Westinghouse Electric Corporation

Robert K Gjertsen

John F Wilson

Samuel Cerni

John M Shallenberger

James A Sparrow

Ronald P Knott

Harry M Ferrari

Stephen N Tower

Joseph B Mayers

Edgar A Huckestein

Luciano Veronesi

Raymond A George

Robert B Salton

William R Carlson

John V Miller

William E Kirby

Elmer A Bassler

Walter F Weiland, Jr

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. Two embodiments of locking features can be used in conjunction with the upper and lower plug portions for locking them together so as to resist their unthreading from one another.

Reconstitutable control assembly having removable control rods with

A burnable absorber cluster assembly includes a support plate, a plurality of burnable absorber rods, and an improved attachment joint for detachably connecting an upper end of each of the absorber rods to the support plate. The attachment joint includes a plug insert defined on the end of each of the rods, a hollow annular wall extending outwardly from each plug insert, holes defined through the support plate for receiving the plug inserts, and recesses formed in the support plate and connected with the holes therein. Each recess is conical-shaped and extends in flared fashion outwardly from one hole to a maximum diameter greater than the diameter of the hole. The annular wall on each plug insert is deformed into conformity with the shape of one of the recesses for providing an interengaging connection between the insert plug and the support plate in which the plug insert is disposed within the support plate hole. The annular wall is also redeformable upon application of a predetermined axially-directed force on the plug insert so as to remove the plug insert from the support plate hole and thereby detach the rod from the support plate. Also, each recess and annular wall have respective interengaging eccentric portions which prevents the plug insert on each rod end from rotating in its corresponding hole.

Burnable absorber rod push out attachment joint

A nuclear reactor includes a plurality of upstanding guide thimbles and a plurality of control rods received in the guide thimbles and supported for movement relative to the thimbles between inserted and withdrawn positions. The control rods each include a tubular cladding member and an end plug attached to a lower end of the member. The improvement relates to the end plug having a stabilizing configuration which reduces lateral vibratory motion and contact between the control rod and its respective guide thimble. The end plug has an asymmetrical shape which places its terminal tip end in a position offset to one side of the central axis of the control rod and its end plug. As a result of interaction of the asymmetrical plug tip with coolant flowing along the control rod, a lateral steady-state force is imparted to the end plug which maintains the control rod end plug pressed against the wall of tis respective guide thimble. Several different asymmetrical configurations can be employed on the end plug.

Control rod end plug with a stabilizing configuration

A nuclear reactor includes a plurality of upstanding guide thimbles and a plurality of control rods received in the guide thimbles and supported for movement relative to the thimbles between inserted and withdrawn positions. The control rods each include a tubular cladding member and an end plug attached to a lower end of the member. The improvement relates to an wear sleeve disposed on the end plug so as to provide a contact interface between the control rod and its respective guide thimble. The sleeve is composed of material similar to that of the guide thimble and attached to the end plug by an interlock connection. The interlock connection includes a circumferential groove formed in the end plug and a circumferential protuberance swaged or mechanically roll formed in the sleeve so as to extend into the end plug groove.

Wear sleeve for a control rod end plug

A radial neutron reflector for a water moderated nuclear reactor. The space surrounding the nuclear core is provided with a plurality of side-by-side stacked reflector roads having a square cross-sectional shape. Blocks of reflector material having axial grooves are fitted within a square enclosure. The assembly is subjected to high pressures and temperatures which collapse the enclosure onto the blocks eliminating the assembly clearance. The enclosure material flows into the grooves of the blocks leaving wrinkle-free surfaces over the flat remainder of the enclosure. Square shaped reflector rods result in high solid-to-void ratios in the radial reflector region of the reactor. The resulting grooves allow for coolant flow and cooling of the rods.

