U.S. patent application number 13/585446 was filed with the patent office on 2016-08-11 for structure of top nozzle for nuclear fuel assembly.
This patent application is currently assigned to KEPCO NUCLEAR FUEL CO., LTD.. The applicant listed for this patent is Ki-Sung Choi, Kyong-Bo Eom, Kyeong-Lak Jeon, II-Kyu Kim, Jin-Sun Kim, Kyu-Tae Kim, Seong-Ki Lee, Shin-Ho Lee, Joon-Kyoo Park, Nam-Gyu PARK, Gyu-Cheol Shin, Jung-Min Suh. Invention is credited to Ki-Sung Choi, Kyong-Bo Eom, Kyeong-Lak Jeon, II-Kyu Kim, Jin-Sun Kim, Kyu-Tae Kim, Seong-Ki Lee, Shin-Ho Lee, Joon-Kyoo Park, Nam-Gyu PARK, Gyu-Cheol Shin, Jung-Min Suh.
Application Number | 20160232992 13/585446 |
Document ID | / |
Family ID | 56567008 |
Filed Date | 2016-08-11 |
United States Patent
Application |
20160232992 |
Kind Code |
A1 |
PARK; Nam-Gyu ; et
al. |
August 11, 2016 |
STRUCTURE OF TOP NOZZLE FOR NUCLEAR FUEL ASSEMBLY
Abstract
Disclosed herein is a joint structure between a top nozzle and a
guide thimble. The joint structure includes an outer guide post, an
inner-extension tube head, an inner-extension tube body, a wedge
and the guide thimble. The outer guide post is provided with an
external thread formed on a lower end thereof. The inner-extension
tube head includes an annular retaining part formed on an upper end
thereof. An internal thread is formed on a medial portion of the
inner-extension tube head. An external thread is formed on each of
upper and lower ends of the inner-extension tube body. A stop
protrusion is provided under a lower end of the wedge. The wedge is
welded to the inner-extension tube body after the top nozzle has
been joined with the guide thimble. A stop protrusion receiving
depression is formed in the guide thimble.
Inventors: |
PARK; Nam-Gyu; (Daejeon,
KR) ; Kim; Kyu-Tae; (Daejeon, KR) ; Suh;
Jung-Min; (Daejeon, KR) ; Lee; Shin-Ho;
(Daejeon, KR) ; Eom; Kyong-Bo; (Daejeon, KR)
; Park; Joon-Kyoo; (Daejeon, KR) ; Kim;
Jin-Sun; (Daejeon, KR) ; Shin; Gyu-Cheol;
(Daejeon, KR) ; Lee; Seong-Ki; (Daejeon, KR)
; Kim; II-Kyu; (Daejeon, KR) ; Choi; Ki-Sung;
(Daejeon, KR) ; Jeon; Kyeong-Lak; (Daejeon,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PARK; Nam-Gyu
Kim; Kyu-Tae
Suh; Jung-Min
Lee; Shin-Ho
Eom; Kyong-Bo
Park; Joon-Kyoo
Kim; Jin-Sun
Shin; Gyu-Cheol
Lee; Seong-Ki
Kim; II-Kyu
Choi; Ki-Sung
Jeon; Kyeong-Lak |
Daejeon
Daejeon
Daejeon
Daejeon
Daejeon
Daejeon
Daejeon
Daejeon
Daejeon
Daejeon
Daejeon
Daejeon |
|
KR
KR
KR
KR
KR
KR
KR
KR
KR
KR
KR
KR |
|
|
Assignee: |
KEPCO NUCLEAR FUEL CO.,
LTD.
