Abstract: A foreign matter filter provided between a DFBN and a lower grid has two adjacent thin straps assembled into a lattice. The straps are equipped on the front and back sides with axially continuous protrusions.

Abstract: Transverse vibrations of the pellet columns included in the fuel rods of fuel elements are limited by elastically mounting the fuel rod jacket tubes in the mesh of spacer grids. When the fuel rods are supported in this way, flexural vibrations of a higher order occur that lead to damage to the jacket tubes caused by fretting. These vibrations are the less dampened the more rigid the fixture of the fuel rod is. These vibration conditions are more easily excited and more strongly dampened when the pellet columns are more mobile, thereby removing vibration energy from the fuel element and avoiding damage caused by fretting. The mobility of the columns can be increased by increasing the gap between the pellet and the jacket tube, or by using constructions in which a torque M?10 N mm on the fuel rod leads to a tilting angle ??0.1°.

Abstract: An improved grid for use in a fuel assembly of a nuclear reactor includes a plurality of straps that are interconnected with one another in a lattice fashion to define a plurality of cells, with the straps being configured to include a plurality of relatively more compliant springs and a plurality of relatively less compliant dimples, whereby each cell includes only one pair of springs and one pair of dimples disposed therein. The springs and dimples are contoured to engage a fuel rod or a thimble tube disposed within the cell. Each spring directly confronts one of the dimples to provide confronting pairs of features that engage the fuel rods or thimble tubes, with each cell including two pairs of confronting features. The ligaments of the springs and dimples extend in a direction generally perpendicular to the direction of coolant flow through the reactor in order to minimize pressure drop.

Abstract: A core plate assembly for a nuclear reactor includes a plurality of support beams, a flat plate positioned on top of the support beams, a plurality of control rod guide tube openings arranged in staggered rows, and a plurality of fuel supports extending through the flat plate. Each guide tube opening has a cruciform shape defines four fuel bundle receiving areas. Each fuel support includes a coolant flow inlet, and a coolant flow outlet sized to receive a lower tie plate of a fuel bundle. The coolant flow inlet is offset from coolant flow outlet so that a centerline of the coolant flow inlet is parallel to a centerline of the coolant flow outlet. The coolant flow inlets are positioned adjacent a support beam, and the coolant flow outlets are positioned in a fuel bundle receiving area.

Abstract: A lips-type multi-purposed spacer grid for supporting fuel rods within a nuclear fuel assembly is disclosed. In the spacer grid, the fuel rods are in contact with dimples and water strider-type springs in an equiangular surface contact manner. The spacer grid distributes load, applied to the springs, to the entire structure of its inner strips, thus reducing peak stress at the contact surfaces between the fuel rods and the springs and diminishing vibration of the fuel rods, and thereby reducing possible fretting wear of the fuel rods due to hydraulic vibration of the fuel rods. The spacer grid also enlarges the allowable elastic range of the springs, and allows the springs to soundly support the fuel rods by using residual spring force. The spacer grid has mixing blades capable of minimizing pressure loss and flow interference, so that the fuel rod cooling efficiency of the nuclear fuel assembly is improved.

Abstract: Transverse vibrations of the pellet columns included in the fuel rods of fuel elements are limited by elastically mounting the fuel rod jacket tubes in the mesh of spacer grids. When the fuel rods are supported in this way, flexural vibrations of a higher order occur that lead to damage to the jacket tubes caused by fretting. These vibrations are the less dampened the more rigid the fixture of the fuel rod is. These vibration conditions are more easily excited and more strongly dampened when the pellet columns are more mobile, thereby removing vibration energy from the fuel element and avoiding damage caused by fretting. The mobility of the columns can be increased by increasing the gap between the pellet and the jacket tube, or by using constructions in which a torque M≦10 N mm on the fuel rod leads to a tilting angle &phgr;≧0.1°.

