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Spatialized study of the coupling between extended defects and mobile species in the nuclear fuel

Abstract : Fission gases (Xe, Kr) produced during irradiation in a nuclear fuel can contribute to significant effects such as swelling and fission gas release which may affect the overall performance of the fuel. The effective diffusion theory, which is generally used in the modelling of base-irradiation of nuclear fuel, cannot predict the intra-granular fission gas release during post-irradiation annealing tests. From the several scenarios proposed, we discuss and analyze three such mechanisms: the directed movement of pressurized intra-granular gas bubbles in a vacancy concentration gradient towards the grain surface, the Brownian movement of these intra-granular bubbles via volume and surface diffusion mechanisms, a scenario of gas bubble movement along with the dislocations via the mechanism of dislocation climb. A new spatially resolved model, BEEP Model, has been developed for gas bubble migration and its interaction with point defects. Analyses done using the BEEP model show that neither of the directed or random movement, nor their combination, could explain the large fission gas release obtained during post-irradiation annealing in our reference experiment. The dislocation climb mechanism has been demonstrated as a prominent gas release mechanism, however, the values for diffusion of vacancies on the dislocations are not known and were chosen to allow gas release. The work carried out in this thesis has provided a better insight to the transport of intra-granular gas bubbles and its impact on fission gas release. This work also emphasized the questions that need to be answered at the lower scales.
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Lokesh Verma. Spatialized study of the coupling between extended defects and mobile species in the nuclear fuel. Condensed Matter [cond-mat]. Aix Marseille Université, 2019. English. ⟨tel-02479378⟩

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