Abstract: A fuel containment containing nuclear fuel rods of a fuel assembly which will be loaded into a reactor core of a fast breeder reactor is formed narrow in width at middle portion of vertical direction and long in length of vertical direction. And as being used in the reactor core, the middle portion of vertical direction of the fuel containment, wherein both of heat generation and swelling are larger than that of other portion, expands more than other portion, but undesirable contact with adjacent fuel assemblies can be avoided as the middle portion is previously formed narrow. Moreover, the other portions, wherein expansion of the fuel containment and undesirable contact with adjacent fuel assemblies are barely caused, are formed previously wide in width by enlarging the coolant flow path of the fuel containment, whereby pressure drop of coolant of coolant used in the reactor core can be reduced.

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: A nuclear fuel assembly having first and second nuclear fuel identification codes marked on the fuel assembly. The first nuclear fuel identification code is of a different expression than the second nuclear fuel identification code and is arranged adjacent thereto.

Abstract: A fuel rod alignment template and method for loading fuel rods in a nuclear fuel assembly. Front and rear guide plates are provided with a plurality of holes corresponding to cells in the fuel assembly to be loaded. The guide plates are rigidly connected together by connecting rods that extend beyond the front guide plate and are sized to be received in the guide tubes of the fuel assembly. When attached to the fuel assembly with the front guide plate abutting the guide tubes the holes in the guide plates and cells in the grid assemblies of the fuel assembly are in coaxial alignment. This provides positive guidance to the fuel rods as they are inserted into the fuel assembly to prevent mis-tracking and damage to the fuel assembly.

Abstract: Herein disclosed is a reactor core including a plurality of fuel assemblies having a plurality of fuel rods. In a central region of the transverse section of the fuel assembly, a plurality of fuel rods are arranged in the form of a square lattice. In the peripheral region surrounding the central region, a plurality of fuel rods are arranged in the form of triangular lattice. The pitch of the fuel rods arranged in the square lattice form is equal to that of the fuel rods arranged in the triangular lattice form. With the arrangement of the fuel rods in the triangular lattice form in the peripheral region, the ratio of the moderator to the fuel of the peripheral region is smaller than that of the central region. As a result, the local power peaking drops. Since the arrangement of the fuel rods is partially in the triangular lattice form, the pitch of the fuel rods can be increased to augment the MCPR.

Abstract: A method of removing bow in a nuclear fuel assembly is disclosed. The fuel assembly has top and bottom ends fittings and a plurality of longitudinally extending thimble tube members interconnecting top and bottom end fittings. At least two transverse fuel rod support grids are axially spaced along the thimble tube members. A plurality of fuel rods are transversely spaced and supported by the fuel rod support grids. In one embodiment, a weight of known magnitude is secured on the bottom end fitting and the fuel assembly is raised with the weight secured thereon so that the weight exerts a downward force on the fuel assembly for straightening the fuel assembly and eliminating compressive stresses within the fuel assembly. In another embodiment, the bottom end fitting is secured onto the upender used for transporting fuel assemblies into and out of the containment building and the fuel assembly is pulled for straightening the fuel assembly and eliminating compressive stresses within the fuel assembly.

Abstract: A fuel assembly in the form of an elongated channel having several corners is connected to a coolant intended to flow through the channel. A bundle of similarly elongated fuel rods, retained by a plurality of spacers, is arranged in the channel, and arranged in the upper part of the fuel assembly, at least between a pair of spacers, is a sleeve formed of a sheet around the bundle. The sleeve has an external shape which conforms closely to the walls of the fuel assembly and is perforated by a large number of openings, the total surface of which is at least as large as the sheet surface remaining on one side of the sleeve.

Abstract: A spring-and-spacer assembly for maintaining fuel rods upright in a fuel assembly of a nuclear reactor core is provided. The spring is in the form of a continuous loop with first and second legs having mid-leg rod-contact regions. Bend regions are positioned on each side of each contact region extending toward the interior of the loop spring. In most positions, the spring is used to load two adjacent fuel rods. In configurations in which there is an unpaired fuel rod, a plate having a tab for contacting the spring is provided. The spring provides the desired force, such as about 2.5 pounds per fuel rod, in a small rod-to-rod spacing of less than about 0.14 inches.

