Abstract:
A seal collar is disclosed and claimed. The seal is provided in two hinged parts that wrap around the piping to be sealed. The seal halves are connected to form a loop. The seal components may be formed of a shape memory alloy. Once the seal is properly positioned about the pipe, heat is applied to shrink the seal to provide a tight, sealing fit about the pipe. Alternatively, the clamp is formed of stainless steel and a bolt is used to secure the clamp halves to the mixer assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of U.S. Provisional Patent Application No. 61/912,221 filed on Dec. 5, 2013, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a clamp, and, more particularly, the present invention relates to a repair device for use, for example, with boiling water reactor jet pumps. 
         [0004]    2. Description of the Related Art 
         [0005]    While the present invention may be used in a variety of industries, the environment of a boiling water reactor (BWR) nuclear power plant will be discussed herein for illustrative purposes. In a BWR, a steam-water mixture is produced when reactor coolant (water) moves upward through the core, absorbing heat produced by the fuel. The steam-water mixture leaves the top of the core and enters a moisture separator, where water droplets are removed before the steam is allowed to enter the steam line. The steam line directs the steam to the main turbine, causing it to turn the turbine and the attached electrical generator. The steam is then exhausted to a condenser where it is condensed into water. The resulting water is pumped out of the condenser back to the reactor vessel. Recirculation pumps and jet pumps allow the operator to vary coolant flow through the core and change reactor power. 
         [0006]    Within the BWR vessel, a core shroud surrounds the core to provide a barrier to separate the downward coolant flow through the annulus/downcomer (the space between the core shroud and the reactor vessel wall) from the upward flow through the core and fuel bundles. In a typical boiling water reactor, jet pumps are located in the downcomer and provide forced flow of coolant through the reactor vessel in order to yield higher reactor power output than would be possible with natural circulation. Twenty jet pumps are located in two semicircular groups in the annular downcomer region of the reactor. Two jet pumps and a common inlet header or riser pipe comprise a jet pump assembly as shown in  FIG. 1 . Each jet pump assembly  1  includes an inlet riser pipe  2 , a short radius elbow  3  welded at the bottom of the riser pipe  2 , a transition piece  4  welded to the top of the riser pipe  2 , two inlet mixer assemblies  5 , and two conical diffuser assemblies  6 . 
         [0007]      FIG. 2  shows a typical inlet mixer assembly  5 . Each inlet mixer assembly  5  includes an elbow  7  and associated converging nozzle  8 , a flow mixing section  9 , and a gravity wedge apparatus  10  that is employed in the lateral restraint of the inlet mixer  5 . 
         [0008]    Inlet risers  2  are utilized for each jet pump assembly  1  to permit the reactor recirculation inlet nozzles to be located below the active fuel region. This prevents significant fast neutron exposure which could adversely affect the mechanical properties of the nozzle penetration welds. Additionally, riser brace arms  11  provide lateral support for the upper end of the jet pump assembly  1  and also allow for the vertical differential expansion between the riser  2  and the reactor vessel during plant heat-up and cool-down. 
         [0009]    The inlet mixer elbow  7  and converging nozzle  8  sections redirect the coolant flow stream 180° and increase the velocity of the flow stream as the coolant passes through the nozzle  8 . This increase in fluid flow velocity results in lower static pressure of the driving flow. This decreased static pressure in the upper end of the inlet mixer  5  draws higher pressure water from the downcomer plenum and the two flows (driving and driven) are then combined together in the mixing section  9  of the inlet mixer  5 . The inlet mixer  5  interfaces with the diffuser assembly  6  at the slip joint  12  of the jet pump. The slip joint  12  provides means to remove the inlet mixer assembly  5  from a jet pump assembly  1  and also accommodates the differential thermal expansion that occurs in the jet pump assembly  1  during plant heat-up and cool-down. This differential thermal expansion is the result of the riser pipe  2  being anchored in the low alloy carbon steel of the reactor vessel and the differing lengths of stainless steel jet pump components. The inlet mixer assemblies  5  are supported laterally by a restrainer bracket  13  that is welded to the riser pipe  2 . The gravity wedge  10  of the inlet mixer and two opposing set screws that are mounted to the restrainer bracket  13  are designed to restrain the inlet mixer  5 . 
