Patent Number: 050531875
Section: description

Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a partial region of a core structure 1 of a water-cooled nuclear reactor plant. The core structure receives a core shroud or barrel 2, the periphery of which is matched to a composite structure of non-illustrated fuel assemblies. Therefore, as viewed in cross-section, the core shroud has a multiplicity of bent-out portions. In the vicinity of each bent-out portion, the core shroud is fastened by screws 3 to the core structure 1. In order to perform inspection or repair of the screws 3, a support plate 4 is disposed on the bottom of the core structure and a mast 5 is supported thereon. At its non-illustrated top end, the mast may be held by a hoist. An inspection or repair device 6 can move along the mast for the inspection or repair of the screws 3. As can be seen from FIG. 2, which is a plan view of a partial region of the support plate 4, a plurality of pairs 7 of bores are formed therein. Bores 8, 8a of the pairs 7 are each associated with a first marking in the form of groove 9. In this configuration, an imaginary continuation of the groove 9 in each case runs through the centers of the bores 8, 8a. The center-to-center distance of a pair 7 of bores is marked by a cross-groove 10, which runs perpendicularly to the groove 9 and intersects it. In order to reach various inspection positions, centering pins 11, 11a associated with the mast 5 and seen in FIG. 3 have to be inserted into the corresponding pairs of bores 7, which have a spacing corresponding to the spacing between the centering pins. In order to position the mast 5, which .is indicated in phantom in FIGS. 3 and 4, a baseplate 12, which serves as a marking element, is fastened on the underside of the mast 5 by means of screws 13. At one bottom edge of the mast, the baseplate 12 protrudes beyond the mast cross section with a region 14 seen in FIGS. 4 and 5. In this region 14, a console 15 which extends parallel to the mast 5 is embedded or let-in and is fastened by a screw connection 16. A television camera 20 is supported in a holder 19 that is fastened by screws 17 in slots 18 formed in the console 15, and the camera is secured by a clamp 21. The holder 19 also receives two lighting fixtures 22, which are secured by means of holding elements 23, 24. The centering pins 11, 11a are screwed into threaded bores 25 in the region 14 of the baseplate 12. . In symmetrical configurations of the centering pins 11, 11a, the region 14 has a recess or clearance 26, which reaches, closer to the console 15 than the threaded bore 25. A bore 27 is formed in side walls 28 of the region 14. In this configuration the bore passes diametrically through the centering pins 11, 11a being screwed-in at that location. A second marking, which has been given the form, of a thread 29 or wire, is fitted in the bore 27 in such a way that it spans the recess or clearance 26. The thread or wire is held in the bore 26 by clamping screws 30. In order to mark the center-to-center distance, a cross-piece 31, which crosses over the thread 29, protrudes from the base of the clearance or recess 26. Once a rough adjustment has been made in order to bring the mast 5 sufficiently far into its position that the television camera picks up not only the thread 29 and the cross-piece 31 but also the groove 9 and the cross-groove 10 of the support plate 4 seen in FIG. 5 on a non-illustrated monitor, the mast 5 is moved sideways by means of a non-illustrated slight adjustment until the thread 29 is brought into line with the groove 9 and the cross-piece 31 is brought into line with the cross-groove 10. The thickness of the thread and the width of the groove correspond in this case, so that the width of the crosspiece and the width of the cross-groove correspond as well. Due to the virtually perpendicular direction of viewing of the single television camera, there is no picture distortion, so that precise positioning through a monitor is possible. While the positioning shown in FIG. 5 is before the markings are brought into line, according to FIGS. 3 and 4 the centering pins 11, 11a and the bores 8, 8a are already on the same axis, so the mast then only has to be lowered until the baseplate 12 of the mast is set down on the support plate 4.