Abstract: The present invention relates to a control rod installed in a boiling water reactor (BWR), and particularly to a control rod using metal. An object of the present invention is to provide a manufacturing method of a control rod for a boiling water reactor, having excellent corrosion resistance in high temperature water and excellent wear resistance at the time of fabrication, and in which the influence of the manufacturing process is slight. In order to achieve the above described object, the present invention provides a manufacturing method of a control rod for a boiling water reactor constructed with sheaths having a U-shaped cross section attached to each end of a tie rod having a cruciform cross section, and rod, plate or oval tube cross section metal hafnium type neutron absorber material contained inside the sheaths, in which an anodized film is provided on a surface of the neutron absorber material as a pre-process of assembly of the neutron absorber material in the structure of the control rod.

Abstract: A neutron absorbing pin including at least, a neutron absorber, a thin-wall pipe surrounding the neutron absorber, and a cladding disposed at a distance from the thin-wall pipe. In the neutron absorbing pin, the difference between the coefficient of thermal expansion (.alpha.1) of the neutron absorber and the coefficient of thermal expansion (.alpha.2) of the thin-wall pipe has an absolute value of .vertline..alpha.2-.alpha.1.vertline..ltoreq.10.times.10.sup.-6 /K.

Abstract: A nuclear reactor fuel assembly includes a fuel assembly base, a fuel assembly head and mutually parallel fuel rods containing nuclear fuel and extending between the fuel assembly head and the fuel assembly base. A water tube having first and second open ends extends parallel to the fuel rods. The first end of the water tube grips and is held at the fuel assembly base. An elongated extension body has first and second ends. The second end of the extension body grips and is held at the fuel assembly head. The second end of the water tube is screwed into the first end of the elongated extension body, or the first end of the elongated extension body is screwed into the second end of the water tube. The elongated extension body has two mutually coaxially disposed partial bodies. One of the partial bodies has the second end of the extension body and the other of the partial bodies has the first end of the extension body. One of the partial bodies is screwed into the other of the partial bodies.

Abstract: The control cluster has a spider constituted by a hub connectable to a drive shaft. Fins radiate from a bottom portion of the hub and provided with vertical fingers distributed in a regular array. It also includes rods provided with plugs that are releasably fixed to the fingers. The fins, their fingers, and at least the bottom portion of the hub constituting a single-piece part obtained by molding or by electro-machining.

Abstract: A control rod includes four panels in cruciform section each containing a plurality of absorber tubes. The absorber tubes are mounted between upper and lower mounting structures having generally T-shaped slots opening toward one another. The absorber tubes have generally T-shaped end plugs for reception in the slots. The slots and end plugs are configured to permit limited axial movement of each absorber tube relative to the control rod and to adjacent tubes. The absorber tubes are maintained in tension during all nuclear operations including during a scram.

Abstract: A neutron absorbing apparatus which includes two adjacent neutron absorbing plates and a mounting assembly with latching means configured to be easily secured to fuel assemblies while the fuel assemblies remain under water in a fuel storage rack, thereby eliminating the need to remove the fuel assemblies or the fuel storage rack for installation. The two neutron absorbing plates are positioned orthogonally to form a chevron cross section which can be placed about the fuel assemblies by insertion in the existing space between the fuel assemblies and the cell walls of a fuel storage rack. A prescribed orientation of the chevron configured neutron absorbing plate in the cells of the fuel storage rack together with the selected use of a single neutron absorbing plate economically provides sufficient neutron absorption in all radial directions about the fuel assemblies to maintain safe storage conditions in closely packed fuel storage racks.

Abstract: A control rod assembly for a nuclear reactor, wherein a plurality of absorber tubes are arranged and welded in a side-by-side array, the improvement wherein each absorber tube is formed with an elongated slot extending substantially the entire length of the absorber tube on one side of the tube, and with an elongated tab extending substantially the entire length of the absorber tube on a diametrically opposed side of the tube such that, for adjacent absorber tubes, a joint is formed wherein the tab of one tube is located within the slot of the other.

