Patent Number: 049884743
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a nuclear reactor fuel assembly 1 in an overview. It consists of many fuel rods 2, which are held in their position by several interim spacer supports 3 which are axially separated. Upper and a lower fuel assembly tie plates 4, 5 are held together by guide tubes that are not shown. The guide tubes or an instrumentation tube, also not shown, carry the spacer supports and attach them at their axial interval. As can be seen from FIG. 2, which shows a partial region of a spacer support on a larger scale, each fuel rod 2 passes through a cell 6, so that it is enclosed by four crosspieces 7 that form the cell, whose jut-out pieces 8 formed in part elastically contact fuel rod 2. If crosspieces lying at the periphery of the spacer support are damaged, then they are removed and their function is taken over by a holding component 9 described in more detail below. The repair process and the respective holding component 9 can be recognized from FIG. 3. Cell 6 exists only as a cell carcass of a fuel rod 2 (corner rod) positioned on a corner of spacer support 3, after separation of the damaged piece 7 indicated by the dot-dash line. A holding component 9 has, as can also be seen in FIGS. 4-8, on each of its free ends an elastically formed projection 10, which engages in a slot 11 of a cross piece 7. The holding component 9 contacting a fuel rod 2 over a part of its circumference thus fixes the fuel rod and prevents an undesired swinging of this fuel rod. The elastic projections assure, on the one hand, a precise positioning of the rod, and, on the other hand, permit a vertical displacement of the fuel rod for equilibrating heat expansions and radiation-conditioned longitudinal changes. Several examples of embodiments of holding component 9 can be seen in FIGS. 4-8. All of the embodiments consist of a metal strip, which displays on its free ends formations of projection 10 engaged in a slot 11 of the crosspiece, which formations are adapted to the particular dimensions of the respective fuel rod. Whereas FIG. 4 shows a holding component consisting of a metal strip, a holding component can be seen from FIGS. 5 and 8, which is provided with a recess 12 for adapting to the elastic force. A jut-out piece 13 according to FIG. 7 which is formed elastically if necessary, reduces the contact surfaces between fuel rod 2 and holding component 9 and also simplifies the passage of the coolant between the fuel rod and the holding component. A holding component 9 with projections 10 according to FIG. 6 with slightly angled sides formed elastically simplifies the introduction of the holding component into grooves 11 of the cell carcass; in this case the latter are arranged at the intersecting points of two crosspieces 7. The metal strip for producing a holding component consists of a material (e.g. Inconel 718 or 750 ), which retains its spring properties even during irradiation. An example of embodiments, which shows a holding component for a "non-corner rod" is described by FIGS. 11 and 12. After removing the peripheral crosspiece 7, a cell carcass with three crosspieces remains. The holding component 9 according to FIG. 11 consists of a sheet metal adapted to the contour of the fuel rod, of which upper and lower edges 14 extend hook-shaped projections 10a. They are also formed elastically and are set into crosspieces 7. The removal of the damaged crosspiece 7 of a cell 6 may be conducted with an installed fuel rod. However, it may also be necessary to dismantle the fuel rod and to replace it by a new fuel rod or a dummy fuel rod 15. The previously described holding components may be inserted for the dummy fuel rod. In order to secure the holding component against axial displacement, a dummy fuel rod 15 may display a snap ring groove 16 (FIG. 9) and/or also a longitudinal groove 17 (FIG. 10). The snap ring groove 16 is thus adapted to the height of a holding component such that there is sufficient play for assuring the rod motion for equilibration of heat expansions. This form of embodiment has the advantage that no parts exist that project over the dummy fuel rod and that would offer an attack surface, e.g., for catching onto the adjacent fuel assembly. The axially running longitudinal groove 17 is then necessary if a mounting tool has parts projecting inside above the holding component. Another form of embodiment directed in particular for use with a dummy fuel rod 15 is shown in FIG. 13. Accordingly, by running crosswise to the axis the dummy fuel rod 15 passes through borehole 18, which is provided with a depression 19. The holding component 9a is formed like a type of split pin. It has a head 20, from which extend two arms 21 formed elastically, which arms have projections 10 of the type shown in FIGS. 4-8 on their free ends, each of which extend from holding component 9. After passing through borehole 18, whereby projections 10 lie against the borehole wall, elastically, arms 21 spread apart again and engage with their projections 10 into slot 11 of crosspieces 7 of spacer support 3. The head 20 of holding component 9a thus comes to lie on the shoulder of depression 19, so that the fixed position of the dummy fuel rod 15 is produced.