Influence of the modelling properties on the seismic response of free-standing spent fuel racks

Free-standing racks are metallic structures designed to store fuel assemblies in the spent fuel pool. Their seismic analysis deals with complex physical phenomena such as transient motion, inertial effects, dynamic contacts, fluid-structure interaction, water coupling, etc. The associated computational effort leads to cost-effective finite element models made up of simple elements: beams, masses and contacts. The modelling properties that describe the physical behaviour of such conceptual elements are uncertain and difficult to estimate. However, they have a certain impact on the computation of the rack response. This paper investigates the weight of the main modelling properties on computed outcomes focusing on sliding displacements and reactions on supports. The conceptual approach is supported with a statistical analysis of 100 simulations conducted in ANSYS Mechanical 14.0. A multivariate sensitivity analysis with scatter plots and variance-based methods is conducted over modelling variables including friction coefficients, contact stiffnesses, assumed fuel gaps, inertias, etc. Furthermore, some advises and rule of thumbs are provided for future designs.