Abstract: A damping area or “dash pot” on the upper ends of control rods absorb energy from dropped control rod assemblies without narrowing the diameter of guide tubes. As a result, coolant can freely flow through the guide tubes reducing boiling water issues. The dampening area reduces a separation distance between an outside surface of the control rod and an inside surface of the guide tubes decelerating the control rods when entering a top end of the guide tubes. In another example, the dampening area may be located on a drive shaft. The dampening area may have a larger diameter than an opening in a drive shaft support member that decelerates the drive shaft when dropped by a drive mechanism.

Abstract: Nuclear reactor fuel assembly comprising fuel elements installed in a frame having guide channels and spacer grids; a bottom nozzle; and a removable head. The head comprising collet tubes, an upper shell, a support element in the form of a tube, and springs. The collet tubes comprise two coaxially arranged tubes that are movable relative to each other and that each have stops on their side surfaces. The stops interact with each other to select the length of the collet tubes. The upper shell has a tube with a rigidly fixed plate interacting with the springs. The plate has plural holes having a shape corresponding to a shape of a respective boss of the support element. The clearance in plan view between a respective hole and a respective boss being at least the mounting clearance between the tube of the support element and the tube of the upper shell.

Abstract: This disclosure relates to reactor control, and more particularly to a control rod drive mechanism and a reactor control system. The control rod drive mechanism includes a lifting-lowering assembly, a mounting assembly and a release assembly. The mounting assembly is configured to mount a control rod. The lifting-lowering assembly includes a fixing component, a scissor-type lifting-lowering mechanism and a lifting-lowering component. An end of the scissor-type lifting-lowering mechanism is connected to the fixing component, and the other end is connected to the lifting-lowering component. The scissor-type lifting-lowering mechanism is configured to drive the lifting-lowering component to move close to or away from the fixing component. The release assembly is movably arranged on the lifting-lowering component, and is detachably connected to the mounting assembly. The release assembly is configured to move relative to the lifting-lowering component when power is off to release the mounting assembly.

Abstract: A control rod assembly including at least one movable control rod including a neutron absorbing material, a control rod drive mechanism (CRDM) for controlling movement of the at least one control rod, and a coupling operatively connecting the at least one control rod and the CRDM. The coupling includes a terminal element engaged with a connecting rod of the CRDM and the at least one moveable control rod, and a kinetic energy absorbing element supported by the terminal element for absorbing kinetic energy during a SCRAM event, the kinetic energy absorbing element configured to act between the terminal element and an upper plate of an associated fuel assembly.

Abstract: A control rod spider assembly connection between a connecting finger and a rodlet. An upper end plug of the rodlet is secured to the inner bore of the hollow connecting finger with a mating one of a right hand or left hand thread interfacing between the interior of the bore and the circumference of the rodlet. The upper end of the rodlet is captured by a second fastener mechanism having the other of the right hand or the left hand thread. The second fastener mechanism is anchored to one or both of the connecting finger or the upper end plug to secure the connection.

Abstract: A nuclear fuel assembly having a tube-in-tube control rod guide tube design that incorporates an end plug that extends axially upward to an elevation above the lower most grid where it is sealed at its upper end to the lower end of the control rod guide tube. The guide tube lower end plug has a threaded recess in its upper surface that mates with a corresponding dashpot end plug threaded extension that is formed as an insert in the lower end of the guide tube. A hole formed through the outer wall of the guide tube end plug at the elevation of the lower portion of the recess provides a positive inspection port for assuring the proper seating of the dashpot. A method of manufacture of such a fuel assembly is also disclosed.

Abstract: A method to design a nuclear fuel assembly having the following steps including establishing the falling speed of the control rod upon entry into the lower damping portion when the control cluster falls in the event of a shutdown of the nuclear reactor, establishing, based on the falling speed established in step a), the progression of the falling speed of the control rod in the lower damping portion, establishing, based on the progression of the speed established in step b), a maximum elevated pressure produced in the liquid contained in the lower damping portion, and establishing, based on the maximum elevated pressure established in step c), a maximum circumferential stress produced in the lower damping portion.

