Abstract: A spacer grid specifically designed for accident tolerant fuel utilizing fuel rods with SiC cladding for implementation in pressurized water reactors. The spacer grid design allows for ease of SiC fuel rod insertion during the fuel assembly fabrication process by providing a smooth contact geometry. The co-planar support allows the fuel rods to be rotated axially more freely at the grid location than a conventional six-point contact geometry used in existing fuel assembly designs. The fuel rod support cells are attached at their corners which are shared between adjacent support cells.

Abstract: A method for manufacturing nuclear reactor fuel assembly. The method comprises applying a protective coating on fuel elements, wherein each fuel element is moved through a protective coating application device installed on an assembly stand. The protective coating comprises a water-soluble lubricant consisting of nonylphenol ethoxylate and monobasic unsaturated fatty acids. The method further comprises installing the coated fuel elements into grid cells of an assembly, wherein during the installing, each coated fuel element is moved on the assembly stand in a horizontal direction along its own axis into the grid cells. At least part of the steps of applying a protective coating and installing the coated fuel elements occur simultaneously. After installing the coating, top and bottom nozzles are attached to the assembly. After attaching the top and bottom nozzles, the fuel elements are washed to remove the protective coating from the fuel elements, which are subsequently dried.

Abstract: A nuclear fuel assembly having lateral support provided by a bimetallic spring that extends from a side of the fuel assembly under certain core conditions to pressure against an adjacent component and withdraws under other core conditions, such as shutdown, to enable the nuclear fuel assembly to be aligned or withdrawn from the core and repositioned.

Abstract: A spacer grid specifically designed for accident tolerant fuel utilizing fuel rods with SiC cladding for implementation in pressurized water reactors. The spacer grid has a generally square design that allows for ease of SiC fuel rod insertion during the fuel assembly fabrication process by providing a smooth contact geometry. The co-planar support allows the fuel rods to be rotated axially more freely at the grid location than a conventional six-point contact geometry used in existing fuel assembly designs.

Abstract: A VVER-1000 nuclear fuel assembly having a modified bottom nozzle with chamfers at the upper edge of the frustoconical transition from a hexagonal upper section of the nozzle to the lower circular end that mounts on a lower core support.

Abstract: Heat exchangers for use in heavy liquid metal coolant mediums that ensure reliable fixation and spacing of heat exchanger tubes. A first embodiment includes one supporting spacer grid having a cylindrical shell and two or more tiers of plates spaced apart at a preset gap, while the width of each plate is parallel to the shell axis. Ends of all plates are fixed to the shell such that plates of any tier are parallel to each other and located at the preset gap. Plates of different tiers are criss-crossed at an angle of 60 degrees along the shell axles and fastened together at the crossing points. Another embodiment includes three dividers which run through the cylinder axis; their ends are connected to the shell and are spaced at an angle of 60 degrees.

Abstract: The present invention provides a top nozzle for use with PWR nuclear reactors and power plants, and in particular, VVER nuclear reactors. The top nozzle includes a plate portion having a peripheral portion; a hub portion spaced from the plate portion; a plurality of support portions extending from the plate portion to the hub portion; and at least one deflector portion extending inwardly from the peripheral portion at an acute angle with respect to the plate portion.

Abstract: A holding fixture for assisting in assembly of a support grid for nuclear fuel rods and including a plurality of straps each having a plurality of slots extending approximately half a height of the straps and tabs formed beside or between the slots. The holding fixture includes an actuation plate, a support plate having a plurality of receiving members structured to receive therein straps of the support grid and having a plurality of cells, and a plurality of cam assemblies structured to move to deflect every other tab of the straps received in the plurality of receiving members. The cam assemblies are disposed in every other cell of the support plate.

Abstract: A nuclear fuel assembly spacer grid defining a lattice of cells for receiving fuel rods is provided. The spacer grid includes a peripheral band composed of at least one peripheral strip delimiting a portion of the peripheral contour of the spacer grid, and at least one spacer grid positioning spring elastically deformable and formed in the peripheral band.

