Kazuhisa Furuta

Mitigation of Sliding Motion of a Cask-Canister by Fluid-Structure Interaction in an Annular Region

The cask-canister system is a coaxial circular cylindrical structure in which several spent fuels are installed. This system is a free-standing structure thus, it is very important to reduce sliding motion for very large seismic excitations. In this study, we propose a mitigation method for sliding motion. Water is installed in an annular region between a cask and a canister. The equations of motion are derived taking fluid-structure interaction into consideration for nonlinear sliding motion analyses. Based on these equations, mitigation effects of sliding motions are studied analytically. Furthermore, a fundamental test model of a cask-canister system is fabricated and shaking table tests are conducted. From the analytical and test results, sliding motion mitigation effects are investigated.Copyright

Effects of a Gyroscope in Reducing Rocking Motion of a Rigid Vessel Coupled With Inner Structure Subjected to a Base Excitation

Many spent fuels coming out of the nuclear power station 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. The canister, in tern, will be installed in the outer cylinder called cask that is a free-standing structure. When this system is subjected to strong seismic excitations, sliding or rocking motion will be induced. And, in the worst case, the cask may collide to each other or overturn. Therefore, it is very important to reduce sliding and rocking motions of the cask in order to avoid the consequent contamination of radio active substances. The authors have already reported the studies on the sliding and rocking motions of the cask subjected to a seismic excitation that contains a vibration system in it, and clarified the effects of the vibration of the inner canister. It was shown that the inner canister gives very large influences on the sliding and rocking motions of the outer cask. In this study, we applied a gyroscope at the top of the outer cask for reducing rocking motion of the cask. The effects of the gyroscope are studied for various excitation frequencies, excitation amplitudes and the structural dimensions of the gyroscope such as weight and rotational frequency. It is found that the gyroscope is very effective for reducing rocking motions of the cask-canister system subjected to seismic excitations.Copyright

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.Copyright