U.S. patent application number 11/888777 was filed with the patent office on 2008-02-07 for jet pump slip joint with axial grooves.
Invention is credited to Martin R. Torres.
Application Number | 20080031741 11/888777 |
Document ID | / |
Family ID | 39029343 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080031741 |
Kind Code |
A1 |
Torres; Martin R. |
February 7, 2008 |
Jet pump slip joint with axial grooves
Abstract
A uniform leakage flow device for the slip point of piping
systems, and particularly in reactor pressure vessels, selectively
imposes a steady, uniform flow of fluid through the slip joint
between two adjacent pipe surfaces to thereby eliminate the
detrimental flow-induced vibration associated with the unsteady and
non-uniform leakage of fluid through the slip joint field. The
uniform leakage flow device comprises a plurality of axial grooves
that are formed in the wall surface of the slip joint.
Inventors: |
Torres; Martin R.; (San
Jose, CA) |
Correspondence
Address: |
MORRISS OBRYANT COMPAGNI, P.C.
734 EAST 200 SOUTH
SALT LAKE CITY
UT
84102
US
|
Family ID: |
39029343 |
Appl. No.: |
11/888777 |
Filed: |
August 2, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60834929 |
Aug 2, 2006 |
|
|
|
Current U.S.
Class: |
417/151 |
Current CPC
Class: |
F04F 5/46 20130101; F04F
5/464 20130101 |
Class at
Publication: |
417/151 |
International
Class: |
F04F 5/00 20060101
F04F005/00 |
Claims
1. A uniform leakage flow device for a jet pump assembly having an
inlet mixer coupled to a diffuser and defining a slip joint
therebetween, comprising: a plurality of axial grooves formed in
the wall surface of the slip joint defined between an outer wall
surface of the inlet mixer and an inner wall surface of the
diffuser.
2. The uniform leakage flow device of claim 1 wherein said
plurality of axial grooves is formed in the outer wall surface of
the inlet mixer.
3. The uniform leakage flow device of claim 1 wherein said
plurality of axial grooves is formed in the inner wall surface of
the diffuser.
4. The uniform leakage flow device of claim 1 wherein the number,
width and depth of each said plurality of axial grooves is defined
by the following equations when the axial grooves area is equal to
the slip join leakage area, where A is the slip joint leakage area,
N is the number of axial grooves, D is the outer diameter of the
inlet mixer, w is the width of the axial groove, d is the depth of
the axial groove and g is the distance of the radial gap, then:
A=3.14159.times.D.times.g=N .times.w.times.d hence,
w=3.14159.times.D.times.g/(N.times.d).
5. The uniform leakage flow device of claim 1 wherein the number of
axial grooves formed in said wall surface is at least four.
6. The uniform leakage flow device of claim 1 wherein said depth of
each said axial groove of said plurality of axial grooves is two to
four times the distance of the radial gap of the slip joint, said
radial gap being defined as the distance between the outer wall
surface of the inlet mixer and the inner wall surface of the
diffuser.
7. A method of forming a uniform leakage flow device in the slip
joint of a jet pump assembly having an inlet mixer positionable
within a diffuser, comprising: forming a plurality of axial grooves
in the wall surface of one of the outer wall surface of the inlet
mixer or the inner wall surface of the diffuser; and positioning
the inlet mixer within the diffuser.
8. The method of claim 7 wherein said axial grooves are formed in
said outer wall of said inlet mixer.
9. The method of claim 7 wherein said axial grooves are formed in
said inner wall surface of said diffuser.
10. The method of claim 7 wherein said axial grooves are machined
in said wall surface underwater.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a non-provisional application claiming
priority to provisional patent application Ser. No. 60/834,929
filed Aug. 2, 2006.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to tubular jet pumps used
in various industries to transport and/or circulate cooling liquid
in heat-generating systems, such as nuclear reactors and
hydroelectric generation systems. More particularly, this invention
relates to means for uniformly controlling the leakage flow rate
through a slip joint to thereby eliminate detrimental vibration in
the slip joints of such jet pumps.
