Abstract:
A method and apparatus for a Boiling Water Reactor (BWR) jet pump inlet mixer support that provides rigid support for inlet mixers. The inlet mixer support attaches to a conventional BWR jet pump assembly to pull the inlet mixer away from the centerline of a riser pipe or maintain the existing inlet mixer position. The inlet mixer support may provide redundant support that may otherwise be provided by set screws of a conventional restrainer assembly. The inlet mixer support may, alternatively, be used in lieu of conventional set screws. The inlet mixer support may also counter-act additional side loading that may be applied to inlet mixers to stabilize inlet mixer movement and vibration when the BWR jet pump assembly is in operation. Optionally, the inlet mixer support may also prevent removal of existing restrainer bracket set screws.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Example embodiments relate generally to nuclear reactors, and more particularly to a method and apparatus for a Boiling Water Reactor (BWR) jet pump inlet mixer support that provide rigid support for inlet mixers. The inlet mixer support may attach to a conventional BWR jet pump assembly to pull the inlet mixer away from the centerline of a riser pipe or support them in there exiting position. 
         [0003]    2. Related Art 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. However, the set screws may back out of position if the tack welds that hold the set screws in place fail. 
       SUMMARY OF INVENTION 
       [0007]    Example embodiments provide a method and an apparatus for providing redundant and/or additional contact between the inlet mixers and a restrainer bracket of a BWR jet pump assembly. Specifically, a support band may be used to provide an additional point of contact between an inlet mixer and a support bracket. The support band may be held in place by mixer support mounting blocks that may be attached directly to the restrainer bracket and attach the support band to the restrainer bracket. By securing the support band to the restrainer bracket, the support band may provide an adjustable point of contact between the restrainer bracket and the inlet mixer, thereby stabilizing the inlet mixer even in the event that conventional set screws on the restrainer bracket fail. Therefore, example embodiments maintain the inlet mixer position even if the set screws move out of position. Example embodiments also prevent the removal and/or expensive and time-consuming repair of the set screws, should the set screws fail or otherwise require maintenance. 
         [0008]    Example embodiments also provide additional stability in the case where additional side loading of the inlet mixers may be applied through the use of a jet pump support system. Such side loading provides a lateral force that pulls the inlet mixers toward the centerline of a riser pipe of a BWR jet pump assembly. Because conventional set screws are not designed to support such additional lateral loading, example embodiments provide redundant and/or additional stability of the inlet mixers to ensure that potential set screw failure does not lead to unacceptable vibration of the inlet mixers. 
         [0009]    Furthermore, auxiliary wedges have conventionally been used to restore points of contact between the inlet mixers and restrainer brackets. The auxiliary wedges fill gaps that form between the set screws and the inlet mixers, thereby restoring stability for the inlet mixers. Example embodiments thereby provide an alternative to the use of auxiliary wedges. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    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. 
           [0011]      FIG. 1  is a perspective view of a conventional boiling water nuclear reactor (BWR) jet pump assembly; 
           [0012]      FIG. 2  is a detailed view of a conventional jet pump restrainer assembly; 
           [0013]      FIG. 3  is a detailed view of a conventional jet pump restrainer assembly with conventional auxiliary wedges; 
           [0014]      FIG. 4  is a detailed view of a BWR jet pump inlet mixer support, in accordance with an example embodiment; 
           [0015]      FIG. 5  is a detailed view of a BWR jet pump inlet mixer support in use on a conventional BWR jet pump restrainer assembly, in accordance with an example embodiment; 
           [0016]      FIG. 6  is a side-view of a BWR jet pump inlet mixer support in use on a conventional BWR jet pump restrainer assembly, in accordance with an example embodiment; and 
           [0017]      FIG. 7  is a bottom-view of a BWR jet pump inlet mixer support in use on a conventional BWR jet pump restrainer assembly, in accordance with an example embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    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. 
         [0019]    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. 
         [0020]    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 teims 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. 
         [0021]    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.). 
         [0022]    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. 
