Abstract
Corrosion and hydriding processes occur as major degradation mechanisms in zirconium alloy fuel cladding in light water reactors. Although studies of nuclear cladding materials have examined the differences in hydride precipitation and location in different zirconium alloys, there is no definitive mechanism describing why the addition of 1% niobium in Zr-1%Nb alloys lowers hydrogen pickup, which prevents hydride precipitation that would otherwise be detrimental to in-reactor performance. This thesis provides a number of methodologies to continue the understanding of these mechanisms, in both ZIRLO™ and Zircaloy-4, through advanced correlative microscopy. Through the combined use of cutting-edge surface analysis techniques, these methodologies have been documented in the following work:1. The use of high-speed data acquisition in the Bristol NanoDynamics Ltd. HS-AFM to image Iodine Stress Corrosion Cracking (I-SCC), with the design and development of a procedure towards capturing I-SCC in-situ.
2. A methodology for correlative mapping of grain orientation and Work Function (WF) using Energy-Filtered Photoemission Electron Microscopy (EF-PEEM), allowing for large area WF mapping in an Omicron NanoESCA II, demonstrating the close link of WF to grain orientation in ZIRLO™, and leading towards the study between WF and corrosion potential.
3. Optimisation of the electrolytic hydrogen charging method, and NanoSIMS investigation into the differences in hydrogen absorption between secondary phase precipitates in Zircaloy-4, and grain-based hydrogen features in ZIRLO™.
4. The synthesising, and XRD/XRR and STEM analysis of a UO2/ZIRLO™ interface to study the pellet-cladding interface, providing an avenue for further research into the effects occurring at the interface, using very low activity samples.
The implications of the development of a correlative approach to microscopy techniques is that they can be applied to further research into materials and degradation mechanisms experienced within the nuclear industry.
| Date of Award | 22 Mar 2022 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Tomas L Martin (Supervisor) & Thomas Bligh Scott (Supervisor) |