Abstract:
Slip joint clamps are installed against guide ears of diffusers at jet pump slip joints. Clamps may prevent vibration and/or movement in the slip joint while not being rigidly attached to the diffuser. Clamps include a compression flipper pressing against a guide ear of the diffuser in a substantially radial direction, a biasing member between the compression member and guide ear that presses the flipper against the guide ear, and supporting structures that hold the flipper and biasing member to the inlet mixer about the guide ear. Systems of slip joint clamps are installed against several guide ears of a single diffuser. Each clamp may radially stabilize the diffuser and inlet mixer while permitting upward relative movement of the inlet mixer. Placement and tensioning of clamps in such systems may be varied so as to prevent or reduce vibrations and/or oscillations between an inlet mixer and diffuser.

Description:
BACKGROUND 
       [0001]    A reactor pressure vessel (RPV) in a light water reactor, such as a boiling water reactor (BWR), typically includes a core shroud surrounding the nuclear fuel core and supported by a shroud support structure.  FIG. 1  is a partial sectional view, with parts cut-away, of a related-art RPV  20  for a BWR. RPV  20  has a generally cylindrical shape and is closed at one end by a bottom head (not shown) and at its other end by removable top head (not shown). A top guide (not shown) is spaced above a core plate  22  within RPV  20 . A shroud  24  surrounds core plate  22  and is supported by a shroud support structure  26 . An annulus  28  is formed between shroud  24  and sidewall  30  of RPV  20 . 
         [0002]    An inlet nozzle  32  extends through sidewall  30  of RPV  20  and is coupled to a jet pump assembly  34 . The hollow tubular jet pumps in the shroud annulus provide the required reactor core water flow. Jet pump assembly  34  includes a riser pipe  38 , a plurality of inlet mixers  42  that make up the upper portion of the jet pump and are connected to a plurality of riser pipes  38  by a plurality of transition assemblies  44 , and a diffuser  46 . Each inlet mixer  42  is laterally positioned and supported against two opposing rigid contacts within restrainer brackets that support inlet mixer  42  by attaching to adjacent jet pump riser pipe  38 . Riser pipe  38  extends between and substantially parallel to shroud  24  and RPV sidewall  30 . A slip joint  48  couples each inlet mixer  42  to a corresponding diffuser  46 , which is the lower portion of the jet pump. Slip joint  48  between jet pump inlet mixer  42  and jet pump diffuser  46  has about 0.015 inch operating clearance to accommodate relative axial thermal expansion movement between the upper and lower parts of the jet pump, which results in leakage flow from the driving pressure inside the pump. 
         [0003]      FIG. 2  is a partial side view, with parts cut away, of related-art slip joint  48 . Inlet mixer  42  is generally cylindrical and includes an outer surface  50 . Inlet mixer  42  is received in diffuser  46 . Diffuser  46  includes an inner surface  52  positioned adjacent to inlet mixer outer surface  50 . Operational clearance  54  is shown at an interface  56  between inlet mixer outer surface  50  and diffuser inner surface  52 . A diffuser guide ear  45  projects outward from a top of diffuser  46  to provide proper alignment between diffuser  46  and inlet mixer  42 . Several guide ears  45  may be positioned about a top perimeter edge of diffuser  46 , for example, four guide ears  45 , at 90 degree intervals. 
         [0004]    Slip joint  48  may be stainless steel in inlet mixer outer surface  50  with a cobalt alloy hardfacing extending over interface  56 . Diffuser inner surface  52  may also be stainless steel, with only localized areas of cobalt alloy hardfacing extending into interface  56 . 
       SUMMARY 
       [0005]    Example embodiments include slip joint clamps installed against guide ears of diffusers at jet pump slip joints. Example embodiment jet pump slip joint clamps may prevent vibration and/or movement in the slip joint while not being rigidly attached to the diffuser. Example embodiment clamps may include a compression flipper pressing against a guide ear of the diffuser in a substantially radial direction or otherwise and a biasing member, such as a spring, between the compression member and guide ear that presses the flipper against the guide ear. Example clamps may also include supporting structures that hold the flipper and biasing member to the inlet mixer about the guide ear. 
         [0006]    Example embodiments further include systems of slip joint clamps installed against several guide ears of a single diffuser. Each clamp may radially stabilize the diffuser and inlet mixer while permitting upward relative movement of the inlet mixer. Placement and tensioning of clamps in example embodiment systems may be varied so as to prevent or reduce vibrations and/or oscillations between an inlet mixer and diffuser. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]      FIG. 1  is an illustration of a prior art Reactor Pressure Vessel with parts cut away to show a jet pump assembly. 
           [0008]      FIG. 2  is a detail illustration of a slip joint between an inlet mixer and diffuser of a prior art jet pump assembly. 
           [0009]      FIG. 3  is a profile view of an example embodiment slip joint clamp installed at a slip joint. 
           [0010]      FIG. 4  is a top view of an example embodiment slip joint clamp installed at a slip joint. 