Abstract: A spacer grid includes interlocked straps comprising metal sheets or plates welded together to define a spacer grid having a top and bottom. The interlocked straps define a plurality of cells comprising vertical passages connecting the top and bottom of the spacer grid. The cells include: upper dimples proximate to the top of the spacer grid and distal from the mid-plane of the spacer grid; lower dimples proximate to the bottom of the spacer grid and distal from the mid-plane of the spacer grid; cantilevered upper springs having fuel rod engagement surfaces proximate to the top of the spacer grid and distal from the mid-plane of the spacer grid; and cantilevered lower springs having fuel rod engagement surfaces proximate to the bottom of the spacer grid and distal from the mid-plane of the spacer grid.

Abstract: A nuclear fuel assembly body with a lengthways axis includes first and second tubular segments made from a metal material forming the lengthways ends of the assembly body. A frame made from a metal material connects the first and second segments. The frame is openworked. A ceramic tubular internal structure is positioned between the first and second segments inside the frame.

Abstract: A grid including at least two meshed grid parts intended to be superposed in a longitudinal direction, each grid part extending in a transverse plane, and the grid parts being moveable one relative to the other in at least one transverse direction between an open configuration for the insertion of nuclear fuel rods in the longitudinal direction through the grid parts, and a closed configuration allowing each fuel rod inserted through the grid parts to be clamped transversely between the grid parts. According to one aspect of the invention, the grid includes elements for transversely immobilizing the grid parts in the closed configuration, the immobilizing elements being designed to engage as the superposed grid parts are moved closer together in the longitudinal direction.

Abstract: Disclosed herein is a spacer grid for a nuclear fuel assembly. The spacer grid has dimples for supporting fuel rods and is formed from grid strips which are assembled in a lattice shape to form lattice cells. Each grid strip has at least one hole which is formed separately from the dimples. Therefore, when coolant is drawn into the fuel assembly, a pressure difference between opposite sides of the holes is reduced, and friction generated between cut edges of the holes and the coolant reduces the magnitude of the vibration and causes a damping effect, thus reducing flow-induced vibration. The hole formed in the grid strip function to widen the range of the frequency of the flow-induced vibration caused by vortex sheddings formed around the edges of the grid strip, thus reducing the possibility of the generation of resonance with the natural frequency of the spacer grid.

Abstract: A soft pivot dimple nuclear fuel assembly grid that utilizes a “dog bone” shaped window cutout and radius coining of edges perpendicular to coolant flow, to reduce the susceptibility of fuel rod leaking during the reactor operation. Radius coining allows the fuel rod to smoothly transition over the radiused edge to the flat rod contact section of the dimple. The symmetric “dog bone” shape enables the dimple to pivot during rod loading resulting in improved alignment between the dimple and the fuel rod, thereby minimizing scratching. The “dog bone” shape also allows for a large contact area dimple to be softer than a typical dimple which reduces contact stresses and fretting wear during reactor operations.

Abstract: A truss-reinforced spacer grid and a method of manufacturing the same are provided, in which truss members having a small diameter are woven to form a truss structure surrounded by an external plate, and the truss structure is joined to the external plate to thereby improve the strength of the mechanical structure. The truss-reinforced spacer grid includes a truss structure in which horizontal trusses formed by horizontally weaving a plurality of truss members are vertically disposed at regular intervals, and an external plate is joined with ends of the horizontal trusses and surrounds the truss structure.

Abstract: A spacer grid includes intersecting straps defining cells with springs and dimples arranged to hold fuel rods passing through the cells. The springs are dual cantilevered springs with a bridge section between the distal end of the spring and the base. The distal portion of the spring is less stiff than the bridge section. The bridge section creates a bump which acts as a stop or travel limiter to prevent loss of grip force due to excessive spring deflection.

Abstract: A spacer grid includes intersecting straps defining cells with springs and dimples arranged to hold fuel rods passing through the cells. The direction of the springs switches at a switch point in the spacer grid that is not at the center of the spacer grid. The intersecting straps may include a first set of mutually parallel straps including a first transition strap and a second set of mutually parallel straps including a second transition strap, with the second set intersecting the first set. The springs of the first set of mutually parallel straps face away from the first transition strap, and the springs of the second set of mutually parallel straps face away from the second transition strap. The outer straps in some embodiments include dimples but not springs.

Abstract: A fuel assembly for a nuclear reactor that employs dissimilar materials for the fuel assembly grid and the control rod guide thimbles. The guide thimbles are secured to the grid employing a through grid cell sleeve that is welded to the grid and spot weld rings that are secured over the sleeve and welded directly to the guide tube through windows in the sleeve.

