Integrity confirmation tests and post-irradiation test plan of the HTTR first-loading fuel

Since the first-loading fuel of the High Temperature Engineering Test React or (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 Res earch Institute (JAERI) carried out the tests to certify the fuel integrity during operation. The tests comprise (1) as-fabricated SiC failure fractio n measurement, (2) high- temperature heatup test of irradiated fuel and (3) accelerated irradiation test. For (1), the SiC failure fraction was measur ed 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 degreesC criterion, the high- temperature heatup test of irradiated fue l compact was carried out. The result showed that no failed particle was pr esent in the fuel compact after heating. The diffusion coefficient of metal lic fission products in SiC layer was also examined in a series of post- ir radiation heating tests. The measured diffusion coefficient of Cs-137 showe d a good holding ability as those obtained for research and development fue l specimen. The measured fission gas release rate in accelerated irradiatio n test showed no additional failure up to 60 GWd/t which was about two time s higher than 33 GWd/t of the maximum burnup in the HTTR core. Through the tests, integrity of as-fabricated first-loading fuel of the HTTR was finall y confirmed. The future post- irradiation test plan, which will be carried out to confirm the fuel irradiation performance and to obtain the data on i ts irradiation characteristics in the core, is also described.