Abstract: A lips-type multi-purposed spacer grid for supporting fuel rods within a nuclear fuel assembly is disclosed. In the spacer grid, the fuel rods are in contact with dimples and water strider-type springs in an equiangular surface contact manner. The spacer grid distributes load, applied to the springs, to the entire structure of its inner strips, thus reducing peak stress at the contact surfaces between the fuel rods and the springs and diminishing vibration of the fuel rods, and thereby reducing possible fretting wear of the fuel rods due to hydraulic vibration of the fuel rods. The spacer grid also enlarges the allowable elastic range of the springs, and allows the springs to soundly support the fuel rods by using residual spring force. The spacer grid has mixing blades capable of minimizing pressure loss and flow interference, so that the fuel rod cooling efficiency of the nuclear fuel assembly is improved.

Abstract: Corner of each square pipe is molded into a terrace shape having steps. When a basket is constructed by these square pipes, steps of adjoining square pipes are assembled together face to face. Fuel rod aggregates are housed inside the square pipes and in a cells formed between the square pipes. Since the adjoining square pipes are assembled in a staggered arrangement, boundaries of the cells are defined by the walls of the square pipes itself.

Abstract: A fuel assembly for a pressurized-water reactor includes fuel rods held in cells of spacers, control rod guide tubes, and a headpiece and a foot piece, by which it is fixed to upper and lower core grids, respectively. A spacer having a first part, which lies on a radially outer side with respect to a longitudinal center axis of the fuel assembly, and a second part, which lies on a radially inner side and is completely surrounded by the first part are included to reduce the size of gaps between fuel assemblies. The second part is formed of Zircaloy. The first part is made of a metallic material, and when compared to the Zircaloy of the second part, has a lower growth in the radial direction, caused by neutron radiation and a higher coefficient of thermal expansion.

Abstract: A fuel assembly having a plurality of fuel rods arranged in a square lattice array. The fuel rods include a plurality of short-length fuel rods each having a fuel active length shorter than that of each of remaining ones of the fuel rods. At least one water rod is arranged in a region in which one or more of the fuel rods are arrangeable in the array, and a plurality of fuel spacers are provided at a plurality of positions in the axial direction for holding the plurality of fuel rods and the at least one water rod, with mutual radial intervals therebetween being kept immovable. The plurality of short-length fuel rods include at least one first short-length fuel rod arranged in the outermost peripheral region of the square lattice array. Each of the plurality of fuel spacers include a plurality of cylindrical members.

Abstract: One object of the present invention is to provide a production method for a nuclear fuel assembly support grid that improves the corrosion resistance of welded parts without impairing the characteristics of the support grid so as to be able adequately withstand highly efficient operation. In order to achieve the object, the present invention provide a production method for a nuclear fuel assembly support grid comprising the steps of: assembling a plurality of straps in a grid form; welding intersections of each strap; and carrying out annealing thereafter to precipitate an intermetallic compound on the welded parts.

Abstract: A spacer grid for nuclear fuel assemblies is disclosed. This spacer grid has a plurality of side weld supports, that is, main supports, upper sub-supports and lower sub-supports, on its interlaced inner straps, with two flow mixing vanes integrally extending upward from each of the main supports. This spacer grid is fabricated by seam-welding the interlaced first and second inner straps to each other along the upper axial junction lines of the crossing main and upper sub-supports at the top of the intersections, and along the lower axial junction lines of the crossing lower sub-supports at the bottom of the intersections, thus forming side weld lines at the intersections.

Abstract: A spacer grid for use in a nuclear fuel assembly has double-deflected vanes that guide an axial flow of coolant around fuel rods and thereby generate swirl flow. The vanes each have a double bend projecting upwardly from first inner straps and projecting toward one fuel rod. The vanes are sufficiently wide at their bases to prevent inadvertent deformation due to contact with fuel rods during an insertion of fuel rods into the cells. The vanes also make a smooth variation in the cross-sectional area of the coolant channel at the outlet of the spacer grid, thus reducing a loss of pressure during reactor operation.

