Abstract:
A compression sleeve for use in BWR jet pump sensing line repairs is configured to maintain its physical characteristics in an operating nuclear reactor environment. The sleeve includes shaped ends to accommodate deformation and flow of the sleeve so as to form a seal between jet pump sensing line components. A mechanical coupling assembly for repairing a jet pump sensing line is configured to include the compression sleeve.

Description:
BACKGROUND 
     1. Field 
     Example embodiments generally relate to sleeves usable in nuclear reactors for piping and component repair and replacement, such as to repair and replace piping in a Boiling Water Reactor (BWR) and jet pump sensing lines in BWRs. 
     2. Description of Related Art 
     Generally, BWRs include jet pumps as part of a recirculation system to effectively move coolant and moderator through a nuclear core. In order to evaluate operating conditions within the nuclear core, it may be desirable to monitor the flow rate through the core, including flow rate of coolant from the jet pumps. Typically, a jet pump sensing line is used to measure flow rate from the jet pumps by measuring a pressure differential between the inlet and nozzle of the jet pumps. 
       FIG. 1  is an illustration of related art BWR jet pump nozzles with jet pump sensing lines coupled to a diffuser at the base of the jet pump nozzles. The jet pump sensing lines  100  are shown attached on a lower diffuser  110  of each of a plurality of jet pumps  150 . The sensing lines  100  connect to various points on the jet pump  150  in order to measure pressure differentials. The sensing lines  100  are typically welded or otherwise integrally coupled with the diffuser  110  and as such can be subject to flow-induced vibration in the jet pump  150 . 
     The jet pumps  150  are typically installed within a BWR and only accessible during scheduled plant outages for refueling and repair. These outages typically occur at several month intervals, and thus components within the core, including the jet pumps and jet pump sensing lines, must operate for lengthy periods before being inspected and/or repaired. 
     Further, BWR core operating conditions include high levels of radioactivity due to fission occurring in the fuel rods. Radioactivity, particularly the neutron flux generated in an operating nuclear reactor core, degrades the material strength and elasticity of core components over time. Components within the core, including jet pump sensing lines  100 , are thus subject to premature brittling and cracking due to this radiation exposure. Accordingly, flow-induced vibration and lengthy operating cycles coupled with radiation can cause jet pump sensing lines to crack, rupture or otherwise fail, preventing an effective and/or accurate measurement of core flow rate within the core. 
     Related art jet pump sensing line repair mechanisms, for example, U.S. Pat. No. 5,752,807, involves replacing an entire failed jet pump sensing line, or using a slip-fit shrink memory alloy coupling, which must be specially fitted for the jet pump sensing line to be replaced. 
     SUMMARY 
     An example embodiment is directed to a compression sleeve for use in BWR jet pump sensing line repair. The sleeve includes shaped ends to accommodate deformation and flow of the sleeve so as to form a seal between jet pump sensing line components. A mechanical coupling assembly for repairing a jet pump sensing line is configured to include the compression sleeve. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       The present invention will become more apparent by describing, in detail, example embodiments thereof with reference to the attached drawings, wherein like elements are represented by like reference numerals, which are given by way of illustration only and thus do not limit the example embodiments herein. 
         FIG. 1  is an illustration of related art BWR jet pump nozzles with jet pump sensing lines coupled to a diffuser on the base of the jet pump nozzles. 
         FIG. 2  is an isometric view of a compression sleeve in accordance with an example embodiment. 
         FIG. 3  is a cut-away view of sleeve in  FIG. 2  showing inner and outer diameter features of the sleeve. 
         FIG. 4  is an exploded view of a jet pump sensing line repair assembly using a compression sleeve in accordance with an example embodiment. 
         FIG. 5  is a cross-sectional view of the assembly shown in  FIG. 4 . 
         FIG. 6  is an isometric view of a mechanical coupling assembly for installation in a BWR. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  is an isometric view of a compression sleeve in accordance with an example embodiment. The compression sleeve (“sleeve  200 ”) may have a generally annular and/or cylindrical body  210 . The inner diameter of the sleeve  200  cooperates with an outer diameter of a jet pump sensing line  100  segment outer diameter so that the sleeve  200  fits over a sensing line segment and/or a replacement segment. For example, if a sensing line  100  segment has an outer diameter of 0.55 inches, the inner diameter of the sleeve  200  may be slightly greater than 0.55 inches. The maximum outer diameter of the sleeve body  210  is configured to provide sufficient strength when used as a replacement segment. 
     The sleeve  200  includes two tapered ends  220 , one at either end of the sleeve body  210 . The tapered ends  220  are shaped to deform and provide a seal between sensing line  100  segments and/or replacement segments as the sleeve  200  is fastened thereto. The tapered ends  220  may also be configured to properly seat a fastening device that holds the sleeve  200  onto components of a sensing line during and after a repair evolution. 
