Fission products behaviour in UO₂ submitted to nuclear severe accident conditions

The objective of this work was to study the molybdenum chemistry in UO₂ based materials, known as SIMFUELS. These materials could be used as an alternative to irradiated nuclear fuels in the study of fission products behaviour during a nuclear severe accident. UO₂ samples doped with 12 stable isotopes of fission products were submitted to annealing tests in conditions representative to intermediate steps of severe accidents. Samples were characterized by SEM-EDS and XAS. It was found that Mo chemistry seems to be more complex than what is normally estimated by thermodynamic calculations: XAS spectra indicate the presence of Mo species such as metallic Mo, MoO₂, MoO₃ and Cs₂MoO₄. (paper)