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The performance of a growing sulphate reducing bacteria consortium for Sr2+, Co2+ and Cs+ removal from solution in a batch sulphidogenic bioreactor was investigated. Metal removal by the growing bacterial consortium, and microbial culture growth and metabolic activities (biological sulphate removal) were continuously monitored in the bioreactors over the duration of the treatment period. On the other hand, diversity changes within the bacterial consortium before and after bioreactor operation (28 days) were performed using the partial 16S rRNA fingerprinting method. In the original bacterial consortium, Enterococcus and Staphylococcus sp. were the dominant bacterial species. However, the presence of Sr2+, Co2+ and Cs+ in the growth media, resulted in the emergence of new bacterial species belonging to the Citrobacter, Paenibacillus, and Enterococcus and Stenotrophomonas genera, respectively. The Citrobacter and Paenibacillus sp. demonstrated high tolerance towards the presence of the divalent cations, Sr2+ and Co2+, respectively, while the Enterococcus and Stenotrophomonas sp., demonstrated Cs+ high tolerance. The bacterial growth and sulphate removal rate were significantly decreased at initial metal ion concentrations ≥100 mg/L. The toxicity and inhibitory effects of the metals on the present SRB consortium was observed in the order Sr>Co>Cs. The metal uptake capacity (qτ) of the bacterial consortium decreased with increasing initial metal concentration, and complete Sr2+, Co2+ and Cs+ removal was observed at initial metal concentrations ≤75 mg/L. Overall, the present SRB consortium demonstrated a superior Sr2+ removal capacity (qmax= 405 mg/g), and the least for Cs2+, where qmax = 192 mg/g. The present SRB culture exhibited a superior Sr+ and Cs+ binding capacity, compared to other studies in literature. Results from Sr2+, Co2+ and Cs+ biosorption kinetics indicate that initial concentration and solution pH played a vital role in determining the rate of metal removal kinetics. The experimental data was successfully analysed by the pseudo-second-order rate model, demonstrating that chemisorption is the main rate limiting step for the removal of Sr2+, Co2+ and Cs+ from solution. In this study, the adsorption behaviour of protons and of Sr2+, Co2+ and Cs+ onto the bacterial consortium cell surfaces was evaluated under anaerobic conditions as a function of pH (4-10), ionic strength (0.01, 0.05, 0.1M) and temperature (25, 50 and 75°C). Acid-base titrations of the bacterial suspension indicated that the titration data could be adequately described by a four site non-electrostatic model, with pKa values of 4.41, 6.69, 8.10 and 10. The Sr2+, Co2+ and Cs+ adsorption data could be fitted with a two site non-electrostatic model, involving the type 1 and 2 sites (carboxylic and phosphoryl sites). Increasing the ionic strength had a negative effect on the adsorption of metal ions from solution. There was no observed temperature dependence on the adsorption of Co2+ and Cs+ from solution. In summary, results obtained in this study have shown that the processes involved in microbial Sr2+, Co2+ and Cs+ removal from contaminated sources is a direct function of the microbial characteristics and efficiency, mass transfer and surface complexation effects under varying environmental conditions. One important goal to be achieved in future studies will be the determination of the intrinsic stability constants and the structure of the formed metal complexes species. These constants can be used directly in risk assessment programs. / Thesis (PhD(Eng))--University of Pretoria, 2011. / Chemical Engineering / unrestricted

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samples were irradiated for approximately 45 minutes to allow for the saturation of fission products. The first method used the beam port shutter and allowed for longer counting and irradiation times, but was unsuitable for examining fission products with half-lives below 10 seconds. The on/off method used a cycle of equal irradiation and counting times of one minute. The second method is able to measure track the production of fission products with half-lives of less than 10 seconds. This method used a borated aluminum wheel beam chopper to stop the irradiation of the sample during counting. The beam chopper was set to cycle for approximately one second of counting following half a second of irradiation. The spectra from both methods were analyzed and the peaks were assigned to the appropriate fission products. The majority of the peaks were composed of gamma-rays from multiple nuclides. The peaks created by gamma-rays from decays of a single nuclide were used to calculate the detection limits of the system. Using the beam chopper system, 21 peaks would be above the detection limits of our system 95% of the time for uranium samples of less than one kilogram. / text

Thesis (Ph. D.)--Leiden Rijksuniversiteit, 1971. / Vita. Summaries in English and Dutch. Includes bibliographical references.

