Progress is reported in several areas of development of fueled graphite containing coated particles for nonpurged gas-cooled reactor systems. The sol-gel process has been modified for making spherical particles of both thorium/uranium carbide and thorium/uranium oxide suitable for coating. Equipment has been assembled and methods have been developed for deposition of pyrolytic-carbon coatings under well-controlled conditions. Damage to coated particles during fabrication into a graphite matrix depends on the molding pressure and the volumetric content of coated particles. Vendor-supplied coated particles and fueled graphite spheres have been evaluated extensively in both in- and out-of-reactor tests. Duplex- and triplex-coated particles have excellent fission-gas retention at 2050 F to burnups of 15 at.%. Fueled graphite spheres containing coated particles have good irradiation performance, but the fission-gas-release rates are somewhat higher than for unsupported coated particles. Fueled graphite spheres react with water vapor about as rapidly as do Speer Mod-2 and ATJ grades of graphite. The diffusion rates in pyrolytic carbon are the same for uranium, thorium and protactinium. The diffusion rates in the direction parallel to the deposition plane are much higher than those in the perpendicular direction.