13 research outputs found
Catalytic oxidation of soot: Potential for reduction of diesel particulate emissions
No full textApplied Science
Mechanical behaviour and diffusion of gas during neutron irradiation of actinides in ceramic inert matrices
No full textFission of actinides from nuclear waste in inert matrices (materials without uranium) can reduce the period in time that nuclear waste is more radiotoxic than uranium ore that is the rock from which ordinary reactor fuel is made. A pioneering study is performed with the inert matrices: MgO, MgAl2O4, Y3Al5O12, Y2O3 and CeO2-x. These inert matrices contain inclusions of actinide-oxides with a diameter of about 200 μm. UO2 is used as a phase of actinides to simulate the implantation of fission products in inert matrix fuels. After neutron irradiation, inter-particle fracture was present in fuels with matrices that do not form a solid solution with UO2. These cracks are caused by swelling of the actinide phase and insufficient creep of the matrix. The diffusion length of fission gases is significantly reduced by inter-particle fracture and thereby fission gas releases till 50% were measured. This inter-particle fracture may be prevented when inert matrix fuels are fabricated with porous actinide inclusions embedded in inert matrices that are polluted by actinides. The amount of helium generated during neutron irradiation of a few actinides from nuclear waste can be far larger than the amount of fission gases. Parameters and diffusion mechanisms to simulate diffusion of helium in MgAl2O4 were derived by thermal evolution of He concentration profiles, atomistic calculations and numerical analysis using original definitions of diffusion coefficients for inert gas in materials with defects for single crystal as well as polycrystal media. This study shows that, amongst others, the material degradation of MgAl2O4, caused by the generated amount of defects and He during irradiation conditions, is acceptable. But the pioneering study with UO2 as a phase of actinides, shows that the solid state swelling by fission products in MgAl2O4 is about ten times larger than this swelling in 238UO2 that is the matrix in fuel for commercial reactors. The commercial feasibility of reduction of actinides from nuclear waste, by neutron irradiation in inert matrices, requires more research.Interfaculty Reactor Institut
Copper catalysis for particulate removal from diesel exhaust gas. Copper fuel additives in combination with copper coatings.
No full textThe formation of carbon surface oxygen complexes by oxygen and ozone. The effect of transition metal oxides
No full text
Transport of Ions Through Clays of the Peize and Waalre Formation
No full textHigh-level waste can be radiotoxic for thousands of years and should be carefully handled to prevent accidents. The research for geological disposal of radioactive waste focuses on the construction and durability of a geologic disposal facility in Dutch clays or salts. One of the challenges is assessing these host rocks’ capability to retard radionuclides and prevent them from entering the biosphere. This research focuses on disposal in clay. Because of clay’s low permeability, water movements are slow, and radionuclides transport is expected to occur predominantly by diffusion. The Peize and Waalre formations, situated on the interface between brackish and salt groundwater, serve as a natural analogue for targeted deeper, poorly indurated host rocks. The known disparity in chlorine levels between the aquifers adjacent to these clays qualify these formations for NaCl-tracer research. A cutting sampling study determined the conductivity of these clays’ porewater. Combining this with a one-dimensional modelling study, the saline history of this formation has been simulated. NaCl gradients were demonstrated at different drilling locations. The most manifested gradient is attempted to fit in the one-dimensional model. The model results suggest that this gradient originates from adjacent aquifer salinity, the clays’ physical properties and the difference in hydraulic head. The observed salinity discrepancy between aquifers and ion concentration gradient in the firstWaalre Clay confirm the assumption that the member can be a natural analogue. Uncertainty on the continuity of the total system prohibits concluding that diffusion-dominated transport in Dutch poorly indurated clays can be assumed. The best fitting scenario this research found fitting the empirical Waalre clay salinity curve is combined transport by diffusion and advection. The finding of diffusion-advection transport implies that the Waalre clay shows more complexity than initially expected.Applied Earth Science
Desenvolvimento de um carvão adsorvente para remoção de íons ferro em águas naturais
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-graduação em Engenharia Química, Florianópolis, 2003Este trabalho teve como objetivo o desenvolvimento de um carvão adsorvente a partir do carvão mineral de Santa Catarina, para ser utilizado para o tratamento de águas naturais. Foram testados vários tipos de carvão mineral, com diferentes concentrações de cinzas, e carvões minerais submetidos a diferentes processos de beneficiamento. Foi desenvolvido um carvão mineral beneficiado que apresentou bons resultados para a remoção de íons metálicos em águas, com ênfase na remoção de íons ferro. A elevada concentração de íons ferro é uma característica comum das águas subterrâneas no Estado de Santa Catarina. Foram realizados testes para utilização do carvão adsorvente para a remoção de íons ferro em águas naturais, em escala de bancada, escala piloto e em larga escala
