Abstract: A nuclear reactor fuel assembly includes a plurality of fuel rods, a plurality of guide channels, two nozzles, one of which has a bearing plate with openings, elements for the detachable connection of the nozzles to the guide channels, a detachable connection locking device and locking device fasteners. The elements for the detachable connection of the nozzles to the guide channels have a cross-section size greater than the size of openings in the nozzle bearing plate.

Abstract: The invention refers to a fuel assembly comprising a lower end structure, an upper end structure including a top nozzle (5), a plurality of fuel rods and a plurality of guide thimbles (3). The top nozzle includes a passageway and an annular groove (10) in said passageway. A sleeve (11) is provided for attaching the guide thimble (3) to the top nozzle (5). The sleeve has at least three slots (12) and includes at least three bulges (13). Each bulge (13) has two ends and extends between two of the slots (12). At least one of the ends of the bulge (13) extends to a position at a distance (d) from the respective slot (12). The invention also refers to a guide thimble device (9) for use in a fuel assembly.

Abstract: A fuel assembly for a nuclear boiling water reactor is provided. The reactor comprises a plurality of such fuel assemblies and a plurality of control rods. Each control rod is insertable between the fuel assemblies. The fuel assembly has a longitudinal center axis and includes a plurality of elongated fuel rods and an elongated channel box. The channel box has inner sides, facing the fuel rods, and outer sides. Each inner and outer side has a longitudinal center line extending in parallel with the center axis and along the length of the channel box. A number of protrusions are distributed along the center line of at least two of the outer sides. The protrusions are configured to ensure a minimum distance between the outer side and an adjacent control rod and to enable the control rod to easily slide over and on top of the protrusions.

Abstract: The present invention provides a gray rod control assembly (GRCA) containing an improved neutron absorber comprised of a porous matrix of refractory metal infused with a neutron absorbing metal or metal alloy for a nuclear reactor. The reactor has a plurality of fuel assemblies, each including numerous elongated fuel rods supported in an organized array by substantially transverse support grids, and a plurality of guide thimbles disposed through the support grids and along the fuel rods. The GRCA includes a spider assembly structured to provide controlled insertion of gray rod assemblies within the thimbles of the fuel assembly, thereby controlling the rate of power produced by the reactor. Each gray rod assembly includes an elongated tubular member, a first end plug, a second end plug and the improved neutron-absorber disposed within the tubular member.

Abstract: Disclosed embodiments include nuclear fission reactor cores, nuclear fission reactors, methods of operating a nuclear fission reactor, and methods of managing excess reactivity in a nuclear fission reactor.

Abstract: A fuel assembly for a boiling water reactor contains a plurality of fuel rods maintained laterally by spacers and surrounded by a fuel assembly case. The outer walls of a spacer are provided with projecting elements that maintain a minimum space between the outer surface of the spacer and the fuel assembly case, the opening span of a spacer being smaller than the internal width of the fuel assembly case. The fuel assembly is characterized in that the spacer is maintained in an off-center position by a force acting laterally thereon such that an external space located between an outer surface of the spacer associated with the outer surface of a central cell and the fuel assembly case is narrower than an internal gap opposite the external space and oriented towards the center or towards a control element disposed at the center.

Abstract: A nuclear fuel assembly having a tube-in-tube control rod guide tube design that incorporates an end plug that extends axially upward to an elevation above the lower most grid where it is sealed at its upper end to the lower end of the control rod guide tube. The guide tube lower end plug has a threaded recess in its upper surface that mates with a corresponding dashpot end plug threaded extension that is formed as an insert in the lower end of the guide tube. A hole formed through the outer wall of the guide tube end plug at the elevation of the lower portion of the recess provides a positive inspection port for assuring the proper seating of the dashpot. A method of manufacture of such a fuel assembly is also disclosed.

Abstract: A nuclear fuel assembly having a tube-in-tube control rod guide tube design that incorporates an end plug that extends axially upward to an elevation above the lower most grid where it is sealed at its tipper end to the lower end of the control rod guide tube. The guide tube lower end plug has a threaded recess in its upper surface that mates with a corresponding dashpot end plug threaded extension that is formed as an insert in the lower end of the guide tube. A hole formed through the outer wall of the guide tube end plug at the elevation of the lower portion of the recess provides a positive inspection port for assuring the proper seating of the dashpot. A method of manufacture of such a fuel assembly is also disclosed.

