Abstract:
A visual inspection device configured to traverse a steam dam around a perimeter of a nuclear boiling water reactor vessel and support a camera for performing visual inspections. The device includes a trolley having at least two roller assemblies coupled by a connecting member. The roller assemblies steer the trolley around the perimeter of the reactor vessel. At least one of the roller assemblies is driven by a first motor. The device also includes a mast upstanding from the trolley, an elevating mechanism coupled to the mast, a carriage coupled to the mast and the elevating mechanism, the carriage being responsive to activation of the elevating mechanism for movement relative to and along the mast, a first arm rotatably coupled at a first end to the carriage, and a second arm rotatably coupled to a second end of the first arm, the camera being supported by the second arm.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to devices used in the boiling water reactor industry, and more specifically to devices that perform maintenance on vessel components.  
         BACKGROUND OF THE INVENTION  
         [0002]    In the boiling water reactor industry, the reactor is a pressure vessel where the nuclear reaction takes place. The nuclear reaction generates heat, which boils water to create steam; the steam then powers turbines to generate electricity. In the reactor, welds are inspected for cracks while in-vessel components are also inspected for wear. This is called In-Vessel Visual Inspections (“IVVI”). The reactor is disassembled for refueling outages and in-vessel servicing takes place at this time. Typically, the following components and welds are inspected during in-vessel servicing:  
           [0003]    Feedwater spargers &amp; nozzle welds  
           [0004]    Feedwater end brackets &amp; T-Box welds  
           [0005]    Feedwater nozzle penetrations  
           [0006]    Core spray piping &amp; downcomers  
           [0007]    Core spray spargers &amp; T-Box welds  
           [0008]    Core spray brackets &amp; end caps  
           [0009]    Top guide hold down bolts  
           [0010]    Shroud welds  
           [0011]    Jet pump assembly  
           [0012]    Nozzle penetrations  
           [0013]    Baffle plate inspection  
           [0014]    Core verification  
           [0015]    Fuel spotting support  
           [0016]    In-vessel maintenance is also performed during the refueling outage. Examples of in-vessel maintenance include:  
           [0017]    Nozzle flushing  
           [0018]    Lost parts retrieval  
           [0019]    Weld cleaning  
           [0020]    Underwater vacuuming  
         SUMMARY OF THE INVENTION  
         [0021]    In the past, contractors have performed IVVI for the utility industry. The basic practice has been to use a hand-held underwater camera system from the refueling bridge. This practice required the sole use of the refueling bridge by the contractors, which delayed moving fuel into the reactor core. This practice also extended the duration of the refueling outage. Any lost time on the critical path (the amount of time between shut down and start-up of the reactor) costs the utility company large amounts of money. Camera systems have been improved for better performance, but inspection time was still required. Eventually, the industry began to use an auxiliary bridge and two IVVI teams to help decrease the duration of the refueling outage. This increased the cost of the outage, but saved millions of dollars by shortening refueling outages from 90 days to 30 days.  
           [0022]    Certain time windows must be placed on the refueling schedule. One of those windows is refueling the reactor core with new fuel bundles. This task requires the sole use of the refueling bridge. Any work that can be performed while fuel movement is taking place gains time on the critical path. All previous attempts to do this have failed. Some have attempted to perform IVVI from an aluminum boat while moving fuel; this was deemed an unsafe work practice and has never been attempted since. Therefore, a need exists in the industry for a device that performs IVVI while moving fuel into the reactor core. This device also needs to be self-contained so that set-up and tear down times are minimized. Each construction of the present invention fulfills one or more of these needs.  
           [0023]    Th present invention provides a device that addresses some of the needs of the boiling water reactor industry and the shortcomings of prior art. The present invention is a delivery device for an underwater camera system that performs visual inspection and maintenance of welds and reactor components while traversing a nuclear reactor vessel. Since the vessel is filled with water, the device must operate underwater to perform the visual inspection and maintenance. IVVI can be performed remotely by the device while refueling the reactor. The preferred device comprises a trolley, mast, carriage, swing arm, and support arm. A commonly available pan and tilt camera system is mounted to the carriage through a support arm that rotates about a swing arm. The support arm is rotatable between a standard and inverted position. The swing arm swivels off the carriage to allow the camera system to rotate about an axis parallel to an axis defining the mast length. The carriage moves vertically on the mast that is centrally mounted on the trolley. The trolley rolls around the steam dam, which is essentially the perimeter of the reactor vessel. The steam dam is circular and is used as a track to guide the device to different azimuths for inspections or maintenance.  
