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AbstractAbstract
[en] During the irradiation of nuclear fuel pellets, fission reactions lead to a progressive accumulation of new atoms, some of which are gaseous. These fission gases, and the bubbles they form, contribute significantly to the fuel's behavior, whether during operation in nominal conditions or in incidental or accidental cases. This Ph.D. work provides a better description of the fission gases' state at a micrometer scale of high burn up PWR UO2 fuels, thanks to experimental characterization campaigns and improved or new methodologies for data acquisition, processing and analysis. These campaigns were carried out in a high activity laboratory (LECA-STAR), with different microanalysis devices. Two types of fuels were examined, with different initial grain sizes and different burn-ups. The study was conducted along three main axes: morphology of the bubbles, thanks to 2D and mainly 3D FIB-SEM examinations, the microstructural evolutions, thanks to EBSD characterizations, and the quantification of the gases in order to estimate the pressure of the fission gases in the bubbles, by combining microprobe analysis, SIMS and SEM-FIB measurements. This work has allowed to establish new methodologies for fission gas and microstructure analysis. The combination of the results obtained in these different areas has led to a synthetic representation of the gas state, as a function of the radial position, the burn-up, and the initial microstructure of the fuel. This work will allow to enrich, feed and validate the calculation codes for the modeling of the UO2 fuel behavior at high burn-up. (author)
[fr]
Au cours de l'irradiation des pastilles de combustibles nucleaires, les reactions de fission entrainent une accumulation progressive de nouveaux atomes, dont certains sont gazeux. Ces gaz de fission, et les bulles qu'ils forment, contribuent significativement au comportement du combustible, en fonctionnement nominal comme en cas de fonctionnement incidentel/accidentel. Ce travail de these apporte une meilleure description de l'etat des gaz de fission, a l'echelle micrometrique et a fort taux de combustion, grace a de nouvelles campagnes experimentales de caracterisation et des methodologies, ameliorees ou nouvelles, d'acquisition, de traitement et d'analyse des donnees qui en resultent. Ces campagnes ont ete menees en laboratoire de haute activite, avec differents equipements de microanalyse. Deux types de combustibles ont ete examines, avec des tailles de grains initiaux differentes et des taux de combustion differents. L'etude a ete menee selon trois axes: la morphologie des bulles, grace a des examens 2D et 3D au MEB-FIB, les evolutions microstructurales, grace a des cartographies EBSD, et la quantification des gaz afin d'estimer leur densite dans les bulles, en combinant microsonde, SIMS et MEB-FIB. Ces travaux ont permis d'etablir de nouvelles methodologies d'analyse des gaz de fission et de la microstructure. Les resultats ainsi obtenus ont mene a la conception d'une representation synthetique de l'etat des gaz, selon la position radiale, le taux de combustion et la microstructure initiale du combustible. Ce travail va permettre d'enrichir, d'alimenter et de valider les codes de calcul de modelisation du comportement du combustible UO2 a fort taux de combustionOriginal Title
Les gaz de fission dans les combustibles REP irradies: un etat detaille a fort taux de combustion
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1 Jul 2021; 309 p; 113 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; Matiere Condensee et Nanosciences
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Report
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Thesis/Dissertation
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