System for exchanging a control rod drive

A system for exchanging a control rod drive of a nuclear reactor is provided. The system may include an integrated drive exchange assembly system (IDEAS). The IDEAS may include a trunnion cart attached to a tower assembly. The tower assembly may include an integrated extension carriage assembly.The IDEAS may also include a control rod drive adapter; and a lead cart connected to the trunnion cart assembly.

BACKGROUND OF THE INVENTION

The present invention relates generally to nuclear reactors and, more particularly, to removing and installing control rod drives (CRDs) in a nuclear reactor.

Control rod drives are used in a nuclear reactor to control the position of the control rods within the reactor core. The CRDs typically extend from the reactor pressure vessel in the under vessel area.

Occasionally CRDs are removed for maintenance and repair. Subsequent to servicing, the CRDs are reinstalled. CRDs should be moved in a safe and controlled manner to prevent damage to the CRD and/or adjacent equipment. After removal from a housing, the CRD should be rotated from a vertical position to a horizontal position, and secured for transporting out of the tinder vessel area. These activities should be performed by a minimum number of personnel and accomplished quickly and efficiently to reduce radiation exposure.

One known method for exchanging a CRD is to attach an extension tube to the bottom of the CRD and thread a cable over a stationary idler pulley and through the bottom of the extension tube. The cable is secured to a static hanger. A winch then pays out the cable and the CRD is lowered until the extension tube contacts the floor of the under vessel area. A second cable winch is then employed to secure a clamp around the CRD at the approximate mid-length of the CRD. With the second winch securing the weight of the CRD, an operator is required to enter the basement of the under vessel area to remove the extension tube. The second cable winch then pays out cable until the CRD is out of the housing. Once the CRD is out of the housing, the CRD is then manually positioned from the vertical position to a horizontal position as the second winch lifts the CRD up to the equipment platform. When the CRD is above the lower track, or rail, on the equipment platform, a transport cart is rolled into position under the horizontal CRD. The second winch then pays out the cable to land the CRD on the cart. The cable rigging is removed from the CRD, and the cart with the CRD is pulled out of the under vessel area.

Another known system for removing a CRD is a rigid tower system, which allows the CRD to be lowered into a tower supported by a trunnion cart. The CRD is raised and lowered by an elevator secured within the tower. The known tower systems use either roller chains, timing belts, cable or hydraulic cylinders, and employ built-in air or hydraulic motors with supply and control (air) logic and hydraulic lines to raise and lower the elevator tower. The known tower systems also incorporate a separate extension tube, which provides the extended throw required to install or remove a CRD.

There are a few drawbacks with the currently known systems for exchanging CRDs. The currently known systems tend to be complex, time consuming to operate, and are susceptible to causing a CRD to fall onto the floor of the under vessel area. The currently known systems may expose operators to higher levels of radiation. The currently known systems may include built-in drive motors, which may be difficult and time consuming to replace if failure occurs during CRD exchange. The currently known systems may include components subject to damage and failure causing down time and high maintenance costs. The currently known systems may include two parallel screws synchronized with a timing belt to move the CRD, wherein the timing belt may slip causing the elevator to become unleveled; thereby preventing movement of the CRD.

For the foregoing reasons, there is a need for a system for exchanging a CRD. The system should include two independent screws with independent travel. The system should not include: roller chains, timing belts, cable, or hydraulic cylinders. The system should not employ built-in air or hydraulic motors with supply and control (air) logic and hydraulic lines to raise and lower the elevator tower. The system should not require a separate extension tube.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with an embodiment of the present invention, an integrated drive exchange assembly system for moving a control rod drive in a nuclear reactor, the reactor including a reactor pressure vessel, an under vessel area located below the reactor pressure vessel, and an equipment platform between the under vessel area and a basement, the system comprising: a tower forming a control rod drive receiving area comprising an open face and an open trough; a first and a second screw extending substantially the length of the tower, the first and the second screw mounted to opposite sides of the tower, wherein as the first screw is rotated, the second screw does not rotate, and wherein as the second screw is rotated, the first screw does not rotate; an elevator platform coupled to the first screw and movable relative to the first and the second screws, the platform configured to engage a portion of the control rod drive and to substantially support the control rod drive; an extension carriage assembly coupled to the second screw and movable relative to the first and the second screws, the extension carriage assembly configured to engage a portion of a control rod drive (CRD) adapter and to substantially support the control rod drive; and a trunnion cart engaged to the tower so that the tower is rotatable relative thereto; the trunnion cart comprising an automatic vertical lock for locking the tower in a vertical position; wherein the integrated drive exchange assembly system is operable for moving the CRD from the reactor pressure vessel and movable with the control rod drive so that the integrated drive exchange assembly system and the control rod drive are movable together out from the under vessel area.

