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Glassy carbon is a disordered form of carbon with very high temperature resistance, high hardness and strength and chemical stability even in extreme environments. Glassy carbon is also unaffected by nearly all acids and cannot be graphitized even at very high temperature. Because of these characteristics, there is a possibility that glassy carbon can replace copper, iron, titanium alloys and other materials employed in making canisters used in nuclear waste storage. The modification of glassy carbon due to strontium ions implantation and heat treatment is reported. Glassy carbon (GC) samples were implanted with 200 keV strontium ions to a fluence of 2×1016 ions/cm2 at room temperature. Sequential isochronal annealing was carried out on the implanted samples at temperatures ranging from 200 oC - 900 oC for one hour. The influence of ion implantation and annealing on surface topography was examined by the scanning electron microscopy (SEM), while Raman spectroscopy was used to monitor the corresponding structural changes induced in the glassy carbon. The depth profiles of the implanted strontium before and after annealing were determined using Rutherford Backscattering Spectroscopy (RBS). Compared to SRIM predictions the implanted strontium profiles was broader. After annealing at 300 oC, bulk and surface diffusion of the strontium atoms took place. Annealing at 400 oC- 700 oC not only resulted in further diffusion of strontium towards the surface, the diffusion was accompanied with segregation of strontium on the surface of the glassy carbon substrate. Evaporation of the strontium atoms was noticed when the sample was annealed at 800 oC and 900 oC respectively. These annealing temperatures are higher than the melting point of strontium (~769 oC). The Raman spectrum of the virgin glassy carbon shows the disorder (D) and graphitic (G) peaks which characterize disordered carbon materials. Merging of these two peaks was observed when the virgin sample was implanted with strontium ions. Merging of these peaks is due to damage caused by the implantation of strontium. The Raman spectrum recorded after heat treatment showed that only some of the damage due to implantation was annealed out. Annealing at 20000C for 5 hours resulted in a Raman spectrum very similar to that of virgin glassy carbon indicating that the damage due to the ion implantation was annealed out. SEM showed large differences in the surface topography of the polished glassy carbon surfaces and those of as-implanted samples. Annealing did not significantly change the surface microstructure of the implanted samples. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Physics / unrestricted

This thesis was done i cooperation with SKB Clab in Oskarshamn and studies use of sonic waves for detecting voids and irregularities in the weld joints of copper capsules used for long term storage of radioactive waste. Since these could pose material failure and thereby risk radioactive contamination of ground water it is very important to find means of quality control before storage.  During the welding procedure changes occur to the integrity of the material. The homogenous metal – in this case copper – is distorted and voids appear in and around the welded volume. A non-destructive inspection method is needed to make sure that the metal holds for the strains of long term storage. These strains are not completely known at the moment and therefore the goal of this thesis is mainly to add another tool of inspection for future studies. The tests are done using ultrasonic mapping of the welded volume. This is achieved by sending ultrasonic pulse through test samples – welded copper pieces – and recording its reflection. The recorded signals are gathered in data matrices and processed using several different signal processing methods in search of irregularities and voids. To enhance the understanding of the results a graphical user interface (GUI) is developed that allows users to visualize the results.  The welded pieces, the ultrasonic mapping and its resulting data sets were delivered to this thesis and the scope of the thesis is to develop the GUI and apply known signal processing methods to the data set.  It is shown that the irregularities do appear and that ultrasonic detection and use of the processing method is useful for quality control of the material. Further field studies are needed to identify maximum number, size and perhaps shapes of irregularities that can be within tolerance levels of the storage project.

