Abstract: A method of forming a gripper cavity in a nuclear fuel rod end plug includes the basic steps of providing an end plug blank having an internal bore of substantially uniform diameter that opens at an annular outer rim on the end plug blank, cold forming the end plug blank to produce an intermediate end plug in which the annular outer rim is transformed into a conical outer rim having a rounded internal surface that defines an inlet opening to the internal bore of a diameter less than that of the internal bore, and removing an external layer of material from the intermediate end plug and an internal layer of material from the rounded internal surface of the conical outer rim to produce a finished end plug having an internal gripper cavity composed of the internal bore and a cylindrical internal surface defining the inlet opening to the internal bore and being of smaller diameter than the internal bore.

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

Abstract: A fuel assembly has a spring detent spacer grid of intersecting strips for capturing and retaining deleterious debris carried by reactor coolant before it enters the active region of a fuel assembly. A plurality of fuel end caps are peripherally grooved to receive springs projecting from the strips. The end caps are thus captured by springs and debris is wedged and trapped on opposite sides of the strip and against the end caps by pairs of adjacent integral leaves projecting from the stips intermediate and substantially symmetrically arranged about their intersections.

Abstract: An improved upper tie plate is disclosed in a fuel bundle for a boiling water nuclear reactor. The tie plate resides in a fuel bundle including an upper tie plate, a lower tie plate, a matrix of sealed fuel rods supported therebetween, and a surrounding channel. Both the lower tie plate and the improved upper tie plate have two functions; they support the fuel rods in vertical upstanding relation between the tie plates and interior of the channel and permit the passage of moderating coolant through the channel from the bottom of the channel to the top of the channel. This moderating coolant enters through the lower tie plate in the liquid form, passes into the matrix of upstanding fuel rods where steam is generated and exits outwardly through the improved upper tie plate as a water steam mixture at the top of the fuel bundle.

Abstract: A nuclear fuel assembly having an array of longitudinally extending fuel rods and axially spaced transverse grids with cells receiving the fuel rods therethrough employs anti-fretting protective devices for protecting lower end portions of tubular claddings of the fuel rods from damage-inducing contact with debris entrained in upward flow of coolant through the fuel assembly. Each device is in the form of a hollow sleeve disposed about and extending coextensive with the lower end portion of one fuel rod cladding. The sleeve has an upper portion which extends through one grid cell between lower and upper ends thereof, and a lower portion which extends below the grid cell from the lower end thereof to a bottom end of the fuel rod cladding spaced below the grid cell lower end.

Abstract: A nuclear reactor core sub-assembly is provided with a removable lifting head (12)/absorber pin (20) assembly. The absorber pins (20) are connected to the lifting head (12) in such a way that they can be disconnected, inverted and reconnected the other way round, either collectively as a unit or individually. This allows the same absorber pins to be used at least twice over in different sub-assemblies since only the absorber material closest to the core tends to become depleted during irradiation.

Abstract: Control cluster and method for the replacement of a control element in the control cluster comprising a plurality of arms and a plurality of control elements each comprising a shank for respectively passing through an arm. Each shank is provided with a threaded portion situated entirely at a distance above the arm. A fastening piece is screwed on the threaded portion to lock the control element into abutment against the arm. During replacement, the shank and the fastening piece are cut between the arm and the threaded portion and thus the rod to be removed is released.

Abstract: A fuel assembly (10) has a lower end fitting debris collector and end cap spacer grid (20) assembled in the form of a welded assembly of an "eggcrate" grid (21) and cast base (40) with hollow legs (42). Fastener seats (46) in hollow legs (42 ) permit guide tubes (14) with internally threaded ends to be joined to the upper surface of the lower end fitting debris collector (20) by means of slotted fasteners (50). End caps (22) rest on grid (21) at the intersection of slottedly interlocked bars (24 and 26). Thin strips (30) mounted in slots between bars (24) and bars (26) provide small debris catching openings in grid (21). Thick strips (30a) project upwardly between strips (30) to limit lateral movement of the end caps. Projections (70) on bars (24) prevent axial fuel rod movement by engagement of tab (70a) in circumferential groove (23) of end caps (22). Opposing capture force is provided by a wire (72) which is supported in openings in thick strips (30a) and which is received in groove (23).

Abstract: A fuel assembly according to the present invention is formed in such a manner that the small diameter portion of an upper end plug of a fuel rod is inserted into a boss of an upper tie-plate. The upper end plug includes a small diameter portion and a large diameter portion which is disposed below the former. An expansion spring in disposed in the small diameter portion of the upper end plug. A cover member surrounding this expansion spring is disposed in the large diameter portion of the upper end plug, and extends upwardly. Since the cover member surrounds the expansion spring, pressure loss caused by the expansion spring can be reduced.

Abstract: A solid or hollow replacement rod 40 for use in a pressurized water reactor (PWR) fuel assembly 10 inserts into cells of the spacer grids 18, 20 and 22 past mixing vanes 32, without damaging them, because of its asymmetric tip 42 formed by chamfer 54 and elongated curved surface 52 and its offset "x" formed by the bowed end section 44.

