Methods and apparatus for detection of crack initiation

Abstract

Methods and apparatus for detecting the onset of stress corrosion cracking are described. In one aspect, the present invention is a passive detector for in-situ detection of the onset of stress corrosion cracking in a nuclear reactor. The detector includes a ceramic insulator mounting member. A first material sample and a second material sample are secured to the mounting member. In the one embodiment, a metal bolt extends through the first and second material samples and secures the samples to the mounting member. The first material sample is cold worked to induce residual tensile stress and the second material is not cold worked. A first electrical conductor is electrically connected to the first material sample and a second electrical conductor is electrically connected to the second material sample. An electrometer is electrically connected to the first and second electrical conductors, and the electrometer is configured to generate a strain induced differential potential signal representative of a difference in potential between the first sample and the second sample. Alternatively, a strain induced differential current signal can be monitored using a zero resistance ammeter in place of the electrometer. The detector configured to be located within the reactor at the location where monitoring is desired, and during the reactor operation, if transients are observed in the differential signal, this condition indicates that at the location of the detector, an inspection should be performed at the next outage to determine whether cracking is occurring. Active detectors, detection methods, and test apparatus also are described.