Abstract:
A clamp for a boiling water reactor feedwater sparger is disclosed and claimed. The clamp assembly includes abuse and cooperating bolt, a reaction arm, and a cross pin. With the exception of the cross pin, the parts are pre-assembled and then installed over the sparger pin head. The cross pin is then installed through the clamp base and through the sparger pin. The clamp bolt is then tightened, locking the clamp and sparger pin. The clamp provides an increased surface area that extends 360° around the sparger pin. This increased surface area reduces the likelihood of wear of the clamp or bracket during plant operation, and the clamp restores the position of the sparger pin head relative to the contact surface of the end bracket if the original pin head or bracket is worn.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to feedwater spargers in boiling water reactors and, more particularly, to clamps for the end bracket assemblies of feedwater spargers. 
         [0003]    2. Description of the Related Art 
         [0004]    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 as feedwater. Recirculation pumps and jet pumps allow the operator to vary coolant flow through the core and change reactor power. 
         [0005]    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. The feedwater is injected through nozzles in the reactor vessel and distributed by feedwater spargers. The feedwater spargers are located inside the reactor vessel and include a central T-connection with two pipe branches that are curved concentric with the inside radius of the reactor vessel. Each curved pipe has a set of nozzles through which the feedwater is injected. 
         [0006]    Each curved pipe has an end bracket that is welded to the pipe. The end brackets are C-shaped and surround an attachment lug that is welded to the reactor vessel wall. Pins having relatively large diameter heads are inserted through the end brackets and the attachment lug. Each pin has a securing nut on the bottom that is installed tightly against a shoulder of the pin but allows a gap between the nut and the bottom of the end bracket white the head of the pin rests against the top of the bracket. The sparger end brackets are secured axially to the attachment lug, but the end brackets are slotted to allow for relative thermal expansion and contraction of the feedwater sparger assembly.  FIG. 7  shows a partially cut-away isometric view of a typical sparger end bracket assembly, including the pin  2  and bracket  3 . 
         [0007]    Visual inspection of the spargers has revealed wearing of the end brackets and pin heads. The wear is caused by vibration of the pin relative to the bracket, which is believed to be caused by flow induced vibration. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a solution to the wear problems discussed above, and includes several components that collectively act as a clamp that is installed on the feedwater sparger end bracket pin to increase the bearing area of the pin head without removing the feedwater sparger pin. The increased surface area of the clamp spreads the weight of the sparger pin over a larger area of the bracket, thereby reducing the load per unit area of the pin head relative to the surface of the bracket. The larger contact area will reduce future bracket and/or pin wear. In addition, the device also restores the position of the sparger pin head relative to the contact surface of the end bracket if the original pin head or bracket is worn. 
         [0009]    The clamp assembly includes abuse and cooperating bolt, a reaction arm, and a cross pin. With the exception of the cross pin, the parts are pre-assembled and then installed over the sparger pin head after lifting the pin head above the surface of the sparger bracket. The cross pin is then installed through the clamp base and through the (pre-existing) hole in the sparger pin head. The clamp bolt is then tightened, forcing the reaction arm against the top surface of the sparger pin head. This captures the dowel pin (which locks the reaction arm to the clamp bolt) within the clamp base and pushes the sparger pin head against the cross pin, forcing the cross pin against the contact surfaces on the clamp base. A predefined torque is then applied to the bolt to secure the clamp to the sparger pin head. Tightening the clamp bolt lowers the reaction arm, causing the distal end of the reaction arm to capture the cross pin and lock it with the clamp base. To prevent movement of the bolt during plant operation, the crimp cup is deformed into features in the bolt shank. The clamp can be removed from the sparger pin by de-torqueing the bolt. To accommodate the de-torqueing process, the crimp cup is secured to the clamp base with the lock pin to prevent movement of the cup. Re-installation of the clamp is possible after replacing the crimp cup. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0010]    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. 
           [0011]      FIG. 1  shows an exploded perspective view of the components of a clamp assembly of the present invention. 
           [0012]      FIG. 2  shows a cross-sectional view of the clamp assembly of  FIG. 1  in place on the head of a sparger bracket pin. 
           [0013]      FIG. 3  shows an isometric view of the base of the clamp assembly of  FIG. 1 . 
