Abstract: A method for sputter coating the inside surface (30) of a fuel assembly tubular component (10) such as a control rod guide tube (200) with wear or corrosion resistant material. The steps include supporting the component tube in a fixture (12,14) and supporting a source tube (100,300) of e.g., wear resistant material, coaxially within the component tube, thereby defining a cylindrical annulus (24) between the tubes. The annular space is evacuated and backfilled with an inert working gas (26) such as argon, to a pressure sufficient to sustain a plasma discharge. The component tube is positively biased (36) as an anode, and the source tube is negatively biased (34) as a cathode, such that a plasma of the working gas is established in the annular space. A circumferential magnetic field is generated around the source tube to confine and shape the plasma whereby the source tube is bombarded with ions from the plasma substantially uniformly over the length of the source tube.

Abstract: A fuel assembly supporting structure for a nuclear reactor fuel assembly which comprises a two-way shape-memory alloy. A shape-memory alloy is selected which has an overall transition temperature range substantially above atmospheric temperature and substantially below a temperature experienced by the shape-memory alloy under reactor operating conditions. By using a shape-memory alloy in the design, the support structure assumes a first configuration for securely supporting one or a plurality of nuclear reactor components at a temperature above the overall transition temperature range and assumes a second configuration for loosely engaging the reactor components below the transition temperature range.

Abstract: A low pressure drop easy load fuel assembly rod end cap 40 for pressurized water reactor fuel assembly rods 10 has a solid Zircaloy radiused tip 42. The tip 42 blends into a longitudinal profile defined by a smooth convex curve 44,46 which blends into a substantially cylindrical surface portion 48 of a diameter substantially equal to the diameter of the fuel cladding tube or other shank 50.

Abstract: A method for coating the inside surface (18) of tubular components (16) of a nuclear fuel assembly, including the steps of supporting the component within a vacuum chamber (12), positioning a source rod (20) having a field emitter structure (22) within the component, the structure being formed of material to be coated on the surface, and inducing an electrical current flow (26) through the rod sufficient to evaporate at least a portion of the emitter structure, whereby the evaporated material of the emitter structure is deposited on and adheres to the surface as a coating. Optionally, the vacuum chamber is backfilled with a reactive gas (38), and the material evaporated from the emitter structure chemically reacts with the gas before adhering to the surface. The reactive gas can be one of nitrogen, oxygen, or carbon plasma and the coating adhered to the component can be one of a nitride, oxide, or carbide, respectively.

Abstract: A method for enhancing the wear and corrosion resistance of a tubular nuclear fuel assembly component (40), comprising the step of coating the component with a corrosion and wear resistant material by an anodic arc plasma deposition process (70). The coating is preferably a nitride reactively formed during the plasma deposition process. The component is preferably a nuclear fuel rod cladding tube and the coating material is one of ZrN or TiN.

Abstract: A method for sputtering coating the inside surface of a fuel assembly tubular component (10,200,400,700) with absorber material such as a burnable poison or getter. The steps include supporting the e.g., cladding tube (10) in a fixture (12,14) and supporting a source tube (100) of e.g., burnable poison material coaxially within the cladding tube, thereby defining a cylindrical annulus (24) between the tubes. The annular space is evacuated and backfilled with an inert working gas (26) such as argon, to a pressure sufficient to sustain a plasma discharge. The cladding tube is positively biased (36) as an anode, and the source tube is negatively biased (34) as a cathode, such that a plasma of the working gas is established in the annular space. A circumferential magnetic field is generated around the source tube to confine and shape the plasma whereby the source tube is bombarded with ions from the plasma substantially uniformly over the length of the source tube.

Abstract: A nuclear fuel perimeter strip grid corner-piece (12) of increased flatness having at least two flat side sections (18,20) on either side of a transverse bend line (22) is provided. The flat side section (20) or sections (20 and 32) which have small cut-outs for arches (34), as opposed to large spring (36) cut-outs, as the fuel support features adjacent to the bend line (22) of variable radii at portions (24 and 26) are stress-relieved by means of slots (30) of length equal to 1/2 to 1/3 of the width of the flat section. The slot (30) is of a width less than twice the material thickness, so as not to weaken the structure near bend (22).

Abstract: A holddown leaf spring for a nuclear fuel assembly (10) with an upper end fitting (12) having spring retaining slots (30). Two spring stacks (20, 24 and 22, 26), respectively, are made up of unitary elongated metal bar springs having two substantially tapered width leg portions (20a, 20b, etc.) joined by an arcuate transition portion (28) therebetween. The wider opposite end portions (20c, 20d, etc.) are received in slots (30) of end fitting (12) and retained by welded pins (or capped screws) (not shown). The tapered width distributes localized stresses and may be horizontal or vertical. Less chance of debris exists due to retained spring ends. Flow at two opposite corners is opened up by the taper and by transition portion (28) being spaced from the nozzle openings (32 and 34). The assembly requires fewer parts and less machining.

Abstract: A wear resistant coating (50) for fuel rod cladding (20) comprises a ceramic material (52) which is premixed with a glass (54). The cladding tube is heated and the ceramic/glass mixture is flame sprayed onto the cladding tube. The coating is applied to lower portions of the fuel rods (10) in the area of the first support grid (12) where debris tends to fret the fuel rod.

