Corrosion of X18H9T steel after 25 years of operation in steam water environments of the VK-50 reactor

This paper presents the results from testing a VK-50 reactor measuring channel, removed from the reactor after 25 years of operation without signs of integrity loss. Metallography and electron microscopy as well as Auger spectroscopy of elemental composition were carried out. Intergranular corrosion is revealed in a base metal of the measurement channel tube at the core bottom level. A network of non-through, mainly longitudinal cracks of intergranular nature are located at the level of top and center of the core as well as directly under the reactor cover. The investigation results enable us to draw a conclusion that corrosion damage rate of the channel material depends on axial coolant density in the core. The neutron irradiation impact may be provocative but not chief factor for increasing the base metal sensitivity to intergranular corrosion and corrosion cracking. (authors)