Uranium Trioxide Research Articles

Formation of uranium trioxide hydrates on UO 2 fuel in air-steam mixtures near 200°C

The oxidation of unused CANDU TM UO 2 fuel in air-steam mixtures in a closed system at 200 and 225°C is described. At moisture levels above about 50% of saturation, UO 3 hydrates (mainly dehydrated schoepite, UO 3· xH 2O, x ⋍ 0.8) are formed within 20 days at 200°C, and 5 days at 225°C; U 3O 8 also occurred in some cases. Schoepite, UO 3 · 2H 2O, was detected in a number of experiments, but was probably formed as a product of secondary hydration during cooling or subsequent handling. The large volume change upon conversion of UO 2, to UO 3 hydrates creates potential for damage of used fuel with defected cladding, when stored in moist air. The actual extent of damage requires further investigation. In most experiments, reaction was limited to general surface oxidation. The mechanism of reaction appears to be dissolution and precipitation of uranium(VI) species within a liquid-like film of adsorbed moisture on the UO 2 surface. This is analogous to some atmospheric corrosion processes on metals, such as rusting of iron.

Chemical reactivity of uranium trioxide polymorphs in reduction by hydrogen

The α, β, γ and amorphous polymorphs of uranium trioxide have been prepared and their reactivity towards reduction to UO 2 and further conversion to UF 4 studied. The UO 3 polymorphs are characterized by X-ray, porosity measurements and density determinations. Reduction of UO 3 to UO 2 was carried out by differential thermal analysis and the results of the DTA experiments were analysed in terms of the reactivity of the UO 3 sample. The reactivity of the product UO 2 towards hydrofluorination was measured by its oxygen content upon reoxidation after two weeks of air exposure. The ratio O:U depends upon the UO 3 polymorph concerned and the temperature of reduction to UO 2.

Pulsed NMR study of proton motions in uranium trioxide hydrates

Pure samples of UO 2(OH) 2·H 2O, β-UO 2(OH) 2, and “α-UO 3·0.85H 2O” have been synthesized. Pulsed NMR data from a wide temperature range have been interpreted in terms of structural features and proton motions for all three materials. Two types of water molecule reorientation have been observed in UO 2(OH) 2·H 2O and characterized in terms of activation energies and correlation times for the motions (Motion A: T c = 2.2 ± 0.5 × 10 −15 sec, E A = 29.0 ± 4 kJ mole −1; Motion B: T c = 4 ± 0.5 × 10 −13 sec, E A = 31.2 ± 4 kJ mole −1).

New ionic contributions to the vapor pressure of urania

The gas phase equilibrium reaction between uranium dioxide and uranium trioxide is studied.The implications of the high electron affinity of the uranium trioxide molecule on the total equilibrium vapor pressure and on the congruently vaporizing composition of urania are discussed.(AIP)

Chromatographic isolation of144Ce and144Pr from the wastes of irradiated uranium treatment

A two-step chromatographic technique was elaborated to isolate144Ce,144Pr from a solution of uranium fission products in 6M HNO3. The oxidation to Ce(III) by bromate and selective adsorption of144Ce(IV) on anion exchange column were used to concentrate and purify144Ce. Some impurities of uranium,95Zr,95Nb,106Ru remain in144Ce solution after the first step of its isolation. The final purification is achieved by passing the 6M HNO3 solution of144Ce(IV) through the HDEHP-coated teflon column. The decontamination factors of144Ce from main fission products are given. 7.2 mCi of (144Ce+144Pr) are recovered from each gram of irradiated uranium trioxide with the yield greater than 99%. An improvement of known generator was carried out to elute a purer144Pr from maternal144Ce(IV) adsorbed on the anion exchange column.

Metabolism of an industrial uranium trioxide dust after deposition in the rat lung.

Uranium trioxide, produced industrially, was administered to rats either by inhalation or direct injection of an aqueous suspension into the lungs. show that uranium was cleared rapidly from the lungs, mainly to the blood; show that distribution of uranium among body tissues, and the fraction of the systemic content excreted in urine, was similar to that obtained for other transportable hexavalent uranium compounds; suggest that urine monitoring data would be of more value than lung radioactivity counting measurements for assessing occupational human exposure; indicate that for setting exposure limits by inhalation the uranium trioxide should be considered a highly transportable compound. Thus intakes by workers should be restricted to those recommended for short-term exposures and not those based on an annual limit.

