Abstract: A steam/water separating device for a nuclear fuel bundle is located in a vent volume above part-length rods and includes a helical swirl vane. In one form, the swirl device lies below a vent tube and a transition element for flowing liquid laterally outwardly into the interstices of the fuel rods and steam upwardly within the vent tube. In another form, the vane depends from a cylindrical barrel open at its lower end. An annular pick-off tube extends into the open upper end of the barrel and lies in communication through a transition element with a superposed steam vent tube. An annular outlet is defined between the barrel and pick-off tube and the transition element deflects coolant water flowing through the annular outlet in a lateral outward direction for flow into the interstices of and onto the full-length fuel rods. Steam flows upwardly in the barrel through the pick-off tube into the steam vent tube.

Abstract: In order to reduce the flow resistance of a coolant flowing through a passage in a support plate of a boiling water reactor and entering a transition piece at a lower end of a fuel assembly resting on the support plate, a lower rim of the transition piece forms a conically tapered surface which fits into a corresponding conical counter-surface at an upper edge of the passage. The lower rim of the transition piece forms a circular inlet which is concentric with the passage and has a size equal to or slightly larger than the passage. Fingers protruding laterally into the passage and extending down into the passage are used to center the lower rim within the passage. Additionally, end caps of the fuel rods may be stream-lined and the lower tie plate of the fuel assembly may be spaced apart from an inner surface of a fuel channel by a plurality of ribs which form a plurality of peripheral through holes on each of the four inner surfaces of the rectangular-shaped fuel channel.

Abstract: A swirler is releasably attached to a spacer and lies in the opening through the spacer lying above a part-length fuel rod in a nuclear fuel bundle. Adjacent ferrules have upstanding tabs with loops forming part of connecting elements for releasably securing the swirler to the spacer. The spacer is mounted on a mounting ring having radially outwardly directed elements terminating in barbed ends for insertion through the loops in response to rotation of the swirler mounting ring relative to the tabs. The barbed ends can be squeezed together to release the swirler from its attachment with the spacer.

Abstract: A nuclear fuel assembly for use in a pressurized water reactor comprising a top nozzle and a bottom nozzle, fuel rods loaded and supported by grids in cells thereof and interconnected between a lowermost grid and the top nozzle, and a filter member interposed between the lowermost grid and the bottom nozzle.

Abstract: In a fuel bundle for a boiling water nuclear reactor comprising a plurality of fuel rods secured within an array and extending between upper and lower tie plates, and including at least one additional fuel rod extending from the lower tie plate but terminating short of the upper tie plate, an improvement wherein a removable extension rod secured to the at least one additional fuel rod and extending substantially to the upper tie plate. The removable extension rod is in the form of a hollow tube having a plurality of openings therein and an internal flow path over an axial portion of the hollow tube, the flow path serving to cause coolant in the hollow tube to be deposited on adjacent fuel rods.

Abstract: In a foot of a fuel assembly of a boiling water reactor, an upper edge of a transition member is tight against a lower edge of a fuel assembly casing to substantially prevent bypass flow between them. Rather, bypass apertures are provided therefor over all sides of the fuel assembly casing. In a first position of a base plate lying on the transition member, the bypass apertures on some sides are blocked by lateral surfaces of the base plate, while in a second position of the base plate, the bypass apertures of other sides are blocked. The direction of the bypass flow can thus be predetermined regardless of the position of the fuel assembly casing.

Abstract: A deflector is disposed in a steam vent region above the upper ends of part-length fuel rods to deflect upwardly flowing liquid laterally outwardly into the interstices of the full-length fuel rods adjacent the steam vent region. The deflector is supported by a spacer or from the upper tie plate and can be removed from the fuel bundle for access to the part-length fuel rods. The deflector may comprise a flat plate, an inverted pyramid, an inverted cone, a multi-sided pyramidal configuration or a swirl device wherein the horizontally projected area of the deflector is substantially coextensive with the horizontal cross-sectional area of the steam vent area. In this manner, a higher density liquid is provided in the interstices of the full-length rods while the lower density steam flows into the steam vent volume for flow upwardly out of the fuel bundle.

