Patent Number: 050698630
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT Nuclear Plant With Fuel Transfer System More particularly, there is shown in FIG. 1 a nuclear power plant 30, in this case a boiling water reactor plant, for which there are provided a containment building 32 for the reactor (not shown) and an auxiliary building 34 where pools 35 and 37 of water are located for fuel storage. A thick solid concrete containment wall 36 separates the containment and auxiliary buildings 32 and 34. An operating floor 33 extends across the two buildings 32 and 34 and the containment wall 36. A fuel transfer system 38 includes a car 40 that operates on a track 42 having spaced rails 42A and 42B extending from a canal 43 within the auxiliary building 34 through a transfer tube 44 within the containment wall 36 into the containment building 32. The transfer tube 44 may be about fifteen feet long. Within the transfer tube 44, the rails 42A and 42B are bolted to supports 43C which in turn are welded to the transfer tube 44. Respective gaps 45 and 47 exist in the car railing at the entry to the transfer tube 44 on both sides of the containment wall 36. However, the car 40 is provided with wheels that are appropriately located so that the car 40 bridges the rail gaps 45 and 47 when it moves along the track 42. Isolation is provided for the containment building 32 by a hatch 46. An isolation valve 48 can be used to close off the transfer tube 44 from the auxiliary building 34. A conventional upending mechanism 50 (FIG. 1B) in the containment building 32 is employed to turn a basket 51 pivotally supported by the car 40 into the vertical position where fuel transfer apparatus (not shown) can either take a fuel assembly (not shown) from the car basket 51 and install it in the fuel core or it can deposit a spent fuel assembly in the car basket 51 that had previously been obtained from the fuel core. When the car 40 is located at the containment end of the track 42, the leftmost end of the car 40 is located inside the transfer tube 44 thereby facilitating a structuring of a car drive system 60 for bidirectional operation from the auxiliary side of the containment wall 38. The containment building 32 is flooded during shutdown to reduce radiation exposure as fuel assemblies are relocated. In this boiling water reactor case, the containment building 32 is also flooded during normal reactor operation. Another upending mechanism 52 (FIG. 1A) similarly upends the car basket 51 for fuel transfers to and from the storage pool in the auxiliary building 34. Another fuel transfer apparatus (not shown) located in the auxiliary building 34 handles these transfers through a gate area 53 (FIG. 1C) to the storage pool. The auxiliary building is also flooded to a level above the reactor vessel during fuel transfer operations so that the fuel assemblies are always handled at a water depth of 15 to 20 feet. Fuel Transfer Drive System The fuel transfer drive system 60 is preferably unilateral in the sense that it is located on one side of the containment wall 36, yet it is capable of providing bidirectional drive force for the car 40 even though the car 40 is largely located within the containment building 34 at the containment end of the car travel. In accordance with the invention, the drive system 60 operates the car 40 under water with significantly improved operating reliability, fuel transfer performance and manufacturing economy. Preferably, the drive system 60 includes a pair of winches 62 and 64 (FIGS. 1A, 2A, 2B, 2D) supported on a plate 63 (FIG. 1C) above the track 42 at the leftmost end of the canal 43. Cabling 66 is coupled to the car 40 and operated by the winches 62 and 64 to drive the car 40 in one direction or the other direction over the track 42. The winch 62 operates a pair of cables 62A and 62B (FIGS. 4 and 6) that extend vertically downward through slot 62S in the winch support plate 63 to the track level. Similarly, the winch 64 operates a pair of cables 64A and 64B that extend vertically downward through support plate slot 64S to the track level. Cable pairs are employed so that substantially equally applied drive forces can be applied to the two sides of the car 40 in each direction of travel. The cables 62A and 62B are connected to the car 40 to pull the car 40 in the leftward direction as the winch 62 reels in the cables 62A and 62B. The cables 64A and 64B are connected to the car 40 to pull the car 40 in the rightward direction as the winch 64 reels in the cables 64A and 64B. The winches 62 and 64 are coordinated in operation in accordance with the invention so that desired cable tension is substantially continuously maintained as one or the other of the two winches operates as a master drive to reel in cable as the slave winch pays out cable. At the track level, four vertical sheaves 62S and 64S (FIGS. 1A, 6 and 7) are used to redirect the vertical cabling from the winches 62 and 64 to the horizontal direction along the track 42. Generally, the cables 62A and 64A pass over the sheaves 62SA and 64SA which are located within but toward one side of the track and thereafter extend along that side of the track for securance to the underside of the car 40. Similarly, the cables 62B and 64B pass over the sheaves 62SB and 64SB which are located within but toward the other side of the track and thereafter extend along the other side of the track for securance to the underside of the car 40. The cables 64A and 64B pass over the two outermost vertical sheaves 64SA and 64SB to facilitate placing them more closely toward the track rails since they extend along the track 42 to the containment end of the transfer tube 44 where they are directed in the reverse direction to extend back to the car 40 for securance thereto. The spacing between the cables 64A and 64B within the track 42 and to the containment side of the transfer tube 44 is generally sufficient to enable use of a center pivoted car basket without drive cable interference. In some embodiments, however, as in the present one, it may be desirable to provide special cable spreading action to facilitate car basket operation as subsequently described more fully herein. The cables 62A and 62B are secured to the underside of the car 40 to provide leftward drive force for the car 40. The cables 64A and 64B extend to the rightmost end of the track within the transfer tube 44 and return in the opposite direction for securance to the underside of the car 40 to provide rightward drive force for the car 40. A pair of horizontal sheaves 64LHS and 64HHS (FIGS. 8 and 10) are located at the containment end of the transfer