Abstract: A secure connection between the bottom nozzle of a nuclear fuel assembly and the control rod guide thimbles having two or four crimped pockets in the side wall of a bottom nozzle leg counterbore which are formed by drilling two or four blind holes through the top surface of the bottom nozzle. After attaching the bottom nozzle to the fuel assembly with a crimp bolt a pneumatic tool is then inserted into a flanged cup feature on the crimp bolt head and the flanged portion of the cup feature of the crimp bolt is deformed into the crimp pockets. The crimp pockets are contained within the leg counterbore and prevent the screw from rotating or falling out of the assembly in the event of preload loss or screw fracture.

Abstract: A fuel assembly includes a bottom nozzle set on a lower core plate of a nuclear reactor, a top nozzle with a hold down spring to urge the bottom nozzle against the lower core plate, guide thimbles which guide control rods, having passed through the top nozzle, toward the lower core plate, a dashpot formed on each of the guide thimbles to reduce the fall velocity of a corresponding one of the control rods, a thimble screw which connects each of the guide thimbles to the bottom nozzle, and a drain hole formed to extend through each of the thimble screw. The dashpot has a large-diameter portion with substantially the same diameter as that of each of the guide thimbles. The diameter d of the drain hole falls within a range of 0.04 D<d<0.08 D where D is an inner diameter of the large-diameter portion.

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 includes a bottom nozzle set on a lower core plate of a nuclear reactor, a top nozzle with a hold down spring to urge the bottom nozzle against the lower core plate, guide thimbles which guide control rods, having passed through the top nozzle, toward the lower core plate, a dashpot formed on each of the guide thimbles to reduce the fall velocity of a corresponding one of the control rods, a thimble screw which connects each of the guide thimbles to the bottom nozzle, and a drain hole formed to extend through each of the thimble screw. The dashpot has a large-diameter portion with substantially the same diameter as that of each of the guide thimbles. The diameter d of the drain hole falls within a range of 0.04D<d<0.08D where D is an inner diameter of the large-diameter portion.

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: 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: A support grid for laterally maintaining the relative position of elongated fuel elements within a fuel assembly for use within a core of a nuclear reactor. The grid is formed in the shape of a lattice with the intersecting lattice members defining a plurality of cells, most of which respectively support the nuclear fuel elements. The remaining cells support nuclear control rod guide tubes and instrumentation thimbles. The cells supporting the nuclear fuel elements are provided with diagonally positioned springs on two, adjacent walls. The springs support the fuel elements against dimples which protrude from the opposite cell walls. The adjacent, diagonal springs in each fuel element cell are inclined in opposite directions. The walls of the cells supporting the control rod guide tubes are embossed along their height at the locations intermediate the intersection between adjoining walls with a concave notch having a curvature which conforms to the outside surface curvature of the control rod guide tubes.

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 fuel assembly includes a bottom nozzle set on a lower core plate of a nuclear reactor, a top nozzle with a hold down spring to urge the bottom nozzle against the lower core plate, guide thimbles which guide control rods, having passed through the top nozzle, toward the lower core plate, a dashpot formed on each of the guide thimbles to reduce the fall velocity of a corresponding one of the control rods, a thimble screw which connects each of the guide thimbles to the bottom nozzle, and a drain hole formed to extend through each of the thimble screw. The dashpot has a large-diameter portion with substantially the same diameter as that of each of the guide thimbles. The diameter d of the drain hole falls within a range of 0.04D<d<0.08D where D is an inner diameter of the large-diameter portion.

Abstract: A sleeve assembly for refurbishing a fuel rack having cells in which fresh or spent nuclear fuel assemblies may be stored, in which the cells have elongate rack walls extending from a rack base plate and the rack base plate has flow holes communicating with the cells. The sleeve has at least one elongate wall extending from the topside of a sleeve base having an opposed bottom side. The sleeve base has a flow hole extending therethrough that communicates with one of the rack base plate flow holes. A pin assembly disposed in the sleeve base flow hole has resilient tabs extending beyond the bottom side of the sleeve base for extending into a rack base plate flow hole and resiliently engaging the rack base plate when the sleeve assembly is installed in one of the cells. The pin assembly resists horizontal and vertical movements of the sleeve assembly, permits water flow into the cell and permits sleeve assembly removal tools and inspection devices to access the pin assembly.

