Abstract:
A remotely installable piping support device includes a pair of mating tapered wedge segments extending from lever arms connected with a spiral wound spring. The spring is machined integrally with the left lever arm and has a projecting center square drive hub with an internal mounting thread. The right lever arm has an internal square drive which mates with the drive hub. A bolt engages the drive hub and secures the lever arms together. The spring preload on the wedge acting across the shallow angled wedge surfaces maintains rigid contact between jet pump components and takes up the clearance from wear during operation.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to nuclear reactors and more particularly, to apparatus for repairing jet pump assemblies within a nuclear reactor pressure vessel.  
           [0002]    A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., 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 located between the cylindrical reactor pressure vessel and the cylindrically shaped shroud.  
           [0003]    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 restrainer brackets by a gravity actuated wedge. The restrainer brackets support the inlet mixer by attaching to the adjacent jet pump riser pipe. The purpose of the gravity actuated wedge is to maintain contact between the inlet mixer and the restrainer bracket. 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 that are 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. Operating thermal gradients, hydraulic loads, and fluctuations in the hydraulic loads can overcome the lateral support provided by the gravity wedge, allowing gaps or clearances to develop at the opposing two fixed contacts or set screws. Particularly, the tack welds can break and the set screws can loosen permitting the jet pump to vibrate within the restrainer bracket. The loss of contact between the inlet mixer and the restrainer bracket can change the jet pump natural frequency to match some excitation frequency in the system, causing vibration of the piping and exerting increased loads which may cause cyclic fatigue cracking and wear of the piping supports, which can result in degradation from wear and fatigue at additional jet pump structural supports.  
           [0004]    To overcome this problem, gravity wedge supports have been used at locations where clearances have developed in restrainer bracket contacts. The gravity wedge support employed a sliding wedge and a fixed bracket mount that engaged the jet pump restrainer bracket. These gravity wedges were only applicable to restrainer bracket/inlet mixer gap widths from about 1.0 to 2.0 inches, as space was required for a wedge with sufficient weight to give the desired support load. Another solution which was implemented was to reinforce the welded attachment of the two set screws to the restrainer bracket, then reset the inlet mixer against the set screws when the jet pump is reassembled. However, this procedure causes significant downtime and also requires disassembling the jet pumps.  
           [0005]    It would be desirable to provide an apparatus for restoring the tight rigid fit-up provided between the inlet mixer and the adjacent restrainer bracket, replacing the support function of the existing screw type contacts. It would also be desirable to provide an apparatus that can be installed in restrainer bracket/inlet mixer gap widths as small as ¼ inch and provide a continuous adjustment for possible alignment variations between the mixer and diffuser. Further, it would be desirable to provide an apparatus that compensates for after-installation changes in the interface between the mixer and diffuser. Additionally, it would be desirable to provide an apparatus that can be remotely installed by attachment to the existing restrainer bracket without disassembling the inlet mixer.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    In one embodiment of the present invention, a remotely installable piping support device couples to the restrainer bracket of a jet pump inlet mixer at a position adjacent an existing screw type contact, typically, a set screw. The remotely installable piping support device includes a left lever arm and a right lever arm. The right lever arm is coupled to the left lever arm. The device also includes a clamp spring which forces the end portions of the lever arms together. The left and right lever arms are movable in relation to one another about the clamp spring as the clamp spring is torsionally deflected. At least one tapered first wedge segment is mounted on the first lever arm, and at least one tapered second wedge segment is mounted on the second lever arm. The tapered second wedge segment slideably engages the tapered first wedge segment to fill any clearances that develop between an inlet mixer and a restrainer bracket. In an exemplary embodiment, the clamp spring is a spiral wound spring integral with one of the lever arms, and the remotely installable piping support device is referred to as a spring wedge.  
           [0007]    During installation, the spring wedge is spread apart to an open position utilizing an installation tool. The open spring wedge is positioned around a set screw and the plier tool is removed allowing the spring clamp to cause the first lever arm and second lever arm to close together. The tapered first wedge segment and the tapered second wedge segment slideably engage to fill a gap between the mixer inlet and the restrainer bracket, thus, providing a tight fit-up between the mixer inlet and the restrainer bracket.  
           [0008]    The above described spring wedge restores the tight rigid fit-up between the inlet mixer and the adjacent restrainer bracket, enhancing the support function of existing screw type contacts. Additionally the spring wedge is remotely installed by insertion between an existing restrainer bracket and an existing installed inlet mixer. Furthermore, the spring wedge is configured fit in jet pumps which have a restrainer bracket/inlet mixer gap width as small as ¼ inch.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic, partial sectional view, with parts cut away, of a reactor pressure vessel for a boiling water nuclear reactor.  
         [0010]    [0010]FIG. 2 is a front view of a jet pump spring wedge in accordance with an embodiment of the present invention.  
