Abstract: A control rod assembly for a boiling water reactor comprises a tie-rod of a cross-shaped section, and four sheaths. Each of the sheaths is of a U-shaped section and mounted to the respective arms of the tie-rod. One or more neutron absorber materials are disposed within a space defined by the arm and the sheath. The neutron absorber material is axially separated into two portions. One of two portions is supported by a supporting member. The other portion is suspended by a handle.

Abstract: Hybrid nuclear reactor grey rods are described, wherein geometric combinations of relatively weak neutron absorber materials such as stainless steel, zirconium or INCONEL, and relatively strong neutron absorber materials, such as hafnium, silver-indium cadmium and boron carbide, are used to obtain the reactivity worths required to reach zero boron change load follow. One embodiment includes a grey rod which has combinations of weak and strong neutron absorber pellets in a stainless steel cladding. The respective pellets can be of differing heights. A second embodiment includes a grey rod with a relatively thick stainless steel cladding receiving relatively strong neutron absorber pellets only. A third embodiment includes annular relatively weak netron absorber pellets with a smaller diameter pellet of relatively strong absorber material contained within the aperture of each relatively weak absorber pellet.

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: A neutron flux control component for a nuclear reactor. Thin, overlapping segments of highly neutron absorbing material are positioned in the core of a reactor. The self-shielding overlapping segments are moved relative to each other to vary the amount of exposed surface area of poison to control core reactivity and to provide power shaping within the reactor core. The poison segments are mounted to carriers in the form of close-fitting concentric cylinders or rods of V-shaped cross section.

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 control rod for a nuclear reactor comprising a number of absorber plates (13-16) which are connected to each other along a center line on the control rod and which are each provided with a plurality of bored channels (18b), which extend at least substantially perpendicularly to the center line of the rod, contain boron carbide or other absorber material which swells upon irradiation and are sealed off from communication with the surroundings of the control rod. Within at least one region of an absorber plate, each channel is arranged at a smaller distance to an adjacent channel than to the surface of the absorber plate. Preferably, each channel within the stated region of the absorber plate is arranged at a smaller distance to the adjacent channel on one of its sides than to the adjacent channel on its other side.

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: 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.

Abstract: In a control rod for a nuclear reactor having a cruciform shape with four flat planar members, an improved membrane for safeguarding against crevice cracking corrosion is disclosed. Each of the four flat planar members of the control rod is fabricated from side-by-side tubular members containing sealed neutron absorbing poisons. Each of the tubular members has square outside sections. These square outside sections are welded together to form the flat planar members of the control rod. The improvement includes a protective membrane wrapped over the structural flat planar member. The protective membrane surrounds the member and is maintained to the planar member under compression by ambient reactor pressure. The membrane provides an additional margin against crevice corrosion cracking by preventing the water of the reactor from coming into contact with the welded side-by-side square sectioned tubular members.

Abstract: In a control rod construction for moderating and controlling a reaction of a nuclear reactor, a control rod structure is disclosed in which hafnium is welded to stainless steel. Typically, the control rod is confined for movement axially along its length into and out of the reactor. The hafnium is surrounded in the control rod structure by a sheath of stainless steel to inhibit movement relative to the control rod structure other than in the axial direction of control rod movement. The hafnium is friction welded to the stainless steel of the control rod so as to stress the weld in either tension or compression due to dynamic loading occurring from control rod movement. The stainless steel to which the hafnium is welded is in turn conventionally welded or mechanically connected to the remaining steel components of the control rod.

Abstract: A cluster of standardized reduced length burnable absorber rods include a plurality of middle rod sections having a multiplicity of different axial lengths and containing burnable absorber material in sealed chambers therein, a plurality of upper end spacer sections having a multiplicity of different axial lengths and each defining an empty space, and a plurality of lower end spacer sections having a multiplicity of different axial lengths and each defining an empty space. Each of the rods is formed of one middle rod section tandemly arranged between and rigidly interconnecting one upper end spacer section and one lower end spacer section. The three rigidly interconnected sections which form each rod being selected so as to provide the same standard combined axial length for each of the rods in the cluster thereof although the axial lengths of the middle rod sections can vary from rod to rod and thereby the axial location of the burnable absorber material along the rod can also vary from rod to rod.