In accordance with an alternate embodiment of the present invention, an integrated drive exchange assembly system for moving a control rod drive in a nuclear reactor, the reactor including a reactor pressure vessel, an under vessel area located below the reactor pressure vessel, and an equipment platform between the under vessel area and a basement, the system comprising: a tower forming a control rod drive receiving area comprising an open face and an open trough; and further comprising at least one lower bearing block secured at one end of the first and the second screws to the tower, and the first and the second screws extending through the lower bearing block; a first and a second screws extending substantially the length of the tower, the first and the second screws mounted to opposite sides of the tower, wherein as the first screw is rotated, the second screw does not rotate, and wherein as the second screw is rotated, the first screw does not rotate; an elevator platform coupled to the first screw and movable relative to the first and the second screws, the platform configured to engage a portion of the control rod drive and to substantially support the control rod drive; wherein the elevator platform allows for a portion of the control rod drive to extend through the elevator platform; an extension carriage assembly coupled to the second screw and movable relative to the first and the second screws, the extension carriage assembly configured to engage a portion of a control rod drive adapter and to substantially support the control rod drive; wherein the extension carriage assembly comprises an extension channel and wherein at least one link is secured to the tower, the link configured to support the extension channel, the link rotatable relative to the tower so that the extension channel can be moved between a first position and a second position; further comprising at least one link secured to the tower, the link configured to support the extension channel, the link rotatable relative to the tower so that the extension channel can be moved between a first position and a second position; and a trunnion cart engaged to the tower so that the tower is rotatable relative thereto; the trunnion cart comprising an automatic vertical lock for locking the tower in a vertical position; wherein the integrated drive exchange assembly system is operable for moving the CRD from the reactor pressure vessel and movable with the control rod drive so that the integrated drive exchange assembly system and the control rod drive are movable together out from the under vessel area.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used herein for convenience only and is not to be taken as a limitation on the invention. For example, words such as “upper,” “lower,” “left,” “front”, “right,” “top”, “horizontal,” “vertical,” “upstream,” “downstream,” “fore”, and “aft” merely describe the configuration shown in the Figures. Indeed, the components may be oriented in any direction and the terminology, therefore, should be understood as encompassing such variations unless specified otherwise.

The following Figures may include components that are not discussed herein and are shown for illustrative purposes only. The elements of the integrated drive exchange assembly system1000discussed herein may be fabricated of a stainless steel or other material capable of withstanding the operating loads associated with the system1000. The elements discussed herein may be connected, joined, or fastened, or the like, via methods commonly used in the art.

Referring now to the Figures, where the various numbers represent like elements throughout the several views,FIG. 1is a schematic illustrating the environment in which an embodiment of the present invention operates.FIG. 1illustrates a cross sectional view of a boiling water nuclear reactor100including a reactor core105positioned within a reactor pressure vessel110. The reactor pressure vessel110is supported by a reactor pressure vessel support structure115housed within the containment120. A plurality of control rod drives (CRDs)125extend from the reactor pressure vessel110and into an under vessel area130. A CRD equipment platform135is located below the reactor pressure vessel110, and a basement140is located below the equipment platform135. A subpile floor145is located at the bottom of basement140.

The CRD equipment platform135includes rails150upon which a trunnion cart assembly300is mounted. Also, a winch assembly165may be on the rails150.

