In Japan, about seventeen nuclear power stations are operating. The energy generated by nuclear power stations is about 30 percent of gross generated electric power in Japan. A lot of spent fuels come out of the nuclear power stations. The spent fuels are stored in a canister which is put in a concrete cask until reprocessed in the reprocessing facility. The cask is generically free-standing on a horizontal floor. Recently, the huge earthquakes frequently arise, so it is necessary to prevent

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... cask from overturning and the canister from breaking when an earthquake occurs. In this study, the caskcanister system is considered as a dual structure. The structure is freely standing on the floor. We analyze sliding and rocking motions of the structure subjected to a horizontal earthquake excitation.