Abstract: The strip is of the type comprising a wall portion for delimiting a cell for receiving a fuel rod and allowing flow of a coolant upwardly through the spacer grid, a spring provided on the wall portion for biasing a fuel rod extending through the cell away from the wall portion, the spring being cut out in the strip and delimited by a slot and a motion limiter formed in the strip on the wall portion to limit motion of a fuel rod received in the cell towards the wall portion against action of the spring. According to one aspect of the invention, the motion limiter is located on an edge of the slot opposite the spring and defines a risen portion on the edge.

Abstract: The strip is of the type comprising a wall portion for delimiting a cell with interlaced strips, a spring formed in the strip and provided on the wall portion for biasing a fuel rod extending through the cell away from the wall portion, the spring comprising a cantilevered tab formed in the strip and a contact portion formed at least partially in the tab and protruding from the tab for contacting a fuel rod received in the cell.

Abstract: Disclosed herein is a spacer grid for a nuclear fuel assembly. The spacer grid has dimples for supporting fuel rods and is formed from grid strips which are assembled in a lattice shape to form lattice cells. Each grid strip has at least one hole which is formed separately from the dimples. Therefore, when coolant is drawn into the fuel assembly, a pressure difference between opposite sides of the holes is reduced, and friction generated between cut edges of the holes and the coolant reduces the magnitude of the vibration and causes a damping effect, thus reducing flow-induced vibration. The hole formed in the grid strip function to widen the range of the frequency of the flow-induced vibration caused by vortex sheddings formed around the edges of the grid strip, thus reducing the possibility of the generation of resonance with the natural frequency of the spacer grid.

Abstract: Disclosed herein is a spacer grid for a nuclear fuel assembly which is formed from grid strips of an improved structure, thus reducing flow-induced high-frequency vibration. The spacer grid has dimples or grid springs for supporting fuel rods and is formed from a plurality of grid strips assembled in a lattice shape to form lattice cells. Each of the grid strips has at least one slot formed in a planar portion of the grid strip separately from the dimple or grid spring. Therefore, characteristics of the vibration of the spacer grid can be set in a variety of different manners so that flow-induced high-frequency vibration can be reduced.

Abstract: A spacer grid for a nuclear fuel assembly for a light water reactor delimits a substantially regular array of cells housing nuclear fuel rods. The spacer grid further including supporting members which project into the cells from the peripheral belt of walls. The inner surface of at least one supporting member has before irradiation a concave shape in a plane transverse to the longitudinal direction. The inner surface of the contact part of the supporting member also has a convex shape in a longitudinal plane orientated radially with respect to the central axis of the corresponding cell before irradiation.

Abstract: A fuel assembly for a nuclear reactor that employs dissimilar materials for the fuel assembly grid and the control rod guide thimbles. The guide thimbles are secured to the grid employing a through grid cell sleeve that is welded to the grid and spot weld rings that are secured over the sleeve and welded directly to the guide tube through windows in the sleeve.

Abstract: A structural skeleton of a nuclear fuel assembly is assembled by inserting guide tubes through a plurality of spacer grids, and performing pulse arc welding to connect the inserted guide tubes and the spacer grids. In the structural skeleton, the spacer grids may comprise intersecting grid straps, and at least some of the grid straps may include tabs that are pulse arc welded to guide tubes. The structural skeleton may include grid retaining rings installed on the guide tubes and pinning some spacer grids, with the grid retaining rings being pulse arc welded to guide tubes. A fuel assembly includes the structural skeleton, a plurality of fuel rods comprising fissile material passing through the spacer grids, and upper and lower end fittings secured to upper and lower ends, respectively, of the guide tubes.

Abstract: A nuclear pressurized water reactor fuel assembly grid that has a plurality of spring-like, resilient, cantilevered members that extend, substantially adjacent each other, from a wall of a grid cell that supports the fuel rods, into the support cell, with a distal end of each member being compressed by the fuel rod passing through the cell so as to exert a lateral force on the fuel rod. The plurality of cantilevered members replace conventional dimples employed in fuel assembly grid support cells.

Abstract: A nuclear fuel assembly spacer grid defining a lattice of cells for receiving fuel rods is provided. The spacer grid includes a peripheral band composed of at least one peripheral strip delimiting a portion of the peripheral contour of the spacer grid, and at least one spacer grid positioning spring elastically deformable and formed in the peripheral band.

