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Migration du deutérium dans le graphite nucléaire : conséquences sur le comportement du tritium en réacteur UNGG et sur la décontamination des graphites irradiés

Abstract : In France, 23 000 t of irradiated graphite that will be generated by the decommissioning of the first generation Uranium Naturel-Graphite-Gaz (UNGG) nuclear reactors are waiting for a long term management solution. This work focuses on the behavior of tritium, which is one of the main contributors to the radiological inventory of graphite waste after reactor shutdown. In order to anticipate tritium release during dismantling or waste management, it is mandatory to collect data on its migration, location and inventory. Our study is based on the simulation of tritium by implantation of approximately 3 at. % of deuterium up to around 3 μm in a virgin nuclear graphite. This material was then annealed up to 300 h and 1300 °C in inert atmosphere, UNGG coolant gas and humid gas, aiming to reproduce thermal conditions close to those encountered in reactor and during waste management operations. The deuterium profiles and spatial distribution were analyzed using the nuclear reaction 2H(3He,p)4He. The main results evidence a thermal release of implanted deuterium occurring essentially through three regimes controlled by the detrapping of atomic deuterium located in superficial or interstitial sites. The extrapolation of our data to tritium suggests that its purely thermal release during reactor operations may have been lower than 30 % and would be located close to the graphite free surfaces. Consequently, most of the tritium inventory after reactor shutdown could be trapped deeply within the irradiated graphite structure. Decontamination of graphite waste should then require temperatures higher than 1300°C, and would be more efficient in dry inert gas than in humid gas
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https://tel.archives-ouvertes.fr/tel-01128210
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  • HAL Id : tel-01128210, version 1

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Maël Le Guillou. Migration du deutérium dans le graphite nucléaire : conséquences sur le comportement du tritium en réacteur UNGG et sur la décontamination des graphites irradiés. Physique Nucléaire Expérimentale [nucl-ex]. Université Claude Bernard - Lyon I, 2014. Français. ⟨NNT : 2014LYO10227⟩. ⟨tel-01128210⟩

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