The phenomenon of selective retention of cations from aqueous solutions by microbial biomass has been termed biosorption. Samples of waste microbial biomass, originating from industrial fermentations and biological waste water treatment plants, have been tested for their uranium and thorium biosorption potential. Optimum biosorption conditions have been identified. Rhizopus arrhizus was identified as the biomass presenting the highest U or Th uptake capacity, in excess of 170 mg/g. The effect of solution co-ions (namely Fe('+2), Zn('+2)) on the equilibrium biosorptive uptake capacity of Rhizopus arrhizus has been examined. The study of the rapid kinetics of U and Th biosorption has been initiated. Accumulated experimental and theoretical information led to the formulation of a biosorption mechanism hypothesis for the systems U or Th - Rhizopus arrhizus. Biosorption of both U and Th by Rhizopus arrhizus occurs mainly in the cell wall of the mycelium. Complexation by the cell wall chitin, adsorption, and hydrolysis of the complex are the processes participating in the proposed mechanism hypotheses.

Diss. (sammanfattning) Stockholm : Karol. inst., 2002. / Härtill 5 uppsatser.

Thesis (DR. P.H.)--University of Michigan. / No collective t.p.; title from cover.

Thesis (Ph. D.)--University of Pennsylvania, 1903. / Includes bibliographical references.

Thesis (DR. P.H.)--University of Michigan. / No collective t.p.; title from cover.

Thesis (Ph. D.)--University of Pennsylvania, 1903. / Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1955. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 90-92).

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If international agreements regarding the need to significantly reduce greenhouse gas emissions are to be met then there is a high probability that the shipping industry will have to reduce its greenhouse gas emissions. For emission reductions from ships greater than around 40% then alternatives to fossil fuels - such as nuclear energy - will very likely be required. Whilst nuclear powered ships have successfully operated at sea for a number of decades, these have been primarily naval systems (or derivatives of naval systems such as icebreakers) and a few demonstration projects using reactors with low power outputs. The operational requirement for large civilian vessels (for example high capacity factors and limited personnel) mean the naval and past demonstration reactor systems are ill-suited for use in the current fleet of commercial container ships. There have been relatively few studies performed addressing the likely requirements upon core design a marine reactor would have to meet. This study addresses those issues and also implements a Pressurised Water Reactor core design capable of achieving these requirements. Furthermore, in order to simplify reactor operation for a limited number of personnel on board, the chemical reactivity control system has been eliminated during power operation. This has resulted in a novel low power density core that does not require refuelling for 15 years. The neutronic and fuel performance behaviour of this system has been studied with conventional UO2 fuel and thorium-uranium oxide ((Th,U)O2) fuel. With respect to (Th,U)O2 fuel there has been limited analysis comparing the performance of key fuel characteristics, such as fission gas release and thermal conductivity, as a function of uranium content in (Th,U)O2 fuel and their impact on fuel behaviour. Furthermore, the performance of neutronic codes for modelling Th-232 and U-233 from a variety of experiments using modern nuclear data libraries (post 1990) is lacking. Both of these issues are addressed in this study. Whilst it is frequently stated that thorium-based oxide fuel is superior to UO2 fuel it was found that due to the sensitivity of thermal conductivity on temperature and uranium content this was not true for the core designed in this study. The (Th,U)O2 core showed no net economic benefits with respect to the UO2 core and it was found that the fuel performance of (Th,U)O2 fuel was worse than the UO2 fuel in the reactor designed here. The UO2 core design, however, was able to satisfactorily meet the majority of requirements placed upon the system.

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