Patent Publication Number: US-2012032064-A1

Title: Method and apparatus for a bwr jet pump support system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Example embodiments relate generally to nuclear reactors, and more particularly to a method and apparatus for a Boiling Water Reactor (BWR) jet pump support system for mitigating vibratory movement of the inlet mixers, diffusers and riser pipe. 
     2. Related Art 
     A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends (for example 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 between the cylindrical reactor pressure vessel and the cylindrically shaped shroud. 
     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 may be supported by conventional jet pump restrainer assemblies. While conventional jet pump restrainer brackets may provide system stiffness that mitigates vibration of the inlet mixers, diffusers and riser pipe, the restrainer brackets sometimes require costly repair and downtime of the jet pump assembly. Specifically, formation of set screw gaps and wear between the conventional restrainer bracket, the main wedge of the restrainer bracket, and the guide rod require machining and/or replacement of these parts throughout the operational life of the jet pump assembly. 
     Additionally, movement of the inlet mixer relative to the diffuser can be caused by leakage flow between the inlet mixer and the diffuser. This behavior is typically celled slip joint flow induced vibration. The slip joint flow induced vibrations occur anytime that oscillating pressure forces are greater than the forces constraining the inlet mixer and diffuser. Methods for preventing this vibration include either eliminating the leakage flow, sufficiently constraining the inlet mixer and diffuser, or a combination of reducing the leakage flow and constraining the inlet mixer and diffuser. 
     SUMMARY OF INVENTION 
     Example embodiments provide a method and an apparatus for providing a lateral restraining force (i.e., additional side loading) on the jet pump restrainer assembly diffuser and/or the diffuser and inlet mixer to increase Boiling Water Reactor (BWR) jet pump assembly system stiffness. The lateral restraining force may push the diffusers and inlet mixers toward the centerline of the riser pipe to prevent slip joint flow induced vibration, reduce the formation of set screw gaps, and mitigate damage to conventional restrainer assembly brackets, wedges, and guide rods. The lateral restraining force may be easy to install, and may be used in conjunction with conventional jet pump restrainer assemblies, or alternatively in lieu of conventional jet pump restrainer assemblies. 
     Because the additional lateral restraint provided by this disclosure may be used in lieu of using a conventional main wedge, it is sometimes advantageous to remove the wedge from operation (without entirely removing the main wedge from the conventional restrainer bracket), while implementing the example embodiments described herein. Removal of the main wedge from operation may be accomplished via the use of a jet pump main wedge clamp, as described in the General Electric Hitachi application “METHOD AND APPARATUS FOR A BWR JET PUMP MAIN WEDGE CLAMP,” Attorney Docket No. 24NS243873 (HDP #8564-000208/US). 
     The additional lateral restraint and side loading provided by this disclosure may also put undue strain on set screws of a conventional restrainer bracket. Therefore, it may be advantageous to provide redundant rigid support for the inlet mixer (to counteract the forces being placed on the inlet mixer being applied by this invention), while implementing the example embodiments described herein. Redundant rigid support for the inlet mixer may be accomplished through the use of an inlet mixer support, such as the one described in the General Electric Hitachi application “METHOD AND APPARATUS FOR A BWR JET PUMP INLET MIXER SUPPORT,” Attorney Docket No. 24NS243875 (HDP #8564-000209/US). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of example embodiments will become more apparent by describing in detail, example embodiments with reference to the attached drawings. The accompanying drawings are intended to depict example embodiments and should not be interpreted to limit the intended scope of the claims. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
         FIG. 1A  is a perspective view of a conventional boiling water reactor (BWR) nuclear reactor jet pump assembly; 
         FIG. 1B  is a detailed view of a conventional BWR jet pump restrainer assembly; 
         FIG. 2  is a detailed view of a BWR jet pump support system, in accordance with example embodiments; 
         FIG. 3  is a perspective view of a BWR jet pump support system being used on a jet pump assembly, in accordance with example embodiments; 
         FIG. 4  is a detailed view of a BWR jet pump support system with optional contact supports, in accordance with example embodiments; 
         FIG. 5  is a perspective view of a BWR jet pump support system with optional contact supports being used on a jet pump assembly, in accordance with example embodiments; 
         FIG. 6  is a detailed view of a simplified BWR jet pump support system, in accordance with example embodiments; 
         FIG. 7  is a perspective view of a simplified BWR jet pump support system used on a jet pump assembly, in accordance with example embodiments; 
         FIG. 8  is a detailed view of an optional inlet mixer support system, in accordance with example embodiments; 
         FIG. 9  is a perspective view of an optional inlet mixer support system used on a jet pump assembly, in accordance with example embodiments; and 
         FIG. 10  is a perspective view of a BWR jet pump support system and optional inlet mixer support system used on a jet pump assembly, in accordance with example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Detailed example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. 
