Patent Number: 
Section: claims

1. A fuel channel for a nuclear power boiling water reactor, the fuel channel being configured to include a bundle of fuel rods with nuclear fuel, the fuel channel being made of sheet materials and having an elongated shape and defining a longitudinal direction and comprises:an assembly of four discrete major sides, each of said major sides extending between a first axial end and a second axial end of the fuel channel and each of which have an elongated shape in said longitudinal direction and which are connected to each other such that a corner, which has an elongated shape and which extends in said longitudinal direction, is formed where any two of said major sides that are adjacent to one another, meet;wherein said major sides are connected to each other such that the fuel channel has four of said corners;wherein each of said major sides defines an inner surface facing an interior area of the fuel channel, and an outer surface facing outwardly from the fuel channel; andin each of at least two of said corners the sheet materials from two of the major sides that are adjacent to one another, overlap with each other such that each said corner defines a corner region with overlapping sheet materials, said corner region defined by a first of said sheet materials from one of the major sides that are adjacent to one another and an overlapping one of a second of said sheet materials from the other of the major sides that are adjacent to one another;wherein said corner region with said overlapping sheet materials extends in said longitudinal direction along at least fifty percent of the length of the fuel channel;wherein in each of said at least two corners, said first of said sheet materials and said second of said sheet materials overlap with each other to form an overlapping region in which a space is formed between said first of said sheet materials and said second of said sheet materials;wherein in at least one of said corners, an inner one of said overlapping sheet materials is substantially straight, while an outer one of said overlapping sheet materials is configured to form an outer corner shape, such that said space, as seen in a cross section of the fuel channel, has substantially a triangular shape, wherein one corner is bent, or arc shape which is limited by a straight portion of the inner one of said overlapping sheet materials; andwherein in each said corner having said corner region with said overlapping sheet materials, the inner one of said overlapping sheet materials extends from a first of said major sides to a second, adjacent one of said major sides, wherein the first major side defines a first plane and the second major side defines a second plane, the first plane is perpendicular to the second plane, and the inner one of said overlapping sheet materials extends diagonally from a first point on the first plane to a second point on the second plane to form the space formed between said first of said sheet materials and said second of said sheet materials. 2. The fuel channel according to claim 1, wherein in all of said corners, the sheet materials for said corners have major sides that are adjacent to one another and that overlap with each other. 3. The fuel channel according to claim 1, wherein each of said corner region with said overlapping sheet materials extends along substantially the entire length of the fuel channel. 4. The fuel channel according to claim 1, wherein said space is open at the first axial end and the second axial end. 5. The fuel channel according to claim 1, wherein a distance between the first point and the second point is 10-25 mm. 6. The fuel channel according to claim 1, wherein a distance between the first point and the second point is 13-19 mm. 7. The fuel channel according to claim 1, comprising, for each said corner region with said overlapping sheet materials, a first weld joint and a second weld joint each extending in the longitudinal direction, wherein the first weld joint connects the two overlapping sheet materials at a first longitudinally extending contact surface of the corner region with the overlapping sheet materials, and the second weld joint connects the overlapping sheet materials at a second longitudinally extending contact surface of the corner region with the overlapping sheet materials. 8. The fuel channel according to claim 1, wherein each said corner in the fuel channel comprises said corner region with said overlapping sheet materials, wherein the fuel channel is formed by four sheets, wherein all of said sheets have a common shape, wherein each sheet has a first edge located at an inner one of the two overlapping sheet materials of one said corner, and a second edge located at an outer one of the overlapping sheet materials of another of said corner. 9. The fuel channel according to claim 1, wherein each said corner in the fuel channel comprises said corner region with said overlapping sheet materials, wherein the fuel channel is formed by a first sheet, a second sheet, a third sheet and a fourth sheet, wherein the first sheet and the second sheet have a first shape having a first edge comprising a first inner one of the overlapping sheet materials of one said corner, and having a second edge comprising a second inner one of the overlapping sheet materials of another said corner, wherein the third sheet and the fourth sheet have a second shape having a third edge comprising a first outer one of the overlapping sheet materials of one said corner, and a fourth edge comprising a second outer one of the overlapping sheet materials of another said corner. 10. The fuel channel according to claim 1, wherein each said major side is provided with at least one of:a plurality of elongated bulges, which extend substantially perpendicular to the longitudinal direction of the fuel channel, and which contribute to increasing the stiffness of the fuel channel; anda plurality of elongated indentations, which extend substantially perpendicular to the longitudinal direction of the fuel channel, and which contribute to increasing the stiffness of the fuel channel. 11. The fuel channel according to claim 10, wherein at least one of:at least a majority of said bulges have a length of 30-80 mm; andat least a majority of said indentations have a length of 30-80 mm. 12. The fuel channel according to claim 10, wherein at least one of:at least a majority of said bulges have a length of 40-60 mm; andat least a majority of said indentations have a length of 40-60 mm. 13. The fuel channel according to claim 10, wherein at least one of:at least a majority of said bulges have a width of 4.0-13.0 mm; andat least a majority of said indentations have a width of 4.0-13.0 mm. 14. The fuel channel according to claim 10, wherein at least one of:at least a majority of said bulges have a width of 5.0-8.0 mm; andat least a majority of said indentations have a width of 5.0-8.0 mm. 15. The fuel channel according to claim 10, wherein at least one of:all of said bulges have a length of 30-80 mm; andall of said indentations have a length of 30-80 mm. 16. The fuel channel according to claim 10, wherein at least one of:all of said bulges have a length of 40-60 mm; andall of said indentations have a length of 40-60 mm. 17. The fuel channel according to claim 10, wherein at least one of:all of said bulges have a width of 4.0-13.0 mm; andall of said indentations-have a width of 4.0-13.0 mm. 18. The fuel channel according to claim 10, wherein at least one of:all of said bulges have a width of 5.0-8.0 mm; andall of said indentations have a width of 5.0-8.0 mm. 19. The fuel channel according to claim 10, wherein at least one of:a majority of said bulges bulge out between 0.50-1.50 mm from the outer surface; anda majority of said indentations curve in between 0.50-1.50 mm from the inner surface. 20. The fuel channel according to claim 10, wherein at least one of:all of said bulges bulge out between 0.50-1.50 mm from the outer surface; andall of said indentations curve in between 0.50-1.50 mm from the inner surface. 21. The fuel channel according to claim 10, wherein at least one of:each major side comprises at least 50 of said bulges; andeach major side comprises at least 50 of said indentations. 22. The fuel channel according to claim 10, wherein at least one of:each major side comprises at least 80 of said bulges; andeach major side comprises at least 80 of said indentations. 23. The fuel channel according to claim 10, wherein at least 50% of said bulges and said indentations are said bulges. 24. The fuel channel according to claim 10, wherein 100% of said bulges and indentations are said bulges. 25. The fuel channel according to claim 1, wherein the sheet material which forms the major sides of said fuel channel has substantially a constant thickness, except for at least one of:at said corners;at said bulges;at said indentations; andat said overlapping sheet materials. 26. A fuel assembly for a nuclear power boiling water reactor, comprising the fuel channel of claim 1 and a plurality of fuel rods with nuclear fuel material arranged such that the fuel channel surrounds the fuel rods.