Abstract: An apparatus including a lower end fitting having a top planar surface, a bottom planar surface, a counterbore defined therebetween, an opening extending from the counterbore to the top planar surface, and a lock recess that extends both radially outwardly from the counterbore and extends inwardly into the lower end fitting from the bottom planar surface. The apparatus includes a guide tube having a lower end and an end plug configured to connect with the lower end of the guide tube. The end plug has a threaded shaft sized to pass through the opening of the lower end fitting, and a female lock nut has a deformable side wall configured to be swaged into the recess of the lower end fitting. The lock recess remains visible as viewed from the bottom planar surface of the lower end fitting when the female lock nut is fully disposed in the counterbore.

Abstract: A channel box in an embodiment includes a tubular portion. The tubular portion includes a first tubular layer, a second tubular layer, and an intermediate tubular layer. The first tubular layer contains silicon carbide as a major component. The second tubular layer is in parallel to and surrounds or is surrounded by the first tubular layer and contains silicon carbide fibers and silicon carbide complexed with the silicon carbide fibers. The intermediate tubular layer is disposed between the first tubular layer and the second tubular layer and contains a solid lubricant.

Abstract: A nuclear reactor core is disposed in a pressure vessel along with upper internals disposed in the pressure vessel above the reactor core. The upper internals include internal control rod drive mechanisms (CRDMs) mounted on a suspended support assembly. A hollow cylindrical central riser is disposed in the pressure vessel above the nuclear reactor core. A hollow cylindrical section is disposed in the pressure vessel below the hollow cylindrical central riser and surrounding the nuclear reactor core. A riser transition element connects with the hollow cylindrical central riser and the hollow cylindrical section to form a continuous hollow cylindrical flow separator. The suspended support assembly of the upper internals is suspended from the riser transition element. The pressure vessel may comprise upper and lower vessel sections connected by a mid-flange, with the riser transition element welded to the mid-flange by gussets extending outward and upward from the riser transition element to the mid-flange.

Abstract: A control rod guide frame comprises a self supporting stack of two or more columnar elements defining a central passage. The columnar elements may include mating features that mate at abutments between adjacent columnar elements of the stack. The control rod guide frame is suitably used in conjunction with a control rod drive mechanism (CRDM) operatively connected with at least one control rod, and a nuclear reactor core, in which the CRDM moves the at least one control rod into and out of the nuclear reactor core under guidance of the control rod guide frame. In another embodiment, a control rod guide frame comprises a stack of two or more columnar elements defining a central passage having a constant cross-section as a function of position along the central passage. In another embodiment, a control rod guide frame comprises an extruded columnar element providing continuous control rod guidance.

Abstract: A boiling water reactor assembly includes a bayonet plate closure between a control rod guide tube and a drive housing pipe. The bayonet plate closure has a bayonet plate constructed in two parts including a central bayonet ring mounted rotatably about its longitudinal axis and an outer ring completely surrounding the bayonet ring. The outer ring is mounted on the periphery of the bayonet ring and reaches inwards under the bayonet ring periphery. The ring is furthermore permanently supported in the axial direction on the drive housing pipe by spring pressure acting on the control rod guide tube, in order to produce a frictional connection. The spring pressure can be released unhindered from the reactor side by tools.

Abstract: A dual-cooled fuel rod's spacer grid with upper and lower dimples, including a blocking area of a flow passage that coolant flows through is reduced and dual-cooled fuel rods are supported, and reduces a turbulent flow of the coolant as well as vibrations of the dual-cooled fuel rods, thereby lessening fretting damage done to the rods. The spacer grid includes a plurality of unit grid straps, each of which includes a body disposed in a vertical direction, an upper dimple protruding from an upper portion of the body, and a lower dimple spaced apart from the upper dimple in a downward direction and protruding from a lower portion of the body. The unit grid straps form a grid structure that have inner grid holes into which the dual-cooled fuel rods are held, and the held dual-cooled fuel rods are each supported in four directions by the upper and lower dimples.

