Uranium-zirconium alloy nuclear fuels have many advantages as compared with ceramic fuels, especially for fast reactor systems. However, metallic fuels aren’t currently used in commercial power production due in part to issues with fuel swelling during irradiation. A major contributor to this expansion issue, the formation of fission gasses into bubbles, is examined here. Methods to evaluate evolution of fission gas bubbles within a U-Zr alloy are discussed and refined. Specifically, transmission electron microscopy (TEM) for viewing bubbles within the interior of the alloy is investigated. One constraint on the use of the TEM is the lack of literature pertaining to what thinning techniques are successful for U-10Zr alloy. Both initial and final thinning techniques were investigated. After thinning was complete, the specimens were viewed via TEM to determine their suitability. In addition, samples of U-Zr alloy were irradiated with gas atoms in an accelerator to simulate bubble initiation and formation and viewed via TEM. Only preliminary investigations were completed. Evaluated electrolyte solutions included one part phosphoric acid to two parts sulfuric acid and two parts water (A), one part phosphoric acid to one part ethanol and one part glycerol (B), one part hydrochloric acid to one part water (C), two parts methanol to 13 parts phosphoric acid (D), and one part perchloric acid to nine parts acetic acid (G). Positive responses were received from the solutions A, C, and G which generated electron transparent areas with few to no process induced artifacts. TEM trials with each electrolyte were performed on un-irradiated U-10Zr alloy. These trials indicated that the polishing methods would work but are not yet optimal. In addition, U-10Zr alloy was irradiated and viewed in the TEM where those polished with electrolyte A consistently included the presence of large circular features that could indicate bubbles or voids. The foundation was laid for further study to be done on this topic through the use of electropolishing solutions as final thinning techniques. Additional work that is recommended includes: electropolishing parameter refinement; implantation of heavier gas atoms or at elevated temperatures; annealing of the implanted alloy; and computer modeling of resulting first principles phenomena.

Orientador: Heloisa Andréa Acciari / Resumo: Nas últimas décadas houve um enorme crescimento do uso titânio comercialmente puro nos mais variados setores da economia como por exemplo na indústria petrolífera, aeroespacial e biomédica. Na indústria biomédica o uso desse metal se caracteriza por ter propriedades mecânicas semelhantes às do osso do corpo humano, por apresentar excelente resistência à corrosão quando comparado com outros metais, e também por ser biocompatível. A biocompatibilidade do titânio ocorre em função da camada de óxido que é formada sobre a superfície deste metal quando exposto a uma atmosfera em que há a presença de oxigênio. Esta camada pode ser amorfa ou cristalina, geralmente quando formada espontaneamente os filmes são amorfos, porém para o uso biomédico é interessante que a fase cristalina anatase se forme sobre a superfície do titânio, pois de acordo com a literatura esta fase favorece a osseointegração. Sendo assim várias técnicas de modificação de superfície, como por exemplo, anodização, tratamento térmico, eletrodeposição, são estudadas para melhorar as propriedades da camada de TiO2. Por tanto, o objetivo desse trabalho foi investigar como os parâmetros de anodização e características de filmes anódicos estão relacionados. Os filmes foram obtidos por anodização em soluções de 0,25 e 2,5 mol L-1 de H3PO4 em três tempos de anodização (3, 6 e 12 horas), comparando dois tipos de substratos: superfícies de titânio eletropolidas e polidas com alumina, com a finalidade de obter uma superfície m... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In the last decades, there has been a great growth in the use of commercially pure titanium in the most varied sectors of the economy, such as in the aerospace and biomedical industries. In the biomedical industry the use of this metal is due to its properties, such as mechanical strength, which is similar to human bone, as well as its excellent corrosion resistance compared to other metals, and also because of it is a biocompatible element. The biocompatibility of titanium occurs as a function of the oxide layer formed on the surface of this metal when it is exposed to an atmosphere where there is the presence of oxygen. This layer can be amorphous or crystalline, usually when it is formed spontaneously the films are amorphous, but for biomedical use it is interesting that the morphology of the anodic film is composed by the Crystalline phase of the anatase, because according to the literature this phase favors osseointegration. In order to improve the properties of the titanium oxide layer, various surface modification techniques have been studied, such as anodizing, heat treatment and electrodeposition. Thus, the proposal of this work was to investigate how the anodization parameters and the characteristics of anodic films are related. The films were obtained by anodization in 0.25 and 2.5 mol L-1 H3PO4 solutions in three anodization times (3, 6 and 12 hours), comparing two types of substrates: electropolished and non-electropolished titanium surfaces, aimed to create a mo... (Complete abstract click electronic access below) / Mestre