Detection method for crack developing speed of a heat-transfer tube of steam generator

The present invention provides a method capable of successively evaluating developing speed of various shaped cracks formed at various portions of a heat-transfer pipe of a steam generator in a nuclear reactor. Namely, an initial remained stress distribution of the heat-transfer pipe of the steam generator before occurrence of cracks is evaluated for every position. A stress extending coefficient, namely, a K value at each time for the development of cracks is determined for every position by using a three dimensional elastic-plastic analysis based on the evaluation values and the external force when an actual device is used. These K values are applied to a curve showing a relationship between the crack developing speed and a stress extending coefficient of the material of the heat-transfer pipe to determine the crack developing speed on every position of the heat-transfer pipe for various kinds of cracks. These data of the crack developing speed are stored. The state of the heat-transfer pipe to be detected is compared with the stored data to detect the crack developing speed of the heat-transfer pipe. (I.S.)