The goal of the thesis is to develop the numerical model of a reinforced concrete mock-up allowing to associate a mechanical loading state with a realistic three-dimensional cracking pattern (path, aperture, roughness).The results provided by the model should be able to be used as input data for fluid mechanics simulations for the evaluation of leakage rates in severe containment accident conditions (simulations out of the scope of the thesis). This thesis will be based on the experimental results obtained in the framework of the COBRA program (french acronym for « containment of the reactor building in an accident situation » ) planned to start in 2021 on the MACUMBA platform, located on the IRSN (Radioprotection and Nuclear Safety Institute) site at the CEA (Atomic and Alternative Energy Comission) in Saclay. The PhD student will not participate directly in these tests. He will use the finite element code Cast3M, and the discrete element code DEAP developed at the LMT of ENS Paris-Saclay. Half of the thesis will take place at LMT (ENS Paris-Saclay), and the other half at LMAPS (IRSN, Fontenay-aux-Roses). The PhD student will be able to visit occasionally the MACUMBA test facility in order to attend tests and to exchange with the teams on site (SCA). He will rely on the LMT for problems related to the development of the numerical model and on the LMAPS for the post-processing of experimental results and the recalibration of the model. The PhD student will have to interact with the SCA to define the data necessary for this service for the computation of leakage rates. The start of the thesis is scheduled for October 2021, in parallel with the first tests. The duration of the thesis contract is 36 months.