         [0023]    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. 
         [0024]    Referring to  FIG. 1 , a perspective view of a conventional Boiling Water Nuclear Reactor (BWR) 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. 
         [0025]      FIG. 2  shows a detailed view of a conventional jet pump restrainer assembly  10  on a 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  8  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 ). 
         [0026]      FIG. 3  is a detailed view of a conventional jet pump restrainer assembly  10  with conventional auxiliary wedges  25 . The conventional auxiliary wedges  25  assist in filling any gap that may be created between the set screws  15  and inlet mixers  2 , to provide redundant and/or additional stabilization of the inlet mixers  2 . 
         [0027]      FIG. 4  is a detailed view of a BWR jet pump inlet mixer support  30 , in accordance with example embodiments. The inlet mixer support  30  may include inlet mixer support mounting blocks  32 / 34  attached to both ends of an inlet mixer support band  40 . Specifically, an upper mounting block  32  and a lower mounting block  34  may be provided on both end of support band  40 , where the upper/lower mounting blocks  32 / 34  may be attached to each other via one or more clamping bolts  36 . The upper and lower mounting blocks  32 / 34  and clamp bolts  36  may be used to provide a clamping force to secure the mounting blocks  32 / 34  onto a conventional restrainer bracket  12  of a BWR jet pump assembly  10 , as shown in  FIG. 5 . Besides using clamping bolts  36 , other means of connecting upper and lower mounting blocks  32 / 34  to each other, and to a restraining bracket  12 , may include clamps, a vice, wires, welds, or any other material that may securely fasten the mounting blocks  32 / 34  to each other and to a restraining bracket  12 . 
         [0028]    Upper mounting block  32  may include a notch  38  that may be sized to match a thickness of a vertical side wall of a restrainer bracket (shown in better detail in  FIG. 5 ). 
         [0029]    Mounting blocks  32 / 24  may be attached to each end of support band  40  by draw bolts  42 . Draw bolts  42  may mate with threaded connections in the lower mounting blocks  34  and support band  40 . Alternatively, draw bolts  42  may mate with threaded connections of upper mounting blocks  32 , rather than lower mounting blocks  34 . Other means of attaching either upper/lower mounting blocks  32 / 34  to support band  40  may include clamps, a vice, wires, welding, or any other material that may securely connect either one, or both mounting blocks  32 / 34  to support band  40 . The support band may be in the shape of a long slender band that may be shaped with a curvature to fit around the peripheral surface of an inlet mixer  2 . 
         [0030]    An optional capture plate  46  may be included on an outer surface of either an upper mounting block  32  or a lower mounting block  34 . The optional capture plate  46  may be shaped as a thin rectangular plate that may be attached to either the upper or lower mounting blocks  32 / 34  via bolts  44  (shown in  FIG. 5 ). Other securing means between the mounting blocks  32 / 34  and the capture plate  46  may include clamps, a vice, wires, welding, or any other material that may securely connect a capture plate  46  to one or both of the mounting blocks  32 / 34 . 
         [0031]    All inlet mixer support components may be made of 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. 
