Abstract: A reactor pressure vessel includes a reactor pressure vessel body, a nozzle structure connected to the reactor pressure vessel body, a conduit structure connected to the nozzle structure, and a restraint device attached around a portion of the conduit structure. The restraint device includes collar parts that have cross sections corresponding to respective segments of a periphery of the portion of the conduit structure, brackets attached to the nozzle structure, and rods connecting the brackets to the collar parts. The collar parts are connected end-to-end to each other such that a cross section of the collar parts connected to each other corresponds to the periphery of the portion of the conduit structure. The collar parts are pinned to each other. The brackets spaced apart from each other around a periphery of the nozzle structure.

Abstract: A pressurized water reactor (PWR) comprises a pressure vessel containing primary coolant water. A nuclear reactor core is disposed in the pressure vessel and includes a plurality of fuel assemblies. Each fuel assembly includes a plurality of fuel rods containing a fissile material. A control system includes a plurality of control rod assemblies (CRA's). Each CRA is guided by a corresponding CRA guide structure. A support element is disposed above the CRA guide structures and supports the CRA guide structures. The pressure vessel may be cylindrical, and the support element may comprise a support plate having a circular periphery supported by the cylindrical pressure vessel. The CRA guide structures suitably hang downward from the support plate. The lower end of each CRA guide structure may include alignment features that engage corresponding alignment features of the upper end of the corresponding fuel assembly.

Abstract: An assembly to be inserted into a nuclear reactor, such as a liquid sodium-cooled fast neutron reactor, includes an assembly hollow body of elongate shape along a longitudinal axis X. The wall of the hollow body includes at least one through-opening. The assembly also includes an assembly element inserted into the hollow body. The assembly element includes at least one flexible blade of which the free end is shaped into a clip-fastening hook collaborating in clip-fastening fashion with the through-opening from inside the hollow body, so as to connect the assembly element to the hollow body. The assembly also includes at least one removable structure for locking the flexible blade clip-fastened into the through-opening. The removable locking structure makes it possible to prevent the flexible blade from flexing and thus the removable locking structure makes it possible to lock a connection between the assembly element and the hollow body.

Abstract: A spring apparatus in accordance with the disclosed and claimed concept is usable in a nuclear installation. In one embodiment, the spring apparatus includes a plurality of springs that are in a compressed state and that are compressively engaged with an upper core plate of a nuclear reactor when the reactor is in a cold condition. However, when the reactor is in a hot condition, a spring of the plurality of springs is in a free state wherein a free end of the spring is in an uncompressed state and is disengaged from the upper core plate. In another embodiment, the spring apparatus employs a support apparatus that is also in accordance with the disclosed and claimed concept and that includes one or more bumpers that engage the springs of a spring pack from the underside.

Abstract: In a method of designing a nuclear reactor core for uprated power operations, a set of constraints are inputted to be satisfied for uprated power operations, and a test reactor core design is generated based on the constraints. One or more automated tools may be selected from a set of automated tools to evaluate the test core design against the constraints. The selected tool may then be operated. Operation of the selected automated tool includes simulating reactor operation with the test core design, based on the constraints, to produce a plurality of outputs, comparing the outputs against the constraints, and providing data indicating constraints that were violated by the test core design during the simulation, based on the comparison. One or more of the automated tools are iterated until a test core design meets all constraints for uprated power operations, thereby representing an acceptable power uprate core design.

Abstract: A nuclear fuel assembly having a plurality of multi-leaf hold down spring sets extending from a top nozzle. Each spring set consists of a multiple number of springs leafs in order to provide a large working range of spring deflection. Each spring leaf has a straight, flat base section followed by a straight, flat tapered beam with a secondary spring set having a curvature at its peripheral end.

Abstract: A nuclear fuel rod plenum spring assembly that has a spacer affixed to the lower end of the ground torsion spring. The spacer has a substantially flat surface on its underside that presses against the upper surface of the upper fuel pellets to spread the load of the spring over the top surface of the upper most fuel pellet.

Abstract: A hold-down spring unit for a top nozzle of a nuclear fuel assembly. The hold-down spring unit is coupled to the upper end of the top nozzle of the nuclear fuel assembly. The hold-down spring unit includes a first spring which provides a hold-down force upon the nuclear fuel assembly under start-up conditions or hot full power conditions of a nuclear reactor, and a second spring which provides an additional hold-down force upon the nuclear fuel assembly under start-up conditions of the nuclear reactor. The hold-down margin under start-up conditions or hot full power conditions is reduced, thus enhancing the mechanical and structural stability of the nuclear fuel assembly.

