Abstract:
A jet pump stabilizer is disclosed and claimed. The stabilizer includes a clamp body that is affixed about the riser pipe. Two U-clamps are connected to the clamp body, each U-clamp positioned about a jet pump mixer section. A wedge assembly is positioned between the clamp body and each mixer pipe, cooperating with the clamp body and U-clamps to laterally restrain the mixer sections. A clamp ring is positioned about each mixer section and retained in place by the U-clamps, wedge assemblies, and clamp body. A sealing ring is moveably connected to the clamp ring such that it is biased toward engagement with the jet pump diffuser. Seals provided on the stabilizer engage the jet pump assembly above and below the slip joint, preventing vibration-inducing leakage through the slip joint.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of U.S. Provisional Patent Application No. 61/703,734 filed on Sep. 20, 2012, 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 jetpumps. 
         [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, core shrouds surround 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 the lateral restraint of the inlet mixer  5 . 
         [0008]    Inlet risers  5  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 drive 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 drive 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]    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 
       [0012]    The jet pump stabilizer disclosed and claimed herein restricts coolant leakage at the jet pump slip joint. A clamp body is provided in two parts to interconnect around the jet pump riser pipe. In this manner, it can be placed in position without removal of any jet pump assembly components. Two U-clamps are connected to the clamp body, each U-clamp fitted around a separate one of the jet pump inlet mixer pipes. A wedge subassembly is positioned intermediate the riser pipe and each mixer pipe. The wedge assemblies impart a force to the mixer pipe in a direction that is substantially opposite the force imparted to the mixer pipe by the U-clamp. Thus, the mixer is restrained against movement, including flow-induced vibration. The connections between the U-clamp and the clamp body can incorporate mating spherical seats to accommodate any misalignment between the two mixer pipes and the riser pipe. 
         [0013]    A clamp ring is provided for each jet pump mixer. Each clamp ring is provided in two parts to interconnect around the jet pump mixer pipe. In this manner, the clamp rings can be placed in position without removal of any jet pump assembly components. An outboard portion (that is, a portion away from the riser pipe) of each clamp ring is placed between the U-clamp and the mixer pipe, and may be mechanically connected thereto. An inboard portion (that is, a portion towards or adjacent to the riser pipe) of each clamp ring is placed between the wedge and the mixer pipe, and may be mechanically connected thereto. In this manner, the clamp ring is held in the desired position about the jet pump inlet mixer. A seal, preferably a malleable seal, may be provided on the inner perimeter of the clamp ring such that it is in contact with the mixer above the slip joint. This clamp ring seal limits leakage past the jet pump slip joint in an upward direction. 
         [0014]    A sealing ring is attached to each clamp ring. Each sealing ring is provided in two parts to interconnect around the jet pump mixer pipe. In this manner, the sealing rings can be placed in position without removal of any jet pump assembly components. Each sealing ring is connected to its corresponding clamp ring by one or more spring-biased connection pins, allowing movement of the sealing ring relative the clamp ring. A seal, preferably a malleable seal, may be provided on a lowermost portion of the sealing ring. The springs bias the sealing ring downward, causing the seal to contact the jet pump diffuser collar below the slip joint. This sealing ring seal limits leakage past the jet pump slip joint in a downward direction. Slots may be provided in the sealing ring to accommodate the jet pump diffuser guide vanes. The relative movement between the sealing ring and the clamp ring accommodate any thermal expansion or contraction at the slip joint. 
     
    
     
       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 a slip joint clamp of the present invention. 
           [0019]      FIG. 4  shows a slip joint clamp subassembly of the slip joint clamp of  FIG. 3 . 
           [0020]      FIG. 5  shows a cross-sectional view of the slip joint clamp of  FIG. 3  in place on a jet pump assembly as shown in  FIG. 1 . 
           [0021]      FIG. 6  shows a first clamp body of the slip joint clamp subassembly of  FIG. 3 . 
           [0022]      FIG. 7  shows a second clamp body of the slip joint clamp of  FIG. 3 . 
           [0023]      FIG. 8  shows an inlet mixer restraint assembly of the slip joint clamp of  FIG. 3  mounted at a preferred elevation on the riser pipe of the jet pump assembly of  FIG. 1 . 
