U.S. patent application number 16/419620 was filed with the patent office on 2020-11-26 for debris filtering arrangement for nuclear fuel assembly bottom nozzle and bottom nozzle including same.
This patent application is currently assigned to WESTINGHOUSE ELECTRIC COMPANY LLC. The applicant listed for this patent is WESTINGHOUSE ELECTRIC COMPANY, LLC. Invention is credited to ARTEM ALESHIN, YURIY ALESHIN.
Application Number | 20200373025 16/419620 |
Document ID | / |
Family ID | 1000004156870 |
Filed Date | 2020-11-26 |
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United States Patent
Application |
20200373025 |
Kind Code |
A1 |
ALESHIN; ARTEM ; et
al. |
November 26, 2020 |
DEBRIS FILTERING ARRANGEMENT FOR NUCLEAR FUEL ASSEMBLY BOTTOM
NOZZLE AND BOTTOM NOZZLE INCLUDING SAME
Abstract
A filtering arrangement for use in a bottom nozzle of a fuel
assembly in a nuclear reactor includes a top surface, a bottom
surface, a plurality of vertical wall portions arranged in a
generally squared grid-like pattern which extend between the bottom
surface and the top surface and define a plurality of non-circular
passages extending between the bottom surface and the top surface
through the arrangement, and a plurality of first debris filters
which are each positioned between the top surface and the bottom
surface to generally span across a respective one of the plurality
of passages.
Inventors: |
ALESHIN; ARTEM; (COLUMBIA,
SC) ; ALESHIN; YURIY; (CAYCE, SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WESTINGHOUSE ELECTRIC COMPANY, LLC |
Cranberry Township |
PA |
US |
|
|
Assignee: |
WESTINGHOUSE ELECTRIC COMPANY
LLC
CRANBERRY TOWNSHIP
PA
|
Family ID: |
1000004156870 |
Appl. No.: |
16/419620 |
Filed: |
May 22, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G21C 3/3206 20130101;
G21C 1/086 20130101 |
International
Class: |
G21C 3/32 20060101
G21C003/32; G21C 1/08 20060101 G21C001/08 |
Claims
1. A filtering arrangement for use in a bottom nozzle of a fuel
assembly in a nuclear reactor, the filtering arrangement
comprising: a top surface; a bottom surface; a plurality of
vertical wall portions arranged in a generally squared grid-like
pattern which extend between the bottom surface and the top surface
and define a plurality of non-circular passages extending between
the bottom surface and the top surface through the arrangement; and
a plurality of first debris filters, each debris filter being
positioned between the top surface and the bottom surface to
generally span across a respective one of the plurality of
passages.
2. The filtering arrangement of claim 1, wherein each first debris
filter comprises a hollow pyramid or hollow cone-like structure
formed from a lattice structure which is sized and configured to
minimize resistance in regard to coolant flow through the lattice
structure.
3. The filtering arrangement of claim 2, wherein when viewed from
directly above the filtering arrangement or directly below the
filtering arrangement the lattice structure of each first debris
filter is arranged so as to form a first squared grid-like
pattern.
4. The filtering arrangement of claim 2, wherein at least one first
debris filter narrows from bottom to top.
5. The filtering arrangement of claim 2, wherein at least one first
debris filter narrows from top to bottom.
6. The filtering arrangement of claim 1, further comprising a
plurality of second debris filters which are each positioned
between the top surface and the first debris filter to generally
span across a respective one of the plurality of passages.
7. The filtering arrangement of claim 6, wherein each first debris
filter comprises a hollow pyramid or hollow cone-like structure
formed from a lattice structure which is sized and configured to
minimize resistance in regard to coolant flow through the lattice
structure, and wherein each second debris filter comprises a hollow
pyramid or hollow cone-like structure formed from a lattice
structure which is sized and configured to minimize resistance in
regard to coolant flow through the lattice structure.
8. The filtering arrangement of claim 7, wherein when viewed from
directly above the filtering arrangement or directly below the
filtering arrangement the lattice structure of each second debris
filter is arranged so as to form a second squared grid-like
pattern.
