An investigation of the seismic response of a free-standing dry storage cask for spent fuel using the finite element method

In most spent fuel dry storage facilities, the storage casks are free-standing on a concrete pad. This leads to seismic stability concerns for the casks, in terms of their sliding and rocking. In this study, the seismic behaviors of the free-standing vertical cylindrical cask (VCC), which is widely used in existing dry storage facilities, are investigated. The explicit finite element code LS-DYNA was adopted to establish a 3D model of a free-standing VCC on a concrete pad that considered the frictional contact at the interface between them. Analyses of the seismic responses of the cylindrical cask at various values of the friction coefficient were performed. From the results, a borderline value for the friction coefficient, which differentiates the motion type of the cask at the onset of motion between sliding and rocking, was deduced, and it can be related to the ratio of radius to height of the cask. Additionally, the unfavorable nutation motion of the VCC, which usually follows the rocking motion and causes considerable horizontal displacement, is discussed. It can be concluded that the displacement potential of the VCC can be decreased by setting an appropriate friction coefficient to prevent this rocking motion during earthquakes.