Abstract: A nuclear fuel assembly having a tube-in-tube control rod guide tube design that incorporates an end plug that extends axially upward to an elevation above the lower most grid where it is sealed at its tipper end to the lower end of the control rod guide tube. The guide tube lower end plug has a threaded recess in its upper surface that mates with a corresponding dashpot end plug threaded extension that is formed as an insert in the lower end of the guide tube. A hole formed through the outer wall of the guide tube end plug at the elevation of the lower portion of the recess provides a positive inspection port for assuring the proper seating of the dashpot. A method of manufacture of such a fuel assembly is also disclosed.

Abstract: A fuel assembly includes a bottom nozzle set on a lower core plate of a nuclear reactor, a top nozzle with a hold down spring to urge the bottom nozzle against the lower core plate, guide thimbles which guide control rods, having passed through the top nozzle, toward the lower core plate, a dashpot formed on each of the guide thimbles to reduce the fall velocity of a corresponding one of the control rods, a thimble screw which connects each of the guide thimbles to the bottom nozzle, and a drain hole formed to extend through each of the thimble screw. The dashpot has a large-diameter portion with substantially the same diameter as that of each of the guide thimbles. The diameter d of the drain hole falls within a range of 0.04 D<d<0.08 D where D is an inner diameter of the large-diameter portion.

Abstract: A fuel assembly includes a bottom nozzle set on a lower core plate of a nuclear reactor, a top nozzle with a hold down spring to urge the bottom nozzle against the lower core plate, guide thimbles which guide control rods, having passed through the top nozzle, toward the lower core plate, a dashpot formed on each of the guide thimbles to reduce the fall velocity of a corresponding one of the control rods, a thimble screw which connects each of the guide thimbles to the bottom nozzle, and a drain hole formed to extend through each of the thimble screw. The dashpot has a large-diameter portion with substantially the same diameter as that of each of the guide thimbles. The diameter d of the drain hole falls within a range of 0.04D<d<0.08D where D is an inner diameter of the large-diameter portion.

Abstract: A fuel assembly for a pressurized water reactor having control rod guide thimbles (5) each having a dashpot (12) for protecting against flexural deformation which may impair insatiability of a control rod. The fuel assembly includes, a plurality of control rod guide thimbles (5) having bottom and top end portions fixedly secured to a lower nozzle (2) and an upper nozzle (4), respectively, disposed in opposition to each other. The dashpot (12) of each control rod guide thimble (5) includes a small diameter section (13b) having an outer diameter smaller than that of the control rod guide thimble (5) formed at an upper portion of the dashpot (12), and a large diameter section (13a) having an outer diameter substantially equal to that of the control rod guide thimble (5) formed at a lower portion of the dashpot (12). With the length of the control rod guide thimble (5) represented by L, the effective length (S) of the small diameter section (13b) is selected to lie within a range of from 0.03 L to 0.1 L.

Abstract: A tubular blank (22) is rolled on a mandrel (14) in a pilgrim rolling mill. In a first rolling stage, a first part of the blank (22) is rolled on a first part (18, 19) of the mandrel (14), with a reduction of the outside diameter of the blank (22) to the outside diameter of the guide tube and a reduction of the wall thickness of the blank (22) to one of a first wall thickness (e1) and a second wall thickness (e2) exceeding the first wall thickness (e1). The mandrel (14) is advanced in the axial direction. A second part of the blank (22) is rolled on a second part (20,21) of the mandrel spaced from the first part in the axial direction with a reduction of the outside diameter of the blank to the outside diameter of the guide tube and a reduction of the wall thickness of the blank (22) to the other of the first wall thickness (e1) and second wall thickness (e2).

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

Abstract: A fuel assembly for a pressurized water reactor having control rod guide thimbles (5) each having a dashpot (12) for protecting against flexural deformation which may impair insertability of a control rod The fuel assembly includes, a plurality of control rod guide thimbles (5) having bottom and top end portions fixedly secured to a lower nozzle (2) and an upper nozzle (4), respectively, disposed in opposition to each other. The dashpot (12) of each control rod guide thimble (5) includes a small diameter section (13b) having an outer diameter smaller than that of the control rod guide thimble (5) formed at an upper portion of the dashpot (12), and a large diameter section (13a) having an outer diameter substantially equal to that of the control rod guide thimble (5) formed at a lower portion of the dashpot (12). With the length of the control rod guide thimble (5) represented by L, the effective length (S) of the small diameter section (13b) is selected to lie within a range of from 0.03 L to 0.1 L.

