Fission-Gas Release from Pyrolytic-Carbon-Coated Fuel Particles During Irradiation at 2000 to 2500°F

The fission-gas release from pyrolytic-carbon-coated fuel particles during irradiation was studied for gas-cooled reactor application. Duplex-and triplex-type coatings on thorium-uranium carbide cores and on uranium carbide cores were tested at temperatures between 2000 and 2500°F (1093 and 1371 °C). Both types of coatings retained fission gas quite well up to about 20at.% heavy-metal burnup. Postirradiation examination revealed that the particles with the duplex coating were more susceptible to radiation damage (by the formation of a reaction zone at the core/coating interface) than were the particles with the triplex coating. This damage, however, did not affect the fission-gas release rates.