9. The filtering arrangement of claim 8, when viewed from above,
the second squared grid-like pattern is offset a distance from the
first squared grid-like pattern.
10. The filtering arrangement of claim 7, wherein at least one
first debris filter narrows from bottom to top and wherein at least
one second debris filter narrows from bottom to top.
11. The filtering arrangement of claim 7, wherein at least one
first debris filter narrows from top to bottom and wherein at least
one second debris filter narrows from top to bottom.
12. A bottom nozzle assembly for use in a fuel assembly in a
nuclear reactor, the bottom nozzle assembly comprising: a generally
rectangular skirt portion; and a filtering arrangement as recited
in claim 1 coupled to the generally rectangular base portion.
13. A bottom nozzle assembly for use in a fuel assembly in a
nuclear reactor, the bottom nozzle assembly comprising: a generally
rectangular skirt portion; and a filtering arrangement as recited
in claim 6 coupled to the generally rectangular base portion.
Description
BACKGROUND
1. Field
[0001] The present invention relates generally to nuclear reactors
and, more particularly, relates to debris filtering arrangements
for bottom nozzles for use in a nuclear fuel assembly such as
employed in a pressurized water reactor (PWR).
2. Related Art
[0002] During manufacture and subsequent installation and repair of
components comprising a nuclear reactor coolant circulation system,
diligent effort is made to assure removal of all debris from the
reactor vessel and its associated systems which circulate coolant
through it under various operating conditions. Although elaborate
procedures are carried out to help assure debris removal,
experience shows that in spite of the safeguards used to effect
such removal, some small amount of debris, such as metal chips and
metal particles still remain hidden in the systems. Most of the
debris consists of metal wires, chips and turnings which were
probably left in the primary system after steam generator repair or
replacement or similar types of plant modifications during the
refueling process. It is desirable to ensure that this type of
debris does not make its way into the fuel region during plant
operation.
[0003] In particular, fuel assembly damage due to debris trapped at
the lowermost grids has been noted in several reactors in the past.
Debris enters through the fuel assembly bottom nozzle flow holes
from the coolant flow openings in the lower core support plate when
the plant is started up. The debris tends to become lodged in the
lowermost support grids of the fuel assembly within the spaces
between the "egg-crate" shaped cell walls of the grid and the lower
end portions of the fuel rod tubes. The damage consists of fuel rod
tube perforations caused by fretting of debris in contact with the
exterior of the fuel tube. Debris can also become entangled in the
nozzle plate holes and the flowing coolant causes the debris to
gyrate which tends to cut through the cladding of the fuel
rods.
[0004] Several different approaches have been proposed and tried
for carrying out removal of debris from nuclear reactors. Many of
these approaches are discussed in U.S. Pat. No. 4,096,032 to Mayers
et al. U.S. Pat. No. 4,900,507 to Shallenberger et al. illustrates
another approach. Yet other approaches use mesh spires which
protrude out of the body of the nozzle. However, such designs run
the risk of interfering with the fuel rods and have debris
capturing features that may potentially be damaged during
transportation and assembly.
[0005] While some of the aforementioned approaches operate
reasonably well and generally achieve their objectives under the
range of operating conditions for which they were designed, a need
still exists for improved solutions to the problem of debris
filtering in nuclear reactors. New approaches must be compatible
with the existing structure and operation of the components of the
reactor, be effective throughout the operating cycle of the
reactor, and at least provide overall benefits which outweigh any
costs added.
SUMMARY
[0006] Embodiments of the concept as described herein provide an
improved debris capturing feature for a fuel assembly, such as used
in a pressurized water reactor (PWR), while at the same time
minimizing pressure drop when compared to existing bottom nozzle
designs. Embodiments of the invention utilize unique debris
capturing features which are also designed to streamline the flow
passages thereby resulting in a reduced pressure loss coefficient.
The design is especially effective at the higher flow rates
associated with the conditions standard commercial PWR nuclear
reactors see during normal operating conditions.
