Patent Number: 046844910
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to nozzle seals for sealing the nozzles of a nuclear steam generator vessel, and particularly to retraint means for securely holding the nozzle seal in place and preventing inward loosening and displacement thereof by high pressure in the nozzle. 2. Background of the Invention: During refueling operations in a nuclear generating plant, it is desirable to simultaneously perform maintenance on the steam generator. To do this, the inlet nozzle of the steam generator vessel must be closed off. This is accomplished by use of a nozzle seal or dam which is installed in the nozzle from inside the inlet plenum of the generator vessel. One such nozzle seal is disclosed, for example, in copending U.S. application Ser. No. 605,354 filed Apr. 30, 1984, and entitled "Non-Bolted Ringless Nozzle Dam". Since work must be done within the inlet plenum, the nozzle seal or dam must be fully secured in the nozzle. While the nozzle seal is provided with an anchor assembly for anchoring it in place in the nozzle, nevertheless, this may be insufficient to insure that the nozzle seal will not be dislodged or displaced as a result of large pressure buildups within the nozzle, which could result in release of irradiated coolant from the reactor at great hazard to service and maintenance personnel. It has been suggested that retention of the nozzle seal be accomplished by a restraint beam which essentially operates like a bar or beam wedged between the nozzle seal and the environmental ledge of the generator vessel. However, such a beam arrangement is quite heavy and difficult to install, resulting in large exposure times. Furthermore, its construction and manner of installation concentrates all the retaining force at a single location on the steam generator environmental ledge, creating a high risk area at that point. Furthermore, such a device does not readily accommodate manufacturing tolerances in the dimensions of the nozzle and the nozzle seal which result in variations in the seating location of the nozzle seal in the nozzle. SUMMARY OF THE INVENTION It is a general object of the present invention to provide a nozzle seal retaining apparatus which avoids the disadvantages of other retaining devices while affording additional structural and operating advantages. An important feature of the invention is the provision of retaining apparatus for a nozzle seal in a nuclear steam generator vessel which is characterized by relatively light weight and ease of installation. In connection with the foregoing feature, it is another feature of the invention to provide retaining apparatus of the type set forth which is capable of remote installation. Yet another feature of the invention is the provision of retaining apparatus of the type set forth which distributes the retaining forces at plural locations in the vessel. It is another feature of the present invention to provide a retaining assembly of the type set forth which is adjustable to accommodate tolerances in the dimensions of the vessel and installation position of the nozzle seal. In connection with the foregoing feature, it is another feature of the invention to provide lightweight positioning apparatus for determining the necessary adjustment before installation of the retaining apparatus. In connection with the foregoing feature, still another feature of the invention is the provision of the positioning apparatus of the type set forth which is capable of remote operation. Certain of these and other features of the invention are attained by providing in a nuclear steam generator vessel having a part-spherical bottom wall cooperating with a horizontal tube sheet and a vertical divider plate to define a plenum having a nozzle, apparatus for retaining a nozzle seal in the nozzle against displacement into the plenum comprising: rigid beam means disposed in the plenum, attachment means connecting the beam means to the nozzle seal, anchor means connecting the beam means to the tube sheet, and coupling means bracing the beam means against the divider plate, whereby the beam means is securely braced between the tube sheet and the divider plate for transferring thereto forces coupled to the beam means from the nozzle seal. The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.