Abstract: A pressurized water nuclear reactor pressure vessel has an upper core support plate with passageways for the passage of coolant, an upper support plate above the upper core support plate, and peripheral hollow support columns extending upwardly above the passageways in the upper core support plate for supporting the upper support plate above the upper core support plate and for guiding coolant from the passageways into the plenum. Each peripheral support column has a peripherally slotted upper portion for guiding the coolant in the peripheral support column into the plenum and an unslotted lower portion.

Abstract: A fuel assembly and a spacer for a boiling reactor comprises an elongated fuel channel which is connected to a coolant intended to flow therethrough. In the fuel channel there is arranged a bundle of also elongated fuel rods retained by a plurality of spacers. The spacers have an external spacer frame which is provided all around with a plurality of openings. There is arranged, at the inside of the spacer frame, an edge which is obliquely positioned in relation to the longitudinal direction of the fuel assembly and which extends in an inclined manner in a direction downstream of the spacer and toward the corner of the spacer to deflect coolant to the fuel rods arranged at these corners.

Abstract: A spacer for use with a fuel bundle in a nuclear reactor includes a matrix of ferrules for surrounding individual fuel rods within a bundle; a band surrounding the matrix and defining a peripheral wall of the spacer, the band having an upper edge; and a plurality of laterally spaced flow tabs extending upwardly from the upper edge, each flow tab having a lower substantially vertical portion and an upper inclined portion extending away from the vertical portion. The vertical portion and the inclined portion are formed with centrally located creases which define reverse bends in the upper and lower portions of the tab.

Abstract: A control system for avoiding coupled neutronic-thermal hydraulic instabilities during maneuvering of a boiling water nuclear reactor that determines the average elevation in the reactor core of the coolant boiling boundary, and avoids instabilities by maintaining the core average coolant boiling boundary elevation above a target value, which is dependent on reactor design specifics but may be about four feet, in core power-flow operating regions which are subject to instabilities. The system may be implemented without physical modification of existing reactors or reactor instrumentation and control systems through use of the reactor core monitoring computer, which typically has available all core parameters necessary for the computations required in the invention.

Abstract: A fuel assembly is presented in which a plurality of support grids are disposed along the longitudinal direction of the fuel rods. The straps forming the grid cells of the support grids are provided with mixing vanes for generating turbulent flow of the cooling water passing through the grid cells. In a plan view of the support girds, each of the mixing vanes protrudes inwardly of the grid cells and is disposed along a positive diagonal direction and a negative diagonal direction. This configuration of the mixing vanes are effective in preventing the generation of systematic vibrations in the fuel assembly by canceling the effects of the turbulent flows of the cooling water. The direction of protrusion of the mixing vanes can be in two diagonal directions within one support grid, or it can be unidirectional along either diagonal direction within one support grid.

Abstract: A fuel assembly comprises a plurality of fuel rods, tie plates for holding both ends of these fuel rods, and spacers which support these fuel rods. The spacer comprises a plurality of cells into which the fuel rods are inserted respectively, the adjacent cells being joined to each other at axial ends thereof, whereby a space between these cells being held or retained, and a plurality of loop springs held respectively on the cells. Each of the loop springs has a pair of resilient members which are located within the pair of adjacent cells and which urge the fuel rods in a radial direction, and a pair of connections which connect axial ends of the resilient members to each other. Each of the connections have a passage through which coolant flows axially and which is defined by a closed peripheral wall. The closed peripheral wall is not uniform in thickness. The pair of adjacent cells have at axial end portions of peripheral walls openings for accommodating or receiving the connections of the loop spring.

Abstract: A boiling water reactor fuel assembly having a lowered fuel rod support plate and increased fuel rod length while restraining the fuel rods against lateral vibration.