           [0024]    Since the device can be controlled remotely, IVVI can be performed while moving fuel into the reactor core. The device is also self-contained so that set-up and tear down times are minimized. Further features and aspects of the present invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    The present invention is further described with reference to the accompanying drawings, which show preferred constructions of the present invention. However, it should be noted that the invention as disclosed in the accompanying drawings is illustrated by way of example only. The various elements and combinations of elements described below and illustrated in the drawings can be arranged and organized differently to result in constructions which are still within the spirit and scope of the present invention.  
         [0026]    In the drawings, wherein like reference numerals indicate like parts:  
         [0027]    [0027]FIG. 1 is a perspective view of a delivery device embodying the present invention showing a camera system in a standard position with an attached vacuum hose;  
         [0028]    [0028]FIG. 2 is an enlarged view of a carriage of the delivery device of FIG. 1;  
         [0029]    [0029]FIG. 3 is a perspective view of the delivery device of FIG. 1 showing the camera system in an inverted position with an attached water lance;  
         [0030]    [0030]FIG. 4 is a perspective view of a trolley;  
         [0031]    [0031]FIG. 5 is a front view of the trolley of FIG. 4;  
         [0032]    [0032]FIG. 6 is a partial perspective view of a mast including a lead screw and electric motor;  
         [0033]    [0033]FIG. 7 is a front view of the mast of FIG. 6;  
         [0034]    [0034]FIG. 8 is a top view of the mast of FIG. 6;  
         [0035]    [0035]FIG. 9 is a perspective view of a carriage with portions removed;  
         [0036]    [0036]FIG. 10 is a front view of the carriage of FIG. 9 with portions removed;  
         [0037]    [0037]FIG. 11 is a top view of the carriage of FIG. 9 mounted to the mast;  
         [0038]    [0038]FIG. 12 is a side view of the delivery device of FIG. 1 mounted to the reactor steam dam; and  
         [0039]    [0039]FIG. 13 is a front view of the delivery device of FIG. 12 mounted to the reactor steam dam. 
     
    
     DETAILED DESCRIPTION  
       [0040]    With reference to FIG. 1, the present invention comprises a delivery device  40  that traverses the perimeter of a circular steam dam  44 , which acts as a track around the perimeter of the vessel  48 . A trolley  52  provides the propulsion for the delivery device  40  and includes two roller assemblies  56  coupled by a connecting member  60 . Each roller assembly  56  includes a combination of steam dam rollers  64  and shroud flange rollers  68 . The steam dam rollers  64  utilize a v-notch  72  to assist in centering the trolley  52  on the steam dam  44 . The shroud flange rollers  68  also utilize a v-notch  72  to assist in centering the trolley  52  on the shroud flange  76 . In the illustrated construction, each roller assembly  56  includes two steam dam rollers  64  and two shroud flange rollers  68 . Two roller assemblies  56  are utilized in the illustrated construction, each assembly  56  being located at opposite ends of the trolley  52 . Both roller assemblies  56  utilize a 24-volt DC high torque, low speed electric motor  80  capable of both clockwise and counter-clockwise rotation. Torque is transmitted from the motor  80  to the steam dam rollers  64  through a rubber belt  84 . As a result, in the illustrated construction, all four steam dam rollers  64  on the trolley  52  are powered while the remaining shroud flange rollers  68  are not powered.  
         [0041]    In another construction (not shown), the roller assemblies  56  can utilize multiple combinations of steam dam rollers  64  and shroud flange rollers  68 . For example, each roller assembly  56  can utilize more or less than four rollers.  
