Microstructural analysis
Qualification for new graphite needs
Microstructural analysis for graphite qualification focuses on understanding how the structure of graphite affects its performance under reactor conditions. This includes assessing its initial (as-manufactured) microstructure and monitoring changes that occur due to irradiation, thermal stress, and mechanical loading.
Analyzing microstructural features
To support graphite qualification, advanced characterization techniques are used to examine microstructural features across relevant length scales, providing insight into fabrication-related variability and providing material response to service conditions.
High-resolution transmission electron microscopy (HR-TEM) is one technique used to examine microstructural features from the atomic to the nanoscopic scale and to support understanding of how fabrication history, thermal exposure, and irradiation influence graphite behavior.
The HR-TEM micrographs below illustrate microstructural changes observed in the nuclear graphite grade IG-110 following thermal annealing. These observations provide insight into the degree of graphitization, defect structures, and local crystallite morphology that can influence graphite performance under reactor conditions.
Please refer to Johns, et al. (2022) for more information.
Microstructural features such as these are evaluated to support the qualification of existing graphite grades and the assessment of new candidate materials as well as to inform interpretation of irradiation, oxidation, and mechanical performance data used in graphite qualification activities.
The edge of an annealed specimen where fullerene-like structures are abundant.
Evidence of a poorly graphitized phase.
The edge of a crystallite oriented perpendicular to the c-axis, where all basal plane edges have rearranged into faceted, closed structures.
A crystallite decorated with small, fullerene-like structures.