Patent Number: 054003733
Section: summary

BACKGROUND OF THE INVENTION This invention relates to an assembly fixture and method used for the fabrication of metal grids. It relates particularly to apparatus and a method used for the fabrication of metal grids used to support and position the fissionable fuel rods used in a nuclear reactor core. Most nuclear reactors use as fuel, elongated rods of fissionable material arranged and supported in a spaced parallel array between upper and lower core support plates. To provide integrity within the supports, the fuel rods are divided into groups and the fuel rods in each group are formed as an integral fuel rod assembly prior to placement between the reactor core support plates. More specifically, the fuel rods in each group have been typically in the past arranged in spaced, parallel arrangements with each other in supporting and spacing frames or grids. The grids are formed of a plurality of interconnected metal grid straps to provide a square or rectangular structural network of interconnected open grid cells, similar to an "egg crate divider". U.S. Pat. Nos. 3,379,617 and 3,379,619 issued Apr. 23, 1968 to Andrew et al. and assigned to the assignee of the present invention, disclose typical supporting grid assemblies for fuel rods in which the fuel rods are held laterally and longitudinally in the grid cells by resilient, spring-like retainers in selected grid cells of the grid structure. In the past the assembly of the grids has been difficult and time consuming due to the large number of grid strap components, their small size, the flexibility of the individual grid straps and the large number of welds required to connect all the grid straps and components together into an integral structural grid network. In addition, the nuclear fuel assembly grid specifications require that the that the grid straps and other grid components be very accurately aligned, both during and after assembly and welding, in order to hold the group of fuel rods making up a fuel rod assembly in a precise, parallel alignment. Such accurate alignment was often difficult and time consuming to achieve with the previously known multi-step grid assembly and welding fixtures and practices used prior to this invention. SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a grid assembly fixture and assembly method useful for the assembly and welding of grids used to support a fuel rod assembly used in a nuclear reactor. It is a further object of this invention to provide a grid assembly fixture and assembly method useful for the assembly and welding of grids that provides for an easy but precise and accurate alignment and positioning of the thin grid straps, especially those used for the sides of the grid, during its assembly and welding. It is a still further object of this invention to provide a grid assembly fixture and assembly method that allows for faster and more efficient grid assembly and welding procedures. Other and further objects of this invention will become apparent from the following detailed description and the accompanying drawings and claims. It has been discovered that the foregoing objects can be attained by a grid assembly fixture or apparatus for the assembly of a grid structure used to support elongate fuel rods for a nuclear reactor comprising a rectangular grid assembly plate supported above a work surface and having a flange on each four sides of the rectangular grid assembly plate. A clamp support plate attached to each side flange supports a toggle action clamp assembly that is able to move and hold an elongated clamping pad against each side of the grid assembly plate to hold temporarily hold the four border grid straps along the four sides of the grid assembly plate. A rectangular strap retention assembly is then placed around the border grid straps to hold the border grid straps in place against the four sides of the grid assembly plate until they can be welded together. The toggle clamps and associated clamping pads are then released.