Abstract: A fuel assembly has a top nozzle which includes a lower adapter plate and a plurality of guide structures thereon. The lower adapter plate has a peripheral edge. The guide structures are attached to and extend upwardly from the lower adapter plate at locations spaced inwardly from the peripheral edge of the lower adapter plate so as to separate the lower adapter plate into an interior portion extending between interior sides of the guide structures and mountable to the guide thimbles and a peripheral portion extending about exterior sides of the guide structures. The guide structures define a plurality of vertical guide slots.

Abstract: A double enclosure top nozzle subassembly for a nuclear fuel assembly includes an upper structure having a top plate and an outer depending peripheral sidewall enclosure, a lower structure having a lower adapter plate and an inner upstanding peripheral sidewall enclosure disposed below the top plate and within the outer sidewall enclosure. The outer and inner sidewall enclosures are slidably movable relative to one another as the top plate moves toward and away from adapter plate. A plurality of resiliently-yieldable biasing devices, such as leaf springs extend between and engage the top plate and lower adapter plate. Interengagable structure on the lower and upper edges of the respective outer and inner sidewall enclosures limit movement of the top plate and lower adapter plate away from one another so as to retain the outer and inner sidewall enclosures in sliding contacting relationship together.

Abstract: A method and apparatus for replacing an existing fuel guide pin in an upper core plate of a nuclear fuel assembly. The existing guide pin is removed to the level of the bottom of the core plate and inside the bore in the core plate to a point adjacent the pin retaining nut. A longitudinal bore is then created in the remaining portion of the existing fuel guide pin. A replacement fuel guide pin formed from a pin body, collet lock, and bolt is inserted into the bore in the upper core plate and through the bore in the remaining portion of the existing pin. The bolt and collet lock are inserted into a bore at opposite ends of the pin body and threaded together. A tapered shoulder at one end of the collet lock passes through the bore created in the existing guide pin and secures the replacement guide pin to the remaining portion of the existing pin.

Abstract: Bottom end fuel assembly reconstitution is permitted by elimination of weld of Inconel lower grid perimeter strip to stainless steel lower end fitting. Slots in 2 or 3 sides of L.E. Fitting capture ribbed sections of grid perimeter strip, locking screws hold L.E. Fitting in position on guide thimbles. Grids lip on perimeter strip is interlocked by sliding in L.E. Fitting groove.

Abstract: A fuel assembly includes an array of fuel rods and guide thimbles disposed in laterally spaced relation to one another. The guide thimbles have upper ends extending above the upper ends of the fuel rods. The fuel assembly also includes a top nozzle defined solely by a flat rectangular adapter plate having a main central portion and a peripheral portion surrounding and merging with the main central portion. The main central portion of the adapter plate has a plurality of attachment holes receiving the upper ends of guide thimbles for attachment of the adapter plate upon the guide thimble upper ends in spaced relation above the fuel rod upper ends. A first sest of holes are defined through one pair of diagonal corners of the adapter plate for use in attaching sets of spring assemblies directly to and upon the adapter plate for alignment along the peripheral portions thereof.

Abstract: A method of securing a cylindrical centering pin for a nuclear fuel assembly in a bore formed in a plate includes introducing an end of the centering pin into the bore until at least part of a coaxial, radially expandable wall portion of the end to be secured protrudes beyond the plate; and generating pressure in a closed hollow space surrounded by the wall portion with a pressure fluid until the wall portion radially expands and anchors the centering pin. According to another method, the end is introduced into the bore until at least part of the end to be secured, which has a periphery and an interior with radial slits formed therein, protrudes beyond the plate; and a mandrel-like tool is partially brought into the slits in the interior of the end of the centering pin and radially expands the end of the centering pin with the tool for anchoring the centering pin.