[0004] 2. Description of Related Art
[0005] Pipes, tubes and cylinders are used to transport a variety
of fluids, such as water, oil, and liquid chemicals in various
industries including the nuclear industry, the electric power
industry, such as for internal components of heat exchangers, the
hydroelectric power generation industry, the petroleum industry,
such as piping used in refining of oil, the chemical industry, such
as the piping used in processes for making chemical based products,
and the space industry, for spacecraft heat exchangers and other
similar devices.
[0006] Oftentimes, the piping components in such industrial systems
are submerged in the same fluids which the piping is transporting.
As an example, the tubular components that make up a jet pump
assembly are housed within a nuclear reactor pressure vessel and
reside in the fluid that the jet pump is used to transport. That
is, the jet pump assembly transports the cooling water to the
reactor core, but the jet pump assembly itself is also submerged in
that same fluid. The pipes and tubes that comprise such submerged
systems are supported within the surrounding structures by support
or restraining apparatus. The surrounding structures (e.g., a
reactor vessel) may be of a different material, such as carbon
steel (reactor pressure vessel), than the material that the piping
is made of, such as stainless steel (jet pump assembly) with
different thermal coefficients of expansion. In order to
accommodate the different amounts of axial thermal expansion that
will occur between the tubes and the surrounding support structure
at higher operating temperatures, designers install slip joints
along the piping to minimize thermal stress build up within the
tubes.
[0007] Recent engineering experience has shown that if a sufficient
pressure gradient exists across these slip joint interfaces, the
connecting tubular components may incur detrimental flow-induced
vibration, and failure results from either excessive wear or
fatigue of the piping material or support/restraining apparatus.
One exemplar system where such failure occurs is the jet pump
assemblies used in nuclear reactors.
[0008] A reactor pressure vessel (RPV) of a boiling water reactor
(BWR) typically has a generally cylindrical shape and is closed at
both ends with typically a bottom head and a removable top head. A
top guide typically is spaced above a core plate within the RPV and
a core shroud, typically surrounds the core and is supported by
shroud support structure. The shroud has a generally cylindrical
shape and surrounds both the core plate and the top guide. A space,
or annulus, is located between the cylindrical reactor pressure
vessel and the cylindrically shaped shroud. A plurality of jet
pumps are positioned within the annulus. An typical example of such
reactor cores is disclosed in U.S. Pat. No. 4,675,149 to Perry, et
al.
[0009] In a BWR, the hollow tubular jet pumps positioned within the
shroud annulus provide the required reactor core water flow.
Examples of such jet pump assemblies are disclosed in U.S. Pat. No.
6,587,535 to Erbes, et al. The upper portion of the jet pump, known
as the inlet mixer, is laterally positioned and supported against
opposing contacts within the restrainer bracket by a
gravity-actuated wedge and two set screws. The restrainer brackets
support the inlet mixer by attaching to the adjacent jet pump riser
pipe.
[0010] The lower portion of the jet pump, known as the diffuser, is
coupled to the inlet mixer by a slip joint. This construction
facilitates the disassembly and repair of the jet pump. The slip
joint between the jet pump inlet mixer and the jet pump diffuser
collar has about a 0.015 inch diametral operating clearance which
accommodates the relative axial thermal expansion movement between
the upper and lower parts of the jet pump and permits leakage flow
from the driving pressure inside the pump. A limited amount of
leakage may be beneficial to clean the joint of corrosion product
build up.
[0011] Excessive leakage flow, however, can cause oscillation
motion in the slip joint, which is a source of detrimental
vibration excitation in the jet pump assembly. The slip joint
leakage flow rate can increase due to single loop operation,
increased core flow, or deposition of jet pump detritus, or crud,
in the slip joint. Additional detrimental conditions that may lead
to damaging vibration between the inlet mixer and diffuser of the
jet pump assembly are well-known, such as loss of the set screw
support in a jet pump assembly as described in U.S. Pat. No.
6,394,765 to Erbes, et al.
[0012] In addition to affected set screw gaps, thermal and pressure
displacements of the shroud and the pressure vessel can diminish
alignment interaction loads in the jet pump assembly which are
beneficial in restraining vibration. The resultant increased
vibration levels and corresponding vibration loads on the piping
and supports can cause jet pump component degradation from wear and
fatigue.
