Abstract:
A dual drive winch having a drive assembly having a first shaft that is selectively movable between a first engaged position and a first disengaged position, and a second shaft that is selectively movable between a second engaged position and a second disengaged position. When the first shaft is in the first engaged position and the second shaft is in the second engaged position simultaneously, rotation of either the first shaft or the second shaft will, through a coupling mechanism, cause rotation of the other of the first shaft and the second shaft.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates winch mechanisms, and in particular to a dual drive winch mechanism and a maintenance apparatus for use in servicing components of a nuclear reactor vessel, such as a control rod drive mechanism (CRDM), employing such a winch mechanism. 
     2. Related Art 
     In a Boiling Water Reactor (BWR) type nuclear reactor, a number control blades are provided within the reactor vessel, each control blade being positioned between a number of (e.g., four) nuclear fuel bundles. The power output of a BWR is controlled by the elevation position of the control blades within the fuel bundles. The position of each control blade is controlled by a control rod drive mechanisms (CRDM), which selectively raises and lowers the control blade within the BWR vessel. 
     At times, problems may arise with the operation of a CRDM. Some problems are severe and require replacement of the entire CRDM, which is an involved and time consuming process. Certain problems, however, such as leaking from the CRDM bolt-in location at the bottom of the reactor vessel, are less severe and merely require visual inspection and/or replacement of a minor part, such as an O-ring. In these less severe instances, it is only necessary to lower the CRDM to a position below the reactor vessel so that it can be inspected and/or so the problem part can be fixed or removed and replaced. 
     There is thus a need for an apparatus that simplifies and facilitates the lowering of CRDMs or other components in nuclear reactor vessels such as BWRs in order to facilitate inspection and/or maintenance of such components. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of the invention, a dual drive winch assembly is provided that includes a first winch drum, a second winch drum, and a drive assembly. The drive assembly includes a first drive shaft assembly having a first shaft, the first drive shaft assembly being operatively coupled to the first winch drum for driving the first winch drum, a second drive shaft assembly having a second shaft, the second drive shaft assembly being operatively coupled to the second winch drum for driving the second winch drum, and a coupling mechanism. The first shaft is selectively movable within the first drive shaft assembly between a first engaged position wherein the first shaft is coupled to the coupling mechanism and a first disengaged position wherein the first shaft is not coupled to the coupling mechanism, and the second shaft is selectively movable within the second drive shaft assembly between a second engaged position wherein the second shaft is coupled to the coupling mechanism and a second disengaged position wherein the second shaft is not coupled to the coupling mechanism. When the first shaft is in the first engaged position and the second shaft is in the second engaged position simultaneously, rotation of either the first shaft or the second shaft will, through the coupling mechanism, cause rotation of the other of the first shaft and the second shaft. 
     In another embodiment, a nuclear reactor maintenance apparatus for selectively raising and lowering a component of the nuclear reactor is provided that includes an interface assembly coupled to the component, a first cable and a second cable each coupled to the interface assembly, the first and second cables being structured to support the component during the raising and lowering of the component, and a winch assembly as just described for paying out and reeling in either or both of the cables. 
     These and other objects, features, and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. As used in the specification and in the claims, the singular form of “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A further understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with accompanying drawings in which: 
         FIG. 1  is a schematic diagram of an under vessel area of a BWR showing a maintenance apparatus according to an exemplary embodiment of the invention which may be used to support and lower a CRDM for maintenance purposes; 
         FIG. 2  is an isometric view of an interface assembly forming a part of the maintenance apparatus of  FIG. 1  according to an exemplary embodiment of the invention; 
         FIG. 3  is an isometric view of a winch assembly  12  forming a part of the maintenance apparatus of  FIG. 1  according to an exemplary embodiment of the invention; 
         FIG. 4  is an isometric view,  FIG. 5  is an exploded view and  FIG. 6  is a cross-sectional view of a drive assembly forming a part of the maintenance apparatus of  FIG. 1  according to an exemplary embodiment of the invention; 
         FIG. 7  is an isometric view of the drive assembly of  FIGS. 4, 5 and 6  wherein its cover has been removed; and 
         FIG. 8  is an isometric view of the drive assembly of  FIGS. 4, 5 and 6  wherein one of the drive shaft assemblies thereof is in a disengaged position. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Directional phrases used herein, such as, for example and without limitation, top, bottom, left, right, upper, lower, front, back, and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. 
     As employed, herein, the statement that two or more parts or components are “coupled” together shall mean that the parts are joined or operate together either directly or through one or more intermediate parts or components. 
     As employed herein, the statement that two or more parts or components “engage” one another shall mean that the parts exert a force against one another either directly or through one or more intermediate parts or components. 
     As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality). 