Abstract: The control rod for a nuclear reactor includes a plurality of wings each having segments of neutron absorbing material exposed along the length of the rod. During refueling, the segments of neutron absorbing material are rearranged within the control rod and the control rod is reinserted into the reactor core. By rearranging the segments, optimum use of the depletion capacity of each segment is effected, maximizing the number of cycles for which the control rod may be used.

Abstract: The control rod includes a plurality of elongated tubes containing neutron-absorbing material in a planar array to form wings on opposite sides of a central axis of the control rod. Each tube is formed with a plurality of protuberances in excess of four such that the tubes can be welded to adjacent tubes with the weld lines disposed inwardly of the side surfaces of the wings to improve the flexibility of the control rod. The wings of each planar array have connecting elements of each other planar array thereof, enabling lateral movement of the planar arrays of wings relative to one another to further enhance flexibility and movement of the control rod between the fuel channels of the nuclear core.

Abstract: A control rod for a nuclear reactor incorporates a plurality of neutron absorber tubes containing neutron absorbing materials. The absorber tubes are substantially rectangular inside and outside, each tube containing at least one axial stack of substantially round neutron absorbing material segments or capsules.

Abstract: The alloy contains, expressed in atomic percentages, 9 to 12% of indium and 4 to 5.35% of cadmium, the remainder consisting of silver with the exception of unavoidable impurities in very low quantities. The alloy preferably contains 9 to 10% of indium and 4.35% to 5.35% of cadmium. The alloy can be used in the form of pellets or bars placed inside a tubular casing, in order to form a neutron-absorber component of a rod cluster for controlling the reactivity of a pressurized water nuclear reactor.

Abstract: A rod connector assembly for removably securing a control rod to a spider structure and adapted for use in conjunction with a crimping tool. The rod connector assembly includes a tubular boss fixedly secured to the spider structure, the boss including at least one access hole and interior threads formed on an interior surface of the boss. A securement structure includes a coupling adapted to be fixedly secured to the control rod. The coupling includes a shaft having external threads, an upper end, and a lower end, the lower end of the shaft adapted to be fixedly secured to the control rod; a deformable collar projecting upwardly from the upper end of the shaft; and a cap adapted to be fixedly secured to an upper end of the boss and including at least one groove corresponding to the access hole(s).

Abstract: A neutron absorbing apparatus which includes two adjacent neutron absorbing plates and a mounting assembly with latching means configured to be easily secured to fuel assemblies while the fuel assemblies remain under water in a fuel storage rack, thereby eliminating the need to remove the fuel assemblies or the fuel storage rack for installation. The two neutron absorbing plates are positioned orthogonally to form a chevron cross section which can be placed about the fuel assemblies by insertion in the existing space between the fuel assemblies and the cell walls of a fuel storage rack. A prescribed orientation of the chevron configured neutron absorbing plate in the cells of the fuel storage rack together with the selected use of a single neutron absorbing plate economically provides sufficient neutron absorption in all radial directions about the fuel assemblies to maintain safe storage condition sin closely packed fuel storage racks.

Abstract: A diving bell type control rod of sodium bond type. The control rod including a plurality of control elements each comprising a pellet chamber for packing B.sub.4 C pellets and disposed in a cladding tube, an intermediate plug disposed above the pellet chamber, an upper chamber formed above the intermediate plug, a vent tube allowing the pellet chamber to communicate with the upper chamber while penetrating through the intermediate plug, upper and lower vent holes formed in upper and lower two stages in the cladding tube at the upper chamber, a sodium inflow port opening to the upper surface of the intermediate plug, and a sodium introduction tube extending from the sodium inflow port to a position below the lower end surface of the intermediate plug while penetrating through the intermediate plug.