Abstract: A unitary one-piece lower tie plate grid has a lower portion and an upper portion for supporting the fuel rods. The lower tie plate grid includes cylindrical boss portions extending upwardly from the lower grid portion and arranged in square matrices for receiving the lower end plugs of the fuel rods. Web portions extending upwardly from the lower tie plate portion interconnect the boss portions along the sides of the matrices. The lower grid portion includes a plurality of openings which open into the flow spaces defined by the convex portions of the bosses and the webs within each square matrix of the upper portion of the tie plate. Coolant flows through the openings into the flow spaces for further flow upwardly about the fuel rods. The openings are radiussed adjacent their lower ends and have divergent side walls downstream of a throat area to define a flow venturi.

Abstract: Disclosed is a grid structure for supporting fuel rods in a nuclear reactor. The grid structure is formed of a plurality of interconnected thin metal grid straps that are welded or brazed together to provide a structural network of interconnected open grid cells, similar to an "egg crate divider". The grid straps are provided at regular intervals, corresponding to the width of a grid cell, with pairs of spaced, substantially horizontal, slotted spring-like projections and a substantially X-shaped spring-like projection vertically intermediate the horizontal projections. The spring-like projections are designed to support and hold the fuel rods within the grid cells under both balanced and unbalanced forces acting on the fuel rod assembly while it is in service, surrounded by coolant in the nuclear reactor.

Abstract: A nuclear fuel rod spacer grid is formed of slottedly interlocked sets of flat strips. One set of strips is formed with integral coplanar tab portions which have one or more edge portions bent at angles to form integral mixing vanes.

Abstract: A unitary one-piece lower tie plate grid has a lower portion and an upper portion for supporting the fuel rods. The lower tie plate grid includes cylindrical boss portions arranged in square matrices for receiving the lower end plugs of the fuel rods. Web portions interconnect the boss portions along the sides of the matrices. The lower grid portion includes a plurality of openings which open into the flow spaces defined by the convex portions of the bosses and the webs within each square matrix of the upper portion of the tie plate. Coolant flows through the lower flow openings into the flow spaces for further flow upwardly about the fuel rods. The openings are defined by the convex lower portions of the bosses and webs, as well as projections which extend laterally inwardly from the convex surfaces of the lower boss portions toward a central region in the middle of the square matrix.

Abstract: A fuel assembly includes a cluster of mutually parallel fuel rods. A fuel assembly channel laterally surrounds the cluster of fuel rods and has a substantially rectangular cross section and flat channel walls. Grid-like spacers having meshes formed therein each receive a respective one of the fuel rods for guiding the fuel rods in a plurality of axial positions. At least one support spring laterally supports each respective one of the fuel rods in the mesh guiding the fuel rod. Each of the spacers have inner ribs being aligned parallel to the fuel rods and outer peripheral ribs opposite the channel walls. At least some of the inner ribs are fastened to the peripheral ribs, and the outer peripheral ribs are joined together only by the inner ribs.

Abstract: A spacer for retaining a number of elongated fuel rods into a bundle to be placed in a nuclear reactor of BWR or PWR type. The bundle is intended to be traversed in the longitudinal direction by a coolant. The spacer includes a number of cells for the fuel rods surrounded by an outer frame which is formed from a first band standing on edge. This band has possibly been extended by a skirt arranged on the upstream side of the spacer. The band or skirt edge of the spacer located on the upstream side thereof is provided with guiding tabs which are formed from plate flaps which lie in planes which extend in parallel with the flow direction of the coolant and one side edge of which slantingly extends from the first band or skirt edge in an upstream direction towards the center of the spacer.

Abstract: In a fuel assembly, rods are disposed in meshes of a grid. Crossing points of the grid are distributed in a checker-board-like manner, partly in an upstream crossing plane and partly in a downstream crossing plane. Webs of the grid run in zigzag form between the two planes. As a result, flow resistance which is produced by the webs and/or by mixing vanes disposed thereon and by flow turbulences is shifted into different axial planes and is considerably reduced.

Abstract: In a boiling water nuclear reactor fuel bundle, the use of a shortened ferrule spacer in combination with overlying swirl vanes is set forth. In the preferred embodiment, the shortened ferrule spacer is placed under any swirl vanes and has an individual ferrule surrounding each fuel rod at the elevation of the spacer. Each ferrule is given both minimum side wall thickness in the range of 0.020 inches or less as well as reduced height in the order of 0.9 inch or less. The reduced height and thickness of the ferrule spacer is required to maintain pressure drop within acceptable limits and still tends to augment the required liquid film for steam generation over the fuel rod lengths downstream (that is immediately above) the spacer. At the same time, the swirl vane structure is placed immediately above the ferrule spacer overlying the so-called subchannel region of the ferrule spacer between the fuel rods.

