1. Field
The embodiments described herein pertain generally to nuclear steam generator supports and more particularly to a nuclear containment support that can raise, lower, tilt and rotate a steam generator to align the steam generator with the reactor coolant piping that is to be welded to during nuclear plant construction.
2. Description of Related Art
The primary side of nuclear reactor power generating systems which are cooled with water under pressure comprise a closed circuit which is isolated and in heat exchange relationship with a secondary circuit for the production of useful energy. The primary side comprises the reactor vessel enclosing a core internal structure that supports a plurality of fuel assemblies containing fissile material, the primary circuit within heat exchange steam generators, the inner volume of the pressurizer, pumps and pipes for circulating pressurized water; the pipes connecting each of the steam generators and pumps to the reactor vessel independently. Each of the parts of the primary side comprising a steam generator, a pump and a system of pipes which are connected to the vessel form a loop of the primary side of the nuclear power generating system.
For the purpose of illustration,
Each steam generator 18 is a vertical-shell U-tube evaporator with integral moisture separating equipment. The reactor coolant flow enters the steam generator 18 through a single hot leg nozzle 24 before passing into the inverted U-tubes which occupy a substantial portion of the reduced diameter generally cylindrical shell 28, where it transfers heat to the secondary side as it passes through the U-tubes and returns to the cold leg side 26 of the primary coolant piping 20. The flow leaves the steam generator through two cold leg nozzles 30, to each of which a reactor coolant pump 16 is directly attached. The discharge nozzles of the coolant pumps 16 are each connected to a cold leg 26 of the main coolant piping to convey the relatively cool reactor coolant back to the reactor vessel 10 for recirculation through the core 14, where the cycle is repeated. The primary reactor power generating system thus described is an advanced passive nuclear power generating facility known as the AP 1000 plant, designed and sold by the Westinghouse Electric Company LLC, headquartered in Cranberry Township, Pa. During the development of AP 1000 installation procedure, it was recognized that the AP 1000 nuclear plant steam generator has unique features. Previous methods used in erecting legacy steam generators and nuclear plant configurations used spool pieces to join the primary coolant piping to the steam generators and the main coolant pumps were connected to a span of the cold leg of the reactor coolant piping spaced from the steam generators. The prior art steam generators typically had four legged stable supports that supported them from below. The unique features of the AP 1000 nuclear plant design in, for example, having the main coolant pumps directly connected to the bottom of the steam generators required that a different support approach be taken. A single “pogo stick type” pedestal support was designed for this purpose. In addition, the AP 1000 steam generator is designed to be welded to the main coolant piping using no spool pieces, which requires exacting alignment of the main coolant piping with the corresponding nozzles on the steam generators and coolant pumps. Considering that an AP 1000 nuclear plant steam generator weighs approximately 1,463,000 pounds (664 metric tons), a precision alignment device is required during nuclear plant construction to assemble the steam generator in the nuclear plant primary system. Preferably, such an alignment device can support the entire weight of the steam generator assembly to free to the overhead crane typically employed for coarsely positioning the steam generator, for other construction projects.
Thus, it is an object of this embodiment to provide a steam generator alignment fixture that can precisely position and align the steam generator inlet nozzles and pump outlet nozzles with the corresponding primary loop piping.
It is a further object of this embodiment to provide such a fixture that can support the entire weight of the steam generator without the assistance of an overhead crane.
It is an additional object of this embodiment to provide such a fixture that has the ability to raise, lower, rotate and tilt the steam generator into appropriate alignment.
It is an additional object to provide such a fixture that will facilitate the erection of a permanent support for the steam generator.
Further, it is an object of this embodiment to provide such a fixture that can be readily dismantled and reused once a permanent support for the steam generator has been erected.
These and other objects are achieved by steam generator support and alignment structure that supports the steam generator from a floor or an internal wall within a nuclear containment. The support and alignment structure described herein comprises a substantially rigid support fixture that extends from the floor or internal wall of a nuclear containment and is attached to at least two sides of the steam generator. The substantially rigid support fixture includes a base, a support section and means for aligning the generator. The base rests on the floor or internal wall of the containment. The support section is coupled to at least a portion of the circumference of a side of the steam generator. The means for aligning the generator is operable to raise, lower or rotate the support section relative to the base with the generator secured within the support section, to align the generator. Preferably, the means for raising, lowering or rotating the support section includes a plurality of hydraulic jacks between the base and the support section, and desirably, the means for so orienting the support section can tilt and laterally move the support section relative to the base while supporting the entire weight of the steam generator assembly while it is being aligned.
In one embodiment, the means for raising, lowering or rotating the support section relative to the base with the steam generator secured within the support section provides for fine movement of the steam generator sufficient to align the steam generator inlet nozzle and one or more steam generator outlet nozzles respectively with the primary coolant piping of a reactor system. Preferably, such fine movement of the steam generator is in as little as 0.03125 inch (0.07938 centimeter) increments.
