Patent Number: 059011920
Section: summary

FIELD OF THE INVENTION This invention relates generally to nuclear reactors and, more particularly, to an apparatus and methods for securing 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 spray spargers inside the RPV. The core spray piping and spargers deliver water flow to the reactor core. 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, for example, 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 T-boxes and core spray line risers, occasionally require replacement as a result of SCC. Replacing the core spray piping often requires removing and replacing the core spray line riser. The core spray line attachment to the shroud, however, typically is installed during original reactor construction and is difficult to access. In addition, replacing the core spray line riser, particularly the attachment to the shroud, is complicated by the limited available working space. The core spray line riser includes a lower elbow secured to a core spray sparger T-box. There are a number of welds between the lower elbow and T-box, and the integrity of these welds must be maintained to ensure proper operation of the core spray piping. As explained above, it is difficult to access these welds. It would be desirable to provide an apparatus which facilitates providing additional support for the welds between the core spray sparger T-box and the lower weld of the lower elbow of the core spray line riser. It would also be desirable to provide such apparatus which is easy to assemble and install in a limited working space. SUMMARY OF THE INVENTION These and other objects may be attained by an apparatus which, in one embodiment, includes a sleeve sized to be partially inserted within a T-box pipe, and a draw bolt which extends through the sleeve and engages a block so that the draw bolt draws the block into tight engagement with the lower elbow of the riser. More particularly, the sleeve is substantially cylindrically shaped and has a main cylindrical body and a flange at one end. An axial bore extends through the main body, and two opposing water flow openings are located in the sleeve main body. The main body is sized to be inserted into the T-box pipe so that the sleeve flange engages one end of the T-box pipe. The sleeve flange includes an opening sized to receive the draw bolt. The draw bolt is threaded and is of sufficient length to extend through the main body bore and an opening machined in the core spray line riser lower elbow. The block is substantially wedge shaped and includes a threaded opening to engage the draw bolt. To install the repair apparatus, after removing a core spray line riser, a replacement core spray line riser is coupled to the T-box, for example by welding the lower elbow to the core spray sparger T-box. The T-box end plate is then removed and the repair apparatus sleeve is inserted into the open end of the T-box so that the sleeve flange is in contact with and closes off the open end of the T-box. The sleeve is rotated to ensure that the water flow openings are substantially aligned with the core spray spargers attached to the T-box. The core spray line repair apparatus draw bolt is then inserted through the sleeve flange opening, through the main body bore, and through the opening machined in the replacement riser lower elbow. The repair apparatus block is then engaged to the draw bolt. The draw bolt is then torqued and locked in place. As the bolt is tightened into engagement with the block, the apparatus provides axial restraint. The above-described apparatus provides support for the welds between the core spray sparger T-box and the lower weld of the core spray line riser lower elbow. In addition, such apparatus is easy to assemble and can be installed in a limited work space.