Development and Applications of Laser-ultrasonic Testing in Nuclear Industry
A laser-based maintenance system, which includes the las er-ultrasonic testing as a non-destructive testing technology, the laser-peening as a surface stress imp rovement technology and the laser welding as a repair technology, for the in-service maintenance of n uclear reactor internal components is presented. Regarding the laser-ultrasonic testing, surface acoustic wave generated and detected by lasers is used to detect surface-breaking cracks. As the benefits of broad -ban feature of the laser-ultrasonics, this method allows to detect very small cracks having the depth of les s than 0.1mm. Also, a frequency response analysis technique of the surface acoustic wave, which propagates through the crack, is developed to size the depth of the crack. The error of this depth measurement thod is estimated at less than 0.2 mm through a series of experiments using stress corrosion cracki ng. A part of the laser-based maintenance system has been already applied to the actual maintenance works in Japanese nuclear power plants . The developed system and its operation are presented. Finally, m ore recent work to detect and visualize small defects on the weld bead by using leakly-Rayleigh waves is introduced.
Detection and characterization of discontinuities in stainless steel by the laser ultrasonic synthetic aperture focusing technique
The performance of a laser ultrasonic system applied to the detection and characterization of stress corrosion cracks and welding discontinuities in stainless steel is reported. A 50 mJ long pulse laser coupled with a confocal Fabry-Perot interferometer and the synthetic aperture focusing technique are used to enhance weak discontinuity related signals. First, stainless steel plates containing stress corrosion cracks with widths of less than 0.03 mm (1.2 × 10 -3 in.) and depths ranging from 0.5 to 5 mm (0.02 to 0.2 in.) are tested. Both longitudinal and shear waves are used in synthetic aperture focusing technique processing to detect and characterize these cracks from the surface opposite cracking. Images at the breaking surface reconstructed by shear waves provide very detailed structures of branched tight cracks, which are comparable to results obtained by liquid penetrant testing. This excellent imaging is linked to the presence of crosslike features appearing in B-scans that are interpreted and explained. Secondly, a welded stainless steel plate is tested and various weld discontinuities with sizes of about 1 mm (0.04 in.) are detected. Although the material strongly attenuates ultrasound in this case, laser ultrasonics combined with the synthetic aperture focusing technique successfully detects, locates and sizes these discontinuities. These results are compared with those obtained by X-ray computed tomography.
Mechanism of Action of Antibacterial Agents
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