Abstract:
An inspection assembly adapted to traverse an inspection surface, the assembly includes: a crawler body including a first side and a bottom side, wherein the first side is adapted to face a first inspection surface and the bottom side is adapted to engage a second inspection surface separated from the first inspection surface by a gap; a suction module in the crawler body adapted to create a suction between the first inspection surface to bias the crawler body against the first inspection surface; at least one roller mounted in the crawler body adapted to engage the first inspection surface, and at least one mast having a mount to receive a sensor, wherein said mast extendable from the crawler body into the gap.

Description:
BACKGROUND 
   The invention disclosed herein relates generally to inspection of using robots and in particular to inspection of welds of jet pump diffusers and jet pump adapters in boiling water nuclear reactors (BWRs). 
   BWRs typically include jet pumps that participate in recirculating water through the reactors. An array of jet pumps are generally located around the circumferential periphery of the reactor vessel in the BWR. In a typical BWR, there are commonly ten jet pumps each with a pair of diffusers that direct water to the jet pump. Each of the twenty diffusers is attached to or extend past a horizontal baffle plate between the reactor vessel wall and a outer wall of the reactor. While many BWRs have jet pump diffusers that are welded directly to the baffle plates, some reactors attach the jet pump diffusers to an adapter located below the baffle plate. The inspection crawler and method disclosed herein may be used to inspect welds of jet pump diffusers that extend down past the baffle plate. 
   Inspection of the welds between the adapter and diffusers is needed to monitor the integrity of the diffusers and water recirculation system. Inspecting welds of the adapter and diffuser requires an inspection scanner to traverse a narrow gap between the baffle plate and diffuser. The narrow gap has been problematic in inserting ultrasonic inspection scanners down passed the baffle plate to inspect the welds attaching the adapter and diffuser. There is a long felt need for devices to inspect welds of diffusers below a baffle plate. 
   SUMMARY 
   An inspection assembly has been developed that is adapted to traverse an inspection surface, the assembly includes: a crawler body including a first side and a bottom side, wherein the first side is adapted to face a first inspection surface and the bottom side is adapted to engage a second inspection surface separated from the first inspection surface by a gap; a suction module in the crawler body adapted to create a suction between the first inspection surface to bias the crawler body against the first inspection surface; at least one roller mounted in the crawler body adapted to engage the first inspection surface, and at least one mast having a mount to receive a sensor, wherein said mast extendable from the crawler body into the gap. 
   The sensor may be an ultrasonic transducer for weld inspections. The first inspection surface may be upright and circular in cross-section, and the second inspection surface may be substantially horizontal. The crawler body may include a driver module having at least one driver roller extending through the first side of the crawler body and adapted to engage the first inspection surface. Further, the suction module may include an impeller adapted to create a suction between the first side of the crawler body and the first inspection surface. A tracking wheel may be mounted on the crawler body and an encoder may generate a signal indicative of displacement of the tracking wheel across the second inspection surface. 
   An inspection assembly has been developed that is adapted to inspect welds associated with a diffuser in a jet pump in a boiling water nuclear reactor (BWR), the assembly comprising: a crawler housing including a first side surface and a bottom surface, wherein the first side surface faces a side surface of the diffuser and the bottom surface faces a baffle plate of the BWR; a suction device in the first side surface adapted to create a suction between the first side surface and a surface of the diffuser to bias the crawler body against the diffuser, and at least one mast having a mount to receive a sensor and said mast is supported by crawler housing. 
   A method has been developed for inspecting weld joints in a gap between an generally horizontal surface and a generally upright surface using a robotic crawler including a crawler body having at least one mast and a sensor mounted on the mast, the method comprises: positioning the crawler body on the horizontal surface and against the upright surface; establishing a suction between the crawler body and upright surface to seat the body against the upright surface; extending the mast and sensor into the gap below the crawler body; moving the crawler body across the horizontal surface while the suction seats the body against the upright surface, and sensing a condition in the gap with the sensor and conveying signals from the sensor to a control unit. 

   
     SUMMARY OF THE DRAWINGS 
       FIG. 1  is a perspective view of a boiling water reactor (BWR) with a cut away region to show exemplary jet pumps having diffuser shrouds and an adapter. 
       FIG. 2  is an enlarged cross-sectional view of a portion of a diffuser, an edge of a baffle plate and the adapter joining the tail pipe to the baffle plate. 
       FIG. 3  is a perspective view of a crawler for inspecting welds between the diffuser tail pipe, adapter and baffle plate. 
       FIG. 4  is a top down view of a crawler circumnavigating the perimeter of a diffuser and traversing a baffle plate. 
       FIG. 5  is a side view of a crawler seated on a baffle plate and against a diffuser with a mast projecting a scanner transducer between the diffuser tail pipe and adapter to inspect welds. 