Abstract: A double strip mixing grid for nuclear reactor fuel assemblies is disclosed. This grid is fabricated by intersecting at right angles a plurality of double strips, each fabricated by welding two thin sheets together into a single structure with coolant channels. The mixing grid, having the channels, effectively mixes low temperature coolant with high temperature coolant within a fuel assembly, thus improving the thermal efficiency of the fuel assemblies. This mixing grid also effectively prevents the coolant from being partially overheated, thus improving the soundness of nuclear reactors. This mixing grid also has swirling flow blades and/or lateral flow blades to further improve the thermal efficiency of the fuel assembly. This mixing grid elastically supports the fuel rods by the sheets of the double strips, collaterally acting as positioning springs.

Abstract: The assembly apparatus comprises a frame for supporting the straps of the first set of straps in mutually parallel positions, clamping and engagement for clamping on each of the straps of a second set of straps in succession and for engaging them with the straps of the first set in position in the support frame, and at least one comb that is movable between a disengaged position and a position in which it engages each of the straps of the first set.

Abstract: A duct-type spacer grid for nuclear fuel assemblies is disclosed. In this spacer grid, a plurality of duct-shaped grid elements, individually having an octagonal cell, are closely arranged in parallel and are welded together, thus forming a matrix structure. The grid elements do not pass across the center of the subchannel of the assembly, thus effectively reducing pressure loss. Each of the grid elements is formed as an independent cell, and so they effectively resist against a lateral impact. A plurality of integral type swirl flow vanes, having different heights or same height, axially extend from the top of the grid to be positioned within each subchannel. The swirl flow vanes are bent outwardly, and so they do not contact the fuel rods during an insertion of the fuel rods into the cells. In the spacer grid, the fuel rods are supported within the cells by line contact springs without using any dimple.

Abstract: An improved grid for use in a fuel assembly of a nuclear reactor includes a plurality of straps connected in a lattice, with a plurality of mixing vanes being disposed on the straps and being arranged such that the hydraulic forces on the mixing vanes generally cancel one another out. The mixing vanes of diagonal quadrants of the grid are generally aligned with diagonally disposed imaginary alignment planes. Each strap includes a plurality of strap members, with each strap member including a spring and a pair of dimples. The spring includes a contoured spring embossment having a greater radius of curvature in a relaxed condition than the radius of a fuel rod. Each dimple includes a similarly configured contoured dimple embossment. The spring embossment is mounted on a pair of legs that extend nonlinearly between a first plate and a second plate of each strap member to increase compliance thereof.

Abstract: For the redistribution of a coolant flow from a first region into a second region, in particular in boiling-water-reactor fuel elements having an eccentrically disposed water passage, a fuel-rod bundle is constructed in a mirror symmetry manner relative to a diagonal. A distance between adjacent fuel rods increases monotonically in particular along a diagonal. In addition, a fuel-rod bundle as an entity may be offset eccentrically along the diagonal. To compensate for asymmetry in the reactor core, a redistribution of coolant is provided which is advantageous in pressurized-water-reactor fuel elements.

Abstract: In a boiling water fuel assembly, some of the fuel rods are shortened. It is necessary to establish a sufficiently high maximum power for transition to boiling. To optimize this power, spacers are at a constant distance at a bottom and are at a shorter distance at a top. The spacers belonging to upper group have turbulence-generating vanes which, however, do not project above the shortened fuel rods.

Abstract: The present invention relates to a method for making flat, thin elements which consist of: producing a zirconium alloy blank also containing, besides the inevitable impurities, 0.8 to 1.3% of niobium, 1100 to 1800 ppm of oxygen, and 10 to 35 ppm of sulfur; carrying out a &bgr; hardening and hot rolling to obtain a blank and performing on it at least three cold rolling passes with intermediate annealing heat treatments. One of the intermediate heat treatments is performed for a duration of at least 5 hours at a temperature less than 560° C. and all the optional treatments subsequent to the long treatment are carried out at a temperature of less than 620° C. for not more than 15 minutes.