Abstract: A spacer with a spring construction for the fuel bundle having matrix of parallel side by side fuel rods supported within a fuel channel between a supporting lower tie plate and holding upper tie plate is illustrated. The spacers each have a corresponding matrix of individual ferrules each surrounding the discrete fuel rods to be spaced within the matrix of fuel rods at any given elevation within the fuel bundle. Each of the individual ferrules surrounding the individual fuel rods are provided with stops against which the fuel rods are biased to ensure the required side-by-side spacing. Each ferrules must have at least one spring for forcing the fuel rods against the stops of its spacer ferrules to enable the spacer to assure required side-by-side alignment of the fuel rod. The springs are provided with a continuously looping main body having protruding tabs on opposite sides of the springs.

Abstract: A fuel assembly has a top nozzle which includes a lower adapter plate and a plurality of guide structures thereon. The lower plate has a periphery bounding an interior thereof mounted by guide thimbles. The guide structures are attached to and extend along the periphery of lower plate and upwardly therefrom. The top nozzle also includes upper hold-down plate and a plurality of leaf spring assemblies. The upper plate is mounted to the guide structures for slidable movement relative thereto such that the upper plate can move toward and away from the interior of the lower plate within the space bounded by the guide structures as the upper plate slidably moves along the guide structures. The leaf spring assemblies are interposed between and engaged with the lower and upper plates so as to yieldably support the upper plate in spaced relation above the lower plate and bias the upper plate for movement away from the lower plate.

Abstract: The present invention provides a structural component for constituting a reactor core comprising one and the other metallic members arranged adjacent to each other in a reactor, and reduction means for reducing a difference in the swelling between the metallic members due to neutron irradiation thereto; a core of the reactor comprising a plurality of such constructural element; and a method for operating a reactor having metallic tubular members arranged in a core of the reactor and each enclosing a plurality of metallic cladding tubes in each of which substance heated by neutron irradiation thereto and cooled by passing coolant through the reactor core is filled, wherein the reactor is operated under a condition that an average used temperature of the cladding tubes is higher than an irradiation temperature that the swelling rate of the cladding material due to neutron irradiation thereto becomes maximum and an average used temperature of the tubular members is lower than an irradiation temperature that the

Abstract: An improved spacer and method of making a spacer is disclosed for use in a nuclear fuel bundle wherein a plurality of fuel rods enclosed within a channel are maintained in parallel side-by-side relation by a plurality of the spacers. Each spacer is placed within the fuel bundle at selected elevations between upper and lower tie plates. The improved spacer is a member of the class of spacers wherein solid strips of material are welded at interstitially placed tube members between the fuel rods to form the continuous spacer grid. The improvement constitutes forming separate upper and lower reduced section grids from separate, normally aligned, first and second parallel sets of grid members. One grid is formed for the top of the spacer; the remaining grid is formed for the bottom of the spacer. Tube members placed interstitially between the fuel rods are used to interconnect the grids.

Abstract: A debris screen for a fuel assembly for a reactor to which coolant fluid is supplied comprises a substantially planar plate member having an array of coollant openings extending through the plate member dimensioned to trap at least a portion of debris particles carried by the coolant; and a skirt member enclosing the periphery of the plate member; each of the coolant flow openings having a coolant entry region at a lower surface, a coolant exit region at an upper surface and a coolant flow path extending between the entry and exit regions, the flow path including an intermediate segment laterally offset from the entry and exit regions to cause coolant to change direction of flow in the intermediate segment and thereby prevent at least a portion of the debris particles from passing through the plate members.

Abstract: A nuclear fuel element for use in the core of a nuclear reactor is disclosed having an improved corrosion resistant cladding. The cladding is comprised of zirconium alloys containing in weight percent 0.5 to 2.0 percent tin, or 0.5 to 2.5 percent bismuth, or 0.5 to 2.5 percent bismuth and tin, and about 0.5 to 1.0 percent of a solute composed of a member selected from the group consisting of molybdenum, niobium, tellurium and mixtures thereof, and the balance zirconium. Composite claddings are disclosed having a surface layer of one of the corrosion resistant zirconium alloys metallurgically bonded to a Zircaloy alloy tube. Claddings may contain an inner barrier layer of a moderate purity zirconium metallurgically bonded on the inside surface of the cladding to provide protection from fission products and gaseous impurities generated by the enclosed nuclear fuel.