Abstract: A tubular blank (22) is rolled on a mandrel (14) in a pilgrim rolling mill. In a first rolling stage, a first part of the blank (22) is rolled on a first part (18, 19) of the mandrel (14), with a reduction of the outside diameter of the blank (22) to the outside diameter of the guide tube and a reduction of the wall thickness of the blank (22) to one of a first wall thickness (e1) and a second wall thickness (e2) exceeding the first wall thickness (e1). The mandrel (14) is advanced in the axial direction. A second part of the blank (22) is rolled on a second part (20,21) of the mandrel spaced from the first part in the axial direction with a reduction of the outside diameter of the blank to the outside diameter of the guide tube and a reduction of the wall thickness of the blank (22) to the other of the first wall thickness (e1) and second wall thickness (e2).

Abstract: A pressurized water reactor fuel assembly with a guide tube and a method for producing a guide tube for control elements are provided. Such guide tubes in pressurized water nuclear reactors which are composed of zirconium alloys (zircaloy-2 and zircaloy-4) show sharp radiation-induced growth in the axial direction at the commencement of their use in the reactor core. The sharp initial growth of the tubes is compensated by an inherent contraction of the tubes. For this purpose, the guide tubes are given internal stresses which are reduced by tube contraction as a result of a radiation-induced supply of energy. During production, guide tubes which are too short are first produced and subsequently lengthened by at least 0.3% to a final dimension in a last production step. In order to lengthen the tube, it may be stretched on a straightening bench.

Abstract: A control rod guide tube for a nuclear reactor fuel assembly consists of several mutually portions of zirconium-based alloy. They define a passage that is narrow in a bottom portion of the tube. The guide includes a top length extending over at least 70% of its total length, and a bottom length of thickness greater than that of the top length. The top of the bottom length is engaged in the top length and is welded to the top length along the terminal edge of the top length.

Abstract: The invention relates to a fuel element for a pressurized-water reactor comprising a number of fuel rods arranged in a square lattice and wherein certain positions in the lattice contain guide tubes for receiving control rods, wherein the fuel element can be used for higher burnup by manufacturing the guide tubes of the element such that their irradiation-induced growth is reduced and their corrosion resistance is increased compared with conventionally manufactured guide tubes. This is achieved by finally heat-treating the guide tubes in two steps, the first step being a beta quenching and the second step a heat treatment in the alpha-phase region.

Abstract: The present invention relates to a miniaturized nuclear utilizing improved pressure tube structural members. More particularly, the present invention relates to a new miniaturized nuclear reactor utilizing novel structural members that are used to support the loads and stresses of multiple nuclear reactor fuel channel pressure tubes and calandria tubes in a moderator.

Abstract: A neutron absorbing apparatus which includes two adjacent neutron absorbing plates and a mounting assembly with latching means configured to be easily secured to fuel assemblies while the fuel assemblies remain under water in a fuel storage rack, thereby eliminating the need to remove the fuel assemblies or the fuel storage rack for installation. The two neutron absorbing plates are positioned orthogonally to form a chevron cross section which can be placed about the fuel assemblies by insertion in the existing space between the fuel assemblies and the cell walls of a fuel storage rack. A prescribed orientation of the chevron configured neutron absorbing plate in the cells of the fuel storage rack together with the selected use of a single neutron absorbing plate economically provides sufficient neutron absorption in all radial directions about the fuel assemblies to maintain safe storage condition sin closely packed fuel storage racks.

Abstract: A pressure vessel of a pressurized-water reactor has an upper part in which coolant is collected in a plenum. The coolant enters the plenum through a grid plate on which tops of the fuel assemblies are supported and the coolant is removed from the plenum laterally. Support columns and control-rod guideways form obstacles to the flow of the coolant which can lead to damming-up below the grid plate with horizontal pressure differences and corresponding horizontal flows. Throttle plates inserted in the top of the fuel assemblies or throttle inserts in apertures in the grid plate produce a uniform pressure in the coolant below the grid plate so that it flows uniformly and in a vertical direction through the individual fuel assemblies.

