System for dampening vibration

An embodiment of the present invention takes the form of a system that may reduce the level of flow-induced vibration (FIV) experienced by a jet pump assembly or other similar object within a pressure vessel. Essentially, an embodiment of the present invention may reduce the slip-joint leakage, which may be a cause of the FIVs, by adding a flow-limiting component to an outlet of the slip joint. This component may take the form of a collar, channel, and/or other component that may be connectable to a component of the jet pump assembly. After installation, an embodiment of the present invention may lower the amplitude of, and/or change the frequency of, the FIVs experienced by the jet pump assembly.

BACKGROUND OF THE INVENTION

The present invention relates generally to piping used in various industries to move fluid; and more particularly to a system for mitigating flow-induced vibrations (FIV) associated with transport and/or circulating a cooling fluid in heat-generating systems, such as nuclear reactors and hydroelectric generation systems.

Structural conduits, such as, but not limiting of, pipes, tubes, and cylinders are commonly used to transport a variety of fluids. Typically, the conduits are submerged in the same fluids that the conduit is transporting. For example, but not limiting of, the tubular components of a jet pump assembly are housed within a nuclear reactor pressure vessel (RPV) and reside in the fluid that the jet pump transports. Here, the jet pump assembly transports the cooling water to the reactor core, while the jet pump assembly is submerged in the same cooling fluid.

The conduits that comprise such submerged systems are typically supported within the surrounding structures (e.g., the RPV) by a restraining apparatus. The surrounding structures may be formed of a material different than the conduit material. For example, but not limiting of, the RPV may be formed of carbon steel; and the jet pump assembly may be formed of stainless steel. These different materials tend to have different thermal coefficients of expansion. In order to accommodate for the different amounts of thermal expansion associated with RPV operation, slip joints are installed along the conduits to minimize thermal stress within the conduits.

Experience has shown that if a sufficient pressure gradient exists across slip joint interfaces, the connecting tubular components may incur detrimental FIV. This may lead to a failure possibly resulting from excessive wear and/or fatigue of the conduit material or the support/restraining apparatus. These failures may occur to the jet pump assemblies used in RPVs.

The slip joint typically has an operating clearance that accommodates the relative axial thermal expansion movement between components of the jet pump assembly. This clearance permits a leakage flow from the driving pressure inside the jet pump assembly. Excessive leakage flow, however, can cause an oscillatory motion in the slip joint, which may be one source of FIV experienced by the jet pump assembly.

Some known systems and methods for mitigating this FIV may be insufficient in producing a long-term and effective reduction of the vibration. In addition, those systems and methods may impose a lateral force on the slip joint. This lateral force may prevent axial movement in the slip joint, and not properly allow for adequate thermal expansion in the slip joint.

Based on the above discussion, there may be a desire for a system for reducing the FIVs experienced by a conduit submerged within the fluid that the conduit transports. The system should provide a simplified way to prevent and/or mitigate the FIVs.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with an embodiment of the present invention, a system configured for mitigating flow induced vibrations (FIV) experienced by a conduit system partially submerged within a fluid that the conduit system transports, the system comprising: a slip joint for a pressure vessel, wherein the slip joint integrates an inlet mixer and a diffuser; and a collar adapted for reducing leakage associated with the slip joint, wherein the collar limits a fluid flow exiting the slip joint, and wherein the collar is located adjacent the slip joint.

In accordance with another embodiment of the present invention, a jet pump system for configured for dampening a level of vibration experienced by a pipe within a power plant; the system comprising:a. a pressure vessel (RPV);b. an inlet mixer;c. a diffuser integrated with the inlet mixer via a slip joint; and a collar adapted for reducing leakage associated with the slip joint, wherein the channel limits a fluid flow exiting the slip joint and wherein the channel is located adjacent the slip joint.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology may be 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”, “horizontal”, “vertical”, “upstream”, “downstream”, “fore”, and “aft” merely describe the configuration shown in the FIGS. Indeed, the components may be oriented in any direction and the terminology, therefore, should be understood as encompassing such variations unless specified otherwise.

As used herein, an element or step recited in the singular and preceded with “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “an embodiment” of the present invention are not intended to exclude additional embodiments incorporating the recited features.

The present invention takes the form of a system that may reduce the level of flow-induced vibration (FIV) experienced by a jet pump assembly or other similar object within a nuclear reactor pressure vessel RPV10. Essentially, an embodiment of the present invention may reduce the slip-joint leakage, which may be a cause of the FIVs, by adding a flow-limiting component to an outlet of the slip joint. This component may take the form of a collar, channel, and/or other component that may be connectable to a component of the jet pump assembly. After installation, an embodiment of the present invention may lower the amplitude of, and/or change the frequency of, the FIVs experienced by the jet pump assembly.

