Abstract:
A device for inspecting submersed plant parts is particularly suited for ultrasonic inspection of screws in the core baffle of a nuclear reactor pressure vessel. The device includes a remote-controlled underwater vehicle that is provided at its end face with a carrier that can be pivoted about a pivot axis oriented parallel to the longitudinal central axis of the underwater vehicle, and is provided with a holding device for an inspection head that is arranged on the carrier spaced apart from the pivot axis.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a device for inspecting plant parts that are submersed under water, in particular for ultrasonic inspection of screws in the core baffle of a nuclear reactor pressure vessel.  
           [0003]    It is necessary in a range of applications to undertake inspection of safety-related plant parts located at points under water that are difficult to access. Such a safety-related plant part is, for example, the screws with which the core baffle is fastened on the core barrel in the reactor pressure vessel of a nuclear reactor. In order to permit ultrasonic inspection of these screws, it is necessary to position an ultrasonic inspection head on the head of the screw by remote control with the aid of a manipulator, arranged outside the refueling cavity, in a water depth of up to 10 m.  
           [0004]    Instead of the use of a manipulator arranged outside the refueling cavity, for the purpose of inspecting a cladding of a fuel pit, Japanese patent application JP 042 40 597 A, for example, discloses using a remote-controlled underwater vehicle fitted with an ultrasonic inspection head. However, because of the drives, illuminating devices and cameras required for it to be freely maneuverable, such an underwater vehicle has a relatively high intrinsic weight and, not least, because of a relatively voluminous float required thereby also has correspondingly large dimensions. It is therefore not not readily possible to approach points in the region of interior edges, for example the screws in the corner regions of the core baffle of a nuclear reactor pressure vessel.  
           [0005]    In order to be able to use such an underwater vehicle also to position the inspection head at points that are difficult of access, it has become known in principle from U.S. Pat. No. 5,193,405 and European patent EP 0 461 506 B1 to arrange the inspection head at the free end of a manipulator arm having six axes. However, controlling such a freely movable manipulator arm is complicated, and because of the torques exerted by the force of gravity on the freely floating underwater vehicle as a function of the position of the manipulator arm, it is difficult to keep the vehicle in a stationary floating state. For these reasons, the prior art underwater vehicle is provided with a plurality of suction cups with the aid of which it must be fixed on a smooth surface. The field of use is thus limited to plant parts with smooth walls.  
         SUMMARY OF THE INVENTION  
         [0006]    It is accordingly an object of the invention to provide an inspection device for submersed plant parts which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for an underwater vehicle that is not technically complicated and can also be used in the corner regions of a core baffle.  
           [0007]    With the foregoing and other objects in view there is provided, in accordance with the invention, a device for inspecting submersed plant parts, comprising:  
           [0008]    a remote-controlled underwater vehicle having an end face and a longitudinal central axis perpendicular to the end face;  
           [0009]    a carrier pivotally mounted at the end face exclusively about a pivot axis oriented parallel to the longitudinal central axis of the underwater vehicle; and  
           [0010]    a holding device for an inspection head mounted to the carrier at a spacing distance from the pivot axis.  
           [0011]    The device is, in particular, configured for ultrasonic inspection of plant parts such as screws in a core baffle of a nuclear reactor pressure vessel.  
           [0012]    In other words, the device includes a remote-controlled underwater vehicle that is provided at an end face with a carrier that can be pivoted or rotated exclusively about a pivot axis that is oriented parallel to a longitudinal central axis, running perpendicular to the end face, of the underwater vehicle. There is also provided a holding device for an inspection head that is arranged on the carrier at a spacing from the pivot axis. It is possible by this measure to move the inspection head into different positions relative to the underwater vehicle with the underwater vehicle stationary, and so it is also possible to inspect plant parts that are located offset from the longitudinal central axis of the underwater vehicle.  
           [0013]    In a particularly advantageous refinement of the invention, the carrier provided with the test head is balanced out in such a way that virtually no torque acting on the carrier about the pivot axis is exerted by the force of gravity irrespective of the pivoting position of the inspection head. Owing to this measure, different inspection positions can be approached with a freely floating underwater vehicle without the need of further complicated control measures for balancing and maintaining the floating state.  
           [0014]    In accordance with an added feature of the invention, the pivot axis is disposed at a spacing from the longitudinal central axis. Preferably, the pivot axis is disposed at an edge of the underwater vehicle. It is advantageous when the location and orientation of the pivot axis on the underwater vehicle and a spacing of the holding device from the pivot axis are coordinated with one another such that the inspection head can be brought into mutually opposite positions that project over a lateral edge of the underwater vehicle, or extend at least into a vicinity of it.  
           [0015]    In accordance with an additional feature of the invention, there are provided a multiplicity of support elements on the carrier. They are disposed in a circumferential direction about the pivot axis and spaced apart from one another in the circumferential direction.  
           [0016]    In accordance with another feature of the invention, a universal joint is provided for mounting the inspection head in the holding device.  
           [0017]    In accordance with a further feature of the invention, the carrier comprises a ring having a center on the pivot axis, the ring is fixed on a shaft of a first rotary drive with at least one radial spoke.  
           [0018]    In a preferred embodiment, the carrier is an optically transparent disc.  
           [0019]    In accordance with a concomitant feature of the invention, the inspection head is rotatably mounted in the holding device about a central axis extending parallel to the pivot axis.  
