Abstract: A nuclear power system includes a reactor vessel that includes a reactor core that includes nuclear fuel assemblies configured to generate a nuclear fission reaction. A representative nuclear power system further includes a riser positioned above there actor core and a primary coolant flow path that extends from a bottom portion of the reactor vessel, through the reactor core, and through an annulus between the riser and the reactor vessel. A primary coolant circulates through the primary coolant flow path to receive heat from the nuclear fission reaction and release the heat to a power generation system configured to generate electric power. The nuclear power system further includes a control rod assembly system positioned in the reactor vessel and configured to position control rods in only two discrete positions.

Abstract: A nuclear-reactor control-absorber drive mechanism includes a device for monitoring a potential situation of increase to overspeed of the absorber, configured to measure the number of control steps delivered to at least one of the first, second and third phases of the stator during a time window of preset duration or the number of rotation steps of the rotor during a time window of preset duration. The drive is also configured to compare the number of measured control steps with a preset maximum or the number of measured rotation steps with a preset maximum.

Abstract: Disclosed are an in-vessel control rod drive mechanism and a nuclear reactor with the same. The in-vessel control rod drive mechanism includes a control rod drive mechanism for regulating and a control rod drive mechanism for shutdown provided at an upper or lower space of a reactor core to insert or withdraw a regulating rod and a shutdown rod into/from the reactor core based on an operation state of the nuclear reactor, wherein the control rod drive mechanism for regulating and the control rod drive mechanism for shutdown are alternately arranged in the vertical direction. Therefore, a space of containment can be minimized due to the installation of the in-vessel control rod drive mechanism, and thus a rod ejection accident can be prevented, and a loss-of-coolant accident can be reduced.

Abstract: A top head of a reactor pressure vessel includes control rod drive mechanism (CRDM) penetration pipes arranged in a square grid-like pattern. The CRDM penetration pipes are joined with one another by a tube support member. The top head is placed on a tank and water is filled in an inner region of the tank and the top head. A travel apparatus moves a nozzle lifting and lowering apparatus to a predetermined location. A lifting and lowering mechanism of the nozzle lifting and lowering apparatus lifts a jet nozzle above the tube support member among the neighboring four CRDM penetration pipes. An ejection outlet of the jet nozzle is directed to a weld between one of the CRDM penetration pipes and the top head, and a water jet is ejected. A nozzle turning mechanism turns the jet nozzle, and WJP is executed sequentially to the four CRDM penetration pipes.

Abstract: An upper hole 37A and a lower hole 37B are provided at two positions, namely, upper and lower portions, of a side surface of a guide tube 27, and a thimble tube 22 is pressed against an inner circumferential surface of the guide tube 27, by a differential pressure between coolant inside and outside the upper hole 37A and the lower hole 37B.

Abstract: An integrated reactor missile shield and crane assembly (IRMSCA) is disclosed and claimed. The IRMSCA replaces the existing concrete missile shields and reactor services crane. The IRMSCA is moveable such that the missile shield can be moved away from the reactor head, allowing the integral crane to lift the control rod drive mechanism components and other routine loads at the refueling cavity.

Abstract: An upper hole 37A and a lower hole 37B are provided at two positions, namely, upper and lower portions, of a side surface of a guide tube 27, and a thimble tube 22 is pressed against an inner circumferential surface of the guide tube 27, by a differential pressure between coolant inside and outside the upper hole 37A and the lower hole 37B.

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 control rod drive contains a drive housing, in which a control rod carrying element is moveable between a basic position and an end position. The control rod carrying element is guided over a portion in a throttle bush. Formed across the throttle bush is a free flow cross section for a pressure fluid which varies in dependence on a position of the control rod carrying element. During an emergency shutdown, in which the control rod carrying element is moved hydraulically via a pressure fluid, the flow resistance for the pressure fluid is reduced, when the control rod carrying element reaches the end position. Therefore, a braking of the control rod carrying element takes place before it reaches the end position, thus reducing mechanical loads during braking. A flow resistance change takes place via a variable outside diameter of the control rod carrying element and/or by a bypass orifice.

Abstract: With this method it is possible to evaluate opposing friction forces occurring after a certain operating time on a mobile object in a guide. The method consists of measuring the variations in the speed of movement of the mobile object, of calculating the theoretical speed of movement without friction, of combining these two results and thereby deducing outside opposing forces through calculation of the acceleration of the mobile object. Particular application to the evaluation of additional friction forces acting on a mobile control cluster assembly in the core of a pressurized water nuclear reactor.

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 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: An omega seal (32) between a housing (24) having a circumferential omega lip (38) including a free end, and a reactor vessel nozzle (22) having a complimentary omega lip (40) including a free end. A semi-rigid, annular seat member (60) is placed within one of the lips, and the housing is positioned in vertical alignment with the nozzle so that the free end of the housing lip and the free end of the nozzle lip are juxtaposed, thereby forming an omega structure having a cavity (44) occupied by the seat member, a gap (42) between the free ends of the lips, and an outer surface (47,49) on either side of the gap. A semi-rigid ring (46) is positioned in conforming relation to the outside surface of the omega structure. A compressive force is applied and maintained on the exterior of the seal ring, thereby extruding a portion of the ring into the gap.