         [0042]    In yet another construction (not shown), the roller assemblies  56  can be configured to power the shroud flange rollers  68  rather than the steam dam rollers  64 . In addition, only one of the roller assemblies  56  can be configured to propel the trolley  52 .  
         [0043]    In the illustrated construction, the roller assemblies  56  are rigidly coupled to the connecting member  60  using ordinary fasteners. Each roller assembly  56  is coupled at an angle relative to the connecting member  60 . As a result, the trolley  52  traverses an arc of a predetermined radius.  
         [0044]    In another construction (not shown), the roller assemblies  56  can be pivotally coupled to the connecting member  60  to allow the trolley  52  to traverse an arc of virtually any radius. Using this configuration, the trolley  52  could also traverse an arc having a varying radius rather than a constant radius.  
         [0045]    With reference to FIGS. 1 &amp; 3, a mast  88  provides a vertical guide for a carriage  92 . In the illustrated construction, the mast  88  is centrally mounted on the trolley  52  and attached through a base plate  96  using common fasteners. To help minimize component weight, the mast  88  may be constructed using aluminum square tubing. The mast  88  also has a handle  100  used for installation and removal.  
         [0046]    In the illustrated construction, an elevating mechanism in the form of a lead screw  104  spanning the entire length of the mast  88  is mounted to one side of the mast  88 . The lead screw  104  is mounted to the mast  88  by two pillow blocks  108  positioned at opposite ends of the mast  88 . The elevating mechanism also includes a 24-volt DC high torque, low speed electric motor  80  that directly drives the lead screw  104 . The 24-volt DC high torque, low speed electric motor  80  is capable of both clockwise and counter-clockwise rotation.  
         [0047]    The lead screw  104  provides vertical movement for the carriage  92 . As shown in FIGS. 1-3 &amp;  9 - 11 , the carriage  92  utilizes a threaded member  112  that includes internal threading matched to engage the threading of the lead screw  104 . The threaded member  112  is affixed to the carriage  92  such that rotation of the lead screw  104  results in vertical movement of the carriage  92  on the mast  88 . A series of rollers  116  guide the carriage  92  along the mast  88 . The rollers  116  are configured such that the mast  88  is disposed between two sets of four rollers  116 . The rollers  116  are mounted to opposing walls of a box structure  120  that fits entirely around the mast  88 . Alternatively, the rollers  116  can be configured in any way such that the carriage  92  traverses in a stable manner along the mast  88 .  
         [0048]    In another construction (Appendix), the carriage  92  ascends or descends the mast  88  using the 24-volt DC high torque, low speed electric motor  80  coupled to a spur gear (Appendix) that engages a rack (Appendix). The electric motor  80  can be mounted on the carriage  92  towards one side of the mast  88 . The electric motor  80  is positioned on the carriage  92  such that a spur gear coupled to the electric motor  80  engages the rack. Torque applied by the electric motor  80  to the spur gear results in a vertical movement of the carriage  92 .  
         [0049]    In yet another construction (not shown), the carriage  92  can utilize powered rollers  116  to provide vertical movement for the carriage  92 . The rollers  116  can be driven by another 24-volt high torque, low speed electric motor  80  through a belt (not shown) similar to the arrangement used in the trolley  52 . The rollers  116  can include a sticky surface to maintain traction along the mast  88 . Alternatively, treads (not shown) can be wrapped around a configuration of rollers  116  (similar to a tank tread configuration) to provide additional grip to the mast  88 .  
         [0050]    In the illustrated construction, another 24-volt DC high torque, low speed electric motor  80  is mounted on the carriage  92 . This motor  80  is also capable of clockwise and counter-clockwise rotation. This electric motor  80  swivels a swing arm  124  off the carriage  92 . The swing arm  124  is mounted to the carriage  92  by two pillow blocks  108  that support an intermediate shaft  128 . The intermediate shaft  128  includes a sprocket  132  that is driven by the electric motor  80  through a belt  136 . The electric motor  80  drives the belt  136  using another sprocket  140 . The sprockets  132 ,  140  are sized to provide an increase in torque and a decrease in speed to the intermediate shaft  128 . The swing arm  124  is mounted to the intermediate shaft  128  at a 90-degree angle such that the swing arm  124  swivels about an axis coaxial with the intermediate shaft  128 . The swing arm  124  has the capability of about 270 degrees of rotation.  