Abstract: A bottom nozzle plate for a fuel assembly in a nuclear reactor. The bottom nozzle plate is formed from a rigid substantially square plate having legs adapted to be positioned on the lower core plate of the reactor for supporting the fuel assembly above coolant inlet openings in the core plate. The rigid square plate has two types of coolant flow holes therethrough. The first flow holes are grouped in clusters of four to define a square pattern relative to the sides of the plate such that the width of the sections of the plate between the flow holes in each cluster is less than the width of the sections of the plate between the clusters of four holes. Each of the second flow holes is formed in an irregular pattern to define a substantially clover leaf shape. The second flow holes are positioned so as to be above the coolant inlet openings in the core plate when the bottom nozzle plate is installed in the reactor.

Abstract: A nuclear fuel assembly has mechanical elements which constrain the flux thimble tube within the instrumentation tube to maintain physical contact with the interior surface of the instrumentation tube at a plurality of points staggered on a single-diametral plane and spaced substantially throughout the length of the instrumentation tube. The staggered mechanical elements induce a controlled elastic sinuous deflection of the inner thimble tube. The mechanical elements can take several different forms, for example, dimples or cantilevered spring fingers formed in the wall of the instrumentation tube and projecting radially inwardly therefrom.

Abstract: A nuclear reactor fuel element is helically wound with a strip which on one face at regular intervals along its length has dimples, and has a continuous rib on the opposite face. The strip contacts the associated fuel pin cladding via the dimples which effectively act as point contacts, and it contacts the neighboring fuel pins via the rib which also provides point contact. The regions between adjacent dimples are clear of the cladding and provide coolant flow paths thereby avoiding stagnant regions. The dimples may be arranged in two staggered sets one on each side of a central rib, and the strip then wound so that the dimples in each set each align axially with a respective dimple of the other set.

Abstract: In a nuclear fuel bundle, an improved lock washer is disclosed for permitting ease of remote removal of hex nuts on tie rods for the remote submerged disassembly of fuel bundles after use in a reactor. The improved lock washer includes two spaced apart and interconnected tie rods surrounding washer members, each of these tie rod washer members having radially inwardly extending keys. These keys register to corresponding keyways in the threaded ends of the tie rods to prevent tie rod rotation and threaded disengagement from the lower tie plate. Each washer member is manufactured from a spring material and includes at least one and preferably two radially protruding tangs T. These tangs are elongate and bent in an inverted U-shaped configuration. The inverted U-shaped configuration commences at the washer member and extends upwardly and outwardly away from the hex bolt to be locked. Reversal of the spring member occurs at the end of the U with the spring member returning angularly back towards the tie rod.

Abstract: An nuclear fuel assembly including an instrumentation tube adapted for insertion of an in-core detector tube and at least two equi-angularly disposed springs for holding the in-core detector tube concentrically within the instrumentation tube to prevent detector tube vibration is related herein. The springs are preferably secured to the inner surface of the instrumentation tube immediately above the bottom nozzle. An extension sleeve may be provided which extends upwardly or downwardly from the bottom nozzle to surroundingly receive the in-core detector tube. This will effectively increase the axial length of the in-core detector tube that is likely to abut the inner surface of the extension sleeve thus rendering the in-core dectector tube less susceptible to wear due to reactor coolant flow induced vibration.

Abstract: A debris filter bottom nozzle in a fuel assembly has support structure in the form of four legs adapted to rest on a lower core plate of the nuclear reactor and a nozzle plate fixed one side of the four legs facing toward a lowermost grid of the fuel assembly. The nozzle plate has defined therethrough only a plurality of flow holes individually smaller in size than the maximum dimension of unoccupied spaces through the lowermost grid which allow flow of liquid coolant through the nozzle plate. Therefore, any debris being carried by the liquid coolant flowing through the bottom nozzle from the lower core plate to the fuel assembly which is small enough in size to pass through the flow holes will also pass through the unoccupied grid spaces, whereas any debris which is large enough to not pass through the unoccupied grid spaces and collect in the grid will not pass through the aperture plate flow holes.

