9 Non-destructive Examination of Multiphase Material Distribution in Uranium Hexafluoride Cylinders. . . 87 Fig. 9.7 Scan results from bottom section of a UF6 5A cylinder excited at 175 kHz scan results. In future investigations, effort should be made to verify the fill profile and determine the extent of the welds’ effect on the scan results. One source of uncertainty was inherent to the LDV system. The resolution of the scan was dependent on the wavelength of the excitation waves induced in the object scanned by the piezoelectric transducer; the shorter the wavelength, the higher the resolution. However, exciting the transducer at higher frequencies produces a smaller response in the object, consequently decreasing the anomaly detection ability of the LDV system. The resolution of the scan is also limited by the power of the transducer; the more energy that is put into the object by the transducer, the larger the vibrational response measured. For larger objects that dissipate more energy, such as a larger UF6 cylinder, more powerful or a greater number of transducers may be needed to induce an adequate vibrational response for scanning. 9.4 Summary and Conclusions The steady-state ultrasonic laser Doppler vibrometer is a promising method for scanning UF6 cylinder profiles. The test scans were largely successful; as long as the material inside the cans or affixed to the back of the plates were well coupled to the outside surface, a satisfactory image could be obtained. The cylinder scans also showed positive results; they show a low wavenumber region in the area expected based on the hypothesized UF6 fill height. However, the scan results from the UF6 cylinders were made somewhat uncertain because the hypothesized fill height fell within the scan resolution of a weld on the cylinder. To conclusively identify the fill profile with this scanning system, the distance between the hypothesized fill height and the welds would need to be substantially larger. This study indicates that, given further investigation, this scanning system could be a useful tool for imaging UF6 cylinder fill profiles. Future experiments using laser Doppler vibrometer systems to measure UF6 distribution in cylinders should ensure that hypothesized fill heights are sufficiently distant from other distinguishable features given the known system resolution. On larger storage cylinders such as the 30B and the 48Y models typically found in enrichment plants, more scanning area is available that is free of complicating features such as welds. However, the thicker walls of these larger cylinders would likely dissipate more excitation energy, generating smaller wavenumber signal to noise ratios than thinner cylinders would.
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