In a moderated and/or water-cooled nuclear reactor, a loss of cooling systems may result in partial or total melting of the core, which may then interact with any water present in the vessel or outside the vessel, as it happened during the Fukushima-Daiichi nuclear accident in 2011. The study of the interactions between corium and water is now a prerequisite for defining the source terms for radionuclides in the course of serious accidents that may escape from the containment by alteration and leaching, whether with residual water from the reactor or by a later voluntary injection of water or with environmental water. This requires a better knowledge of the crystallographic structures of coriums concretes incorporating fission products and their mechanism of interaction and release during contact with water.
In order to provide answers, this thesis project is part of an original experimental approach by combining structural and microstructural studies on prototypical coriums concrete in which stable isotopes simulating fission products present in corium have been introduced, to leaching tests. The materials based on siliceous and silico limestone concrete developed on the PLINIUS Platform of the CEA Cadarache, will be characterized at the LMAT laboratory of the CEA of Marcoule by the use of different techniques in surface analysis (MEB, EDS, WDS Castaing microprobe for elementary measurement of contents less than 1% mass). The study of phase formation in coriums concretes (segregation, crystalline and amorphous forms) can be conducted by crystallographic analysis performed by diffraction techniques at the SOLEIL synchrotron and by neutron diffraction at the ILL. Fine crystallographic analysis will implement the Rietveld method. The properties of the micro texture can be qualified on solid material and thin film by EBSD, TKD, DRX, and by Laue micro diffraction in the ESRF synchrotron. First leaching tests under oxidative conditions will be carried out with the LEMC laboratory of the CEA of Marcoule in parallel to the characterization campaigns in order to identify the main mechanisms of weathering. This knowledge will feed into a database of 'serious accident materials' useful for the management of coriums during the accident and beyond. The skills acquired by the doctoral student around the characterization of materials may be valuable for the doctoral student in many fields in materials science. The profile of the student will require knowledge of materials and instrumentation. The theme «serious accident» and interaction with water will also be of interest to the doctoral student in the field of environment and more particularly discharges.