Abstract:
A method and apparatus for vertically lifting and supporting a main wedge of a Boiling Water Reactor (BWR) jet pump restrainer assembly, to ensure that the wedge is no longer contacting a restrainer bracket of the restrainer assembly. A main wedge clamp with an upper and lower clamp jaw is used to attach to the upper support of the restrainer assembly, the lower clamp jaw being fashioned with a prong or prongs that fit underneath the crown of the main wedge and provide the vertical lift for the main wedge.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Example embodiments relate generally to nuclear reactors, and more particularly to a method and apparatus for a Boiling Water Reactor (BWR) jet pump main wedge clamp that physically restrains a BWR jet pump main wedge, to prevent wear to the wedge and a jet pump restrainer bracket. 
     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 a BWR, hollow tubular jet pumps positioned within the shroud annulus provide the required reactor core water flow. The upper portion of the jet pump, known as the inlet mixer, is laterally positioned and supported against two opposing rigid contacts within jet pump restrainer brackets by a gravity actuated wedge. The restrainer brackets support the inlet mixer by attaching the inlet mixer to the adjacent jet pump riser pipe. 
     The jet pump main wedge maintains contact between the inlet mixer and the jet pump restrainer bracket. More specifically, the wedge works in cooperation with two set screws which are tack welded to the restrainer bracket to maintain contact with the inlet mixer. The flow of water through the jet pumps typically includes pressure fluctuations caused by various sources in the reactor system. The pressure fluctuations may have frequencies close to one or more natural vibration modes of the jet pump piping. The jet pump piping stability depends on the tight fit-up, or contact, of the restrainer brackets and the inlet mixers. The vibrations present in the jet pump system cause excessive movement of the main wedge against the restrainer bracket and main wedge rod resulting in subsequent damage to the various contact surfaces. Previously worn main wedges and restrainer brackets required replacement and/or new wear surfaces which may be bolted onto the existing restrainer bracket. These procedures have been found to require a significant and expensive downtime of the jet pumps. 
     Disassembly and/or complete removal of the restraining bracket and wedge can, in and of itself, be expensive. Therefore, a need exists to remove the main wedge from active use by vertically lifting the main wedge away from direct contact with the restraining bracket, thereby allowing the wedge and restrainer bracket to remain attached to the inlet mixer while ensuring that no additional wear occurs between the wedge and the restrainer bracket. 
     SUMMARY OF INVENTION 
     Example embodiments provide a method and an apparatus for providing vertical support of a jet pump main wedge in a jet pump restrainer assembly. Specifically, a clamping or restraining device may be used to vertically lift the jet pump main wedge in a fixed position, typically against the upper support and away from any contact with the restrainer bracket. By clamping the wedge in position, wear between the wedge and the restrainer bracket is eliminated, as the wedge and restrainer bracket are no longer in direct contact. 
     Because example embodiments remove the restrainer bracket and main wedge from active use, it may be advantageous to use alternative means to restrain the inlet mixers which may be implemented in conjunction with example embodiments. Alternative means of restraining the inlet mixer may be accomplished for instance by providing additional side loading to the inlet mixer, as described in the General Electric Hitachi application “METHOD AND APPARATUS FOR A BWR JET PUMP SUPPORT SYSTEM,” Ser. No. 12/850,218. 
    
    
     
       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 conventional boiling water nuclear reactor jet pump assembly; 
         FIG. 2  is a detailed view of a conventional jet pump restrainer assembly; 
         FIG. 3  is a side view of a jet pump main wedge clamp, in accordance with example embodiments; 
         FIG. 4  is a detailed view of a jet pump main wedge clamp in use on a jet pump restrainer assembly, in accordance with example embodiments; and 
         FIG. 5  is an overhead view of a jet pump main wedge clamp in use on a jet pump restrainer assembly, in accordance with example embodiments. 
     
    
    
