Papers by Keyword: Uranium

Abstract: The influence of uranium simulated waste water on the hydration properties of the cement was studied by modern test methods such as TAM air, XRD, FTIR, and SEM-EDS. The results show that uranium can promote the hydration of mineral C₃S, and inhibit the hydration of mineral C₃A. By comparing scanning of hydration products, it was found that the existence of uranium significantly changed the morphology of clinker hydration products , but uranium had little effect on the type of clinker hydration product.

Abstract: The goal of the present work was to perform bioleaching of uranium from low grade ore from Vostok deposit (Republic of Kazakhstan), which was previously subjected to long-term acid leaching. The ore initially contained from 0.15 to 0.20% of uranium in the form of uraninite, but ore samples used in the study contained about 0.05% of uranium, as it was exhausted during acid leaching, and uranium was partially leached. Representative samples of ore were processed in 1 m columns, leach solutions containing 5, 10, 20 g/L of sulfuric acid and bacterial cells (about 10⁴) were percolated through the ore. Leaching was performed at ambient temperature for 70 days. In one of the percolators, the leaching was performed with leaching solution containing 10 g/L of H₂SO₄, cells of A. ferrooxidans, and 0.5 g/L of formaldehyde. Leaching with the solution containing 5, 10, and 20 g/L of sulfuric acid made it possible to extract 50, 53, and 58% of uranium. Addition of formaldehyde in leach solution led to the decrease in uranium extraction extent down to 37%. Thus, the results of the present work demonstrated that uranium ore exhausted during long-term acid leaching may be successfully subjected to bioleaching, that allows extracting residual quantities of uranium. Leaching rate of uranium from exhausted ore depended on both sulfuric acid concentration and microbial activity of bacteria isolated from acid mine drainage, formed on uranium deposit. In the same time, acid mine drainage may be used as a source of inoculate, to start bioleaching process.

Abstract: The effect of different oxidants on extraction of uranium from low grade ore was studied. Leaching was performed using sulfuric acid solutions at a concentration of 10 to 30%. Ferric sulfate Fe₂(SO₄)₃, ammonium persulphate (NH₄)₂S₂O₈, and potassium permanganate KMnO₄ at different concentrations were used as oxidants in different variants of the experiment. In addition, solutions collected at Vostok deposit containing 6.86 g/L Fe³⁺ and 10⁶ cells/mL of the bacteria Acidithiobacillus ferrooxidans were used for leaching. The rate of uranium extraction with sulfuric acid solutions without oxidants was low and did not exceed 19.4%. Addition of oxidants made it possible to increase rate of uranium extraction. In the presence of ferric sulfate, ammonium persulphate, and potassium permanganate rates of uranium extraction were up to 68, 95.2, and 69.6%, respectively. The rate of uranium leaching in the experiments with the AMD sample was high and reached about 95%. Therefore, it can be concluded that using not only oxidizing agents, but AMD, which are formed during the natural oxidation of sulfide minerals contained in the ore of the deposit, can significantly increase the rate of uranium recovery.

Abstract: Monolithic fuel plates have been developed utilizing low enriched U alloyed with 10 wt.% Mo to replace highly enriched fuels in research and test reactors, in accordance with the goals of the Materials Management and Minimization Reactor Conversion Program. The fuel plates consist of U10Mo fuel, Zr diffusion barrier, and AA6061 cladding. They are fabricated by co-rolling the U10Mo and Zr, which are then encapsulated via hot isostatic pressing of the entire U10Mo/Zr/AA6061 assembly. During fabrication, the metal constituents of the fuel plates undergo phase transformations as well as interdiffusion and reactions at interfaces. The areas of interest are the U10Mo fuel, U10Mo/Zr interface, U10Mo/AA6061 interface, Zr/AA6061 interface, and AA6061-AA6061 bond line. Knowledge of the transformations and growth in the plates is necessary to optimize fabrication parameters and predict behavior as they relate to irradiation performance. Numerous studies have been conducted to analyze these reactions in monolithic fuel plates, and a summary of their observations is provided in this paper.

