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, Le caractère BE implique la prise en compte des sources d'incertitudes sous la forme de biais et de variance. Un cadre d'analyse d'incertitudes cohérent avec l'utilisation de modélisations BE a été développé pour bien prendre en compte ces incertitudes. On parle d'approche Best Estimate Plus Uncertainties (BEPU) et cette approche donne lieu à de nombreux travaux de R&D à l'international en simulation numérique. L'étude BEPU d'un transitoire multi-physique avec fort couplage comporte de nombreux dés tant en modélisation physique qu'en analyse d'incertitudes

T. Dans-cette, Éjection de Grappe de contrôle (REA-Rod Ejection Accident) dans un Réacteur à Eau Pressurisée (REP), on étudie la quantication d'incertitudes multi-physiques dans le cas d'un transitoire d

. Dans-la-première-partie-de-la-thèse, On utilise ces outils pour aborder certains de ces dés prélistés pour nalement développer une méthodologie de quantication d'incertitudes pour une modélisation multi-physique BE d'un transitoire REA. On met l'accent sur deux points: la prise en compte des sorties fonctionnelles et la réduction de la dimension des entres pour faciliter la construction des modèles de substitution. Pour le premier point, des indices Shapley agrégés ont été utilisés pour l'analyse de sensibilité globale, on examine diérents outils statistiques disponibles dans la littérature scientique dont la réduction de dimension, l'analyse de sensibilité globale, des modèles de substitution et la construction de plans d'expérience

. Dans-la-deuxième-partie-de-la-thèse, Un couplage Best Eort pour la simulation d'un transitoire REA est disponible au CEA. Il comprend le code ALCYONE V1.4 qui permet une modélisation ne du comportement thermomécanique du combustible. Cependant, l'utilisation d'une telle modélisation conduit à une augmentation signicative du temps de calcul du transitoire REA ce qui rend actuellement dicile la réalisation d'une analyse d'incertitudes à partir d'une approche Best Eort. Pour cela, une méthodologie de calibrage d'un modèle analytique simplié pour le transfert de chaleur pastille-gaine (Hgap) basée sur des calculs ALCYONE V1.4 découplés a été développée. L'incertitude du modèle est quantiée basée sur l'erreur de calibrage en prenant en compte l'incertitude de l'état initial. Le modèle calibré est nalement intégré dans la modélisation BE pour améliorer sa prédictivité sans augmenter le temps de calcul

, Les deux méthodologies développées sont maquettées initialement sur un c÷ur de petite échelle représentatif d'un REP puis appliquées sur un c÷ur REP à l'échelle 1 dans le cadre d'une analyse multi-physique d'un transitoire REA. Les conclusions des applications montrent que les entrées dominantes sont les paramètres neutroniques: sections ecaces et fraction eective des neutrons retardés. L'écart à la crise d'ébullition est très sensible à la modélisation du Hgap. En améliorant sa modélisation et sa quantication d'incertitudes entre BE et IBE, l'importance du Hgap est fortement diminuée. Finalement, on a utilisé la modélisation IBE pour propager les incertitudes et eectuer une analyse de sensibilité globale sur des sorties fonctionnelles 3D

. Mots-clés, Couplage Multi-Physique, Éjection de Grappe (REA), Best Estimate Plus Uncertainty (BEPU), Quantication d'incertitudes