A tower assembly500extends from, and may be rotatably secured to, the trunnion cart assembly300into the basement140and towards the CRDs125. As illustrated inFIG. 1, the tower assembly500may be aligned with a CRD125, and an extension carriage assembly570extends from an upper section of tower assembly500to the CRD125. A cable170attaches to the lower section of the tower assembly500to a winch assembly165mounted on an upender cart160.

As described below, the winch assembly165may move the tower assembly500from a vertical position to a horizontal position. Moreover, after the CRD125is loaded into tower assembly500in the vertical position, the winch assembly165, with the aid of the upender cart160, may rotate the tower assembly500to a horizontal position for transporting up a transfer chute175.

Referring now toFIG. 2, which is a perspective view of an integrated drive exchange assembly system1000in accordance with an embodiment of the present invention. The integrated drive exchange assembly system1000(IDEAS) may include the following sub-components: a trunnion cart assembly300attached to a tower assembly500; a CRD adapter900for supporting a CRD; and a lead cart assembly800connected to the trunnion cart assembly300.

The foregoing description provided an overview of the IDEAS1000. The following sections describe the components of the IDEAS1000, illustrated inFIG. 2, more detail.

Tower Assembly

FIG. 3is an exploded perspective view of the tower assembly500ofFIG. 2, in accordance with an embodiment of the present invention. The tower assembly500may include a tower505; a plurality of screw assemblies517, here illustrated as screws, but other screws and/or gears, such as a worm gear, are possible and within the scope of the invention discussed below; an elevator platform535; and an extension carriage assembly570

The tower505may have a substantially open face507that may include an open trough509. The tower505may have a length approximately equal to the length of a CRD125. A tower clamp510and a tower clamp knob515may be connected to the tower505near a distal end. A portion of the tower clamp510may be shaped to envelope a portion of the CRD125and to limit the movement of the CRD125within the tower505. The tower clamp knob515may be a spring-loaded mechanism that secures the position of the tower clamp510. Also attached near the distal end of the tower505may be a tower gate530. An end of the tower gate530may be connected to a first side of the tower505, as illustrated inFIG. 3. An opposite end of the tower gate530may be rotatably connectable to a second side of the tower505. The tower gate505may serve to secure the CRD125within the open trough509.

The tower505may include a plurality of mounting plates540. The mounting plates540may be connected on opposite sides of the tower505. Attached to each mounting plate540may be a trunnion axle542. The mounting plate540and trunnion axle542may allow for the trunnion cart assembly300(discussed below) to be connected to the tower505. A vertical lock assembly550may also be connected to the tower505and may ensure that the CRD125is locked in a vertical position, as discussed below.

Each of the plurality of screw assemblies517may include: either a first or a second screw520,522. Each screw520,522may be connected to the tower505via an upper bearing block524and a lower bearing block528. As illustrated, the upper bearing block524may be connected to an upper portion of the tower505; and the lower bearing block528may be connected to a lower portion of the tower505. Slidably engaged to each of the screws520,522may be at least one elevator platform spring555, which may dampen a portion of the load of the CRD125experienced by the tower505.

Connected to a lower end of the tower505may be a plurality of cam wheel assemblies545, which allows for the tower assembly500to slide along the rails150. The cam wheel assemblies545may also be integrated with an end plate assembly560. The end plate assembly560may allow for lateral movement of the cam wheel assemblies545, necessary when rotating the tower assembly500from a horizontal to a vertical position.

An extension carriage assembly570may be coupled with the second screw522. As discussed below, the extension carriage assembly570may extend beyond the overall length of the tower assembly500, allowing for the CRD adapter900to install or remove a CRD125within the reactor pressure vessel110.

An elevator platform535may be coupled to a first screw520. The elevator platform535may receive an end of a CRD125and move the CRD125from the under vessel area130to the bottom of the tower505. The elevator platform535may be movable relative to the first and the second screw520, as is further discussed below.

