Integrity Confirmation Tests and Post-irradiation Test Plan of the HTTR First-Loading Fuel

Abstract

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 coefficient of metallic fission products in SiC layer was also examined in a series of post-irradiation heating tests. The measured diffusion coefficient of 137 Cs showed a good holding ability as those obtained for research and development fuel specimen. The measured fission gas release rate in accelerated irradiation test showed no additional failure up to 60 GWd/t which was about two times 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 finally confirmed. The future post-irradiation test plan, which will be carried out to confirm the fuel irradiation performance and to obtain the data on its irradiation characteristics in the core, is also described.

Fuel and Fission Gas Behavior during Rise-to-Power Test of the High Temperature Engineering Test Reactor (HTTR)

“…(18) should be investigated in detail by comparison to measured data from the 94F-9A capsule irradiation test which used coated fuel particles fabricated by the same process as the first loaded HTTR fuel. 13,14) (2) The prediction was underestimated at low reactor power. In this model, 10 µm of the recoil distance is employed both for the UO 2 kernel and the fuel compact matrix.…”

Preliminary Test Results for Post Irradiation Examination on the HTTR Fuel

“…Before the X-ray radiograph, the coated fuel particles (density 4.3 g/cm 3 ) and the dummy particles (2.8 g/cm 3 ) were divided by the floating method with tetrabromoethane (2.96 g/cm 3 ). Then, the coated fuel particles and the dummy particles were sectioned in groups with 200-300 particles, and the X-ray radiograph as shown in Fig.…”

“…They have been irradiated by using 94F-9A sweep gas capsule in the JMTR for the accelerated irradiation test on the first loading fuel of the HTTR to confirm its intactness during the HTTR operation. [3][4][5] Coated fuel particles in these fuel compacts were taken from the fabrication line of the first-loading fuel. For each fuel compact sample, the value of 30% of the volume packing fraction was settled which is same as the first loading fuel of the HTTR.…”