MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) is a flexible fast-spectrum research reactor under design at SCK•CEN, the Belgian Nuclear Research Center. MYRRHA is a pool-type reactor with Lead Bismuth Eutectic (LBE) as the primary coolant. Like many liquid metal reactor (LMR) designs, the MYRRHA fuel assembly (FA) design uses a helical wire-spacer to preserve the spacing between the individual fuel pins. The relatively long and slender structure of the fuel pin geometry may result in flow-induced vibrations (FIV) resulting from fluid-structure interactions (FSI). The knowledge and understanding of these vibrations is critical to estimate the possible impact of mechanical wear, such as fretting, on the structural integrity of the pin during its operational life.
Recently, SCK•CEN performed experimental testing of a full-scale 127-pin mock-up of the MYRRHA fuel assembly in flowing LBE, to characterise the FIV modal characteristics in the fuel assembly. While the experiments were successful in determining the modal frequencies and vibration amplitudes, accurate knowledge of the forces and the associated mechanical degradation is still missing. As such, the development of accurate simulation models for FIV are valuable to provide insight into the dynamic mechanical loading associated with the FSI in the FA.
The primary objective of this PhD study is to develop new coupled FSI modelling techniques to account for the possible contact between neighbouring fuel pins. By coupling the CFD code Fluent with the (Finite Element Analysis) FEA code Abaqus, dynamic overset meshing techniques (so-called Chimera techniques) will be developed to simulate the compact spaces between fuel pins and allow contact between pins. In doing so, these new modelling techniques will be applied to a multiple-pin MYRRHA FA geometry, to ultimately determine possible fuel pin impact loading for further fretting analysis.