Patent Number: 
Section: description

FIG. 1 is a cross section view of a boiling water nuclear reactor 10 including a reactor core 12 positioned within a reactor pressure vessel 14. Reactor pressure vessel 14 is supported by a reactor pressure vessel support structure 16. A plurality of control rod drive housings 18 containing control rod drives (CRDs) 20 extend from reactor pressure vessel 14. Each CRD 20 includes a CRD flange tail section 22. A control rod drive equipment platform 26 is located below reactor pressure vessel 14 an under vessel area 24. CRD equipment platform 26 includes two rails 30 and 32. A winch cart 34 is located on uppermost rail 32. A CRD handling assembly 40 is shown in a vertical handling mode and includes a trunnion cart 42 configured to ride on lower rail 30. Another CRD handling assembly 40 is shown in a shown in a horizontal transport mode. FIG. 2 is a side view of CRD handling assembly 40. In addition to trunnion cart 42, each CRD handling assembly 40 includes a tower 50 coupled to trunnion cart 42, a drive screw 52 coupled to tower 50, an elevator 54 movably engaged with drive screw 52, and a pair of linear slide rails 56 and 58 mounted to tower 50. Trunnion cart 42 includes a plurality of cart wheels 60, a support frame 62 extending between cart wheels 60, and a pair of trunnion axles 64 coupled to support frame 62. In the exemplary embodiment, trunnion cart 42 includes four cart wheels 60. Trunnion cart 42 supports tower 50 on trunnion axles 64 and facilitates pivoting tower 50 between the horizontal transport mode and the vertical handling mode. Trunnion cart 42 also facilitates movement of CRD handling assembly 40 when in the horizontal transport mode. Tower 50 includes an open cavity 66, a first end 68, a second end 70, a first side 72, a second side 74, and a tower back 76. A pair of pillow blocks 78 are mounted to first side 72 and second side 74. Pillow blocks 78 receive trunnion axles 64 and pivotally coupled tower 50 to trunnion cart 42. More specifically, tower 50 is pivotable on pillow blocks 78 about trunnion cart axles 64 between the horizontal transport mode and the vertical handling mode. Tower 50 includes a wheel assembly 80, a first tie plate 82 and a second tie plate 84. Wheel assembly 80 is spaced from pillow blocks 78, located generally adjacent tower second end 70. Wheel assembly 80 includes at least one cam-out wheel 86, which is retractable to facilitate operation of CRD handling assembly 40. In the exemplary embodiment, two cam-out wheels 86 are provided for stability and are shown in an extended position. Cam-out wheels 86 are generally aligned with trunnion cart wheels 60 to facilitate operation on rail 30 (shown in FIG. 1). Wheel assembly 80 is secured to second tie plate 84. FIG. 3 is an enlarged, schematic, end view of first tie plate 82 and FIG. 4 is an enlarged, schematic, end view of second tie plate 84. Referring to FIGS. 2, 3, and 4, first tie plate 82 is located generally adjacent first end 68 while second tie plate 84 is located generally adjacent second end 70. Second tie plate 84 includes a drive screw bearing 88 and a CRD bore 92. Drive screw bearing 88 facilitates rotation of drive screw 52, while supporting drive screw 52. CRD bore 92 allows CRD flange tail section to extend through second tie plate 84. First tie plate 82 includes a drive screw bearing 94, a thrust bearing 96, and at least one CRD support roller 98. Drive screw bearing 94 and thrust bearing 96 drive screw 52 adjacent tower first end 68. Thrust bearing 96 limits linear motion of drive screw 52 relative to first tie plate 82. Each CRD support roller 98 extends from first tie plate 82 to support CRD 20 when CRD handling assembly 40 is in the horizontal transport mode. In the exemplary embodiment two retractable CRD support rollers 98 extend from first tie plate 82. First tie plate 82 also includes a load transfer device 100. Drive screw 52 is threaded and extends from second tie plate 84 to first tie plate 82. In the exemplary embodiment, drive screw 52 includes a drive operator 106 that extends from drive screw 52 through first tie plate 82. Drive operator 106 facilitates the rotation of drive screw 52 using a hand held wrench or portable powered drive tool 108 (shown in FIGS. 8 and 9). FIG. 5 is a cross section view and FIG. 6 is an edge view of elevator 54. Referring to FIGS. 2, 5 and 6, elevator 54 includes an elevator plate 110, an elevator nut recess 112, an