Abstract: A pressure vessel of a pressurized-water reactor has an upper part in which coolant is collected in a plenum. The coolant enters the plenum through a grid plate on which tops of the fuel assemblies are supported and the coolant is removed from the plenum laterally. Support columns and control-rod guideways form obstacles to the flow of the coolant which can lead to damming-up below the grid plate with horizontal pressure differences and corresponding horizontal flows. Throttle plates inserted in the top of the fuel assemblies or throttle inserts in apertures in the grid plate produce a uniform pressure in the coolant below the grid plate so that it flows uniformly and in a vertical direction through the individual fuel assemblies.

Abstract: A method of manufacturing a guide tube for a nuclear fuel assembly, in which a tubular blank of constant thickness is prepared, the thickness of the blank is reduced over a fraction of its length in the range 70% to 90% while maintaining a constant inner diameter, and then that section of the blank which has retained its original thickness is forced inwardly by an amount such that a tube is formed which has a constant outside diameter and a variable thickness.

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: A control rod drive having a magnetic coupling device which eliminates the need for packing-type seal assemblies for preventing leakage from the reactor pressure vessel adjacent the spindle. The magnetic coupling device includes a driving rotor and a driven rotor separated by a pressure barrier which forms part of the reactor pressure boundary. The driven rotor and the driving rotor are coupled magnetically so that the driven rotor rotates in response to rotation of said driving rotor, whereby the control rod displaces in response to operation of the drive motor. The driven and driving rotors are each constructed by stacking a plurality of circular magnetic rings concentric with a centerline axis. Each circular ring has multiple poles circumferentially distributed thereon. An anti-rotation device is incorporated to prevent free rotation of the spindle when the drive motor is removed during maintenance operations. The anti-rotation device includes a push rod actuator which penetrates the pressure barrier.

Abstract: A locking piston drive system and valve assembly is provided for shutdown of a nuclear reactor. "Chatter" in a check valve assembly which occurs during charging and/or re-charging of control fluid within a control line is eliminated by providing a valve head and a resisting portion defined on the valve head to resist movement of the valve head when it is urged from sealing engagement on its seat during the charging or re-charging procedure.

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 vent tube (66) and housing nut (62) replace the original housing plug (52) on a pressurized water nuclear reactor. The vent tube engages the installed vent stem (38) cross-slot (48) with a cross-shaped projection (70). During operation, the vent tube (66) is pushed down to engage the vent stem (38) and rotated to allow vented air to travel through stem (38) and tube (66). After venting, the vent stem is rotated back and tightened. The invention provides visual indication of a leaking ball (32) since any leakage lifts vent tube (66). Time required for venting is reduced and no removal of installed ball seal (32,34), a proven primary seal, is required.

Abstract: A device for the centering and fixation of a cluster guide flange and of a core plate of a nuclear reactor, extending parallel to one another in horizontal planes with a predetermined spacing. The device includes at least two axial guiding spindles of flange with respect to the core plate, diametrically opposite and rigidly connected to the plate or to the flange in order to engage into a housing in register formed in the flange or in the plate, respectively, and an assembly of self-locking shoes, adapted for sliding with a clearance within bores formed in the flange in order to be pressed on the plate surface, these shoes being each associated with a position control mechanism, carried by the flange and exerting on the shoes a force having a transverse component so as to cause, by reaction, immobilization of the flange with respect to the plate.

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 dashpot in a control rod guide thimble for a nuclear fuel assembly includes a lower tubular portion of an elongated main tube of the guide thimble, an auxiliary hollow tube inserted in the lower portion of the main tube, and an end plug attached to a lower end portion of the auxiliary tube. The auxiliary tube has an outside diameter slightly less than an inside diameter of the main tube to permit a close fitting relationship between an exterior surface of the auxiliary tube and an interior surface of the main tube lower portion. The auxiliary tube also has an upper end portion with an inside surface portion in axial cross-section flaring upwardly and outwardly to provide a tapered transition extending between and connecting an interior surface of the auxiliary tube with the exterior surface thereof.

Abstract: A high speed air cylinder in which the longitudinal movement of the piston within the air cylinder tube is controlled by pressurizing the air cylinder tube on the accelerating side of the piston and releasing pressure at a controlled rate on the decelerating side of the piston. The invention also includes a method for determining the pressure required on both the accelerating and decelerating sides of the piston to move the piston with a given load through a predetermined distance at the desired velocity, bringing the piston to rest safely without piston bounce at the end of its complete stroke.

