Patent Number: 053435087
Section: summary

FIELD OF THE INVENTION This invention relates to a nuclear reactor fuel assembly and, more particularly, to a nuclear reactor fuel assembly skeleton structure and, still more particularly, to a device which retains a nuclear fuel rod spacer grid on a fuel assembly. BACKGROUND OF THE INVENTION Commercial nuclear reactors used for generating electric power include a core composed of a multitude of fuel assemblies which generate heat used for electric power generation purposes. Each fuel assembly includes an array of fuel rods and control rod guide tubes held in spaced relationship with each other by grids of "egg-crate" configuration spaced along the fuel assembly length. The grids are generally of a first and second plurality of half-slotted Inconel or Zircaloy straps in egg-crate configuration and are spaced along the fuel assembly to provide support for the fuel rods, maintain fuel rod spacing, promote mixing of coolant, provide lateral support and positioning for control assembly guide tubes and provide lateral support and positioning for an instrumentation tube. The grids along with the control assembly guide tubes and the top and the bottom nozzles form what is known as the skeleton of the fuel assembly. Typically, the guide tubes are screwed into the top and bottom nozzles, the multiple Zircaloy spacer grids are welded to the guide tubes, and the Inconel grid is mechanically attached to the bottom nozzle or guide tube. There is the problem, however, that the skeleton twists from the torquing of the screws as the guide tubes are fastened to the bottom nozzle reducing the straightness of the skeleton. Previously, attaching the Inconel spacer grid to the guide tubes has required complicated machined or welded components which are costly. Thus, it is a problem in the prior art to reliably and economically increase the integrity of the skeleton assembly. SUMMARY OF THE INVENTION It is an object of the present invention to economically provide a device for reliably retaining a spacer grid on a fuel assembly. It is a further object of the present invention to increase the integrity of a nuclear reactor fuel assembly skeleton structure. It is a further object of the present invention to provide a device which reduces the twisting of the fuel assembly skeleton resulting from torquing of the screws which connect the bottom nozzle to the guide tubes. It is a further object of the present invention to provide a simple, low cost device to replace more complicated machined and/or welded components to retain a spacer grid on a fuel assembly. Additional objects, advantages and novel features of the invention will be set forth in the description which follows, and will become apparent to those skilled in the art upon reading this description or practicing the invention. The objects and advantages of the invention may be realized and attained by the invention of appended claims. To achieve the foregoing and other objects, in accordance with the present invention, as embodied and broadly described herein in a nuclear reactor fuel assembly having top and bottom nozzles and nuclear fuel rod spacer grids therebetween for supporting at least one nuclear fuel rod and at least one guide tube fastened to the top and bottom nozzles, a device is for retaining a nuclear fuel rod spacer grid on the guide tube and on the top and bottom nozzles. The tubular retainer means has a first end and a second end and a lumen extending longitudinally therethrough. The retainer means has an upper portion located at the first end for retaining the spacer grid and a lower portion located at the second end for retaining at least one of the guide tubes. The lower portion has an aperture communicating with the lumen whereby the guide tube is inserted through the lumen of the retainer means and a shoulder portion on the guide tube extends through the aperture to retain the lower portion of the retainer means between the shoulder of the guide tube and a surface of the bottom nozzle when the guide tube is attached to the nozzle thereby retaining the spacer grid on the guide tube and bottom nozzle.