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 a nuclear reactor vessel includes a plurality of fuel rods, at least one coolant rod, a lower tie plate supporting the fuel rods and coolant rod, and a channel surrounding the fuel rods, coolant rod and tie plate. The lower tie plate is supported by the channel such that the channel carries a load of the fuel assembly. In one aspect of the invention, a conventional upper tie plate is removed and a handle assembly is provided that includes two spring loaded latch pins engageable with corresponding apertures in the channel. A transition member supports the lower tie plate and is rigidly secured to the channel. Thus, when lifting the fuel assembly from the reactor, the channel bears the load of the fuel assembly. If it is desired to remove the fuel bundle from the channel, the handle assembly is released from the assembly by releasing the latch pins.

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

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

Abstract: In a fuel bundle assembly (B) for a nuclear reactor wherein a plurality of fuel rods (R) and at least one water rod (W) extend between an upper tie plate and a lower tie plate, an improvement includes a fixed connection between the water rod (W) and the lower tie plate (L), the fixed connection including a threaded lower end plug of the water rod and a threaded hole in a boss formed in the lower tie plate adapted to receive the threaded lower end plug, the threaded lower end plug (50) formed with a diametrical slot (54) therein and the boss (56) formed with a pair of slots (60, 62) extending from opposite sides of the hole such that the diametrical slot (54) and the pair of slots (60, 62) are alignable when the threaded lower end plug (50) is threaded into the boss (56); and a key (64) insertable within the aligned slots to thereby fix the water rod against rotational movement.

Abstract: A grid-shaped spacer includes a sheet-metal web having a web aperture formed therein defining two spaced mutually opposite aperture edges. The aperture edges oppose an elongation of an elongate spring which is curved about a direction transverse to its own longitudinal direction and which has a tab that engages through the web aperture at each of two spring ends. At least one of the tabs is snapped into a notch formed in one of the spring edges opposing the elongation of the spring.

Abstract: A fixturing tool includes a sleeve having a central region with a circular axial opening and four leaf springs projecting from each of the opposite ends of the central region. The central region is cruciform in cross-section with arcuate side walls between the projections of the cruciform. Unit cells are arranged on a base having openings corresponding in location to the centers of the unit cells in their final assembly in a spacer for a nuclear fuel rod bundle. Fixturing devices are freely and loosely disposed within the unit cells and pins are partially inserted through the fixturing devices to expand the leaf springs to engage the unit cells. Once the cells with fixturing devices and partially inserted pins are centered over the base openings, the pins are advanced into the openings in the base to accurately align each unit cell relative to one another to enable final welding of adjacent cells to one another.

Abstract: A unitary one-piece lower tie plate grid has a lower portion and an upper portion for supporting the fuel rods. The lower tie plate grid includes cylindrical boss portions extending upwardly from the lower grid portion and arranged in square matrices for receiving the lower end plugs of the fuel rods. Web portions extending upwardly from the lower tie plate portion interconnect the boss portions along the sides of the matrices. The lower grid portion includes a plurality of openings which open into the flow spaces defined by the convex portions of the bosses and the webs within each square matrix of the upper portion of the tie plate. Coolant flows through the openings into the flow spaces for further flow upwardly about the fuel rods. The openings are radiussed adjacent their lower ends and have divergent side walls downstream of a throat area to define a flow venturi.

Abstract: Spring assemblies are employed in adjoining ferrules of a spacer in a nuclear fuel bundle to bias the fuel rods against stops and hence position the fuel rods in the spacer. The spring assemblies in one form include back-to-back spring bodies having central leaves with forward projections extending through rectilinear openings in adjacent ferrules to engage fuel rods to bias the rods against stops at the opposite sides of the ferrules. Outer pairs of leaves straddle the central leaf and project rearwardly and join the spring bodies one with the other whereby the central leaves, end portions of the springs connected to the central and outer leaves, and the outer leaves act as paired springs in series, providing a low spring constant. In another form, a single spring body has a central leaf with a projection extending through an aperture of a ferrule to bias the fuel rod. The outer leaves bear against the outer surface of the adjoining ferrule.

