Patent Number: 052326586
Section: claims

1. A fuel assembly for a boiling water reactor, comprising an elongated box having box walls with flat outer surfaces defining a polygonal outer cross section with rounded corners, an interior and a longitudinal axis, a bundle of fuel rods being disposed in said box and aligned parallel to one another and to the longitudinal axis of said box, said fuel rods being disposed beside one another in rows parallel to said box walls, said box walls having reinforcements protruding into said interior in the vicinity of said rounded corners defining a relatively increased wall thickness, and said box walls having a relatively reduced wall thickness between said reinforcements, said bundle of fuel rods having no fuel rod at intersections of two of said rows of fuel rods adjacent to two of said box walls bordering one another at said rounded corners. 2. The fuel assembly according to claim 1, wherein said elongated box extends between a top part and a bottom part. 3. The fuel assembly according to claim 1, wherein two of said fuel rods in said rows within said bundle are spaced between apart by a minimum spacing being equal to a spacing between two fuel rods in a row parallel to one of said box walls. 4. The fuel assembly according to claim 1, wherein said fuel rods of two adjacent rows are staggered relative to one another in the direction of said box walls. 5. The fuel assembly according to claim 1, wherein said relatively reduced wall thickness is less than approximately 2.4 mm, and said relatively increased wall thickness in the vicinity of said rounded corners is between approximately 2.5 and 3.0 mm. 6. The fuel assembly according to claim 1, wherein said relatively reduced wall thickness is less than approximately between 1.5 and 1.7 mm, and said relatively increased wall thickness in the vicinity of said rounded corners is between approximately 2.7 to 2.9 mm. 7. In a boiling water reactor having a core zone with a given geometry and a plurality of fuel assemblies, each of said fuel assemblies comprising an elongated box having box walls with flat outer surfaces defining a polygonal outer cross section with rounded corners, an interior and a longitudinal axis, said outer cross section being defined by the given geometry of the core zone, a bundle of fuel rods being disposed in said box and aligned parallel to one another and to the longitudinal axis of said box, said fuel rods being disposed beside one another in rows parallel to said box walls, said box walls having reinforcements protruding into said interior in the vicinity of said rounded corners defining a relatively increased wall thickness, and said box walls having a relatively reduced wall thickness between said reinforcements, said bundle of fuel rods having no fuel rod at intersections of two of said rows of fuel rods adjacent to two of said box walls bordering one another at said rounded corners.