Abstract: A fast reactor core in which a coolant flows comprises a plurality of fuel assemblies each loaded with a fissionable material and a plurality of gas sealed assemblies disposed between the fuel assemblies and sealed with a gas, wherein a surface level of the coolant in the gas sealed assembly changes from an axially upper portion including a core top level to an axially lower portion at a time of core power increase or a core coolant flow quantity decrease. Each of the gas sealed assemblies includes an inner cylindrical member for reducing a horizontal cross sectional area of the flow of the coolant at a portion in height corresponding to an axial central portion of the core and the cylindrical member includes a member for generating heat by radiation.

Abstract: A replacement rod for insertion into a nuclear fuel assembly to replace a fuel rod containing a neutron absorbing, fissile fuel, includes Hafnium sufficient to substantially replace the neutron absorption capacity of the fuel rod. The replacement rod also includes a non-fissile second material that is commonly used for structures in nuclear fuel assemblies. The second material is preferably selected from the group consisting of a stainless steel, a zirconium alloy and zirconium. In one embodiment, the Hafnium is fabricated into a cylindrically-shaped rodlet, or core, and the second material is fabricated into an annulus around the core. Alternatively, the Hafnium and the second material are each distributed about uniformly throughout a cylindrical volume of the replacement rod. Refurbishing nuclear fuel assemblies by replacing damaged fuel rods with replacement rods according to the invention obtains an improved peaking factor over prior art methods.

Abstract: A generally cruciform-shaped control rod for a nuclear reactor is formed by vertical stiffeners laterally spaced one from the other and interconnected by horizontal stiffeners at their ends defining discrete compartments in each wing of the cruciform-shaped control rod. Sheathing overlies the stiffeners to seal each of the compartments from its surrounding environment. Neutron-absorbing material, such as boron carbide and/or hafnium tubes, are disposed in each compartment. Each wing is secured to a generally cruciform central tie rod formed of planar plates superposed one over the other alternately at right angles with the outer edges of the plates welded to the inner edges of the wings, affording structural support to the control rod.

Abstract: A window in the control rod for a nuclear reactor has flanges along its opposite sides. A latch handle has slots along its opposite sides. The latch handle is sized and configured such that in a first angular orientation, the latch handle may be received within the plane and peripheral confines of the window and, upon rotation of the latch handle through 90.degree. into a second orientation, engages the slotted sides of the latch handle with the flanges of the window to capture the latch handle within the window while simultaneously enabling linear vertical movement of the latch handle relative to the window. The latch handle is then attached to a shaft for operating a coupling mechanism between the control rod and the control rod drive.

Abstract: A neutron-absorber control rod tube includes end plugs welded at opposite ends to the tube with each end plug having a bore opening into the interior of the tube. A hafnium rod is disposed inside the absorber tube and has reduced diameter end portions providing an interference fit with the bores of the end plugs. The end faces of the hafnium rod terminate short of the inner end faces of the bores of the end plugs defining gas pockets therebetween. The interference fits between the bores of the end plugs and hafnium rod, respectively, afford substantial frictional resistance to relative movement of the end plugs and absorber rod, while the gas pockets provide a viscous dampening effect upon relative movement of the end plugs and absorber rod, in response to acceleration or deceleration loads on the structure in an axial direction of the absorber tube and the absorber rod.

Abstract: Method of fabricating a multi-ply carbon fibre fabric, preform or composite material from a layer of unidirectionally aligned carbon fibres of ultra-high modulus and a layer of low modulus carbon fibre comprising the steps of: arranging in superimposed relationship the layer of unidirectionally aligned carbon fibres of ultra-high modulus and the layer of low modulus carbon fibres so that at least a substantial number of the fibres of low modulus are disposed transversely of the fibres of the ultra-high modulus fibre layer, and connecting the two layers by interlacing fibres of the layer of low modulus fibres with those of the layer of ultra-high modulus fibres by needle-punching using felting needles orientated and configured so that their barbs snag only the low modulus fibres during passage through the layers.