Abstract: A grid structure is presented in which grid cells are formed by orthogonally intersecting straps prefitted in the longitudinal direction with a plurality of slitted spring frame members. Therefore, when the straps are assembled, the spring frame members are also orthogonally intersected. The spring frame members are made of Inconel and provided with welding tabs while the straps are made of zircalloy and provided with their own welding tabs. Therefore, welding can be performed to firmly join the spring frame members to each other while the straps can also be welded firmly to weld the like metals. The spring sections are thus firmly joined and attached to the straps which are firmly joined. The grid of this configuration thus provides an excellent service life without the losing The fuel rod retaining power, which would result from neutron radiation and thermal damages on holding devices made of zircalloy.

Abstract: According to one embodiment, a fuel assembly includes a bundle of fuel rods. Approximately mutually parallel upright webs extend between the fuel rods in a plane approximately perpendicular to the fuel rods. The webs have upper edges and tabs on the upper edges. The tabs have ends and the tabs are twisted continuously more severely toward the ends away from the webs. According to another embodiment, the fuel assembly includes a bundle of fuel rods defining flow channels and an axis approximately parallel to the fuel rods. Lengthwise webs extend approximately parallel to one another between the fuel rods in a first plane extending approximately perpendicular to the fuel rods. Crosswise webs, which extend approximately perpendicularly to the lengthwise webs, are disposed in a second plane approximately parallel to the first plane and join the lengthwise webs to one another between the fuel rods. Tabs are twisted about the axis and disposed in the flow channels.

Abstract: Spacers (10) with a cell-formed lattice-work for retaining parallel elongated elements such as fuel rods (5) into a bundle in a nuclear reactor fuel assembly are arranged in a suitable spaced relationship to each other along the bundle, and the cells are formed from tubular sleeves (1). Each one of these sleeves (1) offers a passage for one of the elements in order to fix the elements in relation to each other. Substantially half the number of sleeves (1) in a spacer (10), distributed evenly over the cross section of the bundle, are located in a first plane across the bundle and are joined to each other inside a first frame (11) surrounding the bundle, thereby forming a lattice of sleeves (1) and gaps (13). The remaining sleeves (1) of the spacer (10) are joined together inside a second frame (12) surrounding the bundle and are located in a second plane, separate from the first plane, across the bundle.

Abstract: A method of manufacturing fuel channels made of zirconium-based alloy by combining heat treatment, warm forming and thermal sizing. Fuel channel strip material is heated to a temperature which initiates the transformation from a hexagonal close-packed to a body-centered cubic crystallographic phase and then quenched at a rate which initiates transformation to a hexagonal close-packed crystallographic phase having a texture factor f.sub.L =0.28-0.38. The heat-treated strips are formed into fuel channel components by bending at an elevated temperature sufficient to increase the ductility of the strip material. After the fuel channel components are welded together, the fuel channel is annealed by thermal sizing.

Abstract: An all Zircaloy spacer having integral springs and single metallic layer spacer thickness between fuel rods is disclosed. Each spacer cell includes upper and lower octagonal crowns. These octagonal crowns have a full panel height adjoining the defined sub-channel volume between fuel rods and half panel heights adjoining adjacent cells. The crowns at opposite ends of each octagonal spacer cell are designed to interleave to form a single wall thickness of the spacer material. Accordingly, half wall heights at one crown are defined toward the spacer cell while half wall heights at the other crown end are defined away from the spacer cell. By inverting and adjoining the respective spacer cells at their respective crowns, the crowns form upper and lower crown matrices holding adjoining cells of the spacer together. From two adjacent sides of the four sub-channel adjacent full height sides, cell legs extend between the crowns with upper and lower stops immediately adjacent the crowns.

