The widespread use of MOX fuels (based on (U,Pu)O2 mixed oxides) in nuclear reactors is an option currently being studied in France. Such a strategy could help to stabilise the plutonium inventory while conserving natural uranium resources. Such scenario involves the multi-recycling of plutonium, which requires an upgrade of the existing infrastructures to enable the reprocessing of spent MOX fuel at industrial scale. Consequently, the development of innovative processes and related basic research is then imperative.
The oxidation of MOX spent fuel by ad hoc thermal treatment could overcome a major technological barrier identified, i.e. how to separate the fuel from its cladding prior to the dissolution step. However, there is limited data available on the oxidation of (U,Pu)O2 and even less has investigated the impact of fission products and the fuel microstructure properties. The aim of this PhD thesis is to help fill this gap. The selected student will study (U,Pu)O2 samples with a microstructure identical to that of industrial MOX fuels, as well as (U,Pu)O2 doped with inactive fission products, thus simulating irradiated fuels, as shown in a thesis defended in the laboratory. The experimental work will focus on oxidation experiments coupled with in-situ and multi-scale analyses using laboratory technics and synchrotron radiation-based characterizations. These results will lead to the proposal of a phenomenological description linking the kinetics of (U,Pu)O2 oxidation with the fission products chemistry, the O2 partial pressure and the temperature and duration of the thermal treatment.
By the end of this PhD, the graduate student with a background in physical chemistry of materials will have developed expertise in a broad range of experimental techniques. These skills will open up many career opportunities in academic research or industrial R&D, both within and beyond the nuclear sector.