Made available in DSpace on 2014-10-09T12:32:54Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:46Z (GMT). No. of bitstreams: 0 / Três métodos de obtenção de pó de U3O8 de alta densidade foram estudados: trituração de pastilhas sInterizadas de U3O8; sinterização de grânulos de U3O8 calcinado; e sinterização de grânulos de diuranato de amônio (DUA). Testes foram conduzidos variando-se a temperatura e o tempo de calcinação do DUA, bem como o tempo de sinterização, resultando em dez lotes de U3O8. Os processos foram comparados em termos de características dos pós obtidos, rendimento granulométríco e número de etapas. O teor de impurezas, a área de superfície específica, a estequiometria, a morfologia, a densidade, a distribuição de porosidade e a identificação de fases foram considerados como parametros de caracterização dos pós. As principais conclusões mostraram que o segundo método (no qual o DUA foi calcinado a 600°C por 3h) forneceu os melhores resultados. Além disso, o terceiro método também produziu bons resultados, porém com dificuldades de manuseio do DUA. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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O bagaço de cana-de-açúcar é um resíduo proveniente da agroindústria da cana-de-açúcar. Trata-se de um material biodegradável, com baixo custo e apresenta afinidade por compostos orgânicos e metais tóxicos. Neste trabalho preparou-se o bagaço de cana-de-açúcar combinado com nanopartículas de magnetita, o qual foi chamado de biossorvente magnético. A magnetita foi sintetizada por precipitação simultânea adicionando-se uma solução de NaOH à solução aquosa contendo Fe2+ e Fe3+. O material foi caracterizado por microscopia eletrônica de varredura, espectrometria de infravermelho por transformada de Fourier, análise termogravimétrica, difratometria de raios-X e medidas de magnetização. O biossorvente magnético apresentou uma alta magnetização de saturação sem histerese, comportamentos atribuídos aos materiais superparamagnéticos. Estudaram-se as variáveis do processo de adsorção de íons uranilo pelo biossorvente magnético em meio nítrico. O estudo do tempo de equilíbrio indicou um aumento de adsorção em função do tempo. Verificou-se que quanto menor o tamanho do biossorvente, maior a porcentagem de remoção. A máxima remoção ocorreu em pH 5. O aumento da velocidade de agitação do sistema soluto mais biossorvente favoreceu a adsorção, sendo encontrado o equilíbrio a partir de 300 r.p.m. Verificou-se que o aumento da dose de biossorvente magnético aumentou a remoção até tornar-se constante a partir de 10 g.L-1. Estudou-se a isoterma de equilíbrio segundo os modelos de Langmuir e Freundlich. O modelo de isoterma de Langmuir correlacionou-se melhor aos dados experimentais. A capacidade máxima de adsorção encontrada foi de 17 mg de U por g de biossorvente. Os mesmos estudos de adsorção foram realizados com o biossorvente de bagaço a fim de comparar os resultados. / Sugarcane bagasse is a residue from the sugarcane agroindustry. It is a biodegradable material, with low cost and presents affinity for organic compounds and toxic metals. In this work, the sugar cane bagasse combined with nanoparticles of magnetite was prepared and called magnetic biosorbent. The magnetite was synthesized by simultaneous precipitation by addition a solution of NaOH to the aqueous solution containing Fe2+ and Fe3+. The material was characterized by scanning electron microscopy, Fourier Transformer Infrared Spectroscopy, thermogravimetric analysis, X-ray diffractometry and measurements of magnetization. The magnetic biosorbent showed a high magnetization of saturation without hysteresis, behavior attributed to superparamagnetic materials. Variables of adsorption process of uranyl ions by magnetic biosorbent in nitric solutions were investigated. The study of the equilibrium time indicated an increase in the adsorption in function of time. Smaller biosorbent particle sizes resulted in greater removals. The maximum removal occurred at pH 5. The increase of stirring speed of the solute plus biosorbent system favored the adsorption, reaching the equilibrium at 300 r.p.m. The increase of the biosorbent dosage increased the removal, which became constant for doses above of 10 g.L-1. The equilibrium isotherm was verified according to the Langmuir and Freundlich adsorption isotherm models. The results correlated better to the Langmuir isotherm model, being found a value of maximum capacity of adsorption of 17 mg of U per g biosorbent. The same studies of adsorption were performed with the bagasse biosorbent in order to compare the results.

