HYDRIDE BEHAVIOR IN ZIRCALOY-4 DURING THERMOMECHANICAL CYCLING

Hydrogen ingress into zirconium alloy fuel cladding during operation in nuclear reactors can degrade cladding performance, both during operation and under dry storage, due to formation of brittle hydrides. At temperature and under stress, hydrogen redistribution and reorientation can occur, reducing cladding resistance to failure. Thus, it is crucial to understand the kinetics of hydride dissolution and re-orientation under stress and at temperature. High-energy and micro-beam synchrotron diffraction are used to study the kinetics of hydride reorientation and hydride distribution near a crack tip in previously hydrided Zircaloy sheet. Reorientation of hydrides in bulk samples is studied in situ (at temperature and under applied tensile stress). In-situ transmission diffraction data provides unique strain and orientation information on the hydrides. Micro-beam diffraction has been performed on previously cracked compact tension specimens under load. Measurement of the hydride distribution and associated strains can be performed with the micro-beam to determine hydrogen response to an applied strain field.