[0007] As one aspect, a filtering arrangement for use in a bottom
nozzle of a fuel assembly in a nuclear reactor is provided. The
filtering arrangement comprises: a top surface; a bottom surface; a
plurality of vertical wall portions arranged in a generally squared
grid-like pattern which extend between the bottom surface and the
top surface and define a plurality of non-circular passages
extending between the bottom surface and the top surface through
the arrangement; and a plurality of first debris filters, each
debris filter being positioned between the top surface and the
bottom surface to generally span across a respective one of the
plurality of passages.
[0008] Each first debris filter may comprise a hollow pyramid or
hollow cone-like structure formed from a lattice structure which is
sized and configured to minimize resistance in regard to coolant
flow through the lattice structure.
[0009] When viewed from directly above the filtering arrangement or
directly below the filtering arrangement the lattice structure of
each first debris filter may be arranged so as to form a first
squared grid-like pattern.
[0010] At least one first debris filter may narrow from bottom to
top.
[0011] At least one first debris filter may narrow from top to
bottom.
[0012] The filtering arrangement may further comprise a plurality
of second debris filters which are each positioned between the top
surface and the first debris filter to generally span across a
respective one of the plurality of passages.
[0013] Each first debris filter may comprise a hollow pyramid or
hollow cone-like structure formed from a lattice structure which is
sized and configured to minimize resistance in regard to coolant
flow through the lattice structure and each second debris filter
may comprise a hollow pyramid or hollow cone-like structure formed
from a lattice structure which is sized and configured to minimize
resistance in regard to coolant flow through the lattice
structure.
[0014] When viewed from directly above the filtering arrangement or
directly below the filtering arrangement the lattice structure of
each second debris filter may be arranged so as to form a second
squared grid-like pattern.
[0015] When viewed from above, the second squared grid-like pattern
may be offset a distance from the first squared grid-like
pattern.
[0016] At least one first debris filter may narrow from bottom to
top and at least one second debris filter may narrow from bottom to
top.
[0017] At least one first debris filter may narrow from top to
bottom and at least one second debris filter may narrow from top to
bottom.
[0018] As another aspect, a bottom nozzle assembly for use in a
fuel assembly in a nuclear reactor is provided. The bottom nozzle
assembly comprises: a generally rectangular skirt portion and a
filtering arrangement as previously described coupled to the
generally rectangular base portion.
[0019] These and other objects, features, and characteristics of
the present invention, as well as the methods of operation and
functions of the related elements of structure and the combination
of parts and economies of manufacture, will become more apparent
upon consideration of the following description and the appended
claims with reference to the accompanying drawings, all of which
form a part of this specification, wherein like reference numerals
designate corresponding parts in the various figures. It is to be
expressly understood, however, that the drawings are for the
purpose of illustration and description only and are not intended
as a definition of the limits of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] 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:
[0021] FIG. 1 is an elevational view, partly in section, of a
conventional fuel assembly including a conventional debris filter
bottom nozzle, the assembly being illustrated in vertically
foreshortened form with parts broken away for clarity;
[0022] FIG. 2 is an isometric view of the conventional debris
filter bottom nozzle of the fuel assembly of FIG. 1;
[0023] FIG. 3 is a section view of a generally central portion of a
debris filter bottom nozzle of such as shown in FIG. 2 shown with
example fuel rods (shown schematically in section) disposed on the
flow plate of the bottom nozzle along with straps of a support grid
disposed about the fuel rods and resting on the flow plate;
[0024] FIG. 4 is a perspective view of a filtering arrangement in
accordance with an example embodiment of the present invention;
[0025] FIG. 5 is another perspective view of the filtering
arrangement of FIG. 4 shown sectioned along line 5-5 of FIG. 4;
[0026] FIG. 6 is a top view of the filtering arrangement of FIG.
