High-power laser heating is an experimental technique developed within the Fuel Study Department that allows the induction of thermal transients on nuclear ceramic samples. It notably makes it possible to reproduce, at the laboratory scale, the thermomechanical conditions representative of an incidental or accidental sequence, in order to study fundamental mechanisms such as fuel cracking or fragmentation.

Indeed, in certain situations, such as a thermal transient of the Reactivity-Initiated Accident (RIA) type, fuel fragmentation (or over-fragmentation) can lead to the release of fission gases and ultimately result in the rupture of the fuel rod cladding.

This type of transient is particularly characterized by a complex spatiotemporal evolution of temperature within the fuel, which is difficult to reproduce at the laboratory scale. To date, only high-power laser heating techniques make it possible to replicate the heating rates reached during such transients and to reproduce the thermomechanical conditions of an RIA at the scale of a manipulable sample in the laboratory.

In this context, the PhD project aims to provide experimental data related to fuel fragmentation and over-fragmentation under Reactivity-Initiated Accident conditions. To achieve this, the student will be required to improve and develop the existing experimental setup and perform experiments aimed at reproducing the thermomechanical conditions leading to fuel fragmentation. A combined experimental/modeling approach will be necessary to optimally design and interpret the experiments. The data obtained will be used to validate the fragmentation models developed at CEA and should also allow projections for integrating these experimental techniques into shielded cells.

The PhD will be conducted within a collaborative framework (CHAIRE MATLASE) between LAMIR (Laboratory for the Analysis of Radionuclide Migration) within the Institute for Research on Nuclear Systems for Low-Carbon Energy Production (IRESNE) at CEA Cadarache, and the ILM team (Laser-Matter Interaction) at the Institut Fresnel in Marseille. The latter will provide expertise in high-power laser/material interactions and optical instrumentation for the development of the system and complex optical diagnostics.

This environment will allow the doctoral student to work in a stimulating scientific setting and to disseminate their research both in France and internationally, through conferences and publications in peer-reviewed journals.

[1]M. Reymond, J. Sercombe, L. Gallais, T. Doualle, and Y. Pontillon, ‘Thermo-mechanical simulations of laser heating experiments on UO2’, Journal of Nuclear Materials, vol. 557, 2021, doi: 10.1016/J.JNUCMAT.2021.153220.
[2]M. Reymond et al., ‘High power laser heating of nuclear ceramics for the generation of controlled spatiotemporal gradients’, J Appl Phys, vol. 134, no. 3, p. 33101, Jul. 2023, doi: 10.1063/5.0146541.
[3]Hugo Fuentes et al., ‘Numerical and experimental simulation of nuclear fuel fragmentation via laser heating of ceramics’, TopFuel 2024. Accessed: Oct. 02, 2025. [Online]. Available: https://www.researchgate.net/publication/386167297_Numerical and experimental simulation of nuclear fuel via laser heating of ceramics