Capability Development for Probing AGR Fuel Cladding Performance - Implementing In-situ Observations to Access the Effect of Strain and Corrosion

This PhD project is centred on developing capability for probing the performance of AGR fuel cladding subjected to applied strain and exposure to aqueous environment to support the UK Nuclear Decommissioning Authority (NDA) strategy for implementing extended wet/dry storage of spent advanced gas-cooled reactor (AGR) fuel.

The overarching goal is to provide a new methodology and confidence in probing miniature AGR fuel cladding samples, that can be transferred to hot cell working conditions on irradiated ex-service material. The Workington site provides access to a Deben 5KN miniature tensile rig and the unique set-up to simulate handling materials under hot cell conditions essential for this work. A set of manual straining rigs developed at Manchester and a similar miniature Deben rig (NNL) may also be accessed. The rigs will be interfaced with a range of characterisation techniques (e.g. Raman), allowing experiments to be carried out simulating different fuel storage scenarios.

This project provides: (i) new capability for in-situ straining, corrosion, and stress corrosion cracking (SCC) testing of AGR cladding, (ii) assess Raman spectroscopy as a potential tool for AGR fuel cladding inspection, (iii) provide transferable knowledge/skills critical for probing AGR cladding in a hot-cell set-up to meet NDA strategy.

The following key milestones will be addressed in this project: (i) A bench-top optical imaging system will be interfaced with these rigs to observe the cladding surface during straining for carrying out image correlation techniques. This will provide information about the distribution of surface strain. (ii) Application of Raman spectroscopy will be explored to assess the presence of NbC/NbCN precipitates, and their behaviour during the application of strain, and passive film characteristics. The latter will include probing the cladding surface before/after surface corrosion for exposing and dissolving these precipitates. NbC have been implemented to play a key role in the cladding degradation process. (iii0 A in-situ electrochemical cell (developed in a parallel NDA funded project) will be used for in-situ (stress) corrosion tests under electrochemical control to mimic wet pond storage conditions. (iv) The effect of minimal data on data quality will be explored with statistical means.