Abstract: A fuel bundle assembly for a nuclear reactor, wherein a plurality of fuel rods and at least one water rod extend between an upper tie plate and a lower tie plate, includes upper end plugs secured to a pair of water rods and having axial cut-out portions defined by upper and lower shoulders. A latching mechanism for securing the pair of water rods to the upper tie plate includes a latch bar mounted on an upper surface of the upper tie plate and rotatable into and out of the cut-out portions in the end plugs when the end plugs extend above the upper surface of the tie plate upon installation of the upper tie plate on the fuel bundle assembly. A locking pin is provided which prevents the latch bar from being accidentally unlocked.

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

Abstract: An expandable top nozzle for a nuclear fuel assembly having zircaloy thimble tubes has a cylindrical barrel and an assembly slidable in the barrel which includes a hub and a thin rod ejection plate fixed in spaced relation to the hub by support tubes through which the control rods extend. The support tubes extend through the hub and a spring retainer plate biased against an annular shoulder in the barrel by helical compression springs concentrically mounted with the support tubes in counterbores in the hub and spring retainer plate. A centrally located instrument guide robe has a spring loaded plunger which extends through the spring retainer plate and sets the height of an RCCA below the top of the barrel despite expansion and compression of the nozzle with changes in thimble robe length relative to the other internals. The top nozzle is removably attached to a fuel assembly by tubular inserts fixed to the thimble robes and having collapsed fingers with an annular outward bulge adjacent the free end.

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

Abstract: A 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: A new configuration of a pressurized water reactor nuclear fuel assembly having a disengaging upper tie plate corner portion (60) which will disengage if the fuel assembly is unintentionally lifted, thus precluding the lifting of the fuel assembly from the reactor core and thereby avoiding the potential risk of dropping the irradiated nuclear fuel assembly.

Abstract: An apparatus is presented for removing the inner and outer keys from a support grid of a fuel assembly automatically or by mechanical methods. The apparatus removes a line of keys from a loaded assembly inserted into a grid through an opening section of the grid to deflect the springs. Both ends of the keys are engaged with the engaging members, and one set of keys are rotated in one direction while the other set of keys are rotated in the opposite direction. The springs are then released to press on the fuel rods firmly in place between the springs and the dimples in the grid cell. The keys are removed from the grid by clamping or holding the keys and moving the keys together with the clamping/holding device in the key axis direction by operating the driving device until the keys are removed completely from the grid.

Abstract: An fuel or control assembly for a nuclear reactor includes an elongated case having a longitudinal axis, side walls extending parallel to the axis and defining an interior with a polygonal cross section, two ends, a rim, and at least one case opening being surrounded by the rim at one of the ends. The side walls have inner surfaces with a groove-like profile being machined therein and extending at a predetermined distance from the rim. A bundle of rods parallel to the axis or an elongated absorber body is disposed in the interior of the case. An end part has lateral surfaces extending parallel to the axis and being adapted to the polygonal cross section of the interior. The end part has corners disposed between the lateral surfaces being rounded and shaped in the axial direction to form dovetail-like protrusions.

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

Abstract: A pressurized water reactor fuel assembly includes a can with a flange engaging an upper surface of an upper tie plate through a bore and carrying a collar projecting beyond a lower surface of the upper tie plate and having an external thread. A bush at an upper end of a guide tube has an internal thread and an end surface which abuts the lower surface of the upper tie plate. A profile at the periphery of the bush engages a corresponding counter profile of the lower surface of the upper tie plate. This removable screw connection, which is also suitable for coolant tubes of boiling-water fuel assemblies, requires little of the cross-sectional area required for coolant bores and no individual tolerance equalization of the screw connections of an individual plate.

Abstract: An integral reusable locking arrangement between the guide tube and upper end fitting of a reconstitutable fuel assembly that eliminates all loose fastener components at the reactor site. A retainer sleeve is fabricated as an addition to or part of the upper end sleeve of the guide tube assembly. The retainer sleeve is formed from a cylindrical tube that has a plurality of flexible tabs spaced around the circumference of the tube at the lower end and substantially at the mid section of the tube. The lower tabs serve to center the guide tube in a hole in the upper end fitting or top nozzle. The mid section tabs extend beyond the shoulder of a counterbore in the hole in the upper end fitting or top nozzle and serve to retain the guide tube and upper end fitting in the installed position. A sleeve or collet may be inserted into the counterbore to force the tabs inward and unlock the retainer and guide tube from the upper end fitting.

