Patent Number: 06320925&
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to the figures of the drawings, in which identical elements bear the same reference symbols, and first, particularly, to FIG. 1 thereof, there is seen a portion of a spacer 1 of a fuel assembly, th e remainder of which is not illustrated. The spacer 1 is constructed as a matrix which is formed from a plurality of intersecting webs 3. These intersecting webs 3 form cells 5 having an essentially square base area, through which non-illustrated fuel rods of the fuel assembly project. The cells 5 of the spacer matrix 1 surround the outer circumference of the fuel rods which are thus held in their position relative to a longitudinal axis of the fuel assembly. For this purpose, as a rule the webs carry bosses, springs or other auxiliary members which engage the fuel rods. Such known engagement aids, in particular springs 54 and bosses 56, are illustrated once in FIG. 13 as an example for the other figures in which they are omitted. In the present exemplary embodiment, the spacer matrix 1 is formed by two groups of identical intersecting parallel webs. Each web of one group intersects each web of the other group at right angles at precisely one intersection location or point 7. Each web 3 has an assembly gap 9 which is disposed at an intersection location 7 and receives part of a wall of the respectively intersecting web. Moreover, a metallurgical connection 60 of the intersecting webs is made in the vicinity or region of the intersection location 7. As a rule, these connections are welded connections. However, other connections may also be envisaged, which fix the intersecting webs closely to one another. The firm connections are preferably made in each case in the vicinity or region of the intersection location at an upper edge of the spacer matrix standing on edge and correspondingly at a lower edge of the spacer matrix standing on edge. However, the metallurgical connections are advantageously not restricted only to the edge of the spacer matrix. The connections are also advantageously continued virtually along the entire length of that part of each assembly gap having a width which corresponds essentially to the wall thickness of the other web. FIG. 2 illustrates two intersecting webs 11, 13 with their associated assembly gaps 15, 17 and with their intersection location 7. For greater clarity, the intersecting webs 11, 13 are shown in the state prior to assembly. The upper web 11 having a center axis 19 is taken from the first group of webs and the lower web 13 having a center axis 21 is taken from the second group. The webs 11, 13 are assembled along an assembly axis 23 which is perpendicular to the two center axes 19, 21. The assembly gap 15 of the upper web 11 extends along the assembly axis 23 from the center axis 19 as far as the lower edge of the upper web 11, while the assembly gap 17 of the lower web 13 runs similarly from the center axis 21 toward the upper edge of the web 13 in the opposite direction. If the two webs 11, 13 are assembled along the assembly axis 23, each of the assembly gaps 15, 17 in each case receives part of the wall of the intersecting web. The total height of the spacer matrix 1 which is thus formed then corresponds to the width of the individual webs 11, 13. FIG. 3 shows a portion of a spacer provided for a fuel assembly of a nuclear power station, with two mutually parallel first outer strips 20A, 20B and two mutually parallel second outer strips 22A, 22B that are disposed perpendicularly to the first outer strips 20A, 20B. The spacer also has first webs 13 standing on edge and disposed parallel to the first outer strips 20A, 20B and second webs 11 standing on edge, disposed parallel to the second outer strips 22A, 22B and intersecting the first webs 13. In this case, the stated object is achieved, according to the invention, in such a way that: a) each end of each web in each case engages into an outer strip 20A, 20B, 22A, 22B and is fixed there; PA1 b) th e first webs 13 have an upper edge 39 running from one outer strip 22A to the other outer strip 22B with an assembly gap 17 that is disposed at an intersection location 7 with a second web 11, is directed toward a lower edge 40 and through which part of an intersecting second web 11 passes; PA1 c) the second webs 11 each have an assembly gap 15 which is disposed at their corresponding lower edge 40 at an intersection location 7 with a first web 13, is directed toward their upper edge 39 and through which part of an intersecting first web 13 passes; PA1 d) each assembly gap 15, 17 is closed at the edge of each web through the use of a metallurgical connection 60 of the web (see FIGS. 1 and 12) with the intersecting web; and PA1 e) each assembly gap 17 has a region 30 (see FIG. 13) through which part of the intersecting web passes and which is so wide that the two webs do not touch one another. In FIG. 3, each end of each web has a latch 26 each engaging into a slot 24 in a respective outer strip and preferably being welded there. FIG. 4 shows a side view of the web 13 after it has been assembled together with the web 11. The assembly gap 17 has received the wall of the web 11 along the assembly axis 23. The assembly gap 17 has a width in the vicinity of its upper and lower end or regions 25, 27 which corresponds to the wall thickness of the intersecting web 11, as well as a greater width in a region 29 between the ends 25, 27. A gap 31 is thus formed between the edge of the assembly gap 17 and the wall of the web 11 on both sides of the assembly axis. The width of the gap 31 is selected in such a way