Dynamic behavior of liquid storage tanks

Fluids which have an essential contribution to the safety of nuclear reactors, such as borated water or auxiliary feedwater, are stored in large storage tanks. Typical dimension of these tanks are 2 to 3 meters diameter, 3 to 4 meters height, 0,5 to 5 mm thickness. The designer of these tanks has to take into consideration seismic ground motion and to verify that a safe margin exists between design earthquake and the level of earthquake excitation which would lead to buckling (main failure mode for large thin-walled structure) and, therefore, potential fluid leakage. In order to carry out this verification for French PWR reactors, FRAMATOME and CEA have completed a research and development program aimed at better understanding the behavior of liquid storage tanks under dynamic loading, and more specifically seismic ground motion. This program includes the following steps : Experimental investigation of two thin-walled tanks filled with water, on a shake table, using sine sweep and simulated earthquake excitation. Dimension of these tanks are : 0.95 diameter, 2 m height, 0.5 mm wall thickness. These dimension are not directly scaled down from a particular tank but are representative of typical height over diameter and thickness over diameter ratios found in reactor storage tanks. They also exhibit shape defects which are commonly found for large tanks when expressed in term of defect amplitude over thickness ratio. Experimental modal analysis of the same tanks, filled with water, prior to the shake table test and comparison with prediction calculation. Calculation of the level of table acceleration leading to tank failure for the shake table test configuration, using non linear buckling analysis, and comparison with test results.