Local Amorphization and Dislocation Interactions at Low Neutron Flux in NBG-18 Graphite

摘要

While graphite is known to get amorphized [13] under neutron irradiation, well-defined amorphous regions at rather low doses are somewhat surprising. The proclivity to rapid disordering and amorphization may stem from the pre-existing lattice disorder which can include cross-linking defects such as metastable Frenkel pairs and interplanar divacancies, and the attendant stresses from different phases of NBG-18 which arise from neutron irradiation. Thus in nuclear graphite grades the dimensional changes can be influenced by the formation and growth of localized amorphous regions, along with the stacking faults and dislocations which extend across the crystallites. The continued growth of amorphous regions can also be instrumental in formation of voids and porous regions at larger doses.