Abstract: A drive mechanism for a neutron absorbing bar of a liquid cooled nuclear reactor has a drive shaft movable within upper internals and a shock absorber. The shock absorber has a hydraulic cylinder arranged to bear on the upper internals, formed with a bore comprising an upper portion of larger diameter provided with discharge holes spaced longitudinally along the bore and with a lower portion of smaller diameter, a piston, movable within and along the cylinder, having a diameter corresponding to that of the upper portion and defining a shock absorbing chamber with the upper portion, the chamber having exhaust means comprising the discharge holes located to be progressively covered by the piston during downward movement thereof within the cylinder, and a resetting spring biasing the piston towards a top position where it uncovers the discharge holes.

Abstract: The present invention provides an apparatus for handling core constituent elements of a reactor that comprises a core having as core constituent elements control rod assemblies each containing a control rod and fuel assemblies each containing nuclear fuel, a small rotating plug rotatably provided on the core, and a control rod drive mechanism provided on the small rotating plug, the control rod drive mechanism being characterized by comprising a plurality of grippers each having a hook projecting inwards so as to be able to engage with a handling head of the control rod and a hook projecting outwards so as to be able to engage with a handling head of each of the core constituent elements as a distance in the longitudinal direction; an operational head for opening and closing the grippers; and a third elevating drive mechanism for vertically driving the operational head; a second elevating frame for supporting the third elevating drive mechanism and the grippers; a second elevating drive mechanism for vertical

Abstract: A nuclear fuel assembly for a spectral shift reactor has an upper end piece and a lower end piece secured to a structural element belonging to the upper end piece by guide tubes arranged for receiving a cluster of control elements. The upper end piece further comprises a support member arranged for receiving said cluster at the end of the fall thereof, means for guiding said support member. The support member is guided for movement parallel to the axis of the guide tubes. Springs are contained within the end piece and disposed between the structural member and the plate for braking the cluster at the end of the fall thereof.

Abstract: A coupling device between a nuclear reactor control rod and an actuating mechanism has a gripper body having resilient gripping fingers, belonging to the mechanism and, on the bar, a terminal pommel for engagement by the fingers and a shoulder directed towards the pommel. The coupling device comprises an additional member, such as a sleeve, movable with respect to the gripper body between a position in which it allows resilient fingers to be released from the pommel and another position in which it locks the resilient fingers onto the pommel. The sleeve has an end face bearing on the shoulder of the pommel. A prestressed spring exerts a force tending to move the sleeve away from the fingers so as to hold the end face of the sleeve firmly applied against the shoulder when the fingers are locked on the pommel.

Abstract: An intermediate seismic support system (100) comprises substantially square-shaped seismic support base members (102) which are suspendingly supported from rod position indicator coil assemblies (48) so as to peripherally surround control rod drive mechanism latch housings (20) in order to restrain deflections of the control rod drive mechanisms (12) under seismic conditions. In addition to being remotely installed and removed as a result of being mounted upon the RPI assemblies (48), the seismic supports are also remotely adjustable relative to one another through means of radially movable adjustment blocks (126) which are caused to move radially by means of axially movable actuator blocks (130). The latter blocks (130) are controlled by means of vertically extending actuator rods (134).

Abstract: Apparatus for limiting the effect of axial hydraulic flow force exerted on the fuel assemblies by the hydraulic pressure of a coolant in a water-cooled nuclear reactor comprises slit cylindrical elastic sleeves positioned within recesses in cylindrical housings carried by the fuel assemblies, the sleeves receiving centering pins connected to upper and lower core plates of the reactor and exerting frictional force thereon so as to control the axial movements of the fuel assemblies during transient variations in hydraulic flow force.

Abstract: A velocity limiting device providing greater resistance to motion through a fluid in one direction than in the opposite direction. The device includes a toroidally shaped control member having a smooth generally conical surface on one side for low resistance movement through the fluid in the one direction. On its opposite side the control member is formed with at least one groove providing a concave surface spaced from which is an arrangement of vanes forming a jet for directing a stream of fluid into the groove upon movement in the opposite direction whereby the resultant increase in fluid turbulence increases resistance to rapid movement in this opposite direction.

Abstract: A control rod drive uses gravitational forces to insert one or more control rods upwardly into a reactor core from beneath the reactor core under emergency conditions. The preferred control rod drive includes a vertically movable weight and a mechanism operatively associating the weight with the control rod so that downward movement of the weight is translated into upward movement of the control rod. The preferred control rod drive further includes an electric motor for driving the control rods under normal conditions, an electrically actuated clutch which automatically disengages the motor during a power failure and a decelerator for bringing the control rod to a controlled stop when it is inserted under emergency conditions into a reactor core.

Abstract: A hydraulic shock absorber of the dash pot kind for use with electrically conducting liquid such as sodium, has magnet means for electro magnetically braking a stream of liquid discharged from the cylinder. The shock absorber finds use in a liquid metal cooled nuclear reactor for arresting control rods.

Abstract: Braking of the motion of a fluid-actuated drive is provided by a buffer arrangement which is normally sealed to prevent vaporization of the fluid in a buffer cylinder and which isolates the drive piston rings from braking pressures.