Nondestructive evaluation of nuclear spent fuel dry cask structures using non-contact ACT-SLDV Lamb wave method

Abstract

Since 1986, the above-ground dry cask for spent fuel rods was employed to the Surry Nuclear plant as a temporary solution for high-level waste storage until a more permanent solution could be found. During the service of the dry cask storage, when the crack occurs, it will grow progressively as time goes on. This greatly threatens the safety of the multilayer dry cask structures. Ultrasonic Lamb waves have been shown as an effective nondestructive evaluation (NDE) method due to their ability to propagate a long distance with less energy loss as well as their sensitivity to various defects on the surface or inside the structure. In this study, the research was focused on the laboratory investigation of the nondestructive inspection of the multilayer structures using a fully non-contact Lamb wave method. The non-contact system was constructed using an air-coupled transducer (ACT) for actuation and scanning laser Doppler vibrometer (SLDV) for sensing. The ACT provided a narrowband wave actuation, while SLDV provided high-quality wavefield signals for damage detection and evaluation. To systematically develop the method for dry cask structure inspection, crack inspection in a simple 1-mm aluminum plate was first conducted; then crack inspections in more complicated multilayer structures were further carried out. Besides, to evaluate the crack inspection, two imaging techniques were further developed using a full-wave energy method and a scattered wave energy method for crack detection. The cracks in both simple aluminum plate and multilayer structures were successfully inspected.