Daejeon
KR
|
Family ID: |
56567008 |
Appl. No.: |
13/585446 |
Filed: |
August 14, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12187455 |
Aug 7, 2008 |
|
|
|
13585446 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 30/30 20130101;
G21C 3/3315 20130101; G21C 3/33 20130101; G21C 3/334 20130101; Y02E
30/40 20130101 |
International
Class: |
G21C 3/334 20060101
G21C003/334 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2008 |
KR |
10-2008-0024071 |
Claims
1. A joining structure for joining a top nozzle and a guide
thimble, the joining structure comprising: an outer guide post
having a hollow cylindrical shape and an external thread formed on
an outer circumferential surface of a lower end portion of the
outer guide post; an inner-extension tube head comprising an
annular retaining part formed on an upper end portion of the
inner-extension tube head and having an outer diameter greater than
that of other portion of the inner extension tube head, and an
internal thread formed on an inner circumferential surface of a
medial portion of the inner-extension tube head; an inner-extension
tube body having a hollow cylindrical shape and including a first
external thread formed on an outer circumferential surface of an
upper portion of the inner-extension tube body, and a second
external thread formed on the outer circumferential surface of a
lower end portion of the inner-extension tube body; and a wedge
having a hollow cylindrical shape and including at least one stop
protrusion formed on a bottom surface of the wedge, the stop
protrusion extending a predetermined length in an axial direction
of the wedge, the wedge being separated from the inner-extension
tube body and the outer guide post, wherein the inner-extension
tube body is coaxially inserted into the outer guide post, the
inner-extension tube head is mounted on a top of the outer guide
post, the first external thread of the inner-extension tube body is
engaged with the internal thread of the inner-extension tube head,
the second external thread of the inner-extension tube body is
engaged with an internal thread of the guide thimble, and the wedge
is mounted on the outer circumferential surface of the
inner-extension tube body and disposed between a bottom end of the
outer guide post and the guide thimble.
2. The joining structure as set forth in claim 1, wherein the
inner-extension tube body further includes at least one
rotation-preventing surface formed on the outer circumferential
surface of the inner-extension tube body adjacently with the second
external thread, the rotation-preventing surface being formed by
cutting out a portion of the inner-extension tube body in a
circumferential direction to form a planar shape.
3. The joining structure as set forth in claim 1, wherein the
inner-extension tube head further includes a threaded-portion
introducing part provided on a lower portion of the inner-extension
tube head, the threaded-portion introducing part having an inner
diameter greater than inner diameters of other portions of the
inner-extension tube head, and wherein the inner-extension tube
body further includes a threaded-portion guide part provided on an
upper end portion of the inner-extension tube body, the
threaded-portion guide part having an outer diameter less than
outer diameters of other portions of the inner-extension tube.
4. The joining structure as set forth in claim 2, wherein the
inner-extension tube head further includes a threaded-portion
introducing part provided on a lower portion of the inner-extension
tube head, the threaded-portion introducing part having an inner
diameter greater than inner diameters of other portions of the
inner-extension tube head, and wherein the inner-extension tube
body further includes a threaded-portion guide part provided on an
upper end portion of the inner-extension tube body, the
threaded-portion guide part having an outer diameter less than
outer diameters of other portions of the inner-extension tube.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a Continuation-in-part application of U.S.
application Ser. No. 12/187,455, filed on Aug. 7, 2008, which
claims the benefit of priority from Korean Patent Application No.
10-2008-0024071, filed on Mar. 14, 2008, the disclosures of both of
which are expressly incorporated by reference herein in their
entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to joint structures
between top nozzles and guide thimbles of nuclear fuel assemblies
and, more particularly, to a joint structure between a top nozzle
and a guide thimble which is configured such that an
inner-extension tube is prevented from undesirably rotating when
the top nozzle is separated from the nuclear fuel assembly, and
assembly and disassembly between the top nozzle and the guide
thimble is facilitated.
[0004] 2. Description of the Related Art
[0005] A nuclear reactor refers to a device that is designed to
exert artificial control over the chain reaction of the nuclear
fission of fissile materials, thereby achieving a variety of
purposes such as the generation of heat, the production of
radioisotopes and plutonium, the formation of radiation fields, or
the like.
[0006] Generally, enriched uranium that is obtained by raising the
ratio of uranium-235 to a range between 2% and 5% is used in a
light water nuclear reactor. The uranium is molded into a
cylindrical pellet that weighs 5 g and processed into nuclear fuel
that is used in a nuclear reactor. Numerous pellets are embedded
into a cladding tube made of Zircaloy which is in a vacuum state.
Thereafter, a spring and helium gas are put into the tube, and then
a top end closure stopper is welded thereon, thereby making a fuel
rod. A plurality of fuel rods constitutes a nuclear fuel assembly
and is burned in a nuclear reactor by nuclear reaction.
