Over 80% of the UK’s current nuclear fleet are graphite-moderated reactors. In addition to moderating the energies of neutrons in the fission process, the graphite core provides structural support, contains the fuel and control rods and allows for coolant flow. The graphite blocks are subject to high levels of neutron irradiation resulting in chemical and physical property changes, which in turn affect neighbouring reactor components. The lifetime of such reactors is therefore primarily limited by the performance of the irreplaceable graphite within the working reactor, so an accurate measure of its condition is essential for economic success and plant safety. This talk outlines the research which has been done to understand these mechanisms at a range of length scales.