Abstract: The invention relates to a fuel assembly (1) and a spacer (7) for a nuclear reactor wherein the spacer comprises a plurality of cells (9) for retaining and mutually fixing parallel elongated elements (3, 8) extending through the cells to form a bundle in the fuel assembly. The cells are tubular and internally provided with four elongated, non-independently resilient supports (10), formed in the sleeve material, or with two elongated, non-independently resilient supports (10), formed in the sleeve material, and two independently resilient supports (16), wherein the supports are intended to provide an all-sided positioning of the elongated element. (FIG.

Abstract: In a fuel bundle assembly for a nuclear reactor wherein a plurality of fuel rods and tie rods extend between upper and lower tie plates and wherein some of the fuel rods are partial length fuel rods extending between the lower tie plate and a spacer located between the upper and lower tie plates, an improved end plug is provided for at least each of the partial length fuel rods, each end plug secured between a respective partial length fuel rod and the lower tie plate. The end plug includes an upper portion constructed of a first alloy material and including an exterior fuel rod receiving surface and a tapped hole in a lower end thereof, and a lower portion constructed of a second alloy material and including upper and lower threaded sections, the upper threaded section receivable within the tapped hole and the lower threaded section receivable within a tapped hole in the lower tie plate. The threaded end plug may be used with full length fuel rods as well as bundle tie rods.

Abstract: In a fuel bundle for a boiling water nuclear reactor comprising a plurality of fuel rods (20) secured within an array and extending between upper and lower tie plates (24, 22), and including at least one additional partial length fuel rod (20') extending from said lower tie plate (22) but terminating short of said upper tie plate (24), an improvement in the form of a removable extension rod (32) secured to said at least one additional fuel rod (20') and extending substantially to said upper tie plate (24). The removable extension rod (32) also permits variance in the reactivity of the partial length fuel rod (20') particularly in the two phase region of the bundle (10).

Abstract: A nuclear fuel channel has four corners and four elongated sidewalls disposed between the corners so as to provide a polygonal transverse cross-section. Each of the channel sidewalls has a longitudinal centerline that coincides with a line of maximum stress that is imposed on the sidewall during in-reactor service. The sidewalls have one or more longitudinal off-center lines that are located between the longitudinal centerline and one of the corners abutting the elongated sidewall. The longitudinal off-center line coincides with a line of minimum stress imposed on an elongated sidewall during in-reactor service. A weld is formed along the length of the off-center line on at least two of the sidewalls. At least one of the off-center line welds is also a seam weld. The disclosed arrangement provides improved resistance to bulging of the channel sidewalls during in-reactor service.

Abstract: A fuel assembly has part length and full length fuel rods, and a pair of large-diameter water rods which occupy an area which can accommodate 7 fuel rods. Natural uranium regions are provided in the upper and lower end portions of the effective fuel zone of the fuel assembly. An intermediate region between these upper and lower natural uranium regions provides an enriched uranium region which has three axial sections: an upper section, a middle section and a lower section. The middle section has the highest average enrichment, the lower section has the medium average enrichment and the upper section has the smallest average enrichment. The difference in the average enrichment between the middle section and the lower section is smaller than that between the middle section and the upper section. The upper section has a lower concentration of burnable poison than other sections of the enriched uranium region.

Abstract: The lower tie plate grid includes cylindrical bosses and webs interconnecting the bosses for supporting nuclear fuel rods and defining flow channels through the grid for flowing coolant upwardly about the fuel rods. The grid includes shaped body members having flow openings, the members being disposed in each of the flow channels. In one form, the members define with the side walls of the bosses and webs a debris retention zone. In another form, sets of generally parallel, laterally spaced bars are disposed at discrete elevations in the flow channels. The bars are orthogonally related to one another whereby the effective debris catching area is defined by the openings through the crossed bars in plan, while the coolant flow area comprises essentially the space between each set of bars.

