Abstract:
A method and apparatus for securely fastening a pipe collar or a bracket to a riser pipe of a boiling water reactor (BWR) jet pump assembly. A pipe plug assembly includes an angled pipe plug that acts as a wedge to expand a bushing assembly as the pipe plug is drawn into the overall pipe plug assembly. Expansion of the bushing assembly allows a tight tolerance to exist between an outer diameter of the pipe plug and an inner diameter of the collar/bracket and riser pipe. Expansion of the bushing assembly allows a straight hole to be match drilled into the collar/bracket and riser pipe, thereby avoiding a more complicated tapered hole to be drilled into the collar/bracket and riser pipe. An ensuing tight fit between the pipe plug assembly, the collar/bracket and the riser pipe mitigates vibration of components and minimizes leakage to acceptable levels for use in the flooded environment of the annulus region where the jet pump assembly exists in the BWR.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Example embodiments relate to an expandable, pipe plug assembly that may be used on a riser pipe of a Boiling Water Reactor (BWR) jet pump assembly. The pipe plug assembly may be used to secure a pipe collar or bracket to the riser pipe for riser pipe repair. The pipe plug assembly includes a pipe plug that acts as a wedge to expand bushing sections to assure a tight fit within a hole that may be match drilled to ensure a uniform hole exists in the riser pipe as well as the collar or bracket that may be fashioned to the riser pipe. A thin shape of the bushing sections and the existence of narrow gaps between bushing sections mitigate leakage to acceptable levels especially in flooded environments such as the annulus region where the riser pipe exists with the Boiling Water Reactor (BWR). 
     2. Related Art 
     A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends (for example by a bottom head and a removable top head). A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. There is a space or annulus between the cylindrical reactor pressure vessel and the cylindrically shaped shroud. 
     In the BWR, hollow tubular jet pumps of a jet pump assembly are positioned within the shroud annulus. The jet pump assembly accepts energized water from outside of the reactor recirculation system and provides the required reactor core water flow to the reactor via diffusers. The formation of minute cracks in the riser pipe may sometimes require repair, which may require the fashioning of a collar or bracket to the outer surface of the riser pipe. 
     Conventionally, fashioning of a collar or bracket to the rounded surface of the riser pipe may cause complications, especially in the case where access to the inside diameter of the riser pipe is unavailable. Specifically, outer surfaces of a plug that may be used to secure the collar or bracket to the circumferential surface of the riser pipe may be out of alignment with holes drilled in the collar, the bracket, or the riser pipe itself, causing vibration and leakage. Additionally, conventional plugs may not provide radial forces (pressure) to ensure a tight fit between a plug and the collar and/or riser pipe holes. 
     Alternative to the example embodiments described below, tapered holes with tapered plugs have been considered to securely fashion a collar or bracket to the riser pipe. However, lack of control during electrical discharge machining (“EDM”) burns may not guarantee tight tolerances in a tapered angle, resulting in a weak connection between a collar and riser pipe, leakage, as well as deformation or cracking of components. 