           [0014]      FIG. 4  shows an isometric view of the bolt of the clamp assembly of  FIG. 1 . 
           [0015]      FIG. 5  shows an isometric view of the reaction arm of the clamp assembly of  FIG. 1 . 
           [0016]      FIG. 6  shows an isometric view of the crimp cup of the clamp assembly of  FIG. 1 . 
           [0017]      FIG. 7  shows a partially cut-away isometric view of a typical sparger end bracket and pin assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]      FIG. 1  shows an exploded perspective view of the components of a clamp assembly  1  of the present invention, and  FIG. 2  shows a cross-sectional view of the clamp assembly  1  in a use position on the head of a sparger bracket pin  2 . The clamp  1  includes a base  10  with a body that defines a chamber  101  configured to fit over and around the head of the sparger pin  2 . In a preferred embodiment, the base  10  includes one or more side walls  110  and a top wall  112 . While the embodiment of the base  10  illustrated in  FIGS. 1 and 2  has an angular shape with multiple side walls  110 , the base  10  may have alternate profiles such as a round or circular shape in which it may have only a single side wall  110 . In any event, the base  10  has a body defining a chamber  101 , which may be chamfered or beveled to facilitate positioning the base  10  over the sparger pin  2 . 
         [0019]    The body of the base  10  defines a plurality of holes therethrough. The base body  10  defines a hole  102  passing through the side wall  110 . Preferably, a corresponding hole  102  passes through the opposite side wall  110  to define a path completely through the base  10 . The base  10  further defines a hole  104  passing through the top wall  112 . This top hole  104  is threaded to engage corresponding threads on the bolt  12 . 
         [0020]    The clamp assembly  1  further includes a reaction arm  14  that is configured to engage with the base  10  through the side wall opening  102 . In a preferred embodiment, the reaction arm  14  has an L-shape defining substantially perpendicular arms  141  and  142 . The reaction arm is configured to pass over a ledge of the base side wall  110  formed by the side hole  102  such that proximal arm  142  extends downward adjacent the base side wall  110 . As seen in  FIG. 2 , the reaction arm  14  is thus cantilevered relative the base  10 . 
         [0021]    The reaction arm  14  extends through a majority of the thickness of the base  10  such that the reaction arm  14  overlies the sparger pin  2 . The reaction arm  14  has a first surface  145  configured to engage the top surface of the sparger pin head. In a preferred embodiment, this may include an engagement portion that extends away from body  141  of the reaction arm  14 . The reaction arm  14  further comprises a second surface  146  configured to engage the clamp bolt  12  as is discussed in more detail below. 
         [0022]    The clamp assembly further includes a bolt  12  that is configured to matingly engage the threaded opening  104  through the base top wall  112 . An abutment surface  121  is provided at the lower end of the bolt  12 . By engaging the threaded region  122  of the bolt  12  with corresponding threads in the upper base opening  104 , the bolt abutment surface  121  can be lowered into contact with the reaction arm upper surface  146 . A force can thus be applied to the reaction arm  14 , which is transferred through the reaction arm lower surface  145  to the sparger pin  2 . This locks the clamp assembly  1  to the cross pin  18 , as is discussed further below. The reaction arm upper surface  146  may contain an indentation or depression therein configured to engage the bolt abutment surface  121 . 
         [0023]    The clamp assembly  1  further includes a cross pin  18  that is configured to extend through the base  10  and a hole  21  provided in the head of the sparger pin  2 . Preferably, as shown in the illustrated embodiment of  FIG. 1 , the base side opening  102  contains V-channels in the lower ledges of the side wall  110  in which ends of the cross pin  18  rest. The V-channel on the side opposite the reaction arm  14  does not extend completely through the base side wall  110 , however, so that the opposite end of the cross pin  18  contacts an internal surface of the base side wail  110  to lock the cross pin  18  within the base  10  and prevent it from becoming dislodged from the clamp assembly  1 . The cross pin  18  may include a ridged recess  181  in an end thereof to facilitate insertion and, if desired, removal of the cross pin  18  from the clamp assembly  1 . 
