Abstract:
A reactor head inspection system for use in performing a non-destructive inspection of tubular components mounted on an interior surface of a reactor head is disclosed. The inspection system includes a movable carriage assembly including a elevation arm and an inspection device mounted at a distal end of the elevation arm. The inspection device includes a C- or U-shaped collar having an interior surface of sufficient interior dimension to enable positioning of the interior surface of the collar in close proximity of an exterior surface of a tubular component and also includes a magnetic and/or eddy current sensor. A plurality of video cameras and light sources are also provided on a distal surface of the collar such that, when mounted on the elevation arm, the collar can be controllably positioned in close proximity adjacent a tubular component of the reactor head to achieve a 360° view and inspection of a surface of the tubular component.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a method and apparatus for inspecting the head assembly of a reactor vessel. Particularly, the invention describes a system for performing remote external (visual) and internal (e.g. magnetic field, eddy current) inspection on site of the interior of a head of a reactor vessel during periods of servicing and recharging the reactor vessel. In particular, the method of the invention employs a sensor system which includes an ability to not only locate flaws, i.e. cracks, in the reactor head components, but also includes an ability to predict the formation of flaws by monitoring the magnetic permeability of the reactor head components. A visual inspection device of the invention functions both as a positioning device for precise location of an inspection device and as a 360° evaluation device of the surfaces of a reactor component, e.g., J-weld. Further, the internal inspection device of the invention performs a 360° evaluation of a reactor component. The transport system of the invention includes a remotely controlled carriage which can be moved into position after the reactor head assembly is placed onto a support structure and can be precisely placed for deployment of the internal and external inspection device.  
         [0003]     2. Description of Related Art  
         [0004]     Conventionally, the internal components of a reactor are inspected by removing the components and placing the components on a support stand which enables remote inspection of the components. See U.S. Pat. No. 5,544,205 in which reactor fuel rod components are removed from the reactor to a support station, and inspected using a remote camera to position a carriage supporting the inspection device. The support station assembly before inspection must undergo a setup operation which includes filling the inspection station with water and positioning a complementary overhead mast structure to cooperate with the inspection device. The inspection device, such as a remote measurement sensor, i.e., a reflected laser light source/photodetector, is coupled with the overhead mast for vertical positioning inside the guide tubes of the reactor. U.S. Pat. No. 4,272,781 teaches a similar inspection device in which a camera for controlling the position of a measurement probe. The positioning camera and probe are each mounted on a movable carriage for movement over a variety of surfaces, preferable smooth curved surfaces. U.S. Pat. Nos. 5,745,387 and 6,282,461 teach other video positioning systems for inspection probes in which the video camera is mounted at the distal end of a manipulator arm.  
         [0005]     Visual inspection devices for control rod guide tubes also well known, as shown in U.S. Pat. No. 5,078,955. This system employs an internal inspection device which is positioned within the guide tube and moved to a position for visually inspecting openings in the guide tube. U.S. Pat. Nos. 4,729,423 and 5,604,532 teach other methods and apparatus for visually inspecting the ends of reactor tubes or the inside of a pressurized vessel utilizing a camera mounted on the end of a laterally adjustable boom mounted inside the vessel.  
         [0006]     The inspection of the interior of welds on reactor tubes, tube sheets and support plates can be performed utilizing sonic, magnetic and electric field sensors. U.S. Pat. Nos. 6,624,628, 6,526,114, 5,835,547 and 5,710,378 teach the use of such sensor probes to evaluate the interior of reactor components. Additionally, many variations of a movable carriage, such as those described in U.S. Pat. Nos. 5,350,033, 6,672,413 and 4,569,230, are known for positioning inspection probes within reactor vessels.  
         [0007]     For reactors, particularly nuclear reactors, it is necessary to perform an inspection of each component of the reactor at regular periodic maintenance intervals. Inspection devices, like those discussed above, have not been developed to inspect the components of the reactor head without requiring the extensive setup procedure. For example, the conventional reactor head can include a plurality of openings having secured therein guide sleeves which are welded in place. The sleeves can receive a rack assembly extending in closely spaced tolerance within the sleeve and a prescribed distance into the reactor. A reliable inspection system is needed for repeatedly evaluating each sleeve component of the reactor head to not only determine that the tolerances of the rack assembly within a sleeve are within an acceptable range, but also to determine the fitness of each component weld, i.e., determine the presence of actual flaws (cracks) in the component and predict the likelihood of flaws occurring by sensing the magnetic permeability of the component. None of the inspection systems of the prior art discussed above provides a robust, versatile inspection device and/or carriage for performing these inspection functions for reactor head components.  
