| 摘要 |
PURPOSE: To remarkably reduce the tensile stresses generated in heat exchanger tubes, by confirming the number of heat exchanger tubes having deteriorated parts which may cause leakage to the secondary side front the primary side, expanding parts of the end sections of the heat exchanger tubes having the deteriorated parts in the radial direction, and then, engaging the expanded end sections with the holes of a tube plate surrounding the heat exchanger tubes in leakage preventing states. CONSTITUTION: The number and positions of heat exchanger tubes 9 having deteriorated parts 17 which may cause leakage are decided by means of an eddy current probe. The maximum allowable leakage at the end section of each tube 9 is decided by dividing the general allowable leakage flow rate of 0.350 g/m by means of NRC by the heat of the heat exchanger tubes 9 having the deteriorated parts 17 and the length L, and radially expanding pressure P required for forming a leakage preventing section 21 which can achieve the maximum allowable leakage flow rate are confirmed. When the leakage preventing section 21 and the full-length section 22 of the tube 9 are actually expanded, the full-length section 22 of the tube 9 is first expanded by using Pmin obtained by analysis, and then, the leakage preventing section 21 is formed by expanding the section 21. The expansion of the full-length section 22 is performed so that an overlapping section may gradually increase toward the upper surface 3 of the tube plate 1 from the lower surface of the plate 1. |
