General Electric Company

Gary Paul Wozadlo

Samson Hettiarachchi

Thomas Pompilio Diaz

Robert L Cowan, Ii

Robert Lee Cowan, Ii

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.

Methods and apparatus for detection of crack initiation

A method for mitigating crack growth on the surface of stainless steel or other metal components in a water-cooled nuclear reactor. A compound containing a noble metal, e.g., palladium, is injected into the water of the reactor in the form of a solution or suspension. This compound has the property that it decomposes under reactor thermal conditions to release ions/atoms of the noble metal which incorporate in or deposit on the interior surfaces of the crack. The compound may be organic, organometallic (e.g., palladium acetylacetonate) or inorganic in nature. The palladium deposited inside a crack should exhibit catalytic behavior even if the bulk surface palladium is depleted under high fluid flow conditions. As a result, the electrochemical potential inside the crack is decreased to a level below the critical potential to protect against intergranular stress corrosion cracking.

Noble metal doping or coating of crack interior for stress corrosion

A method for mitigating crack growth on the surface of stainless steel or other alloy components in a water-cooled nuclear reactor wherein a solution or suspension of a compound containing a noble metal is injected into the coolant water while the reactor is not generating nuclear heat, e.g., during shutdown or recirculation pump heatup. During shutdown, the reactor coolant water reaches temperatures as low as 120.degree. F., in contrast to the water temperature of 550.degree. F. during normal operation. During pump heatup, the water temperature reaches 400.degree.-450.degree. F. At these reduced temperatures, the rate of thermal decomposition of the injected noble metal compound is reduced. However, radiation-induced decomposition also occurs inside the reactor. In particular, the noble metal compound can be decomposed by the gamma radiation emanating from the nuclear fuel core of the reactor. The noble metal compound decomposes under reactor thermal and radiation conditions to release ions/atoms of the noble metal which incorporate in or deposit on the oxide film formed on the stainless steel and other alloy components. As a result, the electrochemical potential of the metal surface is maintained at a level below the critical potential in the presence of low levels of hydrogen to protect against intergranular stress corrosion cracking.

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Los Gatos, CA, United States of America

Gary Paul Wozadlo