STRESS-DISTRIBUTION AND HYDRIDE ORIENTATION IN ZR-NB-CU GARTER SPRING UNDER COMPLEX LOADING

A garter spring of the tight fit design in a PHWR experiences three type of loads: an axial load due to spring tension, a compressive load due to coolant tube resting on it and a torus moment due to bending. The influence of these, on the hydride orientation in Zr-2.5Nb-0.5Cu garter springs has been studied by stress analysis and out-of-pile simulation experiments. The stress analysis showed that the magnitude of the stress is maximum at the surface and it decreases rapidly towards the core of the spring wire of rectangular cross section. This trend has also been observed in the experimental results. The preferred orientation of hydrides was found to be confined to the surface up to a depth of 300 mum. A random distribution of hydrides was observed at the central region where the stress was evidently below the threshold value for reorientation. Further a map of the planes of maximum principal stresses at the sur-face layer of the spring helix, constructed by stress analysis was found to be consistent with the observed hydride distribution. The diametrical compressive load did not show much influence on the hydride morphology in the range of 0-4 kg/turn under the axial load of 1 kg. It was also seen that the axial load of 1 kg imposed by the tight fit design did not significantly alter the hydride distribution which is primarily governed by torus bending.