ELECTROMAGNETIC ACOUSTIC TRANSDUCER (EMAT) DEVELOPMENT FOR NONDESTRUCTIVE INSPECTION OF SPENT NUCLEAR FUEL STORAGE CANISTERS

Stress corrosion cracking (SCC) is a potential degradation mode that could undermine the long-term integrity of stainless steel canisters for spent nuclear fuel storage. Due to limited accessibility and harsh environments, ultrasonic nondestructive inspection for the canisters demands robot deliverable and environmentally tolerant transducers. Development of electromagnetic acoustic transducers (EMATs) for remote ultrasonic guided wave SCC inspection of stainless steel canisters is described. These noncontact EMATs use transduction based on the Lorentz force. Among the infinite possibilities of guided wave modes and frequencies to select from, shear horizontal (SH) waves are chosen due to their favorable sensitivity to cracks oriented both parallel and perpendicular to the wave vector. The EMAT components (i.e., magnets, electrical coils, connectors, casing, and cables) are carefully selected and tested under high temperature and gamma radiation dosage. The performance of the constructed compact EMATs is evaluated by experiments on a 304 stainless steel plate containing machined notches. Specifically, the distances from which the EMATs can detect surface-breaking defects of minimal size are determined.