Patent Number: 052895130
Section: summary

CROSS REFERENCE TO RELATED APPLICATIONS This patent application is related to copending U.S. patent application Ser. No. 07/884,972 titled "A Nuclear Fuel Assembly For Increasing Utilization Of Nuclear Fuel Contained Therein" filed May 15, 1992 in the name of David R. Stucker and copending U.S. patent application Ser. No. 07/968,647 titled "Fuel Assembly Including Deflector Vanes For Deflecting A Component Of A Fluid Stream Flowing Past Such Fuel Assembly" filed Oct. 29, 1992 in the name of Edmund E. DeMario et al. BACKGROUND This invention generally relates to fuel assembly spacer grids and more particularly relates to a method of making a fuel assembly lattice member and the lattice member made by such method. Fuel assembly spacer grids are known. One such spacer grid is disclosed in U.S. Pat. No. 3,281,327 titled "Nuclear Fuel Assemblies" issued Oct. 5, 1966 in the name of John Webb, et al. This patent discloses a spacer grid comprising a support member in the form of an outer metal sleeve of regular hexagonal cross-section. This patent also discloses that the spacer grid has a parallel array of spacer diaphragms adapted to be penetrated by fuel elements. According to this patent, the spacer diaphragms act as deflector vanes imparting to a main flow stream a component of flow transversely of the fuel elements. Although the Webb, et al. patent discloses a fuel assembly spacer grid comprising a support member in the form of an outer metal sleeve of regular hexagonal cross-section, the Webb et al. patent does not appear to disclose a method of making a fuel assembly lattice member and the lattice member made by such method, as described and claimed hereinbelow. Another fuel assembly spacer grid is disclosed in U.S. Pat. No. 4,547,335 titled "Fuel Rod Support Grid" issued Oct. 15, 1985 in the name of Robert E. Downs et al. This patent discloses a support grid for triangular arrays of nuclear fuel rods associated with hexagonal fuel assemblies. Although the Downs, et al. patent discloses a support grid for hexagonal fuel assemblies, the Downs et al. patent does not appear to disclose a method of making a fuel assembly lattice member and the lattice member made by such method, as described and claimed hereinbelow. Although the above recited patents disclose fuel assembly spacer grids, these patents do not appear to disclose a method of making a fuel assembly lattice member and the lattice member made by such method, as described and claimed hereinbelow. Therefore, what is needed is a suitable method of making a fuel assembly lattice member and the lattice member made by such method. SUMMARY Disclosed herein is a method of making a fuel assembly lattice member and the lattice member made by such method. The method includes placing a plurality of elongate metal straps on a computer controlled conveyor which successively conveys the straps into alignment with each of a plurality of computer controlled piercing and drawing dies belonging to a progressive die machine. The dies are selectively actuated by the computer to form such elements as curved deflector vanes and spring members on each strap member. After the piercing and drawing operations are completed, the straps are joined by welding to form a lattice member of hexagonal cross section, the lattice member defining a plurality of rhombic-shaped fuel rod cells and a plurality of generally rhombic-shaped guide tube thimble cells therethrough. The rod cells are capable of receiving respective ones of a plurality of fuel rods and the thimble cells are capable of receiving respective ones of a plurality of thimble tubes. The rhombic shape of the rod cells cooperate with the deflector vanes to deflect a component of a fluid stream about the longitudinal center axis of each fuel rod for maintaining liquid substantially single-phase fluid flow over the surface of each fuel rod in order to avoid Departure from Nucleate Boiling (DNB) on the surface of the fuel rods. An object of the present invention is to provide a method of making a fuel assembly lattice member and the lattice member made by such method. Another object of the present invention is to provide a lattice member for a fuel assembly, the lattice member capable of deflecting a component of a fluid stream flowing past the fuel assembly, so that liquid substantially single-phase coolant flow is obtained over the surface of the fuel rods in order to avoid Departure from Nucleate Boiling (DNB) on the surface of the fuel rods. A feature of the present invention is the provision of a method of making a fuel assembly lattice member comprising the steps of engaging a plurality of metal strap members with a computer controlled conveyor, successively advancing each strap member into alignment with a pneumatically actuatable deflector vane piercing die by controllably moving the conveyor and pneumatically actuating the deflector vane piercing die by operating the computer, so that each strap member is pierced to form at least one deflector vane thereon. Another feature of the present invention is the provision of a method of making a lattice member comprising the steps of advancing a preselected pair of metal strap members into alignment with a pneumatically actuatable trihedral drawing die by controllably moving the conveyor; pneumatically actuating the trihedral drawing die by operating the computer to draw the pair of strap members such that each of the strap members obtains a trihedrally-shaped transverse cross section; and joining the pair of trihedrally-shaped strap members by activating a welding device so as to form an outer strap member having a regular hexagonally-shaped transverse contour. Yet another feature of the present invention is the provision of a lattice member for a fuel assembly, the lattice member being capable of receiving elongate fuel rods therethrough and comprising a plurality of curved deflector vanes thereon for deflecting a component of a fluid stream flowing past the fuel assembly, such that the deflected component of the fluid stream swirls about the longitudinal center axis of each fuel rod. An advantage of the present invention is that it obtains a cost-effective method of making lattice members, the method necessarily requiring only one machine set-up, rather than multiple machine set-ups, in order to efficiently make lattice members of varying designs. Another advantage of the present invention is that it reduces fabrication time for making lattice members. Yet another advantage of the present invention is that it obtains a lattice member that reduces the risk of tool hang-up and resulting damage to the lattice member during reactor refueling operations. Still another advantage of the present invention is that it obtains a lattice member capable of reducing the risk of Departure from Nucleate Boiling (DNB) on the surface of each fuel rod passing through the lattice member. These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described illustrative embodiments of the invention.