This thesis will be carried out at the Navier laboratory (navier-lab.fr) at the École des Ponts ParisTech (Champs-sur-Marne, close to Paris), with occasional travel in France as part of interactions with the project's partner laboratories (MADIREL and CEREGE in Marseille, PROMES in Odeillo, CEA Cadarache), and for the presentation of results at national and international conferences. The thesis will be funded by the CNRS as part of the ANR IMMOC project.

Concrete is widely used in the field of nuclear energy, in particular for the construction of reactor buildings and their protective components, such as foundation raft and reactor containment. It offers excellent mechanical performance under normal conditions of pressure and temperature. However, its microstructure and behaviour gradually deteriorate when subjected to increasing temperatures, as could be the case in major accident conditions where a mixture of nuclear fuel and molten metals, known as corium, can flow onto and damage the concrete. The IMMOC (Interaction of Molten Metals/Oxides with Concretes) project funded by the French National Research Agency (ANR), of which this thesis is part of, aims to understand the interaction of molten metals/oxides with the constituent elements of concrete at the microstructural scale and the associated damage mechanisms.

The thesis will focus on the experimental part of the project and will aim to characterise the damage kinetics of the material's microstructure when subjected to high temperatures (up to 800°C). This characterisation will be carried out using X-ray microtomography, which will make it possible to observe the evolution of the internal structure of the concrete and in particular to detect the networks of microcracks induced by thermal shock, and using nanoindentation to probe the local mechanical properties of the damaged material. Tests will be carried out on concrete specimens brought into contact with metal heated to its melting point and on others heated to different temperatures by an appropriate heating device. No radioactive materials will be used in this project. The thesis will cover both the development of experimental procedures using the laboratory's equipment (ex situ and in situ tomography tests, sample preparation, etc.) and the processing of the data obtained (3D image processing, in particular by image correlation, statistical analysis of indentation measurements), taking care to combine measurements carried out by microtomography and nanoindentation.

Candidates should have a Master's degree or equivalent in mechanics, materials science or civil engineering (or a related field), with a strong interest in experimental science and data analysis. Knowledge of image processing and/or programming languages would be appreciated. Applications should include a CV, covering letter and Master's transcripts.