Étude et modélisation des phénomènes de transport de matière couplés à la morphologie de la poudre lors de la pyrohydrolyse réduite du difluorure d'uranyle

Abstract : In France, the UO2 powder used for the manufacturing of fuel pellets is produced by a dry conversion process UF6 - UO2F2 - UO2. The reducing pyrohydrolysis of UO2F2 into UO2 is carried out in an inclined rotary kiln equipped with lifters. The main purpose of this work is to develop a model describing the morphological evolution of the powders in the rotary kiln, in order to have a tool for predicting the morphological characteristics of the UO2 powder according to the operating conditions. The first part of this work consisted in modelling the transport of the powder in the furnace and in describing the mass transfer between the dense phase (powder bed) and the dispersed phase (airborne particles). A strong feature of the model developed is its ability to take into account the role of the lifters for the calculation of the dynamical variables. The second part was devoted to identify, describe and couple with the preceding dynamic model the phenomena responsible for the morphological evolutions (Brownian agglomeration, agglomeration by differential sedimentation, presintering, fragmentation, chemical conversion by exnucleation or growth). By solving a population balance, the model predicts the granulometric evolution of the powder, for given values of the physical parameters that are characteristic of the various morphological phenomena. Results of dynamic and morphological calculations were compared with available measurements
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Stéphane Hébrard. Étude et modélisation des phénomènes de transport de matière couplés à la morphologie de la poudre lors de la pyrohydrolyse réduite du difluorure d'uranyle. Autre. Institut National Polytechnique de Lorraine, 2004. Français. ⟨NNT : 2004INPL005N⟩. ⟨tel-01777161⟩

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