Patent Number: 046831150
Section: description

Referring now to the drawing and first, particularly, to FIG. 1 thereof, there is shown a square, grid-shaped spacer, formed of a nickel-iron alloy in a nuclear reactor fuel assembly according to the invention, the spacer being mode up of two flat, planar outer straps 2 and 3 which are disposed at right angles to one another. On the inside of these outer straps 2 and 3, inner straps 21 to 23 are arranged which are parallel to the outer strap 2, and inner straps 31 to 33 which are parallel to the outer strap 3 and which mutually intersect at right angles, forming square grid meshes. In these meshes, respectively, a control rod guide tube or a nuclear fuel-containing fuel rod of the nuclear reactor fuel assembly is arranged, the inner and outer straps being disposed perpendicularly thereto. In the interest of greater clarity, only a single fuel rod 4 is shown in the outermost square corner grid mesh 5 formed by the outer straps 2 and 3 of the spacer, the lateral surfaces of the inner and outer straps being parallel to the longitudinal direction of the fuel rod 4 i.e. the inner and outer straps 2 and 3 being arranged on edge. Inside the square grid meshes, the inner straps 21 to 23 and 31 to 33 are formed with firm bumps 311, 321 and 331 as well as 211, 221 and 231 and are provided with springs corresponding to inwardly-directed springs 6 of the outer strap 2 and inwardly-directed springs 7 of the outer strap 3. The bumps and springs provide the grid-shaped spacer with a positive locking support for the control rod guide tubes extending through individual grid meshes, and a positive locking support in the spacer for fuel rods extended through other grid meshes. At the edges extending in the spacer perpendicularly to the mutually parallel control-rod guide tubes and fuel rods, the outer straps 2 and 3 have slightly inwardly inclined rejection tabs 8 and 9. The outer straps 2 and 3 are connected to one another by means of an intermediate strip 10 which is located between these two outer straps 2 and 3 at the outer edge of the spacer, that outer edge being parallel to the mutually parallel control rod guide tubes and fuel rods, the intermediate strip 10 being likewise parallel to these control rod guide tubes and fuel rods. This intermediate strip 10 is formed by a fishplate on the outer strap 2 which overlaps with a corresponding fishplate on the outer strap 3 and is welded at an inner side thereof to the fishplate on the outer strap 3. The intermediate strip 10 is flat and planar and is inclined relative to the two outer straps 2 and 3, respectively, at an angle of 45.degree. i.e. this intermediate strip 10 is perpendicular to the diagonal of the corner grid mesh 5 and, thereby, to the spacer diagonal between the two outer straps 2 and 3. On the outside of this intermediate strip 10, in the middle between the ends thereof, at the edges of the outer straps 2 and 3 perpendicular to the control rod guide tubes and the fuel rods in the spacer, a rejection or refusal rise 11 is provided which is formed by being embossed or stamped out of the fishplate on the outer strap 2 in the respective directions of the diagonal of the corner grid mesh 5 and the spacer diagonal between the two outer straps 2 and 3. This rejection rise 11 is inclined transversely to the two outer straps 2 and 3 and towards the two ends of the intermediate strip 10 i.e. in longitudinal direction of the control rod guide tubes and the fuel rods contained in the spacer, forming respective chamfered surfaces 12. In addition, the two outer straps 2 and 3 are inclined at the corners, starting from the edges thereof perpendicularly to the control rod guide tubes and fuel rods contained in the spacer and towards the intermediate strip 10 located between these outer straps 2 and 3, forming thereby chamfers 13 and 14 of like inclination. As is shown in FIG. 2, the rejection rises 11 alternatingly engage the respective fuel rods 4 in the corner grid mesh 5 if there is relative movement in longitudinal direction of two parallel nuclear reactor fuel assemblies arranged diagonally adjacent one another in the checkerboard pattern with spacers constructed in accordance with FIG. 1, and thereby force the two intermediate strips 10 apart to such an extent that the two intermediate strips 10 of the two diagonally adjacent spacers, and consequently the nuclear reactor fuel assemblies, cannot become hooked at the ends thereof when there is relative movement of the fuel rods 4 in the longitudinal direction. In FIG. 3, like parts of the grid-shaped square spacer are identified by the same reference characters as in FIG. 1, but the bumps and springs in the individual grid meshes are not shown. The spacer according to FIG. 3 differs from that of FIG. 1 in that the intermediate strip 10 is formed flat and planar between the two outer straps 2 and 3 which are welded together therewith, and in that a spring strip 15 is suspended from the ends of this intermediate strip 10 which are located at the edges of the outer straps 2 and 3 which are perpendicular to the control rod guide tubes and fuel rods in the spacer. This spring strip 15 is formed of spring steel and covers the intermediate strip 10. Furthermore, this spring strip 15 has, in the middle, between the ends thereof, a rejection rise 11 which, like the rejection rise 11 of the spacer according to FIG. 1 projects outwardly, respectively, in the diagonal of the corner grid mesh 5 and in the spacer diagonal between the two outer straps 2 and 3, and is inclined transversely to the two outer straps 2 and 3, forming chamfered surfaces 12 in longitudinal direction of the fuel rod 4. This spring strip 15 can be retrofitted or applied afterwards to the previously manufactured grid-shaped spacer and is therefore well suited for retrofitting previously completed and already available nuclear reactor fuel assemblies. In the square spacer according to FIG. 4, like parts are also provided with the same reference characters as in the spacer according to FIG. 1. The spacer according to FIG. 4 differs from that of FIG. 1 in that the rejection rise 11 is formed by a tab 16 which is cut out in the middle of the fishplate forming the intermediate strip 10 on the outer strap 2. This tab 16 has, at both lateral edges thereof, a respective pointed cutout 31, 32. Respective points of these two cutouts 31 and 32 lie on a bending or folding edge 33 which is parallel to the rods in the spacer i.e. especially also to the control rod guide tube 4 in the corner grid mesh 5. At this folding edge 33, the tab 16 is bent or folded perpendicularly. The bent-away end of the tab 16 is soldered or welded to the outer side of the other outer strap 3 in a pre-stamped or pre-embossed depression 34 formed in the outer strip 3. The one part of the tab 16 which is formed on the one outer strap 2 and is limited by the bending or folding edge 33 lies in the plane of this outer strap 2, while the other part of the tab 16 virtually lies in the plane of the other outer strap 3 starting from the bending or folding edge 33. In the spacer according to FIG. 4, embossing of the rejection rise 11 is therefore avoided, which is particularly advantageous if this spacer is formed of a zirconium alloy. The chamfers or inclinations of the rejection rise 11 of FIG. 4 are formed by the edges of the tab 16 in the cutouts 31 and 32. Advantageously, a rectilinear inclination 13 and 14 is continued, in the spacer according to FIG. 4 at the corners of the two outer straps 2 and 3, into the intermediate strips 10, forming a pointed cutout 19 at the two ends of this intermediate strip 10, so that thereat, a further improvement in the sliding-off of a spacer on a diagonally adjacent nuclear reactor fuel assembly in the checkerboard pattern is effected. The foregoing is a description corresponding, in substance, to German application P 3330 850.0, dated Aug. 26, 1983, International priority of which is being claimed for the instant application, and which is hereby made part of this application. Any material discrepancies between the foregoing specification and the specification of the aforementioned corresponding German application are to be resolved in favor of the latter .