Increase in pyrolytic carbon optical anisotropy and density during processing of coated particle fuel due to heat treatment

Measurements of pyrolytic carbon optical anisotropy and density have been made on a series of tri-isotropic (TRISO) coated particles prepared for the United States Department of Energy’s Advanced Gas Reactor Fuel Development and Qualification (AGR) program. These measurements show the effect of varying the deposition conditions, especially the deposition temperature, on the density and optical anisotropy of the carbon layers. Additional heat treatment studies of the coated particles at various stages illustrate the strong effect of post-deposition thermal processing on these two pyrolytic carbon properties. Such post-deposition heat treatment occurs during SiC deposition and fuel compact firing, resulting in increased anisotropy and density of the pyrolytic carbon layers.