Development of a Friction Welded Tube for Preventing a Leakage of Coolant into a Capsule

An instrumented capsule has been developed at HANARO (High flux Advanced Neutron Application ReactOr) for the neutron irradiation tests of nuclear reactor materials. The temperature of the specimens during a irradiation is controlled by adjusting the internal He gas pressure in the capsule. After an irradiation test, the main body of a capsule is cut off at the bottom of the protection tube with a cutting system and it is transported to the IMEF hot cell and dismantled for post irradiation tests. At this cutting stage, the reactor coolant leaks into the capsule through the gas control pipe and it causes some troubles for the post irradiation analysis. To prevent a coolant leakage during a cutting, aluminum tube is especially attractive because of its superior workability. However, present structures made of stainless steels can not be entirely replaced with aluminum structures, by taking into account the strength, although it is possible to replace part of a structure with aluminum tube. In this case, it is necessary to join stainless steel to aluminum. Sound joints have been hardly obtained, owing to the formation of a large amount of brittle intermetallic compounds in the weld and to their big difference of the thermal expansion coefficients when using a conventional fusion welding. Friction welding is known to be more effective in joining dissimilar metals when compared with a fusion welding, because it is a solid state process. The friction welded tube has been also known to be applied in the irradiation capsules in JMTR (Japan Materials Testing Reactor). In the present study, a friction welded tube developed for the prevention of a coolant leakage into a capsule is described. The friction welded tube will be applied to all of the material capsules in HANARO