Abstract: Monolithic fuel system with U – 10 wt.% Mo (U10Mo) fuel alloy has been developed for the Materials Management and Minimization reactor conversion program to replace highly-enriched fuels in research and test reactors with low-enriched fuels. Interdiffusion and phase transformations in the system constituents, i.e., U10Mo fuel, AA6061 cladding, and Zr diffusion barrier, have been investigated using fuel plates fabricated via rolling and hot-isostatic pressing. Diffusion couples, utilizing the constituents of the fuel system were also carried out to help understand the findings from fuel plates based on phase equilibria and diffusion kinetics. Findings from both fuel plates and diffusion couples can provide a comprehensive knowledge to assess, model, and predict the performance of monolithic low-enriched fuel system from fabrication to irradiation. This paper summarizes the experimental results reported from characterization of the fuel plates and diffusion couples with emphasis on interactions at the fuel-cladding, fuel-diffusion barrier, cladding-diffusion barrier, and cladding-cladding interfaces. Constituent phases and relevant diffusion kinetics are compared and contrasted, taking into account differences in thermodynamics and kinetics variables such as pressure, temperature, and cooling rate.

Abstract: Diffusion at infinite dilution of U in metals, with particular emphasis in those used in nuclear facilities, is revisited. Early works present some particularities such as activation enthalpies lower than the vacancy formation enthalpy in the matrix, large differences with self-diffusion in the base material, up to four orders of magnitude differences between measurements performed by different authors in similar temperature ranges, etc. In particular U self-diffusion was qualified as abnormal when compared with other metals. Recent studies by means of α-spectrometry reveal a normal behaviour: activation enthalpies and pre-exponential factors similar to the self-diffusion one and diffusion coefficient values in the same order of magnitude than self-diffusion. The possible influence of short circuits, impurities and/or uncertainties in the techniques used in the early works is discussed in order to explain the differences obtained.

Abstract: A novel ternary compound, namely U₃Pt₁₂Si_4, which is best described by the crystallographic formula U₃Pt_12+x-ySi_4-x-z (x = 0.15, y = 0.23, z = 0.16), has been discovered in the U-Pt-Si phase diagram. It crystallizes in a hexagonal unit cell (P6₃/mmc space group) with a = 8.7267(1) Å and c = 9.3385(2) Å. Its structure is an ordered variant of the EuMg_5.2 type with partial occupancies of the Si 4e and Pt 2b positions and mixed Si/Pt occupancy of the 6g site. Magnetic properties measurements revealed that the compound is a Curie-Weiss paramagnet with an effective magnetic moment μ_eff = 3.18 μ_B. Its low temperature specific heat is moderately enhanced (its Sommerfeld coefficient γ is equal to 79(1) mJ mol_U^-1 K^-2) and the electrical resistivity exhibits some characteristic features of dense Kondo lattices.

Abstract: In some mines where sulfide minerals can occur in form of pyrite acid mine drainage (AMD) may occur, and it constitutes one of the main environmental impact. In order to prevent that AMD compromises aquifers layers and reaches mine surroundings, a treatment that consists in its neutralization with the use of a hydrated lime suspension is usually conducted. Contaminants that are soluble in AMD are precipitated, remaining in the solid phase. The work here presented aims recover uranium and rare earths found in one of these precipitates, which consists of calcium diuranate and metal hydroxides in a calcium sulfate matrix. This material contains approximately 0.25% of triuranium octoxide (U₃O₈) and 2.5% of rare earth oxides (TR₂O₃). The recovery of uranium and rare earths contained in the precipitate was performed through a hydrometallurgical process. The test resulted in a leaching with sulfuric acid presented solubilization of 96% for uranium and 90% for rare earths. A percentage yield of 99.7% and 99.9% was obtained in the steps of uranium extraction and re-extraction from the leachate, respectively.

Abstract: Accurate quantification of uranium and thorium elements was performed in the absence of standards for the XRF analysis. This quantification method uses standard addition method. The standard addition method was first established by performing a micofocus XRF onto a sample. In the calibration graphs of uranium, the R² was 0.9997 white the R² value for thorium was 0.9915. Once the baseline quantity of both uranium and thorium were obtained, they were used to normalize all the quantification of other samples prepared by grab and vibratory methods. It was found out that the vibratory method gives more accurate results.

Abstract: Hybrid materials were synthesized by chemical grafting of different compounds (diethylenetriamine DETA, cysteine, alanine and serine) on chitosan/magnetite nanoparticles. The sorbents were characterized by TEM, XRD and FTIR analysis and vibrating sample magnetometry (VSM) before being tested for uranium sorption. The nanometric size of sorbent particles reduces the impact of diffusion resistance and uptake kinetics are quite fast. Sorption isotherms are modeled by the Langmuir equation. The sorption is spontaneous and exothermic. Uranium is desorbed using acidic thiourea and the sorbent can be recycled for at least 4/5 cycles.