Patent Number: 045267448
Section: summary

TECHNICAL FIELD The present invention relates to a fuel assembly for a boiling water reactor, the fuel assembly comprising a plurality of vertical fuel rods, which are surrounded by a fuel channel device with a vertical longitudinal axis, the fuel rods constituting four partial bundles or subassemblies, the fuel rods in each partial bundle being positioned by means of a corresponding group of spacers arranged vertically one after the other, each of the partial bundles resting on a corresponding bottom grid. BACKGROUND ART A fuel assembly of this kind is known from U.K. Patent Specification No. 931,676. In the known fuel assembly the fuel rods are distributed among four partial bundles, each of which is provided with a bottom grid and with a top grid. Each fuel rod is provided with slotted end portions and arranged with the slots in engagement with and hard-soldered to the top grid and the bottom grid, respectively. Further, such a fuel assembly is known from U.S. Patent No. 3,389,056. Which discloses a fuel assembly in which the fuel rods are distributed among four partial bundles, which are positioned with respect to each other by means of a plurality of upwardly-directed fixing members, disposed outside the fuel channel device and extending from one partial bundle each, said fixing members being attached to the top grid of the reactor core. With conventional boiling water reactor fuel assemblies of the kind comprising several partial bundles, it is not possible to lift all the partial bundles out of the fuel channel device in one and the same lifting operation. DISCLOSURE OF THE INVENTION The invention aims to provide a four-part fuel assembly which permits simplified and less time-consuming fuel handling than what is possible when using the above-mentioned prior art fuel assemblies. According to the invention, the majority of the fuel rods in each partial bundle is arranged in the bottom grid freedom of movememnt in a direction vertically upwards. At least one fuel rod in each partial bundle is a tie rod which is detachably arranged in a tensile force transmitting connection with the bottom grid of the partial bundle. The partial bundles are positioned in relation to each other by means of a common top tie plate, positioned above the fuel rods and surrounded by an upper portion of said fuel channel device. The top tie plate is detachably arranged in a tensile force transmitting connection with the bottom grids by means of the tie rods and is provided with a lifting loop adapted for lifting all the partial bundles of the fuel assembly in one and the same lifting operation. A simultaneous lifting is time-saving in case of inspection of the fuel and when, at a certain burnup stage, it is desirec to change the positions and/or orientations of the various partial bundles with a view to achieving better fuel economy.