[0013] High levels of flow-induced vibration (FIV) are possible in
some jet pump designs at some abnormal operational conditions
having increased leakage flow rates. Reducing leakage flow through
the slip joint prevents or reduces oscillatory slip joint motion
and suppresses FIV. Prior efforts to reduce the leakage flow rate
in jet pump slip joints have been disclosed in U.S. Pat. No.
6,394,765, which discloses an external clamp apparatus for
laterally stabilizing the slip joint; U.S. Pat. No. 6,438,192 to
Erbes, et al., which discloses a split ring seal and latch assembly
positioned at the upper end of the diffuser tube to stabilize the
inlet mixer; U.S. Pat. No. 6,450,774 to Erbes, et al., which
discloses a device for producing a lateral support load on the slip
joint by causing an ovate deformation in the diffuser when
attaching it to the inlet mixer; and U.S. Pat. No. 6,587,535 to
Erbes, et al., which discloses a labyrinth seal in the slip joint
for reducing slip joint leakage flow.
[0014] Each of the previously disclosed inventions has demonstrated
some characteristic which has rendered the device or method
insufficient in producing effective reduction of slip joint-induced
vibration, and none has been directed to providing a means for
selectively controlling leakage flow rate through the slip joint to
ameliorate the damaging effects of excessive leakage flow rate
through the slip joint. In addition, those devices and methods that
impose a lateral force on the slip joint also prevent axial
movement in the slip joint, which does not properly allow for
thermal expansion in the slip joint.
[0015] It would be advantageous in the industry to provide a device
for reducing or eliminating non-uniform, or unsteady, leakage flow
rates though a slip joint by selectively controlling the uniform
leakage of fluid through a slip joint in order to control, and
thereby eliminate, the detrimental vibration and other damaging
conditions that occur in unsteady slip joints, i.e., those slip
joints through which non-uniform leakage flow occurs.
BRIEF SUMMARY OF THE INVENTION
[0016] In accordance with the present invention, a uniform leakage
flow device is provided in a slip joint between intercoupled pipes
to selectively control the amount of fluid allowed to leak through
the slip joint, thereby selectively eliminating the amount of
detrimental vibration or oscillation that otherwise occurs at the
slip joint. The present invention may be adapted for use in any
slip joint between intercoupled pipes, but is disclosed herein with
respect to jet pump assemblies of the type used in reactor pressure
vessel, by way of example.
[0017] The uniform leakage flow device of the present invention
comprises forming a selected number of axial grooves in the slip
joint between an inlet mixer and the diffuser. The axial grooves
may be formed in either the outer wall surface of the inlet mixer
at the slip joint or in the inner wall surface of the diffuser at
the slip joint. The axial grooves are machined into the wall
surface either at initial assembly of the jet pump components, or
after operation of the reactor pressure vessel has taken place.
Methods for effecting formation of the axial grooves both prior to
and after operation of the reactor pressure vessel are
disclosed.
[0018] The axial grooves are formed in a precise manner to
selectively control and make uniform the flow of fluid leakage
through the slip joint. The number, size and positioning of the
axial grooves in the wall surface is determined by the application
of equations as disclosed herein.
[0019] In known slip joint structures, mechanical devices have been
invented to eliminate or reduce the slip joint leakage flow and in
turn eliminate the detrimental slip joint flow induced vibration
mechanism. The present invention is directed to a completely
different approach by providing a means to directly destroy the
flow induced vibration mechanism by allowing the leakage flow to
pass uniformly through the slip joint by way of machined axial
grooves. In the presence of these axial grooves, the slip joint
leakage flow will always be uniform and even around the
circumference of the slip joint.
[0020] Further, in known slip joint structures, both the total
leakage flow and the leakage flow around the annulus and within the
slip joint varied depending on the relative position of the mating
parts. Non-uniform slip joint leakage flow, in both the total flow
and peripheral flow, incurred time-varying lateral forces on the
mating parts of the slip joint. These time-varying lateral forces
incurred relative motion of the mating parts. This relative motion
lead to increased non-uniform flow and higher fluid forces that, in
turn lead to higher levels of vibration and wear of the mating jet
pump components. This spiraling condition lead to higher and higher
vibration levels of the mating parts. The axial grooves of the
present invention impose uniform leakage flow at the slip joint
location. The imposed uniform leakage flow does not change in its
total amount, nor periphery within the slip joint annulus due to
relative motion of the slip joint mating parts. The uniform leakage
flow cannot incur net, time-varying lateral fluid forces that cause
detrimental vibration and relative lateral motion of the slip joint
mating parts.
