DETERMINATION OF CHANGES IN MECHANICAL PROPERTIES OF METAL OF FEEDWATER PIPELINES BENDS AND “HOT” STEAM OF THE SECOND POWER UNIT OF PIVDENNOUKRAINSK NPP FOR THE SECOND 100,000 h OF OPERATION

An analysis of the results of periodic testing of hardness of metal of pipelines bends of power unit No. 2 of Pivdennoukrainsk Nuclear Power Plant (PNPP) after ~100,000 and ~200,000 h of operation was carried out. It is shown that during the operation of feedwater and “hot” steam pipelines during the second 100,000 h of operation, the aging of the metal is observed, which is manifested in a partial, at least in their surface layers, uneven decrease in the strength of the metal. An increased rate of aging of the metal of pipeline bends is observed in areas where the metal was subjected to the greatest plastic deformation during the pipe manufacturing process (compressed and stretched sides of the bends). The critical parameter among the normalized mechanical properties of bending metal is the tensile strength, which is the first to reach a critical level when extrapolating the obtained data. While maintaining the rate of change in the mechanical properties of the metal at the level of the second 100,000 h of operation for post-project operation, the projected residual resource of metal bends of feedwater pipelines and "hot" steam is ~590,000 and ~380,000 h, respectively.