FIG. 4is a top plan view, partially exploded, of the screw assembly517ofFIG. 3in accordance with an embodiment of the present invention. As discussed, each screw assembly517may include a screw520,522; an upper bearing block524, a lower bearing block528; and a head526connected to a top end of each screw520,522. Head526is illustrated as a hex head inFIG. 4, but other heads capable of rotating the screw520,522are possible and within the scope of the invention. A lower end of the screw520,522may include a portion allowing for mating and securing with the lower bearing block528. An upper portion of the screw520,522may include a portion for allowing for mating and securing with the upper bear block524. The overall length of the each screw520,522may extend substantially along the length of the tower. The first and the second screws520,522may be mounted to opposite sides of the tower505.

FIG. 5is a perspective view of the elevator platform535ofFIG. 3in accordance with an embodiment of the present invention. The elevator platform535may be coupled to the first screw520(not illustrated inFIG. 5), and may be movable relative to the screws520and522. Furthermore, as screw520rotates, elevator platform moves up or down, depending on the direction of rotation of the screw520. Elevator platform535may be configured to receive an end portion of the CRD125, partially inserted therein.

FIG. 6is a perspective view of the end plate assembly560in accordance with an embodiment of the present invention, illustrating the end plate assembly560, which may include slides handles562; screw openings564; and an end plate opening566.

The slide handles562may be used to adjust the lateral position of the cam wheel assemblies545(illustrated inFIG. 3). The slide handles562may extend the lateral position of the cam wheel assemblies545, allowing for the horizontally positioned tower assembly500to slide along the rails150. The slide handles562may retract the lateral position of the cam wheel assemblies545, allowing for the tower assembly500to pivot, around an axis of the trunnion cart assembly300, into a vertical position.

One screw opening564may receive an end of the first screw520; and the second screw opening564may receive a similar end of the second screw522. The end plate opening566may be sufficiently sized to allow for a portion of the CRD125(not illustrated inFIG. 6) to extend through.

FIG. 7is a top plan view of the extension carriage assembly570ofFIG. 3in accordance with an embodiment of the present invention. The extension carriage assembly570may include an extension channel575; an extension roller housing580; an upper extension roller link585; a lower extension roller link590; and an extension channel opening595.

The extension roller housing580may integrate with the tower505and allow the extension carriage assembly570to engage the CRD adapter900while the IDEAS1000is installing or removing a CRD.

As illustrated inFIG. 8, which is a top plan view of the components of the extension carriage assembly570, an end portion of the extension channel575may be connected to a portion of the extension roller housing580. The extension channel575may be used to provide the extra length required to install or remove a CRD125. Since the length of tower assembly500in the vertical position may be fixed, the tower assembly500may not extend into the under vessel area130, (as illustrated inFIG. 1); therefore, the extension channel575may be used to complete the operation.

The extension channel575may have a substantially rectangular shape with an end portion secured to the extension roller housing580and an opposite end portion may allow for the extension channel575to mate with the CRD adapter900, as illustrated inFIGS. 7 and 8. The width and depth of the extension channel575may be sized to allow for the extension channel575to pass through the elevator platform535. The extension channel575may be of sufficient strength to bear a substantial portion of the weight of the CRD125.

Also connected to the extension roller housing580are an upper extension roller link585and a lower extension roller link590, as illustrated inFIGS. 7 and 8. Links585and590may connect the tower505to the extension carriage assembly570. Links585and590may allow for the extension channel575to move between a first position within the tower505and a second position within the open trough509of the tower505, as discussed below.

The extension roller housing580may also include an extension channel opening595, which may allow for a portion of the second screw522to travel through.

FIGS. 9aand9b, collectivelyFIG. 9, are perspectives views illustrating the extension carriage assembly570ofFIG. 7connected to a tower assembly500, in accordance with an embodiment of the present invention.

FIG. 9aillustrates a portion of the extension carriage assembly570connected to the tower505in a first position. The first position may be considered a position where the extension carriage assembly570is stowed within a portion of the open trough509of the tower505. The shape of the extension channel575may allow for covering the second screw522while the extension channel575is in the first position. The first position may allow for the elevator platform535(not illustrated inFIGS. 9aand9b) to be lowered and positioned adjacent the end plate assembly560, wherein for example, but not limiting of, the CRD125may be transported. In this first position the upper extension roller link585and the lower extension roller link590are not extended and the extension channel575is not positioned for use.