[0007] FIG. 1 is a schematic view showing a general nuclear fuel
assembly.
[0008] Referring to FIG. 1, the nuclear fuel assembly includes a
skeleton and a plurality of fuel rods 1. The skeleton includes a
top nozzle 4, a bottom nozzle 5, a plurality of spacer grids 2, a
plurality of guide thimbles 3 and a instrument tube 6. The fuel
rods 1 are inserted longitudinally into an organized array by the
spacer grids 2 in such a manner as to be supported by means of
springs (not shown) and dimples (not shown) which are formed in the
spacer grids 2. In order to prevent the formation of scratches on
the fuel rods 1 and damage to the springs upon assembling the
nuclear fuel assembly, lacquer is applied to the surfaces of the
fuel rods 1 before the fuel rods 1 are inserted longitudinally into
the skeleton of the nuclear fuel assembly. Subsequently, the top
and bottom nozzles are secured to the opposite ends of the nuclear
fuel assembly, thereby finishing the procedure of assembly of the
nuclear fuel assembly. After the lacquer is removed, the following
items of the assembled nuclear fuel assembly are tested: the
distance between the fuel rods, distortion, dimensions including
the length, etc., thus completing the process of manufacturing the
nuclear fuel assembly.
[0009] As shown in FIG. 2, the top nozzle 4 includes a hold-down
plate 8, hold-down springs 43, inner-extension tubes 45, outer
guide posts 44, and a flow plate 7.
[0010] Referring to FIGS. 1 and 2, the inner-extension tubes 45 of
the top nozzle 4 are connected to the respective guide thimbles 3
so that the nuclear fuel assembly can be firmly fixed in the
reactor and the structural stability of the nuclear fuel can be
ensured during the burn-up of the nuclear fuel.
[0011] The top nozzle 4 and the guide thimbles 3 are joined to each
other in such a way as to be removably connected to each other,
thereby ensuring a path along which the fuel rods 1 can be drawn
out when disassembling the top nozzle 4. Disassembly of the top
nozzle 4 from the guide thimbles 3 is carried out in a storage
tank. A worker must remotely perform the disassembly work to
minimize the harm caused by radiation. Accordingly, the joint
structure between the top nozzle 4 and the guide thimbles 3 must be
designed such that assembly or disassembly between them can be
conducted remotely.
[0012] FIGS. 2 and 3 illustrate a typical method of joining the
guide thimbles 3 with the top nozzle 4. Referring to the drawings,
the method of joining the guide thimbles 3 and the top nozzle 4
will be described. As shown in FIG. 2, an external thread is formed
on a lower end 451 of each inner-extension tube 45. As shown in
FIG. 3, an internal thread is formed on an inner surface of a
threaded portion 31 of each guide thimble 3. The top nozzle 4 and
the guide thimbles 3 are joined with each other by
thread-coupling.
[0013] An external thread is formed on a lower end of each outer
guide post 44. The outer guide posts 44 are threadedly coupled to
the flow plate 7. The threaded lower end of each outer guide post
44 is partially welded to the flow plate 7 to prevent the outer
guide post from rotating. Furthermore, in order to prevent each
inner-extension tube 45 from becoming loose, a head of the
inner-extension tube 45 is partially crimped in a radial direction
in such a way as to be put in contact with the outer guide post 44.
Moreover, the inner-extension tube 45 can be separated from the
outer guide post 44 only when torque of more than a specific
strength is applied to the head.
[0014] However, in the state where the inner-extension tube 45 is
joined with the outer guide post 44, when the inner-extension tube
45 of the top nozzle 4 is rotated to be separated from the outer
guide post 44, since the distance between an outer surface of the
inner-extension tube 45 and an inner surface of the outer guide
post 44 is too short, it is difficult to rotate the inner-extension
tube 45 along the threads if concentricity is not congruous or if
foreign substances have gotten stuck between the outer face and the
inner face. That is, due to frictional heat generated by the
contact surface, the inner-extension tubes 45 and the outer guide
posts 44, which are made of stainless steel, are fused together by
a cold welding effect, and hence, loosening does not occur.