elevator nut 114, a drive screw bore 116 extending through elevator plate 110, and linear bearing 120 and 122. In another embodiment, one linear bearing 120 extends from elevator 54. Elevator 54 extends substantially across tower open cavity 66 from linear slide rail 56 to linear slide rail 58. Elevator plate 110 includes a CRD tail bore 124, sized to receive and support CRD flange tail section 22 (shown in FIG. 8). More specifically, elevator 54 is configured to have CRD 20, including a CRD flange tail section 22, partially inserted through CRD tail bore 124. Elevator nut recess 112 is sized to receive elevator nut 114. In the exemplary embodiment, elevator nut recess 112 is machined into elevator plate 110 and presents a cylindrical cross-section. Drive screw bore 116 intersects elevator nut recess 112 and is sized to allow drive screw 52 to extend through elevator 54. Elevator nut 114 includes a threaded nut bore 126 sized to threadedly engage drive screw 52. When elevator nut 114 is positioned in elevator nut recess 112 and engaged with drive screw 52, elevator nut 114 is restrained from rotating by contact with elevator plate 110. Additionally, elevator nut 114 is retained in elevator nut recess 112. Rotation of drive screw 52 while threadedly engaged elevator nut 114 is in elevator nut recess 112 results in linear movement of elevator nut 114. Because elevator nut 114 is in contact with elevator plate 110, linear movement of elevator nut 114 results in linear movement of elevator 54. More specifically, as drive screw 52 rotates, elevator 54 moves up or down, depending on the direction of rotation of drive screw 52. Drive screw 52 rotation is translated by elevator nut 114, elevator plate 110, and elevator nut recess 112 into linear motion of elevator 54. Linear bearings 120 and 122 extend from elevator plate 110 to slidably engage linear rails 56 and 58 respectively. Linear bearings 120 and 122 align elevator plate 110, maintaining elevator 54 substantially perpendicular relative to linear rails 56 and 58. Linear rails 56 and 58 are substantially cylindrical with support struts 130 coupling linear rails to tower 50. More specifically, support struts 130 secure linear rails 56 and 58 to tower first side 72 and tower second side 74. In one embodiment, support struts 130 present a V-shaped cross-section in securing linear rails 56 and 58 to tower sides 72 and 74. In one embodiment, linear rails 56 and 58 are rectangular in cross-section, engaging rectangular linear slide bearings 120 and 122. In another embodiment, linear rails 56 and 58 present a dovetail cross-section, received in a dovetail slot in linear slide bearings 120 and 122. FIG. 7 is a side view of a CRD positioning apparatus 200 in accordance with another embodiment of the present invention. CRD positioning apparatus 200 also facilitates handling of CRD 20 in nuclear reactor 10. CRD positioning apparatus 200 includes at least one linear slide rail 202, a drive screw 204 coupled to slide rail 202, an elevator 206 movably coupled to drive screw 204, and at least one linear bearing 210 fixed to elevator 206 and slidably engaged with slide rail 202. Linear slide rail 202 and drive screw 204 are substantially parallel. Linear side rail 202 includes a first end 212 and a second end 214. In one embodiment, linear side rail 202 presents a generally circular cross-section. In another embodiment linear slide rail 202 presents a dovetail cross-section, a rectangular cross-section or other similar cross-section. Drive screw 204 is threaded and includes a first end 220 and a second end 222. First end 220 includes a drive operator 224 to rotate drive screw 204. A first tie plate 230 is coupled to linear side rail first end 212 and drive screw first end 220, and a second tie plate 232 is coupled to linear side rail second end 214 and drive screw second end 222. Second tie plate 232 includes a drive screw bearing 234, a drive screw thrust bearing 236, a CRD bore 240 and a pair of wheels 242. Second tie plate drive screw bearing 234 and thrust bearing 236 facilitate rotation of drive screw 204 while coupling drive screw 204 to second tie plate 232. Drive screw 204 and linear side rail 202 are thus coupled at their respective second ends 222 and 214. CRD bore 240 allows CRD flange tail section 22 to extend through second tie plate 232. CRD positioning apparatus first tie plate 230 includes a drive screw bearing 250, a thrust bearing 252, at least one