       FIG. 3  is a cut-away view of sleeve  200  showing inner and outer diameter features. The tapered ends  220  include three sections  221 ,  222 ,  223  that enable the deforming and seating configuration discussed above. The first section  221  is closest to the sleeve body  210 . As can be seen in  FIG. 3 , the first section  221  has the greatest maximum thickness and is generally continuous with the sleeve body  210  where the first section  221  joins the body  210 . The first section  221  may be tapered such that its outer diameter and thickness continuously decrease with linear distance away from the sleeve body  210 ; its inner diameter remains constant. The first section  221  may be fabricated so as to be increasingly more resistant to deformation under pressure from a fastening device and/or to impede further progression of a fastening device such as a nut and collar along the sleeve  200  due to its increasing thickness. In this way, the first section  221  may properly seat a fastening device used in a sensing line repair. 
     The second section  222  is adjacent to and generally continuous with the first section  221 . The second section  222  may be shaped to deform and flow under the compressive forced exerted by a fastening device. As shown in  FIG. 3 , the second section  222  may be generally concave when viewed in profile. The concave shape may allow a fastening device such as a collar and/or nut to readily fit over and collapse the second section  222 , such that the material in the second section  222  deforms to enhance sealing. 
     The third section  223  is adjacent the second section  222  and is farthest from the sleeve body  210 . As shown in  FIG. 3 , the third section  223  is generally continuous with the second section  222  and tapers at about the same angle from horizontal as the first section  221 , although the third section  223  may not be coplanar with the first section  221 . For example, the first section  221  and third section  223  may taper at an approximately 10-degree angle with a horizontal axis of rotation of the sleeve body  210 . The third section  223  has the smallest minimum thickness of each of the three sections  221 - 223 , and, like the first section  221 , may be increasingly resistant to deformation and flow as its thickness increases. Unlike the first section  221 , the entire third section  223  may be deformed and distorted to provide a seal between sensing line  100  components. In this way, fastening devices are impeded by the thickest end of the third section  223  but can extend beyond the thickest end to be properly seated against the first and second sections  221  and  222 . 
     Alternatively, the tapered ends  220  may take any shape which facilitates a seal and/or component seating when used in a sensing line  100  repairs. For example, the ends  220  can have any number of sections shaped to provide deformation and seating at different rates or displacements along the ends  220 . 
     The tapered ends  220  may be configured to prevent fretting, or separation and tearing, of any part of the sleeve during installation and operation. As shown in  FIGS. 2 and 3 , the inner surface of each tapered end  220  has a stepped or crenulated pattern  225 . The pattern  225  has a maximum depth small enough to prevent fretting given the outside diameter of the tapered ends  220  and the compressive force applied thereto. The pattern  225  provides a labyrinth seal with sensing line repair components within the inner diameter of the sleeve  200 , facilitating an improved seal as compared to that achieved through pure deformation and flow of the tapered ends  220 . 
     The example sleeve  200  is fabricated from a material designed to maintain physical properties in an operating nuclear core environment. The materials may be generally malleable and/or elastic in order to properly compress and flow when used in a sensing line  100  repair. The materials have a minimum strength to maintain sensing line  100  integrity and resistance to radiation-induced material failure. Example materials include malleable metals, for example, ninety-nice percent (99%) heat-annealed Nickel (Ni). These materials are subject to heat-annealing at high temperatures (2000° F. and greater) in order to yield the desired malleability. 
       FIG. 4  is an exploded view a mechanical coupling assembly using the compression sleeve in accordance with an example embodiment; and  FIG. 5  is a cross-sectional view of the assembly shown in  FIG. 4 . The mechanical coupling assembly  400  includes the compression sleeve  200 , a replacement tube  320  and a fastening means such as a collar  300  and nut  310 . The replacement tube  320  is designed to replace a segment of a jet pump sensing line  100  and to abut the remaining ends of the sensing line  100  after the segment is removed. 
     As shown in  FIG. 5 , when completely installed, the sleeves  200  fit over the two abutting portions of the sensing line  100  and the replacement tube  320 . The collar  300  and compression nut  310  are then fit over the sleeves  200  and replacement tube  320 . As the compression nut  310  is advanced onto the collar  300 , the collar  300  and compression sleeves  200  are compressed against the sensing line  100  and the replacement tube  320 . With increased compressive force, the sleeve  200  begins to deform. The ends  220  of the sleeve  200  thus deform and flow under the nut  310  and/or collar  300  to provide a seal with the sensing line  100  or replacement tube  320 . The nut  310  is then seated against the sleeve end  220  which is thicker to prevent further deformation and nut  310  progress. An is isometric view of the mechanical coupling assembly  400  is shown in  FIG. 6 . 
     The example embodiments can be varied in many ways and still achieve repair of a jet pump sensing line  100 . For example, the shape of the collar  300  and compression nut  310  can be varied to fit different configurations or seat differently against the compression sleeve  200 . Further, several different sensing line  100  sizes can be accommodated by varying the inner diameter of one or more components in the mechanical coupling assembly  400 . Such variations are not to be regarded as departure from the spirit and scope of the exemplary embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.