     SUMMARY OF INVENTION 
     Example embodiments provide a method and an apparatus for an expandable pipe plug assembly that may be used on a riser pipe of a Boiling Water Reactor (BWR) jet pump assembly. The pipe plug assembly may be used to secure a collar or bracket to the riser pipe for riser pipe repair. The pipe plug assembly includes an angled pipe plug that acts as a wedge to expand bushing sections to press the bushing sections against an inside diameter of a hole in the collar and the riser pipe. A thin shape of the bushing sections and a slight (minute) angle of the pipe plug allow tight tolerances to exist between the outer diameter of the installed pipe plug assembly and the inner diameter of the collar and riser pipe holes. An ensuing tight fit between the pipe plug assembly, the collar and the riser pipe mitigates vibration between components as well as minimizing leakage to acceptable levels for use in the flooded environment of the annulus where the jet pump assembly exists in the BWR. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of example embodiments will become more apparent by describing in detail, example embodiments with reference to the attached drawings. The accompanying drawings are intended to depict example embodiments and should not be interpreted to limit the intended scope of the claims. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
         FIG. 1  is a perspective view of a boiling water nuclear reactor (BWR) jet pump assembly with an expandable plug assembly, in accordance with an example embodiment; 
         FIG. 2  is a front side-angle perspective view of an expandable pipe plug assembly, in accordance with an example embodiment; 
         FIG. 3  is a rear side-angle view of an expandable pipe plug assembly, in accordance with an example embodiment; 
         FIG. 4  is a front exploded view of an expandable pipe plug assembly, in accordance with an example embodiment; 
         FIG. 5  is a rear exploded view of an expandable pipe plug assembly, in accordance with an example embodiment; 
         FIG. 6  is a perspective view of a pipe plug of a pipe plug assembly, in accordance with an example embodiment; 
         FIG. 7  is a detailed view of a bushing section of a pipe plug assembly, in accordance with an example embodiment; 
         FIG. 8  is a detailed view of a bushing assembly and retaining ring of a pipe plug assembly, in accordance with an example embodiment; 
         FIG. 9  is a detailed view of a bushing assembly with a retaining ring installed, in accordance with an example embodiment; 
         FIG. 10  is a perspective view of an EDM plug assembly of a pipe plug assembly, in accordance with an example embodiment; 
         FIG. 11  is a perspective view of a keeper of a pipe plug assembly, in accordance with an example embodiment; 
         FIG. 12  is a side-view of a ratchet nut of a pipe plug assembly, in accordance with an example embodiment; 
         FIG. 13  is a cross-sectional view of a pipe plug assembly (in an initial installation condition) outside of a hole that has been drilled in a collar and riser pipe wall, in accordance with an example embodiment; 
         FIG. 14  is a cross-sectional view of a pipe plug assembly (in an initial installation condition) inside of a hole that has been drilled in a collar and riser pipe wall, in accordance with an example embodiment; and 
         FIG. 15  is a cross-sectional view of a pipe plug assembly (in an installed condition) installed in a hole that has been drilled in a collar and riser pipe wall, in accordance with an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Detailed example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. 
     Accordingly, while example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the figures. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.). 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular fauns “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
       FIG. 1  is a perspective view of a nuclear boiling water reactor (BWR) jet pump assembly  50  located in an annulus between a cylindrical reactor pressure vessel (RPV) and a cylindrical shaped shroud of a BWR. Water entering the riser pipe  51  provides the drive flow (energy) for the jet pump assembly. Energized water enters riser pipe  51  and is distributed into inlet mixers  52  and diffusers  54  before being discharged into the reactor core. The riser pipe  51  is susceptible to minute cracks and therefore repairs may need to be performed on the riser pipe  51  which may include securing a collar or bracket to the riser pipe  51 . The repairs may include installing a pipe plug assembly  1  on the riser pipe  51  as shown in  FIG. 1 . 
       FIG. 2  is a front side-angle perspective view of an expandable pipe plug assembly  1  (as shown installed in  FIG. 1 ), in accordance with an example embodiment. Features of the pipe plug assembly F may include a somewhat spherical electrical discharge machining (“EDM”) plug  10  with a ratchet nut  12  which may be located in a recessed front face of the plug  10 . The back of the EDM plug  10  may include a pipe plug  14  located inside of an expandable bushing assembly  16 . The pipe plug assembly is to be inserted/installed into a hole that may be drilled in the riser pipe  51  of a jet pump assembly  50  (as shown in  FIG. 1 ), by inserting the plug assembly  1  into the riser pipe in the direction A (i.e., the pipe plug  14  end of the pipe plug assembly  1  is inserted into a hole in the riser pipe). 
       FIG. 3  is a rear side-angle view of an expandable pipe plug assembly  1 , in accordance with an example embodiment. The EDM plug  10  may be a somewhat cylindrical shape with threads  18  provided on an outer circumferential surface of the EDM plug  10 . Note that ratchet teeth  20  may also be provided along the circumferential surface of the EDM plug  10  for anti-rotational purposes. A keeper (not shown) may be used to ensure that the EDM plug  10  may not rotate in a counterclockwise direction once the pipe plug assembly  1  is field installed. 
