This internship is part of a CEA project aimed at modeling and simulating the evolution of porosity in mixed uranium and plutonium oxide fuels used in fast neutron reactors. Understanding the behavior of these porosities is key to optimizing fuel performance and, in this context, one of the main objectives is to accurately assess the rate of porosity migration in the fuel.

To this end, one of the approaches taken by the teams in the CEA fuel research department (DEC) is to develop numerical simulation tools based on the phase field method to predict the behavior of manufacturing porosity.

This internship aims to contribute to the development of these tools by implementing a phase field model from the literature [1] in an HPC finite element solver [2]. The objective of this work is twofold: on the one hand, to better understand the modeling already published internationally to address this issue, while highlighting the limitations of these initial models. In a second step, the results obtained can be compared with those obtained by a new model developed by the supervising team. This comparison may also contribute to the optimization of the CEA phase field model.

By contributing to the development of a calculation tool, the student will acquire a wide range of skills, working on the following points:

• Physical modeling: the phenomena governing porosity migration will be described using the phase field method, which simulates the spatiotemporal evolution of a continuous interface between two phases, as well as heat transport.
• Numerical development: the equations will be implemented in the SLOTH HPC finite element code [2], dedicated to phase field simulations of the physicochemical evolution of materials.
• Analysis of the microstructural evolution of fuel under irradiation: the model will be used to study the evolution of the morphology of porosities during their movement
• Validation and applications: compare the model predictions with experimental data and other models available in the code.

The internship is offered at the research institute on nuclear systems for low-carbon energy production (IRESNE), based at the CEA Cadarache site. The institute conducts R&D activities on nuclear fuels with the aim of increasing the safety and performance of current reactors and developing fuels for future reactors. These activities combine numerical simulation/modeling and experimentation. A successful internship may be followed by a doctoral thesis within the host units.

[1] C. Liu et al., Nucl. Eng. Des. 425, 2024.

[2] https://github.com/Collab4Sloth/SLOTH