Abstract: At regular intervals, the grid strap has formed therein notches for assembly with transverse straps. Between at least some pairs of notches, it has a rod-holding spring comprising two resilient strips cut out from the plane wall of the strap and integral therewith. Each strip extends transversely relative to its strap and is connected to the common portion of the strap at its two ends. In the free state, the strips project towards the inside of the cell concerned and they are interconnected in the middle by a transverse bridge which projects relative to the two strips.

Abstract: A spacer for use with a protective grid of a fuel assembly of a nuclear reactor is a generally washer-shaped plate of material having an engagement surface and a retention surface opposite one another. The protective grid is formed of a plurality of straps to define a plurality of fuel rod cells and a plurality of thimble cells, with the straps adjacent the thimble cells being notched to receive the spacer therein. The retention surface of the spacer is disposed against the notches, and the engagement surface of the spacer protrudes outwardly from the protective grid. When the engagement surfaces of the spacers are engaged against a lower nozzle of a fuel assembly of a nuclear reactor, the spacers space the protective grid from the lower nozzle. The spacer is integrally welded with the protective grid in a single arranging and welding operation.

Abstract: A spacer grid for PWR assemblies is characterized by curved flow channels between adjacent fuel rods and straight, essentially flat strips connecting opposite side plates of the spacer. The latter strips prevent bowing-out of the side plates during fuel assembly fabrication and during operation in the reactor. Additionally, the spacer grid allows accurate positioning of the fuel rods on a square lattice with a precisely defined pitch, and support of the rods in their spacer cells is such that rod bow will be minimized. The direction of the nozzles on the flow channels has been chosen to promote cross-flow of the coolant through the assembly.

Abstract: A fuel assembly includes a plurality of fuel rods placed in a square lattice array of 9-rows/9-columns and at least one water rod. In this fuel assembly, the fuel rod pitch of the plurality of fuel rods is in a range of 14.15 mm to 14.65 mm, and means for offsetting and holding a fuel bundle composed of the fuel rods and the water rod is provided in such a manner that the center in a cross section of the fuel bundle is offset from the center in a cross section of the lower tie plate toward the channel fastener side. With this configuration, it is possible to provide a fuel assembly for a D-lattice core, which is capable of achieving the fuel economy comparable to that of a C-lattice core without reducing the thermal margin, and of using the existing fuel spacers.

Abstract: A boiling water type nuclear reactor core, in which a plurality of fuel assemblies, each enclosed in a channel box, are loaded and a plurality of control rods, each having control blades, are arranged between the channel boxes. Long blade control rods, each having control rod blades which extend in four directions, are arranged between channel boxes on diagonals of square bundle regions each formed by a plurality of fuel assemblies, and short blade control rods, each having a control rod blade length of about half of the width of one of the square bundle regions, are arranged between the channel boxes in the center of each of the square bundle regions.

Abstract: A spacer for a fuel assembly of a nuclear reactor includes an elongated spring which is held in a mesh in such a way that there is structural freedom with respect to a selection of a shape of the spring and that little spring material is required. Two lateral rims at a top end of the spring are bent around a center of a fuel element out of the mesh in such a way that they protrude through an assembly opening in the web into an adjacent mesh. The two rims approximately form-lockingly encompass an edge of the assembly opening through the use of a profiled section. A lower end of the spring is also correspondingly held on the web through the use of profiled sections on its two rims, which are bent outward. Two springs protruding into adjacent meshes can then also be fastened in the same assembly opening.

