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Communication Dans Un Congrès Année : 2016

Studying fuel failure behavior with a micromechanical approach

Résumé

Under Lost Of Coolant Accident (LOCA) conditions, the temperature gradient evolution within the fuel pellets combined with a reduction of the cladding confinement can lead to fuel fragmentation. This phenomenon provides additional fission gas releases, inducing a higher rod internal pressure and possibly an additional driving force to disperse the smallest fuel fragments out of the cladding when the cladding balloons and bursts. Experiments show the pellets are fractured in many fragments, with size ranges varying from few millimetres to few microns. Usually the hypothesis used to explain fuel pellet fragmentation during transient, is grain cleavage induced by over pressurized fission gas bubbles, located at the grain boundary. This work pays particular attention to the pellet rim, where amount of bubbles increases owing to a higher irradiation level. This area, called “High Burnup Structure” (HBS), has a specific behaviour because of a microstructure reorganization composed of small grains about 100 nm compared to 10 μm for usual fuel. The aim of this study is to define a fragmentation threshold based on a micro mechanical approach to have a better understanding of the fuel mechanical behaviour. This paper introduces a stepwise micromechanical method: firstly, we detail how to model the HBS microstructure including pressurized porosities, based on experimental or numerical data and define a Representative Volume Element (RVE). Then we use 3D full field computations in order to define a crack map. Elastic computations are performed to identify the bubbles pressure level which is required to reach the cracks initiation threshold. Non linear computations, using a local law, are conducted to identify the failure modes. The latter will then be used as an input data to homogenize the RVE behaviour, the final objective being to extend the analysis from a microscopic scale to a macroscopic scale. Eventually, these results will be compared to those obtained directly with an another behaviour law.
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Dates et versions

hal-01474287 , version 1 (22-02-2017)

Identifiants

  • HAL Id : hal-01474287 , version 1

Citer

Coralie Esnoul, Rodrigue Largenton, Charles Pétry, Jean-Claude Michel, Bruno Michel, et al.. Studying fuel failure behavior with a micromechanical approach. The 12th World Congress on Computational Mechanics (WCCM 12), Jul 2016, Seoul, South Korea. ⟨hal-01474287⟩
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