Abstract: A control rod for use in a nuclear reactor core to provide xenon compensation includes an elongated inner cylindrical member and an elongated outer cylindrical member surrounding the inner member. Each of the members is composed of axially-extending, alternating black poison and nonpoison regions. Also, the inner member is axially movable relative to the outer member to adjust the degree to which the poison regions of the members overlap with the nonpoison regions thereof and thereby change the overall worth of the rod in an axially uniform manner. The inner cylindrical member has a solid cross-sectional configuration, whereas the outer cylindrical member has an annular cross-sectional configuration and concentrically surrounds the inner member. Each of the poison regions in the members is about the same axial height, while each of the nonpoison regions is about the same axial height.

Abstract: A burnable poison rod for use in a nuclear reactor comprises a metallic tube with upper and lower closure means, a neutron absorber positioned within the cladding and a neutron moderating spacer means positioning the neutron absorber in spaced relation to the lower closure means. The neutron moderating spacing means can comprise a solid neutron moderating material, or a liquid coolant moderator contained within the lower section of the cladding with a sealing plug positioned between the neutron absorber and the liquid coolant moderator.

Abstract: In a fast breeder reactor provided with a core comprising a core region packed with a fissile material and a blanket region which surrounds the outside of said core region and most of which is formed of a fertile material, and a plurality of control rods which are put in and out of the above core region by a control rod driving device, the fast breeder reactor of the present invention is characterized in that each of said control rods is constructed of a neutron absorber region packed with a neutron absorber and a gas region disposed in the end portion on the side further separated from said control rod driving device than said neutron absorber region. With this invention, the spectral shift effect can be produced by utilizing said gas region, thereby increasing the core reactvity of the fast breeder reactor.

Abstract: A control rod for a nuclear reactor comprises a number of elongated absorber plates (13-16) which are each provided with a plurality of channels (18b), said channels extending substantially perpendicularly to the longitudinal direction of the absorber plate, containing powdered boron carbide or other powdered absorber material which gives off gas and swells upon irradiation, and being hermetically separated from the surroundings of the control rod by an edge portion (30), which is arranged at an edge (31) running in the longitudinal direction of the absorber plate and comprises a gas-tight edge (31) and a longitudinal space (32) arranged inside said edge and being in open communication with and permitting a gas flow between the different channels in the absorber plate.

Abstract: A cluster of standardized reduced length burnable absorber rods include a plurality of middle rod sections having a multiplicity of different axial lengths and containing burnable absorber material in sealed chambers therein, a plurality of upper end spacer sections having a multiplicity of different axial lengths and each defining an empty space, and a plurality of lower end spacer sections having a multiplicity of different axial lengths and each defining an empty space. Each of the rods is formed of one middle rod section tandemly arranged between and interconnecting one upper end spacer section and one lower end spacer section. The three interconnected sections which form each rod being selected so as to provide the same standard combined axial length for each of the rods in the cluster thereof although the axial lengths of the middle rod sections can vary from rod to rod and thereby the axial location of the burnable absorber material along the rod can also vary from rod to rod.

Abstract: This is a non-uniform resistance heating tube constituting a simulated nuclear fuel cluster in a heat transfer test facility for nuclear reactor. This resistance heating tube has a fixed outside diameter and its thickness is molded so that an electric resistance distribution changes continuously corresponding to the power distribution state of nuclear fuel rod in the axial direction of the tube. This resistance heating tube can be obtained by drawing an original pipe, rolling it into an axially uniform thick, then grinding its outer surface so that its thickness becomes non-uniform continuously in the axial direction of the tube, and thereafter smoothing the outer surface of the tube by swaging so that its outside diameter becomes uniform.

Abstract: A control rod for use in a nuclear reactor core to provide xenon compensation includes an elongated inner cylindrical member and an elongated outer cylindrical member surrounding the inner member. Each of the members is composed of axially-extending, alternating black poison and nonpoison regions. Also, the inner member is axially movable relative to the outer member to adjust the degree to which the poison regions of the members overlap with the nonpoison regions thereof and thereby change the overall worth of the rod in an axially uniform manner. The inner cylindrical member has a solid cross-sectional configuration, whereas the outer cylindrical member has an annular cross-sectional configuration and concentrically surrounds the inner member. Each of the poison regions in the members is about the same axial height, while each of the nonpoison regions is about the same axial height.

Abstract: A neutron absorber control rod for use in a fuel assembly of a nuclear reactor includes an elongated hollow tubular member having opposite ends and a hermetically sealed chamber defined therein between its opposite ends, one of the member ends being a leading end and the other of the member ends being a trailing end upon insertion of the control rod into the fuel assembly. A first neutron absorber material in the form of boron carbide pellets is contained in the chamber and located nearer to the leading than to the trailing end of the member, whereas a second neutron absorber material in the form of silver-indium-cadmium pellets is contained in the chamber and located nearer to the leading than to the trailing end of the member. The second neutron absorber material has a length approximately three times longer than that of the first neutron absorber material.

