Os experimentos realizados e apresentados nesta dissertação resultaram na caracterização neutrônica de núcleos na configuração cilíndrica com 30 varetas combustíveis de diâmetro com um espaço, criado pela retirada de 16 varetas centrais, preenchido com água leve (H2O) ou água pesada (D2O) no reator nuclear de pesquisa IPEN/MB-01. Nestes núcleos, efetuou-se experimentos de correlação de canais nucleares, calibração de barras de controle e irradiação de detectores de ativação de diversos materiais em forma de folhas, cujas faixas energéticas de atuação abrangem grande parte do espectro de nêutrons do núcleo do reator, para a obtenção de parâmetros nucleares, como excessos de reatividade, reatividades totais, atividades saturadas por núcleo alvo, razões espectrais, razões de cádmio e fluxo de nêutrons multigrupo. Com a irradiação de fios de ativação de ouro na parte radial foram obtidas as formas espaciais dos fluxos de nêutrons térmicos e epitérmicos. Os resultados mostraram as características espectrais dessa nova configuração com o espaço das 16 varetas combustíveis preenchido com os dois materiais moderadores. No espaço com a água leve houve um aumento significativo de 294% do fluxo de nêutrons térmicos em comparação com a configuração padrão retangular de 28×26 varetas combustíveis. Com a água pesada aumentou-se a reatividade do sistema com ρ = (783 ± 54) pcm a mais de excesso de reatividade que na configuração com água leve. Os resultados calculados foram simulados nos códigos computacionais MCNP5, SANDBP e CITATION, onde se obtiveram resultados acurados e precisos para as atividades saturadas por núcleo alvo, as distribuições energéticas e espaciais dos fluxos de nêutrons da parte ativa e de parte do refletor e as comparações diretas das seções de choque entre as razões espectrais experimentais e calculadas. / The experiments performed and presented in this thesis results in the neutronic characterization of the core with cylindrical configuration with 30 fuel rods diameter and a space, created by the removal of 16 central rods, filled with light water (H2O) or heavy water (D2O) in the IPEN/MB-01 nuclear research reactor. In these cores were performed experiments of nuclear channels correlation, control rod worth and irradiation of activation detectors of various materials in foils shapes, whose energy performances cover much of the reactor core neutron spectrum, to obtain nuclear parameters, such as, reactivity excesses, total reactivities, saturated activities per target nucleus, spectral ratios, cadmium ratios and multigroup neutron flux. Activation gold wires detectors were irradiated in radial part to obtain the spatial forms of thermal and epithermal neutron fluxes. The results show the spectral characteristics of this new configuration with the space of 16 fuel rods filled with the two moderator materials. In the space with light water there was a significant increase of 294% of the thermal neutron flux compared to standard rectangular configuration of 28×26 fuel rods. With heavy water the system reactivity was increased, more ρ = (783 ± 54) pcm in excess reactivity than in the light water configuration. The calculated results were simulated in computational codes MCNP5, SANDBP and CITATION, where accurate and precise results were obtained for saturated activities per target nucleus, the energy and spatial distributions of the neutron fluxes for the active part and part of the reflector and the direct comparisons of cross sections between the experimental and calculated spectral ratios.