that corrosion layers, which occur at the edge of the assembly gap 17 and the wall of the intersecting web 11 and continually reduce the size of the gap 31 during operation, cannot completely clog this gap 31 over the entire operating period of the spacer. This prevents the possibility of an undesirable solid pressure building up on the web 13 outside the end regions 25, 27 of the assembly gap 17. FIG. 5 shows a modified embodiment of the web 13 illustrated in one of FIGS. 2 to 4. The position and extent of an assembly gap 63 of a web 65 correspond to the structures shown in FIGS. 2 to 4. As in FIG. 4, the assembly gap 63 has a width in the vicinity of its upper end 67 which corresponds to the wall thickness of an intersecting web 71. The assembly gap tapers in a V-shaped manner in the vicinity of its lower end 69. In this region, the wall of the intersecting web 71 is likewise integrally formed in a V-shaped manner and engages, in the same way as in a knife-edge bearing, in the V-shaped end of the assembly gap 69. As a result, this end of the wall of the intersecting web 17 is fixed. The solid pressure possibly occurring in this region as a result of corrosion is greatly reduced due to the small bearing surface. FIG. 6 shows a further embodiment of a web 33. An assembly gap 35 extends from a center axis 37 along the assembly axis 23 as far as the upper edge 39 of the web 33. As in the exemplary embodiment shown in FIG. 4, the assembly gap 35 has a width in the vicinity of its lower and upper ends 41, 43 which corresponds essentially to the wall thickness of an intersecting web 45. In a remaining region, the assembly gap 35 is constructed to be widened in a similar way to the assembly gap 17 in FIG. 3. In order to reduce the longitudinal expansion of the web 33 occurring as a result of corrosion in the region of the lower end 41 of the assembly gap 35, two recesses 47, 49 are provided in this region on both sides of the assembly gap 35. These recesses 47, 49 absorb the deformation of the web 33 caused by a change in length. Two indentations 51, 53 are provided on both sides in the region of the upper end 43 of the assembly gap 35 and absorb undesirable longitudinal expansion in this region in a similar way to the recesses 47, 49. FIG. 7 illustrates a further embodiment of a web 55 of a spacer. In contrast to the preceding exemplary embodiments, an assembly gap 57 extending along the assembly axis 23 from a center axis 59 upward does not have a region at which its width corresponds essentially to the wall thickness of an intersecting web 46. The assembly gap 57 is constructed in such a way that an edge thereof touches the wall of the intersecting web 46 at a support location 61, in each case on only one side of the assembly axis 23. In contrast, an edge of the assembly gap 57 which is located opposite the support location 61 does not touch the wall of the intersecting web 46. Altogether, two support locations 61 are provided on each of the two sides of the assembly axis. The support locations in each case alternately touch one side of the wall of the intersecting web and thus fix the latter in its position in the assembly gap 57. The structure of the assembly gaps in these exemplary embodiments minimizes the contact surface of the two intersecting webs at the intersection location, in such a way that a stable connection of the two webs engaging one into the other is still ensured. Nevertheless, there is sufficient space outside the contact regions, so that corrosion of the webs in the assembly gap does not lead to deformations and growth of the webs. In this case, the term "assembly gap" refers only to those regions of a gap in a web through which parts of the other web pass. However, in cases in which the assembly gap opens into a wide aperture in the web, solid parts of the other web do not pass through this aperture. In other words, the assembly gap terminates where it opens into the aperture. Such apertures have sometimes been provided in the prior art for other reasons. Thus, the intersecting webs of the spacer according to German Published, Prosecuted Patent Application DE 25 50 932 B2 possess a middle region between their upper edge and their lower edge. The middle region is curved into grid meshes of the grid-like spacer and carries bosses on which the fuel rods are supported. In order to ensure that those curved webs can be inserted one into the other, the middle regions of two webs carry an aperture in each case at the intersection location. No solid parts of the webs pass through one another in the region of those two middle parts, but instead a common orifice is obtained in the two webs. Consequently, in one of the two webs, the assembly gap leads from the upper edge of one web as far as this aperture, while the other web has an assembly gap which reaches from the lower edge of the other web as far as this aperture. Similar apertures, which form a common orifice passing through both webs at the intersection location of two webs, are also provided in U.S. Pat. Nos. 3,933,583 and 4,124,444. Outside those apertures, which perform a particular function, the intersecting webs possess assembly gaps having a uniform width which is virtually equal to the wall thickness of the webs and therefore does not prevent the webs from being spread and experiencing a growth in length as a result of corrosion taking place in the assembly gap. Assembly gaps, which are associated with apertures provided for the use of bosses and springs for supporting the fuel rods, are also known from European Patent 0 527 244 B1. There, a web carries two apertures which are disposed on one