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: A cantilevered hold-down spring (68) for a nuclear fuel assembly (10), comprising an elongated metal bar including a substantially straight long leg portion (66) having one end adapted to be mounted (38) to a fuel assembly, an arcuate transition portion (70) at the other end of the long leg, and a straight short leg portion (76) extending from the transition portion at an acute included angle with the long leg portion, and a load transfer means (64) projecting from the straight leg intermediate the transition portion and the long leg first end. As the load on the primary loading point (80) on the transition portion increases, the load is transferred to the projection (64), thereby effectively shortening and stiffening the spring.

Abstract: Upper and lower core structures of core internals carry a plurality of centering pins which have free ends protruding into recesses in a fuel assembly endpiece. In the case of the upper core structure in particular, the nuts for fixing the centering pins are difficult to access in the event of a subsequent exchange of pins. Therefore, core internals which do not require a nut for securing on the centering pins are preferred. For this purpose, a centering pin is provided with a center bore passing through it. The ends of the center bores facing away from the fuel assemblies are in the form of conically tapering stepped bores. Each stepped bore has a plug which is displaceable in axial direction relative to the centering pin. The peripheral surface of the plug is conically formed in the same direction and with the same pitch as the stepped bore. The centering pin enters into a play-free fitting connection with a bore in a grid plate.

Abstract: A self-latching reactivity-reducing device contains neutron absorbing material and is installable in a guide thimble of a spent fuel assembly for reducing the reactivity of the assembly to allow its storage in an on-site fuel storage facility. The device includes an elongated rod which contains the neutron absorbing material and has a central passage extending between opposite ends of the rod. A self-latching mechanism is disposed on a leading end of the rod and engagable with a lower end portion of the guide thimble upon full insertion of the rod in the guide thimble so as to render the self-latching mechansim unlatchable from the guide thimble without the use of an independent tool inserted solely through the rod passage from a trailing end thereof. A closure plug is removably fastened to the trailing end of the rod for closing the passage therethrough.

Abstract: A nuclear reactor fuel assembly has a plurality of fuel rods filled with nuclear fuel, and a fuel assembly base having a longitudinal axis, a jacket, and a resilient support element in the form of a shock-absorbing leg to be placed upon a support structure of a nuclear reactor. The shock-absorbing leg is parallel to the longitudinal axis and disposed on the outside of the jacket. The shork-absorbing leg has a lower end forming a stop surface for the support structure.

Abstract: A fuel assembly has a top nozzle with improved clamps for retaining hold-down spring assemblies. Each clamp includes a clamp block formed integral with a flange of the top nozzle at each of a pair of diagonal corners thereof. Each clamp block has a pair of interconnected clamp slots formed therein. Each clamp slot is formed in the clamp block with interconnected openings at the front and outer side thereof. The front and outer side openings permit sideways insertion of the hold-down spring assembly at a base end thereof to position the spring assembly for attachment to the top nozzle. The clamp slot also provides a flat bottom surface in the clamp block for clamping the hold-down spring assembly.

Abstract: A pressurized water reactor of an advanced design comprises, in vertically spaced relationship, a lower barrel assembly having lower and upper core plates, an inner barrel assembly and an axially removable calandria assembly having a lower calandria plate. A plurality of rod guides are cantilever-mounted in parallel axial relationship within the inner barrel assembly and, specifically, are rigidly mounted at the lower ends thereof to the upper core plate. Axially extending sleeves are affixed to the upper ends of the rod guides and telescopingly receive therein generally cylindrical supports which are affixed to and depend downwardly from the lower calandria plate and define alignment axes for the respectively associated rod guides.

Abstract: The core is constituted by detachable assemblies (21) disposed vertically and maintained in position by a support or bolster (22) receiving the lower part or foot (21a) of the assemblies (21) inside sleeves having a vertical axis (25). Each of the sleeves (25) includes at least one orientation configuration (31) for the assembly (21) and each of the assemblies (21) includes on its foot (21a) at least one orientation configuration (30) adapted to cooperate with the orientation configuration (31) of the sleeve (25). The charging of the first core of the reactor may be carried out in a simple operation without a prior charging of false assemblies in an air atmosphere.

