Uranium oxidation rates

The reaction data indicate that the uranium oxidation rate is one-half order dependent on the UO2 present. The magnesium oxidation rate, in general, is first order with respect to magnesium concentration. Other experiments show that if additional amounts of magnesium are added to the solution after the oxidation, most of the UO2 can be reduced back to uranium. These data are given in Table 20-1. 

Fig. 5.12 Oxidation rates of uranium in distilled water, air, CO2 and CO as a function of...

The Sohio technology is based on a catalyst of bismuth an4 molybdenum oxides. Subsequent catalyst improvements came from the use of bismuth phosphomolybdate on a silica gel, and more recently, antimony-uranium oxides. Each change in catalyst was motivated Jby a higher conversion rate per pass to acrylonitrile. 

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... 

Microbes can control the local geochemical environment of actinides and alfect their solubility and transport. Francis et al. (1991) report that oxidation is the predominant mechanism of dissolution of UO2 from uranium ores. The dominant oxidant is not molecular oxygen but Fe(III) produced by oxidation of Fe(II) in pyrite in the ore by the bacteria Thiobacillus ferroxidans. The Fe(III) oxidizes the UO2 to UOl. The rate of bacterial catalysis is a function of a number of environmental parameters including temperature, pH, TDS, fo2, and other factors important to microbial ecology. The oxidation rate of pyrite may be increased by five to six orders of magnitude due to the catalytic activity of microbes such as Thiobacillus ferroxidans (Abdelouas et al., 1999). 

One of the early studies was the work of Trillat and Hayman who showed that the oxidation rate of freshly polished uranium was reduced by argon implantation. 

The uranium uptake rate of hydrous titanium oxide is demonstrated in Fig. 7. 

The uranium uptake rate increases with decreasing granular size because of the specific surface enlargement. Yet, after ten days both curves show a distinct flattening. After this time, hydrous titanium oxide granules of 0.6 mm diameter attain a uranium loading of 100 ppm. The demonstrated uptake rates seem to be realistic for mechanically rather stable hydrous titanium oxide granules. 

Uranium oxides Interpretation of observations for the dissociations of uranium oxides (and hydroxides) are complicated by the large number of phases and solid solutions mentioned in the literature. Karkahnavala and Phadnis [76] conclude that the thermal stabilities of the following phases increase with symmetry. The same sequence is shown by the enthalpies, rates and values of for these reactions, decomposition temperatures are shown in brackets ... 

Radioactivity is spontaneous. This means that it does not require any help to start or to continue. The rate of disintegration does not depend upon temperature. This is in contrast to chemical reactions, whose rates are often drastically affected by changes in temperature. The radioactive decay of the nucleus of an atom is unaffected by the presence of other atoms and cannot be catalysed. For example, uranium-235 decays at the same speed (and into the same products) whether it is pure uranium, combined as uranium oxide (UO2) or as uranium fluoride (UFg). 

The reactor is a 1000-MWe, sodium-cooled, mixed plutonium-uranium oxide fuel unit with a thermal rating of 2500 MW. Sodium at the reactor outlet temperature of 1100°F is used to produce steam at 3500 psia... 

Critical Experiments and Calculations in Some Very Under mode rated. Slightly Enriched, Uranium-Oxide/Woter Lottices/i4. R. 

Commercial fabrication of uranium oxide fuels for light-water reactors is the fastest maturing segment of the nuclear fuel cycle. Some ten commercial fuel faibii-cators now routinely manufacture uranium fuels bn a more or less mass production basis. With this maturing comes an increased incentive to increase production rates and thereby reduce fuel fabrication costs. One astutely observes that the criticality safety. K, therefore, behooves us to periodically reexamine plant equipment in light of advances in criticality safety technology and to adjust limits wherever possible to enhance the economics of the fuel cycle. 

Agreement is reasonable, with the exception of the U capture rate in the center of the uranium oxide plates. Hie perturbation phase of REAC was used to calculate the reactivity of material worth samples. We represented the experiments in one-dimensional slab geometry. We assumed that the structure of the sample holder is equivalent to 2-mm stainless steel. This has an effect of 10% on the worth of U compared to a homogeneous case. The normalization Integral was taken from a 2-b diffusion calculation. 

Figure 3.16. Xenon concentration as a function of the relative pellet radius in LWR uranium oxides with a 95% theor. pellet density and different linear heat ratings (Kleykamp, 1985 with kind permission of Elsevier Science - NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands)...

According to the thermodynamic calculations performed by Besmann and Lin-demer (1978), the presence of pure H2O vapor in the gap does not effect an oxidation of UO2+X to U4O9 (UO2.25). This oxidation step, which is accompanied by a phase transformation of the uranium oxide, should only be possible in the presence of oxygen in the steam. However, as a consequence of radiolytic reactions the steam in the gap will contain oxygen in any case so that continued oxidation of the UO2-1-X should be possible. Under such conditions, the Csl assumed to be present as the most stable iodine compound in the gap of an intact fuel rod will become thermodynamically unstable in favor of elemental I2 and, in contact with zirconium metal, of Zrh or Zrh, with the rate of oxidation and its extent depending on the concentration of oxygen present in the steam. These oxidized iodine species have a measurable vapor pressure under the prevailing conditions. 

Recent work has concentrated on the adjustment of conditions to give a single product, primarily by using aqueous hydrogen peroxide at low temperatures (5° to 15°c) in the presence of catalytic concentrations of soluble tungsten, molybdenum and uranium oxides . Oxidations with tungsten catalysts have been reviewed In this way, ketoximes can be obtained in high yields fix)m secondary-alkyl primary amines (equation 74) , but the rate is slow with bulky... 

The limitations on possible linear rating and burn-up levels imposed by the characteristics of metallic uranium have led to the development of ceramic forms of fuel such as uranium oxide (UO2) and uranium carbide (UC) pellets. While fuel performance is considerably enhanced by the use of the ceramic form, problems arise due to densification of the fuel and fuelcladding interaction in a radiation environment, leading to the formation of interpellet gaps and clad flattening. 

The rate constants of fluorination of uranium oxide at various temperatures are listed below. 

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