         [0024]    With the cross pin  18  positioned within the base  10  and sparger pin  2 , the bolt is torqued to lower its abutment surface  121  into contact with the reaction arm upper surface  146 . Continued torqueing of the bolt  12  causes the reaction arm  14  to lower, causing the reaction arm lower surface  145  to lower and exert a force against the top surface of the sparger pin  2 . The sparger pin  2  and cross pin  18  are thus forced downward. When the bolt  12  is tightened to a predetermined torque, the clamp assembly  1  is fixedly locked to the sparger pin  2 . A lower flange  114  of the base  10  is thus positioned to engage an upper surface of the sparger end bracket with an increased surface area with respect to the original contact surface area provided by the head of the sparger pin  2 . Additionally, the clamp assembly  1 , and the flange  114  in particular, provides 360° contact around the sparger pin  2 . This provides assurance of contact regardless of whether discrete areas of the end bracket top surface have been worn or eroded through operation of the reactor prior to installation of the inventive clamp assembly  1 . 
         [0025]    A crimp cup  16  may be included with the clamp assembly  1 . The crimp cup  16  is configured to be positioned intermediate the base  10  and the bolt  12 . A cylindrical portion  161  contains external threads  162  that matingly engage the threaded upper base opening  104  and internal threads  163  that matingly engage the bolt threads  122 . A non-threaded region  165  of the cylindrical portion  161  extends beyond threaded region  162 . 
         [0026]    The crimp cup  16  is inserted into the base upper opening  104  from the lower side thereof; that is, through the base internal chamber  101 . The external threads  162  are matingly engaged with the base upper opening  104  until a flange  166  on the lower portion of the crimp cup  16  comes into contact with an internal surface of the base upper wall  112 . The bolt is then coupled to the internal threads  163  of the crimp cup  16 . 
         [0027]    As shown in  FIG. 2 , the non-threaded region  165  of the crimp cup  16  will extend beyond the base upper wall  112  when the flange  166  abuts the base  10 . The crimp cup  16  is formed of a malleable material, such as stainless steel. Once the bolt  12  is torqued to the prescribed force and the clamp assembly  1  is locked to the sparger pin  2 , the non-threaded region  165  of the crimp cup  16  can be plastically deformed into channels  123  formed on he shaft of the bolt  12 . This crimping locks the bolt  12  in place, preventing it from backing out and becoming dislodged from the clamp assembly  1 . 
         [0028]    Preferably, the thermal  163  and external  162  threads of the crimp cup have opposite thread configurations. For example, the external threads  162  may be left-handed and the internal threads  163  may be right-handed. This help ensure the crimp cup  16  remains in place during engagement of the bolt  12  as rotation of the bolt  12  into the crimp cup  16  will work to tighten the coupling of the crimp cup  16  to the base  10 . 
         [0029]    The clamp assembly  1  can be removed from the sparger pin  2  by exerting a torque of enough magnitude, such as 20-25 foot-pounds, to release the crimped portion  165  of the crimp cup  16  from the bolt channels  123 . The bolt  12  can then be backed out of the clamp assembly  1 , relieving the force exerted against the cross pin  18  and freeing it for removal from the assembly  1 . The clamp assembly  1  can be re-used with the replacement of the crimp cup  16 . 
         [0030]    A dowel pin  20  may be provided with the clamp assembly  1 . The dowel pin  20  is inserted through a hole  103  in the base  10  into a groove  201  cooperatively formed by a groove  124  formed in the bolt  12  and a groove  143  formed in a distal end of the reaction arm  14 . The hole  103  is located such that the bolt groove  124  is aligned with the hole  103  when the bolt  12  is partially inserted into the base  10 . Further tightening of the bolt  12 —with the dowel pin  20  within the groove  201 —lowers the dowel pin  20  below the hole  103 . The dowel pin  20  is thus captured within the base  10  such that it cannot become dislodged or separated from the clamp assembly  1 . The hole  103  can also be deformed such as by striking its edge with a tool to provide further assurance that the dowel pin  20  does not become dislodged. 
         [0031]    With the dowel pin  20  in place within the groove  201 , the reaction arm  14  is locked to the bolt  12 . This prevents the reaction arm  14  from becoming dislodged from the clamp assembly  1  prior to full torqueing of the bolt  12  to clamp the assembly  1  to the sparger pin  2 . Thus, the reaction arm  14  is fixed to the clamp assembly  1  during installation of the clamp  1  into the reactor prior to insertion of the cross pin  18 . 
