By addition of hardener to phenolic resin binder, the mechanical properties of fuel matrices are improved. On the other hand, the irradiation-induced shrinkage as well as the anisotropy of the dimensional changes of these materials are increased, which can be compensated by the use of natural graphite with smaller grain size. 155. Resin fuel particles for high-temperature gas-cooled reactors* M. D. Silverman and C. B. Pollock (Metals and Ceramics Division, Oak Ridge National Laboratoy, Oak Ridge, Tennessee). Fuel kernels for HTGR's have been prepared from both strong-and weak-acid cation exchangers. Carbonization and heat-treatment studies conducted on these uranium-loaded resins have yielded kernels whose composition can be widely varied and correlated with theoretical predictions. 156. Structural changes and microporosity in pyrocarbon and graphite K. Koizlik, P. Krautwasser and H. Nickel (petite fer ~e~~~~~~, K~foyschu~~a~~ge Josh GmbH, W. Germuny). The change of microporosity in matrix material, graphite and pyrocarbon has been studied by X-ray small-angle scattering. During neutron irradiation, microporosity increases in graphite, in matrix material, however, an additional graphitization process reduces the concentration of small pores. During heattreatment, the anisotropy of crystallographic orientation increases. It could be shown that the process mainly responsible for the anisotropy increases is the stress-directed diffusion of thermally activated point defects. 157. Irradiation stability of carbon coatings on HTGR fuel particles* J. H. Coobs, C. B. Pollock, W. P. Eatherly and J. M. Robbins (Mean and Ceramics ~iv~~~, Oak Ridge h$&onalLaboratory, Oak Ridge, Tennessee). Two-layer carbon coatings were designed and a series of 4OOand 500~pm-dia ThO, particles were prepared such that some would fail during irradiation in HFIR to fast fluences ranging from 2 to 18 X 102' neutrons/cm 2. Correlation of results with calculated stresses, using reasonable creep coefficients, indicate that failures occur when creep stress exceeds 25,000 psi.