Patent Number: 046831096
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to tool manipulation apparatus which permits the remote manipulation of tools with respect to an object to be worked on. The invention has particular application to apparatus for cleaning debris from the fuel assemblies of a pressurized water nuclear reactor. 2. Description of the Prior Art Conventional pressurized water nuclear reactor fuel assemblies comprise a plurality of elongated fuel rods and control guide thimble tubes held in an organized array by grids spaced along the fuel assembly length. Top and bottom nozzles at opposite ends of the fuel assembly are secured to the thimble tubes, which extend above and below the ends of the fuel rods. The spacing between the fuel rods is relatively small, typically less than 1/4 inch, and during installation and operation, the small spaces between the grid straps and the fuel rods acts as a filter which serves to trap debris carried in the primary coolant. This debris has been found to include metal chips, pieces of wire, and other unidentified metallic fragments, and usually becomes lodged between the first grid of the fuel assembly and the bottom nozzle adapter plate. It has been found that such fuel assemblies have experienced a relatively significant number of cladding failures, i.e., leaking fuel rods, caused in part by the accumulation of debris. Once the debris is trapped, coolant flow can cause the debris to vibrate against the fuel rod and fret a hole in the cladding. Accordingly, it is necessary to remove such debris when it accumulates in the fuel assembly. Heretofore, this debris removal operation has been effected manually. More specifically, the fuel assembly is suspended under water, such as in a spent fuel pool. Workmen stationed above the pool then manually attempt to remove debris, utilizing tools on the end of long poles or rods which are manually extended down to the desired position on the fuel assembly. Remote video cameras may be used to assist this operation, but it is still an extremely time consuming and difficult procedure, which depends entirely on the skill of the workmen. The changing of tools requires complete withdrawal of the tool and rod from the pool. Also, the manual procedure involves considerable man-rem exposure. Furthermore, there is considerable risk of damage to the fuel assembly, since it is extremely difficult to judge the force being applied to the fuel assembly when the tool comes in contact therewith, not to mention the difficulty of accurately positioning a tool manually at a distance of about 30 feet under water. SUMMARY OF THE INVENTION It is a general object of the present invention to provide an improved debris removal system which avoids the disadvantages of prior manual techniques, while affording additional structural and operating advantages. An important object of the invention is the provision of a tool manipulation system which can be remotely operated with respect to a nuclear fuel assembly and minimizes man-rem exposure. It is another object of the invention to provide a tool manipulation system of the type set forth, which permits the manipulation of any of a plurality of tools under remote control. In connection with the foregoing objects, it is another object of the invention to provide a tool manipulation system of the type set forth, which permits accurate control of the movement of the tools and which effectively prevents damage to the nuclear fuel assembly being operated on. Still another object of the invention is the provision of a tool manipulation system of the type set forth, which is relatively transportable and can be easily mounted and demounted in underwater locations. Yet another object of the invention is the provision of a system for removal of debris from nuclear fuel assemblies, which includes a tool manipulation system of the type set forth. These and other objects of the invention are attained by providing apparatus for manipulating tools with respect to a nuclear fuel assembly at a work station, the apparatus comprising: a transportable support movable to and from a work position at the work station adjacent to the nuclear fuel assembly, a tool carriage mounted on the support, a plurality of tools mounted on the tool carriage, the tool carriage including selection means accommodating disposition of a selected one of the tools in a work configuration with respect to the associated nuclear fuel assembly, motive means on the support for effecting movement of the tool carriage and the selected tool along any of three orthogonal axes for performing work with respect to the nuclear fuel assembly, and control means for remotely controlling operation of the motive means.