Patent Number: 052767213
Section: description

Referring now in detail to FIGS. 1 and 2 of the drawing as a whole, there are seen fuel rods 4 which are disposed at an inside or inner surface 3 of an upper end plate 2, are filled with nuclear fuel, and have longitudinal axes at right angles to the inner surface 3 of the upper grid plate 2. While ends of these fuel rods 4 are spaced apart from the inner surface 3, control rod guide tubes 5, which are parallel to the fuel rods 4, are firmly screwed to both the inner surface 3 of the upper end plate 2 and the inner surface of a non-illustrated lower end plate. At the lower end plate, the ends of the fuel rods 4 are likewise spaced apart from the inner surface of the lower end plate. The control rod guide tubes 5 are each guided through a hole or space in non-illustrated gridlike spacers, which are located between the two end plates and are form-lockingly secured to individual control rod guide tubes. A form-locking connection is one which connects two elements together due to the shape of the elements themselves, as opposed to a force-locking connection, which locks the elements together by force external to the elements. Each fuel rod 4 is likewise extended through one hole of the gridlike spacer and is retained force-lockingly inside this hole with the aid of compression springs. The upper end plate 2 is square in cross section, and one leaf spring 11 is assigned to each edge of an outside or outer surface 12 of the upper end plate 2. A leaf spring 11 of this kind is bent at an acute angle 13. A first leg 14 of the leaf spring 11 rests perpendicularly on the outer surface 12 of the end plate 2, where it loosely engages an elongated guide groove 15 in the outer surface 12. The longitudinal direction of this guide groove 15 is parallel to the edge of the outer surface 12 on which the leaf spring 11 is located. An end of a second leg 16 of the leaf spring 11 meets the outer surface 12 of the upper end plate 2 at an acute angle. This end of the second leg 16 is fastened between the outer surface 12 and an angle element 17 firmly screwed to the outer surface 12, and is thus rigidly retained. The two legs 14 and 16 define a plane that is parallel to the edge of the outer surface 12 on which the leaf spring 11 is located. This plane is also perpendicular to the outer surface 12. A supplementary leaf spring 21 is likewise bent at an acute angle 23 and is disposed between the two legs 14 and 16 of the leaf spring 11. One end 24 of the supplementary leaf spring 21 has a fork which fits loosely around the leg 14 of the leaf spring 11. Another end 26 of the supplementary leaf spring 21 is bent outward in hooklike fashion in the plane defined by the legs 14 and 16 and is reduced to the width of the leg 14 of the leaf spring 11. With this end 26 bent in hooklike fashion, the supplementary leaf spring loosely engages the elongated guide groove 15. In order to install the leaf spring 11, its first leg 14, which has a crosswise strut 14a on its end, is first inserted by that end into the guide groove 15 through an insertion bore 12a and moved away from the insertion bore 12a, so that the crosswise strut 14a fits behind a shoulder 15a that narrows the guide groove 15 at the top of the outer surface 12. The second leg 16 of the leaf spring 11 is then rigidly secured to the outer surface 12 of the upper end plate 2 by screwing the angle element 17 onto the outer surface 12. This produces prestressing of the spring 11. In order to install the supplementary leaf spring 21, it is prestressed by narrowing the distance between its two legs having the ends 24 and 26. This accordingly prestressed supplementary leaf spring 21 is then inserted between the leg 16 of the leaf spring 11 and the outer surface 12 of the upper end plate 2. Next, the two legs having the ends 24 and 26 are freed so that the end 26 which is curved in hooklike fashion locks into place between the shoulders 15a of the elongated guide groove 15, and the leg 14 of the leaf spring 11 locks into place inside the fork at the end 24 of the supplementary leaf spring 21. Arrows 30 symbolize forces with which an upper core grid plate in a nuclear reactor presses the fuel assembly against a lower core grid plate in the direction of the longitudinal axes of the fuel rods 4. Under the influence of these forces, the leg 14 of each of the four leaf springs 11 in the applicable guide groove 15 moves away from the end of the other leg 16 of the applicable leaf spring 11 that is rigidly secured to the outer surface 12, thereby increasing the prestressing of the applicable leaf spring 11. At the same time, there is a decrease in the spacing between the legs of the supplementary leaf springs 21 having the ends 24 and 26. As a result, these springs are prestressed as well and they act with their spring force parallel to the spring force of the leaf springs 11.