Abstract: A hold-down spring unit for a top nozzle of a nuclear fuel assembly. The hold-down spring unit is coupled to the upper end of the top nozzle of the nuclear fuel assembly. The hold-down spring unit includes a first spring which provides a hold-down force upon the nuclear fuel assembly under start-up conditions and hot full power conditions of a nuclear reactor, and a second spring which provides an additional hold-down force upon the nuclear fuel assembly under start-up conditions of the nuclear reactor. The hold-down margin under start-up conditions and hot full power conditions is reduced, thus enhancing the mechanical and structural stability of the nuclear fuel assembly.

Abstract: A method to confine a nuclear reactor fuel bundle assembly including: inserting a lower portion of the fuel bundle assembly into an open end of a lower fuel particle barrier; supporting the lower portion of the fuel bundle with the lower fuel particle barrier; grasping the lower portion of the fuel bundle assembly with the lower fuel particle barrier; lowering an upper fuel particle barrier over an upper tie plate of the fuel bundle assembly; moving at least a portion of a handle fixed to the upper tie plate through an open slot in the upper fuel particle barrier; closing the open slot with a closure device after the handle passes through the slot, and preventing fuel particles being released from the nuclear reactor fuel bundle assembly by the upper and lower fuel particle barriers.

Abstract: A hold-down spring unit for a top nozzle of a nuclear fuel assembly. The hold-down spring unit is coupled to the upper end of the top nozzle of the nuclear fuel assembly. The hold-down spring unit includes a first spring which provides a hold-down force upon the nuclear fuel assembly under start-up conditions or hot full power conditions of a nuclear reactor, and a second spring which provides an additional hold-down force upon the nuclear fuel assembly under start-up conditions of the nuclear reactor. The hold-down margin under start-up conditions or hot full power conditions is reduced, thus enhancing the mechanical and structural stability of the nuclear fuel assembly.

Abstract: The present invention relates to a top nozzle for a nuclear fuel assembly that has a two-stage elastic section such that a pushing force against the axial movement of the nuclear fuel assembly under normal conditions is optimized and at the same time a suppressing force against a drastic uplifting force of the nuclear fuel assembly under transient conditions is strengthened, and that lowers the elastic coefficients of the springs operating under normal conditions more than those of existing coil springs, thereby providing an optimal pushing force against the nuclear fuel assembly.

Abstract: A nuclear fuel rod plenum spring assembly that has a spacer affixed to the lower end of the ground torsion spring. The spacer has a substantially flat surface on its underside that presses against the upper surface of the upper fuel pellets to spread the load of the spring over the top surface of the upper most fuel pellet.

Abstract: A nuclear reactor fuel bundle confinement system including: a fuel bundle with an upper tie plate; a channel enclosing the fuel bundle; a handle for the fuel bundle extending above the fuel bundle; an upper fuel particle barrier positioned over the upper tie plate and above the fuel rods, wherein the fuel particle barrier has a permeable panel at least co-extensive with an open area of the upper tie plate; a slot in the permeable panel through which passes the handle, and a closure device on the fuel particle barrier having a closed position which covers the slot and an open position that leaves the slot open; a lower fuel particle barrier positioned over the lower tie plate and below the fuel rods, wherein the lower portion of the fuel bundle assembly is grasped by the lower fuel particle barrier.

Abstract: A plate mounted fuel assembly hold-down system that provides a defined channel for both the insertion and removal of reactor head mounted, fixed in-core detector instrumentation, provides a guided path for the fixed in-core detector during insertion, and shields the instrument shroud against coolant cross flow. The hold-down assembly includes a base plate that seats on the adapter plate of the fuel assembly and has openings that align with the control rod guide thimbles. A hollow sleeve extends through and below a central opening in the base plate to mate with the fuel assembly instrument thimble. The sleeve extends above the base plate and through and above an upper core plate of the reactor. A hold-down bar is slidably mounted on the sleeve and is restrained below the top of the sleeve. A spring is positioned around the sleeve and is captured between the hold-down bar and the base plate.