Abstract: A fuel assembly having a plurality of fuel rods arranged in a square lattice array. The fuel rods include a plurality of short-length fuel rods each having a fuel active length shorter than that of each of remaining ones of the fuel rods. At least one water rod is arranged in a region in which one or more of the fuel rods are arrangeable in the array, and a plurality of fuel spacers are provided at a plurality of positions in the axial direction for holding the plurality of fuel rods and the at least one water rod, with mutual radial intervals therebetween being kept immovable. The plurality of short-length fuel rods include at least one first short-length fuel rod arranged in the outermost peripheral region of the square lattice array. Each of the plurality of fuel spacers include a plurality of cylindrical members.

Abstract: A nuclear fuel spacer grid, fabricated by intersecting a plurality of zircaloy or inconel grid strips and used for placing and supporting a plurality of elongated fuel rods within a nuclear fuel assembly, is disclosed. In the spacer grid of this invention, each of the grid strips is not cut away to form separate springs or dimples for supporting the fuel rods, but has an axial slot extending from one end of each strip to a length. The grid strips are intersected at the slots prior to being welded together into a single grid structure at a welding tap formed at an outside end or a middle portion of each of the slots. Each of the grid strips also has a dipper-shaped coolant mixing vane, or a dipper vane, at each of the upper and lower ends thereof. The spacer grid thus maximizes the thermal hydraulic coolant mixing effect within a fuel assembly and stably supports the fuel rods within the assembly while improving the mechanical/structural strength of the assembly, such as a buckling strength.

Abstract: Disclosed is a fuel assembly, particularly, a fuel assembly including short-length fuel rods and fuel spacers, used for a boiling water reactor, which is capable of sufficiently reducing the pressure loss of at least one, of the fuel spacers, positioned upward from the upper ends of the short-length fuel rods irrespective of arrangement of the short-length fuel rods, and also ensuring the structural strength of the fuel spacer. The fuel assembly includes fuel rods located in a square lattice array, two water rods arranged in a region in which seven pieces of the fuel rods are arrangeable, two fuel spacers for holding the fuel rods and the water rods with mutual intervals kept immovable. Each of the fuel spaces includes cells which are connected to each other and in which the fuel rods are to be inserted respectively, and a band for surrounding the outermost peripheries of the cells.

Abstract: A fuel assembly, particularly, a fuel assembly including short-length fuel rods and fuel spacers, is used for a boiling water reactor, which is capable of sufficiently reducing the pressure loss of at least one of the fuel spacers positioned above the upper ends of the short-length fuel rods, irrespective of the arrangement of the short-length fuel rods, and also ensuring the structural strength of the fuel spacer. The fuel assembly includes fuel rods located in a square lattice array, two water rods arranged in a region in which seven of the fuel rods are arrangeable, two fuel spacers for holding the fuel rods and the water rods with mutual intervals kept immovable. Each of the fuel spacers includes cells which are connected to each other and in which the fuel rods are to be inserted, respectively, and a band for surrounding the outermost peripheries of the cells. The short-length fuel rods include four first short-length fuel rods arranged in the outermost peripheral region of the square lattice array.

Abstract: A duct-type spacer grid for nuclear fuel assemblies is disclosed. In this spacer grid, a plurality of duct-shaped grid elements, individually having an octagonal cell, are closely arranged in parallel and are welded together, thus forming a matrix structure. The grid elements do not pass across the center of the subchannel of the assembly, thus effectively reducing pressure loss. Each of the grid elements is formed as an independent cell, and so they effectively resist against a lateral impact. A plurality of integral type swirl flow vanes, having different heights or same height, axially extend from the top of the grid to be positioned within each subchannel. The swirl flow vanes are bent outwardly, and so they do not contact the fuel rods during an insertion of the fuel rods into the cells. In the spacer grid, the fuel rods are supported within the cells by line contact springs without using any dimple.