CRD support roller 254 and a pair of wheels 256. Drive screw bearing 250 and thrust bearing 252 support drive screw 204 at first end 220. Thrust bearing 252 limits linear motion of drive screw 204 relative to first tie plate 230. CRD support rollers 254 extend from first tie plate 230 to support CRD 20 when CRD positioning apparatus 200 is in the horizontal transport mode. Wheels 256 facilitate the transportation of CRD positioning apparatus 200. First tie plate 230 couples drive screw 204 and linear slide rail 202 at their respective first ends 220 and 212 to provide a structurally stable positioning apparatus 200. Elevator 206 includes an elevator plate 260, an elevator nut recess 262, an elevator nut 264, and a drive screw bore 266 extending through elevator plate 260. Elevator plate 260 includes a CRD tail bore 270 sized to receive and support CRD flange tail section 22. Elevator nut recess 262 is sized to receive elevator nut 264. In one embodiment, elevator nut recess 262 is machined into elevator plate 260 and presents a cylindrical cross-section. Drive screw bore 266 intersects elevator nut recess 262 and is sized to allow drive screw 204 to extend through elevator 206. Elevator nut 264 threadedly engages drive screw 204. When elevator nut 264 is positioned in elevator nut recess 262 and engaged with drive screw 204, elevator nut 264 is restrained from rotating by contact with elevator plate 260. Additionally, elevator nut 264 is retained in elevator nut recess 262. Rotation of drive screw 204 while threadedly engaged elevator nut 264 is in elevator nut recess 262 results in linear movement of elevator nut 264. Because elevator nut 264 is in contact with elevator plate 260, linear movement of elevator nut 264 results in linear movement of elevator 206. More specifically, as drive screw 204 rotates, elevator 206 moves up or down, depending on the direction of rotation of drive screw 204. Linear bearing 210 is secured to elevator 206 and extends to engage linear slide rail 202. More specifically, linear slide rail 202 is slidably retained within linear bearing 210. Linear bearing 210 aligns elevator 206 substantially perpendicular to linear bearing 210, and maintains that alignment as elevator 206 is repositioned by rotation of drive screw 204. In use, CRD handling assembly 40 and CRD positioning apparatus 200 perform in similar fashion. FIGS. 8 and 9 are side views of CRD handling assembly 40 shown receiving CRD 20. Referring to FIG. 8, CRD handling assembly 40 is aligned with CRD 20 in a vertical handling mode. An extension tube 300 is seated in elevator CRD bore 92. Portable powered drive tool 108 is coupled to drive operator 106 and operated to rotate drive screw 52, moving elevator 54 to a position adjacent tower first end 68 so extension tube 300 engages CRD flange tail section 22. Particularly, an extension tube receiver cup 302 receives CRD tail section 22. CRD 20 is then disconnected from CRD housing 18. CRD 20 is supported by elevator 54 through extension tube 300. Linear bearings 120 and 122 extend from elevator plate 110 to engage linear rails 56 and 58 and align elevator 54 substantially perpendicular to linear rails 56 and 58, supporting CRD 20. Drive screw 52 is operated to lower elevator 54 until CRD flange tail section 22 is adjacent first tie plate 82. Referring to FIG. 9, load transfer device 100 engages CRD flange 304 to support CRD 20. Elevator 54 is lowered to disengage extension tube 300 (shown in FIG. 8) from CRD flange tail section 22 and then raised to receive CRD flange tail section 22 in CRD tail bore 124 and support CRD 20. Load transfer device 100 is disengaged and drive screw 52 rotated to lower elevator 54 and CRD 20. When CRD 20 has been lowered sufficiently CRD handling assembly 40 is pivoted to the horizontal transport mode and CRD 20 and CRD handling assembly 40 are transported from under vessel area 24 as required. Handling assembly 40 and positioning apparatus 200 facilitate removal and installation of CRD 20 from CRD housing 18 under reactor pressure vessel 14. Handling assembly 40 and positioning apparatus 200 include a reduced number of components, facilitating a reduction in contaminated material. Furthermore, handling assembly 40 can improve reliability and reduce maintenance time, as compared to conventional CRD handling equipment, with an overall reduction in maintenance cost and reduced outage time. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.