     Accordingly, while example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the figures. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.). 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
     Referring to  FIG. 1A , a perspective view of a conventional Boiling Water Reactor (BWR) nuclear reactor jet pump assembly is depicted. The jet pump assembly includes conventional jet pump restrainer assemblies  10  attached to the riser pipe  1 . The jet pump restrainer assemblies  10  stabilize any movement of the inlet mixers  2  relative to the riser pipe  1  while the jet pump assembly is in use. 
       FIG. 1B  is a detailed view of a conventional BWR jet pump restrainer assembly  10 . Each restrainer assembly  10  includes a restrainer bracket  13  with three points of contact (two set screws  11 , and one main wedge  16 ) to stabilize vibratory movement of an inlet mixer  2 . The main wedge  16  is a gravity wedge riding on a wedge rod  15  that pushes inlet mixer  2  toward a centerline of the riser pipe and up against two sets of set screws  11  to reduce movement of the inlet mixers  2  when a BWR jet pump assembly is operating. Conventionally, set screw gaps may form during operation (an undesirable space is formed between the inlet mixer  2  and the set screws  11 ), causing vibration and damage between the inlet mixer  2  and the set screws  11 . Additionally, vibration of the jet pump assembly may cause the wedge rod  15  to become damaged or worn and wear between the restrainer bracket  13  and wedge rod  15  may also occur. All of this wear may cause costly repair and downtime of the jet pump assembly. 
       FIG. 2  shows a detailed view of a BWR jet pump support system  30 , in accordance with example embodiments. The support system  30  may include a riser pipe clamp  20  that may be fitted to a riser pipe  1  of a BWR jet pump assembly. The support system  30  may also have diffuser clamps  22  that may be fitted to diffusers  4  of a jet pump assembly. The clamps  20 / 22  may be provided with bolts  24  and nuts  26  to affix the clamps  20 / 22  to the riser pipe  1  and diffuser  4  of a jet pump assembly. The clamps may include eyelits  28  which may be penetration points on each cuff of clamps  20 / 22 , providing a means by which the bolts  24 /nuts  26  may be used to easily affix the clamps on a jet pump assembly. 
     Draw bolts  32  may be provided in order to provide the actual lateral restraining force for the support system  30 . Draw bolts  32  may be provided in both the front and the rear of the support system  30 . The draw bolt  32  may include one long bolt that may be affixed to both diffuser clamps  22  and the riser pipe clamp  20 . Alternatively, a smaller draw bolt  32  may be provided that is affixed to the riser pipe clamp  20  and one of the diffuser clamps  22 , and a separate draw bolt  32  may be provided that is affixed to the riser pipe clamp  20  and the other diffuser clamp  22 . Draw bolts  32  may be affixed to the diffuser clamps  22  and riser pipe clamps  20  by penetrating clamp eyelits  28  in the clamps and being secured via draw bolt nuts  33 . The draw bolts  32  may be threaded bolts that mate with threaded eyelit connections  28 . Alternatively, draw bolts  32  may be attached to the riser pipe clamp  20  and diffuser clamps  22  via other means such as welding, spot welding, hooks, clamping devices, or any other means to securely fasten the draw bolts  32  to clamps  20 / 22 . 
     As with all embodiments shown in  FIGS. 2-10 , draw bolts may instead be replaced with wire, durable cord, high tensioned spring, or other resilient material that is able to provide enough tension and support to pull the diffusers and/or inlet mixers toward the centerline of the riser pipe  1 . As with all embodiments shown in  FIGS. 2-10 , one draw bolt may attached to the clamp assemblies instead of two draw bolts (i.e., a single draw bolt may be used in either the front, the back, or the mid-plane of the jet pump assembly). Alternatively, more than two draw bolts may be attached to clamp assemblies, to apply additional lateral support and stability. 
     All support system components may be made by materials that are known to be acceptable for a nuclear environment. For instance, stainless steel (304, 316, XM-19, or equivalent) or nickel based alloys (Iconel, X-750, X-718, or equivalent) may be used. 
       FIG. 3  is a perspective view of a BWR jet pump support system being used on a jet pump assembly, in accordance with example embodiments. The jet pump support system  30  may be fashioned on the jet pump assembly such that the diffuser clamps  22  may be clamped to the diffusers  4 , and the riser pipe clamp  20  may be clamped to the riser pipe  1  in an area in between the diffusers  4 . Draw bolts  32  on the front and back of the jet pump assembly help to stabilize vibratory motion of the inlet mixers  2 , the diffusers  4 , and the riser pipe  1 . As with all of the embodiments shown in each of  FIGS. 3 ,  5 ,  7 ,  9 , and  10 , draw bolts  32  should provide enough tension on the clamps that the diffusers  4  and/or inlet mixers  2  are drawn in toward the centerline of the riser pipe, or simply rigidly help in position, to mitigate vibration in the system and/or ensure that the inlet mixers stay pressed against the set screws (see for instance the set screws  11 , shown in  FIG. 1B ) in the jet pump restrainer assemblies  10 . 
