Modelling of fuel bundle vibration and the associated fretting wear in a CANDU fuel channel

Abstract

In this paper a numerical model is developed to predict the vibration response of a CANDU11CANDU® is a registered trade-mark of Atomic Energy of Canada Limited (AECL). fuel bundle and the associated fretting wear in the surrounding pressure tube. Two excitation mechanisms are considered in this model: turbulence-induced excitation caused by coolant flow inside the fuel channel, and seismic excitation. For the seismic excitation, simulated accelerograms of a magnitude 6 earthquake for the eastern part of Canada are considered. These accelerograms are compatible with the 2005 national building code of Canada uniform hazard spectrum (UHS). The numerical model can be easily adapted to include the effects of fuel bundle impact during the refuelling and start-up of the reactor, and the acoustic pressure pulsations caused by the primary heat transport (PHT) pumps. The simulation is performed for a typical CANDU fuel bundle with 37 fuel elements using INDAP, which is an in-house general purpose finite element program capable of simulating the nonlinear dynamics of nuclear and power equipment subjected to fluid excitation. The clearances between the buttons of the inner fuel elements, and between the bearing pads of the outer fuel elements and the pressure tube, were measured from a typical CANDU fuel bundle. Some variability among the measured clearance values was observed. Therefore, probability density functions of the measured clearance values were established and the simulation was performed for the probabilistic distribution of the clearance values. The contact between the fuel bundle and the pressure tube is modelled using pseudo-force contact method. The results, along with the proposed modelling technique, can be used in future CANDU reactors to avoid fuel and pressure tube fretting damage due to the aforementioned excitation mechanisms.