Study of Vipac Fuel Fabrication for FUJI Project -Literature Survey and Recent Experiment in JNC

Shigetome, Yoshiaki

Vipac fuel pins that are composed of irregular shape fuel granules will be fabricated and irradiated as well as Sphere-pac and pellet fuel pins in the frame of PSI/JNC/NRG collaboration (FUJI project) to compare their performances. This report describes the outline of the past vipac filling performed at ORNL, RIAR and in Japan and the results of the experiments recently conducted in JNC. Main factors that dominate performance of the vipac filling process are vibration condition and granule size distribution. The effect of vibration condition is significant and large acceleration is necessary to generate high packing fraction. In addition, sweeping frequency is necessary to break the bridging of the powder and it is effective to promote the granules movement to settle in the closely packed arrangement. The effect of granule size distribution was examined. One of the promising mixing ratios was deduced through parametric survey. The packing fraction more than 75% would be possible if granule size less than 45 m was applied. Though the small granule size is necessary to obtain high packing fraction, the diameter of the granules must be restricted to prevent the fine granules from infiltrating into the insulator sphere region. Therefore the smallest granule diameter must be defined carefully. Fabrication of vipac pins is one of the most unpredictable processes in this project because both PSI and JNC have quite little vipac experience. Filling test with inactive materials (ZrO and UO) and vipac granule fabrication test have been ongoing to overcome this situation and to allow fabricating vipac pins as close as the targeted specifications. Further investigation of filling process should be performed combined with the results of the vipac fabrication test.