       FIG. 6  a perspective view of a mast module for the crawler device. 
       FIG. 7  is a cross-sectional view of the mast module. 
       FIG. 8  is an enlarged perspective side view of a mast and scanner transducer. 
       FIG. 9  is an enlarged side view of a mast and scanner transducer extended into a cross-section of the gap between a diffuser tail pipe and adapter ring. 
       FIG. 10  is a perspective view of a first side of a driver module for the crawler body including drive rollers and a suction fan. 
       FIG. 11  is a perspective view of a second side of a driver module for the crawler with the frame of the module illustrated in outline to show the internal components of the body. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a perspective view of a BWR with a cut-away view to show a jet pump assembly  10  which is mounted on a baffle plate  12  between the wall  14  of the reactor pressure vessel and inner reactor core  16 . The jet pump assembly includes a pair of diffusers  18  that extend through an aperture  20  in the baffle plate. 
     FIG. 2  is a cross-sectional side, enlarged view of an edge of the baffle plate  12 , a diffuser conical tail pipe  22  and an adapter ring  24  connecting the tail pipe to the baffle plate. The adapter ring  24  drops the base of the diffuser tail pipe below the baffle plate. An annular gap  26  exists below the baffle plate and extends between the outer diffuser wall on one side and the baffle plate and adapter ring on the other side. A U-joint  32  at the bottom of the gap  26  joins the adapter ring to the diffuser  22 . 
   The aperture  20  in the baffle plate is defined by a circular edge of the baffle plate around the aperture. A narrow, annular gap  26  exists between the aperture edge of the baffle plate and the cylindrical side wall of the tail pipe  22 . Deep down in the gap  26  are a pair of annular welds, which include a weld  28  that joins the tail pipe  22  to an annular U-joint  32  and the weld  30  that joins the U-joint  32  to the annular adapter ring  24 . These welds  28 ,  30  require periodic inspection, but are deep in the gap  26  and difficult to reach with conventional weld inspection scanners. Another annular weld  34  joints the adapter ring  24  to the baffle plate  12 , is near the surface of the baffle plate. 
   In the annular gap  26 , the ultrasonic sensing heads must be inserted to inspect the welds  28 ,  30  and  34  that extend circumferentially around the diffuser and adapter ring. The welds are in the tight annular gap  26  below the baffle plate and around the periphery of the diffuser. It is difficult to insert ultrasonic sensing units to this annular gap. There is a long felt need for an ultrasonic inspection tool that can inspect the welds below the baffle plate that attach the diffuser of a jet pump to the adapter that connects the jet pump to the baffle plate. 
     FIG. 3  is a perspective view of a robotic weld inspection tool  40  has been developed that includes an arc-shaped crawler body  42  which traverses the baffle plate  14  as it circumnavigates a diffuser tail pipe  22 . The crawler device driven circumferentially around the diffuser  18 .  FIG. 4  is a top down view of a crawler body  42  leaning against a tail pipe  22  as it moves in a circular path  44  on the baffle plate  12  and around the tail pipe. 
   The crawler  40  includes multiple sensor masts  46  that may be extended down from the crawler body  42 . The masts extend into the annular gap  26  between the baffle plate aperture  20  and outer sidewall of the diffuser tail pipe  22 . The masts  46  support ultrasonic transducer units  48 ,  50  that transmit ultrasonic signals at welds  28 ,  30  and receives reflected signals from the welds and surrounding joined structures. The transducer units may be alternatively Eddy current transducers and imaging devices, e.g., a video camera. Further, the transducer units may have multiple types of sensors, such as one or more of an ultrasonic transducer, an Eddy current sensor and a video camera. 
   The masts  46  extend the transducer units down in the gap  26  until each unit is adjacent a corresponding weld. For example, the transducer head of unit  48  faces outward towards the outer weld  28  between the tail pipe diffuser and U-joint and the transducer head of unit  50  faces inward towards the inner weld  30  between the U-joint and adapter ring  24 . A third (optional) transducer head  51  may be positioned adjacent the weld  34  between the adapter ring and baffle plate. 
     FIG. 5  shows the crawler  40  with the crawler body  42  leaning against the sidewall of the diffuser tail pipe  22  and riding on the upper surface of the baffle plate  12 . The crawler body extends the respective masts  46  down into the gap  26 . (only the mast for transducer unit  48  is shown in  FIG. 5  for illustrative purposes). 
   The crawler body extends the transducer unit  48  down to the weld  28  to be inspected. The crawler may extend the transducer unit down a predetermined distance known to correspond to the location of the weld  28 . Alternatively, a transducer signal from the transducer unit  48  may be monitored as the mast extends and a characteristic change in the signal may be used to determine when the transducer unit is adjacent the weld  28 . Transducer signals, as well as power and control signals for the crawler body and masts, are conveyed through an umbilical connection that comprises power and signal wires extending from the body  42  to a power and control unit  54 , external to the reactor. 
