Étude cinétique de la nucléation et de la croissance cristallline au cours de la précipitation oxalique dans l'industrie nucléaire

Abstract : ln spite of an extensive use in chemical industry, most of precipitation processes are based on global and empirical knowledge. However, in the recent years, fundamental and phenomenological theories have been developed and they can be used to better understand the mechanisms of precipitation of plutonium IV oxalate, which is a significant stage of the irradiated fuel reprocessing. For this reason, appropriate methods were developed to study nucleation and crystal growth kinetics in a nuclear environment under a wide range of operating conditions. Each phenomena was studied individually in order to reduce the free parameters of the system. This study bears on the oxalates of plutonium and elements which simulate plutonium behaviour during the precipitation, neodymium III and uranium IV. A compact apparatus of a specific construction was used for nucleation measurements in accordance with the Nielsen's method. The state of the mixing was characterised at the reactor scale (macromixing) and at molecular scale (micromixing). The experimental results for the studied oxalates are in good agreement with the Volmer and Weber's theory. We propose primary nucleation kinetic laws over a wide range of operating conditions (temperature, non stoichiometric conditions, acidity ... ). An original method, using a high seed charge, was developed for the determination of crystal growth kinetics, in a batch crystalliser. The crystal growth rate is first order with respect to the supersaturation and the kinetic constant follows an Arrhenius type relation with activation energies of 14,29 and 36 klmor1 for respectively neodymium III, uranium IV and plutonium IV oxalates. The ove raIl growth process is surface integration controlled, with a screw dislocation mechanism.
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Theses
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http://docnum.univ-lorraine.fr/prive/INPL_T_1999_ANDRIEU_M.pdf
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https://hal.univ-lorraine.fr/tel-01750553
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Submitted on : Thursday, March 29, 2018 - 12:49:03 PM
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Murielle Andrieu. Étude cinétique de la nucléation et de la croissance cristallline au cours de la précipitation oxalique dans l'industrie nucléaire. Autre. Institut National Polytechnique de Lorraine, 1999. Français. ⟨NNT : 1999INPL132N⟩. ⟨tel-01750553⟩

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