         [0032]    A lock pin  22  may be provided with the clamp assembly  1 . The lock pin  22  is inserted into a hole provided in the base top wall  112  and into an upper surface of the crimp cup flange  166 . The lock pin  22  prevents rotation and decoupling of the crimp cup  16  from the base  10  if the bolt  12  is detorqued (that is, rotated in a direction to remove it from the base  10 ). The hole into which the lock pin  22  is inserted may be deformed such as by striking its edge with a tool to prevent it from becoming dislodged from the clamp assembly  1 . The lock pin  22  may include a ridged recess in an end thereof to facilitate insertion and, if desired, removal of the lock pin  22  from the clamp assembly  1 . 
         [0033]    In use, the clamp  1  is partially pre-assembled prior to its installation into the reactor. First, the crimp cup  16  is coupled into the base  10  by threading it into the top wall hole  104  such that the flange  166  abuts a lower surface of the base upper wall  112 . The bolt  12  is then coupled to the crimp cup  16  by threading it into the crimp cup internal threads  163 . The bolt  12  is inserted to the point when its groove  124  is aligned with the base dowel pin hole  103 . The reaction arm  14  is then inserted into the base side opening  102  such that its groove  143  is adjacent the bolt groove  124 , thereby forming the dowel pin groove  201 . The dowel pin  20  is then inserted through the base hole  103  into the groove  201 . This insertion may be performed in known manner, such as via a plunger or air cylinder. The bolt  12  is then threaded further into the base  10 , capturing the dowel pin  20  within the base  10  and locking the reaction arm  14  to the bolt  12 . The bolt  12  is inserted far enough to capture the dowel pin  20 , but to still leave clearance between the reaction arm  14  and the V-channel of the lower edge of the base side opening  102 . The base  110 , bolt  12 , reaction arm  114 , crimp cup  16 , and dowel pin  20  are now fixed together as a subassembly or unit. 
         [0034]    The preassembly is then loaded into a specially designed tool for insertion into the reactor. Additional openings in the base  10  may be provided to facilitate gripping of the subassembly by the tool. The tool also holds the cross pin  18 , such as by the positioning of a detent within the recess  181 . The tool and clamp assembly components are then lowered into the reactor to the location of the sparger pin  2  of interest. Arms of the tool are engaged to lift the sparger pin bolt, creating clearance between the sparger pin head and the sparger bracket. With the subassembly positioned atop the sparger pin head, the cross pin  18  is inserted through the base side opening  102  and sparger pin  2 . An air cylinder or plunger of the tool may be used to insert the cross pin  18 . 
         [0035]    With the cross pin  18  in place, the bolt  12  is torqued to lock the clamp assembly  1  to the sparger pin  2 . This is accomplished by the tooling, which torques the bolt  12  to approximately 20 foot-pounds. Torqueing the bolt  12  also lowers the reaction arm such that its proximal arm  142  covers the cross pin  18 , capturing it within the clamp assembly  1 . A notch  144  in a lower surface of the proximal arm  142  allows the tooling to be engaged with the cross pin  18  while the bolt  12  is being torqued. However, the notch  144  is smaller than the cross pin  18  and will not allow it to pass therethrough. Finally, the upper portion  165  of the crimp cup  16  is crimped, locking the bolt  12  in place. The clamp assembly is thus fixedly locked to the sparger pin  2 , and the tooling is removed from the reactor. 
         [0036]    Sparger pins  2  are typically formed of  304  stainless steel. The materials of the clamp assembly  1  components are chosen such that thermal expansion caused by engagement and operation of the reactor will cause the clamp I to tighten on the sparger pin  2  rather than becoming loose. Thus, the clamp assembly material has a lesser coefficient of thermal expansion than the sparger pin  2 . One preferred material for the clamp assembly  1  is XM19 stainless steel. 
         [0037]    While directional references such as top, bottom, upper, and lower have been referenced herein, they are used for explanatory purposes relative the illustrated embodiments shown in the drawing figures only and should not be construed as limiting. 
         [0038]    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.