Effect of high-temperature neutron irradiation on the crystallites of graphite materials

Abstract

Changes in crystal lattice parameter, c-axis lattice strain and apparent crystallite height induced by neutron irradiation at 720–1350°C were investigated by means of X-ray diffraction for fourteen specimens which included five bands of nuclear graphite and two kinds of pyrolytic graphite. All irradiated materials show a marked increase in c-axis lattice strain, while changes in the lattice parameters are very small. The relation between lattice strain and layer spacing was analyzed for pre- and post-irradiated graphites, and it is inferred that, whereas the predominant constituent of strain in the unirradiated graphite is the statistical fluctuation in distribution of layer spacings, for the irradiated material it is the distortion of layer planes. On the basis of the relation between c-axis lattice strain and apparent crystallite height, the stacking height of graphite layer planes is estimated to be about 70 Å for pre-irradiated graphite.