Abstract: Apparatus and method for providing on-site storage of all spent fuel rods removed from a nuclear reactor during its lifetime. Spent fuel rods are removed from spent fuel assemblies and stored in a container in a vertical position, and on a pitch which is less than the pitch of the fuel rods when in a fuel assembly. The removed fuel rods preferably are positioned in a triangular array, and with most fuel rods having line contact along their length with adjacent fuel rods. This arrangement imparts support to all fuel rods in the container and thereby maximizes the available storage space for fuel. To facilitate the loading process, the vertically disposed fuel rods may be installed on steps in the container or on a flat bottom plate therein, all with the assistance of a guidance plate which orients and directs each fuel rod into the container.

Abstract: An improved control rod guide tube for use in a fuel assembly in a nuclear reactor. The guide tube extends the complete length of the fuel assembly and has its upper end fastened in a cylindrical housing by swaging the guide tube material into grooves formed in the housing walls. To eliminate wear on the guide tube inner walls caused by hydraulic induced vibratory forces on a control rod adapted to move therein, a thin-walled chrome plated sleeve is threaded into the top end of the guide thimble and extends downwardly a distance sufficient to be engaged by the control rod during reactor operation. The sleeve serves as a highly resistant wear surface between the control rod and walls on the guide tube in the fuel assembly.

Abstract: A reconstitutable fuel assembly for a nuclear reactor which includes a mechanical, rather than metallurgical, arrangement for connecting control rod guide thimbles to the top and bottom nozzles of a fuel assembly. Multiple sleeves enclosing control rod guide thimbles interconnect the top nozzle to the fuel assembly upper grid. Each sleeve is secured to the top nozzle by retaining rings disposed on opposite sides of the nozzle. Similar sleeves enclose the lower end of control rod guide thimbles and interconnect the bottom nozzle with the lowermost grid on the assembly. An end plug fitted in the bottom end of each sleeve extends through the bottom nozzle and is secured thereto by a retaining ring. Should it be necessary to remove a fuel rod from the assembly, the retaining rings in either the top or bottom nozzles may be removed to release the nozzle from the control rod guide thimbles and thus expose either the top or bottom ends of the fuel rods to fuel rod removing mechanisms.

Abstract: A top nozzle for a nuclear reactor fuel assembly which includes an orifice plate designed to receive control rod guide tubes extending upwardly from the top of the fuel assembly. Nozzle pin extensions connected to the orifice plate are axially coextensive with the guide tubes and project upwardly through a top nozzle hold-down plate, and through openings in the upper core plate in the reactor. The hold-down plate is spring biased into an upper core plate engaging position and since the pin extensions are adapted to move in the core plate and against the action of the springs, the top nozzle thus becomes effective in accommodating upwardly acting hydraulic forces which tend to lift the fuel assembly, and to accommodate differential expansion of parts in the fuel assembly as compared to the core barrel in which the assembly is located.

Abstract: A grid for a nuclear reactor fuel assembly which includes intersecting straps arranged to form a structure of egg crate configuration. The cells defined by the intersecting straps are adapted to contain axially extending fuel rods, each of which occupy one cell, while each control rod guide tube or thimble occupies the space of four cells. To effect attachment of each guide thimble to the grid, a short intermediate sleeve is brazed to the strap walls and the guide thimble is then inserted therein and mechanically secured to the sleeve walls. Each sleeve preferably, although not necessarily, is equipped with circumferentially spaced openings useful in adjusting dimples and springs in adjacent cells. To accurately orient each sleeve in position in the grid, the ends of straps extending in one direction project through transversely extending straps and terminate in the wall of the guide sleeve.