Patent Number: 052456390
Section: summary

BACKGROUND OF THE INVENTION This invention relates generally to devices and techniques for plugging flow holes. More particularly, the present invention relates generally to devices and techniques for plugging the flow holes of the core support barrel of a nuclear reactor. In some nuclear installations, fuel rod wear has been directly associated with the characteristics of the flow path through the reactor core. For example, it has been established that baffle jetting causes fuel rod wear under certain conditions. In some installations, the flow characteristics can be suitably modified to alleviate the wear to the fuel rod by modifying the reactor core flow path to an upflow-type core flow path. In order to implement the flow modification, it is necessary that existing core barrel flow holes be plugged. In some reactor designs, this may require the plugging of 16 angularly spaced core barrel flow holes. Moreover, the flow holes to be plugged are typically positioned below the level of the adjacent surrounding thermal shield, and thus the thermal shield may present a significant obstacle to the hole plugging process. SUMMARY OF THE INVENTION Briefly stated, the invention in a preferred form is a plug assembly and a plugging technique for a core barrel flow hole wherein a thermal shield surrounds the barrel and is space adjacent to the flow hole. The plug assembly comprises an offset arm having first and second end portions. The first end portion includes a plug which is dimensioned to seal against the core barrel boundaries of the hole. The plug may include a circumferential sealing lip or a tapered sealing surface. The second end portion constitutes a mounting head having a pair of openings which receive bolts. The bolts are anchored in threaded bores of the core support barrel. The arm is dimensioned so that the plug is inserted into the flow hole and the bolts are positioned above the level of the thermal shield to provide headroom for completing the installation of the plug assembly. An installation method, in accordance with the invention, for plugging the flow hole of a core barrel having a thermal shield spaced from and surrounding the barrel adjacent to the hole comprises machining a threaded bore in the core barrel above the thermal shield. A plug member is positioned in the flow hole, and the plug member is staked to the threaded bore by bolts. The threaded bore is machined into the barrel. An object of the invention is to provide a new and improved plug assembly and installation technique for plugging the flow hole of a core support barrel. Another object of the invention is to provide a new and improved plug assembly which may be installed to the core barrel in an efficient process to provide a plug of high integrity. A further object of the invention is to provide a new and improved plug assembly and installation method therefor which is designed to overcome the headroom constraints presented by the thermal shield. Other objects of the invention will become apparent from the drawings and specification.