Abstract: A fuel assembly for use in a pressurized water nuclear reactor includes an assembly having guide tubes joined at their upper ends to posts having heads against which is biased a holddown plate spaced from a flow plate. The holddown plate is slidably mounted on the posts. The flow plate is fixed to the posts. The joints have one either post or tube member with spring fingers with projecting steps to lock in abutting relation behind the flow plate with a ring projection on the other captured in a recess in the adjacent finger surfaces. This structure provides a quick connect joint between the tube and the post.

Abstract: A nuclear fuel assembly for a pressurized water reactor having lower and upper tie plates, guide tubes, spacer grids, an instrumentation tube, and extended fuel rods which extend to the lower tie plate and which are spaced radially and supported along the guide tubes by the spacer grids, at least one of the extended fuel rods having at a lower end a fuel rod lower end cap secured by a first spring within an aperture in the lower tie plate and which exerts a lateral force against the lower end cap. The upper tie plate further includes a fuel rod support housing which extends down over the upper end of the at least one of the extended fuel rods and has a second spring positioned in a bore in the fuel rod support housing which exerts a lateral force on the upper end of the extended fuel rod positioned within the bore in the fuel rod support housing.

Abstract: A neutron absorbing apparatus which includes two adjacent neutron absorbing plates and a mounting assembly with latching means configured to be easily secured to fuel assemblies while the fuel assemblies remain under water in a fuel storage rack, thereby eliminating the need to remove the fuel assemblies or the fuel storage rack for installation. The two neutron absorbing plates are positioned orthogonally to form a chevron cross section which can be placed about the fuel assemblies by insertion in the existing space between the fuel assemblies and the cell walls of a fuel storage rack. A prescribed orientation of the chevron configured neutron absorbing plate in the cells of the fuel storage rack together with the selected use of a single neutron absorbing plate economically provides sufficient neutron absorption in all radial directions about the fuel assemblies to maintain safe storage conditions in closely packed fuel storage racks.

Abstract: A fuel assembly for a nuclear reactor, comprising a number of parallel fuel rods which are retained by means of spacer grids, arranged along the fuel rods, as well as guide thimbles wherein the guide thimbles, are fixed to the spacer grids. The guide thimbles with associated fuel rods are further fixed between a top nozzle and a bottom nozzle. In the top nozzle, through-holes are arranged for connection to a top sleeve joined to the upper end of the respective guide thimble. In the top sleeve, a first locking element is arranged for cooperation with a second locking element arranged on a guide sleeve, which guide sleeve is insertable through that hole in the top nozzle which corresponds to the respective top sleeve. The locking elements are interlocked in connected position by means of a locking sleeve insertable into the guide sleeve. The locking sleeve comprises a third locking element in the form of a through-opening arranged in the wall, a corbelled-out portion being arranged in the edge of the opening.

Abstract: Disclosed is a quick release removable top nozzle assembly for use with a nuclear fuel element assembly. The top nozzle assembly disclosed herein is comprised of a top plate member, an enclosure frame and an adaptor plate having a plurality of spaced openings therein. A plurality of tubular insert support members each adapted to fit within a selected opening in the adaptor plate has an enlarged collar section adapted to contact and support the underside of the adaptor plate. The assembly also includes a plurality of quick release joints each adapted to fit within another selected opening in the adaptor plate. Each quick release joint has a tubular lock insert which fits within the selected opening of the adaptor plate. The upper portion of the tubular lock insert is provided with a circumferential groove below a plurality of lobes. A locking ring is retained in a recess in the top of the adaptor plate by a retainer ring.

Abstract: A retainer is for retaining a grid on a fuel assembly. The retainer has at least one aperture at one end thereof for receiving a shoulder on a guide control tube and legs on the other end thereof for welding to the grid. The one end of the retainer is captured between the shoulder and a surface on the bottom nozzle of the fuel assembly when the guide tube is attached to the bottom nozzle. The retainer reduces the rotation of the guide tube resulting from torquing of the screws which connect the guide tube to the bottom nozzle thereby increasing the integrity of the assembly.

