One of the degradation processes of zirconium-based nuclear fuel assemblies is irradiation-induced growth, an anisotropic, stress-independent, macroscopic deformation mechanism that elongates fuel cladding tubes axially. Irradiation-induced growth is driven by the irradiation-induced formation of dislocation loops, where the evolution of the loop structure can be complex, with the initial formation of loop generating transient growth, while the later formation of component dislocation loops, or loops, leads to accelerated growth. A full mechanistic understanding of loop nucleation is as yet unforthcoming. This thesis utilizes the diffraction peak broadening analysis software, named extended Convolutional Multiple Whole Profile, to study the dislocation structure evolution of neutron- and proton-irradiated zirconium alloys in order to validate proton-irradiation as a effective tool for the study of irradiation damage in relation to irradiation-induced growth. The diffraction profiles obtained exhibit unexpected features present in the tails of the Bragg peaks, tentatively attributed here to either strained regions of matrix, or diffuse scattering from severely distorted regions around nucleating precipitates, both originating from an increased solute concentration. The diffraction results indicate that the proton-irradiated samples exhibit qualitatively similar behaviours as seen from neutron-irradiation, such as a threshold irradiation dose before the formation of loops, however, a continued increase of loop dislocation density determined from peak broadening analysis is not observed by transmission electron microscopy. It is also shown that the Nb-containing Low-Sn ZIRLO® alloy has a lower dislocation density than the Nb-free Zircaloy-2 after the formation of loops correlating well with the relative irradiation-induced growth behaviours observed in- reactor. A correlation between a reduction in the loop dislocation density and the formation of loops is observed in Low-Sn ZIRLO® and Zr-1.60Sn-0.033Fe, providing support for the hypothesis that vacancy loops transform into loops. Zr- 0.61Sn-0.024Fe and Zr-1.60Sn-0.033Fe alloys show a rapid increase in the loop dislocation density in the initial stages of proton-irradiation, likely due to the low irradiation-resistance of the precipitates present in these alloys.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:722282 |
| Date | January 2016 |
| Creators | Seymour, Thomas |
| Contributors | Preuss, Michael |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/synchrotron-xray-diffraction-peak-profile-analysis-of-neutron-and-protonirradiated-zirconium-alloys(5765de34-361d-4a74-a9b0-22eb047dd6f3).html |
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