Abstract: A nuclear fuel assembly comprises a bundle of elongated fuel rods distributed at nodes of a regular lattice and a structure for retaining said fuel rods. The structure has a lower end piece, and upper end pieces, tie rods connecting said end pieces and grids distributed along the tie rods for maintaining the fuel rods at the nodes. The structure consists of two substructures slidable with respect to each other in the direction of the fuel rods. Springs located between the two substructures spread apart the two end pieces for respective abutment against a lower core plate and an upper core plate.

Abstract: A guide pin assembly for aligning the upper hold down plate of the top nozzle of a fuel assembly with the upper core plate of a pressurized water nuclear reactor includes a guide pin, a nut and a locking cup. The guide pin includes a nose, a threaded portion, a shaft, and an end. The radial alignment section of the shaft has a diameter that is approximately the diameter of a bore in the upper core plate of a nuclear reactor. The lower section of the shaft has a diameter less than that of the radial alignment section. The end includes a top having a diameter greater than that of the diameter of the bore in the upper core plate. The guide pin is insertable within a bore in the upper hold down plate of the top nozzle of the fuel assembly and through the bore in the upper core plate so that the nose and at least a portion of the threaded portion of the guide pin protrude above the upper core plate. The nut is adapted to be threaded onto the threaded outer surface of the threaded portion of the guide pin.

Abstract: A nuclear fuel assembly for a spectral shift reactor has an upper end piece and a lower end piece secured to a structural element belonging to the upper end piece by guide tubes arranged for receiving a cluster of control elements. The upper end piece further comprises a support member arranged for receiving said cluster at the end of the fall thereof, means for guiding said support member. The support member is guided for movement parallel to the axis of the guide tubes. Springs are contained within the end piece and disposed between the structural member and the plate for braking the cluster at the end of the fall thereof.

Abstract: A fuel assembly for a pressurized water nuclear reactor incorporating fluid moderator spectral shift control means. During the first part of the fuel cycle when there is excess reactivity, neutron moderation may be decreased by replacing a portion of the water within the core with a less effective moderator such as heavy water. During the life of the fuel, the heavy water is gradually replaced with regular water. The fuel assembly incorporates the necessary means and apparatus to effectuate such control.

Abstract: An integral reusable locking arrangement for a top nozzle of a reconstitutable fuel assembly includes a thin-walled tubular section on the upper end portion of each guide thimble of the fuel assembly above an externally threaded section thereon and an axial section on ecah alignment sleeve of the top nozzle above its lower internally threaded section. The tubular section has an annular circumferential protrusion defined thereon having an external diametric size which is greater than that of the remainder of the tubular section. The axial section on the sleeve has an internal diametric size which is greater than that of the tubular section but less than that of the protrusion.

Abstract: The hold-down plate of the top nozzle of a fuel assembly is interconnected to the upper extension members of the fuel assembly guide thimbles by an improved joint structure associated with each of a plurality of passageways through the hold-down plate which receives an upper end portion of each one of the guide thimble upper extension members. The improved joint structure includes an internal annular ledge on the hold-down plate within the passageway at a lower portion thereof so as to surround the upper end portion of the extension member, an annular recess on the upper end portion of the extension member, and an annular spring member fitted on the upper end portion of the extension member within the recess.

Abstract: An improved bottom nozzle of a fuel assembly includes a housing and a modified adapter plate formed by a network of ligaments which extend across the housing and are connected to the side walls of the housing a short distance below its upper peripheral edge so as to define an open region therein. The improved bottom nozzle also includes a debris trap having a structure disposed within the open region of the housing upon the adapter plate and adapted to capture and retain debris carried by collant flowing from openings in the lower core plate of the nuclear reactor to the fuel assembly. The trap structure is composed of a plurality of straps aligned with one another in a crisscross arrangement and defining a plurality of interconnected wall portions which form a multiplicity of small cells each having open opposite ends and a central channel for collant flow through the trap.

