Impact Limiter Computer Simulation and Verification by Drop Tests

Abstract

Impact limiters are often used to protect equipment by minimizing the load inflicted to the equipment due to an impact or fall. This paper presents a computer simulation of a simple and effective impact limiter used in a storage cask carrying a Multi-Purpose Canister (MPC) containing nuclear spent fuel assemblies and compares the analysis results with the actual drop test performed for the prototype of the impact limiter. The impact limiter consists of an array of stainless-steel tubes with small holes in each to define and accelerate the collapse of the tubes following an impact. The small holes drilled at the strategically picked location on the tube ensures a very uniform tube collapse pattern and thus a well-controlled overall impact limiter behavior. The numerical simulation is conducted with computer modeling in LS-DYNA with appropriate geometric parameters and material properties. The behavior of the impact limiter tubes is captured by the true stress true strain curve of the material. The numerical analysis reveals how the tubes collapse due to an impact from a drop accident and what the collapse pattern looks like. The prototype test is conducted to verify the accuracy of the computer model, and the collapse of the tubes is observed and recorded using a high-speed camera. Both the measured impact limiter deformation and impact acceleration match well with the predictions by the computer model. This simple impact limiter device is extremely effective in absorbing energy and the required design objective can be reliably confirmed by computer simulation.