           [0011]      FIG. 5  is a top view of an example embodiment slip joint clamp system installed at a slip joint. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Hereinafter, example embodiments will be described in detail with reference to the attached drawings. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The example embodiments may be embodied in many alternate forms and should not be construed as limited to only example embodiments set forth herein. 
         [0013]    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. 
         [0014]    It will be understood that when an element is referred to as being “connected,” “coupled,” “mated,” “attached,” or “fixed” to another element, it can 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.). 
         [0015]    As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the language explicitly 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. 
         [0016]    It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures or described in the specification. For example, two figures or steps shown in succession may in fact be executed substantially and concurrently or may sometimes be executed in the reverse order or repetitively, depending upon the functionality/acts involved. 
         [0017]    Excessive leakage flow can cause oscillating motion in slip joints, which is a source of detrimental vibration excitation in the jet pump assembly. The slip joint leakage rate can increase due to single loop operation, increased core flow, or jet pump crud deposition. The resultant increased vibration levels and corresponding vibration loads on the piping and supports can cause jet pump component degradation, including jet pump wedge, set screw, and riser piping damage, from wear and fatigue caused by the vibration loads. High levels of flow induced vibration (FIV) are possible under some abnormal operational conditions having increased leakage rates. 
         [0018]      FIG. 3  is an illustration of an example embodiment slip joint clamp  100  shown installed in a related-art slip joint  48 . As shown in  FIG. 3 , the example embodiment slip joint clamp includes a compression flipper  115  and biasing element  130 . Compression flipper  115  is positioned and aligned against a guide ear  45  on a top outer perimeter of diffuser  46 . 
         [0019]    Biasing element  130  biases compression flipper  115  against guide ear  45 . By biasing between guide ear  45  of diffuser  46  and inlet mixer  42 , example embodiment slip joint clamp  100  may reduce or prevent vibration and/or oscillation between diffuser  46  and inlet mixer  42 . Biasing element  130  may be any component capable of providing a force between inlet mixer  42  and compression flipper  115 , including a single-direction bias or multi-direction damping force. For example, biasing element  130  may be a spring, elastic rod, transducer, etc., pushing between compression flipper  115  and inlet mixer  42 . A spring constant or other biasing force of biasing element  130  may be chosen to minimize flow-induced or other vibration in slip joint  48 . For example, biasing element  130  may be a spring having a spring constant chosen to destroy or not match a natural frequency of diffuser  46  and/or inlet mixer  42 , based on the flow rates expected through slip joint  48 , frequency testing of these components, etc. Biasing element  130  may be attached to only one of compression flipper  115  and inlet mixer  42 , in order to permit some vertical relative movement, such as vertical thermal expansion, between these structures without changing a length of biasing element  130 . 
         [0020]    Compression flipper  115  is aligned with and is driven against guide ear  45 . Compression flipper  115  may be rotatably coupled by a pivot pin  120  to a support  110  affixed to a surface of inlet mixer  42 . For example, compression flipper  115  may be permitted to move and/or rotate only in a plane with guide ear  45  by pivot pin  120  fixing compression flipper  115  with respect to inlet mixer  42  except to permit rotation against guide ear  45  about pivot pin  120 . In this way, compression flipper  115  and biasing element  130  may provide a substantially radial biasing force from a center of diffuser  48  and inlet mixer  42 . While biasing element  130  is shown positioned between inlet mixer  42  and compression flipper  115 , it is understood that biasing element  130  could also be a wound spring on pivot pin  120  or another structure and bias compression flipper  115  in a radial direction. 
         [0021]    Compression flipper  115  may be shaped to provide a substantially even biasing force to guide ear  45  and/or damping force between diffuser  46  and inlet mixer  42 . For example, compression flipper  115  may be curved to provide equal force as compression flipper  115  rotates counterclockwise and biasing element  130  elongates, such that as biasing element  130  pushes with less force, the force is more directly transmitted to guide ear  45  and guide ear  45  is pushed with substantially even force away from inlet mixer  42 , regardless of a relative position between guide ear  45  and inlet mixer  42 . Such curvature may also permit some relative vertical movement between diffuser  46  and inlet mixer  42  while maintaining a radial urging against guide ear  45 . Compression flipper  115  may further include a divot  116  where biasing element  130  joins thereto, to provide a linear path for biasing element  130  between compression flipper  115  and inlet mixer  42  and/or protect a junction area between biasing element  130  and compression flipper  115  from damage due to flow or debris fretting. 
         [0022]    Example embodiment clamp  100  may further include a stop pin  125  fixed to support  110 . Stop pin  125  may be placed in a path of movement of compression flipper  115  so as to stop further movement of compression flipper  115 . For example, if compression flipper  115  is not joined to guide ear  45 , stop pin  125  may be positioned to prevent compression flipper  115  from biasing against guide ear  45  once compression flipper has reached a maximum desired extension. Or, for example, stop pin  125  may be positioned with pivot pin  120  to prevent compression flipper  115  from extending past a relaxed length of biasing element  130  or extending to a position where compression flipper may become caught against guide ear  45 . 