         [0011]    [0011]FIG. 3 is a side view of the jet pump spring wedge shown in FIG. 2.  
         [0012]    [0012]FIG. 4 is a front view of a left lever arm of the spring wedge shown in FIG. 2.  
         [0013]    [0013]FIG. 5 is a front view of a right lever arm of the spring wedge shown in FIG. 2.  
         [0014]    [0014]FIG. 6 is a cross-sectional view of the spring wedge shown in FIG. 2 along line C-C.  
         [0015]    [0015]FIG. 7 is a front view of the spring wedge shown in FIG. 2 in an open position engaging a restrainer bracket.  
         [0016]    [0016]FIG. 8 is a bottom cross-sectional view of the spring wedge shown in FIG. 7.  
         [0017]    [0017]FIG. 9 is a front view of the spring wedge shown in FIG. 2 in a closed positioned around a set screw of a retainer bracket.  
         [0018]    [0018]FIG. 10 is a bottom cross-sectional view of the spring wedge shown in FIG. 9.  
         [0019]    [0019]FIG. 11 is side view of the spring wedge shown in FIG. 2 installed on an inlet mixer and restrainer bracket  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    [0020]FIG. 1 is a schematic, partial sectional view, with parts cut-away, of a reactor pressure vessel (RPV)  20  for a boiling water reactor. 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 a side wall  30  of RPV  20 .  
         [0021]    An inlet nozzle  32  extends through side wall  30  of RPV  20  and is coupled to a jet pump assembly  34 . Jet pump assembly  34  includes a thermal sleeve  36  that extends through nozzle  32 , a lower elbow (only partially visible in FIG. 1), and a riser pipe  38 . Riser pipe  38  extends between and substantially parallel to shroud  24  and RPV side wall  30 . A plurality of riser braces  40  stabilize riser pipe  38  within RPV  20 . There are a plurality of jet pump assemblies in RPV  20 .  
         [0022]    Jet pump assembly  34  also includes a plurality of inlet mixers  42  connected to riser pipe  38  by a transition assembly  44 . A slip joint  48  couples each inlet mixer  42  to a corresponding diffuser  46 . Each diffuser  46  includes four lower guide ears  50  equally spaced around diffuser  46  at slip joint  48 . Above each slip joint  48  is a restrainer bracket  52  that holds each inlet mixer  42 . Each restrainer bracket  52  includes a pair of set screws (not shown in FIG. 1) to provide a tight fit-up or contact between each inlet mixer  42  and each respective restrainer bracket  52 .  
         [0023]    [0023]FIG. 2 is a front view and FIG. 3 is a side view of a jet pump spring wedge  60  in accordance with an embodiment of the present invention. Spring wedge  60  includes a left lever arm  62  coupled to a right lever arm  64 . FIG. 4 is a front view of left lever arm  62  and FIG. 5 is a front view of right lever arm  64 .  
         [0024]    Referring to FIGS.  2 - 5 , left lever arm  62  includes a first end portion  66  and a second end portion  68 . Left lever arm  62  also includes a spiral clamp spring  70  having a lever end  72  connected to first end portion  66  of left lever arm  62 . Spring  70  includes a hub end  74  that includes a projecting square drive hub  76 . In an exemplary embodiment, spring  70  is machined integrally with left lever arm  62 , i.e., left lever arm  62  is machined from a single piece of material. Two tapered wedge segments  78  and  80  extend from second end portion  68  of left lever arm  62 . Wedge segments  78  and  80  are space apart axially along left lever arm  62 . A lug  82  extends from first end portion  66  of left lever arm  62 . First end portion  66  further includes an installation tool gripping notch  84 .  
         [0025]    Right lever arm  64  includes a first end portion  86  and a second end portion  88 . Two tapered wedge segments  90  and  92  extend from second end portion  88  of right lever arm  64 . Wedge segments  90  and  92  are space apart axially along right lever arm  64 . A lug  94  extends from first end portion  86  of right lever arm  64 . First end portion  86  also includes an installation tool gripping notch  96  and a spring mating portion  98 . A square hub opening  100  extends through mating portion  98 . Hub opening  100  is sized to receive hub  76 . In an alternate embodiment, hub opening  100  and mating hub  76  can be any matching polygonal shape.  
         [0026]    Left lever arm  62  and right lever arm are joined together by inserting hub  76  into hub opening  100 . A capture bolt  106  having a head  108  threadedly engages a threaded bolt opening  110  in hub  76 . In an exemplary embodiment, bolt  106  is locked to mating portion  98  by a locking pin  104  After tightening bolt  106 , a locking pin hole  112  is machined through head  108  into mating portion  98 . Locking pin hole  112  is sized to receive locking pin  104  in a tight fit. Locking pin  104  is inserted through locking pin opening  112  in bolt head  108  and into mating portion  98  of right lever arm  64 . The open end of hole  112  is then peened partly closed to capture locking pin  104 .  
