Structural Characterization of HTGR Pyrocarbon Fuel Particle Coatings

Four characterization techniques were used conjointly to assess the irradiation stability of propylene‐derived pyrocarbon coatings on fuel particles for the high‐temperature gas‐cooled reactor (HTGR). The resultant data further clarify the structural properties of the coatings. The characterization methods include oxygen‐plasma etching, small‐angle X‐ray scattering, optical anisotropy evaluation, and transmission electron microscopy. The results of the analysis of pyrocarbon coatings subsequently irradiated in the high‐flux isotope reactor are compared. The optimal microstructure in these pyrocarbons exhibits spheroidal growth features ranging in size from < 0.1 to ∼1 μm and a relatively homogeneous distribution of fine fibrous carbon around the larger growth features.