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: An integral, reusable locking arrangement between the guide tube assembly and upper end fitting of a reconstitutable fuel assembly that eliminates all loose fastener components at the reactor site. A retainer sleeve is fabricated to cooperate with the upper end sleeve of the guide tube assembly. Slots adjacent to the upper end of the sleeve receive rigid tabs on the upper end sleeve to hold the retainer sleeve and upper end sleeve together. The retainer sleeve is formed from a cylindrical tube that has a plurality of flexible curved tabs spaced around the circumference of the tube substantially at the mid section of the tube. Optional lower tabs serve to center the guide tube assembly in the upper end fitting and provide a more rigid connection. The mid section tabs are received against the shoulders of slots provided along the walls of the hole in the upper end fitting and serve to retain the guide tube assembly and upper end fitting in the installed position.

Abstract: A shipping shim (30) for restraining nuclear fuel rods (11, 12, 13) in a nuclear fuel assembly (10) which accommodates varied sized gaps (g.sub.1, g.sub.2, g.sub.3, g.sub.4) between fueled and non-fuel bearing members in the fuel assembly.

Abstract: In a fuel assembly, lower end pieces of fuel rods, guide tubes and coolant pipes, etc., are inserted and/or screwed into a base plate and secured against lifting by a bolt. In the case of fuel rods, in particular fuel rods which do not extend over the entire length of normal rods, the bolt is screwed onto connecting parts in such a way that a releasable bayonet closure is produced. In the case of coolant pipes of boiling water reactors, there is provided in particular a screw connection which is irreleasably secured against torsion by the bolt.

Abstract: A fuel assembly for a boiling water reactor includes approximately mutually parallel fuel rods in a bundle having upper and lower ends. A skeleton holding the bundle has a handle, an upper tie plate retained on the handle at the upper end of the bundle, a lower tie plate at the lower end of the bundle, and at least one support element joining together the lower tie plate and the upper tie plate. The skeleton and the bundle are inserted in a fuel assembly case. A redundant support device holds the lower tie plate, the fuel assembly case and the upper tie plate together, when the handle is lifted.

Abstract: A method and an apparatus for locking the tie rods to block rotation relative to either the upper or lower tie plates utilizing the required fuel bundle channel. A conventional lock nut is provided for threading to the upper threaded end of the tie rods. This lock nut has attached extending wings, these wings when rotated interfering with a placed fuel bundle channel. In installation to the fuel bundle, and assuming that the tie rod has been fully threaded to the lower tie plate, the winged lock nut is rotated overlying the upper tie plate to cause full engagement of the upper tie plate to the tie rods. In such fastening, the winged lock nuts are rotated to an angle that provides no interference with the subsequently placed channel. Thereafter, and when the channel is placed, the channel interference with the rotational path of the wings of the lock nut and thus prevents relative rotation between the tie rod and winged lock nut.

Abstract: An apparatus for attaching a key member to a nuclear fuel assembly grid and detaching the same therefrom is disclosed. The apparatus includes a supply and recovery mechanism, an inserting and removing mechanism, and a rotating mechanism. The supply and recovery mechanism operates to supply the key member to a prescribed position adjacent to the grid and recover the same. The inserting and removing mechanism is disposed between the supply and recovery mechanism and the grid, and operates to insert the key member supplied from the supply and recovery mechanism into the grid and remove the key member from the grid to recover the same to the supply and recovery mechanism. The rotating mechanism is disposed adjacent to the inserting and removing mechanism, and operates to rotate the key member inserted in the grid in a prescribed direction about the longitudinal axis to attach the same to the grid and rotate the same in a direction opposite to the prescribed direction to detach the same from the grid.

Abstract: The present invention relates to an apparatus for manipulating the springs which hold the fuel rods firmly inside the grid cells of the grids in a nuclear fuel assembly. Conventionally fuel rods are inserted into the grids while the grid springs are in the active position, thus exposing the rods to possibilities of surface scratches and potential problems. The invented automatic apparatus avoids the formation of such surface damage on the fuel rods, by inserting the keys to inactivate the grid springs before inserting the fuel rods into the grids and removing the keys after all the rods are in place. The apparatus thus contributes to efficient manufacturing of the fuel assembly by simplifying the key quantity management operations and other tasks associated with the assembling operations.