         [0010]    The inlet mixers  5  are subject to flow induced vibration resulting from the mixing action of the driving and driven flow components in the mixing section  9  of the inlet mixer  5 . In addition, unstable pressure fluctuations result from the passage of coolant through the slip joint  12  to the lower pressure downcomer annulus. Consequently, abnormal wear of jet pump assembly  1  components has been experienced at several BWR plants. Components affected have been the inlet mixer  5  and diffuser collar  6  at the slip joint location  12 , and the gravity wedge  10  and interfacing surface of the restrainer bracket  13 . Isolated cracking has also been experienced at the set screw tack welds, riser brace  11  to riser pipe  2  weld, and short radius elbow  3  to thermal sleeve weld. 
         [0011]    Attempts have been made to stop damage due to flow induced vibration. Such prior attempts include slip joint clamps and auxiliary spring wedge assemblies. Slip joint clamps act like a c-clamp to lock the mixer pipe to the diffuser. Auxiliary spring wedges work in place of a set screw that is no longer touching the jet pump mixer assembly. Some power plants have removed the mixer assemblies and machined grooves on the sealing surface in the slip joint to create a labyrinth seal. However, each of these attempts has proven to be ineffective at preventing damage to the jet pump assemblies. 
         [0012]    Thus, there is a need to provide a simple mechanical device which will minimize or limit coolant leakage at the slip joint location and also provide supplemental structural support to the jet pump assembly. 
       SUMMARY OF THE INVENTION 
       [0013]    This invention is a seal collar that is hinged in two halves that wraps around the jet pump mixer assembly and sea n top of the diffuser collar assembly. In one embodiment, the clamp is formed of stainless steel and a bolted joint is used to secure the clamp halves to the mixer assembly. Alternatively, the clamp halves are connected to form a loop that is made out of a shape memory alloy, and when properly positioned are contracted onto the mixer assembly. The clamp may include notches that fit around the diffuser collar fins and have enough clearance to allow for the mixer to be offset from the diffuser. A flexure geometry is included in the design that will allow the diffuser o grow thermally without overstressing the clamp material. 
         [0014]    For the shape memory alloy clamp, the seal components are curved to an initial shape that corresponds to the outer surface of the jet pump mixer. The seal components are then plastically deformed, such as by stretching, to increase the sizes thereof. The enlarged seal components are then positioned about the mixer and ends thereof are connected together to form a continuous loop about the mixer. The enlarged seal components have greater radii of curvature, providing clearance and facilitating positioning about the inlet mixer. Once in position about the mixer, the connected seal components are heated to return them to their original size, thereby clamping them to the jet pump mixer. The seal components are positioned adjacent the slip joint, and the clamping force imparted by the seal prevents jet pump vibration by restricting the flow path in the slip joint. The bottom edges of the seal components provide a seal with the jet pump diffuser. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0015]    The present invention is described with reference to the accompanying drawings, which illustrate exemplary embodiments and in which like reference characters reference like elements. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. 
           [0016]      FIG. 1  shows a typical jet pump assembly. 
           [0017]      FIG. 2  shows a typical inlet mixer assembly. 
           [0018]      FIG. 3  shows two slip joint seals of the present invention in place on a jet pump assembly. 
           [0019]      FIG. 4  shows one component of the slip joint seal of  FIG. 3 . 
           [0020]      FIG. 5  shows a first view of a connection of the seal components of the seal of  FIG. 3 . 
           [0021]      FIG. 6  shows a second view of a connection of the seal components of the seal of  FIG. 3 . 
           [0022]      FIG. 7  shows a third view of a connection of the seal components of the seal of  FIG. 3 . 
           [0023]      FIG. 8  shows a partial cross-sectional view of the seal of  FIG. 3 . 
           [0024]      FIG. 9  shows another slip joint seal of the present invention in place on a jet pump assembly. 
           [0025]      FIG. 10  shows a partial close-up view of one component of the slip joint seal of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIG. 3  shows two slip joint seals  20  of the present invention in place on a jet pump assembly. The seal  20  includes two components or halves  22 ,  24 .  FIG. 4  shows an exemplary view of one of the seal halves  22 ,  24 . In a preferred embodiment, the seal components  22 ,  24  are substantially identical. Each seal component  22 ,  24  has an arcuate profile that covers approximately 180° about a central axis of rotation. Flanges  26  are positioned on circumferential ends thereof. Preferably, two such flanges  26  are positioned on a first end of the seal component  22 ,  24  and one such flange  26  on a second end of the seal component  22 ,  24 . The flanges  26  are sized and positioned such that they matingly correspond and intermingle with the flanges  26  of the other seal component  24 ,  22  when placed in the use position. 