Abstract: The present invention relates to a fuel assembly for a light-water reactor with a substantially square cross section wherein the fuel assembly comprises a plurality of fuel rods (4). The fuel rods (4) extend between a bottom tie plate (5) and a top tie plate (6) and a coolant is adapted to flow upwards through the fuel assembly. At least one of the top tie plates (6) or the bottom tie plates (5) comprises flow openings (22, 22a, 22b) for the passage of the coolant and side supports (17) for supporting the fuel rods (4) in the lateral direction. The side supports (17) are designed in one and the same sheet-metal piece as the flow openings (22, 22a, 22b) and the side supports (17) are folded substantially 90° in relation to the other structure of the top tie plate (6) or the bottom tie plate (5).

Abstract: An adjustment tool is provided, having a probe, a head, an arm and a micrometer attached to the head. With the probe inserted into a spacer cell opening, the micrometer handle is rotated to a predetermined setting to pivot the arm. The opposite end of the arm from its engagement with the micrometer drive head engages and displaces the spring of the spacer cell to adjust its spring force. In one form, the arm is housed within the probe and the micrometer drive head displaces the distal end of the arm outwardly to correspondingly displace the spring outwardly, thereby decreasing the spring force. In another form of the spacer tool, the arm is spaced from the probe and has pivotal contact surfaces to straddle the spring. Movement of the drive head by rotating the micrometer handle to a predetermined setting causes the spring to be displaced inwardly of the spacer cell opening to increase the spacer spring force.

Abstract: A nuclear fuel assembly grid has a plurality of mutually interleaved straps forming an array of fuel rod receiving cells. Each strap is formed with regularly distributed slots for interleaving with other straps of the grid. The strap has dimples located between some at least of the slots for maintaining fuel rods in the cells. An uptstream portion of the plate extending in transverse relation to a coolant flow direction has a double sided concave chamfer.

Abstract: A spacer of a fuel assembly having intersecting webs undergoes reduced longitudinal expansion as a result of corrosion during an operating period. The webs have intersection locations at which assembly gaps are provided. The assembly gaps have widths which correspond essentially, at most over a fraction of their total length, to the wall thickness of an intersecting web, but are wider in a remaining region. Since corrosion layers growing from an edge of an assembly gap toward the intersecting web cannot touch the web, no solid pressure, which could lead to longitudinal expansion, builds up.

Abstract: A sub-assembly for a spacer in a nuclear fuel bundle includes at least first and second ferrules lying adjacent one another for receiving respective nuclear fuel rods. Each ferrule has fuel rod contacting points along one side of the ferrule for abutting a fuel rod within the ferrule, and a substantially I-shaped opening along a side of the ferrule opposite the one side. A substantially I-shaped spring adapted to seat within the opening includes a spring body lying in a plane and having opposite horizontal end portions connected by a vertical stem portion, a central portion of each of the horizontal end portions projecting away from the substantially I-shaped opening to one side of the plane and a center portion of the vertical stem projecting into the substantially I-shaped opening to an opposite side of the plane.

Abstract: The present invention relates to a fuel assembly for a light-water reactor with a substantially square cross section wherein the fuel assembly comprises a plurality of fuel rods (4). The fuel rods (4) extend between a bottom tie plate (5) and a top tie plate (6) and a coolant is adapted to flow upwards through the fuel assembly. At least one of the top tie plates (6) or the bottom tie plates (5) comprises flow openings (22, 22a, 22b) for the passage of the coolant and side supports (17) for supporting the fuel rods (4) in the lateral direction. The side supports (17) are designed in one and the same sheet-metal piece as the flow openings (22, 22a, 22b) and the side supports (17) are folded substantially 90° in relation to the other structure of the top tie plate (6) or the bottom tie plate (5).

Abstract: The spacer/water rod retention assembly includes a clip secured to the spacer having a slot perimetrically bounded both axially and laterally spaced portions of the clip. A resilient tab projects from one side portion into the slot. A water rod has a projecting tab which, upon relative rotation of the spacer and water rod, engages and deflects the clip tab to enable the water rod tab to reside in the clip slot. When the clip tab returns to its initial position, substantial relative rotation between the water rod and spacer is precluded and axial connection between the spacer and water rod is assured. In another form, the water rod tab projects into a slot of the clip. An adjacent water rod prevents rotation of the water rod tab in the opposite direction, thereby capturing the spacer and water rod and preventing relative axial movement.

