ON THE MECHANISM OF DIMENSIONAL CHANGE OF NEUTRON-IRRADIATED GRAPHITE

In order to investigate the mechanism of large volume expansion of graphite due to neutron irradiation we have made in situ observation of damage structure of graphite with a high resolution transmission electron microscope (HRTEM). Both bending and randomizing the orientation of broken basal planes are proposed to be the origin for the large volume expansion of the irradiated graphite. It is also found that graphite easily loses its lattice ordering in the basal planes as demonstrated by halo rings in the (1010BAR) diffraction pattern, while hardly losing its layered structure, i.e., (002) spots are retained.