[0021] The placement of axial grooves in the slip joint reduces or
eliminates non-uniform or unsteady leakage flow through the slip
joint and thereby reduces or eliminates vibration levels associated
with non-uniform or unsteady slip joint leakage flow. The present
invention provides the further advantage of allowing axial movement
between the jet pump components and supporting structure to
accommodate thermal expansion in the jet pump assembly, and does
not impose undue stress in the inlet mixer. The present invention
also eliminates the use of structures, such as clamps and the like,
which present a potential detriment of having loose parts moving in
the jet pump assembly, recirculation system or reactor core. These
and other advantages of the present invention will become more
clear in light of the following detailed description.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0022] In the drawings, which illustrate what currently is
considered to be the best mode for carrying out the invention:
[0023] FIG. 1 is a partial, schematic view of a nuclear reactor,
shown in cutaway, illustrating a conventional jet pump assembly
positioned in the annulus of the reactor;
[0024] FIG. 2 is an enlarged view in cross section of a slip joint
between the inlet mixer and diffuser of a jet pump;
[0025] FIG. 3 is an enlarged view in cross section of a slip joint
in which the uniform leakage flow rate device of the present
invention is provided;
[0026] FIG. 4 is a cross section view taken at line 3-3 of FIG. 3
illustrating the size, number and positioning of axial grooves in
the inlet mixer outer wall;
[0027] FIG. 5 is an enlarged view in cross section of an
alternative embodiment of the invention where the axial grooves are
formed in the inner wall of the diffuser; and
[0028] FIG. 6 is a cross section view taken at line 5-5 of FIG. 5
illustrating the size, number and position of axial grooves in the
diffuser wall.
DETAILED DESCRIPTION OF THE INVENTION
[0029] FIG. 1 is a schematic illustration of a portion of a
conventional reactor pressure vessel (RPV) 20 for a boiling water
reactor. Such reactors are previously described in U.S. Pat. No.
4,675,149 and U.S. Pat. No. 6,587,535, the disclosures of which are
incorporated herein. The RPV 20 has a generally cylindrical shape
and is closed at one end by a bottom head (not shown) and at its
other end by removable top head (not shown). A top guide (not
shown) is spaced above a core plate 22 within RPV 20. A shroud 24
surrounds the core plate 22 and is supported by a shroud support
structure 26. An annulus 28 is formed between the shroud 24 and
sidewall 30 of the RPV 20.
[0030] An inlet nozzle 32 extends through the sidewall 30 of the
RPV 20 and is coupled to a jet pump assembly 34. The jet pump
assembly 34 includes a riser pipe 38 and a plurality of inlet
mixers 42 connected to the riser pipe 38 by a transition assembly
44. A diffuser 46 is connected to and positioned below each of the
inlet mixers. A slip joint 48 couples each inlet mixer 42 to a
corresponding diffuser 46.
[0031] FIG. 2 is illustrates in an enlarged cross sectional view
the relative positioning of an inlet mixer 42 and diffuser 46. It
can be seen that the inlet mixer 42 is generally cylindrical and
has an outer wall surface 50. The inlet mixer 42 has an open end 58
which is received in an open end 60 of the generally cylindrical
diffuser 46. The diffuser 46 has an inner wall surface 52
positioned adjacent to the outer wall surface 50 of the inlet mixer
42. An operational clearance 54 exists at an interface 56 between
the outer wall surface 50 of the inlet mixer 42 and the inner wall
surface 52 of the diffuser 46. When fluid is pumped through the
inlet mixer 42 into the diffuser 46, in the direction of arrow 62,
leakage of some of the fluid occurs through the clearance 54 in the
slip joint 48, as shown by arrow 64.
