Fission product release behavior of individual coated fuel particles for high-temperature gas-cooled reactors

Postirradiation heating tests of TRISO-coated UO2 particles at 1700 and 180 0 degrees C were performed to understand fission product release behavior a t accident temperatures. The inventory measurements of the individual parti cles were carried out before and after the heating rests with gamma-ray spe ctrometry to study the behavior of the individual particles. The time-depen dent release behavior of Kr-85, Ag-110m, Cs-134, Cs-137, and Eu-154 were ob tained with on-line measurements of fission gas release and intermittent me asurements of metallic fission product release during the heating tests. Th e inventory measurements of the individual particles revealed that fission product release behavior of the individual particles was not uniform, and l arge particle-to-particle variations in the release behavior of Ag-110, Cs- 134, Cs-137, and Eu-154 were found X-my microradiography and ceramography s howed that the variations could not be explained by only the presence or ab sence of cracks in the SiC coating layer The SiC degradation may have been related to the variations.