Abstract: A method for sputter coating the inside surface (30) of a fuel assembly tubular component (10) such as a control rod guide tube (200) with wear or corrosion resistant material. The steps include supporting the component tube in a fixture (12,14) and supporting a source tube (100,300) of e.g., wear resistant material, coaxially within the component tube, thereby defining a cylindrical annulus (24) between the tubes. The annular space is evacuated and backfilled with an inert working gas (26) such as argon, to a pressure sufficient to sustain a plasma discharge. The component tube is positively biased (36) as an anode, and the source tube is negatively biased (34) as a cathode, such that a plasma of the working gas is established in the annular space. A circumferential magnetic field is generated around the source tube to confine and shape the plasma whereby the source tube is bombarded with ions from the plasma substantially uniformly over the length of the source tube.

Abstract: The present invention provides a locking assembly for locking in place an upper support plate above a nuclear fuel bundle. The locking assembly includes several different components, including one rotatable member that is movable between a first position for locking the support plate in place and an unlocked position for releasing the support plate so that it can be removed from the guide tubes in the fuel bundle assembly. The rotatable member is resiliently maintained at its locked and released positions, and the entire locking assembly is an integral unit without any loose parts regardless of the position of the rotatable member.

Abstract: The invention relates to a fuel assembly (1) for a nuclear reactor and comprises a number of parallel fuel rods (2) which are held together by means of spacers (4,5) arranged along the fuel rods as well as guide tubes (3) arranged between the fuel rods (2) and parallel thereto. The guide tubes extend through the spacers (4) and are fixed between a top nozzle (6) and a bottom nozzle (7). According to the invention, bottom sleeves (8) for the guide tubes (3) are arranged in the bottom spacer (5). These bottom sleeves (8) are rigidly fixed to the bottom spacer (5) and rest against the bottom nozzle (7). Each bottom sleeve (8) is provided with a first locking member (9) for receiving a second locking member (10), arranged at the end of the respective guide tube (3), in order to rigidly lock the guide tube (3) to the bottom sleeve (8).

Abstract: In a grid for the nuclear fuel assembly, a grid member with springs and a grid member with dimples of the grid are arranged face to face such that grid cells of the grid member with springs and the grid member with dimples communicate with each other. Fuel rods are inserted into the grid cells of the respective grid members while the springs and the dimples are shifted sufficiently relative to each other so as not to contact the fuel rods. Subsequently, the grid members are moved to align the respective grid cells whereby the fuel rods are clamped by contacting with the dimples and springs. The grid members are then connected to each other. The grid cells of the grid member with dimples includes a thimble cell, and the grid cells of the grid member with springs include a thimble cell in alignment with one another.

Abstract: A fuel assembly for a nuclear reactor is provided with a number of parallel fuel rods, which are retained by means of spacers (2), and guide tubes (3) between the fuel rods. The guide tubes (3) are also attached to the spacers (2) as well as to a top nozzle and a bottom nozzle (4, 5). The guide tubes (3) are provided, at least at the spacers (2), with external threads (7) for improved fixing to the spacers.

Abstract: A fuel assembly for a nuclear reactor with a number of parallel fuel rods which are retained by means of spacer lattices and guide tubes (3), which guide tubes (3) are also fixed to the spacer lattices, a top tie plate (4) and a bottom tie plate between which the guide tubes (3) with associated fuel rods are fixed. The top tie plate (4) has been provided with through-holes (10) for connection to a top sleeve (7) joined to the upper end surface of the respective guide tube (3). According to the invention, there is arranged inside the top sleeve (7) a first locking element (9) for cooperation with a second locking element (13). This is arranged on a guide sleeve (11) which is insertable through a hole (10) in the top tie plate (4), which hole corresponds to the respective top sleeve (7).

Abstract: A guide tube insert assembly for receiving and guiding a control rod assembly through mutually aligned apertures formed in an upper support plate and an upper core plate of a nuclear reactor is disclosed. The guide tube insert assembly includes a plurality of guide plates with each guide plate including a plurality of bores with respective bores of each of the guide plates being axially aligned with one another so as to form a plurality of axial passages for conducting rodlets of the control rod assembly into and out of the fuel rod assemblies of a nuclear reactor. A plurality of tie rods are provided and extend between an uppermost guide plate and a lowermost guide plate, the tie rods being concentrically surrounded by a plurality of spacer sleeves of a predetermined length, with the spacer sleeves being positioned between adjacent guide plates so as to space the guide plates a predetermined distance from one another.