         [0008]     While the inspection systems of the prior art above do not solve the need for repeatedly inspecting the components of a reactor head, those systems are also quite complicated, require extensive manufacturing operations and considerable expense. A simpler system is needed for repeatedly, visually inspecting the exterior surfaces of reactor head components and non-destructively inspecting the inside of the same components to determine the presence of flaws and to predict the likely location of the formation of flaws.  
       SUMMARY OF THE INVENTION  
       [0009]     A primary object of the present invention is to provide an apparatus and method for transporting a sensor assembly to the inside a reactor head and easily, repeatedly positioning a visual inspection and/or non-destructive inspection probe into close proximity along a component of a reactor head for inspection of the component surface and/or the interior of the component, particularly, to determine the presence of flaws and predict the likelihood of the formation of flaws in the component, as well as any loss of tolerances in the component.  
         [0010]     This object of the invention is achieved by providing a movable carriage having elevation support elements for positioning the inspection probe and providing a simple probe element which will enable 360° inspection of the exterior and/or interior of the reactor head components.  
         [0011]     In one embodiment of the invention, the probe is constructed as an open-ended inspection collar, e.g., C- or U-shaped inspection collar, having embedded video cameras and, a non-destructive inspection device, such as an eddy-current measurement sensor, ultrasonic sensor, magnetic field sensor. In a preferred embodiment, the collar is mounted at the end of an elevator arm supported by a movable carriage and includes a magnetic inspection probe having a magnetic permeability sensor which determines the location of actual flaws in the reactor component, and also enables accurate prediction of the location of the formation of flaws at some later time.  
         [0012]     The method of inspection of the invention involves precisely positioning the C- or U-shaped collar in close proximity to a reactor head component utilizing the video cameras, e.g. position adjacent a guide sleeve and rack assembly, such that both a 360° video inspection of the exterior surface and tolerances of the components can be performed employing the video cameras. The video cameras also enable precise positioning of an internal, non-destructive inspection device to enable a 360° non-destructive inspection of the interior of the components to be performed, e.g., an inspection of each weld of the components.  
         [0013]     The invention is explained in greater detail below with reference to the embodiments and the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIGS. 1A and 1B  show a reactor head and components to be inspected at an inspection station;  
         [0015]      FIG. 2  shows, in an exploded view of a portion A of  FIG. 1B , a detailed representation of a reactor penetration component, and a rack assembly within a thermal guide sleeve of the reactor head;  
         [0016]      FIGS. 3A, 3B  and  3 C show an inspection device of the invention;  
         [0017]      FIGS. 4A-4C  show the U- or C-shaped inspection device of  FIG. 3B  positioned adjacent a rack assembly for inspection of a penetration component of a reactor head;  
         [0018]      FIGS. 5A and 5B  show a movable carriage of the invention, in the collapsed and extended state, respectively, employing a elevation boom having an inspection device positioned on the distal end thereof;  
         [0019]      FIGS. 6A, 6B  and  6 C show a preferred magnetic field sensing and eddy current sensing probe to be mounted on the inspection device;  
         [0020]      FIGS. 7A and 7B  show another embodiment of the inspection device of the invention for inspecting a J-weld, as well as the reactor interior surfaces and exterior surfaces of a reactor penetration component; and  
         [0021]      FIGS. 8A-8C  show isometric and bottom views of the blade head of  FIGS. 7A and 7B  and the sensing probe of  FIGS. 6A-6C  mounted thereon. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     The reactor head  1  of  FIG. 1A  is shown to be resting on an inspection station  2 ; while  FIG. 1B  illustrates a cross sectional view of both the reactor head and the inspection station  2 . Specifically, the reactor head  1  includes a shell  3  through which penetration components  4  extend and each penetration component is welded to the shell  3  by a conventional J-weld. Each penetration component  3  has a rack assembly  5  extending concentrically therein; the details of which are shown in  FIG. 2 . Additional in-core penetration components  6  are shown distributed around the penetration components  4  and, like the penetration components will be inspected by the inspection system of the invention.  FIG. 2  illustrates in an exploded view a penetration component  4  and the rack assembly  5  concentrically assembled. Additionally, between the penetration component  4  and rack assembly  5  is positioned a thermal guide sleeve  7  which insulates the penetration component from the temperatures of the rack assembly.  
         [0023]     The support stand  8  of the inspection station  2  includes support columns  14 , e.g., four, upon which the rim  9  of the reactor head rests. The support stand  8  further includes a shield wall  10  having an access port  11  through which the moveable carriage  12 , containing the inspection probe  13 , moves in order to be positioned for inspection of the penetration components. Prior to the actual inspection, the reactor head is removed from the reactor vessel and placed onto the support columns. Thereafter, the carriage  12  can be moved beneath the reactor head  1  and the inspection process begun.  