Abstract: Apparatus and a method for retracting in-core instrument thimble tubes from the reactor core prior to refueling a nuclear reactor with top mounted instrumentation. The apparatus includes a penetration flange interposed between the head flange and the reactor vessel flange through which the instrumentation cabling passes. The penetration flange is connected to the upper internals and can be raised relative thereto to retract instrumentation thimbles from the core prior to removal of the upper internals from the reactor vessel for refueling. The penetration flange is removed from the vessel with the upper internals.

Abstract: An alignment plate that is attached to a core barrel of a pressurized water reactor and fits within slots within a top plate of a lower core shroud and upper core plate to maintain lateral alignment of the reactor internals. The alignment plate is connected to the core barrel through two vertically-spaced dowel pins that extend from the outside surface of the core barrel through a reinforcement pad and into corresponding holes in the alignment plate. Additionally, threaded fasteners are inserted around the perimeter of the reinforcement pad and into the alignment plate to further secure the alignment plate to the core barrel. A fillet weld also is deposited around the perimeter of the reinforcement pad. To accommodate thermal growth between the alignment plate and the core barrel, a gap is left above, below and at both sides of one of the dowel pins in the alignment plate holes through which the dowel pins pass.

Abstract: A pressure vessel comprises an upper vessel section and a lower vessel section. A nuclear reactor core comprises fissile material contained in a containing structure and disposed in the lower vessel section. Upper internals are disposed in the lower vessel section above the nuclear reactor core. The upper internals include at least guide frames and internal control rod drive mechanisms (CRDMs) with CRDM motors mounted on a suspended support assembly including a plurality of hanger plates connected by tie rods. The plurality of hanger plates includes a lowermost hanger plate having alignment features configured to align the upper internals with the containing structure that contains the nuclear reactor core.

Abstract: A pressure vessel comprises an upper vessel section and a lower vessel section. A nuclear reactor core comprising fissile material is disposed in the lower vessel section. Upper internals are disposed in the lower vessel section above the nuclear reactor core. The upper internals include at least internal control rod drive mechanisms (CRDMs) with CRDM motors and a suspended support assembly with a plurality of hanger plates connected by tie rods. The internal CRDMs are supported from beneath by a first hanger plate and are laterally aligned by a second hanger plate disposed above the first hanger plate.

Abstract: A pressure vessel comprises an upper vessel section and a lower vessel section. A nuclear reactor core comprising fissile material is disposed the lower vessel section. Upper internals are disposed in the lower vessel section above the nuclear reactor core and are mounted on a suspended support assembly including a plurality of hanger plates connected by tie rods. The upper internals include at least guide frames and internal control rod drive mechanisms (CRDMs) with CRDM motors. The plurality of hanger plates includes a mid-hanger plate that is not the uppermost plate of the plurality of hanger plates and is not the lowermost plate of the plurality of hanger plates. The internal CRDMs are disposed above the mid-hanger plate, the guide frames are disposed below the mid-hanger plate, and the mid-hanger plate engages both the internal CRDMs and the guide frames.

Abstract: A fixed cluster for the core of pressurized-water nuclear reactor including rods and a holder for rods. The holder includes: an upper head; fins extending radially towards the outside from the upper head; systems for mounting the rods and distributed on the fins; and at least two abutment elements on the upper plate of the core, each of the abutment elements protruding longitudinally from a respective fin beyond the mounting systems so as to be vertically oriented towards the top when the fixed cluster is provided on a nuclear fuel assembly.