           [0024]      FIG. 9  shows a stabilizing wedge system of the slip joint clamp of  FIG. 3 . 
           [0025]      FIG. 10  shows a cross-sectional view of a U-clamp subassembly of the slip joint clamp of  FIG. 3 . 
           [0026]      FIG. 11  shows the connection of one U-clamp of the slip joint clamp of  FIG. 3  to its corresponding restraint clamp body about the inlet mixer of the jet pump assembly of  FIG. 1 . 
           [0027]      FIG. 12  shows a cross-sectional view of a U-clamp pad of the slip joint clamp of  FIG. 3  in contact with the outboard clamp ring of the slip joint clamp. 
           [0028]      FIG. 13  shows optional stop bolts that can be used in the slip joint clamp of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]      FIG. 3  shows a slip joint clamp  20  of the present invention, and  FIG. 4  shows a slip joint clamp subassembly  30  thereof. The subassembly  30  includes inboard  31  and outboard  32  semicircular clamp segments, which are joined together by a pair of slip joint bolts  40  and bolt keepers  41  to form a circular clamp ring  33 . A seal ring  36  includes inboard  34  and outboard  35  semicircular seal segments that are joined to the clamp ring  33  by several guide pins  37 . Captive to the guide pins  37  are spring elements  38 , which collectively provide a separation force between the stationary clamp ring  33  and the moveable seal ring  36 . The seal ring  36  is designed to move axially upward in response to the thermal growth of the diffuser  6  relative to the inlet mixer  5 . This upward axial movement is resisted by the compressive action of the spring elements  38 . 
         [0030]    The inboard  31  and outboard  32  semi-circular clamp segments are configured with an opposing tongue-and-groove design to ensure proper alignment of these two clamp segments. Additionally, slots are provided in the seal ring  36  to allow for clearance with the diffuser  6  guide vanes. These engineered slots are sized to minimize slip joint coolant leakage by providing a tight fit with the diffuser guide vanes. 
         [0031]    Malleable metal seals  39  may be integrated into the clamp  33  and seal  36  rings to provide a more positive seal against coolant leakage. A preferred spatial orientation of these metal seals is depicted in the cross-sectional view of  FIG. 5 . The clamp ring  33  is held stationary and in the desired position on the inlet mixer  5  by the clamping action of the U-shaped clamp pads  73  and the mixer wedge element  63  of the wedge clamp  10  components of the inlet mixer restraint subassembly  50 . 
         [0032]    The inlet mixer restraint assembly  50  preferably includes a right clamp subassembly  51  and a left clamp subassembly  52 .  FIGS. 6 and 7  show preferred right  51  and left  52  clamp bodies, respectively. Bearing surfaces  501  of these subassemblies  51 ,  52  are joined together at the desired elevation on the riser pipe  2  by a pair of clamp bolts  53  and clamp nuts  54 . Clamp bolt keepers  55  are also provided to prevent loss of mechanical preload in the bolted joint. Preferably, the design of the clamp bolts  53  and the clamp nuts  54  incorporates spherical seats  56  that interface with mating spherical seats  56  in the right  51  and left  52  clamp bodies. This ensures proper clamp fit-up in the event that the centerlines of the riser pipe  2  and attendant inlet mixers  5  are not coplanar. 
         [0033]    One of the clamp body portions  51 ,  52  may be provided with one or more “tongue” features  57  that interface with a corresponding pair of mating “groove” features  58  that may be provided on the other clamp body  52 ,  51 . This tongue-and-groove arrangement can help ensure proper subassembly alignment and ease of remote installation. For example, the right clamp body  51  can incorporates a pair of tongue features  57  that interface with a pair of mating groove features  58  of the left clamp body  52  as shown in the illustrated embodiments of  FIGS. 6 and 7 .  FIG. 8  shows the inlet mixer restraint assembly  50 , with connected right  51  and left  52  clamp bodies, mounted at a preferred elevation on the jet pump riser pipe  2 . 