Abstract: To allow manipulation of the fuel assemblies in a nuclear reactor, the assemblies are provided with a lifting handle at the upper end. A top support is provided at the lifting end of the fuel assembly to determine the spacing. An upper end portion of the fuel channel for the fuel assemblies surrounds a lifting plate or the like for the fuel rods, where the lifting plate and handle together may form a lifting member cast in one piece. To simplify manipulation of the fuel assemblies during fuel inspection, for instance, and reduce the risk of losing small parts, a top support lock (1) for the top support (2) has been constructed in the handle (3). When assembling the top support (2), the top support lock (1) is moved to its open position and the angle-piece ends (5) are inserted through recesses (8) in the fuel channel (7) up to the openings (4) in the handle (3).

Abstract: A nuclear reactor fuel assembly having fuel rods containing nuclear fuel, includes a fuel assembly box in which the fuel rods are disposed, a head plate in the box having feedthroughs formed therein in which fuel rods are guided, at least some of the fuel rods being fastened to the head plate in the feedthroughs, a corner bolt disposed on top of the head plate, a cross piece disposed on the corner bolt at an upper inside corner of the box, an angular part disposed on two outer surfaces of the box, two leaf springs each extended in longitudinal direction of the box on a respective one of the two outer surfaces, a screw bolt connecting the box and the angular part to the corner bolt, the screw bolt having an expansion shank formed therein with a reduced diameter at the corner bolt, the screw bolt having a screw head with two ends, the screw head having a constriction formed therein between the ends thereof defining a coaxial screw head shank with a reduced diameter disposed in a hole formed in the angular part,

Abstract: A debris resistant bottom nozzle in a fuel assembly has a support structure in the form of four legs adapted to rest on a lower core plate of a nuclear reactor and a top flat plate fixed on one side of the four legs facing upwardly toward a lowermost grid of the fuel assembly. The flat plate is of a substantially solid configuration with a plurality of spaced cut-out regions defined therethrough in alignment with and directly above a plurality of inlet liquid coolant flow holes in the lower core plate. A plurality of open separate criss-cross structures are provided, each being fixed to the plate and extending across one of the cut-out regions therein within the plane of the plate.

Abstract: A device for relieving thermally induced stresses developed in a nuclear fuel assembly during reactor heatup is disclosed herein. The device generally comprises a stress relieving fastener capable of connecting a fuel assembly top nozzle, which may be stainless steel, to a threaded stud, which may be Zircaloy. The stud is attached to a fuel assembly channel. The fastener includes a threaded nut having a deformable portion for relieving thermally induced stresses developed in the stud by the differential thermal expansion of the top nozzle and stud. In a first embodiment of the nut, the deformable portion comprises a circumferential, deformable ridge which is substantially recessed from the marginal edge of the nut and which is disposed on the bottom most surface of the nut. The ridge contacts the top nozzle when the nut threadedly engages the stud. A second embodiment of the nut is similar to the first embodiment except that the deformable ridge is disposed flush with the marginal edge of the nut.

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.

Abstract: In a BWR fuel assembly, fuel rod spacers are disposed in desired axial positions along the fuel rods by a plurality of yieldably-resilient arcuate-shaped leaf springs. Some of the springs are disposed between an interior side of the fuel assembly outer channel and exterior sides of the spacers, whereas others are disposed between an exterior side of a central water cross and the exterior sides of the spacers. The springs thus contact the spacers and either the channel or water cross and exert sufficient contacting force thereon to maintain the spacers substantially stationary in the desired axial positions along the fuel rods. The springs extend generally parallel to the axial direction of the fuel rods and are spaced apart from one another in a direction generally transverse to such fuel rod axial direction. Each spring can be fixedly attached at one end to the spacer or clipped on an edge of the spacer.

Abstract: A nuclear reactor fuel assembly bottom nozzle to guide thimble attachment system and method allowing bottom nozzle removal and replacement without inverting the fuel assembly. At manufacture, a bottom-insertable, two-headed bolt secures the bottom nozzle adaptor plate to the guide thimble bottom end plug. The two-headed bolt is unthreadable in the guide thimble from the top of the upright fuel assembly. At reconstitution, a top-insertable bolt fastener secures the replacement or original bottom nozzle adaptor plate to the guide thimble bottom end plug. The bolt fastener is inserted in the guide thimble from the top of the upright fuel assembly. The bolt fastener is unthreadable in the guide thimble from the top of the upright fuel assembly for a second reconstitution. Less preferably, the bolt fastener also can be used for original manufacture (in place of the two-headed bolts previously discussed).