In another embodiment, the support section comprises an upper support section, connected to an upper cylindrical section of the steam generator, and a lower support section, connected to a lower cylindrical reduced diameter cylindrical section of the steam generator and the means for raising, lowering or rotating the support section relative to the base is connected between the upper support section and the base. Preferably, the lower support section is located below the base and the steam generator dead weight, i.e., weight without water, is substantially supported by the upper support section from at least two substantially diametrically opposed lift links which engage trunnions on the side of the steam generator. Desirably, where the steam generator is at least partially surrounded by an internal containment wall, the upper support section is supported upon at least four points on the wall and preferably a support at each of the at least four points on the wall has at least one lateral hydraulic member for laterally moving the steam generator. Desirably, the at least one lateral hydraulic member comprises two lateral hydraulic members respectively moveable in an X and Y direction. In one embodiment, the upper support section includes a support ring that substantially surrounds a circumference of the upper cylindrical section of the steam generator and each of the lateral hydraulic members respectively engages the support ring to laterally move the support ring and thus the generator when the lateral hydraulic members are activated. Preferably, the support ring supports and engages a plurality of vertical hydraulic members, wherein each of the vertical hydraulic members is positioned adjacent a corresponding lateral hydraulic member. Desirably, each of the vertical hydraulic members engage and support a support frame which is engaged with each steam generator lift link.
In still another embodiment, the lower support section is braced against at least two diametrically opposed points on an inside of the internal containment wall in a manner that will permit the steam generator to rotate and move up, down and laterally a given distance, but limit the side-to-side movement of the steam generator. Preferably, the lower support section includes lateral hydraulic extension arms that brace against the inside of the internal containment wall. Desirably, the lateral hydraulic extension arms retract towards the steam generator so that the steam generator can be initially positioned within the internal wall.
In a further embodiment, the means for raising, lowering or rotating the support section relative to the base comprises a plurality of hydraulic members and preferably some of the hydraulic members act in combination with a bearing plate or roller support to effect movement of the steam generator.
A further understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
The lower portion of a nuclear steam generator that contains the primary side of the reactor coolant loop is typically shielded by a concrete cubicle in which the steam generator is supported. The embodiments described herein provide a temporary installation and alignment tool for supporting the steam generator within its concrete shielding in the course of construction of a nuclear power plant that enables the steam generator to be raised, lowered, rotated and tilted so it can be aligned with the connecting reactor coolant piping and the erection of a permanent steam generator support. While the support and alignment fixture described herein can be used as a permanent steam generator support, it serves more value as a temporary support during construction where it can be moved from generator to generator to facilitate the attachment of each of the steam generators to the reactor primary coolant system. The support fixture described herein uses structural steel support framing and hydraulic jacking and control monitoring devices to lift, jack, laterally move, tilt and rotate a steam generator during its installation process.
Previous nuclear steam generators required stable base supports to be installed prior to setting the generators in position. The steam generators were fastened to the base supports and became self-supporting. Such a support is not practical for the type of steam generator illustrated in
The embodiments described herein are unique in that they stabilize and support the entire weight of the steam generator after the steam generator is initially situated within its shielding compartment and maneuver the steam generator into alignment with the coolant piping to which it is to be welded. Thus, the embodiments set forth herein permit the overhead crane to be disengaged from the steam generator so that it is available for other construction work. Accordingly, the support fixtures described herein enable the setting of an unbalanced steam generator which has two reactor coolant pump casings welded on the bottom end of the steam generator, while supporting and enabling movement of the loaded steam generator in three directions and installation of permanent upper, lower and intermediate lateral supports and snubbers.
While the alignment fixture of the embodiments described herein are illustrated as being applied to an AP 1000 nuclear plant, and more particularly an AP 1000 nuclear steam generator, it should be appreciated that the principles described herein can be applied to most any tube and shell steam generator design. One embodiment of the alignment and support fixture claimed hereafter is disclosed in
As shown in
The steam generator temporary support upper support frame 42 thus described is supported by the cubicle walls 36 at an elevation of approximately 153 feet above the operating floor of the containment and has a relatively small operator platform 54 and control box 52 for controlling the operation of the various hydraulic members. The vertical hydraulic members enable up and down movement of the steam generator up to approximately six inches (15.24 centimeters) in 1/32 inch (0.08 centimeters) increments. Similarly, the lateral hydraulic members enable lateral and transverse movement of the steam generator up to six inches (15.24 centimeters) in 1/32 inch (0.08 centimeters) increments. The system of this embodiment also enables correction of the steam generator vertical axis by 0.50 degrees. Control of the several hydraulic members can be had from the control unit 52 which can be accessed on the control platform 54 which is temporarily cantilevered from the top of the concrete walls 36 that surround the generator 18.
As an alternate to the system illustrated in
In operation, the embodiments illustrated in
Two exemplary, alternate lower restraint assemblies are shown in
An upper lateral support with a snubber 84 may also be used to engage the steam generator 18 to the concrete walls 36 as shown in
While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. For example, pneumatic cylinders may be employed in place of the hydraulic cylinders. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.
This application claims priority to provisional application Ser. No. 61/447,892, filed Mar. 1, 2011.
Number | Date | Country | |
---|---|---|---|
61447892 | Mar 2011 | US |