Partial oxidation of isobutene over molybdenum trioxide (MoO3)-uranium trioxide (UO3)-silicon dioxide catalysts. A reaction network

Partial oxidation of isobutene over molybdenum trioxide (MoO3)-uranium trioxide (UO3)-silicon dioxide catalysts. A reaction network

Calculation of oxygen isotope fractionation between uranium dioxide, uranium trioxide and water

Reduced partition function ratios (r.p.f.r) for uranium dioxide and uranium trioxide are calculated using selected crystal field models for optical modes and Debye functions for acoustic modes at temperatures ranging from 0 to 1000°C. The contribution of the acoustic modes is negligibly small in the calculated values of r.p.f.r. in all temperature ranges. The uncertainty of the r.p.f.r. is calculated from the standard deviation of the force constant used for the calculation, which is about ± 5%. at 0°C, ±2%. at 200°C and ±0.2%. at 1000°C for both oxides. The r.p.f.r. for both uranium oxides are lower than that of water, implying that uraninite is depleted in 18O with respect to associated fluids at almost all temperature ranges. The fractionation factors between uranium oxides and water are expressed as: 10 3 ln α = 3.29 10 6 T 2 −13.63 10 3 T + 4.65 , and 10 3 ln α = 3.63 10 6 T 2 −13.29 10 3 T + 4.42 for α-UO 3 and UO 2, respectively. The values of r.p.f.r. for uranium oxides are low compared to those for common rock-forming minerals, however they are similar to the values for other metal oxides, such as magnetite, rutile and probably cassiterite.

Solubility and hemolytic activity of uranium trioxide

UO 3 is often classed as an isoluble material by reason of its low solubility in water, but its solubility is greatly enhanced in solutions of some inorganic salts. Dissolution in NaCl, KCl, or KNO 3 solutions occurs by conversion of UO 3 to uranyl hydroxide hydrate (UHH) followed by cation exchange with structural hydroxyl groups. Acid formed by release of exchanged protons dissolves some solid. This mechanism offers a reasonable explanation for the high solubility of UO 3 in tissue fluid and accounts for some observed effects in vivo. Hemolysis of washed erythrocytes by UO 3 arises from the reaction of dissolved uranium with constituents of the cell membrane. For a given time of incubation the extent of hemolysis is a complex function of dose (pg UO 3/cell) and the nature of dissolved U(VI) species.

On the thermal decomposition mechanism of uranyl and uranium(IV) acetates

Abstract The methods of isothermal kinetics. X-ray spectrography, mass spectrometry and IR spectroscopy were used to study the thermal decomposition of uranyl acetate, UO 2 (CH 3 COO) 2 , and uranium(IV) acetate, U(CH 3 COO) 4 . The data obtained were supported by the results of the chemical analysis of products formed in decomposition processes and in model reactions. The compounds studied are assumed to be decomposed by a single mechanism including the following elementary stages: (1) breaking the carbon—oxygen bond of the carboxyl group, (2) forming a new carbon—oxygen bond with the appearance of an intermediate compound (co-ordinated to uranium atoms) with the structure of acetic anhydride, (3) breaking the uranium—oxygen bond with a subsequent rotation of the acetyl group, (4) transferring a hydrogen atom from a methyl radical of one acetate group to the oxygen of another and evolving a molecule of acetic acid which is the primary product of metal acetate decomposition. Arguments are presented in favour of the suggested mechanism. Despite a great number of papers on the thermal decomposition of metal salts of organic acids, there is no commonly recognized picture of its mechanism even for such relatively simple systems as metal formates and acetates. This is especially true for uranium compounds which are insufficiently studied in general. In the present work, an attempt is made, by using a variety of methods such as elementary chemical and X-ray phase analysis. IR spectroscopy, modelling separate reactions, measurement of the vapour pressure of volatile decomposition products and time-of-flight mass spectrometry, as well as some methods of isothermal and non-isothermal kinetics, to inquire into the process of the thermal decomposition of hexa-and tetravalent uranium salts of acetic acid, viz. UO 2 (CH 3 COO) 2 , UO 2 (CH 3 COO) 2 - CH 3 COOH, UO 2 (CH 3 COO) 2 - 2H 2 O, U(CH 3 COO) 4 . Comparison of regularities in the decomposition of uranium tetraacetate and uranyl acetate is of interest in the sense that in each case the solid products contain one and the same oxide, viz. UO 2 1,2 . It could be expected, therefore, that this comparison would lead to an understanding of the process of formation of decomposition products, to get a more comprehensive idea of the thermal destruction of metal acetates and to draw more convincing conclusions about the separate elementary stages. According to the X-ray spectrographic and IR spectroscopic data obtained by the authors on decomposing the above four compounds, no intermediate stable solid substances are formed 3, 4 . As to the final product, it is found to contain 0.45 g at C/g at. U in the case of uranyl acetate and one order less (≈ 0.04 g at C/g at. U) in the case of uranium tetraacetate. Of the volatile products of decomposition in vacuum, low temperature traps cooled by liquid nitrogen were used to collect and then to separate and identify (by vapour pressure and IR spectra) the following substances: acetic acid, acetic anhydride, ketene, acetone, carbon dioxide, carbon monoxide and water 3, 4 . To the authors' knowledge, there is only one paper available 3 in which ketene is mentioned as a product of metal (potassium) acetate decomposition. The radical mechanism of the thermal decomposition of metal acetates suggested by Bell and Reed 6 cannot explain the formation of acetic acid as the main decomposition product of acetates of metals such as copper, silver and others, including uranium acetate. Poppl's explanation 3 , which attributes the formation of acetic acid to hydrolysis, can hardly be satisfactory. At the same time, the occurrence of acetone among the thermal decomposition products of acetates of uranium (as well as other metals) may be conditioned by both the catalytic transformation of acetic acid and the processes leading to the elimination of acetone as an initial product. These points were to be verified and this was done by means of model reactions 1 , Study was made of the transformation of vapours of acetic acid, acetic anhydride and acetone on uranium dioxide and trioxide at 300°C ± 2°C. The experiments 4 have shown that (1) acetone does not undergo any transformation under these conditions; (2) acetic acid yields acetone, carbon dioxide and water in accordance with the well-known equation of ketonization

