As part of the post-Fukushima accident scenario, the qualification of a water-filled cylindrical tank subjected to tornado missile impact was required to ensure the availability of water inventory in the tank to mitigate the post-accident effects.

Most of the classical tornado missile impact analysis and design involves using empirical formulas that have been developed based on tests. It is recognized that water backed structures provide additional resistance to perforation of the missile due to the mass and properties of the water. Therefore, a finite element analysis was used to qualify the tank for two controlling postulated missiles, namely, 2 ½” diameter schedule 40 pipe and bolted wood decking.

The location on the tank for the missile impact, angle of impact and orientation of the missile were selected to develop the most critical response. The analysis was performed using the LS-DYNA computer program. The true stress-strain material properties were used for both the tank material and the missile types. These material properties were given a bilinear elastic-plastic curve.

It was determined that, even if an impact at the thinnest section at the top of the tank occurs and the missile penetrates, the remaining inventory of water in the tank will be sufficient to mitigate the needs for a post-Fukushima scenario. Impact on the lower elevation of the tank was investigated for any potential failure or tearing of the tank wall. The maximum of equivalent (Von Mises) stress, shear stress, and plastic strain were calculated. The results show that these values are less than the limiting values with additional available margin. Consequently the analysis shows that the tank will survive a hit in the lower portions, and the water inventory of the tank is sufficient to mitigate the effect of a post-Fukushima scenario should a missile penetrate the thinner, upper section of the tank.

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