No abstract

We analyze the results of investigations of the in-service defects of heat-exchange tubes of steam generators of WWER reactors and the metal of pipelines and welded joints. The specific features of damage to heat exchangers and welded joints of the collectors with branch pipes of the bodies steam generators are analyzed. The causes of degradation of materials of the secondary coolant circuit are established. The directions of subsequent investigations aimed at increasing the reliability and duration of service life are outlined.The experience of operation of nuclear power plants (NPP) in the Ukraine shows that the unplanned shutdowns of WWER-1000 power-generating units often occur as a result of damage to the secondary coolant circuit and, in particular, due to the presence of corrosion defects in steam-generator and condenser units and in pipelines. In the process of aging of the equipment, these defects are encountered more and more often. From the viewpoint of technological processes running in the secondary coolant circuit, it can be regarded as a complex engineering structure. The heat carrier is in different states of aggregation. Various types of equipment are required to transform heat into the production of the working medium, i.e., steam. To make the thermal cycle closed, the secondary coolant circuit is equipped with condensers and heaters made of different materials satisfying the requirements imposed on their thermal and strength properties, namely, stainless and high-strength steels, copper, and copper alloys. The system includes a long branchy network of pipelines and steam lines, hundreds of types of regulating and stop valves also made from different metals and alloys. According to the design, the chemical composition of water used in this system must meet certain specific requirements in order to suppress corrosion processes. However, the number of events of damage in the secondary coolant circuit increases with the time of its operation, mainly in the units of steam generators.For many years, the National Scientific Center "Kharkov Physico-Technical Institute" (NSC KPTI) of the National Academy of Sciences of Ukraine in cooperation with the Ukrainian NPP have studied the in-service defects of the heat-exchange tubes of steam generators of WWER reactors, the metal of pipelines, and the weld metal [1][2][3][4]. An atlas of defects [5] created as a result of these investigations accumulates and systematizes the corresponding metallographic data and the results of eddy-current testing. The accumulated experimental results make it possible to solve numerous practical problems encountered in trying to extend the service life of pipelines.In the present work, we analyze the specific features of defects formed in heat-exchange tubes and welded joints of collectors with branch pipes in the bodies of steam generators (welded joints No. 111). For our analysis, we choose objects of various sizes used for different purposes and made of different materials. The aim of our investigations is to reveal the caus...

The test data for ring specimens from heat exchanger tubes without defects are compared to those for specimens with various types of defects. A relation between strength characteristics of the specimens and the nature and depth of defects has been clarified.

No abstract

No abstract