Abstract: A mixer grid for a nuclear reactor fuel assembly has a plurality of strips arranged in interlocking rows and columns defining a plurality of cells. A stopper is fixed to each corner of each cell for both directing coolant flow, providing coolant mixing and providing a smooth contact surface for the fuel rod. The stopper is either cone-shaped or cylindrical for directing and channeling coolant flow. The stopper also has a smooth, flat chamfered surface for contacting the fuel rod and minimizing damage upon the shifting of the fuel rod. The grid is attached to the nuclear reactor fuel assembly by using guide cells comprising a plurality of support arches for welding to the nuclear reactor fuel assembly.

Abstract: A fuel spacer for a fuel assembly comprises a plurality of tubular ferrules each forming a fuel rod insertion passage, a belt-like support member for supporting the tubular ferrules bundled in a lattice arrangement and a spring member for axially supporting the fuel rods disposed in the ferrules. The adjoining ferrules are joined together horizontally, each of the ferrules has at least one end to which a plurality of cutout portions are formed circumferentially of the end portion and at least one flat portion is formed between adjoining petal portions at which the adjoining ferrules are spot welded. Each of the cutout portions and petal portions of the tubular ferrule has various shapes such as trapezoidal, rectangular, triangular, V or M shape. The cutout portions and petal portions may be formed at both axial ends of the tubular ferrule.

Abstract: A boiling water reactor includes fuel assemblies having a case containing fuel rods which are parallel to walls of the case. Flow subchannels are formed by each four of the fuel rods. At least two and preferably four vanes in the flow subchannels are tapered in a vertical coolant flow direction and are three-dimensionally curved in such a way as to generate a swirl in the coolant flow. It is therefore possible to obtain a relatively high output from the fuel assembly.

Abstract: In order to obviate the use of supporting rods, an upper end piece of a coolant tube penetrates a fuel assembly head of a nuclear reactor fuel assembly and is supported on the fuel assembly head. A lower end piece of the coolant tube is fastened to and supported by a fuel assembly foot, in particular with rods of partial lengths. A supporting skeleton therefore includes the foot and the coolant tube with spacers. The fuel assembly head and a handle are placed on the skeleton and screwed onto the coolant tube after fuel rods are pushed into meshes of the spacer.

Abstract: A reactor core with each fuel rod surrounded by an individual cylindrical channel is disclosed. This individual channel on each fuel rod provides thermal hydraulic and heat transfer advantages to enable all fuel rods within the fuel bundle to uniformly approach their own thermal limits. The preferred fuel rod pitch is a triangular pitch between the individual fuel rods as they are discretely surrounded by their own channel. The new triangular geometry provides for more uniform (flat) power distributions within all fuel rods--and hence all groups of fuel rods. Bypass flow is introduced uniformly between the fuel rod channels, rather than heterogeneously in the channel gap and water rods as in present BWR fuel designs. Individual fuel rod channels can be orificed differently, as required, to match inlet flow to fuel rod power output to maintain uniformity between all fuel rods as they approach their respective thermal limits.

Abstract: The grids (14) of a nuclear fuel assembly (10) include an outer strip, or perimeter plate (100), having outwardly projecting formations (104,106) spaced from the side edges (110) of the internal grid strips (108), for resiliently absorbing lateral forces before such forces are transferred directly to the internal strips. The load dissipating feature of the present invention can be enhanced by providing orifices (552) in the substantially flat, central region (502) of each perimeter plate. This produces an hydraulic damping effect that can be pre-established by selecting the orifice sizes for a given set of impact load conditions.

Abstract: A nuclear fuel assembly grid (100) made from a plurality of interlaced corrugated metal strips (102-116) forming an egg-crate configuration so as to define plurality of four-walled cells (118) for receiving respective individual fuel rods (120). The spaced apart vertical bend lines (160,162) of the currugation define vertices (130,132) and consecutive body panels (164,166) which alternate generally inwardly and outwardly between consecutive bend lines. A vertical slot (168) extending from one of the strip upper or lower edges (176) into each panel midway between consecutive bend lines, and overlapping a slot from an interlaced strip to form an hourglass-shaped cell having opposed convex walls and opposed concave walls and four 90 degree corners (150). Spring (148) and stop (153) structure projects from each wall of a cell, for centering and supporting the fuel rod within the cell.

