Observations of crystal strains in filler and QI particles through TEM examination – Effect of processing and grain size

Nuclear graphite serves as a moderator and structural support in British Advanced Gas-cooled Reactors
(AGRs) and is a candidate for the next generation of nuclear reactors. Graphite is comprised of three main
phases: binder, filler and porosity; which are dependent on the manufacturing process and raw materials.
During the graphitisation process, graphite components are subjected to high temperatures which may
lead to significant strains and also creation of cracks known as Mrozowski cracks. Transmission electron
microscopy observations confirmed the existence of strain fields generated by Mrozowski cracks, manufacturing
and neutron irradiation in multiple graphite grades. This research confirms the existence of
crystal strains in filler particles and quinoline insoluble (QI) particles. The observations gathered in this
research indicate that crystal strains provide different degrees of rigidity to the filler and binder phase. A
comparison between crystal strains of QI particles and filler particles may explain the irradiation
response of these phases.