Abstract: A nuclear reactor core is disposed in a pressure vessel along with upper internals disposed in the pressure vessel above the reactor core. The upper internals include internal control rod drive mechanisms (CRDMs) mounted on a suspended support assembly. A hollow cylindrical central riser is disposed in the pressure vessel above the nuclear reactor core. A hollow cylindrical section is disposed in the pressure vessel below the hollow cylindrical central riser and surrounding the nuclear reactor core. A riser transition element connects with the hollow cylindrical central riser and the hollow cylindrical section to form a continuous hollow cylindrical flow separator. The suspended support assembly of the upper internals is suspended from the riser transition element. The pressure vessel may comprise upper and lower vessel sections connected by a mid-flange, with the riser transition element welded to the mid-flange by gussets extending outward and upward from the riser transition element to the mid-flange.

Abstract: In a pressurized water reactor with all of the in-core instrumentation gaining access to the core through the reactor head, each fuel assembly in which the instrumentation is introduced is aligned with an upper internals instrumentation guide-way. In the elevations above the upper internals upper support assembly, the instrumentation is protected and aligned by upper mounted instrumentation columns that are part of the instrumentation guide-way and extend from the upper support assembly towards the reactor head in hue with a corresponding head penetration. The upper mounted instrumentation columns are supported laterally at one end by an upper guide tube and at the other end by the upper support plate.

Abstract: A fuel rod or control rod for a nuclear reactor that has a spacer interposed between an upper end plug and a plenum spring which extends between the spacer and the fissile or absorber material. Preferably, the spacer is a relatively thin sleeve with a radially extending lip that sits above the coil spring wound at least in part around the sleeve.

Abstract: Disclosed herein is a guide thimble of a nuclear fuel assembly, which is capable of improving the cooling performance and the stability of a nuclear fuel, preventing a flow split in dual-cooling nuclear fuel rod and guide thimble sub channels for obtaining high combustion degree and high power, and minimizing a neutron absorption section in a reaction degree region. Since the guide thimble having the dual tube type structure is adopted, a flow split in the fuel rod and guide thimble sub channels can be reduced, and the degradation in performance of nuclear fuel due to increase of a neutron absorption section can be prevented. In order for compatibility with an existing control rod, a typical guide tube is used as an inner guide thimble, and an outer guide thimble is provided outside the inner guide thimble.

Abstract: A control rod guide frame comprises a self supporting stack of two or more columnar elements defining a central passage. The columnar elements may include mating features that mate at abutments between adjacent columnar elements of the stack. The control rod guide frame is suitably used in conjunction with a control rod drive mechanism (CRDM) operatively connected with at least one control rod, and a nuclear reactor core, in which the CRDM moves the at least one control rod into and out of the nuclear reactor core under guidance of the control rod guide frame. In another embodiment, a control rod guide frame comprises a stack of two or more columnar elements defining a central passage having a constant cross-section as a function of position along the central passage. In another embodiment, a control rod guide frame comprises an extruded columnar element providing continuous control rod guidance.

Abstract: Control rod guide tubes for a nuclear reactor having a body with an axial length that defines a lower end portion and an upper end portion and a cavity within a substantial length of the body. Orifices are included at the upper and lower end portions of the body. A control rod chamber is located within the cavity and is configured for receiving a control rod. A plurality of ports is coupled to the cavity and is positioned at a substantial length from the upper end portion of the body. Also included are at least two flow channels within the cavity that extend a substantial portion of the axial length of the body. Each flow channel is fluidly coupled to one or more of the ports for receiving fluid flow from outside the body and an outlet proximate to the upper end portion of the body for providing the received fluid flow.

Abstract: A fixed cluster for the core of pressurized-water nuclear reactor including rods and a holder for rods. The holder includes: an upper head; fins extending radially towards the outside from the upper head; systems for mounting the rods and distributed on the fins; and at least two abutment elements on the upper plate of the core, each of the abutment elements protruding longitudinally from a respective fin beyond the mounting systems so as to be vertically oriented towards the top when the fixed cluster is provided on a nuclear fuel assembly.