Abstract: A neutron absorbing apparatus which includes two adjacent neutron absorbing plates and a mounting assembly with latching means configured to be easily secured to fuel assemblies while the fuel assemblies remain under water in a fuel storage rack, thereby eliminating the need to remove the fuel assemblies or the fuel storage rack for installation. The two neutron absorbing plates are positioned orthogonally to form a chevron cross section which can be placed about the fuel assemblies by insertion in the existing space between the fuel assemblies and the cell walls of a fuel storage rack. A prescribed orientation of the chevron configured neutron absorbing plate in the cells of the fuel storage rack together with the selected use of a single neutron absorbing plate economically provides sufficient neutron absorption in all radial directions about the fuel assemblies to maintain safe storage conditions in closely packed fuel storage racks.

Abstract: A fuel assembly having a water cross or water rod arranged between the fuel rods, an inside of the water cross or water rod being divided into a coolant rising passage and a coolant lowering passage, and a control guide tube disposed inside the water cross or water rod and extending along an axial direction of the water cross or water rod. The coolant rising passage has a coolant inlet port formed to a portion above or under a portion at which the fuel rods are supported by the lower tie plate. The control element guide tube has a coolant outlet port formed at that portion so that a coolant introduced into the coolant rising passage flows vertically upwardly, then turns and flows downwardly along the control element guide tube, and flows into an inside thereof through the coolant outlet port. A reactor core comprises a plurality of fuel assemblies each having a structure described above, a control rod and a control element operated in association with the control rod.

Abstract: A spacer pad for a nuclear control rod includes first and second halves each including a head and a shank. The shanks are configured for joining together the pad first and second halves, and the shanks are independently locked together for preventing the disassembly thereof. In an exemplary embodiment, the first and second shanks are threadingly joined together, and then independently locked together using a complementary hook and ledge respectively supported by the pad halves which allows assembly together of the pad halves but prevents disassembly thereof.

Abstract: A flux trap neutron absorber arrangement for use in a fuel storage body between a pair of fuel storage cans which receive and store nuclear fuel assemblies includes separate pockets spaced from one another and extending vertically along and attached to the exterior of each of the adjacent side walls of adjacent spaced storage cans, an elongated flat plate of a thermal neutron absorber material mounted in each pocket, the plates of thermal neutron absorber material being likewise spaced from one another and defining a fast neutron slow-down region therebetween, a slab of a metal hydride disposed in the fast neutron slow-down region between the plates of thermal neutron absorber material and the separate pockets on the adjacent side walls, a canister containing the slab of the metal hydride being disposed in the fast neutron slow-down region, the canister being connected to at least one of the adjacent side walls of the adjacent storage cans.

Abstract: In a control rod for nuclear reactors with elongated channels for boron carbide or other neutron-absorbing material which swells upon neutron irradiation, the neutron-absorbing material (20a), in at least some of the channels (18b), is provided with projecting portions (20a') or arranged in a casing with portions projecting towards the channel walls. Further, the projecting portions are adapted to form between them and the channel walls unfilled spaces (40) for taking up swelling neutron-absorbing material.

Abstract: The apparatus of the present invention is a plate of neutron absorbing material. The plate may have a releasable locking feature permitting the plate to be secured within a nuclear fuel assembly between nuclear fuel rods during storage or transportation then removed for further use or destruction.The method of the present invention has the step of placing a plate of neutron absorbing material between nuclear fuel rods within a nuclear fuel assembly, preferably between the two outermost columns of nuclear fuel rods. Additionally, the plate may be releasably locked in place.

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

Abstract: An apparatus for achieving increased fuel efficiency in a nuclear reactor wherein spectral shift is utilized to adjust for excess reactivity. This feature is achieved by stationary displacer rods within the fluid moderator of the reactor, with these stationary displacer rods decreasing ineffective volume during operation of the reactor whereby the effective volume of the fluid moderator increases as the nuclear fuel is burned. This decrease in effective volume is achieved by providing a sacrificial material in the displacer rods that is dissolved (or volatilized, etc.) by the fluid moderator. The composition of the sacrificial material can be varied along the length of the rod so as to achieve the desired reduction of volume despite a temperature gradient along the rod.

