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Artificial polycrystalline nuclear grade graphite is used for structural componentsas well as neutron moderators in nuclear reactors. South Africa is currentlydeveloping a Pebble Bed Modular Reactor (PBMR), which is a high temperaturehelium gas cooled reactor, based on earlier German experiences [1]. The core ofthis reactor type is composed of many graphite brick like components, whichserve as both an inner and outer reflector and a passive heat transfer medium.Internal shrinkage, changes induced by irradiation and thermal stresses generatedduring operation may lead to crack initiation in the brittle graphite from keywaycorners and other discontinuities. The structural integrity of the graphite, bestassessed by the fracture mechanics methodology, plays in important role as anydamage or cracking could leak heat or radiation to the core barrel and the outerpressure vessel shell, which may result in unsatisfactory consequences.