Prediction of the in-reactor deformation of Zr-2.5wt%Nb pressure tubes using the crystal plasticity finite element method framework

Abstract

To predict the irradiation induced deformation of the pressure tube material in Canada Deuterium Uranium (CANDU) reactors, a deformation model based on the crystal plasticity finite element method framework was developed in this study. Based on the principle of superimposition, three deformation mechanisms—thermal creep, irradiation growth, and irradiation creep—were incorporated into the model. The model parameters were optimized and verified using in-service inspection (ISI) data from Korean CANDU reactors by considering the irradiation effect on deformation mechanisms and the influence of incompatible grain interactions. We found that the model with optimized parameters could successfully describe the results of not only the pressure tube ISI data but also the simulated mini capsules experiments in a test reactor. By analyzing the optimized irradiation creep parameters and results, the possibility of diffusion-base mechanisms was elucidated and the anisotropy in the activation energy terms along the tube directions was confirmed. For predictions using the model, three strategies for extracting the optimized parameters from available measurement data were examined. As a result, we found that, the better prediction ability can be achieved when only the latest data measured at the same reactor before the predictions are used to optimize the model parameters (method 3).