Performance of EMATs for robotic inspection of cracks in welded stainless steel canisters

The capability of electromagnetic acoustic transducers (EMATs) to detect cracks in stainless steel canisters is described within the context of robot-delivered nondestructive inspection (NDI) of dry storage casks for spent nuclear fuel. NDI of the canister must be performed remotely because of the limited access to the canister, which is enclosed by a concrete and steel overpack structure. Moreover, the environment inside the cask has both elevated temperature and gamma radiation. A potential canister degradation mode that could lead to issues with managing the spent fuel is chloride-induced stress corrosion cracking in the heat affected zone of full-penetration welds. Because access to the outer surface of the canister is limited by guide channels inside the overpack, ultrasonic guided waves are a natural choice for NDI. Shear horizontal (SH) waves sent and received from EMATs aboard a robot are shown to detect flaws in multiple canister mockups.