         [0051]    A support arm  144  is mounted to the end of the swing arm  124  by a shoulder bolt (not shown). The support arm  144  is mounted to the swing arm  124  so that it rotates about an axis coaxial with the swing arm  124 . A float chamber  148  is mounted towards one end of the support arm  144  while a pan and tilt camera system  152  is mounted towards the other end of the support arm  144 . The float chamber  148  is buoyant and is sized to help offset the weight of the camera system  152  acting on the device  40 . In the illustrated construction, the support arm  144  is mounted to the swing arm  124  in one of two positions, the standard position or the inverted position. As shown in FIG. 1, the standard position allows the device  40  to perform lower region inspections. The support arm  144  is rotated such that the camera system  152  is positioned towards the bottom of the device  40  and the float chamber  148  positioned towards the top of the device  40 . As shown in FIG. 3, the inverted position allows the device  40  to perform upper region inspections. The support arm  144  is rotated such that the camera system  152  is positioned towards the top of the device  40  while the float chamber  148  is positioned towards the bottom. When switching from a lower region inspection (standard position) to an upper region inspection (inverted position), the device  40  is pulled from the vessel  48 , the shoulder bolt loosened, the support arm  144  manually rotated, then finally the shoulder bolt is re-tightened to lock the support arm  144  in place.  
         [0052]    In another construction (not shown), a commonly available air cylinder (not shown) mounts to the swing arm  124  and connects to the support arm  144 . The air cylinder maintains the support arm  144  in a vertical position with respect to the installation of the device  40  on the steam dam  44 . The device  40  is installed on the steam dam  44  with the camera system  152  in an upper position with respect to the installation. In the upper position, the air cylinder rod (not shown) is extended. The rod may be retracted to allow the support arm  144  to rotate, thus allowing the float chamber  148  to move to the upper position while the camera  152  moves to a lower position. When the rotation is complete, the rod is extended once again to maintain the support arm  144  in a vertical position with respect to the installation of the device  40  on the steam dam  44 .  
         [0053]    In yet another construction (not shown), a commonly available 24-volt DC high torque, low speed electric motor  80  including an attached gear (not shown) can mount to the swing arm  124  such that the attached gear engages another gear mounted to the support arm  144 . The gear mounted to the support arm  144  can be coaxially mounted with an axis defined by the swing arm  124  such that rotation of the support arm  144  occurs about the swing arm  124 . During operation, the device  40  is installed on the steam dam  44  with the camera system  152  in the inverted position. In the inverted position, the electric motor  80  maintains the support arm  144  in a vertical position whereby the camera system  152  is positioned toward the top of the device  40 . The electric motor  80  can be energized to rotate the support arm  144 , thus moving the float chamber  148  to the upper position while the camera system  152  moves to a lower position. When rotation is completed, the motor  80  is de-energized to maintain the support arm  144  in the standard position.  
         [0054]    The device  40  and camera system  152  are controlled remotely from a station (not shown) located on the refueling floor (not shown). An umbilical (not shown) comprising the camera system cable (not shown) and the power cables (not shown) for the device  40  extend from the device  40  to the remote station. Floats (not shown) are attached to the umbilical to keep it buoyant in the water.  
         [0055]    In the illustrated construction, additional tooling is utilized to perform in-vessel maintenance. Such tooling may include a water lance  156 , an underwater vacuum hose  160 , or remote air operated pliers (not shown). The tooling is attached to a remote arm (not shown) that is mounted to the side of the camera system  152 . As shown in FIG. 1, an underwater vacuum hose  160  is mounted to the camera system  152 , while a water lance  160  is shown mounted to the camera system  152  in FIG. 3. The pan and tilt motion of the camera system  152  allows the tooling to be used on an object in view of the camera system  152 . When the tooling is utilized, either a water hose (not shown) or air hose (not shown) is incorporated with the umbilical to provide the water lance  160  with pressurized water, the vacuum hose with vacuum, and the pliers with pressurized air respectively.