Abstract: An alignment sleeve capture arrangement in the top nozzle of a fuel assembly includes an internal cylindrical wall defining a bore through the upper hold-down plate of the top nozzle below and in communication with a passageway therein through which extends an alignment sleeve of the top nozzle which is used to attach it to the guide thimble of the fuel assembly. The bore has an inside diameter larger than the inside diameter of the passage so as to form a cavity surrounding an upper position of the alignment sleeve which extends axially through the bore as well as the passageway. Also, the arrangement includes an annular shoulder on the upper hold-down plate surrounding the alignment sleeve upper portion and defining an upper limit of the cavity. The shoulder forms a transition between the larger inside diameter of the bore and the smaller inside diameter of the passageway. Additionally, an annular retainer is attached to the upper hold-down plate and spaced below the shoulder.

Abstract: A secondary source positioning mechanism for a fuel assembly in a nuclear reactor locates an individual one of the secondary sources in a respective guide thimble of the fuel assembly aligned with an opening defined through the upper core plate which overlies the fuel assembly. The positioning mechanism has a tapered locating boss which registers with a chamfer on the lower side of the core plate about one of its openings and a resilient holddown device which resiliently couples the upper end of a rod containing the secondary source to the locating boss in a manner which restrains the upper end of the rod in the lateral direction and positions the secondary source rod in the axial direction.

Abstract: A nuclear reactor has a stationary horizontal core plate and a plurality of upright nuclear fuel assemblies all having the same cross-section and located side by side in a regular polygonal network. Each fuel assembly either has two locations for elongated plug elements or is adjacent a fuel assembly having such locations. A device for holding down the fuel assemblies comprises a plurality of locking sets each having at least one deformable locking member and a rigid member one of which is carried by a fuel assembly and the other by the core plate. The deformable locking member is so located with respect to a location and with the associated rigid member that insertion of an elongated element into the location forces the deformable locking member into positive engagement with the associated rigid member.

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 fuel assembly for a boiling water reactor has a bundle of fuel rods consisting of a top tie plate and a bottom part which, together with a plurality of fuel rods, constitutes a rigid unit. The fuel rod bundle is surrounded by a fuel channel (1), to which there is attached a fixing member (2) cast in stainless steel. The fixing member (2) is attached to a vertical projection (3), extending from the top tie plate, by means of a bolt (4) which is loaded with a tensile force and a sleeve (10) which is loaded with a compressive force and which surrounds the bolt and is arranged in the fixing member, the coefficients of thermal expansion of the bolt and the sleeve being less than that of the fixing member.

Abstract: An improved top nozzle has an enclosure with a lower adapter plate and an upstanding sidewall surrounding and attached to the periphery thereof and an upper hold-down plate spaced above the adapter plate for abutmnet with a lower side of an upper core plate by a plurality of coil springs disposed between the lower and upper plates. The lower adapted plate and upper hold-down plate have respective openings and passageways defined therethrough in a pattern which matches that of the upper ends of the guide thimbles of the fuel assembly to which the improved top nozzle is attached. The upper ends of the guide thimbles extend upwardly through the adapter plate which is stationarily mounted on the guide thimbles. Tubular sleeves disposed between the lower and upper plates are surrounded by respective coil springs. The lower ends of the sleeves are releasably threaded to the upper ends of the guide thimbles, while the upper ends of the sleeves extend into the passageways of the upper hold-down plate.

Abstract: Apparatus for limiting the effect of axial hydraulic flow force exerted on the fuel assemblies by the hydraulic pressure of a coolant in a water-cooled nuclear reactor comprises slit cylindrical elastic sleeves positioned within recesses in cylindrical housings carried by the fuel assemblies, the sleeves receiving centering pins connected to upper and lower core plates of the reactor and exerting frictional force thereon so as to control the axial movements of the fuel assemblies during transient variations in hydraulic flow force.

Abstract: A nuclear fuel assembly has fuel rods connected to the lower end plate of the assembly. The connecting structure comprises an attachment plate which is superimposed on the lower end plate and which is formed with openings corresponding to the rods. The openings lead out into parallel grooves machined on the lower surface of the plate. Each rod comprises a lower part having three radial branches at 120.degree., each formed with an end extension projecting radially outwardly from the outline of the rod. The extensions engaged in a groove have a height substantially equal to the depth of the groove. Axial fixing and locking against rotation of the rods are thus ensured.