Abstract: In a method of assembling a nuclear fuel assembly, a deflecting jig is inserted into grid cells in each of a plurality of grids. The diameter of the deflecting jig is enlarged to urge a spring of at least one pair of dimples and spring, associated with the grid cell to deflect the springs away from the dimple. A plurality of elongated key members are inserted into the grid cells through a plurality of openings defined at intersections between the straps forming walls of the grid cells. Each key member is rotated about its axis to cause hooks of the key member to project from a wall surface of the strap in a direction opposite to the projecting direction of the springs. The key member is then moved in a direction to engage the hooks with the wall surface of the strap. Urging of the spring by the deflecting jig is released to allow the same to be withdrawn from the grid cells and, subsequently, the fuel rods are inserted into the respective grid cells.

Abstract: A nuclear reactor fuel assembly includes two end plates having inner and outer surfaces Elongated, nuclear fuel-filled fuel rods are disposed between the inner surfaces and have longitudinal axes perpendicular to the inner surfaces. A leaf spring is disposed on the outer surface of one of the end plates and is bent at an acute angle defining first and second legs. The first leg is substantially perpendicular to the outer surface of the one end plate and loosely engaged in an elongated guide groove formed in the one end plate. The second leg meets the outer surface of the one end plate at an acute angle and has an end rigidly secured to the outer surface of the one end plate. The first and second legs and the guide groove have longitudinal orientations together defining a plane. A supplementary spring is bent at an acute angle and disposed between the legs of the leaf spring.

Abstract: An arrangement for supporting a fuel assembly of a nuclear reactor has upper and lower reactor core support plates, upper and lower tie plates for supporting fuel rods and a coolant path through the assembly. The improvement comprises a redesigned lower tie plate for providing an upward biasing force to the assembly for forcing the upper tie plate against the upper reactor core support plate. The biasing force is in the same direction as a levitation force caused by coolant flow through the assembly. In a preferred form, the tie plate includes an upper and lower section with hold-up springs disposed between the two sections.

Abstract: A key member, a method for insertion and/or removal of the fuel rods in a nuclear fuel assembly using the key member and a method of disassembling the nuclear fuel assembly using the same key member are disclosed. The key member has first projections and second projections formed on the opposite faces of an elongated key body. In the insertion or removal of the fuel rods or in the disassembling the nuclear fuel assembly, the key member is inserted into the grid and rotated to bring the first projections and the second projections into engagement with the straps of the grids and the springs on the straps to thereby deflect the springs in a direction away from the dimples opposing the springs. In this situation, the insertion and removal of the fuel rods can be carried out.

Abstract: An upper end fitting for a nuclear fuel assembly. A main body portion that is square in section has a base rigidly attached thereto. A combined pedestal and holddown spring assembly received in the main body portion is formed from leaf springs attached together by a bolt and nut. The leaf springs are bolted together such that the exterior radius or convex surface of the springs face each other. The bolt and nut are sized and shaped to serve as the pedestal for the control assembly of the reactor. A spring retainer movably received in the main body portion retains the springs inside the main body portion. The retainer is also provided with a bore therethrough sized to allow the bolt/pedestal to extend therethrough.

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: A captive fastener is joinable to a stud for being retained in a nuclear reactor. The fastener includes a head fixedly joinable to the stud, and at least one spring clip extending perpendicularly from the head and having a proximal end fixedly joined thereto, and a distal end in the form of hook for retaining the fastener in the reactor. The hook is resiliently deflectable laterally relative to the head for allowing assembly and disassembly.

Abstract: The spacer pin of this invention is preferably threadably secured to a thermal shield normally found within reactor vessels. It comprises a main body having a cavity therein which houses a locking assembly that alternately engages or disengages the threads of the thermal shield as desired. Ideally, as bolt means are is rotated within the main body, locking keys are either moved into engagement with the threads of the thermal shield or the locking keys are removed from such engagement with the thermal shield. In this fashion, the spacer pin may be locked onto or unlocked from the thermal shield as desired. A locking cap prevents the bolt means from coming unthreaded during use and also insures that the spacer pin remains secured to the thermal shield.