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 fuel assembly is provided with a coolant ascending path for making coolant rise and a water rod having a coolant descending path for conducting the coolant.A ratio of a flow area in a coolant inlet port of the smallest in coolant ascending path 13 on the downstream side than large diameter tube portion 3E to a flow area of the largest in the axial direction of coolant ascending path 13 in large diameter tube portion 3E is set to be 0.2-20%.In the normal operation, the declination degree from the liquid level in the coolant ascending path, corresponding to the coolant flow rate of the liquid level formed in the coolant ascending path can be controlled. Further, at the time of the excess the change speed of the liquid level can also be controlled.

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 debris resistant fuel rod sleeve that is received over the lower end of a fuel rod. The sleeve extends above the top of the lowermost spacer grid. Openings are spaced apart around the circumference of the sleeve to correspond to the location of hard stops in the spacer grid. The hard stops are received in the openings and retain the sleeves in position during operation and during reconstitution or recaging if necessary. The outboard side of the peripheral sleeves may be provided with top and bottom lead-in features to prevent hang-ups.

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 critical power enhancement system is provided for a pressurized fuel channel type nuclear reactor comprising a plurality of fuel bundles contained in a fuel channel and containing a plurality of fuel elements horizontally oriented within the fuel channel. The system comprises at least one appendage strategically located on each of certain fuel elements along its length and projecting outwardly from the surface of the fuel element. The appendages generate turbulence in the coolant flowing at locations along the length of the fuel bundle, where the critical heat flux is most likely to occur. The presence of the appendages suppress the occurrence of the critical heat flux in the fuel bundle thereby increasing the safety limit on the maximum power that can be produced by the reactor.

Abstract: The present invention provides a fuel rod for a light water nuclear reactors that comprises a part-length fuel rod and an extension tube having at least one wall member defining an enclosed flow path therethrough, the extension tube being coupled to a portion of the part-length fuel rod so as to be disposed axially above the part-length fuel rod, and including at least one inlet opening, for allowing fluid that surrounds the rod and initially comprises a two phase mixture of steam and liquid, to enter the enclosed fluid path and at least one outlet opening located above the inlet opening, the extension tube includes means for separating at least some of the steam located in the fluid from the liquid located therein. The improved fuel rod allows steam to bypass the upper active portions of the fuel assembly.

Abstract: A fuel bundle and lower tie plate assembly for a nuclear reactor includes a plurality of fuel rods supported between an upper tie plate and a lower tie plate assembly, the lower tie plate assembly including an upper grid portion and a lower body portion, the upper grid portion having a plurality of fuel rod supporting bosses interconnected by a plurality of webs thus forming flow openings between the bosses. The body portion includes an inlet nozzle and a peripheral wall extending between the bottom nozzle and the upper grid portion to define a flow volume therein. A debris catcher, including a plurality of perforated tubes, is incorporated into the lower tie plate assembly, such that one of the tubes is in abutment with a respective lowermost end of each of the plurality of fuel rod supporting bosses.

Abstract: A fuel assembly for a light-water nuclear reactor includes a plurality of vertical fuel rods (10) which are arranged, in spaced relationship in the lateral direction, between a bottom tie plate (11) and a top tie plate (12). The bottom tie plate and the top tie plate are provided with through-holes (35) for inlet and outlet of coolant for the fuel rods. Below the bottom tie plate, in the flow path of the water, a debris catcher (36) is arranged which includes helical springs (40) that are arranged in a frame having at least two ends (37, 38) in the form of substantially parallel plates, the flat sides of which are interconnected via pins (39). The pins are arranged in spaced relationship in at least two rows between the ends in such a way that the springs, in spaced relationship or adjacent to each other, can be fixed between the rows of pins in one or more layers.

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 tapered divergent walls opening into the flow spaces. In another form, the openings have a step intermediate the upper and lower surfaces of the lower grid portion to define a minimum cross-sectional flow area.

Abstract: A fuel assembly for a light-water nuclear reactor includes a plurality of vertical fuel rods (12) which are arranged, in spaced relationship in the lateral direction, between a bottom tie plate (13) and a top tie plate (14). The bottom tie plate and the top tie plate are provided with through-holes (17a) for inlet and outlet of coolant for the fuel rods. Below the bottom tie plate, in the flow path of the water, a debris catcher (18) is arranged. The debris catcher includes at least one helical spring (19) which is fixed in a holder permeable to the coolant and defining at least one slot which is formed as a plane spiral (30) or several concentric annular slots (23, 27) in which slot/slots the helical spring/helical springs is/are arranged.