         [0034]    The as-built distance between the riser pipe  2  and the inlet mixer  5  preferably is stabilized by a system of wedges  60 . A preferred system of wedges  60  is illustrated in  FIG. 9 . Primary  61  and secondary  62  wedge elements bear on the wedge surfaces  59  of the right  51  or left  52  clamp bodies and the inlet mixer wedge element  63 . As the primary  61  and secondary  62  wedge elements are drawn closed together by virtue of the wedge bolt  64 , the inlet mixer wedge element  63  is brought to bear on the inboard clamp ring  31  of the slip joint clamp  30 . The primary  61  and secondary  62  wedge elements are identical in overall size and shape. The primary wedge  61  design accommodates the wedge bolt keeper  65  and the bearing surface of the wedge bolt  64 . The secondary wedge design  62  provides internal threads that interface with the threaded end of the wedge bolt  64 . 
         [0035]      FIG. 9  also shows a U-clamp subassembly  70  of the restraint assembly. The U-clamp subassembly  70  is attached to both the right clamp body  51  and the left clamp body  52  by U-clamp bolts  71 . Ends of the U-clamp assembly  70  abut the right  51  and left  52  clamp bodies at horizontal surfaces  502  thereof. U-clamp bolt keepers  72  are provided to prevent loosening of the associated bolts  71 . As is the case with preferably all of the mechanical fasteners in the slip joint  30  and inlet mixer restraint clamp  50  assemblies, in a preferred form the bolt keepers are essentially cantilever beam elements with ratchet teeth that interface with mating ratchet teeth integral with the fasteners. The keepers are designed to deflect as the ratchet teeth of the bolts are rotated in a tightening direction, and to resist rotation of the bolt in a loosening direction. A crimp cup is another preferred form of bolt keeper  72 . In this design, the bolt includes a cup portion that surrounds the head and fits into a counter bore. After the bolt has been inserted and tightened, one or more locations along the cup portion are plastically deformed or crimped outward into the counter bore, which features a plurality of machined semi-cylindrical depressions or partial cylindrical features. The interference of the plastically deformed crimp collar with these counter bore features prevents rotation of the bolt. 
         [0036]    In order to eliminate shear stress in the U-clamp bolts  71 , pockets can be provided in the right  51  and left  52  clamp bodies. As shown in the cross-sectional view of  FIG. 10 , the U-clamp  70  is seated on a horizontal surface  504  of the clamp bodies  51 ,  52 . A step feature is provided at both extremities of the U-clamp  70 , which are inserted into these pockets, thus providing a substantial bearing surface  503  to transmit loads from the U-clamp  70  into the clamp bodies  51 ,  52 . 
         [0037]      FIG. 11  shows the connection of one U-clamp  70  to its corresponding restraint clamp body  51 ,  52  about the jet pump inlet mixer  5 , and  FIG. 12  shows a cross-sectional view illustrating a preferred spatial arrangement of the U-clamp pad  73  in contact with the outboard clamp ring  32  of the slip joint clamp  30 . Mechanical preload can be generated in the U-clamp  70  by advancing the U-clamp pads  73  onto the outboard clamp ring  32  of the slip joint clamp subassembly  30 . This can be accomplished via a jack bolt  77 , which is coupled to the U-clamp pad  73  by, for example, a cap screw  78 . The forces thus imparted on the U-clamp pad  73  and the clamp ring  32  coupled with the force applied by the inlet mixer wedge  63  onto the slip joint inboard clamp ring  31  provide the necessary friction to maintain the slip joint clamp  30  in the desired position on the inlet mixer  5 . 
         [0038]      FIG. 12  shows a cross-sectional view illustrating a preferred spatial arrangement of the U-clamp pad  73  in contact with the outboard clamp ring  32  of the slip joint clamp  20 . 
         [0039]    Optionally, in lieu of relying solely on friction to maintain the slip joint clamp  30  in position on the jet pump inlet mixer  5 , stop bolts  75  and accompanying stop bolt keepers  76  can be employed. As illustrated in  FIG. 13 , these stop bolts  75  can be inserted into blind holes that are machined into the inlet mixer  5 . 
         [0040]    This disclosed jet pump stabilizer design restricts coolant leakage at the jet pump slip joint  12 , accommodates thermal expansion at the slip joint  12 , provides additional lateral support to the inlet mixers  5 , accommodates misalignment between the riser pipe  2  and adjacent inlet mixers  5 , and can be installed without removal of any jet pump assembly components, such as the inlet mixer  5 . 
         [0041]    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 to 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.