Os experimentos realizados e apresentados nesta dissertação resultaram na caracterização neutrônica de núcleos na configuração cilíndrica com 30 varetas combustíveis de diâmetro com um espaço, criado pela retirada de 16 varetas centrais, preenchido com água leve (H2O) ou água pesada (D2O) no reator nuclear de pesquisa IPEN/MB-01. Nestes núcleos, efetuou-se experimentos de correlação de canais nucleares, calibração de barras de controle e irradiação de detectores de ativação de diversos materiais em forma de folhas, cujas faixas energéticas de atuação abrangem grande parte do espectro de nêutrons do núcleo do reator, para a obtenção de parâmetros nucleares, como excessos de reatividade, reatividades totais, atividades saturadas por núcleo alvo, razões espectrais, razões de cádmio e fluxo de nêutrons multigrupo. Com a irradiação de fios de ativação de ouro na parte radial foram obtidas as formas espaciais dos fluxos de nêutrons térmicos e epitérmicos. Os resultados mostraram as características espectrais dessa nova configuração com o espaço das 16 varetas combustíveis preenchido com os dois materiais moderadores. No espaço com a água leve houve um aumento significativo de 294% do fluxo de nêutrons térmicos em comparação com a configuração padrão retangular de 28×26 varetas combustíveis. Com a água pesada aumentou-se a reatividade do sistema com ρ = (783 ± 54) pcm a mais de excesso de reatividade que na configuração com água leve. Os resultados calculados foram simulados nos códigos computacionais MCNP5, SANDBP e CITATION, onde se obtiveram resultados acurados e precisos para as atividades saturadas por núcleo alvo, as distribuições energéticas e espaciais dos fluxos de nêutrons da parte ativa e de parte do refletor e as comparações diretas das seções de choque entre as razões espectrais experimentais e calculadas. / The experiments performed and presented in this thesis results in the neutronic characterization of the core with cylindrical configuration with 30 fuel rods diameter and a space, created by the removal of 16 central rods, filled with light water (H2O) or heavy water (D2O) in the IPEN/MB-01 nuclear research reactor. In these cores were performed experiments of nuclear channels correlation, control rod worth and irradiation of activation detectors of various materials in foils shapes, whose energy performances cover much of the reactor core neutron spectrum, to obtain nuclear parameters, such as, reactivity excesses, total reactivities, saturated activities per target nucleus, spectral ratios, cadmium ratios and multigroup neutron flux. Activation gold wires detectors were irradiated in radial part to obtain the spatial forms of thermal and epithermal neutron fluxes. The results show the spectral characteristics of this new configuration with the space of 16 fuel rods filled with the two moderator materials. In the space with light water there was a significant increase of 294% of the thermal neutron flux compared to standard rectangular configuration of 28×26 fuel rods. With heavy water the system reactivity was increased, more ρ = (783 ± 54) pcm in excess reactivity than in the light water configuration. The calculated results were simulated in computational codes MCNP5, SANDBP and CITATION, where accurate and precise results were obtained for saturated activities per target nucleus, the energy and spatial distributions of the neutron fluxes for the active part and part of the reflector and the direct comparisons of cross sections between the experimental and calculated spectral ratios.

A generalized software capability has been developed for the pin-wise loading optimization of light water reactor (LWR) fuel lattices with the enhanced flexibility of control variables that characterize heterogeneous or blended target pins loaded with non-standard compositions, such as minor actinides (MAs). Furthermore, this study has developed the software coupling to evaluate the performance of optimized lattices outside their reflective boundary conditions and within the realistic three-dimensional core-wide environment of a LWR. The illustration of the methodologies and software tools developed helps provide a deeper understanding of the behavior of optimized lattices within a full core environment. The practical applications include the evaluation of the recycling (destruction) of “undesirable” minor actinides from spent nuclear fuel such as Am-241 in a thermal reactor environment, as well as the timely study of planting Np-237 (blended NpO2 + UO2) targets in the guide tubes of typical commercial pressurized water reactor (PWR) bundles for the production of Pu-238, a highly “desirable” radioisotope used as a heat source in radioisotope thermoelectric generators (RTGs). Both of these applications creatively stretch the potential utility of existing commercial nuclear reactors into areas historically reserved to research or hypothetical next-generation facilities. In an optimization sense, control variables include the loadings and placements of materials; U-235, burnable absorbers, and MAs (Am-241 or Np-237), while the objective functions are either the destruction (minimization) of Am-241 or the production (maximization) of Pu-238. The constraints include the standard reactivity and thermal operational margins of a commercial nuclear reactor. Aspects of the optimization, lattice-to-core coupling, and tools herein developed were tested in a concurrent study (Galloway, 2010) in which heterogeneous lattices developed by this study were coupled to three-dimensional boiling water reactor (BWR) core simulations and showed incineration rates of Am-241 targets of around 90%. This study focused primarily upon PWR demonstrations, whereby a benchmarked reference equilibrium core was used as a test bed for MA-spiked lattices and was shown to satisfy standard PWR reactivity and thermal operational margins while exhibiting consistently high destruction rates of Am-241 and Np to Pu conversion rates of approximately 30% for the production of Pu-238.