This project concerns the study of the mechanical response of cemented waste packages containing mainly graphite inclusions, as well as small quantities of metallic inclusions. In cementitious environments, these metallic inclusions are likely to corrode and form highly expansive products that could potentially lead to micro-cracking of the material. We propose to apply a multi-scale numerical approach to simulate the response of waste packages, taking into account the internal expansions associated with inclusion corrosion, as well as the early-age behavior and delayed strains of the cementitious matrix. This approach will be based on simulations of 3D representative elementary volumes of the material consisting of the matrix subject to cracking, the graphite and metallic inclusions, and the imperfect interfaces between inclusions and matrix. The effects of the shape and spatial arrangement of the inclusions and expansive phases on the mesoscopic response and on the initiation and propagation of microcracking will be investigated. These simulations will be used to characterize the macroscopic mechanical behavior of regions of the package with similar stress and strain states, determined using a clustering method. The long-term mechanical response of the packages will then be obtained by iterative calculations on both scales.
It should be noted that at the end of this work carried out in collaboration with Orano, the candidate will have acquired solid expertise in the fields of 1) modeling and analysis of the nonlinear mechanical behavior of highly heterogeneous materials; 2) development and application of 3D multiscale numerical methods and simulations of cracked structures.