Seismic response of cylinder assemblies in axial flow

International audienceEarthquakes are a great challenge for the safety of nuclear reactors. To address thischallenge, we need to better understand how the reactor core responds to seismic forcing.The reactor core is made of fuel assemblies, which are themselves composed of flexiblefuel rods immersed in a strong axial flow. This gives rise to strongly coupled fluid–structureinteractions whose accurate modelling generally requires high computational costs. Inthis paper, we introduce a new model able to capture the mechanical response of thereactor core subjected to seismic forcing with low computational costs. This model isbased on potential flow theory for the fluid part, and Euler–Bernoulli beam theory forthe structural part, allowing us to predict the response to seismic forcing in presence ofaxial flow. The linear equations are solved in the Fourier space to decrease computationaltime. For validation purposes, first we use the proposed model to compute the responseof a single cylinder in axial flow. We then implement a multiple-cylinder geometry madeof four fuel assemblies, each made of 8 × 8 cylinders, corresponding to an experimentalfacility available at CEA. The comparison between numerical results and experimentsshows good agreement. The model can predict correctly the added mass. It can also capturequalitatively the coupling between assemblies and the effect of confinement. This showsthat a potential flow approach can give insight into the complex fluid–structure interactionswithin a nuclear reactor and, in particular, be used to predict the response to seismic forcingat low computational cost