Apresentamos um estudo de solidificaçaõ e lixiviacão de matrizes de vidros porosos de alto teor de sílica armazenando 20% em peso de solução aquosa simuladora de rejeitos nucleares de alto nível de radioatividade do tipo Savanah River Labratory. A matriz porosa foi preparada após o tratamento térmico de um vidro de 65% SiO2-27%B2O3-8%Na2O, que sofreu separação de fase à 560°C por 20 horas e lixiviado em HCl - 3N à 90°C. O tamanho dos poros (tipicamente de 100 à 250Å de diâmetro) , foi determinado utilizando o método BET. Após sinterização à 1300°C em ar, as amostras foram caracterizadas física e quimicamente através de testes de lixiviação padronizados MCC1, Soxhlet (MCC5) e Estagnante durante cerca de 28 dias. Determinamos a perda de peso total, o pH, as taxas de lixiviação diferencial e as concentrações acumuladas para os seguintes elementos: Si, Na, B, Ca, Mn, Al, Fe e Ni com técnicas de ICP e espectroscopia de chama para o caso do Na. Os resultados são comparados com os obtidos com vidros borosilicatos de referência, fabricados por fusão convencional (SRL 131, PNL 76-68, MCC 76-68, SRL TDS 131, AVM-Ml à M7), vidros fabricados pela técnica sol-gel (TDS 211), vidros de alto teor de sílica (CU PGM), synroc-D, cerâmicas manufaturadas, concreto FUETAP e matrizes metálicas. Os valores obtidos são similares àqueles obtidos com os melhores vidros borosilicato presentemente usados. / We present a study of the sinterization and of the leaching behavior of a high silica porous glass matrix containing 20 weight % of simulated solution of high level liquid nuclear waste of the type Savanah River Laboratory. The porous matrix has been prepared after heat treatment of a 65% SiO2-27%B2O3-8%Na2O glass, phase separate at 560°C for 20 hours and leached in 3N HCl at 90°C. The pore size (typically 100-250Å in diameter) has been determined by the BET method. After sinterization in air at 1300°C, the samples have been physically and chemically characterized during 28 days using the MCC1, Estagnant and Soxhlet (MCC5) standard tests. We have determined thetotal weight loss, the pH, the diferential leaching rate and the cumulative concentrations for the following elements: Si, Na, B, Ca, Mn, Al, Fe and Ni by ICP technique, for Na flames spectroscopy. The results are compared with these obtained with other reference borosilicate glasses made by conventional fusion techniques (SRL 131, PNL 76-68, MCC 76-68, SRL TDS 131, AVM-M1 to M7), glasses made by sol-gel technique (TDS-211), porous glasses matrix (CU PGM), synroc-D, tailored ceramics, FUETAP concrete and metallic matrix. The values obtained are similar to those found for the best borosilicate glass presently used.

Apresentamos um estudo de solidificaçaõ e lixiviacão de matrizes de vidros porosos de alto teor de sílica armazenando 20% em peso de solução aquosa simuladora de rejeitos nucleares de alto nível de radioatividade do tipo Savanah River Labratory. A matriz porosa foi preparada após o tratamento térmico de um vidro de 65% SiO2-27%B2O3-8%Na2O, que sofreu separação de fase à 560°C por 20 horas e lixiviado em HCl - 3N à 90°C. O tamanho dos poros (tipicamente de 100 à 250Å de diâmetro) , foi determinado utilizando o método BET. Após sinterização à 1300°C em ar, as amostras foram caracterizadas física e quimicamente através de testes de lixiviação padronizados MCC1, Soxhlet (MCC5) e Estagnante durante cerca de 28 dias. Determinamos a perda de peso total, o pH, as taxas de lixiviação diferencial e as concentrações acumuladas para os seguintes elementos: Si, Na, B, Ca, Mn, Al, Fe e Ni com técnicas de ICP e espectroscopia de chama para o caso do Na. Os resultados são comparados com os obtidos com vidros borosilicatos de referência, fabricados por fusão convencional (SRL 131, PNL 76-68, MCC 76-68, SRL TDS 131, AVM-Ml à M7), vidros fabricados pela técnica sol-gel (TDS 211), vidros de alto teor de sílica (CU PGM), synroc-D, cerâmicas manufaturadas, concreto FUETAP e matrizes metálicas. Os valores obtidos são similares àqueles obtidos com os melhores vidros borosilicato presentemente usados. / We present a study of the sinterization and of the leaching behavior of a high silica porous glass matrix containing 20 weight % of simulated solution of high level liquid nuclear waste of the type Savanah River Laboratory. The porous matrix has been prepared after heat treatment of a 65% SiO2-27%B2O3-8%Na2O glass, phase separate at 560°C for 20 hours and leached in 3N HCl at 90°C. The pore size (typically 100-250Å in diameter) has been determined by the BET method. After sinterization in air at 1300°C, the samples have been physically and chemically characterized during 28 days using the MCC1, Estagnant and Soxhlet (MCC5) standard tests. We have determined thetotal weight loss, the pH, the diferential leaching rate and the cumulative concentrations for the following elements: Si, Na, B, Ca, Mn, Al, Fe and Ni by ICP technique, for Na flames spectroscopy. The results are compared with these obtained with other reference borosilicate glasses made by conventional fusion techniques (SRL 131, PNL 76-68, MCC 76-68, SRL TDS 131, AVM-M1 to M7), glasses made by sol-gel technique (TDS-211), porous glasses matrix (CU PGM), synroc-D, tailored ceramics, FUETAP concrete and metallic matrix. The values obtained are similar to those found for the best borosilicate glass presently used.