Abstract: A refueling machine (100) is provided with a latching/unlatching rod (116) which is provided with a hexagonally configured head portion for mated engagement with a hexagonally configured socket (34) defined within a latching/unlatching screw (22) of a fuel assembly (10) whereby the fuel assembly (10) may be securely mechanically connected to the lower core support plate of the reactor internals. The latching/unlatching rod (116) is fixedly connected to a housing (118) which is co-axially disposed within a torque tube (140), the latter of which is fixedly secured to the lower end of a spur gear (130). The spur gear (130) is rotatably engaged with a drive spur gear (148) through means of an idler gear (128), whereby torque is transmitted to the torque tube (140).

Abstract: A hold down device for a nuclear reactor of the type in which a plurality of assemblies are disposed between an upper plate and a lower plate, which hold down device comprises a member having at least two resilient means, for example leaf springs which, when the device is placed between the top of a first fuel assembly and the upper plate, and downward pressure is applied to the member, are applied against fuel assemblies adjacent the first fuel assembly.

Abstract: Device for fixing a fuel assembly to the lower core plate of a nuclear reactor, comprising a fastening element (23) fixed to the lower core plate (18), in the central part of the opening (19) in this plate (18) corresponding to the assembly, an expandable sleeve fixed to the lower end (3) of the assembly in its central part, a guide tube (10) passing through the assembly in its central part in the axial direction, a rod (25) mounted for sliding movement in the tube (10) and fixed to an oval locking knob (38), and a socket (26) fixed to the upper end of the bar (25) and having a gripping surface for a lifting tool. The fastening element has an axial opening (31) for engagement of the expandable sleeve. The bar (25) and the socket (26) allow displacement of the oval knob (38) between service and out-of-service positions in which the latter spreads the expandable sleeve inside the opening (31) in order to fix the assembly.

Abstract: A heat shield for high thermal loading and particularly pulse heat loading n fusion reactors e.g. as first wall, plasma physics installations, particle accelerators, etc. contains a cooled support plate carrying a large number of shielding or limiter members on its side facing a heat source, e.g. a hot plasma. The shielding or limiter members are detachably connected to the support plate by a good thermally conducting seat, e.g. a bevel, ball or flat seat. By suitably shaping and arranging the limiter members, it is possible to substantially cover the surfaces of practically any desired shape such as, e.g., the inner wall of a toroidal vacuum vessel. As a result of their limited size, the limiter members can be adapted in a optimum manner to locally differing requirements. The size and shape of the support member can be adapted to widely differing boundary conditions.

Abstract: A method of reconstituting a nuclear reactor fuel assembly having a top nozzle subassembly attached to the upper end of its control rod guide thimble wherein the subassembly includes an upper hold-down plate, a lower adapter plate, and a coils spring interposed between the two plates. A force is applied on the hold-down plate to compress the coil spring and transform the subassembly from its operation mode to a reconstitution mode. The wall of the thimble is severed just below a first attaching retainer mounted on the end of the thimble which defines the upward limit movement of the hold-down plate during the operation mode. Containing fingers are placed on the subassembly for removing it as a contained unit. The top nozzle subassembly or a new replacement subassembly is then replaced on the severed thimble in its reconstitution mode and a second attaching retainer is mounted on the upper end portion of the severed thimble in redefining the upward limit movement of the hold-down plate.

Abstract: End fitting for the fuel assembly of a nuclear reactor comprising in per se known manner a device for holding the fuel assembly against an upper or lower plate of the reactor core, wherein the maintaining device is constituted by a plurality of rigid levers, having a first end and a second end, each lever being articulated on an axis A, a closed recess provided in the sides of a frame of the end fitting for each lever and elastic means contained in the recesses and exerting a restoring torque on the corresponding lever.

