As an important structural component in CANDU reactor, the pressure tube, made of coldworked Zr-2.5Nb, experiences a neutron flux under high pressure and elevated temperature during the reactor operation. Notches, existing as defects in the pressure tube, are usually the location where stress concentration and crack initiation happens, which seriously degrade the performance of the pressure tube. However, the concentrated stress at the notch area is expected to be relieved by thermal creep, reducing the possibility of crack occurrence. In this study, synchrotron X-ray diffraction experiments were conducted to collect the lattice strains near the notch in both irradiated and unirradiated Zr-2.5Nb samples which had experienced a thermal creep process for different time periods. Strain maps of the notch area were created for each sample. Stress relaxation over the time is discussed for both parallel and perpendicular to the loading direction and also compared between {10 -10} and {0002} orientations. A FE model was set up for the unirradiated materials, which was verified by the experimental results. This work provides an understanding of the stress relaxation near a notch in Zr-2.5Nb and the stress/strain distribution during the thermal creep, which provides valuable information on the assessment of the reactor operation. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-09-20 19:39:30.593

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