Abstract: A reconstitutable control assembly has a spider structure which supports control rods by detachable attachment joints. Each attachment joint includes a hollow connecting finger on the spider structure and an elongated detachable split upper end plug on each control rod. The split upper end plug includes a pair of separate upper and lower plug portions. The upper plug portion has upper, middle and lower sections, whereas the lower plug portion has upper, middle and lower segments. The upper section of the upper plug portion is rigidly attached to the connecting finger on the spider structure, whereas the lower segment of the lower plug portion is rigidly connected to the control rod. Also, the lower section of the upper plug portion and the middle segment of the lower plug portion have complementary threads defined thereon for rigidly threadably attaching the upper and lower plug portions to one another.

Abstract: The invention relates to a nuclear reactor with improved efficiency.The nuclear reactor comprises a massive partition (18) of material reflecting high energy neutrons at the circumference of the core (7) of the reactor, two layers (19 and 20) of material absorbing low energy neutrons and containing fertile material arranged one at the lower part and one at the upper part of the core (7) and an assembly of neutron energy spectrum variation rods (27). The rods (27) are associated with mechanisms permitting them to be either fully inserted into the core (7), or fully extracted. These rods (27) consist of a material absorbing low energy neutrons and permit a shift of the neutron spectrum towards the high energies.The invention is particularly applicable to pressurized water nuclear reactors.

Abstract: In-core nuclear instrumentation for a fast breeder reactor includes a neutron flux measuring unit disposed in a control rod assembly, whereby it is possible to measure a change in in-core neutron flux reliably and highly accurately without requiring a major modification in core design.

Abstract: A method and apparatus for achieving increased fuel efficiency in a nuclear reactor wherein spectral shift is utilized to adjust for excess reactivity. This feature is achieved by stationary displacer rods within the fluid moderator of the reactor, with these stationary displacer rods decreasing in effective volume during operation of the reactor whereby the effective volume of the fluid moderator increases as the nuclear fuel is burned. This decrease in effective volume is achieved by providing a sacrificial material in the displacer rods that is dissolved (or volatilized, etc.) by the fluid moderator. The compositon of the sacrificial material can be varied along the length of the rod so as to achieve the desired reduction of volume despite a temperature gradient along the rod.

Abstract: A control blade for a nuclear reactor having inserted upper end structural members and inserted lower end structural members connected to a plurality of wings each in the form of a generally rectangular plate having an longitudinal axis extending in the longitudinal direction of the control blade, the wing being disposed to form a cross-shaped section of the control blade. The wings and the structural members are connected to and supported on a central connection member. Each wing or a sheath member formed within each wing is formed from a diluted alloy obtained by diluting a long-lived neutron absorber such as hafnium with a diluent such as zirconium or titanium. A plurality of neutron absorber housing holes are formed in the diluted alloy section.

Abstract: The reactor core of the plant has tubular vertically movable control rods moved by a pressurized flowing coolant. Each control rod so extends around a tubular guide rod which is immobile relatively to the reactor core as to leave a first annular gap between the control rod and the guide rod. The guide rod interior is operative as a first pressure chamber to which the pressurized coolant is supplied. The top end of each control rod is closed and has a vertical spindle which extends into the guide rod interior and co-operates with the guide rod to bound a second annular gap. At least one first restrictor is disposed in the first annular gap and at least one second restrictor is provided in the second annular gap. A second pressure chamber is present between the two restrictors. The coolant inflowing to the guide rod therefore returns by way of the second annular gap, the second pressure chamber and the first annular chamber to the pressure vessel which extends around the reactor core.

