Development of a nondestructive inspection method for irradiation-induced microstructural evolution of thick 304 stainless steel blocks

摘要

Ultrasonic testing was conducted on two long, Type 304 stainless steel blocks with a hexagonal cross-sec-tion that were removed from the reflector region of the decommissioned EBR-II reactor. One block had a dose range of 17-33 displacements per atom (dpa) and based on dimensional measurements exhibited a maximum of ~2% average density decrease across its thickness. The second block had a dose range of ~0.3-4 dpa, and exhibited smaller but positive range of density changes. Comparison of the ultrasonic measurements and the spatial variations in density change, as well as local swelling arising from voids and precipitates as determined by electron microscopy illustrate excellent agreement. Furthermore, this study clearly revealed that radiation-induced microstructural features produce measurable changes in elastic modulus and ultrasonic velocity. These results clearly demonstrate that ultrasonic techniques can be used to nondestructively measure the average swelling across a thick component.