Abstract: Control rod guide tubes for a nuclear reactor having a body with an axial length that defines a lower end portion and an upper end portion and a cavity within a substantial length of the body. Orifices are included at the upper and lower end portions of the body. A control rod chamber is located within the cavity and is configured for receiving a control rod. A plurality of ports is coupled to the cavity and is positioned at a substantial length from the upper end portion of the body. Also included are at least two flow channels within the cavity that extend a substantial portion of the axial length of the body. Each flow channel is fluidly coupled to one or more of the ports for receiving fluid flow from outside the body and an outlet proximate to the upper end portion of the body for providing the received fluid flow.

Abstract: A core of a boiling water reactor as a burner type core of the boiling water reactor having a ratio of 3 or more of number of fuel assemblies loaded in the core to number of control rods installed in the nuclear reactor and using an oxide of low enriched uranium having a mean enrichment of the fuel assemblies of 3 wt % to 8 wt % or a mixed oxide having a mean fissile plutonium enrichment of the fuel assemblies of 2 wt % to less than 7 wt %, wherein a ratio of an inner width of a channel box of the fuel assemblies to a width of 0.79 to 0.865, and a mean thickness of the channel box of the fuel assemblies is 2.10 to 3.55 mm.

Abstract: In a pressurized water reactor with ail of the in-core instrumentation gaining access to the core through the reactor head, each fuel assembly in which the instrumentation is introduced is aligned with an upper internals instrumentation guide-way. In the elevations above the upper internals upper support assembly, the instrumentation is protected and aligned by upper mounted instrumentation columns that are part of the instrumentation guide-way and extend from the upper support assembly towards the reactor head in hue with a corresponding head penetration. The upper mounted instrumentation columns are supported laterally at one end by an upper guide tube and at the other end by the upper support plate.

Abstract: In the method, a reference core design is generated based on a defined set of limits. The set of limits may include a target hot excess reactivity constraint to be satisfied over a given core energy cycle and a given desired control blade definition that is set for the cycle. A reference core design is generated based on the defined limits. A unique subset of fresh fuel bundles is subject to an iterative improvement process including replacing, at each fuel location, at least one of the current fresh fuel bundles with at least one of the selected fresh fuel bundles, and simulating reactor operation on the reference core design to obtain a plurality of outputs to be ranked based on the defined set of limits. The highest ranked output may represent an accepted core design with set control blade definition that satisfies the target hot excess reactivity constraint.

Abstract: In the method, a set of limits are defined and a reference core design is generated based on the limits, and includes an initial loading pattern of current fresh fuel bundles arranged in a plurality of fuel locations. A unique subset of fresh fuel bundles is selected for evaluation as the reference core design is subjected to an iterative improvement process. The iterative process includes replacing, at each fuel location, at least one of the current fresh fuel bundles with at least one of the selected fresh fuel bundles, and simulating reactor operation on the reference core design to obtain a plurality of outputs. The outputs may be ranked based on the defined set of limits, and the highest ranked output may be selected as an accepted core design for the nuclear reactor.

Abstract: In an embodiment of the present invention, the core of a nuclear reactor includes a plurality of fuel cells and a plurality of large control rods. Each large control rod is about two times the width of a conventional control rod and includes four control rod blades extending radially from a central portion and arranged at right angles to each other. The blades define four fuel bundle receiving channels. The core is configured so that the control rods are-arranged in a plurality of staggered rows with four fuel bundles in each receiving channel.

Abstract: A tie rod having a cruciform cross section is provided with steps for fixing sheaths at tips of cruciform arms of the tie rod; the tips of each of sheaths are fitted onto the steps of the tie rod, each of the sheaths having a U-shaped cross section; and each of the sheaths is fixed to the tie rod by performing a laser welding using a YAG laser beam or a CO2 laser beam with the sheath being fitted onto the tie rod to achieve a continuous weld of at least a part of the tie rod in a longitudinal direction thereof. An axial center position of the beam is shifted from an end face position of the step of the tie rod at least toward an axis center of the tie rod.