       FIG. 4  is a front exploded view of an expandable pipe plug assembly  1 , in accordance with an example embodiment. Major features in approximate order from left to right include the following. Ratchet nut  12  may include teeth  12   b , which may contact keeper teeth  22   a  of J-shaped keeper  22  for anti-rotation purposes following installation of the pipe plug assembly  1  (i.e., teeth  22   a  of keeper  22  may be configured to allow ratchet nut  12  to rotate only in a clockwise direction and not in a counterclockwise direction). Ratchet nut threads  12   a  may be provided to mate with plug bolt  14   c , allowing the ratchet nut to be rotated to tighten its hold on plug bolt  14   c  and pipe plug  14  to draw pipe plug  14  toward EDM plug  10 . Washer  24  may be provided within EDM plug recessed center hole  10   a . The washer  24  may be a spherical washer with one face that is concave (the face of washer  24  that contacts ratchet nut  12  is concave, as shown in better detail in  FIG. 13 ). The concave face of washer  24  provides a tolerance in the event that plug bolt  14   c  is not installed at an entirely perpendicular angle with the overall EDM plug  10 . Specifically, a spherical bottom surface of ratchet nut  12  (convex spherical surface  12   c  of ratchet nut  12  is shown for instance in  FIG. 12 ) may allow ratchet nut  12  to pivot as it rides along the spherical surface of washer  24  to provide a tolerance in the event that plug bolt  14   c  penetrates EDM plug  10  at a somewhat off-center angle (i.e., ratchet nut  12  may pivot in the event of angular misalignment). 
     EDM plug keeper recess  10   b  is an approximately “J”-shaped recessed area that contains the approximately “J”-shaped keeper  22 . Opening  10   b   4  is provided in recess  10   b  to allow keeper teeth  22   a  to contact ratchet nut teeth  12   b  for anti-rotation purposes. Note that a first undercut  10   b   1  is shown in recess  10   b . First undercut  10   b   1  is one of three undercuts (the others are shown in  FIG. 10 ) which provides three points of contact to retain keeper  22  in the keeper recess  10   b  (specifically, lip  22   b   1  of keeper  22  shown in  FIG. 5  fits into undercut  10   b   1 ). 
     EDM center hole  10   c  is provided in the center of EDM plug  10  to allow plug bolt  14   c  to fit through the EDM plug  10 . EDM plug recessed center hole  10   a  is also provided in EDM plug  10  to provide tolerances for ratchet nut  12  to rotate within the center hole  10   a  even when plug bolt  14   c  may not intersect EDM plug  10  at a substantially perpendicular angle. Expandable bushing assembly  16  may include separate bushing sections  16   a  that surround plug  14 . Each bushing section  16   a  may have a longitudinal wall that forms a longitudinal wall section of the overall somewhat cylindrical bushing assembly  16 . Bushing sections  16   a  may be held together by a retaining ring  16   b  (shown in more detail in  FIGS. 8 and 9 ). Note that each bushing section  16   a  may include a flat bushing section base  16   d  that provides a flat contact surface which contacts flat inner EDM plug surface  11   b  (shown in  FIG. 5 ) when plug  14  is retracted into the overall pipe plug assembly  1  (thereby pressing bushing base section  16   d  firmly against inner EDM plug inner surface  11   b ). 
     Pipe plug  14  may be a conical wedge shape with a square boss  14   b  that supports plug bolt  14   c  (shown best in  FIG. 6 ). Note that pipe plug  14  may include alignment channels  14   a  that may mate with longitudinal alignment bosses  16   e  (shown in  FIG. 5 ) of bushing sections  16   a  to allow pipe plug  14  to align with expandable bushing assembly  16  to cause bushing sections  16   a  to outwardly expand as pipe plug  14  is drawn into the overall pipe plug assembly  1  during field installation. 
       FIG. 5  is a rear exploded view of an expandable pipe plug assembly  1 , in accordance with an example embodiment. Moving generally from left to right across the figure, additional features shown in this drawing include lip  22   b   1  of keeper  22 . Lip  22   b   1  provides one of three points of contact, which allow keeper  22  to remain in EDM plug keeper recess  10   b  (lip  22   b   1  fits into undercut  10   b   1  shown on  FIG. 4 ). 
