STEAM GENERATOR HEAT TRANSFER TUBE INTEGRITY BASED ON LEAK RATE DETECTING

摘要

In nuclear industry, mainly two kinds of steam generator are used, that is U-tube steam generator and helical coil tube steam generator. The former is used in PWR with loop-type layout reactor coolant system, such as AP1000 and EPR, while the later finds its application in PWR with integral reactor coolant system, such as SMART and IRIS, and HTR. Whatever which kind tube structure is used, if it is too long or its bending radius is too small, application of the volumetric in-service inspection to the helical coil tube is difficult. This paper presents the state-of-the-art of study on the method to guarantee the integrity of the structure without using volumetric in-service inspection. The method uses tests and finite element analyses to determine the leak rate of a heat transfer tube with a crack of specific shape and dimension. Then the functional relation between leak rate and the crack size of a specific shape, such as an axial crack, can be found. Thus, after measuring the leak rate in an in-service inspection, the crack size of a specific shape can be deduced according to the functional relation above, and whether it is equal to the critical crack size can be judged. If not, the fatigue crack analysis software can be used to determine whether the crack propagates under the fluctuating stress cycles during the next in-service inspection interval, and the extended amount is obtained if the crack propagates. Then whether the structure is safe can be judged by comparing it to the critical crack size.