The recycling of uranium and plutonium is a key challenge for closing the nuclear fuel cycle. It involves a stage based on a liquid-liquid extraction separation process, which consists of selectively transferring certain chemical elements from an aqueous phase to an organic phase. How do molecules organise themselves at the interface between these two phases to enable the separation of uranium and plutonium? This question is crucial for developing more efficient processes. This PhD thesis aims to understand, at the molecular level, how the structure of liquid–liquid interfaces controls the transfer of species between the two phases. The PhD student will develop molecular dynamics simulations and advanced computational methods to study various extraction systems, notably those based on monoamides and TBP. The objective will be to link the molecular organisation of the interfaces to the extraction mechanisms and to the thermodynamic and kinetic properties of the transfer, by comparing the simulations with available experimental data. Conducted at the CEA ISEC’s Laboratory of Actinide-Ligand Interactions, in collaboration with the Laboratory of Multi-Scale Theories and Methodologies at the Marcoule Institute of Separative Chemistry, this PhD research lies at the heart of the challenges facing the fuel cycle and the recycling of strategic metals. It will offer in-depth training in molecular modelling, physical chemistry, programming and scientific computing, within a multidisciplinary research environment and in collaboration with experimental scientists involved in process development. The PhD student, who will have a background in physical chemistry, theoretical chemistry or physics, and an interest in modelling, programming and scientific computing, will be encouraged to disseminate their scientific findings through publications and presentations at national and international conferences. The PhD will enable the candidate to acquire expertise in molecular modelling, physical chemistry, programming and numerical computation, with career prospects in academic research, research organisations and industrial R&D, particularly in the fields of nuclear science, materials and processes.