Le comportement à long terme des excavations souterraines est un enjeu social et économique majeur, en particulier dans le contexte du stockage en formation géologique profonde de déchets nucléaires à Haute Activité et Vie Longue (HAVL). Plusieurs galeries expérimentales ont été creusées dans le laboratoire de recherche souterrain de Meuse/Haute-Marne situé près de Bure en France, où des études sont menées pour comprendre le comportement global de la roche constitutive : l’argilite du Callovo-Oxfordien (COx).L’objectif de cette thèse est d’effectuer une modélisation avec Code_Aster d’ouvrages souterrains, et en particulier d’une des galeries du laboratoire de Meuse/Haute-Marne, en prenant en compte une approche non locale, l’effet du fluage et le couplage hydromécanique dans le cadre de la mécanique des milieux poreux, et de comparer les résultats numériques avec les données expérimentales disponibles.Le modèle élastoviscoplastique spécifiquement utilisé pour cette étude est le modèle L&K : il offre d’une part un couplage entre le comportement instantané et différé, et prend en compte d’autre part la dilatance, paramètre qui gouverne les déformations volumiques du matériau lors d’une sollicitation, et ses fortes variations, caractéristique essentielle des géomatériaux et en particulier du COx. La présence d’un fluide s’écoulant à travers le matériau va ajouter une composante hydraulique à la modélisation, dont le couplage avec la mécanique est assuré par les équations de Biot. Une autre nouveauté de ce travail concerne le couplage entre ce comportement rhéologique complexe et une approche non locale dans un cadre industriel. Parmi les méthodes de régularisation disponibles dans Code_Aster, la méthode second gradient de dilatation a été choisie parce que bien adaptée aux géomatériaux. Son but est de corriger la dépendance au maillage et les solutions numériques localisées.Une fois les outils numériques opérationnels et les paramètres du modèle L&K calés sur des essais effectués en laboratoire sur des échantillons, un bon accord général a été trouvé entre les résultats numériques et les mesures in situ, sans aucun recalage des paramètres. Les effets du temps observés expérimentalement sur l’évolution des déplacements et des pressions d’eau sont retrouvés au sein d’une même modélisation, validant ainsi la démarche prédictive suivie / The long term behaviour of underground excavations is a social and economic stake, in particular in the context of storage in deep geological formation of high activity and long life nuclear waste. Several experimental galleries have been dug in the underground research laboratory (URL) of Meuse/Haute-Marne located close to Bure in France, where studies are leaded in order to understand the global behaviour of the constitutive rock which is the Callovo-Oxfordian (COx) argillite.The purpose of this PhD Thesis is to establish a modelling with Code_Aster of underground excavations, and especially of a Meuse/Haute-Marne laboratory gallery, taking into account non local approach, creep effect and hydromechanical coupling in the framework of the mechanics of porous media, and then to compare numerical results with available experimental data.The specific elastoviscoplastic model used in this study is the L&K model: it offers a coupling between instantaneous and delayed behaviour, and it takes into account the dilation, parameter which governs the volume strains of the material during a solicitation, and its strong variation, a specificity of geomaterials and so of COx argillite. The fluid flowing through the material adds a hydraulic component to the modelling, which is coupled to mechanic component thanks to Biot’s equations.Another novelty of this work concerns the coupling between such complex rheological behaviour and a non local approach in an industrial way. Among methods of regularization available in Code_Aster, the second gradient of dilation is well fitted to geomaterials. Its aim is to correct mesh dependency and numerical localized solutions.After describing numeric tools and setting parameters of the L&K model on laboratory tests, a good general agreement was found between numeric results and in situ measures, without resetting parameters. Time effects experimentally measured on displacement and pore pressure evolution are observed in the same modelling, validating the followed predictive approach