4;
[0027] FIG. 7 is a sectional elevation view of the filtering
arrangement of FIG. 4 taken along line 7-7 of FIG. 6;
[0028] FIG. 8 is another sectional elevation view of the filtering
arrangement of FIG. 4 taken along line 8-8 of FIG. 6;
[0029] FIG. 9 is an enlarged perspective view of a representative
repeating unit of the filtering arrangement of FIG. 4 as indicated
at 9;
[0030] FIG. 10 is a top view of the repeating unit of FIG. 9;
[0031] FIG. 11 is a sectional elevation view of the repeating unit
of FIG. 9 taken along line 11-11 of FIG. 10;
[0032] FIG. 12 is a sectional elevation view of the repeating unit
of FIG. 9 taken along line 12-12 of FIG. 10;
[0033] FIG. 13 is a perspective view of another filtering
arrangement in accordance with another example embodiment of the
present invention;
[0034] FIG. 14 is another perspective view of the filtering
arrangement of FIG. 13 shown sectioned along line 14-14 of FIG.
13;
[0035] FIG. 15 is a top view of the filtering arrangement of FIG.
13;
[0036] FIG. 16 is a sectional elevation view of the filtering
arrangement of FIG. 13 taken along line 16-16 of FIG. 15;
[0037] FIG. 17 is an enlarged perspective view of a representative
repeating unit of the filtering arrangement of FIG. 13 as indicated
at 17;
[0038] FIG. 18 is a top view of the repeating unit of FIG. 17;
and
[0039] FIG. 19 is a sectional elevation view of the repeating unit
of FIG. 17 taken along line 19-19 of FIG. 18.
DETAILED DESCRIPTION
[0040] In the following description, like reference characters
designate like or corresponding parts throughout the several views
of the drawings. Also in the following description, it is to be
understood that such terms as "forward", "rearward", "left",
"right", "upwardly", "downwardly", and the like are words of
convenience and are not to be construed as limiting terms.
[0041] Referring now to the drawings, FIG. 1 shows an elevational
view of a prior art fuel assembly, represented in vertically
foreshortened form and being generally designated by the numeral
10, in which embodiments of the present invention may be employed.
The fuel assembly 10 is the type used in a pressurized water
reactor and has a structural skeleton which at its lower end
includes a debris filter bottom nozzle 12 such as described in U.S.
Pat. No. 4,900,507. The bottom nozzle 12 supports the fuel assembly
10 on a lower core support plate 14 in the core region of a reactor
(not shown). In addition to the bottom nozzle 12, the structural
skeleton of the fuel assembly 10 also includes a top nozzle 16 at
its upper end and a number of guide tubes or thimbles 18 which
extend longitudinally between the bottom and top nozzles 12,16 and
at opposite ends are attached thereto.
[0042] The fuel assembly 10 further includes a plurality of
transverse grids 20 axially spaced along and mounted to the guide
thimbles 18 and an organized array of elongated fuel rods 22
transversely spaced and supported by the grids 20. Also, the
assembly 10 has an instrumentation tube 24 located in the center
thereof and extending between and mounted to the bottom and top
nozzles 12,16. With such an arrangement of parts, the fuel assembly
10 forms an integral unit capable of being conveniently handled
without damaging the assembly parts.
[0043] As mentioned above, the fuel rods 22 in the array thereof in
the assembly 10 are held in spaced relationship with one another by
the grids 20 spaced along the fuel assembly length. Each fuel rod
22 includes nuclear fuel pellets 26 and is closed at its opposite
ends by upper and lower end plugs 28,30. The pellets 26 are
maintained in a stack thereof by a plenum spring 32 disposed
between the upper end plug 28 and the top of the pellet stack. The
fuel pellets 26 composed of fissile material are responsible for
creating the reactive power of the reactor. A liquid
moderator/coolant such as water, or water containing boron, is
pumped upwardly through a plurality of flow openings (not numbered)
in the lower core plate 14 to the fuel assembly. The bottom nozzle
12 of the fuel assembly 10 passes the coolant flow along the fuel
rods 22 of the assembly in order to extract heat generated therein
for the production of useful work.
