Patent Number: 059129360
Section: summary

FIELD OF THE INVENTION This invention relates generally to nuclear reactors and, more particularly, to assemblies and methods for coupling piping within reactor pressure vessels of such reactors. BACKGROUND OF THE INVENTION A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Boiling water reactors have numerous piping systems, and such piping systems are utilized, for example, to transport water throughout the RPV. For example, core spray piping is used to deliver water from outside the RPV to core spargers inside the RPV and to cool the core. Typically, core spray piping is coupled between a nozzle in the RPV and a shroud connection in the shroud. Stress corrosion cracking (SCC) is a known phenomenon occurring in reactor components, such as structural members, piping, fasteners, and welds, exposed to high temperature water. The reactor components are subject to a variety of stresses associated with, e.g., differences in thermal expansion, the operating pressure needed for the containment of the reactor cooling water, and other sources such as residual stresses from welding, cold working and other inhomogeneous metal treatments. In addition, water chemistry, welding, heat treatment and radiation can increase the susceptibility of metal in a component to SCC. Reactor internal piping, such as core spray lines inside the reactor pressure vessel, occasionally require replacement as a result of SCC. One known method of replacing a core spray line requires draining the RPV and taking field measurements of the precise distance, e.g., horizontal and vertical, between the nozzle and the shroud connection. A replacement core spray line is then cut utilizing the measurements, and such replacement line is then welded in place. Replacing a core spray line typically requires considerable down time, and is tedious. It would be desirable to provide an assembly which facilitates replacing a core spray line without requiring detailed field measurements and cutting. It also be desirable to provide such an assembly which would enable a core spray line to be replaced without requiring any welding. SUMMARY OF THE INVENTION These and other objects are attained by an assembly which, in one embodiment, includes a pipe connector assembly for replacing a core spray line in a nuclear reactor without field cutting, measuring, or welding such line. The pipe connector assembly includes a first coupling member, a second coupling member, and at least one locking element. The first coupling member includes a flange, a substantially cylindrical pipe engaging portion extending from a first surface of the flange and a spherical convex seat portion extending from a second surface of the flange. The second coupling member includes a flange having a spherical concave seat portion for receiving the convex seat portion of the first coupling member and a substantially cylindrical pipe engaging portion extending from a first surface of the second coupling member flange. The locking element includes at least one spherical washer and a crimp mechanism and couples the first coupling member and the second coupling member. To replace core spray lines, three pipe sections and three pipe connector assemblies are typically used. The pipe sections are sized so that their total length matches or slightly exceeds the total length of the core spray line to be replaced. Generally, the first pipe assembly couples the first pipe section to a the second pipe section, the second pipe assembly couples the second pipe section to the third pipe section, and the third pipe assembly couples the third pipe section to a RPV nozzle. More particularly, and referring to the first pipe connector assembly only, a second end of the first pipe section is inserted into the first coupling member bore. Similarly, a first end of the second pipe section is inserted into the second coupling member bore. The coupling members are then positioned so that their respective bores are aligned, and the first coupling member seat is seated on the second coupling member seat. The locking elements are then extended through the respective stud bores to couple the first and second coupling members, and thus the first and second pipe sections, together. The second pipe connector assembly couples a second end of the second pipe section to the first end of the third pipe section in the same manner. The third pipe connector assembly couples a second end of the third pipe section to the RPV nozzle junction in the same manner. Before fully securing the locking elements, a first end of the first pipe section is coupled to a shroud connector. Thereafter, the second and third pipe sections are positioned so that any excess core spray line length is accommodated by the rotational misalignment of the pipe sections and the pipe connector assemblies. Particularly, the first and second coupling members of each pipe connector assembly are rotated with respect to each other so that the various pipe sections move relative to each other. Thereafter the locking elements are fully secured. The resulting connection is essentially leak tight and is able to resist significant shear, axial, moment, and torsion loads. The above-described pipe connector assembly is particularly suitable for use in nuclear reactor applications and facilitates replacing a core spray line without draining the reactor or welding. In addition, such assembly facilitates replacing a core spray line without requiring precise field measurements or cutting.