In many countries the current plan for the management of intermediate and high level radioactive wastes is to dispose of the radioactive materials underground in a Geological Disposal Facility (GDF) to prevent release of radioactivity to the environment. In the UK, the repository for intermediate level waste may be backfilled with cementitious material and it is clear that grout and cement will be used during many disposal concepts. Upon saturation, the cement will react creating a region of hyperalkaline geochemical conditions extending away from the GDF, within which, significant changes in radionuclide behaviour are expected. Therefore, this thesis utilises a range of experimental and analytical techniques to try to gain a mechanistic understanding of the behaviour of some key radionuclides (U(VI), Np(V) and Eu(III) as an analogue for Cm(III)/Am(III)) in a range of high pH systems of direct relevance to any cementitious GDF. U(VI) interaction with calcite (calcium carbonate, a common component in high pH cements and the natural environment) surfaces was studied in the 'old' (Ca(OH)2 solution; pH 10.5) and 'young' (Na+, K+, Ca2+; pH 13.3) leachates. In the 'old' leachate, luminescence spectroscopy, batch experiments and kinetic modelling suggested that at low concentrations (smaller or equal to 0.42 µM) a Ca2UO2(CO3)3-like surface complex formed. At higher concentrations, batch experiments, extended X-ray absorption fine structure spectroscopy and luminescence suggested that a surface mediated precipitation mechanism was controlling U(VI) concentrations. Further TEM analysis confirmed that a calcium uranate (CaUO4) solid phase was forming on the calcite surfaces. In the 'young' leachate, batch experiments showed that U(VI) had little affinity for the calcite surface, with no statistically relevant removal from solution observed over a 18 month period. Small angle X-ray diffraction data demonstrated that the U(VI) was probably present in the form of U(VI) intrinsic colloids. Np(V) solubility and sorption to calcite under hyperalkaline conditions were studied using batch, X-ray absorption spectroscopy, and geochemical modelling techniques. It was determined that Np(V) solubility in 'old' cement leachates was consistent with the literature. However, in 'young' cement leachates, an unidentified calcium containing phase was controlling solubility. It was demonstrated that sorption to calcite in 'old' leachates was controlled by the formation of a >CO3NpO2 surface complex, whereas, in the 'young' leachates interaction with the calcite surface was controlled by a precipitation mechanism. Eu(III) sorption to a potential GDF backfill material, Nirex Reference Vault Backfill (NRVB) cement, was studied. The kinetics of removal were rapid with 98.5% Eu(III) removal within 24 hours. Ultrafiltration experiments indicated that all Eu(III) remaining in solution was associated with NRVB derived colloids. Additional experiments using ethylenediaminetetraacetic acid (EDTA) as a competing ligand show that removal from solution was significantly reduced at high concentrations (>0.01 M). These EDTA experiments also indicated some irreversibility in the systems, possibly caused by incorporation into the C-S-H or calcite structures.

Canada accounts for 15% of the world’s uranium production (World Nuclear Association). The Athabasca Basin in northern Saskatchewan Canada contains a number of high grade, uranium ore deposits which occur at, or immediately below, an unconformity between Archean and Paleoproterozoic metasediments and intrusive rocks and overlying Proterozoic sandstones. The uranium ores are largely composed of high concentrations of uraninite and Pitchblende with naturally occurring 238U/235U ratios. U- 236 (half-life of 23.42 Myr) will be produced when 235U absorbs a neutron and the nucleus does not fission. Because it is so long lived, a small amount 236U can be maintained at equilibrium levels in the natural uranium ores. One of the main questions of this research is whether or not these equilibrium levels reflect higher grades or larger amounts of uranium minerals as a result of elevated neutron fluxes from 238U and subsequent neutron absorption on 235U. As well, are there other elements within the system that will absorb these neutrons, thereby reducing that which will impinge on 235U. In this study, we have estimated the amount of 236U that is produced by calculating the neutron flux from uranium and evaluating the effects of spatially related elements such as B, Sm and Gd using their elemental neutron cross- sections and abundances. In this project we have calculated and simulated theoretically the production of 236U and then test the theoretical calculations using measurements of uranium isotopes by accelerator mass spectrometry (AMS). Once we understand the factors controlling the 236U concentration, we hypothesize that the relationship between 236U and 238U can be used as a geochemical vector within uranium exploration, with the equilibrium level possibly distinguishing between primary mineralization and remobilization and reprecipitation of this U within spatially associated secondary U mineralization.