side of the assembly gap and in which profiled ends of an inserted supporting spring are held. In order to ensure that those profiled spring ends can be inserted, a larger orifice of the web is provided on the other side of the assembly gap. In that case, the ends of the spring are inserted first of all into the larger apertures and are then pushed into the two apertures beyond the assembly gap on the other side of the latter and interlocked by the two webs being inserted one into the other. Therefore, in that prior art, only one web carries an assembly gap with apertures, while the assembly gap of the other web has a uniform width at that intersection location. FIG. 8 shows that, in that case too, a variable width of both assembly gaps is advantageous. FIG. 8 shows two webs 73, 74, before they are inserted one into the other in the direction of an arrow 75 and connected metallurgically to one another. In this case, upper edges and lower edges of the two webs each carry indentations 76 which can receive appropriate soldering material or welding material during metallurgical connection. Furthermore, bosses 77, which serve for fixing a fuel rod laterally together with a non-illustrated spring supported on the opposite web, are shown on the web 73. Such a non-illustrated supporting spring is held with its profiled ends at corresponding apertures 78 on one side of an assembly gap 80 of the web 73. A larger mounting aperture 79 is located on the other side of the assembly gap 80. During the mounting operation, spring ends which are first inserted into the mounting aperture 79 are pushed laterally into the apertures 78 beyond the gap 80 and are interlocked there as soon as corresponding parts of the web 74 are introduced into the assembly gap 80. These parts of the web 74 which are introduced into the assembly gap 80 and, after mounting, pass through the latter, are illustrated on the web 73 by a broken contour 81. In this case, the total length of the assembly gap 80 is illustrated by reference symbol L and is defined by the dimensions of the parts of the web 74 which pass through the assembly gap 80. Therefore, in the web 73, the assembly gap only has the total length L through which parts of the other web 74 pass. The width of this assembly gap 80 is not constant. In contrast, the other web 74 does not have any aperture at all which would be necessary for inserting the spring. Nevertheless, a corresponding assembly gap 82 of this other web 74 is likewise not constructed with a constant width. Instead, the width of the gap 82 only corresponds to the wall thickness of the web 73 at a few points, and widenings 84 of the assembly gap 82 are provided therebetween. Consequently, if corrosion layers form in the assembly gap 82, these can only lead to stresses and deformations at the few narrower points of this assembly gap. However, the stresses and deformations are compensated in the web, without an occurrence of macroscopic deformations and a growth in length of the web 74. Corresponding widenings 85 are also provided in the assembly gap 80 of the web 73 outside the apertures 78 and 79. Furthermore, FIG. 8 also shows that the parts of one web which are in each case introduced into an assembly gap of the other web carry lateral buttons 86. The lateral buttons 86 guide the other web and fix it laterally while the two webs are being assembled, until the soldering points, weld seams or other metallurgical connections are made. Thus, an appreciable part of the growth in length of spacers can be prevented by the very shaping of the assembly gaps, without the structure or metallurgy of the spacer having to be modified. FIG. 9 shows a portion of a spacer matrix 2 with intersecting webs 14, 16 which include two web plates 10A, 10B shown in FIG. 10. These spacers have proved particularly appropriate, especially in pressurized water reactors. The web plates 10A, 10B bear against one another at least in the vicinity of an intersection location 7 with an intersecting web. In a remaining region, the web plates 10A, 10B are deformed and/or bent relative to one another, so that flow ducts 4 are obtained therebetween. A fuel rod 8 or a guide tube 6 in each case projects through the cells of the spacer matrix. The webs 14, 16 are fastened to two respective outer strips through a fixing 28 similar to the latch and slot already explained with reference to FIG. 3. FIG. 10 shows an embodiment of a web 14 of a spacer according to FIG. 9. Like the previous embodiments, this web 14 also has an assembly gap 36 which receives the intersecting web at an intersection location with an intersecting web 16. The intersecting web includes the two web plates 10A, 10B which bear against one another in the intersecting region and the common thickness of which at the intersection location corresponds to the wall thickness of the intersecting web. The assembly gap 36 has a width, only over a fraction of its total length through which parts of the other web pass, which corresponds essentially to the wall thickness of the intersecting web. In a remaining region, the assembly gap is so wide that the two intersecting webs 14, 16 do not touch one another. In contrast to the embodiments of FIGS. 1 to 7, the assembly gap 36 has a mouth 52 which has an aperture 48 adjoining it. This aperture is substantially wider than the assembly gap 36 and extends beyond a web center indicated by a center axis 21 of the web. Such an aperture is preferably located in the two intersecting webs 14, 16. However, such an aperture may also be made only in one web 14 of the intersecting webs 14, 16. Through the use of the aperture 