         [0024]      FIGS. 5A and 5B  illustrate one embodiment of the moveable carriage  12  of the invention. Specifically, the moveable carriage  12  includes frame  15 , having two drive wheels  16  and two omni-directional wheels  17  which cooperate to move the carriage to a general location beneath a particular penetration component. The inspection probe  13  is mounted for rotational, X-axis, Y-axis and Z-axis movement on the end of an extendable boom  18 , shown in  FIG. 5A  in its collapsed state and in  FIG. 5B  in its extendable state. Any conventional extension elements can be used to extend and collapse the boon  18 , e.g., a lead screw and motor assembly, a hydraulic piston-shaft arrangement or gas sleeve arrangement.  
         [0025]     The details of the inspection probe  13  of one embodiment of the invention are illustrated in  FIGS. 3A and 3B . The sensing probe  13  is mounted on a support base  19  which enables mounting of the inspection probe  13  to the boom  18  and enables rotational movement of the probe  13  around the center axis of the rack assembly. The support base  19  is fixed on the boom at one end thereof and at the other end includes a U- or C-shaped collar  20  to be positioned adjacent a rack assembly  5  as shown in  FIG. 3B . The rotational movement of the sensing probe around the center axis of the probe is effected by the use of a wheel assembly  23  on the support base  19  and track  22  and wheel gear assembly  24  on the inspection probe  13 . The wheel gear assembly  24  is drive by motor gears  25  (only one shown) mounted on the support base  19  which are positioned in spaced apart relationship on the inspection probe such that at least one motor gear  25  is always engaged with the wheel gear assembly. In a similar manner, the opening between the ends of the wheel gear  25  also forms a U- or C-shaped collar and the dimension of the opening is selected such that a portion of the track  22  will always be in engagement with at least one of the wheels  23  on the support base  19 . Such an arrangement will permit the inspection probe  13  to move in a 360° arc around the center of axis of the rack assembly  5 .  
         [0026]     The X-axis and Y-axis movement is effected by movement of the probe boom  26  along a slide  27  on the probe base  28 . Note that the track  22  and wheel gear assembly  24  are affixed to the probe base  28  to enable the 360° arc movement of the inspection probe  13 . The motor  29 , mounted on the probe base  28 , moves the probe boom  26  via conventional gearing (not shown).  
         [0027]     The Z-axis (vertical) movement of the sensing probe blade  30  on the probe boom  26  is accomplished by means cooperation of a slide  31  mounted on the probe boom  26  and probe blade support  32 . A motor  33 , mounted on the probe boom  26 , drives the probe blade support  32  on the slide again via conventional gearing (not shown).  
         [0028]      FIGS. 3A and 3B  also illustrate the placement of the video cameras  35  and light sources  50  on the support base  19  adjacent the collar  20  which are used to effect remote control positioning of the extendable boon  18  as well as precise positioning of the collar  20  of the inspection probe  13  directly adjacent the rack assembly ( FIG. 3B ). Alternatively, or in addition to cameras  35 , video cameras  36  can be mounted at the U- or C-shaped distal end of the probe base  28  which would also enable remotely controlled, precise location of the inspection probe  13  and video inspection of the gap  34  between the rack assembly  5  and the penetration component  4 .  
         [0029]     FIGS.  3 B and  4 A- 4 C show the sensing probe blade  30  in various stages of vertical insertion and removal into and out of the gap  34  between thermal sleeve  7  and the penetration component  4 . After remotely controlled placement of the inspection probe  13  beneath a particular penetration component  4 , the extendable boom is extended and guided, via the cameras  35  and movement controls circuitry (not shown), to a position adjacent a rack assembly  5  ( FIGS. 3B, 4C ). Then the sensing probe blade  30  is moved upwards into the gap  34 . The sensing probe  37 , mounted into the end of the probe blade  30 , moves vertically into the gap  34  along the interior of the penetration component  4  for non-destructive inspection of the interior of the penetration component  4 .  
         [0030]     After inspection along a first vertical line portion of the penetration component  4 , the probe blade  30  is withdrawn downward to a position removed from the gap  34  or a position directly adjacent the mouth of the gap  34 . Thereafter, activation of motor  21  causes incremental rotational movement of the inspection probe  13 , including the probe boom  26 , around the vertical axis of the rack assembly  5  to be carried out to move the probe blade  30  to another circumferential location of the gap  34  in order to repeat the vertical elevation of the probe blade  30  into the gap  34  for inspecting another vertical line of the penetration component until a partial or complete 360° non-destructive inspection of the interior of the penetration component  4  is accomplished.  
         [0031]     With the inspection system of the invention, the process of inspecting each penetration component and each in-core penetration component can be completed in turn without the need for assembling any vertical positioning and movement elements as is done in the prior art.  