Abstract: Fuel assembly including deflector vanes for deflecting a component of a fluid stream flowing past such fuel assembly. The fuel assembly comprises a lattice member having rhombic-shaped rod cells and generally rhombic-shaped thimble cells therethrough. A plurality of parallel fuel rods extend through respective ones of the rod cells and a plurality of parallel control rod guide thimble tubes extend through respective ones of the thimble cells. A plurality of deflector vanes are associated with each rod cell and are integrally attached thereto on the upstream edge of each rod cell. Each deflector vane extends above its associated rod cell and curvilinearly protrudes partially over the rod cell for deflecting a component of the fluid stream onto the exterior surface of the fuel rod that extends through the rod cell.

Abstract: A spacer grid for a nuclear fuel assembly. A plurality of metal strips are interleaved on edge to define a plurality of individual cells. Each cell is sized to receive a single nuclear fuel rod. A series of projections, grid mixing vanes, extend from one edge of each metal strip and are alternately bent to extend on opposite sides of the metal strip. The alternating projections provide four grid mixing vanes that extend into each individual cell.

Abstract: A spacer for a nuclear reactor fuel assembly includes a cell-formed lattice-work for retaining parallel, elongated elements such as fuel rods (4) into a bundle of substantially square cross section. The cells are formed from tubular, preferably round sleeves (1). Each one of these offers a passage for one of the elements for mutually fixing these elements. Each spacer is formed from two sub-spacers (5) somewhat spaced-apart from each other in the longitudinal direction of the bundle. A first sub-spacer in a pair fixes elements lying substantially on one side of a diagonal through the bundle, and a second sub-spacer fixes the other elements such that elements passing through the sleeves (1) of the first sub-spacer pass, possibly with some exception, at the side of the sleeves in the second sub-spacer and vice versa.

Abstract: A flow deflector grid (10) for a nuclear fuel assembly, comprising a plurality of metal strips (12,14) which intersect in a regular array to form an egg-crate type lattice, which defines a plurality of coolant flow channels (16). Each channel has sidewalls (42,44) defined by the strips, a height dimension defined by the height of the strips, a plurality of corners (46) defined by the strip intersections (26), a channel central axis parallel to the height dimension, and a flow cross section normal to the channel axis for coaxially receiving a fuel rod (18) spaced within the channel sidewalls. A unitary flow deflector member (30) is attached to and situated in the corner of each channel so as to be cradled between first and second sidewalls.

Abstract: A low pressure drop spacer for positioning and retaining the fuel rods of a nuclear fuel assembly in which a plurality of upper and lower spring forks which extend through apertures in the side wall of the spacer into the assembly and through apertures in grid members which divide the assembly. The intersection and superposition of the spring forks, side wall and grid members form fuel rod passageways through which the fuel rods extend.

Abstract: A nuclear fuel assembly for a BWR comprises a plurality of fuel rods, a polygonal channel box surrounding the fuel rods, a plurality of spacers axially spaced from each other and each keeping the fuel rods laterally spaced from each other, and a plurality of vanes disposed only in a region at and around a corner within the channel box, for generating swirling flows in the region to thicken a liquid film on each fuel rod in the region.

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: In a fuel bundle for a boiling water nuclear reactor, modification of the spacers at the peripheral spacer band is made to maintain a more uniform spacing of the peripheral fuel rods from the channel walls to avoid critical power limitations. The conventional fuel bundle construction include a plurality of side-by-side sealed vertically disposed nuclear fuel rods in a square array supported at a lower tie plate, at least some of the fuel rods fastened to an upper tie plate, and held in designed spaced apart relation as a unitary mass by intermittent vertically placed spacers. A square sectioned channel surrounds the upper tie plate, the lower tie plate, and the fuel rods and spacers therebetween. The square sectioned channel functions to confined fluid flow interior of the fuel bundle between the tie plates and through the fuel rods. At the same time, the channel separates a core bypass region exterior of the channel having high moderator density from the flow path interior of the fuel bundle.

