Experimental Investigation into the Long-Term Seismic Performance of Dry Storage Casks
A series of eight shake table experiments were conducted to assess the long-term seismic performance of Dry Storage Casks (DSCs). Four scaled specimens were designed to cover a wide range of commercially available DSCs with emphasis on aspect ratios, the radius over the height of the center of mass (r/hc.g.). The aspect ratios were: 0.39, 0.43, 0.56, and 0.62. Three 1/2.5 scale shake table experiments were conducted using an anchored cask with the 0.43 aspect ratio. Of the three anchored cask experiments, two were conducted using stretch length anchors, one using the six-degree-of-freedom (6DOF) shake table and the other conducted on a biaxial shake table in the Earthquake Engineering Laboratory at the University of Nevada, Reno. The final anchored experiment was conducted using conventional length anchors and the biaxial shake table. Five freestanding cask experiments were conducted using the 6DOF shake table. The 0.39 and 0.62 aspect ratio casks had a scale of 1/3.5, while the 0.43 and 0.56 aspect ratio cask had a scale of 1/2.5. During the shake table experiments, casks exhibited a rock, slide, and/or rock-slide motions. Impacts between the concrete footing and cask can also result in a slide behavior. These motions turn into a precession and nutation motion, with or without sliding, when rocking about two or more directions simultaneously. Anchored casks resisted sliding and uplift, and the use of stretch length anchors provided more ductility and resilience when compared to conventional length anchors. A rock, rock-slide, and impact-slide response was seen for freestanding casks, but pure sliding behavior was rarely witnessed for freestanding casks. As the aspect ratio increases, the seismic response of the cask decreases. All casks, anchored and freestanding, showed acceptable performance during long-term seismic events as demonstrated by their generally small residual displacements after ground motions and their ability to resist tip-over during the experimental testing.
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