[0032] Leakage flow from within the jet pump at the slip joint 48
interface between the inlet mixer 42 and the diffuser 46 can become
unsteady and non-uniform due to relative lateral motion between the
two mating parts, the inlet mixer 42 and diffuser 46. This unsteady
slip joint leakage flow is the source of a detrimental vibration
excitation in the jet pump assembly 34. High levels of flow induced
vibration (FIV) are possible in some jet pump designs at some
abnormal operational conditions having increased unsteady slip
joint leakage flow rates. Changing the leakage flow characteristics
from unsteady flow to steady axial flow through the slip joint can
prevent oscillatory slip joint motion and eliminate detrimental,
high level FIV.
[0033] Thus, FIG. 3 illustrates a first embodiment of the invention
where axial grooves 60 are formed in the slip joint 48 interface
between the outer wall surface 50 of the inlet mixer 42 and the
inner wall surface 52 of the diffuser 48. In this particular
embodiment, the axial grooves 60 are formed in the outer wall
surface 50 of the inlet mixer 42. As seen more clearly in FIG. 4, a
plurality of axial grooves 60 may be formed about the circumference
of the inlet mixer 42. In an alternative embodiment shown in FIGS.
5 and 6, the axial grooves 60 may be formed in the inner wall
surface 52 of the diffuser.
[0034] The number of axial grooves that may be formed in the wall
surface (of either the inner mixer or diffuser) may vary, but
should number at least four. In a particularly suitable embodiment
of the invention, the number of axial grooves formed in the wall
surface may be twelve. The number of axial grooves may exceed
twelve in number, however.
[0035] In a particularly suitable embodiment, the depth (d) of the
axial grooves is from two to four times the distance (g) of the
radial rap or operational clearance 54 defined between the outer
wall surface 50 of the inlet mixer and the inner wall surface 52 of
the diffuser 46. The width (w) of the axial groove 60 depends on
the additional slip joint leakage flow area introduced by the axial
grooves 60. The additional slip joint leakage area, defined as the
sum of the areas (w.times.d) of each axial groove, should be
approximately equal to the original slip joint leakage area, or
operational clearance 54. The width of the axial grooves can be
calculated with the above information and the known outside
diameter (D) of the inlet mixer 42.
[0036] The number, width and depth of the axial grooves required to
produce a uniform and steady leakage flow through the slip joint
can be calculated with the following equations, where A is the slip
joint leakage area, N is the number of axial grooves, D is the
outer diameter of the inlet mixer, w is the width of the axial
groove, d is the depth of the axial groove and g is the distance of
the radial gap. In the equations illustrated below, the number "3"
indicates an exemplar equation where the depth of the groove is
three times the measurement (g) of the radial gap.
A=3.14159.times.D.times.g=N.times.w'd=N.times.w.times.3.times.g
Equation 1:
w=3.14159.times.D.times.g/(N.times.3.times.g)=1.0472.times.D/N
Equation 2:
[0037] The uniform leakage flow device of the present invention may
be formed in the slip joint either when the jet pump assembly is
new (i.e., non-irradiated) and being positioned in the RPV, or the
invention can be formed as a retrofit to an existing RPV. In the
first method of formation, the axial grooves are machined into the
wall surface of the slip joint, (either in the inlet mixer or the
diffuser) prior to coupling of the inlet mixer to the diffuser in
assembly of the jet pump.
[0038] In the later method of installing the uniform leakage flow
device of the invention after the RPV has been in operation, the
inlet mixer is removed from the diffuser by means known in the
industry. However, because the jet pump has been irradiated during
operation of the RPV, the components, comprising the inlet mixer
and or diffuser, must be shielded within a water source to protect
the workers who are handling the jet pump components. The axial
grooves are machined in the wall surface of the inlet mixer or
diffuser at the slip joint using tools that may be used underwater.
When the axial grooves have been machined into the wall surface of
the slip joint, the inlet mixer is re-coupled with the diffuser as
is known in the art.
[0039] The uniform leakage flow device described herein produces a
selected steady and uniform flow of fluid leakage through the slip
joint to control detrimental vibration and oscillation in the jet
pump assembly. The present invention also enables axial movement of
the jet pump components due to varying thermal expansion rates in
the components, while maintaining a comprehensive seal at the slip
joint. The number and positioning of the axial grooves may vary
depending on the particular installation specifications and can be
adapted to any variety of piping systems. Therefore, reference
herein to particular embodiments and structures of the invention is
by way of example only and not by way of limitation.
* * * * *