           [0020]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0021]    Although the invention is illustrated and described herein as embodied in a device for inspecting plant parts located under water, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0022]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a schematic outline view of a device in accordance with the invention during use for ultrasonic inspection of screws in the core baffle of a nuclear reactor pressure vessel;  
         [0024]    [0024]FIG. 2 is a perspective view of the device according to the invention;  
         [0025]    [0025]FIG. 3 is an elevational view of the end face of the device; and  
         [0026]    [0026]FIG. 4 is a side elevational view of the device according to the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, the device comprises a basic vehicle in the form of a remote-controlled underwater vehicle  2 . Such a vehicle is known, for example, under the trade name SUSI from Framatome ANP GmbH, of Germany. In accordance with the invention, the underwater vehicle  2  is provided at its end face  4  with a carrier  6  that is pivotally mounted on the underwater vehicle  2  about a pivot axis  10  oriented parallel to the longitudinal central axis  8 , running perpendicular to the end face  4 , of the underwater vehicle  2 . A holding device  12  is disposed on the carrier  6  at a spacing from the pivot axis  10 . The holding device  12  is fitted with an inspection head  14 , an ultrasonic inspection head in the exemplary embodiment, such as is known, for example, from European patent application EP 0 452 516 A1.  
         [0028]    The figure illustrates a situation such as arises from an ultrasonic inspection of screws  16  in the core baffle  18  of a reactor pressure vessel. As illustrated in the figure, a multiplicity of these screws  16  are located in corner positions of the core baffle  18  that cannot be directly (centrally) approached because of the relatively large dimensions of the underwater vehicle  2 . It is now possible to use the rotary or pivotable carrier  6  to inspect screws  16  in corner positions even when the underwater vehicle  2  is located laterally offset from these corner positions.  
         [0029]    In accordance with FIG. 2, the underwater vehicle  2  (drawn only schematically) is provided on its end face  4  with a camera  20  with integrated illumination, which can be used for visual monitoring of the traveling motion of the underwater vehicle  2 . Arranged on the underside of the underwater vehicle  2  is a first rotary drive  22  with a shaft  24  on which the carrier  6  is fastened at the end face. The carrier  6  is constructed in the exemplary embodiment from a ring  62  that is fixed via spokes  64  at the end face on the shaft  24  and can be pivoted—in the exemplary embodiment it can be endlessly rotated—about the pivot axis  10 . The holding device  12  is disposed on the ring  62 . The inspection head  14  is mounted in the holding device by universal joint. A second rotary drive  26  permits the inspection head  14  to be rotated about its central axis  28  in order to enable correct placement on the screw head, for example an internal polygon. Electric sliprings (not illustrated in the figure) serve to supply power to the two rotary drives, and to supply the ultrasonic inspection head  14 . This renders endless rotation of the carrier  6  possible.  
         [0030]    A plurality of support elements  66 , axially parallel pins in the example, are disposed on the end face of the ring  62 ; in the event of faulty positioning they prevent damage to the inspection head  14  and serve for aligning the underwater vehicle  2  (longitudinal axis perpendicular to the wall).  
         [0031]    Moreover, a balancing weight  68  is located opposite the inspection head  14  for the purpose of balancing out a weight load. In other words: the carrier  6  provided with the inspection head  14  is balanced out in such a way that the force of gravity exerts virtually no torque acting on the carrier  6  about the pivot axis  10  irrespective of the rotational position of the inspection head  6 . This measure facilitates the maintenance of a stationary floating state even when there is a rotary movement of the carrier  6 , and thereby facilitates the approach to the inspection position. It may be seen in the plan view of the end face in accordance with FIG. 3 that the inspection head  14  can be brought into lateral positions by rotating the carrier  6  about the pivot axis  10 . The latter is located at a spacing distance from the longitudinal central axis  8  at the edge, below the underwater vehicle in the example. These positions are approximately aligned with the lateral edge  30 , that is to say the lateral rim of the underwater vehicle  2 .  
         [0032]    Instead of a ring  62  illustrated in the figures, it is also possible to provide a transparent disk made from plastic as carrier  12  for the inspection head  14 .  
         [0033]    In accordance with FIG. 4, the inspection head  14  is mounted in the holding device  12  in a resilient fashion in the direction of its transmitting or central axis  28 . This is illustrated by the double arrow. The support elements  66  compel an axially parallel position of the inspection head  14  relative to the screw to be inspected, and prevent the inspection head  14  from being overloaded or damaged by the underwater vehicle  2  drifting away to the side.  
         [0034]    The inspection head  14  is now positioned over the screw head with the aid of the underwater vehicle  2 , and applied flush to the screw head by appropriately controlling the drive units of the underwater vehicle  2 . The correct positioning and coupling can be monitored with the aid of the echo signals picked up by the inspection head  14 . The drive units arranged in the underwater vehicle  2  hold the inspection head  14 , by exerting a slight contact pressure on the screw head, until the inspection is terminated. Further docking measures for holding the inspection position are not required because of the precision of the control of the underwater vehicle  2 .  
         [0035]    This application claims the priority, under 35 U.S.C. § 119, of German patent application No. 103 17 191.6, filed Apr. 15, 2003; the disclosure of the prior application is herewith incorporated by reference in its entirety.