Résumé
consist of ceramic pellets, such as UO2 or (U,Pu)O2, enclosed in a zircaloy cladding tube, leaving an initial gapbetween the pellets and the cladding. As the reactor operates and the fuel undergoes irradiation, both the ceramicpellets and the zircaloy cladding experience transformations, causing the gap between them to gradually close.This phenomenon has a significant impact on the thermomechanical behavior of the fuel rod.Understanding the nature of the bonding that occurs during irradiation is essential for ensuring the safe andefficient operation of the reactor. To investigate the evolution of the contact state between the fuel pellets and thecladding during irradiation, a detailed analysis of the pellet-cladding interface after irradiation is necessary.However, traditional examination methods might be destructive or incapable of providing the desired level ofprecision and resolution.The Institute of Electronic and Systems at the University of Montpellier (IES – UMR CNRS 5214), in collaborationwith the Alternative Energies and Atomic Energy Commission (CEA) and Electricit´e de France (EDF), hasdeveloped a specialized high-frequency acoustic microscope for imaging and non-destructively inspecting thepellet/cladding interface. The design of the acoustic microscope takes into account the complexity of the fuelrod’s structure and the challenges associated with imaging the pellet/cladding interface by utilizing highfrequencyultrasound.In this paper, we present the ability of this acoustic microscope to acquire 2D images with controlled displacementsof the sample rod along both its axial and circumferential directions thanks to a card with a highsampling frequency reaching 2 GHz. This capability is crucial because the geometrical, chemical, and mechanicalproperties of the fuel pellet-cladding contact are not uniform in these directions. By obtaining detailed acousticimages, we can identify specific regions where the fuel pellets and the cladding were in contact during irradiation.In this research, a resolution study is carried out to validate the microscope’s ability to investigate the fuelrod and achieve the desired resolutions.Testing on real samples requires a specific configuration of the microscope, which must be adapted to theirradiation conditions. This is why, before proceeding to this stage, it is necessary to carry out tests on representativesamples to validate the achievement of the desired resolution. So we’re also presenting the first acousticimages obtained on the zircaloy alloy claddings.