FIG. 9billustrates a portion of the extension carriage assembly570connected to the tower505in a second position. The second position may be where the extension carriage assembly570is positioned to provide the extra length required to install or remove a CRD125from the reactor pressure vessel110(not illustrated inFIGS. 9aand9b). In this second position the upper extension roller link585and the lower extension roller link590are fully extended and the extension channel575extends substantially into the open trough509. A plurality of guide stops600may be used to limit the rotation of the lower extension roller link590. The guide stop600may help to ensure that the extension channel575remains in the correct position during operation. As discussed below, the extension roller housing580may move vertically in conjunction with the direction of rotation of the second screw522. As the extension roller housing580moves, the extension channel575may also move in the same direction.

Trunnion Cart

FIG. 10is a top plan view of the trunnion cart300ofFIG. 3in accordance with an embodiment of the present invention. The cart300may include a trunnion cart frame305; a plurality of trunnion cart wheel assembly310; a pillow block315(also illustrated inFIG. 13); and a vertical lock pillow block320(also illustrated inFIG. 14). The plurality of trunnion cartwheel assembly310may be connected to the trunnion cart frame305. Also connected to the trunnion cart frame305may the pillow block315; and the vertical lock pillow block320. The frame305may have a rectangular shape.

FIG. 11is a side elevation view of the trunnion cart300ofFIG. 10in accordance with an embodiment of the present invention. The pillow block315may be mounted to a top portion of the frame305. The vertical lock pillow block320may be mounted opposite the pillow block315. The mounting positions of the pillow block315and the vertical lock pillow block320may allow for trunnion axles542(illustrated inFIG. 3) to rotate therein, when the IDEAS1000is in use.

Briefly referring now toFIG. 15, which is a perspective view of the vertical lock pillow block320ofFIG. 14connected to a tower assembly500, in accordance with an embodiment of the present invention. The tower assembly500is rotated from a horizontal position to a vertical position and the vertical lock pin323may automatically engage. The vertical lock pin323may remain engaged until the vertical lock assembly550is utilized to release the vertical lock pin323. For example, but not limiting of, before an operator may rotate the tower assembly500from a vertical position to a horizontal position, the operator may utilize the vertical lock assembly550to release the vertical lock pin323.

FIG. 12is a rear view of the trunnion cart-wheel assembly310ofFIGS. 10 and 11, in accordance with an embodiment of the present invention; the trunnion cart-wheel assembly310may include a trunnion cart wheel lock325; and a trunnion cart wheel330. The trunnion cart wheel330may include a plurality of ratchet positions, or the like, each of which may be connectable with the trunnion cart wheel lock325. After the trunnion cart assembly300is located in a desired position, an operation may engage the trunnion cart wheel lock325to prevent the movement.

CRD Adapter

FIG. 16is a perspective view of the CRD adapter900ofFIG. 3in accordance with an embodiment of the present invention. The CRD adapter900may include a CRD seating flange910; a CRD adapter cup920; and a CRD channel interface930.

The CRD adapter900generally serves as an interface between the tower assembly500and the CRD125. The CRD seating flange910may be positioned at a first end of the CRD adapter900and may engage an end of the CRD drive125. To connect the first end of the CRD adapter900to the CRD drive125, an operator may rotate the CRD adapter cup920to fit the CRD seating flange910to the CRD drive125.

The CRD channel interface930may be positioned on an opposite second end of the CRD adapter900. The interface930may mate with the extension channel575.

Referring now toFIG. 17, which is a perspective view of the CRD adapter900ofFIG. 16integrated with the tower assembly500ofFIG. 3, in accordance with an embodiment of the present invention. As discussed, the CRD seating flange910may be connected to a portion of the CRD125

FIG. 17also illustrates the connection between the CRD channel interface930and the extension channel575. The interface930may include an opening (not illustrated), which receives an end of the extension channel575. The connection may be of a type that allows for mating between the interface930and the channel930.

