Patent Number: 041749995
Section: summary

CROSS-REFERENCE TO RELATED APPLICATIONS This application is hereby cross-referenced to the following patent applications which were commonly filed herewith and which are commonly assigned: U.S. patent application Ser. No. 781,381 filed Mar. 25, 1977 entitled "Segmented Articulating Manipulator Arm For Nuclear Reactor Vessel Inspection Apparatus," filed in the names of David C. Burns and Lanson Y. Shum; U.S. patent application Ser. No. 781,380 filed Mar. 25, 1977 entitled "Variable Mounting Assembly For Transducers Employed In Nuclear Reactor Vessel Inspection Apparatus," filed in the names of Hans J. Elsner, Ronald F. Antol and Raymond P. Castner; U.S. patent application Ser. No. 781,390 filed Mar. 25, 1977 entitled "Pulley System Including Emergency Locking Means For Nuclear Reactor Vessel Inspection Apparatus," filed in the name of Renato D. Reyes; U.S. patent application Ser. No. 781,401, filed Mar. 25, 1977 entitled "Emergency Braking System For Nuclear Reactor Vessel Inspection Apparatus," filed in the name of Renato D. Reys; U.S. patent application Ser. No. 781,396 filed Mar. 25, 1977 entitled "Emergency Disconnect Means For The Manipulator Arm Of A Nuclear Reactor Vessel Inspection Apparatus," filed in the names of Arthur F. Jacobs and Duane W. Morris; U.S. patent application Ser. No. 781,404 filed Mar. 25, 1977 entitled "Pressurized Cabling And Junction Boxes For Nuclear Reactor Vessel Inspection Apparatus," filed in the names of Charles V. Fields and Raymond P. Castner; and U.S. patent application Ser. No. 781,402 filed Mar. 25, 1977 entitled "Emergency Retraction Means For The Manipulator Arm Of A Nuclear Reactor Vessel Inspection Apparatus," filed in the names of Arthur F. Jacobs and Duane W. Morris. BACKGROUND OF THE INVENTION Nuclear reactor vessels employed in the commercial generation of electrical power are of two types; the pressurized water type or the boiling water type. In either case, the reactor vessel utilizes a generally cylindrical metallic container having a base and a top flange welded thereto. The main cylinder portion itself usually comprises a series of lesser cylinders welded to each other. In addition, a plurality of circumferentially spaced nozzles extend through the main cylinder wall and are welded thereto. Thus, numerous welds are necessarily used in fabricating the reactor vessel, in mating the top flange to the main cylindrical body and in securing the inlet and outlet nozzles to the reactor vessel wall. The reactor vessel, in use, is encased, in a thick concrete containment area. However, the structural integrity of the reactor vessel, the concrete containment notwithstanding, due to the operating environment is of critical importance. The weld areas of the reactor vessel are, of course, inspected prior to its initial use. Such inspection is carried out with all portions of the vessel relatively accessible to an inspection device prior to its encasement in the concrete containment. However, in-service inspection of the reactor vessel welds is not only desirable, but is mandated under governmental regulations. Under such regulations, it is required that the vessel weld areas be subjected to periodic volumetric examination whereby the structural integrity of the vessel is monitored. Due to the nature of an in-service inspection, the device designed to accomplish the specified weld examinations must be capable of successfully operating in an underwater and radioactive environment under remote control while maintaining a high degree of control over the placement and movement of the inspection sensors. The operating constraints are further complicated by the variety of reactor vessel sizes to which the inspection device must be able to be accommodated. Furthermore, the inspection device must not only be compatible with the weld placements of the reactor vessels now in use, but must also be sufficiently versatile to adapt to inspection duty in future vessels. In addition, the inspection device must be arranged in its use to have only minimal impact with normal refueling and maintenance operations. The use of ultrasonic transducers to inspect metal welds is known. One such system is described in the periodical Materials Evaluation, July 1970, Volume 28, No. 7, at pages 162-167. This article describes a transmitter-receiver type ultrasonic inspection system for use in the in-service inspection of nuclear reactor vessels. The positioning arrangement for the transducers uses a track which is mounted on the interior wall of the reactor vessel. A method and apparatus for ultrasonic inspection of a pipe from within is disclosed in U.S. Pat. No. 3,584,504. In the apparatus disclosed therein, a transducer array is mounted on a carrier which is rotatable, by means of a central shaft of the apparatus, within the pipe. In U.S. Pat. No.3,809,607, a nuclear reactor vessel in-service inspection device is detailed, which device is adapted to pemit remotely controlled and accurate positioning of a transducer array within a reactor vessel. This device comprises a positioning and support assembly consisting of a central body portion from which a plurality of radially directed support arms extend. The ends of the support arms are extended to and adapted for being seated on a predetermined portion of the reactor vessel to define a positional frame of reference for the inspection device relative to the reactor vessel itself. Repositioning and support assemblies are provided and include integral adjustment means which cooperate to permit the simultaneous variation of the extension of the support arms thereby allowing the inspection device to fit reactor vessels of differing diameters. A central column is connected to the positioning and support assemblies, which central column extends along the longitudinal axis thereof. One or more movable inspection assemblies are connected to the central column and include drive and position indicating means. Three specific inspection subassemblies include a flange scanner, a nozzle scanner and a vessel scanner. Each of these scanners employ multiprobe transmitter-receiver ultrasonic transducers to permit more accurate volumetric plotting of the integrity of the welds used in fabricating the reactor vessel. Since the development of the above-identified inspection devices, the original inspection code has been amended to call for more reliable and more rigorous inspections. In addition, these prior art devices were unable to accurately measure or reach certain weld areas of the reactor vessel. Still other drawbacks in the prior art inspection devices were the reliability and speed of the actual inspection effort. One particular problem which was not entirely solved by the above-described prior art devices was that of exactly positioning the inspection device with respect to the reactor vessel since knowledge of the position of the transducer array used in connection therewith is critical to accurately defining the size, orientation and location of a vessel or weld flaw. In addition, such exact positioning must be accomplished, that is, the inspection device must be fully seated in the reactor vessel at a known location, without damaging the ability of the top vessel flange to be sealed to its header. SUMMARY OF THE INVENTION Accordingly, there is provided for a reactor vessel inspection device, a support ring sized to accommodate the circular path defined by three or more guide studs extending upwardly from the vessel. The support ring has at least three movably mounted guide stud bushings thereon which can be positionally adjusted to align each bushing with one of the studs. When engaged, the guide studs and bushings yield a coarse positioning of the inspection device relative to the reactor vessel. Also provided are three support legs which are clamped to the support ring and dimensioned to an appropriate length. Two of the support legs have shoes clamped thereto, which shoes are configured to rest on an internal circumferential flange within the reactor vessel. The third support leg is provided with a specially adapted shoe configured to engage a locating element, the exact position of which is known, within the vessel to achieve fine positioning of the inspection device relative to the reactor vessel. The support ring is additionally provided with an annular key which runs longitudinally about the outer periphery thereof. Clamping means utilized to secure the guide stud bushings and the support legs to the support ring are provided with keyways to insure automatic, self-alignment therewith when fully tightened.