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Since the first-loading fuel of the High Temperature Engineering Test Reactor (HTTR) is the first mass-production High Temperature Gas-cooled Reactor (HTGR) fuel in Japan, their quality should be carefully inspected. For the quality control related to the fabrication process, Japan Atomic Energy Research Institute (JAERI) carried out the tests to certify the fuel integrity during operation. The tests comprise (1) as-fabricated SiC failure fraction measurement, (2) high-temperature heatup test of irradiated fuel and (3) accelerated irradiation test. For (1), the SiC failure fraction was measured independently in JAERI in addition to the measurement in the fabrication process. The measured failure fractions agreed within 95% confidence limit. In order to confirm the integrity of the SiC layer with respect to the 1,600°C criterion, the high-temperature heatup test of irradiated fuel compact was carried out. The result showed that no failed particle was present in the fuel compact after heating. The diffusion...

Postirradiation heating tests of TRISO-coated UO2 particles at 1700 and 1800°C were performed to understand fission product release behavior at accident temperatures. The inventory measurements of ...

The ZrC coating layer is a candidate to replace the SiC coating layer of the Triso-coated fuel particle for high-temperature gas-cooled reactors. To understand mechanisms of the good retention capabilities for fission product caesium of the ZrC Triso-coated fuel particles, the particles after post-irradiation heating tests were examined individually with X-ray microradiography and the caesium inventories of the fuel kernel and coating layers of each particle were measured with gamma-ray spectrometry. The fractional content of 137Cs in the fuel kernel was found to be different from particle to particle though 137Cs was not released from the particles practically. The particles, which showed relatively good retention of 137Cs in the fuel kernels, had radially broken inner pyrolytic carbon layers and deformed fuel kernels. The ZrC layer developed the caesium retention capabilities of the fuel kernel through interaction of ZrC with the fuel kernel.