         [0027]    Square drive hub  76  is machined at about a 20 degree angle of rotation with respect to the longitudinal axis of left lever arm  62 . As a result, when left and right lever arms  62  and  64  are assembled in their normally aligned position, spiral spring  70  is torsionally deflected to provide about  12  pounds of preload force to drive the mating wedge segments  78 ,  80 ,  90  and  92  into engagement together. In an alternative embodiment, drive hub  76  is machined at between about an 8 to 40 degree angle of rotation with respect to the longitudinal axis of left lever arm  62  to provide between about 5 to 25 pounds of preload force.  
         [0028]    [0028]FIG. 6 is a bottom cross-sectional view of spring wedge  60  (shown in FIG. 2) along line C-C showing tapered wedge segment  78  slideably engaging mating tapered wedge segment  90 . Wedge segment  78  and wedge segment  90  are machined with about a  10  degree slope angle A between sliding surface  114  of wedge segment  78  and sliding surface  116  of wedge segment  90 . In an alternate embodiment, slope angle A is between five and twenty degrees. In another alternative embodiment, wedge angle A is greater than twenty degrees. In a further alternative embodiment, wedge angle A is less than five degrees. Mating wedge segments  80  and  92  are configured similar to mating wedge segments  78  and  90  described above.  
         [0029]    [0029]FIG. 7 is a front view and FIG. 8 is a bottom cross-sectional view of spring wedge  60  spread apart in an open position to permit the placement of spring wedge  60  between inlet mixer  42  and restrainer bracket  52 , around a set screw  118 . During installation, a plier type installation tool (not shown) engages notches  84  and  96  of right and left lever arms  62  and  64  to pivotably move right and left lever arms to an open position with mating wedge segments  78 ,  80 ,  90 , and  92  disengaged permitting spring wedge  60  to be positioned between restrainer bracket  52  and inlet mixer  42  fitting around set screw  118 . The installation tool is then released allowing spring  70  to preload second end portions  68  and  88  together to engage mating wedge segments  78 ,  80 ,  90  and  92 .  
         [0030]    [0030]FIG. 9 is a front view, FIG. 10 is a bottom cross-sectional view, and FIG. 11 is a side view of spring wedge  60  after installation on inlet mixer  42  around set screw  118 . Tapered wedge segments  78  and  80  of left lever arm  62  slideably engage tapered wedge segments  90  and  92  of right lever arm, with the preload of spring  70 , providing a tight fit-up between inlet mixer  42  and restrainer bracket  52 . Projecting lugs  82  and  94  straddle guide ear  54  to maintain spring wedge  60  in a substantially vertical orientation. Referring to FIG. 10, tapered wedge segment  78  includes a contact surface  120  in addition to wedge sliding surface  114 . Contact surface  120  contacts restrainer bracket  52 . Tapered wedge segment  90  includes a contact surface  122  in addition to wedge sliding surface  116 . Contact surface  122  contacts inlet mixer  42 . The preload of spring  70  induces a wedging action to force contact between surfaces  120  and  122 , contacting restrainer bracket  52  and inlet mixer  42  respectively as wedge segments  78  and  90  slide along sliding surfaces  114  and  116  to a closed position.  
         [0031]    During installation, spring wedge  60  is spread utilizing the plier type installation tool (not shown), as explained above. The installation tool is removed after spring wedge  60  is positioned around set screw  118  and between inlet mixer  42  and restrainer bracket  52 . Because spring  70  is torsionally deflected twenty degrees during assembly of spring wedge  60 , an approximate twelve pound force preloads second end portions  68  and  88  of left and right lever arms  62  and  64  together. Particularly, tapered wedge segments  78  and  80  of left lever arm  62  and tapered wedge segments  90  and  92  of right lever arm  64  are moved together and slideably engage to fill a gap  124  between mixer inlet  42  and restrainer bracket  52 , thereby, providing a tight fit-up between mixer inlet  42  and restrainer bracket  52 . During operation of jet pump assembly  34 , any wear that increases gap  124  will cause tapered wedge segments  78  and  80  and tapered wedge segments  90  and  92  to further slideably engage and fill the increased gap  124 . A tight fit-up is maintained by the preload of spring  70  even though wear during operation of jet pump  34  increases gap  124  between mixer inlet  42  and restrainer bracket  52 .  
         [0032]    The above described spring wedge apparatus  60  restores the tight rigid fit-up between inlet mixer  42  and adjacent restrainer bracket  52 , enhancing the support function of existing screw type contacts such as set screw  118 . Additionally apparatus  60  is remotely installed by insertion between an existing restrainer bracket  52  and an existing inlet mixer  42  without disassembly of jet pump  34 .  
         [0033]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.