Abstract: A nuclear fuel assembly grid (1) has a plurality of flat strips (10,12) that are orthogonally interlaced along vertical slots (38,60) through their upper or lower edges and welded together to form an egg crate-like array of four-walled cells (14) for receiving respective fuel rods (16), each cell including springs (20,30) and arches (32,34) projecting from the walls for contacting and supporting a respective fuel rod in the interior of the cell. At least some of the cells having flow deflection vanes (36,56) projecting integrally from a cell wall into the interior of the cell without contacting the fuel rod. Preferably, the vane is bent along a bend line (52) that is parallel to the upper edge (24) of the strip, into the interior of the cell, thereby forming an angle of between about 15 degrees and 30 degrees relative to the plane defined by the body, or plate portion of the strip.

Abstract: The grid comprises two sets of straps intersecting and fixed at their points of intersection, delimiting cells designed to be crossed some by thimble guides and the others by fuel rods, fitted with mixing vanes. It is provided with a surround carrying guide vanes, connected to at least some of the thimble guides. It is suitable for use in fuel assemblies for pressurized water reactors.

Abstract: A boiling water reactor fuel rod assembly is provided having a plurality of fuel rod spacers which are slidably receivable within an outer channel. Each of the rod spacers is formed of at least one lattice which defines a plurality of fuel rod retaining cells. The lattice is constructed of a plurality of pairs of oppositely facing springy support strips, with each support strip having a plurality of spring-loaded indentations. In an unloaded condition, oppositely facing indentations of each pair of strips, which define each cell, are displaced closer to one another. In a loaded condition, the oppositely facing cell indentations are forced away from each other by the fuel rods so that the springloaded indentations support and retain the fuel rods.

Abstract: A fuel assembly included a plurality of fuel rods, fuel spacers for maintaining gaps between the fuel rods and a channel box. The channel box includes spacer support portions projecting inwardly from an inner surface of the channel box and supporting the fuel spacer in a transverse direction and creep deformation inhibition portions disposed at the lower end portion of the channel box and projecting inwardly. The distance between the spacer support portions disposed to oppose one another in a horizontal direction is smaller than the distance between the creep deformation inhibition portions opposing one another in the horizontal direction.

Abstract: A spacer sleeve for positioning and restraining a nuclear fuel rod in a nuclear fuel assembly, having a thin walled tubular member having an inner wall and an outer end, and extending a height from a lower end to an upper end and being positioned around the fuel rod to form an unrestricted coolant flow passage along the height of the tubular member, the flow passage having a cross-sectional flow area formed between the fuel rod cladding and the inner wall of the tubular member, and a thin tab extending from the tubular member into the unrestricted flow area and secured to a portion of the cladding of the fuel rod.

Abstract: Part length water regions are located above part length fuel rods in boiling water nuclear reactor fuel bundles. The part length water regions include discrete containers having entry ports at the top of the part length water regions for capturing water, and vent ports for permitting internally generated steam to escape. The advantages of improved neutron moderation in the upper portion of the fuel assembly are maintained while the uranium fuel removal requirements are minimized.

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 fuel assembly for a boiling water reactor includes an elongated box extending between a top part and a bottom part, having box walls with flat outer surfaces defining a polygonal outer cross section with rounded corners, an interior and a longitudinal axis. A bundle of fuel rods is disposed in the box and aligned parallel to one another and to the longitudinal axis of the box. The fuel rods are disposed beside one another in rows parallel to the box walls. The box walls have reinforcements protruding into the interior in the vicinity of the rounded corners defining a relatively increased wall thickness, and the box walls have a relatively reduced wall thickness between the reinforcements.

