Patent Number: 052001431
Section: summary

TECHNICAL FIELD The present invention relates to a fuel assembly for a nuclear reactor, preferably of PWR type. BACKGROUND ART A fuel assembly of a known design comprises a plurality of parallel fuel rods and control rod guide tubes, wherein fuel rods and guide tubes are retained into an elongated bundle in predetermined mutual positions by means of a number of spacer grids, referred to below simply as spacers, arranged across the bundle. Top and bottom nozzles are arranged at the ends of the fuel assembly and attached to the control rod guide tubes, which extend somewhat above and below the ends of the fuel rods. In known fuel assemblies each control rod guide tube has been fixed to the bottom nozzle by means of a screw extending through the bottom nozzle and threaded into a corresponding thread in an end plug fixed to the control rod guide tube. This, in turn, has tended to give rise to an axial rotation of the control rod guide tube. Such a rotation may cause a built-in torsional stress in the guide tube, which in turn may lead to the fuel bundle, after irradiation, becoming spirally twisted. This may eventually lead to handling problems when transferring fuel in the core, which, of course, entails a serious drawback. SUMMARY OF THE INVENTION According to the present invention, the above drawback is avoided by arranging, in the spacer nearest the bottom nozzle, bottom sleeves for the control rod guide tubes, these bottom sleeves being rigidly fixed to this spacer (i.e. rigid in the direction of rotation). The bottom sleeves rest against the bottom nozzle and are provided with a first locking member for receiving a second locking member arranged at the end of a control rod guide tube. In this way, the guide tube is locked in a rigid manner in relation to the bottom sleeve. Because the bottom sleeve, in its turn, is rigidly fixed in the bottom spacer, the guide tube is prevented from rotating when, as described above, it is screwed to the bottom nozzle.