Rocking and Sliding Motions of a Freely Standing Structure Coupled With Inner Structure

Many spent fuels coming out of the nuclear power stations are planned to be stored in the special site in Japan until they are reprocessed. In this site, the spent fuels are installed in a cylindrical container called canister. And the canister is installed in an outer cylinder called cask which is a free-standing structure. Therefore, it is very important to reduce the seismic response of the cask during a seismic event. In this study, the sliding and rocking motions of a cask are evaluated analytically. In an analytical model, the cask and the canister are treated as rigid bodies which are connected by a spring, because the cask and canister system is seen as a two-degree-of-freedom coupled system. The equations are derived for the sliding and rocking motions when the floor is subjected to a horizontal excitation. The displacement and the rocking angle of the cask are evaluated by numerical simulations. The effects of the canister vibration on the cask motion are discussed.