The following discussion focuses on an embodiment of the present invention integrated with the jet pump assemblies of the RPV. Other embodiments of the present invention may be integrated with other systems that require a dampening of and/or frequency change in FIVs.

Referring now to the FIGS., where the various numbers represent like parts throughout the several views. A non-limiting example of a nuclear reactor, a conventional boiling water reactor (BWR), is shown inFIG. 1.FIG. 1is a schematic, illustrating a boiling water reactor partially in cross-section, within which an embodiment of the present invention operates. A typical BWR includes: a RPV10; a core shroud30is disposed within the RPV10and surrounds a core plate22; and a nuclear fuel core35. Generally the RPV10has a cylindrical shape and is closed at one end by a bottom head, and at an opposite end by a removable top head. The core shroud30is a cylinder that surrounds the nuclear fuel core35, which includes a plurality of fuel bundle assemblies40disposed within the core shroud30. A top guide45may be spaced above a core plate50and supports each of the fuel bundle assemblies40.

An annular region between the core shroud30and the RPV10is considered the downcomer annulus25. Coolant water flows through the downcomer annulus25and into the core lower plenum55. Feedwater enters the RPV10via a feedwater inlet15and is distributed circumferentially within the RPV10by a feedwater sparger20, which is adjacent a core spray line105. Then, the water in the core lower plenum55flows upward through the nuclear fuel core35. In particular, water enters the fuel bundle assemblies40, wherein a boiling boundary layer is established. A mixture of water and steam exits the nuclear fuel core35and enters the core upper plenum60under the shroud head65. The steam-water mixture then flows through standpipes70on top of the shroud head65and enters the steam separators75, which separate water from steam. The separated water is recirculated to the downcomer annulus25and the steam exits the RPV10via a nozzle110for use in generating electricity and/or in another process.

As illustrated inFIG. 1, a conventional jet pump assembly85comprises a pair of inlet mixers95. Each inlet mixer95has an elbow welded thereto, which receives pressurized driving water from a recirculation pump (not illustrated) via an inlet riser100. Some inlet mixers95comprise a set of five nozzles circumferentially distributed at equal angles about an axis of the inlet mixer95. Here, each nozzle is tapered radially and inwardly at the nozzle outlet. This convergent nozzle energizes the jet pump assembly85. A secondary inlet opening (not illustrated) is located radially outside of the nozzle exit. Therefore, as jets of water exit the nozzles, water from the downcomer annulus25is drawn into the inlet mixer95via the secondary inlet opening, where mixing with water from the recirculation pump occurs.

The RPV10also includes a coolant recirculation system, which provides the forced convection flow through the nuclear fuel core35necessary to attain the required power density. A portion of the water is drawn from the lower end of the downcomer annulus25via a recirculation water outlet80and forced by the recirculation pump into a plurality of jet pump assemblies85via recirculation water inlets90. The jet pump assemblies85are typically circumferentially distributed around the core shroud30and provide the required reactor core flow. A typical RPV10has between twelve to twenty-four inlet mixers95.

FIG. 2is a schematic, illustrating a cutaway of the jet pump assembly85of the RPV10ofFIG. 1. Typically, each jet pump assembly85includes at least the following. A transition piece120, a riser pipe130extending downwardly from the transition piece120to a riser elbow135. The riser elbow135connects the riser pipe130to a recirculation inlet90along a wall of the RPV10. A transition assembly155connects the inlet riser100with the inlet mixers95.

A pair of inlet mixers95extends downwardly from the transition piece120to a pair of diffusers115mounted over holes in a pump deck125. The pump deck125connects a bottom portion of the core shroud30with the RPV10. The riser pipe130is typically tubular and is oriented vertically within the downcomer annulus25, in parallel relation to the wall of the core shroud30. The riser elbow135is typically tubular and bends outwardly toward the recirculation inlet90. The transition piece120extends in opposite lateral directions at the top of the riser pipe130to connect with the inlet mixers95on opposite sides of the riser pipe130. The inlet mixers95are oriented vertically in the downcomer annulus25in parallel relation to the riser pipe130. Restrainer brackets140, located between the inlet mixers95and the riser pipe130, provide lateral support for the inlet mixers95. A riser brace145may support and stabilize the inlet riser100in the region of the downcomer annulus25. The riser brace145may also integrate the inlet riser100with an attachment wall149of the RPV10.