Abstract: After a nuclear reactor has been stopped and allowed to cool down following a period of operation, action is taken in a pool of the nuclear reactor on at least one guide tube of the activated upper internal equipment of the nuclear reactor to enlarge (21b, 21c) guide channels (16b, 16c) of the guide tube (8) in at least one continuous guidance zone. The enlargement is preferably performed by machining discontinuous cavities along the length of the guide channel (16b, 16c). Enlargement is preferably performed on the guide tube (8) in place within the upper internal equipment that has been placed on a storage stand in the reactor pool.

Abstract: A core plate assembly for a nuclear reactor includes a plurality of support beams, a flat plate positioned on top of the support beams, a plurality of control rod guide tube openings arranged in staggered rows, and a plurality of fuel supports extending through the flat plate. Each guide tube opening has a cruciform shape defines four fuel bundle receiving areas. Each fuel support includes a coolant flow inlet, and a coolant flow outlet sized to receive a lower tie plate of a fuel bundle. The coolant flow inlet is offset from coolant flow outlet so that a centerline of the coolant flow inlet is parallel to a centerline of the coolant flow outlet. The coolant flow inlets are positioned adjacent a support beam, and the coolant flow outlets are positioned in a fuel bundle receiving area.

Abstract: A tie rod having a cruciform cross section is provided with steps for fixing sheaths at tips of cruciform arms of the tie rod; the tips of each of sheaths are fitted onto the steps of the tie rod, each of the sheaths having a U-shaped cross section; and each of the sheaths is fixed to the tie rod by performing a laser welding using a YAG laser beam or a CO2 laser beam with the sheath being fitted onto the tie rod to achieve a continuous weld of at least a part of the tie rod in a longitudinal direction thereof. An axial center position of the beam is shifted from an end face position of the step of the tie rod at least toward an axis center of the tie rod.

Abstract: A tie rod having a cruciform cross section is provided with steps for fixing sheaths at tips of cruciform arms of the tie rod; the tips of each of sheaths are fitted onto the steps of the tie rod, each of the sheaths having a U-shaped cross section; and each of the sheaths is fixed to the tie rod by performing a laser welding using a YAG (yttrium aluminum garnet) laser beam or a CO2 laser beam with the sheath being fitted onto the tie rod to achieve a continuous weld of at least a part of the tie rod in a longitudinal direction thereof. An axial center position of the beam is shifted from an end face position of the step of the tie rod at least toward an axis center of the tie rod.

Abstract: A tie rod having a cruciform cross section is provided with steps for fixing sheaths at tips of cruciform arms of the tie rod; the tips of each of sheaths are fitted onto the steps of the tie rod, each of the sheaths having a U-shaped cross section; and each of the sheaths is fixed to the tie rod by performing a laser welding using a YAG laser beam or a CO2 laser beam with the sheath being fitted onto the tie rod to achieve a continuous weld of at least a part of the tie rod in a longitudinal direction thereof. An axial center position of the beam is shifted from an end face position of the step of the tie rod at least toward an axis center of the tie rod.

Abstract: The present invention is a control rod guide tube cleaning apparatus in a nuclear reactor which includes a rod member, one end side portion of which has a thickness such that the end side portion can pass through the inside of a connecting portion between a housing of a control rod drive mechanism and a control rod guide tube, a nozzle for sucking water, mounted on the rod member on the one end side so that the nozzle can go in and out of the rod member, a means for rotating the rod member in a horizontal direction, and a water passage for leading water sucked in the nozzle to an outside of the housing along the rod member. The rod member is inserted into the control rod guide tube through the inside of the housing. Then, the nozzle is rotated downward so that a suction port of the nozzle faces the bottom inside portion of the control rod guide tube for the suction of dust and debris. The nozzle is rotated in the horizontal direction by rotating the rod member in the horizontal direction.