Abstract: A burnable poison rod for use in a nuclear reactor comprises a metallic tube with upper and lower closure means, a neutron absorber positioned within the cladding, and a neutron moderating spacer means positioning the neutron absorber in spaced relation to the lower closure means. The neutron moderating spacing means can comprise a solid neutron moderating material, or a liquid coolant moderator contained within the lower section of the cladding with a sealing plug positioned between the neutron absorber and the liquid coolant moderator.

Abstract: An improved water displacer rod includes an elongated hollow thin-walled tube with a pair of end plugs attached to opposite ends of the tube to hermetically seal the tube and a plurality of support pellets disposed in a stacked relationship within the tube. The pellets allow the thin-walled tube to be laterally flexible while still able to resist collapse due to high external pressure. Each pellet is preferably formed of a body having a hollow annular cross-sectional shape and a pair of end webs extends across and closing opposite ends of the body. The body defines a central void and the webs seal the void. Thus, when the pellets are stacked within the tube, each void is sealed individually one from the next. A double barrier is provided in the displacer rod by the hermetically sealed tube and the individually sealed pellets.

Abstract: A method of operating a gas-cooled nuclear reactor having graphite fuel elements in which, to reduce the reactor, a quenching element is introduced which takes a particle of a reaction-reducing substance in a sheath which will melt or release the substance in vapor form so that the substance can penetrate in gaseous form through the surrounding graphite body and deposit upon fuel elements.

Abstract: A control arrangement which provides enthalpy rise compensation upon reduction of core power includes control rodlets arranged in a cluster. Each control rod cluster has a higher axial worth at an upper portion than at a lower portion thereof. Several different embodiments of control rod clusters are provided. In one embodiment, the worth of the control rod cluster varies in accordance with different lengths of the absorber material contained within its rodlets. In another embodiment, the worth of the control rod cluster varies in accordance with different variations in densities of the absorber material within its rodlets. In a third embodiment, the worth of the control rod cluster varies in accordance with different kinds of the absorber material within the rodlets. In a final embodiment, the worth of the control rod cluster varies in accordance with different variations in diameters of the absorber material within its rodlets.

Abstract: A control rod for a nuclear reactor wherein plates of neutron absorbing material (e.g. hafnium) are used in the upper portion thereof and tubes containing a different neutron absorbing material (e.g. boron) are positioned beneath the plates. To relieve the tubes of the weight of the plates, the plates are attached to support members of the control rod frame, to prevent or reduce the area of a gap between the plates and the tubes, joints therebetween are provided.

Abstract: A fast breeder which is formed with a driver core region having an enriched nuclear fuel substance and allowing liquid metal acting as a coolant to pass therethrough and with a blanket region surrounding the periphery of the driver core region. A reactor stopping control rod to be inserted downward into the driver core region has an axially uniform density of boron-10. A reactor power adjusting control to be inserted downward into the driver core region has a lower density of boron-10 in a lower region than that in an upper region.

Abstract: A control rod for a nuclear reactor according to the present invention is such that neutron absorbing rods are surrounded with a second neutron absorber which differs in material from the neutron absorbing rods. In a case where the neutron absorbing rod is composed of boron carbide powder and a cladding for receiving the powder therein, the second neutron absorber is a sheet of a material having a neutron irradiation lifetime longer than that of boron carbide, for example, hafnium. In a case where the neutron absorbing rod is a round hafnium rod, the second neutron absorber having a neutron absorption worth higher than that of hafnium is located so as to surround the round hafnium rods. Thus, the neutron absorbing rods are effectively used, and the lifetime of the control rod can be prolonged in the former.

Abstract: A control rod for a nuclear fuel assembly has structures formed of boron carbide mounted inside it. The boron carbide structures are provided deformable members between them which will deform at operating temperatures to accommodate the dimensional increase of the boron carbide structures and reduce the level of deformable stress on the rod cladding.

Abstract: A control rod assembly arrangement is disclosed for a light water nuclear reactor. Absorber rods are combined with stainless steel rods to achieve a more homogeneous poison distribution effect which reduces power depression within associated fuel assemblies and thereby flattens the overall power distribution within the core. In addition to improved load follow performance, safety analysis margins are improved due to the reduction in control rod reactivity worth.

