Reducing greenhouse gas emissions requires the development of low-carbon energy production systems, including nuclear power. The acceptability of nuclear power requires a high level of safety, and therefore in-depth knowledge of fuel behavior under irradiation to support the development of Scientific Computing Tools (SCTs). A key challenge for these SCTs is to enhance fuel performance, particularly in terms of flexibility with regard to the energy mix and behavior in design basis accidents.
Uranium dioxide (UO2), with its polycrystalline microstructure, is used as the constituent material of fuel pellets in nuclear power reactors. The mechanical behavior of UO2, coupled with irradiation effects, plays an important role in assessing the integrity of the fuel's first containment barrier. One of the challenges of understanding the mechanical behavior of irradiated fuel is to be able to compute the stresses and strains in the grains and at their interfaces with a physically based modelling at the scale of polycrystalline microstructural heterogeneities.
The main objective of the thesis will be to provide reference simulations in support of multi-scale modeling of the dislocation climbing mechanism, a major phenomenon underlying the mechanical behavior of fuel at high temperatures. The development of a coupling between a dislocation dynamics (DD) code and a finite element (FE) code will be carried out in order to best describe the diffusion and dislocation climbing mechanisms. Calculations based on this coupling will then be used to quantify the impact of dislocation climbing on the microstructure and viscoplastic behavior of UO2 fuel. Ultimately, this work will improve the micromechanical modeling using the finite element method implemented in SCTs of the PLEIADES simulation platform developed in the partnership between CEA, EDF and FRAMATOME.
This thesis will be carried out as part of a collaboration between CEA/IRESNE's DEC and Aix Marseille University's IM2NP. The DRMP at CEA/ISAS and the UMET at the University of Lille will also be involved in this collaboration. The thesis work will be carried out at IRESNE in Cadarache, within the Laboratoire de Modélisation du Comportement des Combustibles, in an environment providing access to a high expertise in multi-scale materials modeling. The research work will be promoted through publications and participation in international conferences in the materials field.