Abstract: Device for guiding nuclear reactor control clusters consisting of several absorbing rods including guide casings, associated respectively with the various control clusters, and, inside each casing, horizontal plates (14) ensuring, in the upper part, discontinuous guidance at intermediate levels for the various elements of the control cluster. In the lower part of the casing, guidance of the rods arranged in pairs sharing one radius is achieved by combining horizontal plates (14) ensuring mechanical guidance of the rods with casings (22) which reduce the hydraulic effects to a minimum by calming the cooling fluid in the radial direction around the said absorbing rods. The invention applies to pressurized water nuclear reactors.

Abstract: A reconstitutable control assembly has a spider structure which supports control rods by detachable attachment joints. Each attachment joint includes a hollow connecting finger on the spider structure and an elongated detachable split upper end plug on each control rod. The split upper end plug includes a pair of separate upper and lower plug portions. The upper plug portion has upper, middle and lower sections, whereas the lower plug portion has upper, middle and lower segments. The upper section of the upper plug portion is rigidly attached to the connecting finger on the spider structure, whereas the lower segment of the lower plug portion is rigidly connected to the control rod. Also, the lower section of the upper plug portion and the middle segment of the lower plug portion have complementary threads defined thereon for rigidly threadably attaching the upper and lower plug portions to one another.

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

Abstract: A nuclear excitation laser type intra-reactor neutron flux measuring system of this invention is comprised of a laser oscillator filled with a nuclear exciting gas such as .sup.3 He, KrF or XeF, mounted on the tip of a control rod. The nuclear exciting gas is made into a plasma by the neutrons or the fragments of fissioned nuclei when the tip is positioned in the reactor core by raising the control rod. Since the nuclear exciting gas made into a plasma itself generates a laser beam or amplifies a laser beam projected from the outside, the behavior of neutrons can be monitored in detail after guiding this light response to the light processing system located outside, distinguishing the energies of neutrons from the spectrum and calculating the density and the flux of the neutron in each energy. Furthermore, the detecting sensitivity can be enhanced by forming the responsive membrane made of U.sub.3 O.sub.8 and so on, on the laser oscillator.

Abstract: The zirconium cladding of a coolant-displacement rod of a nuclear reactor is precollapsed in the zirconium oxide stack of pellets which supports the cladding. Current is conducted through the cladding in an atmosphere at reduced pressure containing residual oxygen, to heat the cladding to a temperature at which its yield strength is reduced. Then, while the rod remains at this temperature, it is subjected to isostatic pressure which collapses the cladding uniformly. The formation, by reason of exposure to neutron flux, of a long unsupported gap in the cladding which might be collapsed under the pressure of the coolant is precluded. In addition, the rod retains its symmetry. The outer surface of the cladding is oxidized, facilitating the movement of the rod into its thimbles of the core and improving the resistances of the cladding to reaction with the coolant.

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

Abstract: A control rod support for mounting within a rod guide of a pressure vessel has plural, parallel axial extending passageway openings therein for receiving corresponding control rods of a control rod cluster. A channel extends from the passageway opening and through the support for accommodating each vane of a spider which supports the control rods and provides for telescoping movement of the control rod cluster relative to the rod guide and associated guide rod supports. Spaced interior side walls of the support defining the channel form junctures with the interior side wall defining the passageway opening; and planar wear surfaces extend from the respective junctures of the channel-defining interior side walls a sufficient lateral distance to provide planar-to-convex wear surface interfaces with the corresponding, contiguous surface segments of a generally cylindrical control rod which is received through the passageway opening and urged against the junctures.

Abstract: An apparatus and process for control rod assembly and construction for a nuclear reactor is disclosed wherein the control rod is of cruciform configuration having a plurality of and preferably four flat planar members. Each planar member is made up with an assembly of square cross sectioned tubular members. Each square cross sectioned tubular member includes a defined cylindrical center and a constant thickness surrounding tubular metallic shell to provide the contained neutron absorbing materials in a cylindrically shaped pressure vessel. The constant thickness surrounding tubular shell constituting the cylindrical shaped pressure vessel has four corner sections added to generate a modified square exterior profile. These added four corner sections comprise an addition to the tubular side wall thickness of the shell. Appropriate chamfers and rounding are provided to the square profile to impart both stress relief and convenient points for automated welding between side-by-side square sections.