         [0032]      FIG. 5  is a detailed view of a BWR jet pump inlet mixer support  30  in use on a conventional BWR jet pump restrainer assembly  10 , in accordance with example embodiments. Clamping bolts  36  may be used to affix the mounting blocks  32 / 34  of the inlet mixer support  30  to restrainer bracket  12 , as shown in the figure. Notice that notch  38  of upper mounting block  32  allows mounting block  32  to fit snuggly on a vertical wall  12   a  of restrainer bracket  12 . Clamping bolts  36  may then be used to securely fasten the mounting blocks  32 / 34  directly to restrainer bracket  12 . Mounting blocks  32 / 34  may be attached to restrainer bracket  12  so that a side surface of the mounting blocks  32 / 34  contacts set screw guide ears  17 , causing guide ears  17  to be a physical stop in the event that mounting blocks  32 / 34  may minutely slide along restrainer bracket  12  while in use. However, it is not necessary that mounting blocks  32 / 34  be positioned directly near guide ear  17 , as mounting blocks  32 / 34  may alternatively attach to restrainer bracket  12  a distance apart from the location of guide ears  17  (i.e., contact between mounting blocks  32 / 34  and guide ear  17  is not necessary). The precise location of the mounting blocks  32 / 34  on restrainer bracket  12  is not entirely critical, as draw bolts  42  may be used to adjust the actual tension that is placed on support band  40 . Draw bolts  42  may therefore be adjusted to ensure that support band  40  fits snuggly against the outer surface of inlet mixer  2 . The purpose of the draw bolts  42  is to adjust the tension on the support band  40  which acts to pull the inlet mixer  2  away from the centerline of the riser piping  1 . Therefore, the tension applied by draw bolts  42  may counter-act any side loading that may be applied to the inlet mixer, where the side loading may be used to pull the inlet mixer toward the centerline of the riser pipe  1 . 
         [0033]    The use of two mounting blocks  32 / 34  (i.e., an upper and a lower mounting block) is not necessary. Rather, one mounting block on each end of a support band  40  may be used to securely fasten the support band  40  in place along the peripheral side surface of the inlet mixer  2 , through the use of clamps, a vice, wires, welding, or any other material that may securely fasten a single mounting block to the restraining bracket. If a single mounting block is used, the single mounting block may still have a draw bolt penetrating the single block so that tension on the support band  40  may still be adjusted. 
         [0034]    In  FIG. 5 , the optional capture plate  46  is shown attached to upper mounting block  32  via bolts  44 . One or more bolts  44  may be used for this purpose, although two bolts  44  are shown in  FIG. 5 . Additionally, clamps, spot welding, or other means may be used as an alternative to bolts  44 . The capture plate  46  may be a thin, rectangular shaped plate that may be positioned to cover set screws  15  (not shown in  FIG. 5 ). The capture plate  46  may provide a physical stop for set screws  15  in the event that the set screws  15  become loose and back out of their holes. In other words, the optional capture plate  46  simply ensures that damaged and/or failing set screws  15  do not fall out of restrainer bracket  12 , especially in the case where tack welds fail and set screws  15  back out of their position in the restraining bracket  12 . 
         [0035]      FIG. 6  is a side-view of a BWR jet pump inlet mixer support  30  in use on a conventional BWR jet pump restrainer assembly  10 , in accordance with example embodiments. Note that the inlet mixer support  30  is shown without the optional capture plate  46  (which is shown instead in  FIG. 5 ) that may otherwise cover the location of set screw  15 . Also note that some degree of separation is shown between the location of upper mounting block  32  and set screw guide ear  17 . Alternatively to what is shown in  FIG. 6 , upper mounting block  32  may be positioned to fit snuggly against set screw guide ear  17 , allowing guide ear  17  to act as a physical stop in the event that mounting block  32  may minutely slide along restrainer bracket  12 . 
         [0036]      FIG. 7  is a bottom-view of a BWR jet pump inlet mixer support  30  in use on a conventional BWR jet pump restrainer assembly  10 , in accordance with example embodiments. In  FIG. 7 , the optional capture plate  46  is again shown covering the location of set screws  15  (set screws  15  are shown in  FIG. 6 , but are obstructed from view in  FIG. 7 ). Note that  FIG. 7  provides a better view of support band  40  interfacing with the inlet mixer  2 . Support band  40  is shaped as a long, rectangular piece that includes a curvature matching the outer peripheral surface of inlet mixer  2  so that it may fit snuggly against the inlet mixer  2 . Draw bolts  42  may be used to adjust the actual tension between support band  40  and lower mounting blocks  34 . Enough tension may be applied via draw bolts  42  to stabilize movement of inlet mixer  2  and pull inlet mixer  2  away from the centerline of the riser pipe  1 , especially in the case where a lateral side force may be applied to inlet mixers  2  to draw the inlet mixer  2  toward a centerline of riser piping  1 . 
         [0037]    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.