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: A nuclear reactor fuel assembly having an improved top nozzle subassembly with a hold-down device incorporated therewithin to prevent the force of the upward coolant flow from lifting the fuel assembly into damaging contact with the upper core support plate, while allowing for changes in fuel assembly length due to core-induced thermal expansion. The construction of the fuel assembly is such that its top surface can be placed in direct contact with the upper core plate. Thermal expansion of the components of the fuel assembly in the upward direction are accommodated within the top nozzle subassembly.

Abstract: Disclosed is a remotely operable releasable sealing coupling which provides fluid-tight joinder of upper and a lower conduit sections. Each conduit section has a concave conical sealing surface adjacent its end portion. A tubular sleeve having convex spherical ends is inserted between the conduit ends to form line contact with the concave conical end portions. An inwardly projecting lip located at one end of the sleeve cooperates with a retaining collar formed on the upper pipe end to provide swivel capture for the sleeve. The upper conduit section also includes a tapered lower end portion which engages the inside surface of the sleeve to limit misalignment of the connected conduit sections.

Abstract: A fuel assembly for a boiling water reactor comprises a plurality of vertical fuel rods (1) and is furnished with a fuel channel device. The fuel rods are arranged with their lower ends resting on a bottom plate and positioned by means of a plurality of spacers (6) attached to the casing. The freedom of movement of the fuel rods in the upward direction is limited by means of a top plate (12) arranged above the upper end surfaces of the fuel rods (1).

Abstract: The fuel assembly locking apparatus comprises a rotatable plate capable of simultaneously and positively engaging all four legs of the bottom nozzle of a fuel assembly for uniformly holding the fuel assembly while the spent fuel rods are pulled from the fuel assembly. The rotatable plate has four notched corners arranged to be rotated over a ledge on each leg of the bottom nozzle of the fuel assembly thereby preventing movement of the fuel assembly. The rotatable plate is also capable of being rotated 45.degree. so that the four corners of the plate are rotated clear of the legs of the bottom nozzle of the fuel assembly thereby allowing the fuel assembly to be placed on or removed from the locking apparatus. The locking apparatus is also provided with a torque actuator for remotely rotating the plate.

Abstract: A device is described for supporting a nuclear fuel rod in a fuel rod assembly which allows the rod to be removed without disturbing other rods in the assembly. A fuel rod cap connects the rod to a bolt which is supported in the assembly end fitting by means of a locking assembly. The device is designed so that the bolt is held securely during normal reactor operation yet may be easily disengaged and the fuel rod removed when desired.

Abstract: The object of the invention is a nuclear reactor fuel assembly including fuel elements arranged in a supporting frame comprising two endpieces, the upper (1) and the lower (2) respectively, to which are attached the ends of a plurality of vertical tubes (3), each endpiece 1(2) including a plane base 11(21) in which are arranged two series of orifices 7 for retaining the tubes (3) and for the flow of the cooling fluid.In accordance with the invention the base (11,21) of each endpiece (1,2) is joined side by side with an inner plate (15,25) equipped with the same series of orifices (70) for retaining the tubes (3) and for the flow of the fluid, and the orifices (70) have an oblong cross-section and are equipped with parts for attachment which cooperate with corresponding parts (31) for attachment of the said tubes (3) by transverse displacement of the inner plate.

Abstract: A fuel assembly in a nuclear reactor comprises a locking mechanism that is capable of locking the fuel assembly to the core plate of a nuclear reactor to prevent inadvertent movement of the fuel assembly. The locking mechanism comprises a ratchet mechanism that allows the fuel assembly to be easily locked to the core plate but prevents unlocking except when the ratchet is disengaged.

Abstract: The present invention relates to an anti-fly-off device for the fuel element of a nuclear reactor.This device, which is applicable to a nuclear reactor, comprises a plurality of sheathed fuel elements kept parallel to one another by a system of spacing grids and a stucture, independent of the fuel elements and formed by two parallel plates, namely an upper plate and a lower plate, between which extend brace rods regularly distributed among the system of fuel elements, whereby at least certain of these brace rods are surrounded by grid sleeves. A casing introduced into the grid sleeves of the lower grid around the brace rods and fixed by its lower end to the lower plate has at its upper end an outer shoulder which, with an appropriate clearance, blocks the upward displacement of the grid sleeve.

