Abstract:
The inventive tool is designed to ensure proper plant operation position of the core shroud head bolt assemblies of a boiling water nuclear reactor. The tool exerts an upward pulling force on stuck retainers to return them to the locking position around the nut. The tool includes a frame, an engagement member, and a collar. The engagement member is lowered toward and end of the bolt until it comes into contact therewith. Further movement of the engagement member causes the frame and collar to move upward, lifting the retainer and extending the spring.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of U.S. Provisional Patent Application No. 61/522,511 filed on Aug. 11, 2011, 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 boiling water reactor core shroud head bolt removal tool, and, more particularly, the present invention relates to a tool for ensuring safe removal and installation of core shroud head bolts to the proper position. 
         [0004]    2. Description of the Related Art 
         [0005]    Core shrouds are components of boiling water nuclear reactors; they are cylindrical structures that surround the core to provide a barrier to separate the downward coolant flow through the annulus from the upward flow through the core. The core shrouds also structurally support and align the fuel assemblies, steam separator assemblies, and control rod guide tubes. A head sits atop the shroud and creates an upper plenum into which a two-phase steam/water mixture enters from the core and is directed to steam separation equipment. 
         [0006]    The core shroud head must be removed to access the core for refueling and inspection of the core internals. During removal and installation of the core shroud head, it is necessary to de-tension and tension the core shroud head bolts. These bolts have a spring pushing upward against a retainer, which locks the nut on the shroud head bolt assembly, preventing the nut from rotating. Due to many years of service, and with the accumulation of grit and grime, the retainers may not return to the locked position with just spring pressure. What is needed is a tool that ensures removal and replacement of the core shroud head bolts with the spring retainers in the proper position, 
       SUMMARY OF THE INVENTION 
       [0007]    The inventive tool is designed to remove and replace core shroud head bolts, while exerting an upward pulling force on stuck retainers, returning them to the locking position around the nut. The tool includes a relatively stationary base or frame, a collar, and an engagement member. With the core shroud bolt in position on the shroud head, tool is positioned about the nut portion of the core shroud bolt assembly such that the frame spans the length of the nut portion with the collar positioned beneath the retainer and the engagement member positioned above the end portion of the bolt. The engagement member, which may be provided in the form of a hex nut, is tightened until its stop seats against the top of the shroud head bolt. Additional torquing of the engagement member causes the tool housing, including the lower collar, to rise up, which in turn pulls the shroud head bolt, retainer back into its lock position. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0008]    The present invention is described with reference to the accompanying drawings, in which like reference characters reference like elements, and wherein: 
           [0009]      FIG. 1  shows a typical commercial boiling water reactor, partially cut-away; 
           [0010]      FIG. 2  shows a detailed view of a typical core shroud head bolt; 
           [0011]      FIG. 3  shows an embodiment of a tool of the present invention; and 
           [0012]      FIG. 4  shows the tool of  FIG. 3  in position on a core shroud bolt. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    In a typical commercial boiling-water reactor, such as illustrated in  FIG. 1 , the core inside the reactor vessel creates heat, a steam-water mixture is produced when water (reactor coolant) moves upward through the core, absorbing heat. The steam-water mixture leaves the top of the core and passes through moisture separation equipment 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 generator, which produces electricity. The unused steam is exhausted into the condenser where it is condensed into water. The resulting water is pumped back to the reactor vessel. 
         [0014]    The reactor core contains fuel assemblies that are cooled by water circulated therethrough. A majority of coolant flows down through an annul us created between the reactor vessel wall and the core shroud  1 , while a portion of the coolant is directed through jet pumps located within the annulus that ensure proper flow upward through the core. 
         [0015]    A head  2  sits atop the core shroud  1  and creates an upper plenum into which a two-phase steam/water mixture enters from the core and is directed to steam separation equipment. The head  2  is attached to the shroud  1  by a plurality of core shroud head bolts  3 , a detailed view of which is presented in  FIG. 2 . A typical shroud-head bolt  3  is 1.75 in. in diameter and 14 ft long. A nut is screwed onto one end of the bolt, and a tee head is welded to the other. A sleeve covers the rest of the bolt  3 , and the base of the sleeve is joined to a collar that is welded to the shaft near the tee head. A part of the collar is cut out to provide space for an alignment pin window. 
         [0016]    The head  2  must be removed from the shroud  1  to access the core for refueling and inspection of the core internals. During removal and installation of the core shroud head  2 , it is necessary to tension and de-tension the core shroud head bolts  3 . These bolts  3  have a spring  31  pushing upward against a retainer  32 , which locks the nut  33  on the shroud head bolt assembly  3 , preventing the nut  33  from rotating. Due to many years of service, and with the accumulation of grit and grime, the retainers may not return to the locked position with just spring pressure. 