Abstract: Fuel rod cladding tube having an inner tubular layer of a zirconium alloy with alloying components of 1.2 to 1.7% tin, 0.07 to 0.2% iron, 0.05 to 0.15% chromium, 0.03 to 0.08% nickel, 0.07 to 0.15% oxygen, with the sum of percentages of iron, chromium and nickel in the range of 0.18 to 0.38%; or with the alloying components 1.2 to 1.7% tin, 0.18 to 0.24% iron, 0.07 to 0.13% chromium, 0.10 to 0.16% oxygen, with the sum of percentages of iron and chromium in the range of 0.28 to 0.37%; and with the inner tubular layer having an outside surface layer of another zirconium alloy with a layer thickness of 5 to 20% of the cladding tube as well as with 0 to 1% iron as an alloying component and with at least one alloying component from the group of: vanadium with 0.1 to 1% by weight, platinum with 0.1 to 1% by weight, and copper with 1 to 3% by weight.

Abstract: A modular component nuclear fuel assembly design in which sub-assembly fuel modules are joined together to form an integral fuel assembly. The invention permits a defective or damaged fuel assembly to be reconstituted from new sub-assembly fuel modules thereby facilitating quick repair. By using sub-assembly fuel modules, the invention allows for modular enrichment and/or burnup variations within a fuel assembly and permits tailoring of reactivity and/or fuel burnup within the core thereby enhancing fuel management and utilization and enabling peaking factors to be reduced. The sub-assembly fuel module design permits easy access to interior fuel rods thereby affording an increased fuel rod surveillance capability and further permits advanced fuel design to be incorporated into a reactor core with a minimum of risk.

Abstract: A fuel assembly has a bundle of elongated fuel rods disposed in a side-by-side relationship so as to form an array of spaced fuel rods, an outer tubular flow channel surrounding the fuel rods so as to direct flow of coolant/moderator fluid along the fuel rods, a hollow water cross extending centrally through and interconnected with the outer flow channel so as to divide the channel into separate compartments and the bundle of fuel rods into a plurality of mini-bundles thereof being disposed in the respective compartments, and a plurality of spacers axially displaced along the fuel rods in each of the mini-bundles thereof. Each of the fuel rods includes an outer cladding tube with an inner clad surface and a plurality of fuel pellets contained within the tube. Each spacer is composed of a plurality of interleaved inner straps and an outer strap encompassing the inner straps.

Abstract: Fuel array for an undermoderated nuclear reactor, comprising rods (6) arranged in a prism-shaped casing (1) parallel to the height of this casing (1). The internal surface of each of the walls (2) of the casing (1) is provided with channels (5) each of the channels (5) is located opposite a rod (6) arranged at the periphery of the array. The projecting parts (9) of the walls (2), between two channels (5), occupy part of the space between two peripheral rods (6). In this way, the moderating level remains constant throughout the cross-section of the array.The invention applies, in particular, to pressurized water reactors.

Abstract: A method of straightening an irradiated fuel assembly having a plurality of control rod guide thimbles in which some of the guide thimbles are bowed and thus greater in length than other of the guide thimbles comprises the steps of determining the length adjustments required for shortening the respective bowed guide thimbles in order to make their respective lengths generally the same as the other guide thimbles, and then forming expansions in the bowed guide thimbles so as to shorten their respective lengths by the amounts of the length adjustments. Usually, a plurality of expansions are made in most of the bowed guide thimbles at spaced locations between opposite ends thereof. Some of the expansions differ in the amount of shortening from other of the expansions. Also, the total amount of shortening of the bowed guide thimbles is controlled by the number of the expansions and the amount of shortening which results from each expansion.

Abstract: An improved top nozzle includes leaf spring assemblies interposed between its movable upper hold-down plate and stationary lower adapter plate and arranged along respective peripheries thereof. The leaf spring assemblies bias the upper hold-down plate in an upward direction into contact with the upper core plate of the reactor and thereby impose a hold-down force on the fuel assembly via the lower adapter plate. In the preferred embodiment, each leaf spring assembly includes opposite lower and upper ends, with the lower end being attached to the lower adapter plate adjacent one of the corners on its periphery and the upper end being movably coupled in a groove on the upper hold-down plate adjacent a next one of the corners on its periphery. The leaf spring assemblies are arranged in a single file about the peripheries of the lower adapter plate and upper hold-down plate, with one assembly extending between each pair of succeeding corners on the respective peripheries of the lower and uper plates.