Abstract: A method for enhancing the wear resistance of a tubular component (62) of a nuclear fuel assembly, including the first steps of supporting the component in an implantation chamber (16), removing ambient air from the chamber such as by a pump (56) and generating a plasma plume (28) of positively charged metal source material by establishing an electrical discharge arc which travels from a cathode (18) of said source material to an anode (24) of a different material. At least a portion of the plasma plume is passed through an electromagnetic duct (14) which filters constituents other than free, high energy source material ions out of the plume. The high energy source material positive ions are directed through the chamber onto the negatively charged component. The chamber can be backfilled with a reactive gas such as nitrogen which forms an ionic compound with the source material ions such as Zr or Ti, and the ionic compound such as ZrN or TiN implants in the component.

Abstract: In a method for fabricating an end fitting (12,200) for a nuclear fuel assembly (10), wherein the end fitting includes at least one spring member (24,202) having an active external surface (32,206) for contacting rigid core support structure (100) in the nuclear reactor, the improvement comprising applying a coating to the active surface of the spring member. The coating is selected from the group consisting of nitrides, Cr, TiC, CrC, ZrC and NiTaB. The spring member is preferably Inconel and the coating is one of ZrN or TiN. Each spring member can be formed by nesting a plurality of spring elements (28,34,36 or 208,210) so that the spring elements are in contact with each other and the method includes applying said coating to each of the spring elements at least where they contact each other.

Abstract: An improved lower end fitting 10 (L.E.F.) having a bell mouth multistage type of flow jet diffuser 30 with stages 31, 31' decreases pressure drop 15-20% over a single stage bell mouth diffuser and more evenly distributes flow and adds strength. It includes neutron thimble flux impingement shield 50 of instrument and/or cable. Each diffuser stage 31, 31' is S.S., of circular cross-sect. and parabolic to optimize diffusion. The multistage shape is based on lower core plate 20 flow hole 24 geometry, L.E.F. design and reactor flow rate. Thinner L.E.F. legs 36, smaller L.E.F. gussets 38 and thinner L.E.F. flow plates 22 are possible.

Abstract: A fuel rod capturing support grid having a spring and arch design which provides performance improvements over current or previous designs by decreasing fuel rod fretting wear. The disclosed spring and arch designs follow the contour of the fuel rod, thus providing an increased, substantially arc-shaped area of contact between the fuel rod and the spring tabs and arches.

Abstract: A fuel element (10) for a nuclear reactor having a zirconium-tin alloy cladding tube (20), with a thin coating (30) of a burnable poison consisting of an enriched boron particles sealed in a boron-containing glass or glass compound deposited from a liquid sol-gel.

Abstract: A fuel assembly grid (10) in which the height dimension of the grid strips (A,B,C,D) varies along the strip length, so that channels or cells (24',28) immediately surrounding the guide tube (30) define a relatively longer flow path, than channels that are relatively remote from the guide tube. In particular, the grids have a first plurality of four-walled first cells (24) for receiving and supporting respective fuel rods (26) and a second plurality of four-walled second cells (28) that are larger in cross-sectional area than, and interspersed among, the first cells, for receiving respective guide tubes (30). The improvement according to the present invention, provides that the height dimension (H2) of each strip (C) that defines walls of particular first and second cells is greater at the walls of the particular second cells, than at the walls of at least some of the particular first cells.

Abstract: A corrosion resistant metallic coating (60) of zirconium nitride is applied to the cladding tube (40) of a nuclear fuel rod (20). The zirconium nitride is reactively deposited on a zirconium-alloy cladding tube by a cathodic arc plasma deposition process. The zirconium nitride coating provides superior wear test results and enhances the corrosion resistance of the cladding tube.

Abstract: Grid strips for a nuclear fuel assembly grid have elongated weld tabs. The weld tabs are bent against the strips along the intersection with an adjacent orthogonal strip. The tabs are dimensioned and positioned to initially extend substantially the entire length of the intersection of two grid strips. The tabs are then melted during the welding process.

Abstract: A removable and reusable cap for fuel rod ends to prevent grid damage during loading permits fuel end configurations to match utility's special tooling for fuel assembly repair and reconstitution. The elastomeric transitory fuel rod guidance ends expand over a flange and temporarily snap into place in a groove in the fuel rod end to provide a tapered guiding surface.

Abstract: A wear resistant coating (50) for fuel rod cladding (20) comprises a ceramic material (52) which is premixed with a glass (54). The cladding tube is heated and the ceramic/glass mixture is flame sprayed onto the cladding tube. The coating is applied to lower portions of the fuel rods (10) in the area of the first support grid (12) where debris tends to fret the fuel rod.

Abstract: Bottom end fuel assembly reconstitution is permitted by elimination of weld of Inconel lower grid perimeter strip to stainless steel lower end fitting. Slots in 2 or 3 sides of L.E. Fitting capture ribbed sections of grid perimeter strip, locking screws hold L.E. Fitting in position on guide thimbles. Grids lip on perimeter strip is interlocked by sliding in L.E. Fitting groove.