tube 44 to redirect the cables 64A and 64B in the reverse direction for securance to the underside of the car 40. In operation, the winch 62 takes up the cables 62A and 62B to pull the car 40 toward the left and at the same time the winch 64 pays out the cables 64A and 64B to follow the leftward car movement. The opposite cable action occurs for rightward car movement. Cable securance to the underside of the car 40 is achieved with the use of a yoke 80 (FIGS. 6, 7 and 11) located near the leftmost end of the car 40. In operation, the yoke is always located to the left of the horizontal sheaves 64LHS and 64HHS. At the rightmost position of the car 40, i.e. when it is located for loading or unloading of the car basket in the containment building 38, the yoke 80 is located to the left of the horizontal sheaves as shown in FIG. 8. The yoke 80 (FIG. 11) preferably includes a shaft 82 supported from a car frame member 84 and by angle struts 84 and 86 through bracket 88. A yoke cross-piece 90 is supported for slight pivotal movement on the yoke shaft 82 in a horizontal plane so as to provide for equal load sharing by the paired cables secured to pivot arms 93 and 95 at the outer ends of cross-arms 92 and 94. The pivot arms 93 and 95 have a slight vertical offset so that they align respectively with the return cables 64A and 64B from the high and low horizontal sheaves 64HHS and 64LHS. As indicated by the reference character 96, each pivot arm 93 or 95 (FIG. 12) is pivotally supported relative to the yoke cross-arm 92 or 94 to provide cable spreading action when the car 40 is moved to its leftmost position in the auxiliary building for a fuel assembly transfer. In this embodiment, cable spreading action is provided since the horizontal return cables 64A and 64B angle slightly toward the center of the track 42 and thus need to be spread outwardly toward the rails 42A and 42B to assure clearance for upending of a center pivoted car basket as in this case. Each pivot arm 93 or 95 includes an extension 97 or 99 (FIG. 6) having a roller 100 or 102 at its end. As the car 40 approaches its auxiliary end of travel the two rollers 100 and 102 strike respective fixed spreader blocks 104 and 106 to move toward the center of the track 42. The pivot arms 93 and 95 thus pivot so that end portions 108 and 110 move outwardly toward the rails 42A and 42B thereby spreading the return cables 64A and 64B outwardly as needed for basket upending. Generally, the track rails 42A and 42B are sufficiently spaced to permit operation of a center pivoted car basket 47 (FIGS. 1A and 6). Additionally, the cables 64A and 64B have portions extending from the vertical sheaves toward the containment, and these are generally sufficiently spread toward the rails 42A and 42B to permit pivotal basket operation within the cable spread space. To this end, various cable guides 64G1 and 64G2 (FIG. 5) secure these portions of the cables 64A and 64B extending from the vertical sheaves to the horizontal sheaves in position toward the track rails. The return portions of the cables 64A and 64B that extend from the horizontal sheaves to the car yoke generally angle inwardly slightly toward the center of the track. The previously described yoke spreading action pushes these cable portions outwardly toward the track rails 42A and 42B to facilitate center pivoted car basket operation when the car 40 is positioned in the auxiliary building for fuel assembly loading and unloading. Each winch 62 or 64 preferably includes a drum 62D or 64D and a two speed electric motor 62M or 64M. A timing belt 112 (FIG. 4) is preferably interconnected between sprockets 62S and 64S to coordinate the operation of the winches for continuous maintenance of desired cable tension in the system. Thus, when the designated master drive winch is operating, the braking is released for the other winch and the cable payout from the released winch is held substantially equal to the cable takeup on the master winch as a result of the timing belt tie between the two winch shafts. The timing belt 112 can be released during system initializing to permit relative winch movement until cable tension is adjusted as desired. Idler pulleys 62P (not shown) and 64P (FIG. 2D) compensate for minor variations in cable tension during normal system operation. Respective slack cable switches 112 and 114 are operated by respective rollers 113 and 115 to deenergize the winches if cable tension is lost and cable slack develops. Respective load cells 116 and 118 sense winch loading and deenergize the winches if overloading develops. A programmable limit switch 120 (FIG. 5) is employed with one of the winches to provide drive system control. Thus, the switch operates in response to the output of a shaft resolver that in this case counts up to 64 shaft turns with 4096 counts per turn. Since the cable tension is essentially maintained constant, winch shaft position directly indicates the car position. Accordingly, to move the transfer car from the existing position to another position (usually from one end of travel to the other end of travel) one of the two motor speeds (13 fpm or 40 fpm in this case) is preset and the destination is entered. The limit switch 120 starts the winch motors designating one of them as the master drive and releasing the brake on the other according to the direction of travel and records shaft counts that measure travel distance as the car is pulled by the cabling 66. When the shaft counter indicates that the car has nearly reached its destination position, the programmable limit switch deenergizes the master winch motor and activates the winch braking system. Since the programmable limit switch 120 is located above water, system adjustments are greatly facilitated. With an actual fuel transfer drive system and its control structured in accordance with the invention as described, a fuel transfer car has been consistently brought to a stop within three sixty-fourths of an inch over a thirty-five foot path of travel. The present invention accordingly provides highly accurate operation. Further, with this drive control arrangement, underwater logic limit switches have been eliminated thereby significantly enhancing system reliability. For example, conventional underwater drive stop limit switches and drive home limit switches are unnecessary with use of the present invention. Just as importantly, reliability is enhanced significantly from a mechanical standpoint as a result of the overall structure and operation of the mechanical portion of the drive system. The structural character of the drive system also provides for economy of manufacture.