     EDM plug  10  includes a square pocket  11   a  that allows for insertion of square boss  14   b  when pipe plug  14  is drawn into EDM plug  10 . Flat inner EDM plug surface  11   b  provides a flat surface for bushing section base  16   d  to contact, which provides a stopping point for bushing assembly when bushing assembly  16  is drawn toward EDM plug  10  (due to the drawing in of pipe plug  14  via ratchet nut  12 ). 
     Bushing assembly  16  is shown with retaining ring  16   b  holding the separate busing sections  16   a  together. Boss  16   d   1 , located on only one of the individual sections, provides a means to hold retaining ring  16   b  in one fixed position while holding the separate bushing sections  16   a  together (this is shown in more detail and discussed at more length, later in the disclosure and the drawings). Note that three separate busing sections  16   a  are shown in this embodiment. A gap  16   c  is located between separate bushing sections  16   a . While retaining ring  16   b  holds the bushing sections  16   a  together, and prior to insertion of pipe plug inside of bushing assembly  16 , the gaps  16   c  are minimal (approximately 0.00 inches) thereby causing the wall of each bushing section  16   a  to exist at approximately 90-degree angles with the plane of the retaining ring  16   b . It should be noted that alternatively to three separate bushing sections  16   a , only one bushing section with one gap may be provided. Also, two or four or more bushing may instead be used. Furthermore, rather than providing bushing sections  16   a  with gaps  16   c  running located directly in between the bushing sections  16   a , the bushing assembly may instead be made of overlapping bushing sections that provide a tortuous or labyrinth path. 
     The bushing sections  16   a  may have alignment bosses  16   e  running along the inside diameter of the bushing sections  16   a . Alignment channels  14   a  align with the alignment bosses  16   e  allowing pipe plug  14  to be inserted into bushing assembly  16 . The alignment bosses  16   e  also cause pipe plug  14  to uniformly expand bush assembly  16  as pipe plug  14  is drawn into EDM plug  10  via ratchet nut  12 . Pipe plug  14  may be a conical shape that is tapered (i.e., pipe plug  14  may have a slight angle  14   c ; the angle  14   c  may be approximately 10-degree, or it may be any other slight angle that causes bushing sections  16   a  to slightly flare out as pipe plug  14  is drawn into EDM plug  10  during field installation). 
       FIG. 6  is a perspective view of a pipe plug  14  of a pipe plug assembly  1 , in accordance with an example embodiment. As shown more clearly in this figure, square boss  14   b  and plug bolt  14   c  may be rigidly connected to pipe plug  14 . Plug bolt  14   c  mates with ratchet nut threads  12   a  of ratchet nut  12 . Square boss  14   b  is sized to fit into square pocket  11   a  of EDM plug  10 . Materials of construction for these components may be 304SS, 315SS and/or XM-19. 
       FIG. 7  is a detailed view of a bushing section  16   a  of a pipe plug assembly  1 , in accordance with an example embodiment. Note that side edge  16   a   1  is approximately normal (90-degrees) with bushing section base  16   d . This causes side edge  16   a   1  of each bushing section  16   a  to be held at approximately 90-degrees from the plane of retaining ring  16   b  (shown for instance in  FIG. 9 ), and it causes gaps  16   c  (shown for instance in  FIG. 5 ) to be negligible (0.00 inches) when retaining ring  16   b  is holding the bushing assembly together (and, prior to insertion of pipe plug  14  into bushing assembly  16 ). Materials of construction for the bushing sections  16   a  may include 304SS or 316SS. 
       FIG. 8  is a detailed view of a bushing assembly  16  and retaining ring  16   b  of a pipe plug assembly  1 , in accordance with an example embodiment. Bushing assembly  16  may include separate bushing sections  16   a  that each include a foot or bushing section base  16   d . At the seam between the vertical walls of the bushing sections  16   a  and the base  16   d  of the bushing sections  16   a  may be a retaining ring groove  16   f  that may be used to hold retaining ring  16   b  in place when retaining ring  16   b  is used to hold the bushing sections  16   a  together. Materials of construction for the retaining ring  16   b  may be X-750. 