Abstract: A dashpot in a control rod guide thimble for a nuclear fuel assembly includes a lower tubular portion of an elongated main tube of the guide thimble, an auxiliary hollow tube inserted in the lower portion of the main tube, and an end plug attached to a lower end portion of the auxiliary tube. The auxiliary tube has an outside diameter slightly less than an inside diameter of the main tube to permit a close fitting relationship between an exterior surface of the auxiliary tube and an interior surface of the main tube lower portion. The auxiliary tube also has an upper end portion with an inside surface portion in axial cross-section flaring upwardly and outwardly to provide a tapered transition extending between and connecting an interior surface of the auxiliary tube with the exterior surface thereof.

Abstract: The sleeve (20) for locking the guide tube has an outer surface comprising successivley a cylindrical and a frustoconical part in the axial direction, without any radially protruding part. The upper cylindrical part (25) of the sleeve constitutes a fastening shell of the sleeve (20) in the end fitting of the assembly and the lower frustoconical part (24) a ring for expanding the guide tube. The fastening shell (25) the thickness of which is substantially smaller than the thickness of the ring (24) can be distorted into cavities machined in the end fitting of the assembly. An annular interlocking groove (20) is machined in the upper part of the ring (24).

Abstract: A fuel assembly for a light water cooled and moderated nuclear reactor comprises a bundle of fuel rods and a structure for holding the bundle in position comprising upper and lower end pieces or nozzles joined together by guide tubes which support grids for maintaining the fuel rods at the nodal points of a regular array. The upper end piece comprises an adapter plate fixed to some at least of the guide tubes and having an upwardly directed shroud arranged to bear directly or indirectly on the upper core plate of the reactor and encircling a coolant passage defining an internal volume into which all guide tubes open. The adapter plate has coolant passages around the shroud. This arrangement makes it possible to direct an adjustable fraction of the cooling water flow outwardly of a cluster guide sleeve associated with the assembly and belonging to the upper internals of the reactor.

Abstract: The guide tube (4) is fixed inside the adapter plate (10) of the demountable end block by a locking sleeve (20). The locking sleeve (20) comprises a part (24) ensuring expansion of the tube (4) and a ferrule (25) for fixing in the adapter plate (10). The fixing ferrule (25) consists of cylindrical segments separated by slits arranged in the direction of the generatrices of the ferrule (25). The cylindrical segments have deformations (29) inside cavities (22) radially directed relative to the through-hole (11) of the adapter plate (10), for ensuring fixing of the sleeve (20). The cylindrical segments of the ferrule (25) can be folded inwards so as to disengage the deformations (29) from the cavities (22), before extraction of the sleeve (20), in order to carry out demounting of the connection of the guide tube (4) and the adapter plate (10).

Abstract: An insert for providing a reduced inside diameter for a structural tube, specifically an instrumentation guide tube, of a nuclear fuel assembly. The insert has forming lobes which coact with the structural tube to plastically deform the structural tube and mechanically lock it with respect to grid straps of a grid assembly. The insert also has centering lobes to prevent it from being expanded in other than a coaxial alignment with the structural tube. An expansion tool is provided for sequentially registering with and expanding sequential forming lobes in a simplified manner whereby all of the operations necessary to assemble the structural tube in the fuel assembly can be easily and accurately performed.

Abstract: A top nozzle adapter plate for use in a fuel assembly of a nuclear reactor includes an upper structural component and a lower functional component supported from the upper component. The fuel assembly has elongated structural members and fuel rods disposed in a predetermined array. The upper structural component of the adapter plate includes spaced and interconnected hubs and ligaments arranged to define substantial open areas for coolant flow therethrough while providing a rigid framework capable of transmitting lifting loads imposed by the fuel assembly. The hubs are connected to the elongated structural members of the fuel assembly.

