Impact of analysis parameters on the seismic response of free-standing spent fuel racks

The computation of the rack seismic response requires an implicit transient analysis with numerical integration of the differential equation of motion. It involves the solution of thousands of time steps throughout the whole earthquake duration. A series of Newton-Raphson trial iterations seek to establish equilibrium within a certain tolerance at each calculation step. The parameters related to such analysis are decisive in the computation of robust and accurate results. This paper carries out a ‘one-factor-at-a-time’ parametric analysis of six key analysis parameters for a simple two-rack system: maximal step size, maximal number of equilibrium iterations, convergence tolerance and Rayleigh and algorithmic damping. This technique examines the impact on the main transient outputs when an analysis parameter is systematically varied while the others remain at their nominal value. Numerical results provide a source of insight into the uncertain seismic response of the rack system and an effective tool to propose an efficient trade-off regarding the computational cost.