Sintering kinetics and mechanisms in UO2 and MOX nuclear fuels for LFR-SMRs
Small Modular Reactors (SMRs) are reshaping the future of nuclear energy, offering scalable, safe, and low-carbon solutions. Among these, Lead-cooled Fast Reactors (LFRs) stand out for their passive safety and efficient actinide management. The European EAGLES-300 initiative aims to commercialize a 350 MWe LFR-SMR by 2039, requiring advanced fuel technologies.
High-plutonium content (20–30 wt.% Pu/[U+Pu]) mixed-oxide (MOX) fuel materials which are required for LFR-SMRs present fabrication challenges. Conventional sintering methods, developed for light-water reactor MOX, are inadequate due to altered thermodynamic behavior. Optimal sintering parameters are essential but complex to define, especially under industrial conditions using continuous furnaces with variable atmospheres. Even minor deviations in oxygen potential can lead to out-of-specification fuel pellets. Furthermore, the fuel microstructure, density, porosity, and stoichiometry, which are vital parameters for in-pile performance and licensing, are critically influenced by the sintering conditions.
This PhD research aims to address these complexities, by investigating the sintering kinetics and mechanisms of UO₂ and high-Pu MOX fuel materials. The scientific objectives focus on characterizing powder properties and their influence on pellet formation, examining the effects of additives and manufacturing routes on fuel pellet microstructure, and investigating densification, grain growth, and sintering behavior through both batch and in-situ techniques. Ultimately, the goal is to improve our understanding on how sintering time, heating rate, and gas atmosphere collectively impact the final pellet quality.
The project will be conducted in SCK CEN’s fuel laboratories using powder metallurgical methods. Liquid-to-solid and thermal conversion techniques will be applied to produce uranium and plutonium precursors and oxide feed powders. Pellets will be fabricated by compacting powders using hydraulic or electromechanical presses, and sintering experiments will be performed, with specific attention to accurate temperature and gas atmosphere control. Solid-state characterization will involve optical and electron microscopy, particle size and surface area analysis, density measurements, and X-ray diffraction. In-situ techniques such as thermogravimetric analysis and dilatometry will be applied, complemented by microstructural examination using electron probe microanalysis.