Radial neutron refelector

A top nozzle adapter plate for use in a fuel assembly of a nuclear reactor includes an upper structural component and a lower functional component supported from the upper component. The fuel assembly has elongated structural members and fuel rods disposed in a predetermined array. The upper structural component of the adapter plate includes spaced and interconnected hubs and ligaments arranged to define substantial open areas for coolant flow therethrough while providing a rigid framework capable of transmitting lifting loads imposed by the fuel assembly. The hubs are connected to the elongated structural members of the fuel assembly. The lower functional component of the adapter plate includes a grid composed of a plurality of spaced and interleaved straps which cross one another to form intersections aligned with individual fuel rods in the array thereof for restraining movement of fuel rods upward from the fuel assembly while defining open channels through the grid for allowing passage of coolant flow therethrough. The grid also contains void areas through which extend the hubs of the upper component. The lower component also includes coolant flow directing means being operable to establish a predetermined desired pressure drop across the top nozzle of the fuel assembly. In one form, the coolant flow directing means is a plurality of tabs connected to the grid straps and extending outwardly therefrom. The tabs are adjustable into various desired positional relationships with respect to the grid channels for controlling coolant flow therethrough. In a modified form, the coolant flow directing means is in the form of a thin flat plate having holes of predetermined desired sizes and shapes formed therein. The plate extends along the interleaved straps of the grid with its holes generally aligned with the open channels of the grid.

Top nozzle adapter plate with fuel rod capture grid having pressure drop

A nuclear reactor fuel assembly bottom nozzle to guide thimble attachment system and method allowing bottom nozzle removal and replacement without inverting the fuel assembly. At manufacture, a bottom-insertable, two-headed bolt secures the bottom nozzle adaptor plate to the guide thimble bottom end plug. The two-headed bolt is unthreadable in the guide thimble from the top of the upright fuel assembly. At reconstitution, a top-insertable bolt fastener secures the replacement or original bottom nozzle adaptor plate to the guide thimble bottom end plug. The bolt fastener is inserted in the guide thimble from the top of the upright fuel assembly. The bolt fastener is unthreadable in the guide thimble from the top of the upright fuel assembly for a second reconstitution. Less preferably, the bolt fastener also can be used for original manufacture (in place of the two-headed bolts previously discussed).

Nuclear fuel assembly bottom nozzle attachment system allowing

A coolant-displacement rod for a nuclear reactor including a stack of zirconium-oxide pellets in cladding of ZIRCALOY-4 alloy. The outer surfaces of certain of the pellets spaced at intervals along the stack are depressed. The cladding grows permanently when exposed to neutron flux but the zirconium oxide is dimensionally stable. Under the hoop stress impressed by the coolant on the cladding, the part of the cladding encircling each of the pellets with the depressed outer surface engages the outer surface compartmentalizing the pellets into sub-stacks. The formation of a long unsupported gap under the cladding which might collapse under the pressure and at the temperature coolant is prevented by forming a plurality of short unsupported gaps instead of one long gap.

Element immersed in coolant of nuclear reactor

A fuel assembly for a pressurized water nuclear reactor incorporating fluid moderator spectral shift control means. During the first part of the fuel cycle when there is excess reactivity, neutron moderation may be decreased by replacing a portion of the water within the core with a less effective moderator such as heavy water. During the life of the fuel, the heavy water is gradually replaced with regular water. The fuel assembly incorporates the necessary means and apparatus to effectuate such control.

Fuel assembly

An improved arrangement for attaching and reattaching a top nozzle of a reconstitutable fuel assembly includes a sleeve member associated with each guide thimble of the fuel assembly and complementary elements for attaching the sleeve member and the upper end portion of the guide thimble together. The sleeve member includes an inner tubular alignment sleeve portion which receives the guide thimble upper end portion and extends between the upper hold-down and lower adapter plates of the top nozzle. The sleeve member also includes an outer tubular shroud portion having a lower annular flange which underlies a coil spring surrounding the sleeve portion and interconnects the shroud portion and the sleeve portion. The outer shroud portion extends upwardly about a portion of the coil spring for protecting the spring from damage by coolant cross flow from adjacent fuel assemblies. The complementary elements include upper primary and lower secondary interior spaced annular grooves formed on the alignment sleeve portion and a primary exterior bulge formed on the guide thimble upper end portion. The primary bulge extends into the primary annular groove to connect the sleeve portion to the guide thimble. The secondary groove is adapted to receive a secondary exterior bulge, being formed on the guide thimble upper end portion after an initial severance of an upper segment of the upper end portion, for reconnection of the alignment sleeve portion and the severed guide thimble together.

