Thermal Expansion of Graphite/Carbon Matrices and Fuel Compacts for HTGR

Coefficients of thermal expansion of graphite/carbon matrices and fuel compacts for a high-temperature gas-cooled reactor (HTGR) were measured using a quartz push-rod dilatometer in the temperature range100-700°C.Graphite/carbon matrices were prepared by mixing needle coke graphite powder or natural graphite-petroleum coke graphite powder with10or 20%of phenol resin followed by pressing and calcination.Fuel compacts were derived from these graphite/carbon matrices with coated particles dispersed in30to 40vol%.The thermal expansion of graphite/carbon matrices increased with increasing temperature and decreased with increasing phenol resin content.The thermal expansion of these matrices in parallel direction were larger than those in perpendicular direction.The matrices with needle coke graphite powder and10%phenol resin was the most anisotropic.Fuel compacts had the same tendency in thermal expansion as that of matrices and the coefficients of thermal expansion and anisotropy ratios of fuel compacts were smaller than those of the matrices.