Abstract: A boiling water nuclear power reactor includes an improved control rod associated with each of its clusters of fuel assemblies. The control rod has an elongated central stem defining a longitudinally extending internal central gas plenum and a plurality of blades orthogonally arranged in pairs to provide a cruciform configuration in which the blades connect to and extend radially outward from the central stem. Each blade incorporates a series of internal cavities arranged in columns and rows across the length and width of the blade, and a neutron absorbing pellet is disposed in each cavity. The cavities communicate with the central plenum so that any gases generated by irradiation of the pellets can expand into the plenum. The cavities and pellets are arranged to form a longer, constant worth section in a body portion of each blade and a shorter, reduced worth section in an end tip portion of each blade.

Abstract: A control rod with a "reduced worth" tip is provided for a nuclear reactor which includes an elongated tubular cladding with its opposite ends closed and having a plurality of pellets of two different types disposed in its lower end portion in an end-to-end relationship. One type of pellets is formed of a neutron absorbing material, such as B.sub.4 C, whereas, the other type of pellets is formed of an inert material, such as ZrO.sub.2. The absorber pellets and the inert pellets are interspaced between one another in the lower end of the rod so as to gradually reduce the rate of change of the neutron flux experienced at the rod's lower end portion as it moves in and out of the fuel assembly to thereby alleviate pellet-clad-interaction and thus reduce the likelihood of fuel rod failure. In one embodiment, the axial heights of the absorber pellets progressively increase from the bottom to the top of the rod's lower end portion while the axial heights of the interspaced inert pellets remain constant.

Abstract: A control rod for a boiling-water reactor having blades arranged in the form of a cross in transverse cross section includes a plurality of poison tubes disposed therein. Boron carbide powder which is a neutron absorbing material causing an (n, .alpha.) reaction to take place is charged in the poison tubes. The control rod has plates of Hf-Zr alloy arranged in the blades in a position nearer to a forward end of the control rod at which the control rod is inserted in a reactor core than the poison tubes. The plates of Hf-Zr alloy are formed of an alloy of Hf having a large neutron absorption cross section and Zr having a small neutron absorption cross section. The concentration of Hf in the plates of Hf-Zr alloy is successively reduced in going from an end thereof adjacent the poison tubes toward and end thereof at the inserting end of the control rod.

Abstract: A displacer rod for use in a mechanical spectral shift pressurized water nuclear reactor comprises a sectioned substantially hollow low neutron absorbing metal rod capable of displacing reactor coolant without absorbing a high amount of neutrons. The tubular sections can be made of stainless steel or Zircaloy tubing and may contain pellets for weighting the displacer rod.

Abstract: An elongated absorber plate, which is stationarily mounted in a gap between two fuel assemblies in a reactor core, comprises a plurality of absorber channels which are filled with a burnable absorber material. The channels (5b) are formed by welding to each other two confronting sheet elements (2b, 3b), of which at least one is corrugated.

Abstract: A method of controlling the reactivity of a gas-cooled core reactor the core of which consists of a pile of poured balls of equal diameter of fuel material which are withdrawn from the pile in downward direction and, if desired, are again added from above in conformity with the extent to which the pile of fuel balls has burned off. The method is characterized primarily in that balls which consist of absorbing material and have a diameter shorter than the diameter D of the balls of fuel material are introduced into the poured pile, the diameter d.sub.A of the balls of absorbing material being d.sub.Z .ltoreq.d.sub.A .ltoreq.d.sub.z +xd, preferably d.sub.Z <d.sub.A <d.sub.Z <+xd.sub.Z if d.sub.Z = D(2.sqroot.3-1) and representing the diameter of the maximum possible ball which can be placed in the densest ball packing between three interengaging balls of fuel material, and when d.sub.Z +xd.sub.Z =D(.sqroot.2-1).

Abstract: A nuclear reactor includes an active portion with fissionable fuel and neutron moderating material surrounded by neutron reflecting material. A control element in the active portion includes a group of movable rods constructed of neutron-absorbing material. Each rod is movable with respect to the other rods to vary the absorption of neutrons and effect control over neutron flux.

Abstract: 1. In a nuclear reactor incorporating a plurality of columns of tubular fuel elements disposed in horizontal tubes in a mass of graphite wherein water flows through the tubes to cool the fuel elements, the improvement comprising at least one control column disposed in a horizontal tube including fewer fuel elements than in a normal column of fuel elements and tubular control elements disposed at both ends of said control column, and means for varying the horizontal displacement of the control column comprising a winch at the upstream end of the control column and a cable extending through the fuel and control elements and attached to the element at the downstream end of the column.