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

Abstract: 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: Surface preoxidation of the substrate is carried out by bringing the substrate into contact with an oxidizing gas excited by a cold plasma, the substrate being situated in the flowing afterglow of the cold plasma used to excite the oxidizing element and being heated to an oxidation temperature of less than 500.degree. C. A metal oxide is formed at the surface of the preoxidized substrate by heterogeneous oxidation of a metal halide with a gas mixture including an oxidizing element activated by a cold plasma. The oxidizing gas mixture is brought into contact with the halide as directly as possible in the vicinity of the substrate arranged in the far flowing afterglow of the cold plasma. The cold plasma is preferably generated by microwaves. The process can be used in particular for producing a protective coating on a cladding tube of a nuclear fuel rod.

Abstract: A control rod guide tube mounting pin for engaging a hole in an upper core plate of a nuclear reactor pressure vessel has a resilient tubular portion with one or more axial crimps which flex allowing for resiliently fitting into a hole in an upper core plate without needing to enlarge or other machine the existing holes or drilling additional holes. Stainless steel mounting pins may be backfit into existing two pin mounting systems of control rod guide tubes adjacent to the outlet nozzles of the pressure vessels by removing the pins mounting the guide tubes adjacent the outlet nozzles to the upper core support plate; and then replacing the removed pins with stainless steel replacement pins.

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

Abstract: The fuel assembly includes an arrangement for quickly fixing the guide thimble into an opening passing through the adaptor plate of a dismountable nozzle of the assembly. This arrangement includes at least two bearing stops inside the opening of the nozzle, a bearing sleeve integral with the end of the guide thimble and a locking ring which includes stops for bearing on bearing surfaces of the stops inside the opening of the nozzle and deformable elastic parts capable of being accommodated in cavities of the opening of the adaptor plate or of the bearing sleeve, in order to place the ring in a position in which the guide thimble is locked or unlocked. The sleeve includes a rim for bearing on a bearing surface of the adaptor plate at the periphery of the opening.

Abstract: A method and an apparatus for repairing a core plate having a cracked support structure. The method entails the step of providing a vertical compression load path between the core plate and one or more control rod guide tubes. This is accomplished by installing a plurality of load-bearing wedges between the core plate and the step of each guide tube. Each load-bearing wedge is placed between the core plate and the guide tube machined step so that core plate pressure loads are reacted by the weight of the fuel rather than the core plate support structure. The load-bearing wedges can be installed without removing the guide tube or the fuel support casting.

Abstract: This control rod drive limiter removes the need for piping for extraction drive, increases the reliability of linkage with respect to the control rod, and removes the need of a speed limiter for the control rod, since there is no need to assume that the linkage might be released, thus reducing the building costs.A stop piston 112 is disposed so as to cover a buffer piston 110 and a buffer spring 111 from above, rollers 113 are disposed above this stop piston 112, and the lower end of a piston tube 107 is fixed to a flange 103a in such a manner that the piston tube 107 does not move in the axial and peripheral directions. A collet piston 115, collet fingers 116, and a return spring 117 are disposed between an outer tube 104 and a cylinder tube 105. A guide cap 120 is disposed at the upper end of the outer tube 104. Guide grooves 106c that engage with the rollers 113 are provided in the index tube 106.

Abstract: A method and an apparatus for repairing a core plate having a cracked support structure. The method entails the step of providing a vertical compression load path between the core plate and one or more control rod guide tubes. This is accomplished by installing a plurality of load-bearing elements between the core plate and the flanges of the guide tubes. Each load-bearing element is placed between the core plate and a guide tube flange so that core plate pressure loads are reacted by the weight of the fuel rather than the core plate support structure. The load-bearing element may take the form of a solid ring, a C-shaped spring collar or a hinged collar.

