Porous carbon vas studied for use as an inner sacrificial layer in two-layer, pyrolytic-carbon coatings on UC2, in attempts to develop particles with improved, stability at 2500 or 2600°C for use in fuel elements for Rover reactors. Four types of migration-resistant pyrolytic carbons were characterized for use as the outer layer. Particles with the various two-layer coatings on carbon-bed UC2 cores and on General Atomic experimental UC2 cores with a complete graphite shell were prepared and tested. Only the particles with the General Atomic cores bad interesting stabilities when the total coating thick¬ness was about 50μ, as required for the particles tc have useful uranium contents. The best particles in the useful category had no more, than 3% of the total uranium exposed by testing for 50 min at 2500 or 2600°C after pretreatment at 2300°C for 4 h to reorganize the outer layer of pyrolytic carbon and subsequent cooling. However, ways were not found to obtain particles in good yield with the required 15- to 25-r-thick porous layer having good uniformity of thickness from particle to particle.
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