Thesis (Ph. D.)--Leiden Rijksuniversiteit, 1971. / Vita. Summaries in English and Dutch. Includes bibliographical references.

Thesis (M.S. in Physics)--Naval Postgraduate School, May 1966. / Thesis Advisor(s): Riggin, John D. "May 1966." Description based on title screen as viewed on June 2, 2010. DTIC Descriptor(s): Reactor Cores, Gases, Fission Products, Gases, Gamma Ray Spectra, Radioactive Isotopes, Krypton, Xenon. DTIC Identifier(s): AGN-201 Reactors. Author(s) subject terms: Reactor Gas, Xenon Gamma Spectrum, Krypton Gamma Spectrum. Includes bibliographical references (p. 36). Also available in print.

L’étape de dissolution des combustibles nucléaires usés, réalisée en milieu nitrique concentré, est complexe notamment du fait de leur complexité chimique et microstructurale à l’issue de leur passage en réacteur. Ainsi, la présence de produits de fission (PF) localisés au sein des différentes phases cristallines constitutives du combustible usé peut en impacter la vitesse de dissolution. Dans ce cadre, trois systèmes représentatifs du matériau combustible initial UO2, de UO2 contenant des PF dissous au sein de la phase fluorine ou formant de précipités métalliques ont été obtenus par conversion de précurseurs préparés par voie humide (oxalate, hydroxyde). Pour chaque système, des pastilles denses et de microstructures proches de celle retrouvée au sein du combustible usé ont été préparées à l’issue d’une étape de mise en forme suivie d’un traitement thermique à haute température.L’étude multiparamétrique de la dissolution (approche macroscopique) conduite dans plusieurs solutions d’acide nitrique et à diverses températures a souligné l’impact important joué par la composition chimique sur la durabilité chimique des échantillons. Ainsi, l’incorporation d’éléments lanthanide a conduit à une augmentation de la vitesse de dissolution par rapport à l’échantillon UO2 de référence, laquelle est demeurée largement inférieure à celle relevée en présence d’éléments platinoïde. Par ailleurs, les effets de l’acidité et de la température du milieu sur la vitesse de dissolution ont été examinés et des modifications significatives dans le mécanisme de dissolution prépondérant ont été suggérées pour des concentrations d’acide nitrique supérieures à 0,5 mol.L-1.Pour les trois systèmes sélectionnés, l’évolution de l’interface solide/solution a également été suivie en cours de dissolution à travers une étude operando, réalisée par Microscopie Electronique à Balayage en mode Environnemental (approche microscopique). En présence d’éléments lanthanide ou à proximité des éléments platinoïde métalliques, ce suivi a démontré l’existence de zones de dissolution préférentielles dont les joints de grains et les jonctions triples. Le couplage des résultats obtenus à travers ces deux approches a permis de fournir des données complémentaires en vue d’une meilleure compréhension des mécanismes de dissolution mis en jeu en présence des différents PF considérés. / The dissolution of spent nuclear fuels, performed in concentrated nitric acid solution, is a complex process due to some chemical and microstructural heterogeneities. As instance, the presence of Fission Products (FP) in various phases constitutive of spent nuclear fuels can affect the chemical durability of the materials. In this context, three systems of interest representing fresh UO2 used as reference material, and UO2 doped with FP products dissolved in the fluorite structure (lanthanide elements) or incorporated as metallic precipitates (platinoids) were prepared by oxalic or hydroxide precipitation. Dense pellets with microstructure representative for spent nuclear fuel were prepared through sintering step at high temperature.The multiparametric study of the dissolution (macroscopic approach) was developed by varying independently several parameters. While incorporation of lanthanide elements induced a significant increase of the normalized dissolution rates, it remained lower compared to that observed for platinoids. Moreover, increase of nitric acid concentration or temperature led to the decrease of the chemical durability of the prepared materials. Additionally, significant modification of the preponderant mechanism of dissolution occurred for nitric acid concentration higher than 0.5 mol.L-1.For the three selected systems, the monitoring of the evolving solid/solution interface (microscopic approach) was performed operando by Environmental Scanning Electron Microscopy. Compared to pure UO2, the presence of FP (lanthanide elements or metallic platinoids) induced preferential dissolution of grain boundaries and triple junctions. Coupling the results obtained from micro- and macroscopic approaches led to complementary data of strong interest in order to improve the understanding of the role of FP during the dissolution of UO2.

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