Abstract: A hollow water cross disposed in an outer flow channel of a fuel assembly so as to divide an array of fuel rods in the assembly into a plurality of subgroups is composed of a plurality of hollow panels which extend radially from a central axis of the water cross and define an open inner flow channel. The panels are interconnected at their outer ends with angularly displaced portions of the outer channel and at their inner ends with one another so as to define a central channel portion which extends the axial length of the water cross. The improvement relates to a cross brace disposed within the central channel portion of the water cross generally along the central axis thereof. The cross brace includes radially-extending portions which extend within and parallel to the respective water cross panels and interconnect with dimples formed in each panel so as to reinforce and stiffen the water cross and thereby the outer channel of the fuel assembly.

Abstract: This invention relates to a fuel assembly for fast reactors and aims to reduce stresses induced in fuel pins by interaction between a wrapper tube and a bundle of fuel elements each of which consists of the fuel pin and a wire spacer wound around the fuel pin. The fuel elements consists of two kinds of fuel elements, one of them consists of conventional fuel pins and wire spacers and the other fuel pins of smaller diameter than the conventional fuel pins and wire spacers of larger diameter than the conventional wire spacers whereby the fuel assembly is provided with larger space therein.

Abstract: The invention provides a fuel assembly comprising a plurality of fuel rods containing a fissionable material and a plurality of moderator rods filled with a burnable poison and a metal hydride as a solid moderator material. All of the burnable poison in the fuel assembly is filled in the moderator rods, and number of the moderator rods is at least 4 and not more than 15% of total number of the fuel rods and the moderator rods.

Abstract: A nuclear fuel assembly channel spring and stop assembly having a separate channel spring assembly and stop assembly. A bi-directional channel spring is mounted by means of a plate to prevent rotation of the spring assembly relative to the upper fixture plate assembly of the fuel assembly. The stop member is formed integrally with the upper fixture plate assembly or mounted with a captive device to prevent rotation of the stop member relative to the upper fixture plate assembly.

Abstract: A fuel assembly for a nuclear reactor is provided with two access plugs in the adapter plate of the top nozzle whereby selected fuel rods can be removed and replaced without disassembling the assembly and while the assembly is in place in its operating position in the core region.

Abstract: A complementary shutdown device for an undermoderated nuclear reactor, comprising, inside certain arrays (3) of the core, guide tubes (7) of which the cross-section is at least equal to the sum of the cross-sections of three rods (6), and which are surrounded by at least one row of fertile rods (8), and a set of shutdown rods, the cross-section of which matches the cross-section of the guide tubes (7). The shutdown is obtained by allowing the shutdown rods, containing a neutron-absorbing material, to fall into the arrays (3) of the core, in the position of maximum insertion. The invention applies, in particular, to pressurized water nuclear reactors.

Abstract: Nuclear fuel assembly having four bundles of fuel rods, at least one fuel bundle being made with twenty symmetrically arranged fuel rod positions, the number of fuel rod positions in each of the remaining fuel rod bundles being at least sixteen and at most twenty-five.

Abstract: Provided is a fuel assembly for a boiling water reactor. The fuel assembly comprises fuel rod arranged in an 8-lines/8-columns square lattice, water rod and a channel box surrounding these fuel rods and water rods. A central portion corresponds to 80% of the fuel rod comprises fuel pellet having an outer diameter of 10.31 mm and inner diameter of 5.95 mm.

Abstract: A fuel asembly with a fuel channel (2) which surrounds a plurality of fuel rods (1) and which is divided, by means of a stiffening device (3) of cruciform cross-section and four wings (5), into four sub-channels (4) each of which comprises a bundle of fuel rods.Each fuel channel side has a plurality of stamped, inwardly-directed projections (6) arranged vertically one after the other, said projections being welded to one and the same stiffening wing. Each one of the wall portions located between the projections (6) defines, together with two adjacently positioned projections and a portion of the stiffening wing, a communication opening between two bundles located on one side each of the stiffening wing.