Abstract: A reusable system for removably attaching the lower end 21 of a nuclear reactor fuel assembly duct tube to an upper end 11 of a nuclear reactor fuel assembly inlet nozzle. The duct tube's lower end 21 has sides terminating in locking tabs 22 which end in inwardly-extending flanges 23. The flanges 23 engage recesses 13 in the top section 12 of the inlet nozzle's upper end 11. A retaining collar 30 slides over the inlet nozzle's upper end 11 to restrain the flanges 23 in the recesses 13. A locking nut 40 has an inside threaded portion 41 which engages an outside threaded portion 15 of the inlet nozzle's upper end 11 to secure the retaining collar 30 against protrusions 24 on the duct tube's sides.

Abstract: A perforated depressor plate extending across the bottom of the instrument ree of a fast breeder reactor cooperates with a circular cylindrical metal bellows forming a part of the upper adapter of each core assembly and bearing on the bottom of the depressor plate to restrict flow of coolant between core assemblies, thereby reducing significantly the pressure differential between the coolant inside the core assemblies and the coolant outside of the core assemblies. Openings in the depressor plate are slightly smaller than the top of the upper adapter so the depressor plate will serve as a backup mechanical holddown for the core. In addition coolant mixing devices and locating devices are provided attached to the depressor plate.

Abstract: A fuel assembly having a lower end fitting and a spidered actuating rod interacting therewith for holding the assembly down on the core support stand against the upward flow of coolant. Locking means and bracing means for interacting with projections on the support stand are carried by the lower end fitting and are actuated by the movement of the actuating rod operated from above the top of the assembly. The locking means include weak springs mounted near some but not all of the end fitting posts, for engaging the support stand. Stiff springs are mounted internal to the other posts, for uring the posts against adjacent support stand projections to provide a bracing for the locking means as the spider portion of the actuating rod presses against the locking spring. The angle and spring rate per unit length of the bracing spring are preset to assure a fairly constant locking force during the life of the assembly.

Abstract: A retainer to provide supplemental holddown force for a control component assembly latched into a fuel assembly of a nuclear reactor. Upon failure of latching mechanism the retainer precludes the ejection of the control component assembly from the fuel assembly by the upward coolant flow drage force. The spring loaded retainer is mounted at the top of the control component assembly and engages both the control component assembly and the core grid plate to form a structural blocking of the grid plate hole thereby precluding the ejection of the control component assembly therethrough.

Abstract: The invention provides a hold-down device which maintains a net downward force on a fuel assembly in a nuclear reactor under all thermal and hydraulic conditions in the reactor core region. The hold-down device is particularly applicable in reactors having stainless steel support barrels and Zircaloy guide tubes.The hold-down device of the preferred embodiment of the invention is comprised of coil springs coaxially disposed about alignment posts which extend upwardly from the top end plate of each fuel assembly. A hold-down plate is slideably mounted on the alignment posts and the coil springs are interposed, in compression, between the hold-down plate and the top end plate. In use, the coil springs bias the hold-down plate upwardly against a core alignment plate to provide a downward force on the fuel assembly. The hold-down plate may also serve as a lifting surface for the fuel assembly during fuel handling.

Abstract: An upper tie plate assembly for a nuclear reactor includes the usual tie plate having holes to receive the tie rod of the fuel assembly. A lower side member is welded to each side of the tie plate and there is a spring seat at each corner, connected to the lower side members. An upper side member parallels each lower side member at a higher elevation. At an intermediate elevation, there are leaf springs paralleling the side members, with their ends received within spring seats provided at the corners of the plate. Sliders are mounted on the upper side members and engage the midpoints of the upper surfaces of the springs. As the fuel assembly expands, the sliders, which engage an upper core plate of the reactor, deflect the springs from their normal, upperwardly bowed position, through a flattened position, to a downwardly bowed position. The ends of the springs are mounted within the spring seats in such a manner that they are free to accommodate extension of the springs.