   As the crawler moves about the diffuser, the ultrasonic transducer units  48 ,  50 ,  51  interrogate the welds  28 ,  30 ,  34  using ultrasonic emissions and collect ultrasonic signal reflections from the welds. These ultrasonic signal reflections are analyzed to determine the quality of the welds, and whether fatigue fractures or other defects exists in the welds. The crawler  40  indexes its movement around the diffuser so that its position is precisely known at each angular position around the diffuser. Accurate information regarding the crawler position is used to determine the location of the weld being inspected by the sensors supported by the crawler. Further, accurate transducer unit elevation information is collected by crawler body  42  as it moves up and down the mast shaft  46  for each transducer unit. The transducer units may be cyclically moved up and down to vertically traverse a weld as the crawler body slowly moves around the diffuser in a horizontal plane. 
   As shown in  FIG. 3 , conveying posts  56  on the crawler body allow hooks on a carriage (not shown) to lower the crawler  40  down into the reactor in the gap between the reactor pressure wall  14  ( FIG. 1 ) and the reactor core wall  16 . The crawler body  42  has a width (W), height (H) and an arc-shaped length (L). The crawler is lowered until tracking wheels  58  on one or both sides of the crawler body rest on the upper surface of the baffle plate. The tracking wheel  58  is rotationally coupled to an encoder  60  that monitors the rotation of the wheel and outputs a signal that can be converted to the distance traversed by the crawler body. The tracking wheel  58  may not be driven and may be turned by the movement of the crawler body across the baffle plate surface. 
   The crawler body  42  has an inside wall surface  62  that faces the tail pipe diffuser and an outer wall side  66 , opposite to the inner side. The inner side is generally rectangular in plan view and is has an arc shaped cross-section. The arc of the body  42  corresponds to an arc from the circumference of the tail pipe diffuser, as is shown in  FIG. 4 . The crawler body is intended to seat against the outer side surface of the tail pipe diffuser  22  ( FIG. 5 ) as the body circumnavigates the diffuser. 
   In one embodiment, the crawler body may form an arc of approximately 84°. The inner wall  62  of the crawler body is curved to conform substantially to the outer wall of the diffuser housing, e.g. the tail pipe. The outer wall  64  of the crawler body may be similarly curved. In one embodiment, the height (H) of the crawler body may be approximately seven inches (18 cm), the width (W) may be 1.2 inches (3 cm), and the length (L) across the arc of the body may be 16 inches (41 cm). 
   The crawler body provides a support frame for the mast modules  70  and a center driver module  64 . The mast modules each support a mast  46  and transducer unit. The driver module  64  includes driving rollers  66 . The modules are mounted in a frame of the crawler body. The frame includes an upper support plate  72  to which each of the modules is attached, e.g., bolted. Further, the conveying posts  56  may be attached to the outermost modules  70  and a tracking wheel assembly and encoder  58  may be attached to a lower corner of one of the outermost modules  70 . 
   The crawler body includes a wiring harnesses  62  and passages for the sensor wires, power wires and other wires  64  from the transducers to a common wiring outlet  66  which may include a plug. The plug connects to an umbilical cord  68  which connects the sensor wires and power wires in the crawler body to an external instrument and power source and control device. 
   The crawler body supports three mast modules  70  each having a mast  46  and one of the ultrasonic transducer units  48 ,  50  and  51 . Each mast module includes wiring for the sensor signals, control actuators and a motor  78  to operate the transducer and mast. The movement of the mast is precisely controlled such that the ultrasonic transducer at a distal end of the mast is accurately positioned with respect to the crawler body. 
     FIG. 6  a perspective view of a mast module  70  for the crawler device and  FIG. 7  is a cross-sectional view of the mast module  70 . The module is a generally rectangular block having an aperture  74  extending vertically through the block to receive the sensor mast. The mast moves up and down through the aperture module  70 . The mast shaft has gear teeth that engage a rotating gear wheel  76  in the mast module. A motor  78  drives the gear wheel  76  through bevel gears  80 . The motor may be powered through the umbilical cord or by batteries. The power and control unit  54  ( FIG. 5 ) may provide power for the motor, control signals to actuate the motor to raise or lower the mast shaft, and receive displacement signals that indicate the movement of the shaft  46  and thus the elevation of the transducer unit. A collar  82  is adjustably attached to the shaft to ensure that the transducer unit is not raised beyond a predetermined elevation. 
