Development of non-destructive inspection technique for microstructures under irradiation using austenitic stainless steel blocks

Ultrasonic testing was conducted on two long (218-245 mm), Type 304 stainless steel blocks with a hexagonal cross-section (50 mm face-to-face thickness) that were removed from the reflector region of the decommissioned EBR-II reactor. Ultrasonic testing is one of the widely used non-destructive testing techniques for material characterization. Ultrasonic waves, currently used as a non-destructive technique to detect cracks, change as a result of interacting with microstructural components and can be employed to measure radiation-induced changes in microstructure. The result of quantitative evaluation of the relationship between the microstructure and the ultrasonic signal have a good agreement between ultrasonic measurements and the spatial variations in density changes, as well as swelling arising from microscopy-observed voids. These results clearly demonstrate that ultrasonic techniques can be used to nondestructively measure the microstructures across a thick component. (author)