[0015] To solve the above-mentioned problems, there have been
disclosed U.S. Pat. No. 4,702,883 entitled "Reconstitutable fuel
assembly having removable upper stops on guide thimbles", and U.S.
Pat. No. 4,687,630 entitled "Top nozzle and guide thimble joint
structure in a nuclear fuel assembly".
[0016] In the prior arts, heads of outer guide posts are removed
without any inner-extension tube, and processed to have threads so
as to minimize the contact surface when the outer guide posts are
removed. That is, thread-coupling portions are not only formed on
an external threaded portion of a lower portion of each outer guide
post and on an external threaded portion of a lower portion of each
guide thimble, but also an additional thread-coupling portion is
provided on an upper portion of the outer guide post.
[0017] Accordingly, when the head of each outer guide post is
rotated to remove the top nozzle, since the outer guide post and
the head thereof are threadedly-coupled with each other, the
thread-coupling between the outer guide post and the guide thimble
may become loosened. Hence, in order to prevent the lower end of
the outer guide post from becoming loosened, the outer guide post
is equipped with a wedge device; however, this has the problem of
the assembling and disassembling processes being complicated.
[0018] Another conventional technique was proposed in Korean Patent
Application No. 10-2007-0086066, which was filed by the applicant
of the present invention and entitled "Joint structure between top
nozzle and guide thimble for nuclear fuel assembly". This technique
is provided with a structure for preventing an inner-extension tube
from becoming loose when the top nozzle is disassembled. However, a
threaded portion is disposed on an end of each of an
inner-extension tube body and the inner-extension tube head, thus
making it difficult to assemble them remotely. In other words,
because the threaded portions must be coupled to each other without
using an introduction portion that can serve as a guide, if two
elements are not coaxially aligned with each other, the
thread-coupling between the two elements may fail.
SUMMARY OF THE INVENTION
[0019] Accordingly, the present invention has been made keeping in
mind the above problems occurring in the prior art, and an object
of the present invention is to provide a joint structure between a
top nozzle and a guide thimble which is configured such that when
an inner-extension tube head that has been threadedly coupled to an
inner-extension tube body is removed from the inner-extension tube
body to disassemble the top nozzle, the inner-extension tube body
can be prevented from being undesirably removed from the guide
thimble, and in which the assembly or disassembly of the top nozzle
of the nuclear fuel assembly which is carried out remotely to
prevent exposure to radioactivity can be facilitated.
[0020] In order to accomplish the above object, the present
invention provides a joint structure between a top nozzle provided
on a flow plate and a guide thimble disposed under the flow plate,
the joint structure including an outer guide post, an
inner-extension tube head, an inner-extension tube body, a wedge
and the guide thimble.
[0021] The outer guide post has a hollow cylindrical shape. An
external thread is formed on a circumferential outer surface of a
lower end of the outer guide post.
[0022] The inner-extension tube head includes an annular retaining
part formed on an upper end of the inner-extension tube head by
expanding an outer diameter thereof. An internal thread is formed
on a circumferential inner surface of a medial portion of the
inner-extension tube head.
[0023] The inner-extension tube body is provided with an external
thread formed on a circumferential outer surface of each of upper
and lower ends of the inner-extension tube body.
[0024] The wedge has a hollow cylindrical shape. At least one stop
protrusion is provided under a lower end of the wedge. The stop
protrusion extends a predetermined length in an axial direction of
the wedge. The wedge is welded to the inner-extension tube body
after the top nozzle has been joined with the guide thimble.
[0025] The guide thimble has a stop protrusion receiving depression
formed in an upper end of the guide thimble. The stop protrusion
receiving depression corresponds to a shape, number and position of
the stop protrusion so that the stop protrusion is seated into the
stop protrusion receiving depression.
[0026] At least one rotation-preventing surface may be formed on
the inner-extension tube body above the external thread formed on
the lower end of the inner-extension tube body. The
rotation-preventing surface may be formed by cutting out a portion
of the inner-extension tube body in a circumferential direction to
form a planar shape. A rotation-preventing portion may be formed on
a circumferential inner surface of a lower end of a flow hole of
the flow plate. The rotation-preventing portion may have a space
corresponding to a cross-sectional shape of the rotation-preventing
surface.
