Deterioration of ZrC-coated fuel particle caused by failure of pyrolytic carbon layer

The ZrC coating layer is a candidate to replace the SiC coating layer of the Triso-coated fuel particles for high-temperature gas-cooled reactors. To understand the behavior of the ZrC-Triso-coated fuel particles at 1800 to 2000°C, a ceramographic examination and an electron probe microanalysis were performed on the ZrC-Triso-coated fuel particles after the post-irradiation heating tests and a thermodynamic analysis of the ZrCUO system was carried out. Based on the results of the examination and analyses, a mechanism of the deterioration of the ZrC-Triso-coated fuel particles was proposed. The deterioration of the ZrC-Triso-coated fuel particles observed at 1800 to 2000°C was caused by the failure of the inner pyrolytic carbon layer.