Sources of uncertainty in the seismic design of submerged free-standing racks

Free-standing racks are 5 m tall structures that store spent fuel removed from the nuclear power reactor on the depths of a spent fuel pool. Rack units are arranged on the floor of this 12 meters deep pool separated by only a few centimeters. Their response to an earthquake event is a troubling safety issue as they are in submerged and free-standing conditions. Such a seismic analysis deals with a highly nonlinear behavior, a transient dynamic response and a fluid-structure interaction problem. To overcome these difficulties in a cost-effective manner, the current analysis methodology implements the hydrodynamic mass concept in commercial finite element analysis software. However, some dispersion of results still exists in the application of this ad-hoc methodology. This paper reviews the seven major sources of uncertainty inherent to the current analysis methodology together with the main challenges of the seismic analysis.