Prediction of the local areas of CANDU feeder pipes highly susceptible to wall thinning due to flow-accelerated corrosion

Flow fields inside feeder pipes have been simulated numerically using a CFD (computational fluid dynamics) code to calculate the shear stress distribution which is the most important factor to be considered in predicting the local regions of feeder pipes highly susceptible to FAC (flow-accelerated corrosion)-induced wall thinning. The CFD approach with schemes used in this study to simulate the flow situations inside the CANDU feeder pipes has been verified by showing a good agreement between the investigation results for the failed feedwater pipe at Surry Unit 2 plant in U.S. and the CFD calculation. Sensitivity studies of the three geometrical parameters such as angle of the 1(st) and 2(nd) bends, length of the 1(st) span between the grayloc hub and the 1(st) bend, and length of the 2 rid span between the 1(st) and the 2(nd) bends have been performed. As the results of CFD analysis, it is seen that the local regions of feeder pipes of Wolsung Unit I in Korea, on which the wall thickness measurements have been performed so far, are not coincident with the worst regions predicted by the present CFD analysis where is the connection region of straight & bend pipe near the inlet part of the bend intrados. Finally, based on the results of the present CFD analysis a guide to the selection of the weakest local positions where the measurement of wall thickness should be performed with higher priority has been provided.