A BEND THICKNESS SENSITIVITY STUDYOF CANDU FEEDER PIPING

摘要

In CANDU reactors, feeder bends close to the connection at the fuel channel may be subjected to thehighest Flow Accelerated Corrosion (FAC) and stresses. Feeder pipe stress analysis is crucial in the lifeextension of aging CANDU plants. Typical feeder pipes are interconnected by upper link plates andspacers. It is well known that the stresses at the bends are sensitive to the local bend thicknesses. It isalso known from the authors' study (Li and et al, 2005) that feeder inter linkage effect is significant andcannot be ignored. The field measurement of feeder bend thickness is difficult and may be subjected touncertainty in accuracy. Hence, it is desirable to know how the stress on a subject feeder could beaffected by the bend thickness variation of the neighboring feeders. This effect cannot be evaluated bythe traditional "single" feeder model approach. In this paper, the "row" and "combined" models developedin the previous study (Li and et al, 2005), which include the feeder interactions, are used to investigatethe sensitivity of bend thickness. A series of random thickness bounded by maximum and minimummeasured values were applied to feeders in the model. The results show that an individual feeder is notsensitive to the bend thickness variation of the remaining feeders in the model, but depends primarily onits own bend thickness. The highest stress at a feeder always occurs when the feeder has the smallestpossible bend thickness. A minimum acceptable bend thickness for individual feeders can be computedby an iterative computing process. The dependency of field thickness measurement and the amount ofrequired analysis work can be greatly reduced.