Patent Number: 048448621
Section: description

DESCRIPTION OF PREFERRED EMBODIMENTS The grid 10 partly shown in FIG. 1 is of generally conventional construction, which may for example be that described in French Patent No. 2,474,229. It will therefore not be described in detail. Grid 10 is formed by two orthogonal sets of plates 11, typically of "zircaloy" base alloy, lap-joined and welded at their connection points 12. However, other materials having a low neutron capture cross-section may be used. Each plate 11 is formed with bosses 13 for holding fuel rods (not shown) in position and with windows cooperating with springs which apply the rods on the bosses. Referring to FIG. 1, only double springs 15a are shown which are inserted into indentations 14 formed in one of the edges of the plates. The springs are of a material retaining resiliency after irradiation, which may have a neutron capture cross-section higher than that of the plates. As shown in FIG. 2a, each of springs 15a may be positioned by sliding its legs on each side of plate 11 until the upper loop of the spring comes into abutting contact with the plate, at the bottom of the indentation 14. Windows 19 are formed in the plate for allowing direct connection of the two legs of the spring on each other by spot welding at 20. The single-action spring 15b shown in FIG. 2b is disymmetric in construction. Its leg 22 is similar to the legs of spring 15a. The other leg 23 is designed to form a swivel joint defined by two bends 24 arranged to engage leg 22 through apertures 25 in the plate, to avoid transmitting the compression forces therethrough. As in the preceding case, the two legs of spring 15b are welded together through windows 19 in the grid. On the other hand, the loop is not positioned at the bottom of an indentation, but in an extension of the upper window 19, formed by one of the stamped-out bosses 13. As shown, one of the legs of each spring has a portion of reduced width in at least one zone and that portion is formed to be received on the other leg which has a U shape in the same zone. In the embodiment shown in FIGS. 1, 3 and 4, the reduction of width of the first leg is such that gaps are formed between the reduced width portion and the edges of window 19 of a size at least equal to the thickness of the strip forming the spring. The other leg is locally of increased width to form appendices 26 which are bent substantially at 90.degree. towards the first leg. The appendices 26 consequently constitute arms which straddle the reduced width portion. They advantageously have a height almost equal to the thickness of the plate (FIG. 4) so as to retain the first leg laterally and to be locked in the window 19. To facilitate insertion of the reduced width portion into the U-shaped leg and to avoid excessive stresses, the bends 27 of appendices 26 are rounded rather than sharp. Again for decreasing stresses, the reduced width portion merges with the current part of the spring gradually, for example through a trapezoidal portion 28 rather than by a 90.degree. step. In the embodiment shown in FIGS. 5 and 6, where the parts corresponding to those of FIGS. 3 and 4 are designated by the same reference numbers, the appendices 26 are so bent that the arms of the U close up slightly. Thus, the reduced width portion snaps into the bottom of the U and is retained therein, which is favorable for safe welding. On the other hand, that does not provide guidance facilitating positioning of the reduced width portion into the U. In the modification shown in FIGS. 7, 8 and 9, the appendices 26 are so bent that the arms of the U flare and guide the reduced width portion during insertion. The reduced width corresponds to the width at the bottom of the U (FIG. 8) so that there may be axial clamping of the legs one against the other. Instead of having trapezoidal connection portions, the spring shown in FIGS. 7 and 9 has portions with curved edges 30 which better position the two legs longitudinally with respect to each other. The invention is not limited to the particular embodiments which have been described above. Numerous modifications are possible. If, in particular, it is desired to avoid an extra width of the strip from which the spring is cut out at the locations of the appendices, the width of the narrowed portion may be further reduced and the arms of the U may then be defined by slits formed in the current part of the strip. Whatever the embodiment, the invention makes it possible to improve the welding conditions and consequently quality of welding; it achieves complete and mutual contact of the two legs and limits the welding projections on the grid plates. Lateral positioning of the springs is also improved particularly in so far as overlapping, gaping of the blades and absence of freedom of movement of the springs are concerned.