Abstract: An improved support grid of a nuclear reactor fuel assembly is described. The support grid has a plurality of first and second straps which are assembled so as to form an eggcrate structure defining grid cells in a square arrangement. The support grid includes a plurality of mixing vanes integrally formed on a side edge of the first and second straps adjacent to an area where the straps cross. The mixing vanes slanted to be adjacent to a fuel rod are each shaped to show no welding apertures formed therein in their horizontal planes of projection thereby maximizing the coolant impinging area to agitate and swirl a coolant flow.

Abstract: A fuel assembly for a nuclear reactor is described, the fuel assembly including: a plurality of fuel pins (12) extending substantially parallel to the axis of the assembly and to each other; at least two structural grids spaced apart from each other, the grids being in contact with said fuel pins (12) and maintaining said fuel pins substantially mutually parallel and preventing contact therebetween, wherein the fuel assembly further comprises at least one mixing grid (50) situated intermediate said at least two structural grids, the fuel assembly being characterized in that said mixing grid (50) is positioned and fixedly located out of substantial contact with said fuel pins (12), the mixing grid also having turbulence inducing means (61) to promote turbulence in a coolant (62) flowing through said fuel assembly in use and in that the mixing grid is formed from sheet metal wherein the plane of the metal sheet from which the mixing grid is formed lies in a plane which is transverse to the axis of the fuel pin

Abstract: A top guide assembly for securing a top guide to a shroud which enables the top guide to be remotely removed without removing any other parts of the shroud or the core support structure is described. In one embodiment, the top guide assembly includes a hanger for being secured in a groove formed in an inner surface of the shroud, and the hanger includes a ledge having a plurality of openings therein. The top guide rests on an upper surface of the ledge. The assembly also includes wedges for being positioned in pockets formed in the top guide and tightly fit between the hanger and the top guide, and threaded studs for extend through respective aligned bores in the wedges and openings in the ledge. A nut and a keeper are engaged to one end of each stud to retain the wedge between the hanger and the top guide grid.

Abstract: A boiling water type nuclear reactor core, in which a plurality of fuel assemblies, each enclosed in a channel box, are loaded and a plurality of control rods, each having control blades, are arranged between the channel boxes. Latitudinal long blade control rods, each having control rod blades which extend latitudinally in four directions, are arranged between channel boxes on diagonals of square bundle regions each formed by a plurality of fuel assemblies, and latitudinal short blade control rods, each having control rod blades which extend latitudinally in four directions with each control rod blade having a latitudinal length of about half of the width of one of the square bundle regions, are arranged between the channel boxes in the center of each of the square bundle regions. The long blade control rods have a latitudinal blade length which is about twice as long as the latitudinal blade length of the short blade control rods.

Abstract: An upper hold-down spring structure for a nuclear reactor fuel assembly. A hold down spring 20 mounted on an upper surface of an upper nozzle 11 of a fuel assembly for a pressurized water reactor is composed of an upper plate spring 21 having plastic spring characteristics and a lower plate spring 23, base ends of which are fixed with a fastening bolt 18 at a common position. The upper spring 21 and the lower spring 23 are made of precipitation hardened nickel base alloy and the thickness of the springs are determined so as to keep the stresses generated less sensitive to stress corrosion cracking.

Abstract: The adaptor plate of a top nozzle assembly is removably secured to selected thimble tubes in a nuclear fuel assembly by quick release couplings. The openings in the adaptor plate aligned with the selected thimble tubes are counterbored from above to form shoulders with diametrically opposed slots extending downward through the shoulders. The quick release couplings include a sleeve secured to the upper end of the thimble tube. A support plate fixed to the sleeve has a pair of upwardly extending bosses engaging the slots in the adaptor plate. A latch member with a pair of diametrically opposed outwardly projecting latch ears rotates on the sleeve between a first position in which the latch ears are aligned with the slots and are positioned over the bosses so that the adaptor plate may be lifted off, and a second position with the latch ears overlaying the shoulder to latch the adaptor plate to the thimble tube.

