Grain boundary damage mechanisms in strained AGR cladding under irradiation

Second-generation Advanced Gas-cooled reactors (AGRs) make use of UO2 pellets contained in austenitic stainless steel SS 20Cr/25Ni/Nb cladding. During the service life inside the reactor, the cladding undergoes significant damage doses of its microstructure due to the constant neutron bombardment at temperatures that may vary between 350C and 700C. Neutron irradiation will generate additional vacancies and interstitials in the SS structure. Those radiation-induced defects will evolve over time and give rise to extended defects such as dislocation loops or channels, strain localization and radiation induced segregation. Those nano-micro scale changes in the SS structure will affect its mechanical integrity and its susceptibility to localised corrosion. In order to be able to potentially extend the lifetime of the AGR reactors and also to store the spent fuel cladding in the cooling ponds safely, we need to develop a thorough fundamental understanding of the radiation damaged SS structures, and how those sub-micron structures govern the possible failure mechanisms of the SS claddings.

The aim of the project is to elucidate the principal radiation damage mechanisms operating at the grain boundaries and their local environment, and to link those atomic-scale mechanisms to the structural integrity and potential localised failure phenomena of AGR stainless steel claddings. You will be based at the Dalton Cumbrian Facility, where you will irradiate SS cladding materials with the intense high-energy ion beams generated by our 5MV electrostatic accelerator. This will allow you to simulate neutron-damaged structures at controlled temperatures with limited activation of the samples. You will characterise the irradiated samples using the advanced characterization techniques available at the School of Materials and, in case of active samples, using the experimental capabilities available at the NNL Central Lab in Sellafield. This project will also give you the opportunity to perform in-situ synchrotron experiments at large scale facilities in the UK, France and Germany.