Using water pool as cushion to mitigate ground vibration due to collapse of cooling tower with simulation of complete debris distribution

Abstract : Large-scale cooling towers in inland nuclear power plants (NPPs) may collapse under extreme conditions. The collapse-induced ground vibrations threat the safety operations of the adjacent nuclear related facilities. Therefore, prediction and possible mitigation of the ground vibrations are significant in the NPP planning. This study proposed a novel method to arrange a water pool as a cushion underneath the cooling tower to mitigate the ground vibrations. The planar dimension of the water pool is determined by the debris distribution of the collapsed cooling tower. To achieve this, first, the mitigation effect was tested using a steel ball impacting on a concrete pedestal. Then, to obtain the complete debris distribution, a technique was developed to reproduce the disappearing elements in the finite element method-based simulation, and was validated against the tests of vase debris. Finally, the “cooling tower-water pool cushion-soil” models were established to demonstrate the vibration mitigation using the water pool cushion. For the concerned case with the water pool of 6 m depth, the vibration reduced by 56% and 59% for the maximum and average of the ground peak accelerations in the horizontal direction, as well as by 65% and 60% for those in the vertical direction, respectively.