         [0023]    Compression flipper  115 , biasing element  130 , pivot pin  120 , and/or stop pin  125  are directly and/or indirectly fixed with inlet mixer  42 , such that vertical movement in inlet mixer  42  will result in each of these elements similarly moving. Example embodiment clamp  100  includes a support  110  as an integral part of or directly adjoining inlet mixer  42 , to which pivot pin  120  and/or stop pin  125  are mated. For example, support  110  may be welded or fastened to inlet mixer  42 . In this way, example embodiment slip joint clamps  100  may not require additional disassembly from other slip join components and may be removable together with inlet mixer  42  during inspection. 
         [0024]    Several alternate arrangements for supporting and aligning compression flipper  115  are possible. For example, as shown in  FIG. 4 , example embodiment clamp  100  may include two supports  110  positioned about guide ear  45 , with pivot pin  120  and stop pin  125  fixed therebetween. In this way, compression flipper  115  may move transversely along pivot pin  120  while remaining in contact with guide ear  45  and not being permitted to slip off guide ear  45  because of supports  110  at respective sides of guide ear  45 . Alternatively, as shown in  FIG. 3 , a single support  110  may be used, and compression flipper  115  may be fixed to pivot pin  120 , which rotates where pivot pin  120  joins support  110 , so as to permit compression flipper  115  to rotate against guide ear  45 . 
         [0025]    Similarly, although only one biasing element  130  is shown in  FIGS. 3 and 4 , example embodiment clamps may include several biasing elements driving compression flipper  115  against guide ear  45  and/or providing a damping force between a compression flipper  115  affixed to guide ear  45 . Further, pivot pin  120  may connect at any point on compression flipper  115 , permitting rotation against guide ear  45  from different rotational directions. One or more stop pins  125  may be placed at any position about compression flipper  115  in order to restrict compression flipper  115  to a desired range of motion, based on where and how compression flipper  115  connects to biasing element  130  and/or indirectly connects to inlet mixer  42 . 
         [0026]    The various components of example embodiment clamp  100  are fabricated of materials that maintain their material properties when exposed to an operating commercial nuclear reactor environment, including high temperatures, volatile chemistries, and radiation encountered therein. For example, zirconium alloys, nickel alloys, aluminum alloys, stainless steel, etc. may be used in example embodiment clamp  100 . Materials may be chosen to reduce fouling and/or electric potential between components of example embodiment slip joint clamps and inlet mixer  42  and/or guide ear  45 . For example, if inlet mixer  42  is stainless steel, example embodiment clamp may be fabricated of stainless steel. 
         [0027]      FIG. 5  is a top view of an example embodiment slip joint clamp system  200  installed at a slip joint  48 . As shown in  FIG. 5 , example embodiment system includes multiple example embodiment slip joint clamps  100 , each positioned at a guide ear  45  of diffuser  46 . Although related art diffusers typically include four guide ears  45  and a clamp  100  is shown at each guide ear, it is understood that other numbers of guide ears and clamps  100  may be used in example embodiment systems. Although slip joint clamps  100  are shown with two supports  110  and other structures as in  FIG. 4 , it is understood that each clamp  100  may be varied and different from each other clamp  100 , as discussed above. 
         [0028]    Each example embodiment clamp  100  biases diffuser  46  apart from inlet mixer  42  via guide ears  45 . The pressure from clamps  100  causes diffuser  46  and inlet mixer  42  to be held in substantially fixed relative position by the opposing, multiple forces provided by the multiple clamps  100  at different positions. As discussed above, an amount, variance, and direction of force provided by example embodiment clamps  100  may be changed by changing biasing member  130  characteristics, compression flipper  115  shape, pivot pin  120  number or location, etc. In this way, a total amount of stabilizing force applied by example embodiment system  200  may be changed based on desired slip joint  48  operating conditions. For example, an amount of force supplied by example embodiment system  200  may be set to best counteract a known or probable oscillation between diffuser  46  and inlet mixer  42 . Similarly, damaging vibration known or expected in a particular dimension may be counteracted by placing opposite example embodiment clamps  100  in that dimension or configuring a resultant stabilizing force from example embodiment clamps  100  to be of a sufficient degree in that dimension. 
         [0029]    Example embodiment system  200  includes example embodiment clamps  100  that are integral with inlet mixer  42  may require no additional disassembly when removing inlet mixer  42  from diffuser  46  or inspecting slip joint  48 . Additionally, because system  200  is fixed with inlet mixer  42 , any vertical or other translation in inlet mixer  42 , such as may be caused by thermal expansion, results in example embodiment system  200  freely moving as well. 
         [0030]    Example embodiments thus being described, it will be appreciated by one skilled in the art that example embodiments may be varied through routine experimentation and without further inventive activity. Variations are not to be regarded as departure from the spirit and scope of the 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.