Fabrication of an aluminum capsule for irradiation in a nuclear reactor by friction welding and its safety test

A series of tests on the conditions of friction welding and the soundness were carried out for considering the method when the practical aluminum capsules for the hydraulic rabbit facility in JMTR are fabricated by friction welding, and the results are reviewed. The friction welding and a jig developed for sealing helium were applied to the fabrication of the capsules on the basis of the cold welding technique which was successful for manufacturing radioisotope containers. As the results, the problems of the defect formation in welding, the thermal effect on the specimens for irradiation, and the high fabrication cost in fusion welding were solved. When the capsules were fabricated by the friction welding, the tests showed that (1) the tensile strength and breaking strength due to internal pressure were sufficiently high in the range from about 7 mm to 15 mm of upset; (2) the upset quantity was 11 +- 2 mm under optimal welding conditions; and (3) radiographical test, liquid-permeating flaw detection test, and leak test are effective for confirming the soundness of welded portions. In addition, for the capsules of welded construction, the following results were obtained: (1) in case of the friction welding, the atmospheric temperature within the capsules is low, so that there is hardly any thermal effect on the specimens for irradiation and (2) development of the jig for sealing helium makes weldability better and simplifies the fabrication of the capsules, consequently good yield was obtained. In conclusion, it was found that the friction welding can produce the capsules of very high safety and excellent in the quality control. (Iwakiri, K.)