The widespread use of MOX fuels (based on (U,Pu)O2 mixed oxides) in current nuclear reactors is an option being studied in France. Such a strategy could make it possible to stabilise plutonium stocks and conserve uranium resources. This scenario involves the multi-recycling of plutonium, which requires an upgrade of the existing plant to enable reprocessing of spent MOX fuel at industrial rates. The development of innovative processes and related basic research is then imperative.
Oxidation of MOX spent fuel by ad hoc thermal treatment could overcome one of the technological barriers identified, i.e. how to separate the fuel from its cladding prior to the dissolution step. The idea is to take advantage of the phase changes that occur as the fuel oxidises to collapse it into powder. However, data on the oxidation of (U,Pu)O2 oxides are currently scarce in the literature. The aim of this PhD thesis is to help fill this gap. The student in charge of this work will first have to characterise the nature of the phases formed during the oxidation of (U,Pu)O2 oxides, as well as the kinetics and mechanisms involved. These results will lead to the proposal of a phenomenological model linking the kinetics of (U,Pu)O2 oxidation with the Pu content, the O2 partial pressure, the temperature and the duration of the thermal treatment.
At the end of this PhD, the graduate student, with initial training in the physical chemistry of materials, will master a wide range of experimental techniques as well as advanced methods for modelling the reactivity of solids. These skills will open up many job opportunities in academic research or industrial R&D, both within and outside the nuclear sector.
Please note: A final internship is also offered in preparation for this PhD position. For further information, please contact the supervising team.