CORROSION DAMAGE TO Kh18N9T STEEL AFTER 25 YEARS OF OPERATION IN THE STEAM-WATER MEDIUM OF A VK-50 BOILING-WATER REACTOR

摘要

The results of an investigation of the material used for the VK-50 measurement channel, which showed no signs of unsealing when it was extracted after 25 years of operation, are presented. The results of metallographic and electron-microscope investigations and Auger-spectroscopy determination of the elemental composition are presented. Intercyrstallite corrosion is found in the main metal of the measurement channel tube at the core-bottom level. A network of nonthrough, mainly longitudinal, cracks of an intercrystallite character, formed at the core-center and core-top levels and immediately under the reactor cover. The investigations show that the degree of corrosion damage to the channel material depends on the coolant density along the core height. Neutron irradiation can be a provoking factor but it is not the main factor making the main metal more likely to undergo corrosion cracking.