Lead Cart Assembly

The lead cart assembly800may assist the tower assembly500in moving the CRD125from the under vessel area130to through the transfer chute175. Referring now toFIG. 18, which is a partially exploded perspective view of the lead cart assembly800ofFIG. 3in accordance with an embodiment of the present invention. The lead cart assembly800may be formed of a stainless steel and may include a lead cart frame805; a lead cart clamp810; a plurality of lead cart wheels815; and a plurality of lead cart cables820.

The plurality of lead cart wheels815and the lead cart clamp810may be connected to the rectangular shaped lead cart frame805. The lead cart clamp810may receive and secure a portion of the CRD125.

A portion of each of the plurality of lead cart cables820may be connectable to the lead cart frame805. An embodiment of the present invention may allow for the lead cart cables820to be separated and reconnected to the lead cart frame805. This may allow for an operator to separate the lead cart assembly800from the trunnion cart assembly300when not in use.

Integrated Drive Exchange Assembly System Operation

As discussed, the integrated drive exchange assembly system1000may include a first520and a second screw522; each screw520,522may operate independently of the other screw520,522. An operator may connect an air-operated wrench, or the like, to the hex head526of each screw520,522. If the operator uses the wrench to rotate the first screw520, then the elevator platform535may move up or down in a vertical direction. If the operator uses the wrench to rotate the second screw522, then the extension channel575may move up or down in a vertical direction.

FIGS. 19a-19c, collectivelyFIG. 19, illustrate an elevation view of the IDEAS1000in use, in accordance with an embodiment of the present invention.

InFIG. 19athe IDEAS1000is in operation to remove a CRD125from the reactor pressure vessel110. As illustrated inFIG. 19a, the CRD adapter900is connected to the extension channel575. The second screw522has been rotated to extend the extension channel575into the under vessel area130. The CRD adapter900is also connected to the CRD125. Also, the positions of the upper extension roller link585and lower extension roller link590are near the equipment platform135.

InFIG. 19b, the CRD125is lowered into the tower505. Here, the second screw522has been rotated in a direction that lowered the extension channel575into the tower505.FIG. 19balso illustrates that the position of the CRD adapter900is within the tower. Also, the positions of the upper extension roller link585and lower extension roller link590are near the end plate assembly560.

InFIG. 19c, the CRD125is fully lowered into the tower505. The second screw522is rotated until the CRD125engages the elevator platform535within the tower505. Then an operator may remove the CRD adapter900from the tower assembly500. The extension channel575may then be stored within the tower505, as discussed. Next, the first screw520may be rotated to lower the elevator platform535until the CRD125is lowered further in the tower505. Here, the position of the elevator platform535is near the end plate assembly560and tower assembly500may be rotated into a horizontal position.

FIG. 20is a schematic illustrating the environment in which a CRD125is loaded into the integrated drive exchange assembly system100in accordance with an embodiment of the present invention.FIG. 20illustrates the integrated drive exchange assembly system1000in operation to remove of the CRD125from the reactor pressure vessel110. After the CRD125is lowered into the tower assembly500, as described inFIG. 19, the vertical lock assembly550(illustrated inFIG. 15) may release the tower assembly500to allow for the rotation from the vertical position to a horizontal position. An operator may use the winch assembly165of the upender cart160to assist with the rotation. Next, the lead cart800may be connected to the trunnion cart assembly300and then used to assist in moving the IDEAS1000through the transfer chute175.

Although the present invention has been shown and described in considerable detail with respect to only a few exemplary embodiments thereof, it should be appreciated that any arrangement that we do not intend to limit the invention to the embodiments since various modifications, omissions and additions may be made to the disclosed embodiments without materially departing from the novel teachings and advantages of the invention, particularly in light of the foregoing teachings. Accordingly, we intend to cover all such modifications, omission, additions and equivalents as may be included within the spirit and scope of the invention as defined by the following claims.