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 hydraulic control rod drive for a nuclear reactor, with a a reactor plenum enclosing the drive, comprises first and second hollow bodies together forming a cylinder and a hollow piston. Working fluid is supplied through one of the hollow bodies. The first hollow body is stationary and the second hollow body is disposed coaxially around the first hollow body. The two hollow bodies define an annular gap therebetween so as to allow axial reciprocating movement of the second hollow body, which forms a carrier body for control elements of the control rod. The second hollow body can be lifted, lowered or suspended by feeding working fluid. A portion of the fluid is removed from the inner space via a throttle passage. A positional measurement system determines the relative displacement of the second hollow body by measuring an ultrasonic measurement path. The system includes an ultrasound reflector and an ultrasonic transducer rigidly mounted remote from the ultrasound reflector.

Abstract: A device for damping the fall of a neutron absorbing bar on the upper end piece of a nuclear fuel assembly, typically a PWR, comprises at least one pair of cylinder-piston sets which are located symmetrically with respect to the vertical axis of the fuel assembly. One of the cylinder and piston in each set is carried by a fixed plate secured to the upper end piece. The other of the cylinder and piston is fixed to a movable plate arranged to receive the bar upon fall thereof and to move vertically toward the fixed plate, damping being achieved by the head loss impressed to the fluid forced out of the cylinders.

Abstract: A neutron absorbing bar for use in a PWR has an integrated damping device comprising a cluster of vertical absorbent rods fixed to the arms of a spider having a central pommel connectable to a drive mechanism. A damping device in the pommel includes a cylinder slidably receiving piston urged into a downward projecting position by springs contained in the cylinder. The cylinder and the piston are so formed that the leak flow at a cross-sectional area offered to the liquid driven out of the cylinder by the piston gradually decrease as the latter moves from an outermost position. The piston carries a hydromechanical damper damping the initial impact of the bar upon a scram.

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: Improvements to guide tubes for the fuel assemblies of light water nuclear reactors, said assemblies being immersed in operation in the cooling water of the core of such a reactor, the guide tubes being of the type made from zircaloy and fixed at their two ends respectively to an upper end part and a lower end part made from stainless steel or Irconel and which incorporate devices for braking the fall of the control rods which they house during the rapid shutdown of the reactor, wherein the said braking devices are constituted by means for restricting the diameter of the guide tubes comprising for each guide tube a zircaloy inner sleeve spot welded to the said guide tube and whose internal diameter permits the passage, with a calibrated clearance, of the corresponding control rod, the sleeve being distributed over the lower portion of each guide tube and associated with orifices made in the actual guide tubes to produce the progressive hydraulic absorption of the end of the fall of the control rods.

Abstract: The drive for an absorber rod for a nuclear reactor has a drive piston guided in a cylinder combined with the absorber rod forming an absorber unit. In order to compensate the forces exerted by the medium of the pressure vessel on the absorber unit and tending to pressure the absorber rod axially outward, an equalizing surface is arranged in the absorber unit. The equalizing surface is exposed on one side to the medium of the pressure vessel and/or the cooling medium of the absorber rod, so that an equalizing force is acting on the absorber unit. In the event of a failure of the drive medium acting on the drive piston of the absorber unit or during fluctuations and changes of the internal pressure in the pressure vessel, the absorber unit remains in its existing position, i.e. no unintentional withdrawal of the absorber rod from the pressure vessel takes place.

Abstract: A control rod having a spring device on its lower end for eliminating oscillatory contact of the rod against its adjacent guide tube wall. The base of the device is connected to the lower tip of the rod. A plurality of elongated extensions are cantilevered downward from the base. Each extension has a shoulder for contacting the guide tube, and the plurality of shoulders as a group has a transverse dimension that is preset to be larger than the inner diameter of the guide tube such that an interference fit is obtained when the control rod is inserted in the tube. The elongated extensions form an open-ended, substantially hollow member through which most of the liquid coolant flows, and the spaces between adjacent extensions allow the flow to bypass the shoulders without experiencing a significant pressure drop.