Conclusions of investigations on pulled tubes for the new steam generators

Based on the investigations of pulled steam generator tubes of PWR plants and on the NDE-results, an assessment is made of the secondary side stress corrosion cracking for the Inconel 600 tubing. The conclusion is especially focused on the new steam generators, equipped with more resistant tube materials. The cold shutdowns can accelerate the corrosion - initiation and propagation- and one of the possible explanations is the existence of electrochemical reactions with Cu and Pb, playing a catalytic role. These cycles are especially activated by oxidants during the shutdowns. High applied stresses can be exerted on the tube, which are probably due to the presence of deposits and sludge. (authors)