This invention relates to nuclear reactors and it has particular relationship to the replacement of the old split-pin assemblies of a guide tube of a nuclear reactor by new split-pin assemblies. The reasons for the replacement and the practice of replacing the old split-pin assemblies are described in detail in Calfo. There are usually about 61 guide tubes in a nuclear reactor and all old split-pin assemblies, two in each guide tube, must be replaced. The guide tubes and the old nut and old split pin of the old split-pin assemblies are highly radioactive. To avoid the hazards of radioactivity the replacement is carried out at a substantial depth under borated water by robotic tools controlled from a robotic command center on a deck above the pool. The command center includes a programmable computer. The guide tube includes an upper section and a lower section, the latter being herein referred to as the lower guide tube or LGT. The split-pin assembly is secured in counterbores of the lower flange of the LGT. The assembly includes an old split pin and an old nut. The nut is threaded onto the split pin and seated on the base of the upper counterbore; the pin has a flange which extends into the lower counterbore.
In processing a guide tube for replacement, the LGT is separated from the upper section and transferred to the robotic work station where it is precisely positioned for processing. Next the old split-pin assembly is severed into fragments from the upper and lower counterbores by metal disintegration machining, the fragments are removed, the counterbores are cleaned, a new nut is placed in the upper counterbore, a new split pin is inserted through the lower counterbore and the new nut is torqued onto the new pin and seated on the base of the upper counterbore. At this point it is necessary to secure the new nut and new split pin together so that they do not rotate with reference to each other. In the old split-pin assembly, this object is accomplished by a dowel pin which traverses the nut and pin near their upper ends and is welded to the old nut. The old nut as well as the new nut is composed of AISI type 304 stainless steel or like alloy. This alloy cannot readily be welded under water. During the replacement the welded dowel-pin joint of the old split-pin assembly is replaced by crimped joint. For this purpose the nut is fabricated with a locking cap secured near its upper end and the new split pin is fabricated with an upper stem having grooves, specifically flutes. After the new nut is torqued onto the new split pin and secured in the upper counterbore, the locking cap extends above the new nut opposite to the flutes in the new split pin. It is necessary to crimp the locking cap securely into the flutes so as to preclude rotation of the new nut and pin relative to each other. It is an object of this invention to provide a crimping tool for accomplishing this object.
In creating a crimping tool one is confronted by a number of serious problems. The robotic work station includes six components in addition to the crimping tool It is necessary that the crimping tool shall be capable of effective operation in cooperation with, and within the limited space confines, afforded by the other tools. It is also necessary that the crimping tool be capable of remote control, from the robotic control center, either step-by-step manually or automatically under the commands of a programmable computer.
The new split-pin assembly, as mounted in the lower flange of the LGT, is accessible only over a cylindrical solid angle of about 180.degree. and is not accessible from the top. As mounted in the lower flange of the LGT, the split-pin assembly, old and new, extends into the "mouse hole" of the LGT and is spanned above by the wall of the LGT whose edge bounds the "mouse hole".
It is an object of this invention to overcome the above drawbacks and disadvantages and to provide a crimping tool which shall be capable of effectively crimping the locking cap secured to the new nut of a new split-pin assembly into the grooves or flutes of the new split pin notwithstanding the limited access available to the locking cap. It is also an object of this invention to provide such a tool that shall be capable of effective operation within the confines afforded by the other tools of the robotic work station.
USPTO Backgrounds
USPTO Backgrounds