To improve the flexibility of civil nuclear reactors, many research programs are conducted by CEA in support of the French nuclear plants operator EDF and fuel fabricant FRAMATOME, specifically concerning the behaviour of fuel elements under irradiation.
The fuel elements consist of a metallic cladding and ceramic pellets. In case of power variations, the presence of a gap between the cladding and the pellets, and the bonding between them in case of contact, are fundamental for the mechanical strength of the fuel element.
To complete the current characterizations after irradiation of the pellet-cladding interface, the feasibility of a non-destructive method based on acoustic imaging has been studied and validated.
As a continuation of this first study, the objective of the thesis is to complete instrumentation of an operating measurement bench with the acoustic measurement chain. This bench is located in a cell which is dedicated to examinations of irradiated fuel elements.
The thesis work includes preparation and implementation of a qualification protocol of the acoustic chain, with images acquisitions on irradiated fuel elements. Acoustic signals processing will be developed to correct the effects of the external corrosion layer. Final expected results are images representing axial and azimuthal localization of the contact or gap between the cladding and the pellets, and the fraction of the bonding zones.
The PhD student will be based within IRESNE, an Institute of the CEA localized in Cadarache (in the south of France) which is specialized in the Research for Nuclear Systems for Low Carbon Energy Production. The work will take place in a nuclear installation which is equipped with various tools for multiscale characterization of the irradiated fuel from nuclear or experimental reactors.
This multidisciplinary work will be carried out in collaboration with a team from IES (Institute for Electronic and Systems - CNRS - Montpellier). This team is specialized in acoustic developments from probes to complete imaging systems.
Thanks to the resources and expertise of the two entities CEA and IES, the student will acquire solid skills in the fields of modeling, instrumentation and metrology. Results will be valorised in international publications and communications.