       FIG. 4  is a detailed view of a BWR jet pump support system  30   a  with optional contact supports, in accordance with example embodiments.  FIG. 4  is identical to  FIG. 2 , but includes optional contact supports  34 / 36 . The contact supports may include adjustable hardstops  34  that may be used to prevent diffusers  4  and the support system  30  from rotating about the centerline of the riser pipe or contacting the reactor vessel. The hardstops  34  may be plates with threaded connections that allow an adjustment bolt to be positioned in the threaded connection in order to provide a physical stop. Alternatively, the hardstop  34  may be simply a plate or a protruding component that may prevent the diffuser  4  and support system  30  from rotating about the centerline of the riser pipe or contacting the reactor vessel. The contact supports may also include compliant stops  36  that are high tension springs that may be used to further prevent diffusers  4  and the support system  30  from contacting the core shroud that surrounds the reactor core of a BWR. 
       FIG. 5  is a perspective view of a BWR jet pump support system  30   a  with optional contact supports being used on a jet pump assembly, in accordance with example embodiments. The support system  30   a  is fashioned to the diffusers  4  and riser pipe  1  in the same manner as the support system  30  shown in  FIG. 3 , but with additional contact supports  34 / 36  included. The optional hardstops  34  may be included on the back side of the jet pump system, such that the hardstops  34  face the reactor vessel wall. Note that the hardstops  34  may be adjusted to contact the reactor vessel wall, prior to operation of the jet pump assembly, to mitigate vibration between the hardstops  34  and the vessel wall once the jet pumps are in operation. The optional compliant stops  36  may be included on the front side of the jet pump system, such that the compliant stops  36  face the core shroud wall when in operation. 
       FIG. 6  is a detailed view of a simplified BWR jet pump support system  46 , in accordance with example embodiments. The simplified support  46  includes diffuser clamps  40  that may be two half-collars that are sized to fit on the sides of each diffuser  4 . Two draw bolts  42  may attach the two diffuser clamps  40 . Alternatively, more than two draw bolts  42  may also be used. Draw bolts  42  may be affixed to the diffuser clamps  40  by providing eyelits that the draw bolts  42  may go through, and nuts  44  to fasten the draw bolts  42  in place. As described in  FIG. 2 , any other means of securely fastening the draw bolts  42  to the diffuser clamps  40  may also be used, such as welding, spot welding, adhesive, hooks, clamping devices, or any other means of securely fastening the bolts  42  to the diffuser clamps  40 . 
       FIG. 7  is a perspective view of a simplified BWR jet pump support system  46  used on a jet pump assembly, in accordance with example embodiments. The diffuser clamps  40  are fashioned to fit around the sides of diffusers  4 , and the draw bolts  42  are used to place a lateral restraining force on the diffusers  4  and pull the diffusers  4  toward the centerline of the riser pipe  1 . 
       FIG. 8  is a detailed view of an optional inlet mixer support system  60 , in accordance with example embodiments. The support system  60  may include inlet mixer clamps  50  that may be two half-collars held together by bolts and nuts  56 , similar to the clamps shown in the other embodiments. Draw bolts  52  may again be used to connect two sets of inlet mixer clamps  50  to each other, in a manner similar to the other embodiments. 
       FIG. 9  is a perspective view of an optional inlet mixer support system  60  used on a jet pump assembly, in accordance with example embodiments. Notice that the support system  60  may be used on the inlet mixers  1  themselves, as opposed to the diffuser  4 . Notice also that the support system  60  may be placed above the jet pump restrainer assemblies  10 , and either above or below the riser brace  3  ( FIG. 9  shows the support  60  just below the riser brace  3 ). 
       FIG. 10  is a perspective view of a BWR jet pump support system  46   a  and optional inlet mixer support system  60   a  used on a jet pump assembly, in accordance with example embodiments. In this embodiment, the inlet mixer clamp  60  is used (between the jet pump restrainers assemblies  10  and the riser brace  3 ) in conjunction with another simplified embodiment of a jet support system  46   a  attached to the diffusers  4 . Alternatively, only the inlet mixer support system  60  may be used, and no jet support system  46   a  may be used. The jet support system  46   a  uses diffuser clamps  40   a  made from two half-cuffs, similar to the diffuser clamps  22  of  FIG. 2 . However, no riser clamp is used in this simplified jet support system  46   a , as the draw bolts  42   a  attach directly to each diffuser clamp  40   a , only. 
     Example embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the intended spirit and scope of example 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.