Conversion of Uranium Trioxide to Uranium Hexafluoride

Conversion of Uranium Trioxide to Uranium Hexafluoride

ChemInform Abstract: THE ANODIC DISSOLUTION OF URANIUM DIOXIDE. II. IN CARBONATE SOLUTIONS

AbstractStationäre potentiostatische und cyclisch voltammetrische Messungen sprechen für den Auflö‐ sungsmechanismus A, in dem der 2‐Elektronenübertragungsschritt geschwindigkeitsbestimmend ist.

The anodic dissolution of uranium dioxide—II. In carbonate solutions

The anodic dissolution of uranium dioxide in alkaline carbonate solutions has been studied. Steady-state potentiostatic and cyclic voltammetric measurements have been shown to be consistent with a mechanism that involves a rate-determining two-electron transfer reaction. The presence of insulating uranium(VI) films on the surface at high anodic potentials has been confirmed by the use of ring-disc electrode measurements and characterized by X-ray-diffraction analyses. The dissolution behaviour of the films has been characterized and compared with that of samples of synthetic uranium trioxide and uranyl carbonate.

Sodium uranium(V) trioxide, NaUO 3: heat capacity and thermodynamic properties from 5 to 350 K

The heat capacity of a sample of NaUO 3 was determined in the temperature range 5 to 350 K by aneroid adiabatic calorimetry. The heat capacity at constant pressure C p o(298.15 K), the entropy S o(298.15 K), the enthalpy { H o(298.15 K) − H o(0)} and the function −{G o(298.15 K) − H o (0)} 298.15 K were found to be (108.87 ± 0.11) J K −1 mol −1, (132.84 ± 0.13) J K −1 mol −1, (20176 ± 20) J mol −1, and (65.17 ± 0.06) J K −1 mol −1, respectively. A non-isothermal peak in the heat capacity, probably correlated with magnetic ordering, was noted at (31 ± 1) K.