Abstract: A fuel assembly (16) for a boiling-water nuclear reactor arranged in groups with four fuel assemblies in each group and with a centrally placed control rod (17) forming a supercell. Each fuel assembly (16) includes a plurality of vertical fuel rods (12) with enriched nuclear fuel material (24), said rods being arranged between a bottom tie plate (13) and a top tie plate (14) in a surrounding vertical fuel channel (1) which is connected to a transition section (2). The transition section is provided with holes (20a-d) for by-pass flow outside the fuel assembly. The fuel assembly is characterized in that the by-pass holes are arranged in such a way that when turning the fuel assembly (16), including the transition section (2), 90.degree., 180.degree. or 270.degree. around the longitudinal axis of the fuel assembly, said holes are adapted to direct the by-pass flow away from the control rod (17).

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: The equipment comprises a bottom plate formed with outlet openings for the coolant, a top plate, spacer rods interconnecting the plates, and cluster guides for guiding control clusters. At least some of the guides have respective top lengths that project above the top plate and bottom lengths that extend between the plates. Each bottom length includes a base bearing against a frustoconical seat secured to the bottom plate, and it is subjected to the force of resilient means. Together, the lengths of each guide constitute a one-piece cartridge suitable for insertion in a corresponding column. The guide also includes a cap for receiving the top length, which cap is fixed to the top plate against which the resilient means bear.

Abstract: Internal equipments located above the core of a nuclear reactor have a bottom plate formed with outlet openings for the core coolant, a top plate, spacer columns interconnecting the plates, and guides for control clusters that are vertically displacable between a position in which they are in the core and a position in which they are out of the core. At least some guides each have a top length projecting above the top plate, and a bottom length extending between the plates and placed in a corresponding spacer column. Each cluster guide constitutes a cartridge insertable in a respective column, provided with a flange for fixing to the top plate and provided at its bottom end with springs for centering the guide within the column.

Abstract: A boiling water reactor includes a pressure vessel containing a reactor core, chimney, steam separator assembly, and steam dryer assembly therein, with the vessel being filled with reactor water to a normal water level through the steam separator assembly. A plurality of control rod drives extend downwardly from the bottom of the pressure vessel and are operatively joined to control rods extending downwardly into the reactor core. The chimney includes a plurality of channels disposed above the core and laterally spaced apart to define guide slots for receiving the control rods as they are selectively translated upwardly out of the core by the control rod drives. The chimney has a vertical height for increasing the normal water level above the reactor core and for providing a space for the control rods withdrawn from the reactor core by the bottom-mounted control rod drives.

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: Control rod guide tube adapted to reduce vibration of a plurality of control rods disposed therein. The guide tube comprises an elongate housing surrounding the control rods, the housing having an opening at an end thereof for receiving a flowing fluid therethrough. The fluid has a velocity component acting transversely to the control rods sufficient to induce vibration of the control rods. However, the housing of the present invention has an intermediate portion pierced by a plurality of apertures for exit of the fluid from the housing to reduce the velocity of the fluid acting transversely to the control rods in order to reduce vibration of the control rods. As control rod vibration is reduced, control rod wear is mitigated.

Abstract: A hafnium alloy consisting essentially of hafnium and containing Sn by 0.1-1.5 weight %, O by 0.03-0.2 weight %, Fe by 0.01-0.15 weight %, Zr by 0.02-2.0 weight %, and (1) Cr by 0.01-0.15 weight %, and Ni by less than 0.10 weight %, (2) Cr by 0.01-0.15 weight %, Ni by less than 0.10 weight %, and Mo by 0.01-0.2 weight %, (3) Nb by 0.2-1.0 weight %, or (4) Nb by 0.2-1.0 weight %, and Mo by 0.01-0.2 weight % has high neutron-absorbing capacity, high resistance to uniform and nodular corrosion, high tensile and creep strength, and good wear resistance, and is suited to be used as neutron absorber for nuclear power reactors.

Abstract: Upper internals for a nuclear reactor comprise an upper core plate and a plate which supports cluster guides tubes connecting the two plates together. The cluster guides project above the support plate. A bottom wall of the support plate is situated at a level just higher than the outlet nozzles of the reactor vessel and each guide is supported by the bottom wall of the support plate by abutment of a shoulder formed in a passage of the bottom wall, in the lower half thereof.