Abstract
Elevated temperature, gamma radiation, and geometric constraints inside dry storage casks for spent nuclear fuel represent a harsh environment for nondestructive inspection of the cask and require that the inspection be conducted with a robotic system. Electromagnetic acoustic transducers (EMATs) using non-contact ultrasonic transduction based on the Lorentz force to excite/receive ultrasonic waves are suited for use in the robotic inspection. Periodic permanent magnet EMATs that actuate/receive shear horizontal guided waves are developed for application to robotic nondestructive inspection of stress corrosion cracks in the heat affected zone of welds in stainless steel dry storage canisters. The EMAT’s components are carefully selected in consideration of the inspection environment, and tested under elevated temperature and gamma radiation doses up to 177 °C and 5920 krad, respectively, to evaluate the performance of the EMATs under realistic environmental conditions. The effect of gamma radiation is minimal, but the EMAT’s performance is affected by temperatures above 121 °C due to the low Curie temperature of the magnets. Different magnets are needed to operate at 177 °C. The EMAT’s capability to detect notches is also evaluated from B-scan measurements on 304 stainless steel welded plate containing surface-breaking notches.
Highlights
There are many cases where nondestructive inspection (NDI) of structures, such as pipelines and containers, needs to occur in harsh environments, including elevated temperature and radioactivity in the nuclear power industry
If it is determined that the resistance change has a significant effect on wave signal quality, it is possible that the impedance matching could be adjusted to a value that is optimized for the anticipated typical Electromagnetic acoustic transducers (EMATs) operating temperature
Temperature and radiation-tolerant EMATs have been developed for robotic nondestructive inspection of stress corrosion cracks in the weld heat affected zone (HAZ) of stainless steel dry storage canisters
Summary
There are many cases where nondestructive inspection (NDI) of structures, such as pipelines and containers, needs to occur in harsh environments, including elevated temperature and radioactivity in the nuclear power industry. They require a large normal force to produce sufficient frictional forces and tend to be highly sensitive to surface conditions of the substrate including surface roughness and surface debris These drawbacks of MSTs make practical application to robotic inspection of spent nuclear fuel storage canisters difficult. There is no need to apply a normal force to the transducer and they are significantly less sensitive to surface debris and surface roughness than MSTs. there is no need to apply a normal force to the transducer and they are significantly less sensitive to surface debris and surface roughness than MSTs For these reasons, EMATs were selected to generate/receive SH waves in the inspection of welded stainless steel canisters that store spent nuclear fuel.
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