Abstract: Fuel bundle and control rod assemblies for a nuclear reactor are described. In one embodiment of the apparatus, the nuclear reactor includes several conventional size fuel bundles and at least one large control rod. The large control rod includes four fuel bundle receiving channels, and each such channel is sized to receive four conventional size fuel bundles.

Abstract: Surface preoxidation of the substrate is carried out by bringing the substrate into contact with an oxidizing gas excited by a cold plasma, the substrate being situated in the flowing afterglow of the cold plasma used to excite the oxidizing element and being heated to an oxidation temperature of less than 500.degree. C. A metal oxide is formed at the surface of the preoxidized substrate by heterogeneous oxidation of a metal halide with a gas mixture including an oxidizing element activated by a cold plasma. The oxidizing gas mixture is brought into contact with the halide as directly as possible in the vicinity of the substrate arranged in the far flowing afterglow of the cold plasma. The cold plasma is preferably generated by microwaves. The process can be used in particular for producing a protective coating on a cladding tube of a nuclear fuel rod.

Abstract: A fuel assembly for a boiling water reactor where the fuel assembly during operation is arranged vertically in the core of the reactor. The fuel assembly comprises a plurality of vertical fuel rods (22) arranged in one or more fuel bundles, wherein at least the majority of the fuel rods comprise a stack of fuel pellets (7) surrounded by a cladding tube (8b) and a plenum tube (23) which is connected to the upper part of the cladding tube (8b), the plenum tube having a cross-section area which is smaller than the cross-section area of the cladding tube.

Abstract: A nested sleeve grid restraint system and a method for making a nested sleeve grid restraint system are disclosed. The nested sleeve grid restraint system comprises an insert tube installed in and secured to the intermediate spacer grid and concentrically around a fuel assembly instrumentation tube, the insert tube having ends extending from the intermediate spacer grid, respectively, above and below the intermediate spacer grid; two spacer sleeves, each having flared ends; the spacer sleeves each being fitted concentrically around the fuel assembly instrumentation tube, respectively, above and below the intermediate spacer grid; the flared ends of the spacer sleeves fitting over the ends of the insert tube extending above and below the intermediate space grid whereby the insert tube nests in the spacer sleeves.

Abstract: A nuclear fuel assembly support grid formed from a lattice structure having an egg-crate design with the interior lattice straps joined to a perimeter strap generally at least three locations along its length; with at least two of those locations being affixed by shear joints. The shear joints are formed from weld tabs extending from the ends of the interior lattice straps, at appropriate locations, which fit into corresponding slots in the perimeter strap. The weld tabs are then brazed or welded, as appropriate to the base metals being joined, after being inserted. The weld segments can be designed with twist tabs at their end, that can be deformed after being inserted into the corresponding slots in the peripheral strap, to hold the fixture in place while it is being bonded. In another embodiment, the interior lattice straps are joined to the perimeter strap by two shear joints formed respectively at the very top and bottom of the interface.

Abstract: A reactor core for a boiling water nuclear reactor includes a plurality of fuel assemblies (40) with a plurality of vertical fuel rods (10) and possibly occasional vertical water-filled rods or channels (32, 48, 49, 50, 51) which are surrounded by a fuel channel (1). Between the fuel assemblies (40) there are arranged water gaps (37a, 37b). At least one fuel assembly (40) has at least one outer, reduced corner portion (41) facing a gap (37a, 37bb), and the number of fuel rods (10) in each such fuel assembly (40) is reduced by a number corresponding to the number of reduced corner portions (41) therein.