The graphite matrix material to be used in the South African Pebble Modular Reactor (PBMR) is a composite comprising natural graphite, electrographite and phenolic resin binder. This material is used to encapsulate the TRISO coated UO2 fuel particles, serves as a neutron moderator as well as heat conductor. In this paper, the raw materials used in the manufacture of the graphite matrix of the pebbles are characterized for their microstructure by Raman spectroscopy and X-ray Diffraction (XRD) to evaluate their extent of graphitization. Their oxidation stability is tested by thermogravimetric analysis (TGA). The optical microscopy (OM) is used to study the distribution of different phases, to evaluate cracks, pore locations, and fissures in the fuel-free graphite matrix pebbles received from supplier. The morphology of the raw materials as well as the pebbles is studied by scanning electron microscopy (SEM). There are three types of pebbles studied, i.e. green, carbonized (950 °C) and annealed (1800 °C). The densities and porosity of the pebbles are evaluated as a function of their heat treatment temperature (HTT).
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