Abstract: Fuel spacers include at least one specialized bathtub on an outer perimeter band. Specialized bathtubs include an elastic resistive extension and a corresponding deflection limiter on a same outer face of the perimeter band. The elastic resistive extension provides flexible resistance to the channel, and the deflection limiter provides rigid movement limitation beyond a particular threshold between channel and spacer. The positioning, spring constant, length, number, and other properties of the specialized bathtub can be chosen based on the desired fuel assembly properties and expected transverse loads in fuel shipping and operation against which specialized bathtubs resiliently protect. The specialized bathtubs can be formed from a simplified stamp operation out of the perimeter band. Bathtubs can be placed on any position(s) on the perimeter band of example embodiment spacers used in nuclear fuel assemblies.

Abstract: Example embodiment fuel bundles use multiple types of spacers within the same fuel bundle. The type for each spacer location may be determined based on the axial position of the spacer, the characteristics of the spacer type, and the location and coolant characteristics for the particular example fuel bundle including the spacers. Historic performance data for the particular bundle location, predictive modeling, etc. may be used to determine what spacer types at which locations result in the best operating conditions and margins for example fuel bundles.

Abstract: A spacer grid includes interlocked straps comprising metal sheets or plates welded together to define a spacer grid having a top and bottom. The interlocked straps define a plurality of cells comprising vertical passages connecting the top and bottom of the spacer grid. The cells include: upper dimples proximate to the top of the spacer grid and distal from the mid-plane of the spacer grid; lower dimples proximate to the bottom of the spacer grid and distal from the mid-plane of the spacer grid; cantilevered upper springs having fuel rod engagement surfaces proximate to the top of the spacer grid and distal from the mid-plane of the spacer grid; and cantilevered lower springs having fuel rod engagement surfaces proximate to the bottom of the spacer grid and distal from the mid-plane of the spacer grid.

Abstract: A support grid for a nuclear fuel assembly, the nuclear fuel assembly including a generally cylindrical fuel rod with a diameter, wherein the support grid includes a frame assembly having a plurality of generally circular cells and a plurality of helical frame members. The helical frame members are disposed in the cells and are structured to contact the cell as well as a fuel rod. The helical fuel rod contact portion may have a variable pitch.

Abstract: A spacer grid for dual-cooling nuclear fuel rods arranged at a narrow interval. The spacer grid solves the problem in which, since the dual-cooling nuclear fuel rods are used to improve the cooling performance and stability of nuclear fuel and obtain high burnup and output, the outer diameter of each dual-cooling nuclear fuel rod is increased, and thus the gap between each dual-cooling nuclear fuel rod and the grid strap is decreased. The spacer grid includes first grid straps and second grid straps, which are crossed and arranged in transverse and longitudinal directions at regular intervals and have the shape of a flat strip, and support structures, which are fitted into the first and second grid straps around intersections of the first and second grid straps so as to support the dual-cooling nuclear fuel rods.

Abstract: Reactor component adapted to be used in fission reactors comprising a core (2) consisting of a first material and a layer (3) consisting of a second material. The layer (3) encloses at least partly the core (2). The reactor component is characterized in that the component (1) comprises and intermediate layer (4) between the core (2) and the layer (3). The intermediate layer (4) has a material gradient that comprises a decrease of the concentration of the first material from the core (2) to the layer (3) and an increase of the concentration of the second material from the core (2) to the layer (3).

Abstract: A support grid for a nuclear fuel assembly, the fuel rod assembly having a generally cylindrical fuel rod with a diameter, wherein the support grid includes a frame assembly having a plurality of outer straps and a plurality of helical frame members. The helical frame members have a contact portion structured to contact an adjacent helical frame member and at least one helical fuel rod contact portion with a lesser diameter. The lesser diameter is generally equivalent to the fuel rod diameter such that a fuel rod disposed in the helical frame member would engage the inner helical frame member at helical fuel rod contact portion. The helical frame members are coupled to each other at the contact portions thereby forming a grid. The plurality of outer straps are disposed about the perimeter of the helical frame members.