48, web locations which are in danger of corrosion are cut out. A plurality of apertures of various shapes are also possible at these locations in order to achieve the object of the invention. Preferably, the web has at least one further aperture 50 disposed along an assembly axis 23 of each assembly gap 36. The apertures 48, 50 cut out web locations which are in particular danger of corrosion and which consequently bring about the longitudinal expansion of the web. Furthermore, the web 14 carries elevations 58 between which the intersecting web is held. These elevations are made on a web part which passes through the assembly gap of the other web. By virtue of the elevations, the inserting webs are held in a more stable manner should the webs not be supported sufficiently because of the presence of the apertures 48, 50, in particular while the spacer is being mounted prior to the metallurgical connection of the webs. FIG. 11 shows a cell of a spacer 2. As already shown in FIG. 9, a web 14 of the spacer includes at least two web plates 10A, 10B bearing against one another at least in the vicinity or region of an intersection location 7. In order to form flow ducts 4, the web plates are bent/deformed relative to one another in a remaining region. In a similar way to the embodiment of a spacer 1 having webs 3 which include an individual web plate, in this case too, each web 14 is metallurgically connected to an intersecting web 16 through the use of at least one connection point 60. In this spacer embodiment, which is preferably used for pressurized water reactors, it is advantageous if both the intersecting webs 14, 16 and the web plates bearing against one another are metallurgically connected to one another in the region of the intersection location 7 through. the use of the metallurgical connection 60. It is advantageous, in particular, if the metallurgical connection extends to regions which are particularly susceptible to corrosion. These are, in particular, the regions of the assembly gaps which have essentially the width of the wall thickness of the intersecting web. Accordingly, FIG. 12 shows a portion of a web having an advantageous structure of metallurgical connections, in this case welded connections 60, 62, particularly for preventing corrosion at those locations of webs and assembly gaps in the spacer 2 which are in particular danger of corrosion. Furthermore, in this embodiment, the web plates of the upright web which bear against one another are in particular metallurgically connected to the intersecting web through the use of a connection location 60 at the upper edge 39 and at the lower edge 40 of the web. In addition, FIG. 12 essentially shows features which have already been explained with reference to FIG. 10. The web plates are connected to one another over a large area through the use of a further metallurgical connection 62, preferably a weld spot, in the region in which the web plates bear against one another over a large area. The weld spot 62 is advantageously applied at the location at which corrosion is particularly pronounced. This is often a location at which the web plates have relatively high radii of curvature. Alternatively to this embodiment, it is possible to make a recess 50 according to FIG. 10 at the same location. Furthermore, FIG. 12 shows that the welded connection in the region of the intersection location 7 of the intersecting webs is not limited only to the upper edge 39 or lower edge 40 of the intersecting webs. In order to avoid longitudinal expansion, which occurs particularly as a result of corrosion in a narrow region 32 of each assembly gap 36, the welded connection 60 extends virtually along the entire length of that part 32 of the assembly gap 36 having a width which corresponds essentially to the wall thickness of the intersecting web. The elevations 58, which were already explained with reference to FIG. 10, are made in such a way that the respectively intersecting web is held between them. In this embodiment, flow ducts 66 serve in each case for cushioning the fuel rods 8 guided in the cells of the spacer matrix. In order to provide for the advantageous mounting of the fuel rods guided in the cells of the spacer matrix along two lines, in each case there is a recess 64 in the region of a respective flow duct 66. In each case the fuel rod bears against the edges of these recesses 64. A particular embodiment of a web 13, which is further modified relative to the structures shown in FIGS. 4 to 8, is shown in FIG. 13. In this particular embodiment, an assembly gap 18 carries a metallurgical connection 60 of the intersecting webs 13, 11 in one region 32. In a further region 30, the assembly gap 18 is so wide that the two webs 11, 13 do not touch one another. In particular, the assembly gap 18 is also so long that the two webs 11, 13 do not touch one another. In order to provide for the cushioning of the fuel rods which pass through the cells of the spacer matrix, each web 13 carries at least one spring 54 stamped out of the web for each cell, and for the same purpose the web 13 also carries at least one pair of stamped-out rigid bosses 56. In a similar way to the embodiment of a spacer 2 which has already been explained with reference to FIG. 12, in this embodiment of a spacer 1, 2 as well, the welded connection 60 in the region of an intersection location of the webs 11, 13 extends at least over that part of the assembly gap which corresponds essentially to the wall thickness of the intersecting web 11. Furthermore, in this embodiment, the intersecting web 11 is held between two elevations 58 of the other web 13.