L’application des approches probabilistes pour tenir compte des incertitudes dans le domaine des barrages est un sujet en développement. Cependant, la plupart des études ont été réalisées sur l’évaluation de la sécurité des barrages pendant leur service. Ce travail de thèse vise à appliquer ce type d’approches et à faire une contribution à l’analyse de risque des barrages en béton compacté au rouleau (BCR) d`es sa construction, à l’aide d’une simulation numérique. Les travaux présentés dans ce manuscrit proposent l’application d’une méthodologie qui vise à quantifier la vulnérabilité vis-à-vis de l’apparition de la fissuration pendant la construction du barrage, ce qui peut affecter `a long-terme la perméabilité et par conséquent, compromettre son comportement structurel. Pour ce faire, l’accent est mis sur les incertitudes liées à quelques caractéristiques des matériaux (e.g., résistance, rapport eau-ciment, entre autres) et aux conditions environnementales pendant la phase de construction. Un modèle thermo-chemo-mécanique est utilisé pour décrire le comportement du BCR. En ce qui concerne le modèle probabiliste, deux aspects sont étudiés: i) comment les incertitudes liées aux variables d’entrée sont propagées dans le modèle, et ii) quelle est l’influence de leur dispersion par rapport à la dispersion totale de la sortie. Ce dernier est évalué par l’intermédiaire d’une analyse de sensibilité globale effectuée avec la méthode RBD-FAST. En outre, la variabilité spatiale des paramètres d’entrée est aussi prise en compte à travers des champs aléatoires bidimensionnels. Par ailleurs, un couplage entre des méthodes de fiabilité et la méthode d’éléments finis est effectué de façon à évaluer le potentiel de fissuration dans chaque couche de BCR lors de sa construction en utilisant un concept de densité de fissuration. Comme résultat important issu de ce travail de recherche, des courbes de probabilité pour la densité de fissuration sont obtenues au niveau de chaque couche en fonction de leur âge et des conditions aux limites, ce qui est considérée comme étant une contribution originale de cette thèse.La méthodologie proposée peut être utilisé pour aider à comprendre comment les incertitudes vont affecter le comportement du barrage pendant sa construction et servir d’appui dans le futur pour améliorer et soutenir la phase de conception du projet de barrage. / The use of fully probabilistic approaches to account for uncertainties within dam engineering is a recently emerging field on which studies have been mostly done concerning the safety evaluation of dams under service. This thesis arises within this framework as a contribution on moving the process of risk analysis of dams beyond empirical knowledge, applying probabilistic tools on the numerical modelling of a roller compacted concrete (RCC) dam during its construction phase.The work developed here aims to propose a methodology so as to account for risks related to cracking during construction which may compromise the dam’s functional and structural behaviour.In order to do so, emphasis is given to uncertainties related to the material itself (i.e.strength, water-to-cement ratio, among others) as well as to ambient conditions during the construction phase of RCC dams. A thermo-chemo-mechanical model is used to describe theRCC behaviour. Concerning the probabilistic model, two aspects are studied : how the uncertainties related to the input variables are propagated through the model, and what is the influence of their dispersion on the dispersion of the output, assessed by performing a global sensitivity analysis by means of the RBD-FAST method. Also, spatial variability of some input parameters is accounted for through bi-dimensional random fields. Furthermore, a coupling between reliability methods and finite element methods is performed in order to evaluate the cracking potential of each casted RCC layer during construction by means of a cracking density concept. As an important outcome of this applied research,probability curves for cracking density within each casted layer as functions of both age and boundary conditions are predicted, which is believed to be an original contribution of this thesis. The proposed methodology may therefore be seen as a contribution to help engineers understand how uncertainties will affect the dam behaviour during construction and rely on it inthe future to improve and support the design phase of the dam project.

Passive safety systems are increasingly being utilized in prospective nuclear power plant designs. Indeed, the use of safety systems driven by natural phenomena might be seen as an unmitigated virtue. However, the low magnitude of the forces involved in such systems, combined with the uncertainty inherent in the factors which affect them, pose a problem in the assessment of their reliability when compared to their active counterparts. Hence, the purpose of this thesis is to investigate and apply a state-of-the-art technique in passive reliability assessment, known as the Reliability Methods of Passive Systems (RMPS) methodology, to the isolation condenser system (ICS) of the prospective BWRX-300 small modular reactor (SMR) design. The ICS is a safety system driven by natural circulation which provides emergency core cooling, residual heat removal, and pressure control for the BWRX-300. Using RMPS to analyze the effect that uncertainties in thermal characteristics of the fuel have on ICS operation, the reliability of natural circulation was quantified with a confidence of 99%. This yielded an immeasurably small failure probability. Considering residual uncertainty, an engineering judgment assigned a failure probability of 1.00E-07. This finding was integrated into a Level 1 probabilistic safety assessment, involving analysis of initiating events, event tree analysis, and failure mode and effect analysis (FMEA) of safety systems, including natural circulation. Analysis of sequences leading to core damage resulted in a core damage frequency of 1.23E-07 yr-1. / Passiva säkerhetssystem används i allt större utsträckning i innovativa kärnkraftverkskonstruktioner. Faktum är att användningen av säkerhetssystem som drivs av naturfenomen kan ses som en oförminskad dygd. Den låga storleken på de krafter som är involverade i sådana system, i kombination med den osäkerhet som är inneboende i de faktorer som påverkar dem, utgör ett problem vid bedömningen av deras tillförlitlighet jämfört med deras aktiva motsvarigheter. Därför är syftet med denna avhandling att undersöka och tillämpa en toppmodern teknik inom passiv tillförlitlighetsbedömning, känd som Reliability Methods of Passive Systems (RMPS) metodologi, på isolationskondensorsystemet (ICS) hos den potentiella BWRX-300 liten modulär reaktor (SMR) design. ICS är ett säkerhetssystem som drivs av naturlig cirkulation som ger nödkylning av kärnan, avlägsnande av restvärme och tryckkontroll för BWRX-300. Med hjälp av RMPS kvantifierades den naturliga cirkulationens tillförlitlighet med en konfidens på 99 %, vilket gav en omätligt liten sannolikhet för misslyckande. Med hänsyn till kvarvarande osäkerhet tilldelade en teknisk dom en felsannolikhet på 1.00E-07. Detta fynd integrerades i en nivå 1 probabilistisk säkerhetsbedömning, som involverade analys av initierande händelser, händelseträdsanalys och felläges- och effektanalys (FMEA) av säkerhetssystem, inklusive naturlig cirkulation. Analys av sekvenser som leder till härdskada resulterade i en härdskadafrekvens på 1,23E-07 år-1.

The thesis is focused on the statistical analysis of the continuity of power distribution in a specified part of the distribution network. Its aim is to explain the basic concepts and calculations in reliability distribution of electrical energy, which is an essential element for improving the quality of electricity supplied to end customers. The work is divided into two parts (theoretical part and a practical part), which are further divided into chapters and subchapters according to individual areas of focus. In the introduction the explains the aim and content of the of chapters work. You are also given a specific issue and its explanation. The conclusion summarizes the results of the practical part. The work is supplemented by annexes a list of images, tables, symbols and abbreviations that are used for better clarity and orientation.