Abstract: Disclosed is a spacer grid assembly with mixing vanes supporting fuel rods of nuclear fuel assemblies and mixing coolant that flows around the fuel rods, and more particularly, a spacer grid equipped with mixing vanes that mix coolant flowing around fuel rods. The spacer grid with hydraulically balanced mixing vane patterns, in the spacer grid equipped with a strip dividing a plurality of unit grid cells and a plurality of springs, protruded in uniform directions of vertical and horizontal directions on a grid surface of the strip and supporting nuclear fuel rods, which includes: a plurality of mixing vanes protruded to the downstream of coolant on an upper end of the inner grid surface, wherein positions and directions of the mixing vanes are formed in regular patterns on the spacer grid. Thus, it can minimize coolant flow induced vibration of the spacer grid by balancing hydraulic load generated by the mixing vanes, around the center of the spacer grids.

Abstract: A spacer grid for a nuclear fuel assembly that exhibits increased crush strength. Each grid strap at the ligaments that support fuel rods has a spring or dimple to support the fuel rods under anticipated external loads during shipping and handling or in a seismic event. One or more elongated embossed ribs are provided on each of the fuel rod grid strap support ligaments to increase its moment of inertia by forming various shapes on the ligaments of the grid strap. Preferably, the ribs have a streamlined shape to prevent any excessive pressure drop. In this manner, the crush strength of a conventional short grid strap is increased without meaningful additional manufacturing costs or adverse effects to the neutron economy of the grid.

Abstract: A spacer grid can be applied to close-spaced nuclear fuel rods. The spacer grid is directed to solve the problem in which, as the outer diameter of each nuclear fuel rod increases due to the use of dual-cooled nuclear fuel rods for improving cooling performance and obtaining high combustion and high output power, the gap between the neighboring nuclear fuel rods is narrowed to thus make it impossible to use an existing spacer grid. The spacer grid is a combination of unit grid straps, each of which has supports for supporting each of the nuclear fuel rods set in a narrow array and has a sheet shape, which are combined with each other. The supports are located at positions shifted from the longitudinal central line of each unit grid strap toward sub-channels.

Abstract: A protector bottom grid for a nuclear fuel assembly that includes three laterally staggered and horizontally oriented protrusions that extend into the fuel rod cell of a support grid below a vertically oriented spring. The three staggered protrusions extend into the cell a distance that maintains a space between the protrusions and the fuel rod. The vertically oriented spring biases the fuel rod against a dimple extending from the opposite cell wall that is at an elevation just above the spring. The protrusions below the spring trap incoming debris in the area of the fuel rod end cap and protect the fuel rod cladding from fretting.

Abstract: Fuel supports have specially configured flow paths useable in reactor cores to achieve desired levels of flow at given positions. Any number of differently-configured inlet orifices, from three to hundreds, are useable in a given core. Inlet orifice configuration may include diameter sizing or presence of flow blockages such as filters, venturis, choke plates, and/or obstructions. Fuel supports may be positioned within a core plate in the nuclear reactor, with openings for a control blade and instrumentation tubes to pass through or between the fuel supports. Different fuel support configurations may be used at outer core periphery, inner core periphery, and central core portions. Example methods configure fuel support characteristics by examining the effect of modifying flow loss coefficients at particular bundle locations and configuring associated inlet orifices to achieve the modified flow loss coefficients, if the effect is a positive one.

Abstract: Disclosed is a zirconium alloy material having high corrosion resistance regardless of thermal history during its manufacturing process. The zirconium alloy material is obtained by providing a zirconium alloy containing on the mass basis: 0.001% to 1.9% of Sn, 0.01% to 0.3% of Fe, 0.01% to 0.3% of Cr, 0.001% to 0.3% of Ni, 0.001% to 3.0% of Nb, 0.027% or less of C, 0.025% or less of N, 4.5% or less of Hf and 0.16% or less of O with the remainder being inevitable impurities and zirconium, being formed of a bulk alloy and a surface layer, in which the surface layer has a plastic strain of 3 or more or a Vickers hardness of 260 HV or more and an arithmetic mean surface roughness Ra of 0.2 ?m or less.

Abstract: A dual-cooled fuel rod's spacer grid with upper and lower dimples, including a blocking area of a flow passage that coolant flows through is reduced and dual-cooled fuel rods are supported, and reduces a turbulent flow of the coolant as well as vibrations of the dual-cooled fuel rods, thereby lessening fretting damage done to the rods. The spacer grid includes a plurality of unit grid straps, each of which includes a body disposed in a vertical direction, an upper dimple protruding from an upper portion of the body, and a lower dimple spaced apart from the upper dimple in a downward direction and protruding from a lower portion of the body. The unit grid straps form a grid structure that have inner grid holes into which the dual-cooled fuel rods are held, and the held dual-cooled fuel rods are each supported in four directions by the upper and lower dimples.

