Predicting leakage of the VERCORS mock-up and concrete containment buildings - a digital twin approach

EDF operates a nuclear power generation fleet made up of 56 reactors. This fleet contains 24 reactors designed as double-walled concrete containment building. The inner concrete containment vessel has no metallic liner and is a prestressed reinforced concrete building. The inner concrete containment vessel is designed to withstand a severe accident, in terms of mechanical and sealing behaviour. The tightness of the containment is tested every 10 years, by carrying out a pressurization test and by measuring the leak rate. The leak rate is required to be below a regulatory threshold to continue operation of the concrete containment building for the next ten years. Ageing of concrete due to drying, creep and shrinkage leads to increase prestress loss and then leak rate with time. For some containment buildings, the leak rate gets closer to the regulatory threshold with time, so important coating programs are planned to mitigate and limit the leak rate under the regulatory threshold. Therefore, it is very important for EDF to have a concrete containment building leak rate prediction tool. To address this issue, an important research program around a 1/3 scale concrete containment building mock-up called "VERCORS" have been launched at EDF. The mock-up is heavily instrumented, and its materials (concrete, prestressing cables) have been widely characterized and studied. An important numerical effort has also been made to implement structural computations of the mock-up and to capitalize these computations as well as their post-processing (so as to compare automatically with the monitoring data) in what can be called a digital twin of the mock-up. This digital twin is now used to predict the leakage of VERCORS mock-up before yearly pressure test, and also to optimize the repair programs on the real containments

Geopolymerization and alkali-activation of injection grouts : structuration, micromechanics and resistance to physicochemical effects

La nécessité de construire de manière durable, rationnelle et écologique incite à l’innovation et la recherche d’alternatives, telles que la géopolymérisation et l’activation alcaline, qui suscitent un intérêt croissant. Dans ce sens, ces technologies permettent de valorise rdes matières premières à plus faible impact environnemental pour le développement d’une nouvelle famille de matériaux. Cependant, ces mécanismes réactionnels sont complexes et il est encore nécessaire de lever plusieurs verrous avant leur implémentation : la confusion entre les deux processus, l’absence d’approches de formulation rationnelles, la méconnaissance de certaines vulnérabilités, etc. La thèse s’intègre dans cette dynamique et a pour objectif une meilleure connaissance des géopolymères et des matériaux alcali-activés. Le cadre de travail est le développement de coulis d’injection. Un programme expérimental basé sur une sélection de compositions est établi afin de caractériser leurs principales propriétés. Les différences entre les deux processus de structuration sont relevées à travers une étude physico-chimique (DRX, RMN) et liées aux évolutions macroscopiques au jeune âge. Un travail d’optimisation de formulation est mené afin de répondre à des critères d’application et définir les paramètres influençant le comportement rhéologique et mécanique des coulis. Une méthodologie basée sur l’analyse micromécanique et l’homogénéisation multi-échelles a permis d’évaluer le module élastique des matériaux et peut servir de plateforme pour une analyse globale du comportement mécanique. Enfin, une étude de la durabilité est entamée en évaluant la sensibilité au séchage et à la lixiviation en milieu acide.The need for more durable, rational and ecological constructions encourages innovation and the search for alternatives, such as geopolymerization and alkali-activation, with a growing interest. These technologies allow the use of resources with a lower environmental impact in developing a new class of materials. However, both reaction mechanisms are complex and some issues need further investigation before a proper implementation: the confusion between these processes, the absence of a rational design approach, the lack of knowledge concerning some mechanisms of degradation, etc. The present thesis joins this dynamic and aims at a better understanding of geopolymers and alkali activated materials to design soil injection grouts. An experimental program has been established based on selected mix designs to study their main properties. The differences between both structuration processes were determined through a physicochemical study (XRD, NMR). They were correlated to the macroscopic phenomena observed at early age. An optimization of the mixtures was carried to satisfy the application criteria and define the parameters controlling the rheological and mechanical behavior of the grouts. Using a micromechanical characterization and multiscale homogenization, a methodology has been designed to determine the elastic modulus of the materials.This can be used as a first tool to analyze the global mechanical behavior. Finally, the sensitivity to drying and exposure to acid environments was assessed

Géopolymérisation et activation alcaline des coulis d’injection : structuration, micromécanique et résistance aux sollicitations physico-chimiques

The need for more durable, rational and ecological constructions encourages innovation and the search for alternatives, such as geopolymerization and alkali-activation, with a growing interest. These technologies allow the use of resources with a lower environmental impact in developing a new class of materials. However, both reaction mechanisms are complex and some issues need further investigation before a proper implementation: the confusion between these processes, the absence of a rational design approach, the lack of knowledge concerning some mechanisms of degradation, etc. The present thesis joins this dynamic and aims at a better understanding of geopolymers and alkali activated materials to design soil injection grouts. An experimental program has been established based on selected mix designs to study their main properties. The differences between both structuration processes were determined through a physicochemical study (XRD, NMR). They were correlated to the macroscopic phenomena observed at early age. An optimization of the mixtures was carried to satisfy the application criteria and define the parameters controlling the rheological and mechanical behavior of the grouts. Using a micromechanical characterization and multiscale homogenization, a methodology has been designed to determine the elastic modulus of the materials.This can be used as a first tool to analyze the global mechanical behavior. Finally, the sensitivity to drying and exposure to acid environments was assessed.La nécessité de construire de manière durable, rationnelle et écologique incite à l’innovation et la recherche d’alternatives, telles que la géopolymérisation et l’activation alcaline, qui suscitent un intérêt croissant. Dans ce sens, ces technologies permettent de valorise rdes matières premières à plus faible impact environnemental pour le développement d’une nouvelle famille de matériaux. Cependant, ces mécanismes réactionnels sont complexes et il est encore nécessaire de lever plusieurs verrous avant leur implémentation : la confusion entre les deux processus, l’absence d’approches de formulation rationnelles, la méconnaissance de certaines vulnérabilités, etc. La thèse s’intègre dans cette dynamique et a pour objectif une meilleure connaissance des géopolymères et des matériaux alcali-activés. Le cadre de travail est le développement de coulis d’injection. Un programme expérimental basé sur une sélection de compositions est établi afin de caractériser leurs principales propriétés. Les différences entre les deux processus de structuration sont relevées à travers une étude physico-chimique (DRX, RMN) et liées aux évolutions macroscopiques au jeune âge. Un travail d’optimisation de formulation est mené afin de répondre à des critères d’application et définir les paramètres influençant le comportement rhéologique et mécanique des coulis. Une méthodologie basée sur l’analyse micromécanique et l’homogénéisation multi-échelles a permis d’évaluer le module élastique des matériaux et peut servir de plateforme pour une analyse globale du comportement mécanique. Enfin, une étude de la durabilité est entamée en évaluant la sensibilité au séchage et à la lixiviation en milieu acide

Alkali-activated grouts with incorporated fly ash: From NMR analysis to mechanical properties

The nanostructure of alkali-activated materials is now better understood. However, very few studies have been carried on grouts. These highly diluted systems are used to improved soil properties for instance. In this study, the evolution of their local structure was monitored via 29Si and 27Al NMR to understand the formation of the binding phase and its evolution at long-term. The results of this analysis were used to question the relationship between the evolution of the chemistry of binding phases and the observed changes in the mechanical properties at material scale. Metakaolin and slag were used, with the partial incorporation of fly ash to study its effects and the potential benefits of its use. The results show that while metakaolin-based systems are very stable at both scales (local and macroscopic), the structure of slag-based grouts tends to evolve, with a negative impact on their mechanical performance