[0044] In order to control the fission process, a number of control
rods 34 are reciprocally movable in the guide thimbles 18 located
at predetermined positions in the fuel assembly 10. Specifically, a
rod cluster control mechanism 36 positioned above the top nozzle 16
supports the control rods 34. The control mechanism has an
internally threaded cylindrical member 37 with a plurality of
radially extending flukes or arms 38. Each arm 38 is interconnected
to a control rod 34 such that the control mechanism 36 is operable
to move the control rods vertically in the guide thimbles 18 to
thereby control the fission process in the fuel assembly 10, all in
a well-known manner.
[0045] As mentioned above, fuel assembly damage due to debris
trapped at or below the lowermost grids 20 has been found to be a
problem. Therefore, to prevent occurrence of such damage, it is
highly desirable to prevent such debris from passing through the
bottom nozzle flow holes and reaching the fuel bundle region.
[0046] Referring now to FIG. 2, the conventional bottom nozzle 12
includes support means in the form of a plurality of corner legs 42
which extend from a generally rectangular skirt portion 44. The
corner legs 42 support the fuel assembly 10 on the lower core plate
14. Bottom nozzle 12 further includes a generally rectangular
planar plate 46 which is suitably attached, such as by welding, to
the skirt portion 44. As seen in FIGS. 2 and 3, the conventional
bottom nozzle 12 has a plate 46 with a plurality of spaced flow
holes 48. The flow holes 48 are sized to "filter out" damaging-size
debris. Such a design is intended to perform such filtering without
appreciably affecting flow or pressure drop through the plate 46
and the fuel assembly 10.
[0047] The diameter of the flow holes 48, as shown in the partial
section view of plate 46 in FIG. 3, does not allow passage of
debris that is of the size typically caught in the lowermost
support grids 20. If the debris is small enough to pass through
these plate flow holes 48, it is likely that it will also pass
through the grids 20 since the diameter of the flow holes 48 is
smaller than the largest cross-sectional dimension of the
unoccupied spaces through a cell of the support grid 20. Such
unoccupied spaces are typically found in adjacent corners formed by
the interleaved straps which compose the grid 20. By ensuring that
the debris is small enough to pass through the grid spaces, the
conventional debris filter bottom nozzle 12 thereby significantly
reduces the potential for debris-induced fuel rod failures.
However, while generally suitable for its intended purpose, the
conventional debris filter bottom nozzle 12 allows for debris with
minimum dimension of 0.200'' and below to pass and still has room
for improvement.
[0048] Embodiments of the present invention generally replace the
plate 46 of the conventional debris filter bottom nozzle 12 of
FIGS. 1-3 with an arrangement that results in a lower pressure drop
as compared to conventional plate 46, while also improving
filtering capability. Additionally, embodiments of the present
invention provide for filtering arrangements which may be tuned in
order to match the pressure drop of an existing fuel assembly
bottom nozzle.
[0049] Having thus described the conventional arrangement in which
embodiments of the present invention improve upon, an example
embodiment of an improved filtering arrangement 100 in accordance
with one example embodiment of the present invention will now be
described in conjunction with FIGS. 4-12 which show various
representative views of filtering arrangement 100 and portions
thereof.
[0050] Referring first to FIGS. 4-8, various views of a
representative portion of an improved filtering arrangement 100 in
accordance with one example embodiment of the present invention are
shown. Arrangement 100 overall is formed as a generally planar
structure which in use is structured to be coupled to a skirt
portion, such as skirt portion 44 (previously discussed in regard
to FIGS. 1-3 and shown schematically in FIGS. 7 and 8), via welding
or other suitable mechanism or mechanisms. Arrangement 100 includes
a bottom surface 102, a top surface 104 disposed parallel to bottom
surface 102, and a plurality of vertical wall portions 106 which
extend a height h.sub.1 between bottom surface 102 and top surface
104. As perhaps best shown in the top view of FIG. 6, wall portions
106 are arranged generally in a generally squared grid-like pattern
which defines a plurality of non-circular passages 108 extending
between bottom surface 102 and top surface 104 through arrangement
100. The areas 110 of the grid-like pattern where wall portions 106
intersect are generally slightly thickened to provide for the
formation of optional flow holes 112 (i.e. venturi or straight hole
with chamfers) (e.g., without limitation, having a diameter in the
range of about 0.020'' to about 0.200'') which extend vertically
through arrangement 100 and are each positioned to be centered
under an end portion of a corresponding fuel rod positioned
thereabove. As used herein, "grid-like" shall be used to refer to
an arrangement of elements which are laid out in a manner which is
similar to a pattern of a grid. Each of venturi flow holes 112 may
include a tapered inlet and outlet so as to minimize undesirable
turbulence and/or pressure drop of fluid passing therethrough. It
is to be appreciated that the general structure of filtering
arrangement 100 thus far described provides for a rigid structure
while generally minimizing the area of the coolant flow potentially
impeded thereby.