     Three seams  16   c  separate the three bushing sections  16   a . Only one of the bushing sections  16   a  has a boss  16   d   1  that ensures that the retaining ring gap  16   b   1  remains in place (on boss  16   d   1 ) when retaining ring  16   b  is pressed up against the bushing section base  16   d . Boss  16   d   1  ensures that retainer ring  16   b  does not rotate such that that ring gap  16   b   1  is relocated to be directly in front of any of one of the gaps  16   c , as doing so may provide a flow path of water through plug assembly  1 . 
       FIG. 9  is a detailed view of a bushing assembly  16  with a retaining ring  16   b  installed, in accordance with an example embodiment. Note that retaining ring  16   b  is pressed up against bushing section base  16   d  and ring gap  16   b   1  is riding boss  16   d   1  to hold retaining ring  16   b  in one fixed position. While retaining ring  16   b  is installed on bushing assembly  16 , gaps  16   c  remain closed (approximately 0.00 inch width). 
       FIG. 10  is a perspective view of an EDM plug  10  of a pipe plug assembly  1 , in accordance with an example embodiment. Keeper recess  10   b  may include a second undercut  10   b   2  that provides a second point of contact for keeper  22 . Specifically, second undercut  10   b   2  provides a point of contact for lip  22   b   2  of keeper  22  (shown in  FIG. 11 ). A third undercut  10   b   3  may provide a third point of contact for keeper  22 , as lip  22   b   1  (shown in  FIG. 11 ) contacts undercut  10   b   3  to ensure that keeper  22  remains in keeper recess  10   b . Opening  10   b   4  allows keeper teeth  22   a  to contact ratchet nut teeth  12   b  for anti-rotation purposes to ensure ratchet nut  12  may not rotate and become loose after being installed in the field. Materials of construction for EDM plug  10  and its sub-components may be 304SS and/or 316SS. 
     Dice markings  10   d  may be provided to record and track the position of the EDM plug assembly  10  while it is installed and being used in the field. This may be used to ensure for instance that EDM plug assembly  10  does not rotate while plug assembly  1  is in field use. 
       FIG. 11  is a perspective view of a keeper  22  of a pipe plug assembly  1 , in accordance with an example embodiment. The keeper  22  may be formed of a resilient material (such as for instance X-750) that causes keeper  22  to act as a spring that may fit into the J-shaped keeper recess  10   b  of EDM plug  10 . Note that three points of contact (lip  22   b   1 , lip  22   b   2  and tab  22   b   3 ) may be provided to mate with undercuts  10   b   1 ,  10   b   2  and  10   b   3  (shown in  FIGS. 4 and 10 ) to ensure that keeper  22  remains in keeper recess  10   b  while plug assembly  1  is in use. 
       FIG. 12  is a side-view of a ratchet nut  12  of a pipe plug assembly  1 , in accordance with an example embodiment. Teeth  12   b  may be provided for ant-rotation purposes by allowing keeper teeth  22   a  to contact teeth  12   b . Note that a spherical, somewhat convex bottom surface  12   c  may be provided for ratchet nut  12 . The convex surface  12   c  of ratchet nut  12  may mate with a spherical, concave surface of washer  24  to provide a tolerance for the positioning and fit of ratchet nut  12  within the recessed center hole  10   a  of EDM plug  10  in the event plug bolt  14   c  is installed such that it is not at an exactly normal (i.e., 90-degree) angle with EDM plug  10  when pipe plug assembly  1  is installed in the field. The mating of the spherical surface  12   c  of ratchet nut  12  and the spherical surface of washer  24  can be seen in better detail in  FIG. 13 . Materials of construction for ratchet nut  12  may include 304SS or 316SS. 
       FIG. 13  is a cross-sectional view of a pipe plug assembly  1  outside of a hole that has been drilled in a collar  60  and riser pipe wall  51 , in accordance with an example embodiment. Pipe plug  1  is shown in an “initial installation condition,” as gaps  16   c  (shown for instance in  FIG. 9 ) in bushing assembly  16  are closed (gaps  16   c  are approximately 0.00 inches). In this “initial installation condition,” diameter d of pipe plug  14  and bushing assembly  16  is smaller than diameter D of the hole in collar  60  and riser pipe wall  51  to allow pipe plug assembly  1  to be inserted into collar  60  and riser pipe  51  in direction A. Note that threads  61  may be machined into collar  60  to mate with threads  18  of the EDM plug  10 . The spherical shape of washer  24  and surface  12   c  of ratchet nut  12  is also shown in more detail in this figure. As described earlier, the spherical shape of washer  24  and surface  12   c  allow ratchet nut  12  to pivot to provide a tolerance in the event that plug bolt  14   c  penetrates EDM plug  10  at an off-center angle (i.e., ratchet nut  12  may pivot in the event of angular misalignment). Materials of construction for the spherical washer may be X-750. 
