An Understanding of Lattice Strain, Defects and Disorder in Nuclear Graphite

In this study, microstructural parameters, such as lattice dimension, micro-strain and dislocation density, of different neutron-irradiated graphite grades have been evaluated using the diffraction profiles of X-ray diffraction (XRD) and the scattering profiles of Raman spectroscopy. Using Gen-IV candidate graphite samples (grade PCEA, GrafTech), subjected to neutron irradiation at 900 °C to 6.6 and 10.2 dpa, and graphite samples of similar grain size and microstructure taken from the core of the British Experimental Pile Zero reactor, which have been irradiated at 100-120 °C to 1.60 dpa, an investigation on the effect of
irradiation dose and temperature on the aforementioned microstructural parameters is presented. Coefficients of variation for the lateral crystallite size, micro-strain and dislocation density, as acquired from XRD and Raman spectroscopy, are at approximately 13%, 17% and 38%, respectively. Quantification of microstructural parameters as a function of neutron dose
from the two complementary techniques are in agreement and imply that the quantified results are reasonable. Supporting evidence for the microstructural information obtained is provided by direct observations made using high-resolution transmission electron microscopy. Damage mechanisms are reviewed and discussed in relation to results presented.