Abstract: A reconstitutable control assembly has a spider structure which supports control rods by detachable attachment joints. Each attachment joint includes a hollow connecting finger on the spider structure and an elongated detachable split upper end plug on each control rod. The split upper end plug includes a pair of separate upper and lower plug portions. The upper plug portion has upper, middle and lower sections, whereas the lower plug portion has upper, middle and lower segments. The upper section of the upper plug portion is rigidly attached to the connecting finger on the spider structure, whereas the lower segment of the lower plug portion is rigidly connected to the control rod. Also, the lower section of the upper plug portion and the middle segment of the lower plug portion have complementary threads defined thereon for rigidly threadably attaching the upper and lower plug portions to one another.

Abstract: A neutron absorbing control device for service in nuclear reactors utilizing fissionable fuel. The control device includes hafnium metal as the neutron absorbing material which is employed in a unique structure which maximizes the advantages of hafnium while minimizing its disadvantages as well as providing other benefits.

Abstract: In the field of commercial nuclear reactors, there is an increasing demand for long-life control blades in order to meet the requirements of higher economy and reduction in the disposal of radioactive wastes. A control blade proposed by the invention stands a long use by virtue of the use of a long-life neutron absorber which is typically made of hafnium. Despite the use of hafnium which has a large specific weight (13.3 g/cm.sup.3), the size, shape and weight of the control blade are substantially the same as those of convertional control blades which employ boron carbides B.sub.4 C as the neutron absorber, so that the control blade can be back-fitted in existing boiling water reactors without difficulty.

Abstract: A control rod has blades each of which includes a neutron absorption region in which neutron absorbers each loaded to the core of a reactor from below and made of absorption nuclear chain type neutron absorber are disposed. The neutron absorption region is divided into two, upper and lower, regions in an axial direction; the boundary between the upper and lower regions is positioned within the range of from 3/8 to 5/8 of the full length of the neutron absorption region in the axial direction from the lower end of the neutron absorption region; and the quantity of the absorption nuclear chain type neutron absorber contained in the lower region in the section perpendicular to the axial direction is smaller than the quantity of the absorption nuclear chain type neutron absorber contained in the upper region in the section perpendicular to the axial direction.

Abstract: A sheath for a nuclear reactor control rod consists of chromium nickel stainless steel. It is protected against friction wear by nitridation over a depth of from 15 to 50 .mu.m obtained by an electric discharge in a nitrogen containing atmosphere.

Abstract: A spider assembly for supporting a corresponding rod cluster in a pressurized water reactor vessel, through which the core outlet flow passes in a predetermined direction. Each spider assembly comprises a generally cylindrical, central hub disposed in parallel axial relationship to the predetermined direction of the core outlet flow and a plurality of vane assemblies. Each vane assembly comprises means for mounting at least one rod to the assembly and at least one vane element connecting the rod mounting means to the hub. Each vane element has generally parallel, major planar surfaces disposed parallel to the predetermined direction of flow and a square trailing edge configuration which mitigates the shedding forcing function on the spider resulting from the core outlet flow thereover, while maximizing material content and thereby the strength thereof.

Abstract: An absorber rod for nuclear reactors with a pile of spherical fuel elements, which is inserted directly into the pile, in order to affect the prevailing neutron flux by absorber material located in an annular gap between two concentric cylindrical rod elements. The absorber rod has concentric rod elements arranged in pairs, a common rod tip and common connecting pieces. The rod elements are cooled by flow of gas and the inner cylindrical rod element performs the support function, i.e., it absorbs and transmits forces and moments originating in the movements of the rod during insertion and extraction.