         [0032]     Turning to the sensing probe  37 ,  FIGS. 6A-6C  illustrate a preferred embodiment of the sensing probe for performing the non-destructive inspection of the interior of a penetration component  4 . Specifically, the sensing probe  37  includes a printed circuit board  38  upon which are mounted raised sections  39  and magnetic field sensors  40  for circumferential and axial measurement of residual magnetic fields in the penetration components. Also included in the printed circuit board  38  is an eddy current sensor coil  41  for further non-destructive inspection of the penetration components.  
         [0033]     Either of the sensors  40  or  41  can detect the presence of faults, i.e., cracks or fissures, in a penetration component utilizing the apparatus and method described above. However, the instant invention also includes the recognition that upon utilizing the magnetic field sensors to sense the residual magnetic field signatures over time in a penetration component, the likelihood of faults occurring at a particular location in the penetration component can be predicted. Such a process of utilizing magnetic field sensors to measure the residual magnetic field signatures over time enables repairs and replacement of components to be set out with much more predictability than all the prior art devices discussed above which only determine the presence of a fault after it has formed.  
         [0034]     While the exact reason why the measurement of the magnetic field signatures over time enables the prediction of the location or locations for the formation of faults is not completely understood, the prediction of the location where a fault would likely occur appears to be based upon the change in residual magnetic field signature over time of a particular location on a penetration component in which the change is caused by the change in carbon content of the component at that particular location. This change in carbon content would appear to cause the formation of corrosive oxides at that particular location and therefore provide an indication of the potential for the formation of faults in that particular location. Upon gathering and compiling historical data for a particular component (or a series of components), the instantaneous magnetic field signature measurements for a particular location on a penetration component can be compared with that historical data or with an inventory or model of the historical changes in the residual magnetic field signatures of similar penetration components which have indicated an actual or probable location of defect and/or fault formation and, accordingly, the determination can then be made to repair or replace the penetration component immediately or at some other time in the future (prior to actual fault formation in the penetration component).  
         [0035]     The method of determining the likelihood of the formation of defects and/or faults at a particular sensed location of a reactor head component would include the following steps: 
        performing the inspection of each component of the reactor head at predetermined time intervals and accumulating a library of residual magnetic field signatures for each sensed location of the component wherein the library includes the residual magnetic field signatures for sensed locations of components which have defects and/or faults at a sensed location and sensed locations of components which have no defects and/or faults at a sensed location,     comparing the residual magnetic field signatures for each sensed location from a most recent inspection to the library of residual magnetic field signatures of each sensed location to determine any change in the residual magnetic field signatures at each sensed location of component, and     determining the likelihood of the formation of a defect or fault at a particular sensed location of a component by a comparison of the most recent sensed residual magnetic field signature for a particular sensed location or a comparison of the change in residual magnetic field signature for a particular sensed location of the component with the library of residual magnetic field signatures for all components.        
 
         [0039]     While the probe blade  30  has been shown for insertion into the gap  34  between the penetration component  4  and the thermal sleeve  7 , the probe blade  30  and the probe blade support  32  can be removed from probe boom  26  and replaced with another design probe blade  30 ′ which can accomplish the non-destruction inspection of a J-weld  48  of the penetration component  4 . Specifically,  FIGS. 7A and 7B  illustrate such a probe blade  30 ′ which includes a shaft slide  43  for the elevation of the probe blade  30 ′ and a blade head  42  which is shaped to complement the surface to be inspected, i.e., a curved or angled surface  44  which matches the surface of a J-weld  48 .  
         [0040]     Note also that in addition to inspection of the J-weld  48  area, the blade head  42  also be used to inspection the inner surface of the reactor head  3  in the area adjacent the J-weld by merely adjusting the angular position of the blade head  42  to present the sensing probe  37  to the inner surface of the reactor head  3 . Similarly, by re-positioning the blade head  42  to present the sensing probe  37  to the exterior surface of the penetration component  4  and moving the blade head  42  in a vertical manner along the exterior surface of the penetration component  4  the non-destructive inspection of the interior of the penetration component can also be performed.  
         [0041]      FIGS. 8A-8C  show the sensing probe  37  of  FIGS. 6A-6C  mounted in the blade head  42  of the probe blade  30 ′. The details of the pad terminals  49  of the sensing probe  37  are also illustrated in  FIG. 8C .  
         [0042]     The non-destructive prediction of the likelihood of fault formation has been described with regard to the inspection of a penetration component of the interior of a reactor head; however, this technique and the sensor head of the invention can be utilized to inspect the components such as hydroelectric generation facilities, aircraft components and shipbuilding elements, i.e. welds, skin panels, motor casing, fluid conduits. For each use, the probe head would be re-designed to complement the object surface to be inspected which would enable the non-destructive inspection for the presence of faults and the prediction regarding the likelihood of the formation of faults at a particular location of the objects at some time in the future.