for more than 20% of the exposure burden, with 20% of the excreted uranium being in the urine (Morrow et al, 1964, 1972, 1982). UO3, being soluble, has a fast dissolution rate (Type F), and is rapidly removed from the lung (half-life of 4.7 days). Uranium... 

The uranium-antimony oxide system remains as a basis of interest for catalysts. The preparation of a new uranyl antimonate has been described and it was prepared by hydrothermal synthesis from UO3, SbsOs and KCl [46]. A detailed structural analysis was reported, but more importantly the U0sSb204 was selective for the oxidation of propylene to acrolein. 

The selective oxidation of toluene has been studied over a number of catalysts based on metal oxides, with the U/Mo oxide system being one of the most achve and selective[50, 51]. The main products in the oxidation of toluene, excluding the non-oxidative coupling products, were benzaldehyde, benzoic acid, maleic anhydride, benzene, benzoquinone, CO and CO2. Under the same reachon condihons toluene may also yield coupling products such as phthalic anhydride, methyldi-phenylmethane, benzophenone, diphenylethanone and anthraquinone, as shown by Zhu and coworkers [51]. A range of different uranium-based oxides were tested [51] and the results obtained are shown in Table 13.4. 

Preliminary TGA and differential thermal analysis (DTA) curves were obtained on individual oxides and on the mixed transition metal-uranium oxides to ascertain the reaction characteristics of the individual systems. The TGA data were obtained on an Ainsworth BR balance equipped with an AU recorder. Samples of 1 gram each were heated to 1100°G. at 10°G. per minute. DTA information was obtained on a Tempres Research Model DT-4A instrument. Samples weighing approximately 50 mg. were heated at 5°G. per minute to 1250°G. Differential temperatures were measured with a platinum-platinum 10% rhodium thermocouple at a recorder sensitivity of 20 microvolts per inch. 

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. 

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