[0051] Continuing to refer to FIGS. 4-8, filtering arrangement 100
further includes a plurality of debris filters 120, each positioned
within a respective passage 108 so as to generally span across each
passage 108 between wall portions 106 that define the each
particular passage 108. Each debris filter 120 is formed generally
as a hollow pyramid or hollow cone-like structure (or other
suitable three-dimensional arrangement) which is formed from a
lattice structure 122 that is sized and configured to minimize
resistance in regard to coolant flow through it, and thus minimize
pressure drop, while also prohibiting debris larger than a
predetermined size (e.g., without limitation, in the range of from
about 0.040'' to 0.100'') from passing through a plurality of
apertures 124 defined by lattice structure 122. In example
embodiments of the present concept, lattice structures having a
width (measured in the horizontal direction) in the range of about
0.005'' to about 0.075'' and thickness (measured in the vertical
direction) in the range of about 0.010'' to 0.100'' have been
employed, although lattice structures of other dimensions may be
employed without varying from the scope of the present concept.
[0052] Each debris filter 120 extends a height h.sub.2 upward from
a base 126 thereof, which may generally coincide with bottom
surface 102 or which may be located upward therefrom, to an apex
portion 128, which may be disposed at, or below, top surface 104.
In other words, each debris filter 120 is positioned between bottom
and top surfaces 102 and 104 so as to not protrude beyond either of
surfaces 102 or 104 and thus have a height h.sub.2 less than, or at
most equal to, height h.sub.1 of filtering arrangement 100.
Although illustrated in the example embodiments herein as being of
a "tip up" orientation (i.e., narrowing from bottom to top), it is
to be appreciated that each debris filter may alternatively be
oriented in a "tip down" orientation (i.e., narrowing from the top
down) without varying from the scope of the disclosed concept.
[0053] In example embodiments of the present concept, debris
filters 120 having a height h.sub.2 in the range of about 0.250''
to about 0.600'' have been employed, although other heights may be
employed without varying from the scope of the present concept.
Accordingly, when viewed in the top view of arrangement 100 shown
in FIG. 6, each debris filter 120 (only three of which are
generally labeled in FIG. 6) extends outward in the FIG. (i.e.,
upward from the plane of the page among the surrounding wall
portions 106). As can be appreciated from the top view of FIG. 6,
lattice structures 122 which form each of debris filters 120 are
formed so as to form a squared grid-like pattern when viewed in a
direction parallel to the general flow of coolant through
arrangement 100. In example embodiments of the present concept,
grid dimensions in the range of from about 0.250''.times.0.250'' to
about 1.000''.times.1.000'' have been employed, however other sizes
may be employed without varying from the scope of the present
concept. It is to be appreciated that such grid-like pattern is not
planar, but instead is "distorted" or "stretched" in a
three-dimensional manner so as to not be disposed in a single
plane.
[0054] Enlarged views of a single passage 108, defining wall
portions 106 thereof, and debris filter 120 are shown in FIGS. 9,
10, 11 and 12 in order to assist in demonstrating such example
embodiment.
[0055] Another example embodiment of a filtering arrangement 200 in
accordance with another exemplary embodiment is shown in FIGS.
13-16, and an enlarged repeating unit thereof is shown in FIGS.
17-19. Filtering arrangement 200 is of a similar arrangement as
filtering arrangement 100, and thus similar elements have been
identified using the same numbering as previously discussed, and
thus will not be described again in detail with filtering
arrangement 200.