Abstract: A spacer sleeve for positioning and restraining a nuclear fuel rod in a nuclear fuel assembly, having a thin walled tubular member having an inner wall and an outer end, and extending a height from a lower end to an upper end and being positioned around the fuel rod to form an unrestricted coolant flow passage along the height of the tubular member, the flow passage having a cross-sectional flow area formed between the fuel rod cladding and the inner wall of the tubular member, and a thin tab extending from the tubular member into the unrestricted flow area and secured to a portion of the cladding of the fuel rod.

Abstract: A reactor core removable fuel assembly includes upper and lower tie plates having pluralities of fuel rods and hollow control rods extending therebetween. The lower tie plate includes a lower manifold therein joined in flow communication with a reservoir containing a neutron absorbing control liquid, with the reservoir being removable from the reactor core together with the fuel assembly. The control liquid is selectively pumped from the reservoir through the lower manifold and into the control rods for selectively varying the level of the control liquid therein for controlling reactivity.

Abstract: A replacement guide pin assembly is provided for aligning a nuclear fuel assembly with an upper core plate of a nuclear reactor core. One embodiment of the guide pin assembly includes an elongated guide pin body, a ferrule, and a lock screw. The guide pin body has a lower expandable base insertable within a hole in the top nozzle, and capable of expanding radially outwardly relative to a longitudinal axis of the guide pin body to provide an interference fit with the top nozzle. The ferrule is insertable within the top nozzle hole, interfitted with the guide pin body, and capable of imparting a radially and outwardly directed force on its lower expandable base to expand it within the hole of the top nozzle and thereby secure the guide pin body to the top nozzle in response to a predetermined displacement of the ferrule relative to the guide pin body along its longitudinal axis.

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: 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: For each of the demountable fuel rods (23), the end part of the protective tube (27), which end part is open towards the exterior, has a reduced diameter over a certain length and comprises at least one seating which does or does not pass through its wall. The end part of the fuel rod (23) is integral with a ferrule (34) which is coaxial with the fuel rod and which surrounds the assembly rod (31) of the fuel rod over part of its length. The ferrule (34) is engaged on the reduced-diameter part of the protective tube (27) when the rod (31) is screwed into the bore (28) of the protective tube. Locking against rotation of the fuel rod in the protective tube (27) is ensured by deformation of the ferrule (34) within the openings of the end part of the protective tube (27). The fuel rod is demounted by exerting a torque on it by way of an engagement surface (37), for example of prismatic form, located near the end of the fuel rod.

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: In a nuclear fuel bundle for a boiling water reactor, the prior art suggested concept of tapered fuel rods forming the bundle array is disclosed in a practical design including a fuel bundle and an improved associated spacer utilized in the upper two phase region of the fuel bundle. A tapered fuel rod is utilized having a large diameter bottom tube for holding corresponding large diameter fuel pellets at the fuel rod bottom, a smaller diameter top tube for holding correspondingly smaller diameter pellets at the top of the fuel rod, and a bell reducer situated between the large diameter lower fuel tube and the smaller diameter upper fuel tube. This bell reducer tapers from the large outside diameter of the lower fuel tube and the smaller outside fuel diameter of the upper fuel tube and forms a smooth transition between the large and small diameter sections of the fuel rod. An improved fuel rod spacer is disclosed for use with the upper and smaller tube portions of the fuel rods.

Abstract: In a fuel bundle having a matrix of parallel side-by-side fuel rods supported between a lower tie plate and an upper tie plate, a new ferrule and spring construction for the required spacers used to maintain the fuel rods in their required precise side-by-side alignment is disclosed. Paired ferrules are each provided with apertures for capturing a single spring between the ferrules. The springs are provided with a continuously looping main body having protruding tabs on opposite sides of the springs. The paired ferrules are confronted at their respective apertures for the capture of the springs. The shape of the apertures permits insertion of the spring after the ferrules have been welded together. The springs are compressed while being inserted. After insertion the springs return to their original shape and are confined between the ferrules. After insertion of the fuel rods, the springs are compressed to an intermediate position, but are still confined within the ferrule apertures.

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: 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: 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.