The diffusers115may be coupled to the inlet mixer95by a slip joint160. This configuration may facilitate the disassembly and repair of the jet pump assembly95. As described, the slip joint160may have an operational clearance175, which accommodates the relative axial thermal expansion between the upper and lower parts of the jet pump assembly85and may permit leakage flow from the driving pressure inside the jet pump assembly85.

FIG. 3is a schematic, illustrating an enlarged view, in cross section, of the relative positioning of the inlet mixer95and the diffuser115within the slip joint160ofFIG. 2.FIG. 3illustrates that the inlet mixer95may be generally cylindrical and has an outer wall surface165. The inlet mixer95has an open end185, which is received in an open end190of the diffuser115, which may have a cylindrical shape. The diffuser115may have an inner wall surface170positioned adjacent to the outer wall surface165of the inlet mixer95. An operational clearance175typically exists at an interface180between the outer wall surface165of the inlet mixer95and the inner wall surface170of the diffuser115. When fluid is pumped through the inlet mixer95into the diffuser115, in the direction of arrow195, leakage of some of the fluid occurs through the clearance175in the slip joint160, as shown by arrow200.

Leakage flow at the slip joint160interface180may become unsteady and non-uniform due to relative lateral motion between the two mating parts, the inlet mixer95and diffuser115. This leakage flow may be the source of a FIV excitation in the jet pump assembly85. Undesirable levels of FIV may be possible in some jet pump designs at some abnormal operational conditions having increased unsteady slip joint leakage flow rates.

FIGS. 4A and 4B, collectivelyFIG. 4, are schematics of an inlet mixer95integrated with an embodiment of a diffuser collar225, in accordance with an embodiment of the present invention. Changing the leakage flow characteristics from unsteady flow to steady axial flow through the slip joint160may prevent oscillatory slip joint160motions and may mitigate the FIV. Adding a flow-limiting component on the outlet side of the slip joint160, indicated by direction arrow200(FIG. 3), may change the leakage flow characteristics.

The goal of an embodiment of the present invention is to provide a simple yet effective component for mitigating FIV. An embodiment of the present invention provides a flow-limiting component to the outlet side of the slip joint160. This may serve to increase the pressure-drop across the slip joint160. This component may take the form a diffuser collar225. The diffuser collar225may also be considered a channel that is connected to a portion of the diffuser115.

An embodiment of the diffuser collar225may reduce the leakage associated with the slip joint160. As discussed, reducing this leakage may mitigate the FIVs experienced by the inlet mixer95. An embodiment of the diffuser collar225may accomplish this by limiting the fluid flow exiting the slip joint160.

An embodiment of the diffuser collar225may be located adjacent the slip joint160. For example, but not limiting of, the diffuser collar225may be located downstream of the slip joint160. Here, the diffuser collar225may partially extend over an outer surface of the diffuser115.

An embodiment of the diffuser collar225may have a U-shape or a parabolic shape. However, other embodiments of the present invention may have diffuser collar's225that have other shapes.

An embodiment of the diffuser collar225may be attached to the diffuser115. Attachments methods such as, but not limiting of, welding forms, or the like, may be used to affix the diffuser collar225to the diffuser115. Other embodiments of the present invention may attach the diffuser collar225to other components of the inlet mixer95or the jet pump assembly85.

An embodiment of the diffuser collar225may comprise at least one slot230. The slot230may serve to allow a guide bar (not illustrated) of the diffuser115to partially extend through the diffuser collar225. An embodiment of the diffuser collar225may comprise a plurality of slots230, as illustrated inFIG. 4B.

The components of an embodiment present invention may be formed of any material capable of withstanding the operating environment to which the diffuser collar225may be exposed.

In use, the diffuser collar225may be affixed in a manner that partially or nearly completely surrounds a downstream portion of the diffuser115. As the RPV10operates, the diffuser collar225may restrict the downstream flow of the fluid exiting the slip joint160. This may increase the pressure drop across the slip joint160, which may also reduce the FIVs experience by the inlet mixer95. For example, but not limiting of, an embodiment of the present invention may increase the pressure in a range of from about 2 to about 4 times a previous pressure drop.

Although the present invention has been shown and described in considerable detail with respect to only a few exemplary embodiments thereof, it should be understood by those skilled in the art 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, omissions, additions and equivalents as may be included within the spirit and scope of the invention as defined by the following claims. For example, but not limiting of, an embodiment of the present invention may be used to: a) introduce a different vibration mode; b) to secure a pipe, cable, wire, or other similar object, at a fixed distance away from a separate structure or other object; or c) to apply a compressive load to at least one of the aforementioned objects.