[0056] In contrast to filtering arrangement 100 which utilized a
single debris filter 120, filtering arrangement 200 includes a
second debris filter 220 positioned above or below, and generally
spaced vertically (typically in a nesting type arrangement) in the
range of from about 0.050'' to about 0.250'' from debris filter
120, thus providing for enhanced debris filtering. In the example
embodiment illustrated in FIGS. 13-19, second debris filter 220 is
of similar shape and structure as debris filter 120 and thus
likewise is formed generally as a hollow pyramid or hollow
cone-like structure (or other suitable three-dimensional
arrangement) formed from a lattice structure 222 that is sized and
configured to minimize resistance in regard to coolant flow through
it, and thus minimize pressure drop, while also prohibiting debris
larger than a predetermined size (e.g., without limitation, in the
range of from about 0.010'' to 0.100'') from passing through a
plurality of apertures 224 defined by lattice structure 222. In
example embodiments of the present concept, lattice structures
having a width (measured in the horizontal direction) in the range
of about 0.005'' to about 0.075'' and thickness (measured in the
vertical direction) in the range of about 0.010'' to 0.100'' have
been employed, although lattice structures of other dimensions may
be employed without varying from the scope of the present
concept.
[0057] Each second debris filter 220 extends a height h.sub.3
upward from a base 226 (FIG. 19) thereof, which is spaced upward
from bottom surface 102, to an apex portion 228, which may be
disposed at, or below, top surface 104. In other words, the
combined double layered structured of debris filter 120 and debris
filter 220 is positioned between bottom and top surfaces 102 and
104 such that neither debris filter 120 or 220 protrudes beyond
either of surfaces 102 or 104. In example embodiments of the
present concept, second debris filters 220 having a height h.sub.3
in the range of about 0.125'' to about 0.600'' have been employed,
although other heights may be employed without varying from the
scope of the present concept. As can be appreciated from the top
view of FIG. 15, and the enlarged top view of FIG. 18, lattice
structures 222 which form each of second debris filters 220 are
likewise formed so as to form a squared grid-like pattern when
viewed in a direction parallel to the general flow of coolant
through arrangement 200. In example embodiments of the present
concept, grid dimensions in the range of from about
0.250''.times.0.250'' to about 1.000''.times.1.000'' have been
employed, however other sizes may be employed without varying from
the scope of the present concept.
[0058] As shown in FIGS. 18 and 19, second debris filter 220 is
offset laterally generally a distance d in both the "x" and "y"
directions such that the grids of each of lattice structures 122
and 222 generally bisect each other. Such offsetting provides for
yet further enhanced debris capturing capability beyond that
provided by simply using second debris filter 220 in conjunction
with first debris filter 120.
[0059] Example embodiments of the invention have been produced via
additive manufacturing processes. Accordingly, some or all of
arrangements 100 or 200 may be formed as a single unitary element.
In an example embodiment, direct metal laser melting has been
employed to form embodiments of the invention from Inconel.RTM.
material. It is to be appreciated, however, that other suitable
methods and/or materials (e.g., without limitation, stainless
steel, titanium) may be employed without varying from the scope of
the invention.
[0060] Accordingly, it is to be appreciated that the invention
presented herein is a completely new and novel design which
incorporates a streamlined flow design which maximizes the flow
area in the main body/support structure of the bottom nozzle while
incorporating debris capturing fine mesh spire features which may
be housed safely within the main body/support structure of the
bottom nozzle and thus generally shielded thereby. Such
arrangements allow for an effective debris capturing feature
without adversely impacting the pressure drop which is primarily
driven by the small flow holes in current bottom nozzle designs.
With the advanced fine mesh spire debris filtering bottom nozzle
design, the additive manufacturing process allows for each of the
desired bottom nozzle design features: debris capture, low pressure
drop, and robust design, to all be integrated into one advanced
bottom nozzle design which could not be easily achieved using
existing conventional manufacturing processes. Thus, the advanced
fine mesh spire debris filtering bottom nozzle design is a
completely new and novel design for use in the nuclear fuel
design.
[0061] 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. 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
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