[0027] A threaded-portion introducing part may be provided on a
lower end of the inner-extension tube head. The threaded-portion
introducing part may have an inner diameter greater than inner
diameters of other portions of the inner-extension tube head. A
threaded-portion guide part may be provided on an upper end of the
inner-extension tube body. The threaded-portion guide part may have
an outer diameter less than outer diameters of other portions of
the inner-extension tube.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The above and other objects, features and advantages of the
present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0029] FIG. 1 is a schematic view of a conventional nuclear fuel
assembly;
[0030] FIG. 2 is a partially sectional view of a conventional top
nozzle;
[0031] FIG. 3 is a sectional view of a conventional guide
thimble;
[0032] FIG. 4 is a perspective sectional view of an outer guide
post according to the present invention;
[0033] FIG. 5 is a sectional view of an inner-extension tube
according to the present invention;
[0034] FIG. 6 is a perspective view illustrating a wedge and a
guide thimble flange according to the present invention;
[0035] FIG. 7 is a perspective sectional view showing the joining
of a top nozzle to a guide thimble according to the present
invention;
[0036] FIG. 8 is a perspective sectional view showing a portion of
a flow plate according to the present invention; and
[0037] FIG. 9 is an upside-down perspective view showing a
rotation-preventing surface of the inner-extension tube and a flow
plate corresponding thereto, according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] Hereinafter, a preferred embodiment of the present invention
will be described in detail with reference to the attached
drawings. Unless otherwise specifically stated, terms such as
`upper`, `lower`, `left` and `right` to indicate directions will be
used based on the orientation shown in the drawings.
[0039] The embodiment of the present invention basically includes
an outer guide post 441, an inner-extension tube 450, a flow plate
700 and a guide thimble flange 300. The detailed description will
be omitted of a hold-down plate and a hold-down spring, which are
elements of a top nozzle but are not directly related to the
structure that joins the outer guide post 441 and the
inner-extension tube 450 to the guide thimble flange 300 through
the flow plate 700.
[0040] First, the outer guide post 441 will be described with
reference to FIG. 4.
[0041] The shape of the outer guide post 441 is that of a hollow
cylinder that has open upper and lower ends. An external thread 442
is formed on a circumferential outer surface of a lower end of the
outer guide post 441 and is used to couple the outer guide post 441
to the flow plate 700.
[0042] A large-diameter part, the diameter of which is larger than
other portions of the outer guide post 441, is provided on an upper
end of the outer guide post 441. An annular retaining part 444 is
formed by this difference in diameter so that, as shown in FIG. 2,
the hold-down plate 8 is stopped by the annular retaining part 444,
thereby restricting extension of the spring 43.
[0043] Crimping grooves 445 are formed in a circumferential outer
surface of the upper end of the outer guide post 441 at positions
spaced apart from each other along the circumferential direction at
regular intervals. Each crimping groove 445 is a groove which
extends for a predetermined length. The detailed use of the
crimping grooves 445 will be explained in detailed in the following
description of the inner-extension tube 450.
[0044] The inner-extension tube 450 will be described with
reference to FIG. 5. The inner-extension tube 450 includes an
inner-extension tube body 451 and an inner-extension tube head
456.
[0045] The inner-extension tube head 456 has a hollow cylindrical
shape and is coupled to an upper end of the inner-extension tube
body 451.
[0046] An annular retaining part 459 is formed on an upper end of
the inner-extension tube head 456. The diameter of the annular
retaining part 459 is larger than other portions of the
inner-extension tube head 456 so that when the inner-extension tube
head 456 is coupled to the inner-extension tube body 451 and then
inserted into the outer guide post 441, the inner-extension tube
head 456 can be prevented from being totally inserted
thereinto.
[0047] An internal thread 458 is formed on a circumferential inner
surface of a medial portion of the inner-extension tube head 456.
The internal thread 458 engages with an external thread 452 which
is formed on an upper end of the inner-extension tube body 451
which will be explained later herein.
