Measurement and modeling of micro residual stresses in pure zirconium and Zr-2.5Nb polycrystals
Abstract
In CANada Deterium Uranium (CANDU) nuclear reactors, Zr-2.5Nb alloy pressure tubes separate the hot water and cold moderator. Pressure tubes are susceptible to the diffusion of hydrogen from water and formation of a brittle phase called zirconium hydrides. The diffusion and formation of hydrides are affected by the state of stresses within the tubes. As such, it is of great significance to understand the source of the stresses that develop within the tubes. This thesis focuses on the characterization of the micro and nano scale residual stresses that develop in pure zirconium and Zr-2.5Nb polycrystals. With using three-dimensional synchrotron X-ray diffraction (3D-XRD) technique and crystal plasticity finite element (CPFE) modeling, it is shown in chapter 2 that the state of micro-residual stresses in pure zirconium is affected by grain size and the specimen texture. In chapters 3 and 4, the variation of microstructure and residual stress in a neutron irradiated Zr-2.5Nb CANDU pressure tube specimens are studied and compared to an unirradiated specimen. It is shown that the microstructure, texture, and the grain-scale residual stresses of the pressure tube vary as a function of the axial position along the pressure tube.