   A roller  84  slides up and down in a slot  86  in the side of the mast module  70 . The roller assists in managing the cables used for control, power and sensor signal transmission with the transducer units  48 ,  50 ,  51 . In each mast module, a cable for the transducer unit is looped over the roller  84 . As the mast is extended, the roller moves upward to reduce the length of cable looped in the slot  86  and to allow cable to be extended with the mast. As the mast is retracted, the roller moves downward to pull up the cable and temporarily store a section of the cable in the slot  86 . 
     FIG. 8  is an enlarged side view of a distal end of a mast  46  and scanner transducer unit  48  (but could be  50  or  51 ) and  FIG. 9  shows the mast and transducer unit extended down into a gap between a diffuser tail pipe and adapter. The transducer unit includes a yolk  88  and a transducer sensor head  90 . The yolk  88  is pivotably attached to a distal end of the mast  46 . Arms on the yolk fit around and support the transducer sensor head  90  which pivots so that the face  92  of the head is adjacent the surface being inspected. A post  94  on the back of the yoke prevents the sensor head from abutting against the wall surface opposite the wall and weld being inspected. The yolk pivots the sensor head  90  such that the sensor face  92  is adjacent, e.g., abuts, the wall surface  22 ,  32 , and weld  28  to be inspected. The yolks on the other masts each similarly pivot a face of a sensor head against a corresponding wall surface and weld. 
     FIG. 10  is a rear perspective view of the driver module  64  and  FIG. 11  is a front perspective view of the driver module with the internal components of the driver visible in the driver housing  96 . The housing is generally rectangular and has a arc-shape to conform to the crawler body and tail pipe diffuser. The driver module  64  may be mounted in a center section of the crawler body. The driver module includes a pair of rotating drive rollers  66  mounted vertically and on opposite sides of the module. The drive rollers engage the surface of the tail pipe to move the crawler around the tail pipe. The drive rollers  66  may extend more than one-half the length of the height of the crawler body to provide good traction between the rollers and tail pipe surface. The rollers  66  extend partially out of the crawler body and past the inside surface  62  to the body so that they may engage the tail pipe. 
   The drive rollers are powered by a motor  98  internal to the drive module  64 . A drive belt  100  or chain is moved by the motor and turns both rollers at a common speed. Rollers  102 , including a tension roller, guide the belt between the motor and rollers and ensure that the belt is under an appropriate amount of tension. The motor for the rollers may receive power through the umbilical cord  52  or from batteries. The motor and/or the gearing for the drive belt are actuated by control signals from the power and control unit  54 . 
   The drive module includes a suction module  104  mounted between the rollers. The suction module creates a slight suction between the crawler body and diffuser to ensure that the crawler body properly seats against the diffuser wall, e.g., tail pipe. The suction module includes an impeller  106  in an annular shroud housing  108 . The impeller is rotatably mounted in the suction module and is driven by a belt extending from the impeller axis to a gear  110  that engages a drive gear powered by a motor in the suction module, e.g., horizontally mounted in the module above the impeller. The impeller  106  creates a slight suction between the inner wall of the crawler body and the wall of the diffuser tail pipe. The motor for the impeller may receive power through the umbilical cord or from batteries. The motor and/or the impeller gearing are actuated by control signals from the power and control unit  54 . 
   In operation, the crawler  40  may be used when the reactor is opened for refueling. The robotic crawler body  42  is lowered into the gap  26  between the reactor pressure wall  14  and core  16 , and positioned on the baffle plate  12  and abutting against a tail pipe  22  of a diffuser for a jet spray pump. The umbilical cord  52  from the crawler body  42  is connected to the power and control unit to provide power to the crawler body, and to establish control and communication with the crawler body. The impeller  108  is started to seat the crawler against the diffuser tail pipe. 
   A technician operates the crawler through the power and control unit  54 . The masts  46  of the crawler body are lowered to position the transducer units  48 ,  50  and  51 , adjacent each of the weld to be inspected. The crawler body may be positioned at particular angular position around the diffuser so that the initial position of the crawler can be determined. The technician confirms that appropriate signals are being received from each of the transducer units and that the crawler is properly communicating with the control unit. The technician commands the drive motor  98  to be actuated and the crawler slowly moves around the diffuser. As the crawler moves, the welds  28 ,  30 ,  34  are interrogated with ultrasonic signals from a respective one of the transducer units. The reflected signals from the welds are analyzed and captured by the computer control unit  54 , and may be displayed on a computer screen for viewing by the technician. The crawler may move the masts and transducer units up and down to sweep the surfaces of the welds as the crawler moves around the diffuser. The movement of the crawler is measured by the tracking wheel  58  that rolls across the baffle plate. An encoder on the tracking wheel generates displacement signals indicating the distance traveled by the crawler body. The weld inspection is completed for a diffuser when the crawler body has traversed the entire circumference of a diffuser tail pipe. The crawler body may be lifted and shifted to another diffuser tail pipe where another weld inspection is performed. 
   While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.