     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 forms “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. 
     Referring to  FIG. 1 , a perspective view of a conventional Boiling Water Reactor (BWR) nuclear reactor jet pump assembly is depicted. The jet pump assembly includes conventional jet pump restrainer assemblies  10  attached to the riser pipe  1 , which stabilize any movement of the inlet mixers  2  relative to the riser pipe  1  while the jet pump assembly is in use. 
       FIG. 2  shows a detailed view of the conventional jet pump restrainer assemblies  10  on the riser pipe  1 . The restrainer assembly  10  includes a restrainer bracket  12  Connected to the riser pipe  1 . Three points of contact locate the inlet mixer  2  in the restrainer bracket  12 . The three points of contact are two set screws  15 , located approximately between each inlet mixer  2  and the riser pipe  1  (only one set screw  15  is shown, with the other set screw  15  on the back-side of the  FIG. 2  image), and the main wedge  14  (the main wedge  14  is the third point of contact). The main wedge  14  assists in ensuring that the restrainer bracket  12  remains against the two set screws  15 . The main wedge  14  is free to move vertically along the wedge rod  20  and is held in place between the inlet mixer  2  and restrainer bracket  12  by gravity. The bottom of the wedge rod  20  is held in place by a lower support including two vertical plates  26  and a horizontal plate  24  (notice the bottom of wedge rod  20  penetrates and is held fast on the horizontal plate  20  of the lower support). The top of the wedge rod  20  is held in place by an upper support including two vertical plates  18  and a horizontal plate  16  (notice the top of wedge rod  20  penetrates and is held fast on the horizontal plate  16  via nut  22 ). 
       FIG. 3  is a side view of a jet pump main wedge clamp  30 , in accordance with example embodiments. The wedge clamp  30  may include a lower clamp jaw that may be a plate with one ore more prongs  35  protruding away from a distal end of the lower clamp jaw  34  plate. The prongs  35  may be sized to fit between the main wedge  14  and a vertical plate  18  of the upper support of the restrainer assembly  10 . The wedge clamp  30  may also include an upper clamp jaw  32  that may be a plate with a clearance hole  38  running through the upper clamp jaw  32 . The clearance hole  38  may be located near the distal end of the upper clamp jaw  32  plate. The clearance hole  38  may be sized to allow the wedge rod  20  and nut  22  (shown in  FIGS. 2 and 5 ) to fit through the clearance hole  38 . The upper clamp jaw  32  plate may be sized to fit between the vertical plates  18  of the upper support of a jet pump restrainer assembly  10 . Both the upper clamp jaw  32  plate and the lower clamp jaw  34  plate may both have an approximate width of 4 inches (to allow the plates to fit between the vertical plates and  18 ), and an overall length of about 5 inches. Both upper clamp jaw  32  plate and lower clamp jaw  34  plate may have a thickness of about 0.5 inches to 1 inch, although the thickness need not be constrained to this range. 
     The wedge clamp  30  may include a clamp bolt or bolts  36 , or other means of attachment that is used to hold the upper clamp jaw  32  to the lower clamp jaw  34 . Other means of attachment may include only one bolt, multiple bolts, or any other reasonable fixture that may be used to hold the clamp jaws  32 / 34  in a fixed position relative to each other. The bolts  36 , or other means of attachment, may ensure that the upper clamp jaw  32  and lower clamp jaw  34  are secured to each other such that the upper clamp jaw  32  and lower clamp jaw  43  are approximately parallel to each other. The clamp bolts  36  may include nuts  40  which may hold the bolts  36  in place. The bolts  36  may be threaded, to mate with threaded connections that may be provided in one or both of the upper and lower clamp jaws  32 / 34 . Other means of attaching bolts  36  to the clamp jaws  32 / 34  may include welding, adhesive, or any other means by which stable connections may be made between bolts  36  and the clamp jaws  32 / 34 . The clamps bolt or bolts  36  may attach the proximal end of the lower clamp jaw  34  plate to the proximal end of the upper clamp jaw  32  plate. 
     All clamp components may be made by materials that are known to be acceptable for a nuclear environment. For instance, stainless steel (304, 316, XM-19, or equivalent) or nickel based alloys (Iconel, X-750, X-718, or equivalent) may be used. 
       FIG. 4  is a detailed view of a jet pump main wedge clamp  30  in use on a jet pump restrainer assembly  10 , in accordance with example embodiments. Note that the prongs  35  of the lower clamp jaw  34  may be two prongs  35  that are fitted to cradle underneath the crown  28  of the main wedge  14 , and each prong  35  may be sized to fit between the side of the main wedge  14  and the vertical plate  18  of the upper support. The purpose of the lower clamp jaw  34  is to lift the main wedge  14  vertically upward and away from restrainer bracket  12  to, in essence, take the main wedge  14  out of operation without additional costly maintenance or down-time to actually remove the wedge  14  altogether. 
     The upper clamp jaw  32  may be fitted to exist between the two vertical plates  18 , allowing the upper clamp jaw  32  to then be attached to horizontal plate  16  (partially obscured in the view of  FIG. 4 ). Attachment to horizontal plate  16  may be through the use of wedge rod  20  and nut  22  which may run through clearance hole  38  (shown in more detail in  FIG. 5 ). Alternatively, upper clamp jaw  32  may be attached to horizontal plate  16  by bolts or welding that may be separate from wedge rod  20  and nut  22 . Additionally, the upper clamp jaw  32  may be fitted to bracket the outside of vertical plates  18  (as opposed to fitting between the two vertical plates  18 ), and may also be alternatively attached directly to one or both of the vertical plates  18 . Alternatively, upper clamp jaw  32  may also be attached directly to the inlet mixer  2 . While threaded clamp bolts  36  and nuts  40  are shown securing the upper clamp jaw  32  to the lower clamp jaw  34 , any other means of stabilizing the connection between upper/lower clamp jaws  32 / 34  may also be implemented. 
       FIG. 5  is an overhead view of a jet pump main wedge clamp  30  is use on a jet pump restrainer assembly  10 , in accordance with example embodiments. This overhead view shows an example embodiment that may include the wedge rod  20  penetrating through clearance hole  38  of upper clamp jaw  32 . Clearance hole  38  may be a recessed hole that allows wedge rod nut  22  to exist within the recessed area, allowing the wedge rod  20  to easily be secured to the upper clamp jaw  32 . 
     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.