Abstract: A fuel assembly for a light-water nuclear reactor includes a plurality of vertical fuel rods (10, 42) which are arranged, in spaced relationship in a lateral direction, between a bottom tie plate (11, 44) and a top tie plate (12, 43), the bottom tie plate, defining through-going vertical channels (50) for conducting water through the bottom tie plate and into the spaces between the fuel rods. The bottom tie plate also defines horizontal channels (51, 52) which cross the vertical channels and which are preferably arranged, at edges (54) on the bottom tie plate, in open communication with the spaces between the fuel rods. Helical springs (61, 62) with horizontal symmetry axis are arranged in at least some of the horizontal channels where the horizontal channels cross the vertical channel so as to trap debris in the water passing upwardly through the through-going vertical channels.

Abstract: A fuel assembly (1) for a nuclear reactor of pressurized-water type with a number of fuel rods (2) retained into a bundle by means of spacers (3) between a top nozzle (4) and a bottom nozzle (5) which includes a plurality of openings for a coolant flow to the fuel rods (2). A partial fuel box (7) is providing at at least the lower part of the fuel assembly and extending from the bottom nozzle (5) and at least up past the lowermost ordinary spacer (3) of the bundle.

Abstract: There is provided a method of manufacturing a grid for a nuclear fuel assembly, the grid having at least two crossed sets of mutually parallel plates which define cells, some of which receive guide tubes and others receive fuel rods, the plates being provided with boss means for limiting the amount of movement available to the rods relative to the nodes of a regular array. The plates are formed with bosses projecting radially inwardly into each cell for receiving a fuel rod by such an amount that they define a passage having a size at least equal to a minimum diameter of the fuel rods. Then the bosses are deformed radially outwardly for imparting to each passage a predetermined radial size, slightly higher than that of one fuel rod and determined by a gauge.

Abstract: A swirl vane is disclosed for addition to a spring metal grid spacer utilized with a conventional nuclear boiling water nuclear reactor. The spring metal spacer includes a matrix of fuel rod containing cells. Each cell has at least one spring leg and at least two fuel rod encircling arms. The spring leg functions to bias a fuel rod contained within the cell at the spacer to one side of the cell. The two rod encircling arms define stops against which the fuel rods are biased. The cells themselves are welded into a unitary matrix and preferably surrounded by a metallic band. The improved swirl vane of this invention includes an "I" shaped spring steel strip. This strip includes top and bottom tabs for engaging the respective top and bottom grid structure of the spacer. The "I" shaped strip is then twisted to provide the swirl vane surface, this twisting being preferably slightly less than or greater than the total twisting required.

Abstract: To provide quality assurance inspection of the dimensional characteristics of cells to be incorporated in spacers utilized in nuclear fuel bundles to establish critical spacings between fuel rods, a cell is placed in a fixture dimensioned to gauge the outer dimensions of the cell. A fuel rod-simulating pin is then inserted through the cell to rest on fuel rod-positioning stops formed on the cell. "Go, no go" feeler gauges then check the dimensions of the gaps between the fixture and pin.

Abstract: The additional mixing grid has no belt and comprises at least two sets of crossed plates that are fixed to each other at their cross-points, the plates being fitted with fins for stirring the coolant, and delimiting cells, some for receiving guide tubes and the others for receiving fuel rods. Each plate is provided, on each of the faces of those internal cells that receive the rods, with bosses that project sufficiently little to leave radial clearance for the rods passing through the cells and the projection of the bosses is proportioned relative to the projection of the fins so that in the event of bending vibration the rods come into contact with the bosses without reaching the fins, the lengths of the plates being such that the footprint of the additional grid is less than the footprint of the polygon constituting the virtual envelope of the rods.

Abstract: In a channel contained fuel bundle for a boiling water nuclear reactor, an improved channel is disclosed. The channel contains a plurality of fuel rods held in spaced apart relation by at least upper and lower tie-plates and/or spacers. In the reactor, the channel contains fuel rods extending between a lower support plate and an upper support grid. When the reactor is operating, the channel confines water flow intimately about the rod bundle on the inside and assures steam generation in a predictable pattern. Water exterior of the channel is at a different and typically lower pressure. To accommodate control blades (which control the fission process) outside of the fuel bundles, the channel is provided with a polygon cross section, most typically a square cross section. In operation, the flat walls tend to bulge due to primarily pressure effects but also due to thermal and radiation effects.