Abstract: In a nuclear reactor, the core is composed of fuel assemblies disposed in side-by-side spaced relationships with an outer group thereof defining the periphery of the core and an inner group thereof positioned inwardly of the outer group. A baffle structure extends about the reactor core adjacent the fuel assemblies in the outer group. Any jetting of coolant fluid through the baffle structure will impinge upon fuel rods in the outer group of fuel assemblies so as to cause vibration of the fuel rods. To prevent such vibration, a plurality of annular anti-vibration grids are axially spaced along and connected to guide thimbles of the fuel assemblies in the outer group thereof between at least some of the support grids of such fuel assemblies. The annular grids are separate from and unconnected to the support grids.

Abstract: In a reconstitutable nuclear fuel assembly, a top-nozzle-to-control-rod-guide-thimble attachment system employing a reusable locking tube having dimples. The guide thimble has longitudinal slots defining fingers therebetween. The fingers have rim (bulge) portions which engage a groove in the control rod passageway of the top nozzle adaptor plate for top-nozzle-to-guide-thimble attachment. The finger rim portions are prevented from moving radially inward, and thus leaving the groove, by a locking tube placed in the guide thimble. The locking tube has dimples at two elevations. The dimples interact with the other components of the attachment system to assure proper seating of the locking tube during locking tube installation and to assure against unintentional longitudinal movement of the locking tube during fuel assembly handling. An improperly seated locking tube complicates the underwater fuel assembly reconstitution operation.

Abstract: The universal fuel assembly has a plurality of elongated corner posts extending longitudinally between and releasably and rigidly interconnecting top and bottom nozzles so as to form a rigid structural skeleton of the fuel assembly. Additionally, a plurality of transverse grids are supported at axially spaced locations along the corner posts and a plurality of fuel rods are supported by the grids. Certain groups of the fuel rods are spaced apart laterally from one another by a greater distance than the rest of the fuel rods so as to define a number of elongated channels extending between the top and bottom nozzles. A cluster assembly having a cluster plate with a plurality of elongated rods is adapted to be removably supported on the top nozzle with its rods extending through the channels. The rods can be a plurality of guide thimbles in the case of one cluster assembly, or a plurality of oversized fuel rods in the case of another cluster assembly.

Abstract: An improved arrangement for attaching and reattaching a top nozzle of a reconstitutable fuel assembly includes a sleeve member associated with each guide thimble of the fuel assembly and complementary elements for attaching the sleeve member and the upper end portion of the guide thimble together. The sleeve member includes an inner tubular alignment sleeve portion which receives the guide thimble upper end portion and extends between the upper hold-down and lower adapter plates of the top nozzle. The sleeve member also includes an outer tubular shroud portion having a lower annular flange which underlies a coil spring surrounding the sleeve portion and interconnects the shroud portion and the sleeve portion. The outer shroud portion extends upwardly about a portion of the coil spring for protecting the spring from damage by coolant cross flow from adjacent fuel assemblies.

Abstract: A control rod for use in a nuclear reactor core to provide xenon compensation includes an elongated inner cylindrical member and an elongated outer cylindrical member surrounding the inner member. Each of the members is composed of axially-extending, alternating black poison and nonpoison regions. Also, the inner member is axially movable relative to the outer member to adjust the degree to which the poison regions of the members overlap with the nonpoison regions thereof and thereby change the overall worth of the rod in an axially uniform manner. The inner cylindrical member has a solid cross-sectional configuration, whereas the outer cylindrical member has an annular cross-sectional configuration and concentrically surrounds the inner member. Each of the poison regions in the members is about the same axial height, while each of the nonpoison regions is about the same axial height.

Abstract: A fuel assembly skeleton includes a top nozzle, a number of longitudinally-extending guide thimbles having upper ends, a number of joints interconnecting the top nozzle and the upper ends of the guide thimbles. All but a few of the joints are structural joints providing rigid connections between all but a corresponding few of the guide thimble upper ends and the top nozzle. Each of the other few joints is a non-structural joint providing a non-rigid connection between a guide thimble upper end and the top nozzle. The number of structural joints constitutes at least a substantial majority of the joints and, in any event, the number is at least three times the number of non-structural joints. Each non-structural joint is composed of a hollow sleeve rigidly connected to the top nozzle and disposed in a slip fit relationship about the guide thimble upper end. The sleeve is bulge fitted in a passageway defined in the top nozzle.