Patent Number: 051732491
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment of the invention will now be described with reference to FIGS. 2-5, wherein like numerals represent like elements. As shown in FIGS. 2a, 4 and 5, a flux thimble removal tool in accordance with the present invention includes two basic units: a lower pulling unit 20 and a cutting/storage unit 22 that sits atop the lower pulling unit. Pulling unit 20 houses a gripper unit 30a, drive motor 68, gears 32, 66, helix drive shaft 40a (all of which are shown in FIG. 4), guide bar 26a, slide bar 24a, and guide tube 36, all of which are adapted to gradually extract neutron flux thimbles 38 one a time from the RV 74 (see FIG. 5) of a PWR, and to feed the thimble in segments to the cutting/storage unit 22. Cutting/storage unit 22 further extracts the thimble, then severs the further extracted portion. The operation is continued until the thimble is fully extracted from the RV and reduced to a quantity of easily-disposable segments. A video camera (not shown) may also be installed to facilitate surveillance of the operation. The walls of pulling unit 20 are fabricated from thin wall pipe. The respective lengths of units 20 and 22 are approximately 1 meter and 2 meters. Cutting/storage unit 22 is coupled via sockets 46 and pins 50 to pulling unit 20. Unit 22 houses a second gripper unit 30b; second drive shaft 40b, which is coupled via a stanchion 44 to drive shaft 40a and which has threads with an equal but opposite pitch to the threads of lower drive shaft 40a; second slide bar 24b and guide 26b and removable radiation shielding 48, all of which is shown in FIG. 2a. In addition, as shown in FIG. 3, unit 22 houses a cutting unit comprising blade 42, cutter block 54, pivot pin 56, tie rod 58, compression spring 60, and connection 62 to a portable hydraulic apparatus (not shown) for activating the blade. In operation, pulling unit 20 is mounted on the seal table 18 of the PWR, which normally serves as a pipe support (see FIG. 5); gripper 30a is then positioned to enable jaws 70 to grip the thimble; helix drive 40a is then rotated, thereby lifting the gripper and thimble upward from seal table 18. This lifting is continued until gripper 30a reaches the top of helix drive shaft 40a, at which time the top of the thimble protrudes into gripper 30b of cutting/storage unit 22. The motor 68 is then reversed, which causes lower gripper 30a to release the thimble and move downward and upper gripper 30b to take hold of the thimble and move upward, thereby pulling the thimble to the top of unit 22. Motor 68 is stopped when the thimble reaches the top of unit 22; the hydraulic apparatus (not shown) is activated to sever the thimble; and the motor is then again reversed, causing upper gripper 30b to release the severed segment and begin pulling up the next segment. Upper unit 22 is separated from lower unit 20 after one or more thimbles are removed and is thereafter transferred to a place where the spent thimbles can be stored permanently. Both the lower and upper units are provided with removable radiation shields 48. The flux thimble removal tool described above is unique in that it facilitates the removal, cutting and disposal of BMI flux thimbles through the seal table as opposed to through the RV; however the true scope of the invention is not limited to the specific, preferred embodiment described above. For example, the preferred embodiment may be adapted to remove thimbles inserted through the top head of the RV, and may also be adapted to remove detector thimbles other than neutron flux thimbles. Many other modifications and variations of the preferred embodiment will fall within the true scope of the invention, which is set forth in the following claims.