Non Destructive Inspection of Nickel Base Alloys in France

Nickel base alloys are commonly used in light water reactors because their properties for thermal exchange and also differential thermal expansion with carbon steels are good to very good. Unfortunately, the alloys 600 and 182 / 82 are sensitive to primary water stress corrosion cracking (PWSCC). The effect of the temperature is important and the crack propagation can increase significantly when it is above 320° C. All pressure water reactors use these alloys and most of them have been or are cracked depending of operating conditions, stress level of the materials and other parameters. Due to the fact these alloys are used for important parts of the primary systems for instance like vessel head penetrations or bottom mounted instrumentation, and also particular welds like dissimilar welds, in-service inspection has been developed to be able to detect, characterize and size IGSCC. In France, since the Bugey 3 VH penetration leakage in 1992, periodic reviews have been produced to understand the phenomena and propose adapted ISI. Firstly, on the areas where defects had been seen and secondly, on the other areas where a hazard was identified. The first category reviews the non destructive techniques applied on VH penetrations, BMI, dissimilar welds, SG channel heads. The second one reviews the case of RPV clevis and repaired zones in nozzles.Copyright © 2011 by ASME