Abstract: A reconstitutable control rod spider assembly includes a spider structure, control rods, and attachment joints for detachably fastening the control rods to the spider structure. Each attachment joint includes a connecting finger of the spider structure having a central bore extending therethrough and a pair of opposing flat segments formed on the interior thereof, and an elongated upper end plug of each control rod inserted through the finger bore and having a pair of opposing flat sectors formed on the exterior thereof beng interfitted with the opposing flat segments on the connectng finger to retain the control rod in a predetermined angular position relative to the finger. The upper end plug also has an externally-threaded portion formed on the exterior thereof above the flat sectors and being disposed above the connecting finger, and a pilot aligning portion formed on an outer terminal end thereof above the externally-threaded portion.

Abstract: A fuel assembly for nuclear reactors which comprises the usual upper and lower tie plates and fuel rods extending between them is made debris-resistant by providing a grid spacer in contact, or very nearly so, with the lower tie plate and so positioned as to subdivide the usual openings in the lower tie plate which are provided for the passage of cooling water. This causes debris to be trapped in the openings of the lower tie plate, and keeps it from contacting the fueled portion of the assembly.

Abstract: A fuel assembly for nuclear reactors comprising a skeleton having two end pieces connected together by elongate elements and several grids spaced apart along the guide tubes and forming cells for holding a bundle of fuel elements in position at the nodes of a regular lattice. The grids comprise median grids adapted for resisting lateral shocks and having fins for creating turbulences in the flow of the coolant along the assembly, bottom grids without fins and ensuring the cross bracing of the elements and top grids with fins and ensuring cross bracing of the elements, the top and bottom grids imposing on the coolant a pressure loss lower than the median grids.

Abstract: A nuclear fuel assembly comprising a plurality of fuel elements, a structure having an upper end piece and a lower end piece rigidly connected together by tie rods and a plurality of spacing grids. The plurality of spacing grids comprises two end grids, one being connected to the fuel elements and secured to the tie rods and the other being connected to the fuel elements and slidably received by the tie-rods, and a plurality of intermediate grids secured to the tie-rods and slidably received by the fuel elements. The bundle of fuel elements can extend and retract from the end grid which is secured to the tie rods while being maintained and supported by the structure.

Abstract: A stuck fuel rod capping sleeve to be used during derodding of spent fuel assemblies if a fuel rod becomes stuck in a partially withdrawn position and, thus, has to be severed. The capping sleeve has an inner sleeve made of a lower work hardening highly ductile material (e.g., Inconel 600) and an outer sleeve made of a moderately ductile material (e.g., 304 stainless steel). The inner sleeve may be made of an epoxy filler. The capping sleeve is placed on a fuel rod which is then severed by using a bolt cutter device.

Abstract: An improved end plug for attachment on an end of a cladding tube of a nuclear fuel rod facilitates using a gripper tool for loading the fuel rod into a nuclear fuel assembly. The end plug includes an inner portion adapted to be inserted into the end of the tube and an outer portion adapted to extend from the end of the tube when the inner portion is inserted therein. The outer plug portion has a body part disposed adjacent the tube end and a leading part disposed remote from the tube end. The leading part of the outer plug portion has a hollow interior cavity defined therein, an exterior annular truncated surface defined on a terminal end thereof and an exterior annular tapered surface defined on a lateral side thereof. The exterior tapered surface extends between and merges with the body part and the exterior truncated surface and provides sufficient angular inclination so as to facilitate insertion of the end plug when mounted on the fuel rod tube end into the fuel assembly.

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: A fuel assembly has a fuel spacer consisting of a water rod having an outer diameter greater than that of fuel rods and a large number of circular sleeves into which the fuel rods are inserted. The fuel spacer has four bridge members. Both ends of these bridge members are fitted to two of eight circular sleeves which are adjacent one another in the diagonal direction of the fuel spacer. Both ends of each bridge member are bent so that its center projects outwardly away from the water rod.

Abstract: A fuel assembly with a square cross section for water-cooled nuclear reactors, the fuel assembly having fuel rods disposed in a square array prescribed by spacers defining square grid meshes includes rods without fuel disposed, instead of the respective fuel rods, at individual positions of the square array distant from the marginal edge of the fuel-assembly cross section, for varying moderation ratio of the fuel assembly, the rods without fuel having a square cross section smaller than the cross section of the respective grid meshes only by a clearance sufficient for assembling the rods without fuel in the respective grid meshes and disassembling the rods without fuel from the respective grid meshes.

Abstract: A thimble tube cap for replacing conventional thimble tube plugs (18) within thimble tubes (10, 110) of a nuclear reactor fuel assembly is fixedly mounted within a holddown assembly base plate (126) so as to cover the upper end of its associated thimble tube (110) fixedly mounted within the fuel assembly top nozzle adaptor plate (114). An axial through-bore (148) is provided within each cap for controlling the volume flow rate of coolant through the thimble tube (110). Each thimble cap includes a disc-shaped base portion (142) and an upstanding shaft portion (144) integrally formed therewith, an annular ledge or shoulder portion (146) being defined therebetween.