Abstract: Disclosed herein is a hold-down spring unit for a top nozzle of a nuclear fuel assembly. The hold-down spring unit is coupled to the upper end of the top nozzle of the nuclear fuel assembly. The hold-down spring unit includes a first spring which acts against a hold-down force with respect to the nuclear fuel assembly under start-up conditions or hot full power conditions of a nuclear reactor, and a second spring which acts against a hold-down force with respect to the nuclear fuel assembly under start-up conditions of the nuclear reactor. The present invention reduces the hold-down margin under start-up conditions or hot full power conditions, thus enhancing the mechanical and structural stability of the nuclear fuel assembly.

Abstract: A top nozzle for a nuclear fuel assembly and a method of manufacturing the top nozzle are provided. The top nozzle can include a coupling plate, a perimeter wall and a hold-down spring unit. The coupling plate can be coupled to a guide thimble of the nuclear fuel assembly. The perimeter wall can protrude upwards from the perimeter of the coupling plate. A spring clamp can be provided on the upper surface of the perimeter wall. The hold-down spring unit can be mounted to the upper surface of the perimeter wall in such a way to couple a corresponding end of the hold-down spring unit to the spring clamp. A fastening pin hole can be vertically formed through an upper surface of the spring clamp. A spring insert hole into which the hold-down spring unit can be inserted and formed by electro-discharge machining in an insert direction of the hold-down spring.

Abstract: The present invention relates to a top nozzle having on-off type of hold-down springs for a nuclear fuel assembly that has a two-stage elastic section such that a pushing force against the axial movement of the nuclear fuel assembly under normal conditions is optimized and at the same time a suppressing force against a drastic uplifting force of the nuclear fuel assembly under transient conditions is strengthened, and that lowers the elastic coefficients of the springs operating under normal conditions more than those of existing coil springs, thereby providing an optimal pushing force against the nuclear fuel assembly.

Abstract: A resilient bush for frictionally engaging a centering pin of the fuel assembly is fixed in each of the through-holes of at least one of the end-pieces of the fuel assembly. The resilient bush comprises an annular member which has a portion for fixing in the hole of the end-piece and resilient arms which are separated by apertures. The flexible arms of the resilient bush comprise, in a free end portion, a supporting surface which projects radially inside the bush whose diameter is smaller than the diameter of a centering pin of the fuel assembly.

Abstract: Assemblies and methods for mounting a fuel assembly in a nuclear reactor include a fuel assembly includes fuel rods within the fuel assembly and a lower tie plate with a fuel assembly mating fixture. A fuel support includes a fuel support mating fixture that is constructed to selectively engage the fuel assembly mating fixture during installation of the fuel assembly onto the fuel support. The fuel support mating fixture and the fuel assembly mating fixture provides for a predefined orientation of the fuel assembly to the fuel support upon mating.

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

Abstract: A delay apparatus delays a rising edge and a falling edge of a digital signal. The delay apparatus includes a first edge detection circuit which detects a first edge or rising edge of the digital signal and generates a detection signal; a set circuit that includes a first counter for generating a count value and clearing the count value in response to the detection signal, wherein the set circuit generates a set signal if the count value reaches the number of the reference clock signals corresponding to the delay period of time; a reset circuit which generates a reset signal if an elapsed period of time since a generation of the set signal equals a period of time the digital signal maintains the second logic level; and an output circuit that outputs a delayed digital signal including edges synchronized with the set signal and the reset signal.

Abstract: The apparatus for positioning a fuel assembly (10) comprises, on a respective side of the core support plate (19) and the upper core plate (9) directed towards an endpiece (15, 14) of the fuel assembly (10) at least two projecting positioning pins (16, 22) adapted to engage in openings in the lower endpiece (15) or upper endpiece (14). Each of the positioning pins (16, 22) is fixed in a blind opening (24) comprising a threaded bore and a support surface perpendicular to the axis of the blind opening (24) and comprises a flange adapted to come into contact with the support surface when the positioning pin (16, 22) is screwed into the threaded bore. A gudgeon enables the positioning pin to be locked to secure it against unscrewing. The invention also relates to a process and apparatus for replacing damaged positioning pins on the core support plate (19) or on the upper core plate (9).