Abstract: A nuclear fuel assembly suitable for use in fast breeders. The fuel assembly has a wrapper tube and a plurality of fuel elements contained in the wrapper tube, each fuel element having a clad tube. The wrapper tube is made of a material which exhibits a larger rate of swelling by neutron irradiation than the material of the clad tube. For instance, the wrapper tube is made of an austenitic stainless steel, and the clad tube is made of an austenitic Ni alloy having a high Ni content. According to this arrangement, it is possible to avoid undesirable contact between the clad tube and the wrapper tube in the last period of the life time of the nuclear fuel.

Abstract: A fuel assembly comprises a plurality of fuel rods arranged in a lattice with a combined quadratic and hexagonal geometry, about one-fourth of the total number of fuel rods in the fuel assembly constituting a group of rods at seventeen fuel rod positions among which nine positions are nodal points in a quadratic lattice portion located in the middle of the group.

Abstract: A plumb nozzle for a nuclear fuel assembly having asymmetric loading of the fuel mass comprising a raised protuberance on the handling tool gripper finger engaging surface of the nozzle to compensate for skewing caused by the asymmetric fuel loading. The protuberance is positioned to be engaged by a gripper finger during handling, loading, or unloading of the fuel assemblies and extends downwardly a predetermined distance with respect to the other gripper finger engaging surfaces so that the fuel assembly hangs plumb.

Abstract: A nuclear fuel assembly includes and upper yoke, a base, an elongated, outer flow channel disposed substantially along the entire length of the fuel assembly and an elongated, internal, central water cross, formed by four, elongated metal angles, that divides the nuclear fuel assembly into four, separate, elongated fuel sections and that provides a centrally disposed path for the flow of subcooled neutron moderator along the length of the fuel assembly. A separate fuel bundle is located in each of the four fuel sections and includes an upper tie plate, a lower tie plate and a plurality of elongated fuel rods disposed therebetween. Preferably, each upper tie plate is formed from a plurality of interconnected thin metal bars and includes an elongated, axially extending pin that is received by the upper yoke of the fuel assembly for restraining lateral motion of the fuel bundle while permitting axial movement of the fuel bundle with respect to the outer flow channel.

Abstract: A device for securing a fuel assembly to a nuclear reactor pressure vessel comprises upper and lower tie plates for supporting the fuel assembly at its lower and upper ends, spacers for supporting the fuel assembly at intermediate portions between the both tie plates, a channel box surrounding the fuel assembly, and a stationary handle attached to the upper tie plate. A movable handle is attached to the stationary handle to be vertically slidable with respect thereto and the movable handle is always urged downwardly by a coil spring. Hook members are connected to the stationary handle to be rotatable in accordance with vertical movement of the movable handle such that the lower end of the hook member engages with an upper grid of the pressure vessel when the movable handle is lowered to a low portion and disengages therefrom when the movable handle is lifted to an upper position.

Abstract: Fuel assembly having square cross-section and a plurality of tube elements (7,8) arranged in a square reactor lattice, at least one of said tube elements being water tubes (8) and a predominant number being fuel rods (7). Each fuel channel wall has a hollow projection (9) lying in a vertical mid-plane. The number of tube elements between two projections (9) lying in the same mid-plane is smaller than nine and greater than two. A plurality of rows of nine tube elements (7, 8) are arranged in parallel with each of the mid-planes.

Abstract: A fuel assembly for a boiling water reactor comprises a plurality of fuel rods (2, 2'), which constitute four partial bundles and are surrounded by a fuel channel system (1) comprising one partial tube for each partial bundle. Each of the four partial bundles rests on a bottom tie plate (19) and is positioned with respect to the others by means of a common top tie plate (31), which is provided with a lifting loop (33) which is sufficiently strong to be able to lift the four partial bundles simultaneously, a major part of the lifting force being transmitted to said bottom tie plates via a plurality of supporting fuel rods (2').

Abstract: An integral nuclear fuel element assembly utilizes longitudinally finned fuel pins. The continuous or interrupted fins of the fuel pins are brazed to fins of juxtaposed fuel pins or directly to the juxtaposed fuel pins or both. The integrally brazed fuel assembly is designed to satisfy the thermal and hydraulic requirements of a fuel assembly lattice having moderator to fuel atom ratios required to achieve high conversion and breeding ratios.