Project outline:
The properties of ceramic nuclear fuel, UO2, are crucial to the fleet of current and future nuclear power plants operating globally. Being the primary nuclear fuel, UO2 has been extensively studied through the years to determine its optimum design and enrichment to cope with high temperatures and degrading radiation environment. The PhD project will enrich the scientific basis of understanding the behavior of nuclear fuel by studying point-defect scale microstructure evolution in stoichiometric and non-stoichiometric depleted UO2 with added alloying elements.

Project objective:
The starting point for the work will be a systematic study on sintered hyperstoichiometric UO2+x, in which the introduction of extra O will have a significant effect on the amount of phases. The UO2 - U4O9 system has been extensively studied in the past yet it is expected that new information about the point defect evolution that drives the phase transformation will be obtained. The course of work will be expanded from the effect of hyperstoichimetry to the effect of additions, such as Gd and Th, and their effect on the phases in depleted hyperstoichiometric UO2+x.

The key topics of the study are listed below:

• The connection between local (PAS and XAS) and extended structures (XRD and TEM) in hyperstoichiometric depleted UO2+x.
• To determine how controlled amounts of additions (such as Th, Gd) modify the lattice and phases of depleted UO2+x.

The proposed work will use sintered polycrystalline depleted UO2+x samples fabricated at SCK-CEN. By controlled sintering conditions and post-processing experiments, the grain sizes and compositions of the pellets will be accurately determined. TEM and XRD examinations will take place at SCK-CEN. The PAS work will be carried out in co-operation with Aalto Univeristy, Finland, and XAS at the Soleil Synchrotron, France.

Requirements:
The applicants should have a degree in Physics/Engineering Physics/Nuclear Engineering/Materials Science. The optimal candidate would be familiar with transmission electron microscopy and have preliminary knowledge on advanced X-ray methods and/or positron annihilation spectroscopy.

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