A Modeling Approach for Interlinked Feeder Pipes in CANDU^® Reactors

The feeder pipes of a typical CANDU^® reactor supply each of the 380 fuel channels with coolant and are individually connected to the large bore primary piping. In some designs, the longer pipes are interlinked with spacer rods, which mitigate vibrations and prevent contact between adjacent feeder pipes. Under severe loading conditions, the spacer rods will yield, which will prevent overstressing the pipes as the stiffness of the coupling gets reduced. Spacer yielding also provides increased damping for dynamic loads. It has recently become practicable to model the entire interlinked system in a single model. This paper presents the modeling approach for seismic analysis and for the fuel channel creep (a radiation induced slow unidirectional anchor motion). Results with and without spacer bars are compared to illustrate the effect of spacers. The importance of representing spacer yielding in the model is discussed.