| Summary: | Cracking from stress concentrations of the graphite neutron moderator, or keyway root cracking, is a potential limit for the lifetime of the UK Advanced Gas-cooled Reactors (AGR), and there is a need to better understand how damage occurs prior to fracture. Gilsocarbon graphite is a heterogeneous and quasi-brittle material, a class that includes concretes and natural materials such as bone. This project has made use of, developed, or participated in the development of advanced neutron and X-ray synchrotron techniques to improve the understanding of the deformation of Gilsocarbon graphite. In-situ High-Resolution Tomography and X-ray Diffraction Mapping has confirmed the non-linearity of graphite deformation in compression of a flattened disc and has highlighted the heterogeneity of the microstructure’s response to stress. To this extent, codes have been written to process and match the DVC and XRD strains and extract comparative strain quantities. A novel in-situ technique and associated post-processing routines have been developed with Neutron Bragg Imaging to investigate grain reorientation, and combined with In-situ Three-dimensional X-ray Diffraction (3DXRD) they reinforced indications that this mechanism is recoverable. In-situ High Speed Synchrotron Tomography provided unique time-resolved observations of crack initiation, propagation and coalescence away from a stress concentration, indicating the prevalence of lenticular cracks. With as much as 72 hours of beamtime, this project has developed reusable techniques and provided unique insight of the damage accommodation in nuclear-grade graphite.
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