The fuel manufacturing lab of SCK•CEN is continuously striving for improvements in its pellet fabrication processes. High quality pellets are produced to meet various demands for fuel research.
Due to the complexity of the fuel pellet fabrication process described above, many parameters can have a distinct role in the final quality of the obtained pellets, which is essentially determined by the chemical purity, microstructure, thermal stability, pellet dimensions and pellet shape.
One parameter for the powder is particularly important: its specific surface area (SSA) (the total surface area per unit of mass). It will determine for the most part, how well a powder can be sintered (densification at high temperature) and its handling properties (flowability, compressability, agglomeration,…etc.). SSA is measured in a so-called BET (Brunauer-Emmet-Teller) analyser that relies the measurement of fine pressure drop caused by the adsorption of an atomic monolayer of a gas on the particle surface at low temperature (cooling by liquid nitrogen). BET analyser can in addition measure porosity in particles or solids (e.g. pellets) through multi-layer gas adsorption (gas molecules are then filling ‘holes’ in porous material).
SCK-CEN has recently acquired two BET analysers from Micromeritics (Gemini VII and Tristar II). They have slightly different working principles and options but should, in principle, provide consistent and reproducible results. It is proposed in this work to benchmark the performance of the two devices for the measurement of SSA using a range of standardized powders. Capabilities to measure porosity should also be investigated and compare to picnometry, an alternative technique available in the lab. Possible extension of the work could include the actual production of UO2 powders with different surface area to be measured by BET and that will serve as starting materials for other research projects.
All practical work will take place in the controlled area of the SCK•CEN where 2 brand new fuel laboratories have been reconfigured to accommodate all the infrastructure and safety precautions necessary for fuel pellet fabrication. The student will be able to work with modern, state-of the-art fabrication and characterisation equipment.