       FIG. 1  is a schematic diagram of an under vessel area  1  including under vessel platform  5  of a BWR showing maintenance apparatus  2  according to an exemplary embodiment of the invention which may be used to support and lower a CRDM  4  for maintenance purposes. In a BWR, the reactor vessel has a bottom head that houses a number of CRDM guide tubes  3 , each of which houses a respective CRDM  4 . In  FIG. 1 , for clarity, only one CRDM guide tube  3  and one CRDM  4  is shown, although it will be understood that in a typical BWR vessel, there are a plurality of such CRDM guide tubes  3  and CRDMs  4 . Each CRDM  4  is held in place by a number of bolts at a flange to flange connection between the CRDM guide tube  3  and the CRDM  4 . 
     As seen in  FIG. 1 , maintenance apparatus  2  includes winch assembly  12 , interface assembly  13  and cables  11 A,  11 B extending between winch assembly  12  and interface assembly  13 .  FIG. 2  is an isometric view of interface assembly  13 , and  FIG. 3  is an isometric view of winch assembly  12 . As described in greater detail below, interface assembly  13  couples maintenance apparatus  2  to CRDM  4 , and, once such coupling is complete, winch assembly  12  and cables  11 A,  11 B raise and lower CRDM  4 . 
     Referring to  FIG. 2 , interface assembly  13  includes cylindrical bucket  6  having seal ring  7  provided within the lower end thereof. Bucket  6  is coupled to and provided on top of cable turning block  16 . Interface assembly  13  further includes guide pins  10  having captive pins  17 , guide pins  15 , dead end assembly  18  and sheave block assembly  19 , the functions of which are described below. 
     Referring to  FIG. 3 , winch assembly  12  includes first winch  8 A which is operatively coupled to cable  11 A and second winch  8 B which is operatively coupled to cable  11 B. Winches  8 A and  8 B are driven by drive assembly  9 , which is described in greater detail herein. Winch assembly  12  further includes CRDM support frame  14  for supporting CRDM  4  when it is lowered for maintenance. Winches  8 A and  8 B and CRDM support frame  14  are mounted and supported on main support frame  28 . Main support frame  28  functions as an under vessel interface and is structured to be attached to under vessel platform  5  by adjustable clamps  29  forming a part thereof. 
     Operation of maintenance apparatus  2  will now be described. First, four of the bolts which are used in the flange to flange connection between CRDM guide tube  3  and CRDM  4  are removed and replaced with guide pins  10  and  15 , which are threaded into the flange of CRDM guide tube  3  ( FIG. 1 ). Guide pins  10  and  15  allow for precise positioning when returning CRDM  4  to its operational position. Next, sheave block assembly  19  is installed onto one guide pin  15  and dead end assembly  18  is installed onto the other guide pin  15 . Bucket  6  is then installed onto CRDM  4  and held in place by seal rings  7 . Next, cable turning block  16  is installed onto bucket  6 , and cables  11 A,  11 B are then attached to dead end assembly  18  and fed through cable turning block  16  and sheave block assembly  19 . Cables  11 A,  11 B are then lead down and attached to winches  8 A and  8 B, respectively. Winches  8 A and  8 B are driven by drive assembly  9  in a first direction in order to take up the slack in cables  11 A and  11 B. As described in greater detail elsewhere herein, winches  8 A and  8 B may be driven by drive assembly  9  either together or independently (wherein one winch  8 A,  8 B is disengaged from drive assembly  9 ). The latter may be done to help control any potential problem with slack in cables  11 A and  11 B. 
     CRDM  4  is now ready for lowering, the remaining bolts coupling CRDM  4  to CRDM guide tube  3  and holding CRDM  4  in place are removed, thereby transferring the load of CRDM  4  to cables  11 A and  11 B. Captive pins  17  thru pins  10  are a safeguard prior to lowering the CRDM  4  after unbolting it. Captive pins  17  are removed and drive  9  (powered by an air wrench coupled to one of the shafts  54  thereof; see detailed description below) is energized to payout cables  11 A and  11 B, which allows CRDM  4  to be lowered. CRDM  4  is lowered to CRDM support frame  14  and is allowed to rest on arms  20  of CRDM support frame  14 . CRDM  4  is then raised slightly and arms  20  are swung to either side via pins  21 . Center guides  24  are then installed into arms  20 . CRDM  4  is lowered below arms  20 , and arms  20  are then swung back into position capturing the upper part of CRDM  4  (above the lower flange) therebetween, thus stabilizing CRDM  4  for the remainder of its lowering cycle. 
       FIG. 4  is an isometric view,  FIG. 5  is an exploded view and  FIG. 6  is a cross-sectional view of drive assembly  9  according to an exemplary embodiment of the invention. Drive assembly  9  includes housing  30  that includes cover  32  and lower housing piece  34 .  FIG. 7  is an isometric view of drive assembly  9  wherein cover  32  has been removed. 
