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The assessment of the internal structural integrity of dry storage casks for used high burnup nuclear fuel assemblies is of critical importance before these are transported to permanent repositories. The size of the casks (5.2 m in height and 2.4 m in diameter), structural complexity and the inability to access the interior make this a challenging task. This project addresses these difficulties through a multi-modal approach involving nuclear, charged particle and acoustic methods. This paper reports on measurements of the vibrational spectra and mode shapes using a 6:1 scaled TN-32 model cask constructed in house. 2-D vibrometric scans were performed with a laser Doppler vibrometer to measure the vibrational mode shapes exhibited by the intact cask. Good agreement is observed between the experimentally measured mode shapes on both full-scale and scaled cask and those determined numerically using a detailed finite element model. Several modes identified will be important in assessing the internal characteristics from external measurements. Furthermore, compared to linear techniques, nonlinear responses acquired suggest higher sensitivity to changes in internal structure.

The assessment of the internal structural integrity of dry storage casks for used high burnup nuclear fuel assemblies is of critical importance before these are transported to permanent repositories. The size of the casks (5.2 m in height and 2.4 m in diameter), structural complexity and the inability to access the interior make this a challenging task. This project addresses these difficulties through a multi-modal approach involving nuclear, charged particle and acoustic methods. This paper reports on linear and nonlinear vibrational spectra of an unloaded full-scale TN-32 cask. These studies use both impulsive and swept continuous-wave excitations with a variety of sensor placement and cask configurations. From the resulting spectra, resonant frequencies, quality factors and harmonic responses of various vibrational modes were determined. A detailed finite element model of the TN-32 was constructed and the experimental results are compared to the modal structure determined numerically.

A band gap in the transmission spectrum of a finite two dimensional phononic crystal is examined in the time domain using pulsed ultrasonic fields. The phononic crystal consists of a hexagonal array of copper cylinders (r = 1.19 mm) in an aqueous matrix with a lattice constant of 2.9 mm. Measurements of the transmission properties of the sample are performed using ultrasonic wave groups of various center frequencies and bandwidths. Among the band gaps in the low-MHz range, we concentrate on the gap from 1.48 MHz—1.70 MHz. The phase velocity, group velocity, and attenuation coefficient spectra are determined and compared with expectations.