Abstract: A high energy absorption top nozzle for a nuclear fuel assembly that employs an elongated upper tubular housing and an elongated lower tubular housing slidable within the upper tubular housing. The upper and lower housings are biased away from each other by a plurality of longitudinally extending springs that are restrained by a longitudinally moveable piston whose upward travel is limited within the upper housing. The energy imparted to the nozzle by a control rod scram is mostly absorbed by the springs and the hydraulic affect of the piston within the nozzle.

Abstract: Apparatus for the determination of radiation induced growth due to burnup of a nuclear reactor fuel assembly in a reactor core.

Abstract: The present invention relates to a fuel assembly (1) and a method therefor. The fuel assembly is intended for a light-water cooled nuclear reactor and comprises a first and a second locking member (9a, 9b, 10), a plurality of elongated elements (3, 3a) wherein each of the lower ends of the elongated elements is provided with an end plug (3b). The end plug (3b) is arranged guided or locked in an end plate (6) which comprises at least two adjacently disposed plug holes (6b) for receiving one end plug (3b) each. The first locking member (9a, 9b) is made in an end plug (3b) and has a concave shape and the second locking member (10) is arranged slidable in a locking hole (6c) which is adapted to extend between the two adjacently disposed plug holes (6b) and opening out into these. The second locking member (10) is made with a length exceeding the length of the locking hole (6c) and has end surfaces with shapes intended for cooperation with the concave surface of the first locking member (9a, 9b).

Abstract: A holder for fuel elements in a reactor, in particular in a boiling water reactor, is provided, as well as a method for repairing such a holder. A core grid is demounted from a core shroud and replaced by a new forged core grid for the purpose of repairing the holder. An adapter ring is to be inserted between the new core grid and the core shroud. There is provision for connecting the adapter ring to the core grid without a welding operation, for example by shrink fitting.

Abstract: An upper hold-down spring structure for a nuclear reactor fuel assembly. A hold down spring 20 mounted on an upper surface of an upper nozzle 11 of a fuel assembly for a pressurized water reactor is composed of an upper plate spring 21 having plastic spring characteristics and a lower plate spring 23, base ends of which are fixed with a fastening bolt 18 at a common position. The upper spring 21 and the lower spring 23 are made of precipitation hardened nickel base alloy and the thickness of the springs are determined so as to keep the stresses generated less sensitive to stress corrosion cracking.

Abstract: The adaptor plate of a top nozzle assembly is removably secured to selected thimble tubes in a nuclear fuel assembly by quick release couplings. The openings in the adaptor plate aligned with the selected thimble tubes are counterbored from above to form shoulders with diametrically opposed slots extending downward through the shoulders. The quick release couplings include a sleeve secured to the upper end of the thimble tube. A support plate fixed to the sleeve has a pair of upwardly extending bosses engaging the slots in the adaptor plate. A latch member with a pair of diametrically opposed outwardly projecting latch ears rotates on the sleeve between a first position in which the latch ears are aligned with the slots and are positioned over the bosses so that the adaptor plate may be lifted off, and a second position with the latch ears overlaying the shoulder to latch the adaptor plate to the thimble tube.

Abstract: Fuel bundle and control rod assemblies for a nuclear reactor are described. In one embodiment of the apparatus, the nuclear reactor includes several conventional size fuel bundles and at least one large control rod. The large control rod includes four fuel bundle receiving channels, and each such channel is sized to receive four conventional size fuel bundles.

Abstract: Each of the square top nozzles (26) of the fuel assemblies of the core includes four locating openings (40) in the vicinity of the vertices of the nozzle. The set of locating pins (35) of the upper core plate (32) includes four pins at each of the positions of fuel assemblies which are intended to be engaged in the four openings (40) of the top nozzle (26). The locating openings (40) of the nozzle may consist of the internal bores of sleeves (36) which are fixed on the nozzle in an axial arrangement and holds the spring leaves (38) of the nozzle. The locating openings may also be machined inside four bosses, projecting at the upper part of the assembly, and each arranged in one corner of the assembly.

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 order to eliminate the need to weld, drill or otherwise machine a shroud structure which is used to surround a plurality of fuel assemblies in a nuclear reactor, a plurality of upper hanger rods interconnect a structure above the shroud to a support ring which is clamped about the upper periphery of the shroud. Lower hanger rods interconnect a lower edge or shoulder portion of the shroud with the support ring. Thus, through the upper and lower hanger rods and the support ring, the shroud can be supported within the RPV. The upper support ring is arranged to clamp the lower ends of the upper hanger rods against the upper outer peripheral portion of the shroud while the lower ends of the lower hanger rods are clamped against the lower peripheral wall portion of the shroud by a lower support ring.

