Release Behavior of Metallic Fission Products from Pyrocarbon-Coated Uranium-Dioxide Particles at Extremely High Temperatures

摘要

Uranium-dioxide particles coated by pyrocarbon (BISO), which were irradiated at 1, 3001, 400°C to burnups of ca. 1% FIMA, were heated isochronally and isothermally at temperatures between 1, 600 and 2, 300°C. Release fractions of 137Cs, 155Eu and 106Ru were larger than 10-2 after heating at 2, 000°C for 2 h; the results were in contrast to much smaller release fractions from TRISO particles with intact silicon-carbide (SiC) coating. The release of 137Cs and 144Ce from the BISO particle was controlled by diffusion in the dense pyrocarbon layer at temperatures between 1, 600 and 2, 300°C, while that of 155Eu and 106Ru was controlled by diffusion in the fuel kernel above 1, 800°C. These results can be used as reference data on release behavior of the fission products from TRISO particles with defective SiC layers.