Neutron powder profile studies of the gamma uranium trioxide phases

Neutron powder profile studies show the existence of three phases in gamma uranium trioxide between 373°K and 77°K. The three phases are closely related and the transitions smooth and displacive. At 373°K, γ-UO 3 is tetragonal, with a = 6.9013 (5) and c = 19.9754 (18) Å, and space group I4 1 amd( D 19 4h) . At 323°K, γ-UO 3 becomes orthorhombic, space group F ddd (D 24 2 h ), with the cell dimensions (293°K) a = 9.787 (3), b = 19.932 (4) and c = 9.705 (3) Å. There is a further transition between 293°K and 77°K, and, at 77°K, the orthorhombic dimensions of the pseudocell are a = 9.8225 (7), b = 19.8487 (15), and c = 9.6318 (7) Å. The neutron diffraction studies show that, in all three phases, the coordination polyhedra of the two crystallographically distinct uranium atoms are octahedral and (dodecahedral-2) respectively. At 293°K, the shortest UO distance is 1.796 (6) Å, and thus there are no pure uranyl bonds, in agreement with the infrared spectrum. The UO distances are precise to about ± 0.006 Å, about ten times the precision of an earlier X-ray single-crystal study, in which the conclusions were in conflict with the infrared spectrum. The structure is made up of parallel chains of edge-fused U(2) octahedra, cross-linked by U(1) dodecahedra. The atomic shifts are not great in going from 373°K to 77°K; at 293°K the data will refine in the pseudotetragonal cell as well as the true orthorhombic cell, and the 77°K data will refine in the F ddd cell.

Tamper and Radiation Resistant Instrumentation for Safeguarding Special Nuclear Material

A tamper-resistant liquid level/accountability instrumentation system for safeguards use has been developed and tested. The tests demonstrate the accuracy of liquid level measurement using TDR (Time Domain Reflectometry) techniques and the accuracy of differential pressure and temperature measurements utilizing a custom designed liquid level sensor probe. The calibrated liquid level, differential pressure, and temperature data provide sufficient information to accurately determine volume, density, and specific gravity. Test solutions used include ordinary tap water, diluted nitric acid in varying concentrations, and diluted uranium trioxide also in varying concentrations. System operations and preliminary test results conducted at the General Electric Midwest Fuel Recovery Plant and the National Bureau of Standards, respectively, suggest that the system will provide the safeguards inspector with an additional tool for real-time independent verification of normal operations and special nuclear materials accountancy data for chemical reprocessing plants. This paper discusses the system design concepts, including a brief description of the tamper and radiation resistant features, the preliminary test results, and the significance of the work.

Effect of Thin Electrodeposited Nickel Coatings on the Corrosion Behavior of U-0.75 Ti

Abstract Thin electroplated coatings of nickel, formed from a sulfamate bath, were shown to affect the corrosion of U-0.75 Ti in moist air at 105 C and in a dilute (50 ppm) NaCl solution at 25 C. Weight losses were observed for all samples in the salt solution, and the corrosion process followed the linear rate law. The corrosion rate of a sample with a coating thickness of 0.25 mil was actually greater than that of the bare alloy, but an increase in the coating thickness to 0.5 mil or greater caused a marked decrease in the corrosion rate. A porous, yellow corrosion product (hydrated uranium trioxide) existed on the bare alloy and on the 0.25 mil sample, the product being located at pores in the coating on the latter samples. The increased corrosion rate for the 0.25 mil sample was attributed to the fact that the uranium alloy is anodic to nickel, and the current density of the alloy at the bottom of the pores in the coating was much greater than that of the bare alloy. The markedly reduced corrosion rat...

Intramuscular retention of UO3 and UO2.

Uranium dioxide (UO2) and uranium trioxide(UO3), in biological terms, are prototype U+4 and U+6 compounds, respectively. The intramuscular injection studies performed in rats described in this report were designed to complement previously reported inhalation studies in dogs and certain “in vitro solubility” assessments of these same materials. The intramuscular retention functions of the two U-235 enriched uranium oxides were found to resemble closely those determined for the lungs; specifically, for UO3: R(muscle) = A0e−0.165t + B0e−0.017 versus R(lungs) = A0e−0.0038t + B0e−0.023t; and for UO2: R(muscle) = A0e−0.0044t versus R(lungs) = A0e−0.0038t where A0 and B0 represent fractional retentions whose sum is 1.0 and t is expressed in days. A single rabbit study with intramuscular UO2 gave a confirmatory retention half time of 172 days.

Thermochemistry of uranium compounds IV. Standard enthalpy of formation of sodium uranium(V) trioxide (NaUO 3)

A pure carefully characterized sample of sodium uranium(V) trioxide, NaUO 3, has been reacted in a calorimeter containing an aqueous mixture of HCl and XeO 3. Based on the enthalpy of reaction, the standard enthalpy of formation, ΔH f o(NaUO 3, c, 298.15 K), has been determined to be −(357.5 ± 0.8) kcal th mol −1. Derived thermodynamic data attest to the significant stability of NaUO 3.

Investigation of the structure of the surface of irradiated aluminum oxide containing uranium trioxide

Investigation of the structure of the surface of irradiated aluminum oxide containing uranium trioxide