       FIG. 14  is a cross-sectional view of a pipe plug assembly  1  inside of a hole that has been drilled in a collar  60  and riser pipe wall  51 , in accordance with an example embodiment. The pipe plug assembly  1  is still in the “initial installation condition,” meaning that gaps  16   c  (shown for instance in  FIG. 9 ) are still closed (gap is approximately 0.00 inches). This causes gaps  62  to exist between bushing assembly  16  and the inside diameter of collar  60  and riser pipe wall  51 . Note that bushing section base  16   d  may act as a lip to hold bushing assembly  16  in place and against the outer surface of a recessed hole that is provided in collar  60 . 
       FIG. 15  is a cross-sectional view of a pipe plug assembly  1  installed in a hole that has been drilled in a collar  60  and riser pipe wall  51 , in accordance with an example embodiment. Pipe plug assembly  1  is shown in an “installed condition” this time, as gaps  16   c  (shown for instance in  FIG. 9 ) have been expanded to cause the diameter of bushing assembly  16  to match the diameter of the hole in collar  60  and riser pipe  51 . The expansion of the gaps may be for instance approximately 0.1 inches. The expansion of bushing assembly  16  is accomplished through the tightening of ratchet nut  12  which provides axial tension that causes plug bolt  14   c  to be drawn through EDM plug  10 , as pipe plug  14  is drawn into bushing assembly  16 . The slight angle of pipe plug  14  outer walls causes the diameter of the bushing assembly  16  to expand, while gaps  16   c  (shown for instance in  FIG. 9 ) increase in size to allow for the expansion. Once installed, the expandable nature of the bushing assembly  16  of pipe plug assembly  1  may provide radial pressure against the inside diameter of the holes in both collar  60  and riser pipe wall  51 . Existence of the pipe plug assembly  1  penetrating both collar  60  and riser pipe wall  51  transfers axial and torsional forces from collar  60  to pipe  51  which may be beneficial during pipe  51  repair. 
     It should be understood that the plug assembly  1  described above is suited to fashion a collar or bracket onto a spherical surface of a pipe, especially in the case where the collar/bracket and pipe wall are EDM match-drilled. Match drilling allows for multiple layers of material (such as the collar or bracket, and the pipe wall) to be drilled at once. In an example embodiment, match drilling may be accomplished by drilling a straight hole through both the collar/bracket and pipe wall at approximately a normal angle (i.e., a 90-degree angle). During match drilling, the drilling of a straight hole is easier to perform than a tapered hole (which, in turn, would require a tapered wedge to plug the tapered hole). The ability of the bushing assembly  16  of the plug assembly  1  allows the straight hole to be plugged without tapering, ensuring that field installation may be performed more easily and with greater degree of success as a tight fit is provided to reduce vibration of components and potential leakage of fluids from the pipe. The expandability of the plug assembly  1  is particularly useful when only an outer diameter of a pipe (such as a riser pipe of a BWR jet pump assembly) may be accessed, while the inside diameter of the pipe is inaccessible. 
     While the example embodiments described above relate to a pipe plug assembly that may be used to fashion a collar or a bracket to a circumferential surface of a pipe such as a riser pipe of a BWR jet pump assembly, it should be understood that the pipe plug assembly may also be used simply to plug a hole. Furthermore, the hole need not be on a circumferential surface of a pipe, as it may instead be a hole that has been drilled into a flat wall or surface. Furthermore, while an example embodiment is drawn toward plugging a hole formed via electrical discharge machining (EDM), it should be understood that any other type of machining or drilling may be used to form the hole that may then be plugged using example embodiments. 
     Example embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the intended spirit and scope of example embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.