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Made available in DSpace on 2014-10-09T12:23:47Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:34Z (GMT). No. of bitstreams: 1 01130.pdf: 682173 bytes, checksum: 29e0e663ccc9f3c06e833bc806ed4c26 (MD5) / Dissertacao (Mestrado) / IEA/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

Made available in DSpace on 2014-10-09T12:54:44Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:28Z (GMT). No. of bitstreams: 0 / Neste trabalho foram determinados os elementos As, Br, Co, Cr, Cs, Fe, K, Na, Rb, Se e Zn presentes em cogumelos comestíveis adquiridos em grandes centros de compra (supermercados), mercados municipais da cidade de São Paulo e diretamente de produtores da região de Mogi das Cruzes, Suzano, Juquitiba e Mirandópolis. A técnica analítica empregada para a determinação dos elementos nos cogumelos comestíveis foi a Análise por Ativação com Nêutrons Instrumental (INAA). Foram adquiridas espécies dos gêneros Agaricus, Lentinus e Pleurotus no período de novembro de 2006 a março de 2007. Cerca de 150 a 200 mg das amostras de cogumelo liofilizado foram irradiadas em fluxo de nêutrons térmicos de 1012cm-2s-1 por 8 horas no reator nuclear de pesquisa IEA-R1 do IPEN/CNEN/SP. Para a validação da metodologia com relação à exatidão e à precisão foram analisados quatro materiais de referência: INCT-MPH-2 Mixed Polish Herbs e INCT-TL-1 Tea Leaves, NIST SRM 1577b Bovine Liver e Mushroom da IAEA. Foi verificada uma variação nas concentrações dos elementos determinados entre os diferentes gêneros. Em algumas amostras apresentaram o elemento arsênio, em baixas concentrações, possivelmente de uma contaminação no cultivo pelo uso de pesticidas nos substratos de onde os cogumelos retiram seus nutrientes. Os resultados mostram que as amostras das espécies de cogumelos analisadas podem ser consideradas como boa fonte nutricional, principalmente devido aos baixos teores de Na, sendo também uma boa fonte de K, Fe e Zn. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP

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No description available.

A nonlinear model is developed for the xenon induced flux oscillation problem that occurs in nuclear power plants. The model is based on Galerkins' method of weighted residuals applied to multigroup diffusion theory. A similar linear model is developed by the same methods in order to consider the effects of the nonlinearities of the system. The effects of multi- and single-energy group considerations are also examined. Finally, the effects of various number of basis functions used to approximate the flux, iodine, and xenon concentrations is determined. A partial listing of the computer program XORA, developed from the nonlinear and linear models, is given along with representative input and output from this program. / Ph. D.

Benchmark calculations are performed for neutron transport in a two material (binary) stochastic multiplying medium. Spatial, angular, and energy dependence are included. The problem considered is based on a fuel assembly of a common pressurized water nuclear reactor. The mean chord length through the assembly is determined and used as the planar geometry system length. According to assumed or calculated material distributions, this system length is populated with alternating fuel and moderator segments of random size. Neutron flux distributions are numerically computed using a discretized form of the Boltzmann transport equation employing diffusion synthetic acceleration. Average quantities (group fluxes and k-eigenvalue) and variances are calculated from an ensemble of realizations of the mixing statistics. The effects of varying two parameters in the fuel, two different boundary conditions, and three different sets of mixing statistics are assessed. A probability distribution function (PDF) of the k-eigenvalue is generated and compared with previous research. Atomic mix solutions are compared with these benchmark ensemble average flux and k-eigenvalue solutions. Mixing statistics with large standard deviations give the most widely varying ensemble solutions of the flux and k-eigenvalue. The shape of the k-eigenvalue PDF qualitatively agrees with previous work. Its overall shape is independent of variations in fuel cross-sections for the problems considered, but its width is impacted by these variations. Statistical distributions with smaller standard deviations alter the shape of this PDF toward a normal distribution. The atomic mix approximation yields large over-predictions of the ensemble average k-eigenvalue and under-predictions of the flux. Qualitatively correct flux shapes are obtained, however. These benchmark calculations indicate that a model which includes higher statistical moments of the mixing statistics is needed for accurate predictions of binary stochastic media k-eigenvalue problems. This is consistent with previous findings. / Graduation date: 2005