Abstract: Self-locking alignment pin and method for aligning a nuclear fuel assembly with respect to a core plate disposed in a nuclear reactor pressure vessel. The fuel assembly has a top nozzle having a first bore formed therein. The core plate has a second bore alignable with the first bore. The second bore has first threads of a first predetermined pitch and second threads of a second predetermined pitch. The alignment pin further includes a shaft that has an end portion having third threads of the first predetermined pitch for threadably engaging the first threads of the second bore. A flange, which has a plurality of recesses in the underside surface thereof, surrounds the shaft and is integrally attached thereto. A locking member surrounds the flange and has exterior fourth threads of the predetermined second pitch for threadably engaging the second threads of the second bore.

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 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 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: 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: 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: The guide pin aligning a top nozzle of a nuclear fuel assembly to an upper core plate of a nuclear reactor, is replaced working exclusively from below the upper core plate. The replacement guide pin has a shaft portion engaged with the upper core plate and the clamping nut which held the original guide pin, by threadable connection and/or by an expansion fitting. A shoulder on the pin bears against a lower surface of the upper core plate, and a nose of the pin is received in the top nozzle of the fuel assembly. A preferred expansion fitting has a bushing with ridges on its outer surface and a conical inside surface, and is inserted into the bored out original guide pin shaft. A threaded conical plug is pulled axially with rotation of the replacement pin shaft to expand the bushing. The ridges rigidly lock the replacement pin between the shoulder and the clamping nut.

Abstract: A gap between a foot part and a channel of a boiling water fuel assembly is sealed against a coolant flow by a spring being supported by a central part thereof against the channel and by sides thereof against the foot part and being clipped and/or clamped on at that location even when all of the fuel rods are removed. For this purpose, the upper edge can extend around the foot part edge or the spring may be constructed as a spring band running entirely around the foot part and being fitted into a lateral groove.

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: 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: A holddown leaf spring for a nuclear fuel assembly (10) with an upper end fitting (12) having spring retaining slots (30). Two spring stacks (20, 24 and 22, 26), respectively, are made up of unitary elongated metal bar springs having two substantially tapered width leg portions (20a, 20b, etc.) joined by an arcuate transition portion (28) therebetween. The wider opposite end portions (20c, 20d, etc.) are received in slots (30) of end fitting (12) and retained by welded pins (or capped screws) (not shown). The tapered width distributes localized stresses and may be horizontal or vertical. Less chance of debris exists due to retained spring ends. Flow at two opposite corners is opened up by the taper and by transition portion (28) being spaced from the nozzle openings (32 and 34). The assembly requires fewer parts and less machining.

Abstract: In a method for fabricating an end fitting (12,200) for a nuclear fuel assembly (10), wherein the end fitting includes at least one spring member (24,202) having an active external surface (32,206) for contacting rigid core support structure (100) in the nuclear reactor, the improvement comprising applying a coating to the active surface of the spring member. The coating is selected from the group consisting of nitrides, Cr, TiC, CrC, ZrC and NiTaB. The spring member is preferably Inconel and the coating is one of ZrN or TiN. Each spring member can be formed by nesting a plurality of spring elements (28,34,36 or 208,210) so that the spring elements are in contact with each other and the method includes applying said coating to each of the spring elements at least where they contact each other.

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 method for fixing a spring package (7) to a top nozzle (6) in a fuel assembly of a nuclear reactor wherein the fuel assembly comprises fuel rods, guide tubes and spacers arranged in a bundle between a top nozzle (6) and a bottom nozzle (5) wherein a T-shaped slot (14) is milled out in a clamp (8) which is welded to or forms an integral part of the top nozzle (6) for receiving one end of the spring package (7), the end of the spring package is then inserted into the slot (14), and the end is then fixed in the slot by means of a locking pin (15).

Abstract: A method and assembly for securing a cylindrical centering pin in a bore formed in a plate includes introducing an end of a centering pin to be secured to a plate into a bore formed in the plate until at least part of a coaxial, radially deformable 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 and assembly, 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 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.