Patent Number: 047737999
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Art The invention relates to an apparatus for sampling a section of tube in a nuclear fuel assembly of the type comprising a skeleton having two end-pieces and a plurality of grids distributed between the end-pieces along the tubes and arranged to retain a bundle of fuel elements between the end-pieces. 2. Prior Art Most fuel assemblies of the above type used at the present time comprise tubes which constitute guides for rods of a control cluster. Each tube is fixed to the lower end-piece by a screw and to the upper end-piece by a sleeve crimped in the end-piece and projecting through the upper grid. It is often desirable to sample a section of the connecting structure between the tube and the upper end-piece to perform a corrosion examination on the sample providing an indication on the condition of the assembly skeleton. At the present time, sampling is carried out generally upon complete dismantling of the assembly. To separate the upper end-piece from the tubes, a cutting tool is used which may be of various types inserted within the tube for sectioning it from inside. The tool may be as described in French No. 2,416,760. Processes and apparatus for completely dismantling fuel assembllies are also known (French No. 2,499,296). SUMMARY OF THE INVENTION It is an object of the invention to provide a method and an installation for sampling a section of tube in its connecting zone with the upper end-piece, whilst preserving the integrity of the assembly and without damaging fuel elements adjacent to the section sampled. For that purpose, there is provided a method including the steps of: cutting out an opening for extraction of the section through the upper end-piece with a milling cutter; sectioning the tube from the inside under the junction thereof with the upper end-piece with a rotary tool inserted through the upper end-piece; and extracting a sample of the latter through the opening. The method is particularly applicable to fuel assemblies whose tubes are fixed to a sleeve welded to the upper end-piece. Then it is possible to cut the assembly consisting of the tube and its fastening sleeve between the upper end-piece and the highest grid. When the assembly must be handled after a tube section has been removed as a sample, it is of advantage to reinforce the connections between the remaining tubes and the upper end-piece before sampling. Reinforcement may be achieved by the method described in French Patent Application No. 86 05796. There is also provided an apparatus for carrying out the above-defined method. The invention will be better understood from the description which follows of a particular embodiment, given by way of example.