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 1800 degrees C were performed to understand fission product release behavior at accident temperatures. The inventory measurements of the individual particles were carried out before and after the heating rests with gamma-ray spectrometry to study the behavior of the individual particles. The time-dependent release behavior of Kr-85, Ag-110m, Cs-134, Cs-137, and Eu-154 were obtained with on-line measurements of fission gas release and intermittent measurements of metallic fission product release during the heating tests. The inventory measurements of the individual particles revealed that fission product release behavior of the individual particles was not uniform, and large 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 showed that the variations could not be explained by only the presence or absence of cracks in the SiC coating layer The SiC degradation may have been related to the variations.