On November 5th, 2015, Ben De Pauw has successfully presented his PhD thesis entitled "Experimental analysis of flow-induced vibration in lead-bismuth cooled nuclear fuel assemblies" during a public session. He demonstrated the accurate characterization of vibrations in the lead-bismuth cooled fuel assembly intended for MYRRHA – the multi-purpose hybrid research reactor for high-tech applications – using optical fibre Bragg gratings as vibration sensors and applying state-of-the-art modal analysis techniques to the measurements.
First, he identified the best applicable vibration sensing technique that complies with the application environment. He first showed that optical fibre Bragg grating sensors are the most adequate sensors that comply with all the environmental constraints imposed by the fuel assembly and liquid metal flow. He evaluated and demonstrated an unprecedented lifetime of fiber Bragg gratings for carrying out dependable measurements in liquid metals.
Second, he developed a robust vibration characterisation methodology that is applicable to vibrating fuel pins clustered in a fuel assembly and that can be applied in operational conditions. Based on a state-of-the-art modal estimator, the methodology significantly improved the estimation precision of modal parameters compared to conventional methods. Moreover and owing to this increased precision, he demonstrated for the first time the identification of coupled vibration eigen-modes in fuel assemblies.
Third and finally, he demonstrated the applicability of his method in an actual liquid lead-bismuth loop containing a fuel assembly mock-up. This PhD research impacted the multidisciplinary fields of optical metrology, operational modal analysis and nuclear engineering. Ben De Pauw established a set of tools required for follow-up research planned as part of the European Research and Innovation Action MYRTE – MYRRHA Research and Transmutation Endeavour.
The PhD has been supervised by Prof. F. Berghmans and Prof. S. Vanlanduit and involved research conducted in collaboration with SCK-CEN , the Belgian nuclear research centre.