Patent Number: 043137938
Section: summary

BACKGROUND OF THE INVENTION This invention relates to providing apparatus for winding stiff tubing onto and off of a reel in a hostile environment, and in particular, for removing and disposing of in-core instrument assemblies from a nuclear reactor. The local power density in nuclear reactors is often measured by the use of a plurality of in-core detectors, each of which is contained in an elongated guide tube which guides the detector through a nuclear fuel assembly. Together, the detector and guide tube are typically called in in-core instrument or instrument assembly. The in-core instruments (ICI) are exposed to very high radiation levels and therefore become very highly radioactive. This radioactivity makes the ICI tube and detector extremely dangerous to handle when exhausted detectors are to be disposed of, usually during the reactor refueling outage. The removal and transfer of exhausted ICI's is performed entirely under a sufficient depth of water to make use of the radiation shielding effect of the water. This requirement, however, often puts the ICI removal activities on the critical path during reactor refueling, especially in reactor installation where the ICI's enter the core through the top of the reactor vessel. Often, the only place in the reactor installation where sufficient water depth exists is directly over the reactor. Thus, the major refueling operations cannot be performed until the ICI replacement operation is completed. During a typical refueling, twenty to thirty ICI's must be individually removed and disposed of. Prior art ICI removal is performed with the overhead crane, which is intended primarily for moving heavy components and accordingly does not provide fine control of the ICI withdrawal rate. One end of a single ICI is connected to the crane and the ICI is, while dangling from the crane, withdrawn from the reactor and dragged along the refueling pool to a storage or disposal area. This is repeated until all exhausted ICI's have been removed. From the foregoing description, it can be appreciated that significant savings in refueling time can be achieved if the removal and handling of the ICI can be performed somewhere in the refueling pool other than above the reactor. Furthermore, the use of the overhead crane for ICI removal is not only unwieldy but also prevents the use of the crane for other activities that could be performed in parallel with ICI removal. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a remotely operable machine for smoothly and controllably removing the ICI from the nuclear reactor and confining the tube in a compact unit which can be easily moved to a disposal area. Furthermore, it is an object of the invention that the ICI may be unwound from the machine with sufficient force to enter into a cutting apparatus and receptacle without the need for an additional driving apparatus. According to the invention, the machine includes a frame and a circular reel having a substantially continuous helical groove extending around the circumference of the reel. The groove is adapted to receive the ICI tube. Means are provided for driving the reel relative to the frame in both circumferential directions whereby in one direction the ICI tube is wound onto the groove of the reel, and in the other direction the tube is wound off the reel. A plurality of cam rollers are carried by the frame and closely spaced around the circumference of the reel. During the winding operation, the rollers force the tube onto the continuous groove. During the unwinding operation, the rolers provide sufficient friction between the tube and the groove so that the tube may be unwound with enough force to enter the cutting tool or to enter the disposal receptacle. Means are provided to straighten the tube as it unwinds to permit more efficient stacking within a disposal container. In the preferred embodiment, the grooved portion of the reel consists of a removable cartridge. After the ICI tube has been fully wound onto the grooves of the cartridge, the radioactive portion of the tube can be fed into the cutter and the nonradioactive portion remaining on the cartridge can be disposed of by removing the cartridge from the reel and disposing of the cartridge. A new cartridge is then attached to the reel and the machine is ready for use on another ICI tube. The present invention can be operated from a deck above the refueling pool while the overhead crane is used for other purposes. This represents a savings of approximately ten hours in a typical refueling operation. Furthermore, in the preferred embodiment, the disposable cartridge permits using the cutter only on the radioactive portion of the ICI tube. Therefore valuable time and the cost of cutting tool replacement parts are greatly reduced because a large portion of the ICI tube can be conveniently disposed of without cutting. Since the receptacle for the cut portions of the ICI will thus contain only radioactive ICI segments, the number of receptacles, and consequently the protective measures associated with their storage, can be significantly reduced.