Patent Publication Number: US-2010119028-A1

Title: Nuclear reactor steam dryer manipulator

Description:
Priority to U.S. Provisional patent application Ser. No. 61/195,585 filed Oct. 8, 2008, is claimed, the entire disclosure of which is hereby incorporated by reference. 
    
    
     The present invention relates generally to nuclear reactor service manipulators for steam dryers. 
     BACKGROUND OF THE INVENTION 
     During the refueling outages at Boiling Water Nuclear Reactor (BWR) plants, the steam dryer is typically positioned in the refueling canal and visually examined to verify the integrity of its structural welds. Since the steam dryer is highly radioactive, the examination is performed remotely and underwater. 
     Many steam dryers BWR reactors have been inspected and have required weld repairs in order to continue to operate. Strict inspection requirements are now in place that require utilities to perform inspections on most of the horizontal and vertical welds used to form the dryer assembly. These dryer inspections have increased maintenance schedules while the utilities continue to drive outage durations down. 
     Previously inspections were performed manually off long poles while the operators stood in either side of the pool or on an auxiliary bridge or platform. This was time consuming, expended dose, required many crew members and did not provide a stable inspection platform. 
     U.S. Pat. No. 7,092,477 discloses a BWR inspection manipulator in which the manipulator is supportable on the BWR reactor shroud and inspects the areas adjacent a BWR shroud without obstructing refueling. The inspection manipulator has an arm extending on an inboard and an outboard side of the BWR body. This patent is hereby incorporated by reference herein. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a visual inspection manipulator for a BWR steam dryer which is of high quality video and from a stable platform. A further additional or alternative object is to provide shorter inspection times of the BWR dryer with less radiation dose expended and without using an existing refuel or auxiliary bridge. 
     The present invention provides a BWR steam dryer remote visual inspection system including a support moveable along a first axis over the steam dryer, the support having a longitudinal direction; a trolley movable along the support in the longitudinal direction; a mast fixed to the trolley and moveable at a predetermined angle with respect to a plane defined by the first axis and longitudinal direction; and a camera coupled to an end of the mast. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One preferred embodiment of the present invention will be described with respect to the drawing in which: 
         FIG. 1  shows a sectional view, with parts cut away, of a boiling water nuclear reactor pressure vessel; and 
         FIG. 2  shows an embodiment of the present invention of a BWR inspection manipulator. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a sectional view, with parts cut away, of a boiling water nuclear reactor pressure vessel  2 . Reactor pressure vessel  2  is typically cylindrical in shape and closed on one end by a bottom end  4  and on the other end by a top head  6 . Top head  6  is removable. A side wall  18  extends from top head  6  to bottom end  4 . A reactor core  20  is surrounded by a shroud  16 . An annulus  24  is formed between shroud  16  and sidewall  18 . A pump deck  26  extends between the base of shroud  16  and side wall  18 . Pump deck  26  is ring shaped and has circular openings used to house jet pumps  28 . Jet pumps  28  are circumferentially distributed around shroud  16 . Reactor core  20  includes fuel bundles  36  of fissionable material, which cause reactor core  20  generate heat. Water is circulated up through core  20  and partially converted to steam. Steam separators  38  separate steam from water, which is recirculated. Residual water is removed from the steam by steam dryers  50 . Steam exits the reactor pressure vessel through a steam outlet  42  near top head  6 . 
       FIG. 2  shows a steam dryer shell  50  of a BWR reactor and a steam dryer remote system (SDRS)  100 . SDRS  100  is an orthogonal, three degree of freedom manipulator used to remotely position a camera  52  near a weld on steam dryer  50  to perform an examination of the weld. Camera  52  can pan, tilt and zoom. Camera  52  is positioned on a long pole  53  that is positioned vertically by a mast  56 . Mast  56  is mounted on a remote center trolley assembly  58  which moves mast  56  in direction Z. Center trolley  58  is moved along a bridge  60  in direction Y. Bridge  60  spans the longitudinal direction L and is mounted on two side trolleys  62 . Side trolleys  62  are driven by a common shaft to assure they move in unison along the sides of the refueling canal in an X direction. Side trolleys  62  travel along two identical sets of side tracks  64 . Side tracks  64  are mounted along the length of the refueling canal. Side tracks  64  are supported by a series of track hangers  66 . Track hangers  66  hook over the curbs of the canal to support side tracks  64 . The SDRS  100  includes cables managed in two cable chains, e.g., two IGUS brand cable chains. A first cable chain is supported by a series of trays  68 . Trays  68  are mounted to the refueling pool hand rails  70 . A second cable chain is contained in trays that mount along the top of the axis of bridge  60 . Except for the first cable tray  68 , the SDRS  100  can be entirely contained inboard of the refueling canal hand rails  70 . 
     All three axes of SDRS  100  are driven by brushless DC gear-motors with integral fail-safe brakes that are able to move at speeds of up to 1 foot per second, one motor for moving mast  56  in the Z direction, a second motor for driving bridge  60  in the X direction and a third motor for driving trolley  58  in the Y direction. The resulting system is capable of rapidly and remotely positioning camera  52  at any location around dryer  50  to permit visual examination of the welds. This three dimension arrangement is a simpler and more cost effective design than previous devices. 
     SDRS  100  can be manually controlled using simple encoded joystick controls or remotely controlled by a computer. 
     The control software of SDRS  100  utilizes a 3D graphical display for control. The operator can simply position and click the mouse on the start of a weld and SDRS  100  moves camera  52  to a start position. The software utilizes state of the art path planning code to pick the correct path to move the tool safely. In addition, the software is equipped with collision avoidance that ensures that the tool slows down in tight areas and stops when necessary. The tool design uses robust simple drive components to manipulate the three axis. A single motor is used with multiple gear boxes to drive two sprockets on opposite rails so that bridge  60  drives straight. 
     Because the present invention can be used for inboard use only to inspect the steam dryer, it requires a less complex and more cost effective structure than prior art that is for both inboard and outboard use.