MARGARETH KAZUYO KOBAYASHI DIAS FRANCO
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Artigo IPEN-doc 30355 Effect of irradiation and chemically aggressive environment on Brazilian mortar cement2024 - YOKAICHIYA, FABIO; FERREIRA, EDUARDO A.G.; VICENTE, ROBERTO; CERCEAU, AUGUSTA; MARUMO, JULIO T.; FRANCO, MARGARETH K.K.D.Radioactive waste disposal, considered a major technical problem, has as one of the solutions, the construction of repositories that will be exposed to a range of environmental conditions in a timescale which involve thousands of years. Cement-based materials, used in the repositories, have a complex porous structure that changes over time and their durability strongly correlates to the transport of water and ions throughout the pore structure. In this study, the influence of the repository's environment was simulated using two different solution conditions: Water and Na2SO4 at different gamma irradiated condition. Two X-Ray techniques were performed simultaneously: (i) diffraction to characterize the phases contents on cement mortar samples; (ii) tomography to investigate the differences between the pore structure and pores volume. The combination's advantage of the XRay techniques shows their potential application to determine the relation amongst the phases and the pores structures, to demonstrate how the environment and the irradiation modify the structure of mortar.Artigo IPEN-doc 28285 Synthesis of geopolymers for immobilization of radioactive waste using sewage treatment plant sludge2021 - CASAS, A.; ARAUJO, L.; GARCIA, R.; VICENTE, R.; FRANCO, M.; MARUMO, J.Artigo IPEN-doc 27079 Effects of gamma radiation on cementitious materials in repository environment2016 - FERREIRA, EDUARDO; VICENTE, ROBERTO; TURRILLAS, XABIER; YOKAICHIYA, FABIANO; FRANCO, MARGARETH; MARTINEZ, LUIS G.; CARVALHO, ALEXANDRE; MARUMO, JULIO T.Cementitious materials are widely used in the management of radioactive waste and have to perform as required for the period of service life of the installation. In order to assess the long term durability of cement paste in a deep borehole for radioactive wastes, specimens were casted in laboratory and exposed to a gamma radiation field. The effects of the radiation in the specimens were evaluated by X-Ray Diffraction, as changes observed in the mineralogy and microstructure of the material after irradiation doses varying between 0 (without radiation) and 10 MGy. It was observed that the specimens exposed to higher doses of gamma radiation (up to 3MGy) presented differences between surface and core, when compared with the samples with no radiation or exposed to low doses. These results are important to model the behavior of cementitious materials under the conditions expected in a borehole repository and to provide data for the safety assessment of the installation.Artigo IPEN-doc 26781 Aplicação da química de radiação à questões tecnológicas do cimento relacionadas ao desenvolvimento de repositórios de rejeitos radioativos do modelo borehole2019 - URBANI, G.L.; FRANCO, M.K.K.D.; YOKAICHIYA, F.; VICENTE, R.Resíduos radioativos são usualmente descartados em repositórios do tipo borehole ou de superfície. Por questões de segurança, devem ser depositados em tambores e cobertos por cimento na sua destinação final. A radiação gama proveniente dos resíduos radioativos interage com a água livre da pasta de cimento e causa o fenômeno da radiólise. Essa interação que decompõe a água da pasta de cimento é estudada pela academia científica e ainda não é um consenso se a mesma afeta a resistência do concreto ou não. Para um melhor entendimento dessa questão, nesse estudo um modelo teórico simples é sugerido para quantificar a porcentagem da água que sofre radiólise e se essa perda é suficiente para afetar a resistência da barreira de cimento. O resultado indica que a quantidade de água perdida neste processo não é suficiente para diminuir a resistência do concreto. O modelo proposto foi aplicado para verificar os resultados experimentais, utilizando as condições iniciais expostas na literatura existente, com o propósito comparação e discussão sobre o fenômeno da radiólise.Artigo IPEN-doc 26393 10000 years cement2019 - FERREIRA, EDUARDO G.A.; MARUMO, JULIO T.; FRANCO, MARGARETH K.K.D.; YOKAICHIYA, FABIANO; VICENTE, ROBERTOThis review is focused on the long-term performance of cementitious materials in a repository for radioactive waste. During the last few years, the disposal of disused sealed radioactive sources (DSRS) in a borehole type repository has been studied by many countries. The borehole concept is particularly useful to dispose of spent nuclear fuel and DSRS. In boreholes for DSRS, cementitious materials are intended to be used as structural material, immobilization matrix and as backfill. The understanding of the performance of these materials is essential to ensure the safety of the facilities during their required lifetime, from centuries to many thousands of years, depending on the initial activity and half-life of the waste. This review approaches the behavior of the cement from the hydration and hardening to the long-term processes that can affect its durability. Three main causes of failure of repository-engineered barriers are recognized: a) the formation of a preferential pathway for the migration of the contained radionuclides to the biosphere; b) loss of resistance and cohesion of the structural cementitious material; and c) the increase in the corrosion processes of the metallic components of the structures that affect the overall containment of the facility.Artigo IPEN-doc 24815 Influence of the irradiation in cement for the Brazilian radioactive waste repositories2018 - FERREIRA, EDUARDO G.A.; YOKAICHIYA, FABIANO; MARUMO, JULIO T.; VICENTE, ROBERTO; GARCIA-MORENO, FRANCISCO; KAMM, PAUL H.; KLAUS, MANUELA; RUSSINA, MARGARITA; GUNTHER, GERRIT; JIMENEZ, CATALINA E.; FRANCO, MARGARETH K.K.D.Powerful characterization techniques have allowed detailing the investigation of cementitious materials that must endure for millennia as an engineered barrier in radioactive waste repositories. Cement is used in the repository, as waste immobilization matrix, structural material and an additional barrier against the contact of the waste with the biosphere. The material properties have to comply with requirements in respect to a number of parameters including homogeneity, permeability, and leachability, as well as withstand mechanical stress, heat, chemical and microbial attack, and the effects of ionizing radiation. The present study aims to investigate the behavior of cementitious materials contributing to the understanding of the processes that occur in hydrated cement under the environmental conditions of a repository and to estimate the durability of these materials. In this study was observed the changes caused by radiation, to which the material was exposed. A reference Portland cement paste and grout samples were compared with irradiated ones by X-ray diffraction and Tomography. Original and valuable results concerning the investigation of the influence of radiation on cement samples were also obtained by quasielastic scattering. These results are not accessible by others techniques.Resumo IPEN-doc 21597 Portland cement paste behaviour under gamma radiation field in geological repository2015 - FERREIRA, E.G.A.; VICENTE, R.; TURRILLAS, X.; VOKAICHIYA, F.; FRANCO, M.; MARTINEZ, L.G.; MARUMO, J.T.Artigo IPEN-doc 21326 Assessment of cement durability in repository environment2015 - FERREIRA, EDUARDO G.A.; VICENTE, ROBERTO; TURRILLAS, XABIER; YOKAICHIYA, FABIANO; FRANCO, MARGARETH K.K.D.; MARTINEZ, LUIS G.; MARUMO, JULIO T.