Abstract: A fuel assembly is charged in a reactor core of a nuclear reactor using a liquid metal as a coolant, and includes a wrapper tube storing a plurality of fuel pins and including an entrance nozzle for introducing the coolant and an operation handling head, grids disposed in the wrapper tube to support the fuel pins in the radial direction of the wrapper tube, liner tubes inserted in the wrapper tube to fixedly hold the respective grids in the axial direction of the wrapper tube, and a fixing device for fixing the grids and the liner tubes in the radial direction of the wrapper tube.

Abstract: A nuclear fuel assembly grid having a vertical, elongated, split spring on each wall of the cells that support fuel rods to provide eight, co-planar, point contacts of support for the fuel rod.

Abstract: A fuel assembly is charged in a reactor core of a nuclear reactor using a liquid metal as a coolant and includes a wrapper tube storing a plurality of fuel pins and including an entrance nozzle at a lower end thereof for introducing the coolant and an operation handling head at an upper end thereof, grids for supporting the plurality of fuel pins in the wrapper tube in the radial direction of the wrapper tube, liner tubes inserted in the wrapper tube for fixedly holding the grids in the axial direction of the wrapper tube, and peripheral flow suppressing members disposed in a peripheral flow passage extending between peripherally disposed ones of the fuel pins and the wrapper tube over a length corresponding to a heat generation length, which is a length range in the axial direction of the fuel pins storing a radioactive fuel material.

Abstract: Example embodiment fuel bundles use multiple types of spacers within the same fuel bundle. The type for each spacer location may be determined based on the axial position of the spacer, the characteristics of the spacer type, and the location and coolant characteristics for the particular example fuel bundle including the spacers. Historic performance data for the particular bundle location, predictive modeling, etc. may be used to determine what spacer types at which locations result in the best operating conditions and margins for example fuel bundles.

Abstract: A support grid for a nuclear fuel assembly, the fuel rod assembly having a generally cylindrical fuel rod with a diameter, wherein the support grid includes a frame assembly having a plurality of outer straps and a plurality of helical frame members. The helical frame members have a contact portion structured to contact an adjacent helical frame member and at least one helical fuel rod contact portion with a lesser diameter. The lesser diameter is generally equivalent to the fuel rod diameter such that a fuel rod disposed in the helical frame member would engage the inner helical frame member at helical fuel rod contact portion. The helical frame members are coupled to each other at the contact portions thereby forming a grid. The plurality of outer straps are disposed about the perimeter of the helical frame members.

Abstract: A nuclear fuel assembly support grid formed from an array of a plurality of orthogonally arranged straps in an egg-crate configuration with angled trailing and/or leading edges that are designed to break the correlation of vortices shed from the edges of the grid straps by varying the phase of the vortices to avoid resonant vibration of the straps.

Abstract: A nuclear fuel assembly support grid formed from an array of a plurality of orthogonally arranged straps in an egg-crate configuration with angled trailing and/or leading edges that are designed to break the correlation of vortices shed from the edges of the grid straps by varying the phase of the vortices to avoid resonant vibration of the straps.

Abstract: A protector bottom grid for a nuclear fuel assembly that includes three laterally staggered and horizontally oriented protrusions that extend into the fuel rod cell of a support grid below a vertically oriented spring. The three staggered protrusions extend into the cell a distance that maintains a space between the protrusions and the fuel rod. The vertically oriented spring biases the fuel rod against a dimple extending from the opposite cell wall that is at an elevation just above the spring. The protrusions below the spring trap incoming debris in the area of the fuel rod end cap and protect the fuel rod cladding from fretting.

Abstract: The present invention relates to an anti-fretting wear spacer grid having a plurality of canoe-shaped springs formed thereon, wherein each of the canoe-shaped springs includes: a fuel rod-contacting part having a flat surface having a predetermined longitudinal length so as to have linear contact with the fuel rod; a curved face-connecting part formed on the upper and lower portions of the fuel rod-contacting part; a leg-connecting part formed on the end portion of the curved face-connecting part; and legs each being formed of a plate shape having a predetermined length and connecting the both sides of the leg-connecting part with one unit grid cell surface.