Abstract: A top nozzle subassembly having a hold-down device incorporated therewithin is provided for a nuclear reactor fuel assembly. The subassembly is slidably mounted on the upper ends of the control rod guide thimbles and is removably attached by internally threaded collars which threadably mate with external threads provided on the upper ends of the guide thimbles. Unthreading of the collars allows the subassembly to be removed from the fuel assembly to gain top access to the fuel rods within the fuel assembly. The invention also includes a special tool for threading and unthreading of the collars.

Abstract: The assembly comprises fuel elements carried and retained by a structure comprising tie rods and end parts. Dismantable holding devices for the plug of at least one element are provided at one end part and comprise a threaded connection. They are actuatable without applying a high torque to the sheath of the fuel element and enable the element to be extracted across an end part.

Abstract: A fuel assembly is disclosed which comprises a fuel channel (1) with square cross-section supported by an inlet sleeve (22) having at its lower part an inlet opening for a flow of coolant flowing through the fuel assembly. The inlet sleeve (22) is made of stainless steel and is mechanically connected to a transition sleeve (21) made of thick zirconium alloy sheet, which is welded to the more thin-walled fuel channel (1).

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

Abstract: 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: Apparatus and method for preventing the rotation of one or more elongated rods used in nuclear fuel assemblies include an end plug secured to one longitudinal end of such an elongated rod and having an out-of-cavity, non-round structure affixed thereto and configured to mate with a complementary shaped structure in a lower tie plate of a nuclear fuel assembly in such a manner as to prevent the rotation of the rod about its longitudinal axis. In one embodiment, the end plug includes a pair of flats formed on a portion of the end plug and configured to abut against a pair of flats formed on the outer surface of a cylindrical boss or sleeve of the lower tie plate, thereby to prevent the rotation of the rod. In another embodiment, four grooves, disposed 90.degree. apart about the periphery of an end plug of a rod form a spline. The grooves are configured to receive four, radially inwardly protruding, key members disposed 90.degree.

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: A composite nozzle for a fuel assembly adapted for installation on the upper or lower end thereof and which is constructed from two components. The first component includes a casting weldment or forging designed to carry handling loads, support fuel assembly weight and flow loads, and interface with structural members of both the fuel assembly and reactor internal structures. The second component of the nozzle consists of a thin stamped bore machine flow plate adapted for attachment to the casting body. The plate is designed to prevent fuel rods from being ejected from the core and provide orifices for coolant flow to a predetermined value and pressure drop which is consistent with the flow at other locations in the core.

Abstract: In a nuclear fuel assembly having a coolant conducting or water tube which also retains the spacers in axial position, the fuel rods experience greater axial growth with exposure than the water tube creating a risk that the water tube might become disengaged from the supporting tie plates. An arrangement for preventing such disengagement is described including lengthened end plug shanks for the water tube, a protective boss surrounding the lower end plug shank to protect it from flow induced vibration, a conical seat for the lower end plug and an arrangement for limiting upward movement of the water tube.

Abstract: An improved nuclear fuel assembly in which the lowermost grid is located close to the lower end fitting of the assembly, and a conventional Zircaloy-clad fuel rod is fitted with a stainless steel tip having a bevelled notch thereon for engaging resilient means on the grid within about one inch (2.5 cm) from the lower tip of the fuel rod. The notch mechanically restrains the fuel rod from lifting upwards during reactor operation, yet is shallow enough to permit removal of the fuel rod in the event reconstitution is required. The stainless steel tip is mechanically secured to the Zircaloy end cap of the fuel rod, and is located in a low importance flux region of the core so that the higher neutron poison absorption cross section of stainless steel is of little consequence. Since the lowermost grid secures each fuel rod within one inch of the lower end of the rod, there is little likelihood that the coolant flowing over the lower ends of the fuel rods will induce significant vibrations.

Abstract: A fuel assembly for the core of a boiling water nuclear reactor has a plurality of boxes each surrounding a respective bundle of fuel rods. These boxes, are connected at one end to a common bottom unit, intended to be connected to an opening in a supporting plate in the core, and are also connected at their other end to a common top unit. The boxes may be detachably connected to the bottom portion and the top unit and be relocatable within the fuel assembly. Alternatively, the bundles of rods may be arranged for easy withdrawal from the boxes to enable transfer of the rod bundles between the boxes.

Abstract: A fuel assembly is disclosed in which the nuclear fuel rods are supported by a grid-shaped bottom plate and a similar top plate, each of which is welded together from thin vertical metal strips, for example of a thickness of 0.6 mm, to define a grid of vertical channels (13, 14) intended for the fuel rods, each vertical channel being surrounded by eight adjacent channels only intended for coolant. (FIG. 2.