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 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: An improved fuel rod is provided having a part-length fuel rod portion that improves performance with respect to typical part-length fuel rods without significant degradation of the benefits that are achieved by using such a system, e.g., improved fuel utilization, stability, and shut down margin. The present invention provides a fuel rod for a light water nuclear reactors that comprises a part-length fuel rod and an extension tube having at least one wall member defining an enclosed flow path therethrough, the extension tube being coupled to a portion of the part-length fuel rod so as to be disposed axially above the part-length fuel rod, and including at least one inlet opening, for allowing fluid that surrounds the rod and initially comprises a two phase mixture of steam and liquid, to enter the enclosed fluid path and at least one outlet opening located above the inlet opening, the extension tube includes means for separating at least some of the steam located in the fluid from the liquid located therein.

Abstract: A method is provided for retrofitting nuclear fuel assemblies in bottom entry fuel assembly type nuclear reactors having a transition piece to guide liquid coolant into a channel entry area. The transition piece is disposed above an entry orifice in a fuel assembly support plate. The transition piece has side walls and a multi-pronged lead-in finger. The method comprises the steps of removing the lead-in finger from the transition piece, machining internal surfaces of the side walls of the transition piece and installing an insert to be disposed within and supported by the machined transition piece.

Abstract: An improved fuel rod is provided having a part-length fuel rod portion that improves performance with respect to typical part-length fuel rods without significant degradation of the benefits that are achieved by using such a system, e.g., improved fuel utilization, stability, and shut down margin. The present invention provides a fuel rod for a light water nuclear reactors that comprises a part-length fuel rod and an extension tube having at least one wall member defining an enclosed flow path therethrough, the extension tube being coupled to a portion of the part-length fuel rod so as to be disposed axially above the part-length fuel rod, and including at least one inlet opening, for allowing fluid that surrounds the rod and initially comprises a two phase mixture of steam and liquid, to enter the enclosed fluid path and at least one outlet opening located above the inlet opening, the extension tube includes means for separating at least some of the steam located in the fluid from the liquid located therein.

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 nuclear fuel assembly lower end fitting. Two plates each having a network of diagonal and lateral ribs in conjunction with hubs for the guide thimble hole pattern are provided. The pitch between ribs corresponds to one-half of the fuel rod pitch. This allows for the fuel rods to be supported by every other rib. One plate is rotated horizontally ninety degrees relative to the other plate so that the lateral ribs of the plates are at right angles. A screen formed from approximately 0.03 inch diameter wire with 0.100 inch pitch is provided with guide tube bosses. The plates and screen are rigidly attached to each other to form a debris filtering lower end fitting.

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: In a boiling water nuclear reactor fuel bundle, a debris catching arrangement is disclosed for incorporation within the flow plenum up stream or below the rod supporting grid of the lower tie plate assembly. The device is preferably placed within the lower tie plate flow plenum between the fuel bundle inlet orifice and the rod supporting grid structure supporting the fuel rods; alternate placement can include any inlet channel upstream of the fuel rods including the fuel support casting. Paired plates defining offset holes and bosses are utilized. The bosses are supported at plate webbing between the respective holes. The holes are preferably square in plan with appropriately relieved and rounded corners defining the edges of the webbing. The bosses may be cylindrical, square or rectangular in cross-section. In confrontation of plates to form the debris catching grid, each boss from one plate confronts a hole from the remaining plate.

Abstract: In a fuel bundle having an array of fuel rods of 9-by-9 or greater, removal of the corner fuel rods from the array occurs. This removal enables the remainder of the array rod-to-rod pitch to be decreased. Further, and over this array with the corner fuel rod removed, a fuel bundle channel having rounded corners of increased radius of curvature or flattened corners imparting a broadly taped curvature is utilized. In both cases, the effective flat span of the fuel bundle sides is reduced with the result that the new fuel bundle incorporates improved resistance to channel bulge with improved critical power.

