Patent Number: 047568771
Section: summary

FIELD OF THE INVENTION The present invention relates to a core barrel support system for a nuclear reactor, such as a pressurized water reactor, wherein the core support plate is engaged about the periphery thereof, and a method for installation of a core barrel in a pressure vessel of a reactor where alignment and securement of the core barrel are readily achieved. DESCRIPTION OF THE PRIOR ART In nuclear reactors, such as pressurized water reactors, the reactor has an upright cylindrical pressure vessel with a hemispherical lower head section and a removable hemispherical head bolted to the upper end of the vessel. A cylindrical core barrel is suspended inside the pressure vessel from a flange extending around the inside of the upper end of the pressure vessel. The barrel includes a bottom core support plate and is positioned within the pressure vessel spaced from the lower head section a substantial distance therefrom. The upper region of the core barrel contains reactor control rod guide tubes, while the core internals, such as the fuel element assemblies, the fuel element assemblies support grid structure, and the like are contained in the lower region of the core barrel. As described in the application of R. M. Blaushild and L. Veronesi, Ser. No. 547,294, filed Oct. 28, 1983, and assigned to the assignee of the present invention, the contents of which application are incorporated by reference herein, while the core barrel is primarily supported at its upper end by engagement with the upper end of the pressure vessel, the lower end of the core barrel is also restrained by engagement means so as to provide lateral stability thereof. As described therein, a preferred means for such lateral stability and auxiliary support is the provision of a plurality of engagement means which are secured to the lower end of the pressure vessel and extend radially inwardly from the upper portion of the walls of the hemispherical lower head section. Each of the engagement means have a recess in the upper surface thereof and keys, such as T-shaped keys are secured to the bottom of the core support plate, which keys are designed to fit into the recesses in the engagement means for lateral stability and to align the core barrel within the reactor vessel. In the conventional assembly of the core barrel within the reactor vessel, the engagement means with recesses are generally welded to the bottom portion of the pressure vessel and keys are bolted and/or welded to the bottom surface of the core support plate. A very precise alignment is required, between the keys and walls of the recesses or keyways, upon assembly of the core barrel into the pressure vessel. Because of the degree of precise alignment required, the core support plate is provided with a manway or access port, usually through the center of the core support plate, with a cover plate therefor, so that an assembler can be lowered through the manway into the area between the core support plate and the bottom wall of the pressure vessel. The assembler, while in that area, can then make measurements to determine the type and number of shims that are needed to be manufactured and then inserted into the keyways to provide the required alignment. At times, the needed shims can be inserted into the recesses only after removal of the core barrel from the pressure vessel, with the shims then placed into the recesses and the core barrel re-inserted into the pressure vessel. This system of alignment is expensive and time consuming and is possible only when the size of the reactor is such that an assembler can be physically lowered through the manway into the area between the core support plate and the bottom wall of the pressure vessel. In small reactors, for example, the pressure vessel may be of a size so small that an assembler cannot be physically located in the area between the core support plate and the bottom wall of the pressure vessel to perform the alignment operations above-described. It is an object of the present invention to provide a nuclear reactor which has an improved system for aligning the core barrel relative to engagement means for the core support plate. It is another object of the present invention to provide an improved method for aligning a core barrel of a nuclear reactor in a pressure vessel. BRIEF SUMMARY OF THE INVENTION An improved means for aligning and securing a core barrel within a pressure vessel of a nuclear reactor relative to engagement means disposed about the periphery of the core barrel and attached to the wall of the pressure vessel, wherein the core support plate has a plurality of apertures therethrough which communicate with recesses in the engagement means, and a key is inserted into the apertures, the lower section of which extends into the recess of the engagement means, the key being secured in said apertures of the core support plate. The keys preferably have an upper flanged portion which fits on a shoulder in the core support plate about the aperture, such that the key is secured in place with its upper surface flush with the upper surface of the core support plate and with the flange secured to the core support plate by welding or by bolted connections.