A method has been developed that uses uranium hexafluoride as the internal standard to quantitatively determine trace impurities in the uranium hexafluoride using relative response factors. A computer program was written to control the mass spectrometer and determine the concentrations of target impurities present. Overlapping spectra are deconvoluted using the Gauss-Seidel iterative method. The composition of the sample is determined by comparing the peak height ratios of the target impurities to the internal standard. Measurement parameters are easily modified using the menu driven program. A flexible database allows the list of target impurities to be extended to accommodate any changes in analytical requirements. The method has been adapted for automatic on-line measurements. The technique was evaluated by analysing a number of carefully prepared standards. Nine target impurities were studied which ranged in concentration from parts per million to percentages. An overall precision of fifteen percent was obtained. / Dissertation (MSc)--University of Pretoria, 1993. / gm2013 / Chemistry / unrestricted

Objective The objective of this study is to examine the exposure- response relationship between prolonged exposure to low levels of silica, uranium, radon progeny and criteria pollutants and the respiratory health of uranium workers. Method Initially two pilot studies were done on selected groups of high-risk workers to determine the prevalence of alpha-1-antitrypsin deficiency and the retained burden of uranium in the lungs of exposed workers. The value of sputum cytology was also evaluated. A cross-sectional study was conducted in 1984 to determine the prevalence of spirometric abnormalities among uranium miners. The data from non-smokers without symptoms was used to develop lung function reference values relevant for the present population. Follow up analytical cross-sectional and case control studies were done in 1996 and 1999 to determine the mean independent effect of uranium on the respiratory health of miners and to detect abnormalities in both smokers and non¬smokers. Data was collected on employment history, smoking habits, pulmonary function and chest radiographs. To determine the independent mean effect of uranium mining on the respiratory health of workers, only data of non-smokers in exposed cohorts were compared with unexposed control cohorts. Results The prevalence of alpha-1-antitrypsin appeared to be high in workers with abnormal spirometric indices. The lung burden of retained uranium in workers in the final product recovery area was within normal limits. The sputum cytology was abandoned because it was found worldwide that cytological screening had no impact on population survival rates. Lung function prediction equations derived from multiple linear regressions were calculated for the study population which differed from Schoenberg et al prediction equations. The data from the analytical cross-sectional study in1996 suggests that the level of exposure in this study group (without the confounding effect of cigarette smoking) is not associated with statistically significant impairment of lung function, increased prevalence of silicosis, tuberculosis and respiratory cancer. Only the FEF75 was found to be an indicator of early lung abnormality. Data from the 1999 study supports the hypothesis that there is a small but significant exposure-response relationship between prolonged exposure to low levels of silica dust, and lung function abnormalities (in the absence of radiologically diagnosed silicosis). The prevalence of chronic obstructive pulmonary disease (COPD) and small airways disease (SAD) was small but significantly higher in exposed workers. The risk of developing COPD was 2.7 times higher for exposed workers. The risk for non-smokers was small but significant. The incidence of tuberculosis and lung cancer was not higher than expected (probably because ex-employees were not fully investigated). Conclusion Calculation of location specific prediction equations, for different ethnic groups is advocated to enable the earliest detection of lung function abnormalities. FEF75 could be used as an early indicator of lung function impairment (provided strict quality control is maintained). Exposure to a combination of silica dust, radon progeny and smoking was associated with an increased risk of lung function abnormalities, but not with tuberculosis, silicosis and lung cancer. Conclusive assessment must await sufficient latency, and ex-employees must be investigated to establish the true magnitude and distribution of the effects of siliceous and uranium dust on the health of workers (which may continue after exposure cease). / Thesis (PhD)--University of Pretoria, 2010. / School of Health Systems and Public Health (SHSPH) / Unrestricted