In situ mechanical testing of nuclear graphite at elevated temperatures: Synchrotron x-ray tomography, neutron diffraction and Raman scattering

High temperature in situ tests of Gilsocarbon polygranular nuclear graphite have investigated the microstructure's deformation at two length scales. At the µm-scale, in situ bending tests observed by synchrotron radiation x-ray computed micro-tomography evaluated the bulk mechanical properties of flexural strength and fracture toughness and observed crack propagation at temperatures up to 1000°C; at the atomic-scale, neutron diffraction data correlated the lattice strain with bulk stress at temperatures up to 850°C. Raman scattering observations at temperatures up to 800°C showed the change of micro-scale residual strains. Gilsocarbon graphite was found to have a higher strength and fracture toughness with increased temperature. The mechanism leading to this behaviour has been attributed to the relaxation of residual strains