Arrangement and method for attaching and reattaching a top nozzle in a

An integral reusable locking arrangement for a top nozzle of a reconstitutable fuel assembly includes a thin-walled tubular section on the upper end portion of each guide thimble of the fuel assembly above an externally threaded section thereon and an axial section on ecah alignment sleeve of the top nozzle above its lower internally threaded section. The tubular section has an annular circumferential protrusion defined thereon having an external diametric size which is greater than that of the remainder of the tubular section. The axial section on the sleeve has an internal diametric size which is greater than that of the tubular section but less than that of the protrusion. Therefore, rotational movement of the sleeve relative to the guide thimble from its raised toward its lowered position to thread its lower internally threaded section on the externally threaded section of the guide thimble causes interference contact of the axial section with the tubular section protrusion so as to produce a locking force. The locking force which must be overcome in order to unthread the internally threaded section of the sleeve from the externally threaded section of the guide thimble and detach the top nozzle from the guide thimble. The locking force takes the form of a constant torsional drag produced between the tubular section protrusion and the axial section interior surface as the sleeve is rotatably moved relative to the guide thimble between its lowered and raised positions. The circumferential protrusion on the tubular section is axilly displaced from the axial section when the internally threaded section on the sleeve is initially rotatably moved into threaded engagement with the externally threaded section on the guide thimble, whereby the mechanical advantage produced by threading the internally threaded section of the sleeve on the externally threaded section of the guide thimble can be used to overcome the torsional drag and force the sleeve onto the guide thimble.

Integral reusable locking arrangement for a removable top nozzle

A reconstitutable fuel assembly has a top nozzle which not only can be readily removed from and replaced back on the fuel assembly as a unitary subassembly, but also can be readily disassembled and reassembled itself in order to repair or replace some of its own components. The top nozzle uses a plurality of reusable locking pins releasably mounted in bores defined in the sidewall of the top nozzle lower adapter plate. The locking pins, in being mounted in the bores, extend across slots formed in the sidewall and, in so doing, close the open upper ends of slots so as to prevent upward movement of elements on the upper hold-down plate lugs out of the slots and thereby prevent disassembly of the upper hold-down plate from the lower adapter plate. In particular, the locking pins have radially flexible end tangs which are actuatable from a normally expanded position for preventing withdrawal of the locking pins from the sidewall bores to collapsed positions for allowing withdrawal and reinsertion of the locking pins from and into the bores. A knockout tool with a tapered end cavity is used to flex the tangs to their collapsed positions for withdrawal. The tool has a cross-sectional size smaller than that of the sidewall bore allowing it to be inserted into the bores during removal of the locking pins. The outer heads of the tangs are tapered or beveled which causes the tangs to flex radially inward to their collapsed position when the locking pins are being reinserted tang end first into the bores.

Removable and reusable locking pin for top nozzle assembly and

A top nozzle subassembly having a hold-down device incorporated therewithin is provided for a nuclear reactor fuel assembly. The subassembly is slidably mounted on the upper ends of the control rod guide thimbles and is removably attached by internally threaded collars which threadably mate with external threads provided on the upper ends of the guide thimbles. Unthreading of the collars allows the subassembly to be removed from the fuel assembly to gain top access to the fuel rods within the fuel assembly. The invention also includes a special tool for threading and unthreading of the collars.

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Monroeville, PA, United States of America

Robert K Gjertsen