Understanding thermophysical properties of nuclear fuels at various length scale
Understanding nuclear fuel performance under irradiation is of paramount importance for the safety of nuclear energy applications in the context of current reactors generation (LWR), future generation (fast reactors, SMR/AMR) and research/material test reactors. Nuclear fuels in reactor are exposed to harsh environment and many fuel behaviors are strongly connected to the properties of the material and their degradation. Within those properties, the study of thermo-physical properties is a critical aspect for the optimization and development of safer and more performing nuclear fuel forms.
The online measurement of fuel temperature during irradiation is virtually impossible and thermal conductivity is a difficult-to-access material property. As a result, only very limited data is available to predict the evolution of the fuel thermal conductivity with burnup for fuels.
SCK CEN recently installed a laser flash analysis (LFA) in hotcell environment in order to measure thermal diffusivity of irradiated materials. Using the LFA method, thermal diffusivity is extracted from the time–temperature curve, then converted to thermal conductivity if density and specific heat are known. However, for the research reactor fuel systems currently under investigation, LFA then gives the effective thermal diffusivity of the whole system, including the contributions of the different compounds (fuel, matrix, interaction layers, cladding, oxide layer) and the interfaces between them. To understand how these different compounds may affect the overall property, a microelectromechanical system – Thermal suspended bridge (MEMS-TSB) device is under development in collaboration with Université catholique de Louvain (UCL).
In general, the PhD topic is targeting the development of a systematic dataset of thermal conductivity evolution in nuclear fuel systems with an emphasis on research reactor fuel, and with the final goal to derive empirical relations for the evolution and assess the underlying mechanisms. The candidate will focus on the systematic measurement of thermal conductivity evolution with burnup in systematic series of samples available at SCK CEN using LFA and, if available, MEMS-TSB method.