Dry casks are vertical reinforced concrete cylinders, which are used for the interim storage of spent nuclear fuel. The casks are freestanding structures and thus vulnerable to large horizontal displacements and/or rocking motions when subjected to seismic loads. Collision between adjacent casks or tip-over might occur due to excessive seismically-induced displacements, potentially leading to structural damage and release of radioactive material. In order to estimate the seismic risk to the vertical dry casks, the response of the structure to seismic loads and associated impact scenarios needs to be studied. Among various tasks required for the risk analysis, the focus of this talk is on the cask structural response to the seismic and tip-over loads and the associated numerical simulation of the problems in a commercial finite element program.
Virtual experiments are designed in both tasks by generating different cask-pad-soil configurations across typical ranges of structural, geometric, and material properties. Nonlinear time history response of the generated configurations subjected to seismic/impact loads is obtained by using validated 3D finite element models, and key structural responses are estimated. Employing stepwise regression, probabilistic seismic demand models are proposed for the maximum horizontal displacement and maximum rocking angle of the casks subjected to seismic loads, and metamodels are developed to predict the maximum strain of the canister and maximum acceleration of the concrete overpack in the tip-over scenario. The resulting probabilistic models are used in fragility and risk analyses, and the annual probability of large seismically-induced motions is evaluated for different locations in the United States. Similarly, the probability of the dry cask failure in a tip-over event is estimated, and recommendations regarding the design of vertical concrete dry casks are provided. Finally, the risk analysis results from the mentioned tasks are combined to estimate the overall tip-over failure probability, and ongoing/future work is mentioned briefly.
This study employs the cloud approach for the fragility and risk analysis, which typically requires significant number of numerical simulations. The talk demonstrates how HPC facilitates development and analysis of the numerical models, and how the NHERI’s DesignSafe cyber infrastructure and similar facility can be utilized to efficiently enable such studies.
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Majid Ebad Sichani is a PhD Candidate in the Civil and Environmental Engineering Department at Rice University. He obtained his Bachelor’s degree from Isfahan University of Technology in 2009 and his Master’s degree from University of Tehran in 2012, both in Structural Engineering and in his home country, Iran. Since starting his PhD program at Rice University in 2013, he has been studying the seismic risk to concrete dry casks structures, used for the storage of spent nuclear fuel.
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