| Description |
Dry storage casks (DSCs) store spent nuclear fuel (SNF) at sites contiguous to nuclear power plants (NPPs), known as Interim Spent Fuel Storage Installations (ISFSIs). DSCs can be stored in concrete bunkers, or designed as free-standing or anchored structures. The primary focus of this study is to investigate response of free-standing DSCs under seismic excitation. Recent consideration of DSCs as a potential midterm solution may increase the operating period (initially 20 years) up to 300 years and requires response reevaluation. A longer compliance period results in larger accelerations, and larger vertical-to-horizontal spectral acceleration ratios that could have destabilizing effects on the cask response. The response of free-standing DSCs under seismic excitations is highly nonlinear, especially under concurrent sliding and rocking motion triggered by multidirectional seismic excitations. It depends on parameters such as aspect ratio, coefficient of friction between cask and foundation pad, and ground motion characteristics, among other factors. This research presents the investigation on the response of free-standing DSCs under long return period seismic events. Dynamic experimental tests were performed on a 6-degree-of-freedom shake table at the University of Nevada, Reno. Ground motions used for the tests were spectrally matched to spectral acceleration for seismic events of 10,000- and 30,000-year return periods. Experimental results were used to validate finite element (FE) models. The validated models were then be used to study casks’ response under full intensity long-term seismic event, tip-over spectrum under sinusoidal excitation and soil structure interaction (SSI). The research also addresses whether the response of DSCs is repeatable under identical ground motions. If the cask response has a relatively large variation (nonrepeatable), the analytical and FE models cannot directly capture this variation. Experimental tests on repeated ground motions showed that the dynamic response is not repeatable, which is the first indicator of chaos or extreme sensitivity to initial conditions. Numerical techniques for chaotic analysis were then implemented, for harmonic excitation, to show that DSCs’ motion is in fact chaotic for certain excitation conditions. This sensitivity was studied in FE models and analytical simulations by varying input parameters by ±1%. This small change resulted in large variation in the response. |