         [0017]      FIG. 3  illustrates an embodiment of a tool  10  for removal and replacement of the core shroud head bolts while ensuring the retainers  32  are returned to the proper position, and  FIG. 4  illustrates the tool  10  in position on a mock-up core shroud bolt  3 . The tool  10  includes a base or frame  101 , an engagement member  102 , and a collar  103 . 
         [0018]    As shown in the exemplary embodiment illustrated in  FIGS. 3 and 4 , the frame  101  may include elongate arms  1011  that provide a height element to the tool  10  such that it spans the distance between the spring  31  and the uppermost end of the nut  3  with clearance to maneuver the tool  10  around the nut  3 . The frame  101  may include a panel  1013  at one end thereof. Preferably, the panel  1013  is oriented such that it is substantially perpendicular to the longitudinal axes of the arms  1011 . The panel  1013  is preferably secured to an end of each arm  1011 . Pairs of arms  1011  may be connected at their second end distal from panel  1013  by a transverse arm  1012  extending between the elongate arms  1011 . The transverse arms  1012  may be separate elements or may be integral to their associated elongate arms  1011 . By connecting the distal ends of the elongate arms  1011 , the transverse arms  1012  help ensure a robust frame  101  that can withstand the stresses and strains of normal use. Two such transverse arms  1012  are shown in the illustrated embodiment of  FIGS. 3 and 4 , but at least a third transverse arm could also be included. One side of the frame  101  should be left open, however, to facilitate placement of the tool  10  on the bolt  3 . 
         [0019]    The engagement member  102  is movably coupled to the frame  101 . Preferably, the engagement member  102  is threadably coupled to the panel  1013  such that the longitudinal axis of the engagement member  102  is substantially parallel to the longitudinal axes of the elongate arms  1011  and substantially perpendicular to the plane of the panel  1013  and the longitudinal axis of the transverse arms  1012 . Ideally, the engagement member  102  is substantially centered in the panel  1013  and between the arms  1011 . Thus, the engagement member  102  preferably is coupled to a substantially central location of the panel  1013  with the longitudinal axis of the engagement member  102  being substantially equidistant from each of the longitudinal axes of the elongate arms  1011 . 
         [0020]    The collar  103  is coupled to the frame  101  at its second end, distal to the engagement member  102 . Preferably, the collar  103  is connected to each of the transverse arms  1012 . The collar has an arcuate shape that facilitates its placement around the spring  31 . The collar  103  extends inwardly away from the frame  101  in a plane that preferably is substantially parallel to the panel  1013 , thus forming a ledge  1031  that can be used to contact and exert force against the retainer  32 . Preferably, the collar  103  is substantially centered in the frame between the elongate arms  1011 . 
         [0021]    After the bolt  3  has been placed in its plant operation position and the nut  33  has been tightened in known manner, the tool  10  is lowered onto the bolt  3  such that the collar  103  is below the retainer  32  and adjacent the spring  31 , and the engagement member  102  is above the uppermost end of the bolt  3 . A crane, such as the plant&#39;s overhead crane, in conjunction with an optional handle  104  may be used to accomplish this movement. Proper position of the tool  10  on the bolt  3  can be ensured via line of sight or through the use of cameras (not shown). The engagement member  102  is then rotated in a clockwise direction (from the perspective above the tool  10 ), which causes the engagement member  102  to be lowered relative the frame  101 . Such rotation continues until the lowermost end of the engagement member  102  comes into contact with the end or stop  35  of the core shroud head bolt  3 . 
         [0022]    Once the engagement member  102  is in contact with the bolt stop  35 , further rotation of the engagement member  102  will cause the frame  101  and collar  103  to move relatively upward, as the bolt stop prevents further downward movement of the engagement member  102 . As the collar is initially positioned adjacent the spring  31 , it will come into contact with the retainer  32 , and with continued engagement member  102  rotation will lift the retainer  32  and extend the spring  31 . Preferably, the ledge  1031  portion of the collar  103  contacts and exerts force against the retainer  32 . Thus, rotating the engagement member  102  to impart a downward force via the engagement member  102  results in an upward force imparted to the retainer  32  via the collar  103 . When it has been determined that the retainer  32  and spring  31  are in their proper plant operation position, the engagement member is rotated in the opposite (counter-clockwise) direction to lower the frame  101  and collar  103 , and to back the engagement member  102  away from the bolt  3  so that the tool  10  can be removed. 
         [0023]    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. Any directional orientation references hereinabove, such as above or below, are provided for ease of explanation and understanding, and should not be taken as limiting. 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.