         [0027]      FIGS. 5 and 6  illustrate how the ends of the seal components  22 ,  24  are connected in a preferred embodiment. The seal components  22 ,  24  are positioned with the lone flange  26  of one seal component  22  positioned within the two flanges  26  of the other seal component  24 . The seal components  22 ,  24  are arranged such that the intermingled flanges  26  of the components  22 ,  24  are substantially aligned, defining a receptacle into which a fastener  35  can be positioned to join the ends of the seal components  22 ,  24 . The fastener  35  can take a variety of forms, one preferred form being a bolt formed of XM-19. The inner surfaces of one or more of the flanges  26  can be threaded to correspond with the bolt threading, or a separate nut can be provided. Preferably, the fasteners  35  include a locking mechanism such as ratcheting or a crimp cup to lock them in position once they are installed. Thus, the fasteners  35  will not unintentionally become loose or separate from the seal components  22 ,  24 . 
         [0028]    With one set of seal ends connected as illustrated in  FIGS. 5 and 6 , the other set of ends are open to allow the seal  20  to be positioned around the mixer body  9  of the jet pump  1 . The seal is the closed and a second fastener  35  positioned within the intermingled flanges  26  of the second set of ends. The closed seal  20  is then seated atop the diffuser collar assembly  6 . 
         [0029]    The seal components  22 ,  24  may be formed of a shape memory alloy (SMA) such as a nickel titanium (NiTi) alloy. Once formed, SMA materials can be bent or stretched and will hold those shapes until heated above a transition temperature. Upon heating, the shape changes back to its original configuration. Each seal component  22 ,  24  is formed and/or machined in known manner to have an inner surface diameter that corresponds with the outer surface of the jet pump mixer  9 . Once formed, the seal components  22 ,  24  are stretched such as with a mandrel arrangement to plastically deform the components  22 ,  24  to enlarge the diameters and provide clearance for installation about the mixer  9 . Once the seal components are connected and placed in the use position as described above, the seal  20  is heated to restore the seal components  22 ,  24  to their original shape. This causes the seal diameter to shrink, tightly clamping the seal  20  to the mixer  9  as illustrated in  FIG. 3 . The seal  20  can be heated in known manner, such as by the application of hot water. 
         [0030]    The seal  20  prevents jet pump vibration by restricting the flow path in the slip joint  12 , which has been shown to cause flow induced vibration. The seal  20  clamps to the mixer assembly  9  adjacent the slip joint  12  and provides a seal to the slip joint  12  by sitting atop of the diffuser  6 . 
         [0031]      FIG. 8  shows a partial cross-sectional view of the seal components  22 ,  24 . A curved flexure geometry  28  is provided on a bottom of the seal  20 . The flexure  28  compensates or flexes to allow the diffuser  6  to grow thermally without overstressing the seal  20  material. Thus, the seal is improved as the jet pump assembly  1  heats up, which causes the diffuser  6  to move towards the collar thereby increasing the load on the flexure geometry on the collar. As shown in  FIG. 7 , overlap may be provided in the flexure geometries of corresponding seal components  22 ,  24 . The seal  20  may also have notches  29  that fit around the fins of the diffuser collar  6 . The notches  29  have enough clearance to allow for the mixer  9  to be offset from the diffuser  6 . The notches may include sealing members such as metal gaskets to prevent leakage. 
         [0032]      FIGS. 9 and 10  illustrate another slip joint seal  20  of the present invention. In this embodiment, the seal  20  is designed to encircle the mixer  9  just above and adjacent the diffuser  6 . The flexure portion  28  is above the diffuser fins, and thus no notches are required for this embodiment. Here, the flexure portion  28  is located in a middle position such that the seal  20  includes a lower edge or surface  25  that is configured to abut the diffuser  6 . 
         [0033]      FIGS. 9 and 10  also illustrate the stainless steel embodiment of the seal  20 . Each seal component  22 ,  24  includes a flange  26  at circumferential ends thereof. When the seal halves  22 ,  24  are arranged, the flanges  26  cooperate to define a receptacle into which a fastener  35  can be positioned to join the ends of the seal components  22 ,  24  and to secure the clamp  20  to the mixer assembly  5 . Here, the receptacles are substantially coplanar or parallel to the plane of the seal  20 , whereas the receptacles in the embodiment illustrated in  FIGS. 3-7  are substantially perpendicular to the plane of the seal  20 . 
         [0034]    While the preferred embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not of limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. Furthermore, while certain advantages of the invention have been described herein, it is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.