     Drive assembly  9  further includes belt and pulley system  36  that is housed within housing  30 . In particular, belt and pulley system  36  includes pulley assemblies  38 A and  38 B that are coupled to one another by timing belt  40 . As seen in  FIGS. 5 and 7 , each pulley assembly  38 A,  38 B comprises an internal component  39  that includes an internal spline structure, the purpose of which is described elsewhere herein. Bushings  42 A and  42 B are mounted into lower housing unit  34 , and pulley assemblies  38 A and  38 B are rotatably mounted in bushings  42 A,  42 B, respectively. In addition, pulley assemblies  38 A and  38 B are axially restrained by bushings  42 A and  42 B and alignment disks  44 A and  44 B attached to cover  32 . 
     Drive assembly  9  also includes drive shaft assemblies  46 A and  46 B. Drive sleeves  48 A and  48 B and associated spacers  49  are attached to lower housing piece  34 . Drive shaft assemblies  46 A and  46 B are rotatably installed into drives sleeves  48 A and  48 B, respectively, and each is axially restrained by an associated thrust bearing  50  and snap ring  52  and an internal step in provided within the associated drive sleeve  48 A,  48 B. 
     Each drive shaft assembly  46 A and  46 B includes a shaft  54  and a hex housing  56  that receives and holds the shaft  54  as described below. Each shaft  54  includes an external spline portion  58 , a hex shaped portion  60  and a recess  62  provided in the top surface of shaft  54 . As seen in  FIG. 7 , the shaft  54  of drive shaft assembly  46 A is received through pulley assembly  38 A in a manner wherein the external spline  58  of the shaft  54  is received in the internal spline of the pulley assembly  38 A. Similarly, the shaft  54  of drive shaft assembly  46 B is received through pulley assembly  38 B in a manner wherein the external spline  58  of the shaft  54  is received in the internal spline of the pulley assembly  38 B. As a result, the drive shaft assemblies  46 A and  46 B, when so positioned, are rotatably engaged with the pulley assemblies  38 A and  38 B. In addition, as seen in  FIG. 6 , each drive shaft assembly  46 A and  46 B includes a central bore  64  in the hex shaped portion  60  in which is received a captive spring  66 . Each hex housing  56  includes a cylindrically shaped central member  68 . When each drive shaft assembly  46 A and  46 B is assembled, the captive spring  66  is received over the central member  68  as shown in  FIG. 6 . The configuration of the central bore  64 , the captive spring  66  and the central member  68  causes each shaft  54  to be biased upwardly to a position wherein the splines are engaged as just described (each shaft  54  is restrained axially by a spiral ring  70  provided on the bottom portion of the shaft  54 ). That same configuration also enables the shaft  54  to be moved downwardly within and with respect to the hex housing  56  when a downward force is applied to the shaft  54 , thereby compressing the captive spring  66 . The significance of this functionality is described below. Furthermore, the hex fit/engagement between the hex shaped portion  60  of each shaft  54  and the hex shaped top opening of each hex housing  56  causes those two components to be rotatably engaged to one another so that they rotate together (within a drive sleeve  48 A,  48 B). 
     As described above, when the shaft  54  of a drive shaft assembly  46 A,  46 B is in the upward, biased position (see  FIGS. 4 and 6 ), the shaft  54  is coupled to the associated pulley assembly  38 A,  38 B via the spline engagement, and therefore the drive shaft assembly  46 A,  46 B is coupled to the belt and pulley system  36 . Thus, if both drive shaft assemblies  46 A and  46 B are in this upwardly biased (engaged) position, rotating/driving one drive shaft assembly  46 A,  46 B (for example by using an air wrench coupled to the recess  62  of the shaft  54  thereof) will cause the other drive shaft assembly  46 A,  46 B to also be rotated through operation of belt and pulley system  36 . Furthermore, either drive shaft assembly  46 A,  46 B can be disengaged from belt and pulley system  36  by applying a downward pressure to the shaft  54  thereof, which causes the shaft  54  to be moved downwardly and disengages the external spline  58  from the internal spline of the associated pulley assembly  38 A,  38 B (see  FIG. 8 ). Once either drive shaft assembly  46 A,  46 B is disengaged in this manner, it can rotate independently of the other drive shaft assembly  46 A,  46 B, and thus may be driven independently (for example by using an air wrench coupled to the recess  62  of the shaft  54  thereof). When driven, each drive shaft assembly  46 A,  46 B rotates within the associated drive sleeve  48 A,  48 B. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the breath of the appended claims and any and all equivalents thereof.