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 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 fuel assembly comprises a plurality of fuel rods supported by an upper tie plate and a lower tie plate respectively at each of upper end portion ad lower end portion, and a channel box surrounding a bundle of the fuel rods and the lower tie plate. The fuel assembly forms a natural uranium region at lower end portion of effective fuel length portion. A wall thickness at a lower thick wall region of the channel box is thicker than the wall thickness at a region disposed upwardly from the lower thick wall region and between corner portions of the channel box. An upper end of the lower thick wall region is disposed from an upper side of the lower tie plate and downwardly from an upper end of the natural uranium region. A wall thickness at the corner portion of the channel box is thicker than the wall thickness at a middle portion of the side wall between the corner positions at the region locating upward from the lower thick wall region.

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: 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 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 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: 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: The lower end nozzle (1) comprises an adaptor plate (2), supporting feet (3) and a particle retention device (6) consisting of a filter plate pierced with holes and attached to the bottom face of the adaptor plate (2) over a substantial portion of its surface.

Abstract: A mixing grid for use in a pressurized reactor comprises at least two sets of crossed fixed together at their cross-points, delimiting cells, some for receiving fuel rods and the others for receiving guide tubes, the plates being provided with coolant stirring fins extending the plates downstream and disposed to deflect the coolant transversely to its general flow direction, each plate being provided with abutment means projecting inwardly from each of the faces of the cells for receiving fuel rods, thereby delimiting a passage that is larger than the size of the rods but small enough to prevent a rod contained in the cell coming into contact with the fins. In each wall the abutment means comprise two portions of plate that are cut out and deformed into a scoop-shape, and that are offset relative to each other in the coolant flow direction, with the scoops projecting in opposite directions and tending to cause coolant to pass from one cell to another.

Abstract: A grid for use on a PWR fuel element comprises a belt of hexagonal shape and three sets of plates secured to the belt. The plates in each set are mutually parallel and are at an angle of 120.degree. with the plates of the two other sets. All plates have the same length and have a 120.degree. bend in their middle. Each plate is parallel to two successive faces of the belt.

Abstract: A fuel bundle and fuel bundle assembly sequence utilizing a peanut sectioned large water rod is shown locking spacers into place along the axial length of the water rod. In a first embodiment, clearance is defined relative to tabs welded on the large water rod so that spacer assembly to the water rods can occur. In a second and preferred embodiment, spacers are individually equipped with springs locking into complimentary apertures in the peanut sectioned water rod. In both embodiments, the spacers are threaded onto the peanut sectioned water rod and locked into alignment for the receipt of the fuel rods. An improved suspension of the water rod relative to the lower tie plate is disclosed in which a transition piece connects the large water rod to a flexible rod which is threaded at its lower end. This rod is screwed into a threaded aperture in the lower tie plate.

Abstract: A fuel assembly comprises a plurality of fuel rods which contain nuclear fuel material inside, a lower tie plate which holds the lower end of the fuel rods and has a path inside to lead coolant between the fuel rods, and a channel box which encloses a bundle of the fuel rods. An orifice, in which a plurality of round rods are arranged to cross the coolant flow path, is installed in a through hole at a side wall of the lower tie plate by connecting to the side wall. Orifice coefficient of the orifice becomes large at small flow rate of coolant which supplied to the fuel assembly, and becomes small at large flow rate of coolant. By using the fuel assembly described above, void fraction in a gap region between fuel assemblies can be altered during beginning and end of an operation cycle of the nuclear reactor.

Abstract: A fuel assembly for a boiling water reactor includes an elongated case having an interior and inner surfaces. A base part has inlet openings discharging into the interior of the case for coolant flowing in a given flow direction and a head part has outlet openings leading out of the interior of the case for the coolant flowing in the given flow direction. Mutually parallel fuel rods containing nuclear fuel are disposed in the case between the base and head parts. The inner surfaces of the case have a profile with a rectilinear alignment as seen in the given flow direction and flow trippers extending transversely to the alignment in the form of bulges protruding inward in the given flow direction. Each of the bulges has a sloped surface facing toward the coolant with an impact surface substantially perpendicular to the given flow direction.

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.