Patent Number: 
Section: claims

1. A fuel assembly (1) for a nuclear pressurized water reactor, said fuel assembly comprising:a lower end structure (6);an upper end structure including a top nozzle (5);a plurality of elongated fuel rods (2);a plurality of longitudinally extended guide thimbles (3) extending in a longitudinal direction from the lower end structure (6) to the top nozzle (5), said top nozzle (5) including a passageway extending through the top nozzle (5) and an annular groove (10) formed in said passageway;an elongated sleeve (11) formed by each of the plurality of longitudinally extended guide thimbles (3), the sleeves (11) each being configured for attaching a portion of the guide thimble (3) to the top nozzle (5) and each having at least three slots (12) in an upper end portion of said sleeve (11), each slot (12) extending downwardly from a top end of said sleeve (11) anda plurality of locking members (15), each locking member (15) being introduced into and positioned within a respective one of the elongated sleeves (11) from above the top nozzle (5),wherein:the upper end portion of the sleeve (11) includes at least three bulges (13), each of which said at least three bulges (13) seat in said annular groove (10) when said sleeve (11) is in an expanded locked position within said passageway;each of said at least three bulges (13) has two ends and extends circumferentially between a nearest two of the slots (12);wherein the two ends of each of said at least three bulges (13) are circumferentially spaced from each other; andat least one of the two ends of each of said at least three bulges (13) is located at a position which is at a spaced circumferential distance (d) from a nearest one of the two slots (12). 2. The fuel assembly according to claim 1, wherein each of said bulges (13) has an end portion at a respective end, wherein the end portion has a curved shape in a longitudinal section and in a transversal section along the bulges (13). 3. The fuel assembly according to claim 1, wherein both ends of each of said bulges (13) extend to a position at a distance (d) from the respective slot (12). 4. The fuel assembly according to claim 1, wherein said bulges (13) are provided so that there is at least one bulge (13) between each pair of adjacent slots (12). 5. The fuel assembly according to claim 1, wherein said bulges (13) are provided circumferentially after each other. 6. The fuel assembly according to claim 1, wherein:the sleeve (11) has a wall thickness seen in a radial direction with respect to the longitudinal direction; andthe distance (d) between the end of each of said at least three bulges (13) and the nearest slot (12) is at least equally long as the wall thickness of the sleeve (11). 7. The fuel assembly according to claim 1, wherein:the sleeve (11) has a wall thickness seen in a radial direction with respect to the longitudinal direction; andthe distance (d) between the end of each of said at least three bulges (13) and the nearest slot (12) is two or three times longer than the wall thickness of the sleeve (11). 8. The fuel assembly according to claim 1, wherein:the sleeve (11) has a wall thickness seen in a radial direction with respect to the longitudinal direction; andthe wall thickness of the sleeve (11) is in the range of from 0.20 to 0.50 mm. 9. The fuel assembly according to claim 1, wherein the sleeve (11) has at least one of 3, 4, 5 or 6 slots (12). 10. The fuel assembly according to claim 1, wherein at least one of the bulges (13) has a cylindrical profile seen in a longitudinal section.