[0048] A threaded-portion introducing part 457 is formed in a lower
end of the inner-extension tube head 456. The inner diameter of the
threaded-portion introducing part 457 is greater than other
portions of the inner-extension tube head 456 so that when the
inner-extension tube head 456 is joined with the inner-extension
tube body 451, the upper end of the inner-extension tube body 451
can be more easily inserted into the inner-extension tube head
456.
[0049] Furthermore, a crimping film 460 is provided under an outer
edge of the annular retaining part 459 provided on the
inner-extension tube head 456. The crimping film 460 is spaced
apart from the body of the inner-extension tube head 456 by a
predetermined distance so that a space is defined therebetween.
When the inner-extension tube 450 is fitted into the outer guide
post 441, a predetermined portion of the crimping film 460 is
crimped into the crimping groove 445 (refer to FIG. 4), thus
preventing the thread-coupling between the elements from becoming
loose.
[0050] The inner-extension tube body 451 is a hollow cylinder which
is longer than the outer guide post 441 and is open on upper and
lower ends thereof in the same manner as that of the outer guide
post 441. The inner-extension tube body 451 is joined with the
inner-extension tube head 456 and inserted into the outer guide
post 441. Hence, the outer diameter of the inner-extension tube
body 451 must be equal to or less than the inner diameter of the
outer guide post 441.
[0051] A threaded-portion guide part 453 is provided on the upper
end of the inner-extension tube body 451. The threaded-portion
guide part 453 guides the insertion of the inner-extension tube
body 451 into the threaded-portion introducing part 457 provided in
the inner-extension tube head 456, so that a process of engaging
the external thread 452 formed on the inner-extension tube body 451
with the internal thread 458 of the inner-extension tube head 456
can be easily carried out remotely.
[0052] A lower external thread 454 is formed on a circumferential
outer surface of a lower end of the inner-extension tube body 451.
The lower external thread 454 is used to join the inner-extension
tube body 451 with the guide thimble flange 300 which will be
explained later herein. Here, when the inner-extension tube body
451 that has been joined with the inner-extension tube head 456 is
inserted into the outer guide post 441, the lower external thread
454 protrudes downwards from the lower end of the outer guide post
441 to allow it to engage with the guide thimble flange 300.
[0053] As shown in an enlarged circle portion of FIG. 5, a
rotation-preventing surface 455 is formed on the lower portion of
the inner-extension tube body 451. The rotation-preventing surface
455 is a planar surface which is formed in the circumferential
direction by cutting out a portion of an annular flange-shaped
part. The rotation-preventing surface 455 increases the area of
contact between it and a tool so that rotational force can be
reliably transmitted from the tool to the inner-extension tube body
451. The rotation-preventing surface 455, along with a
rotation-preventing portion 711 (refer to FIG. 8), functions to
prevent the inner-extension tube 450 from undesirably rotating.
This will be explained in more detail in the description of the
construction of the flow plate 700.
[0054] Hereinafter, the guide thimble flange will be described with
reference to FIG. 6.
[0055] The guide thimble flange of the embodiment of the present
invention is provided with a wedge 200.
[0056] The wedge 200 is a hollow cylinder which is short in the
axial direction. A stop protrusion 201 is provided under a lower
end of the wedge 200. The stop protrusion 201 is formed in such a
way that a portion protrudes from the lower end of the wedge 200
such that it is longer than the other portion of the wedge 200. The
number of stop protrusions 201 may be more than one. Given the ease
of manufacturing or durability, it is preferable that one or two
stop protrusions 201 be provided. The material of the wedge 200 is
the same as that of the inner-extension tube body 451 so that the
wedge 200 can be easily welded to the inner-extension tube body 451
after the guide thimble flange 300 has been joined with the
inner-extension tube body 451. After the wedge 200 has been welded
to the inner-extension tube body 451, the wedge 200 can fulfill its
function of preventing the inner-extension tube body 451 from
undesirably rotating when the inner-extension tube head 456 is
rotated in a direction opposite to the direction in which the
thread is tightened and becomes loosened from the inner-extension
tube body 451.
[0057] Furthermore, a tool contact portion 301 is formed in a
circumferential outer surface of the guide thimble flange 300. The
tool contact portion 301 increases its ability to make contact with
a tool so that the rotational force of the tool can be efficiently
transmitted to the guide thimble flange 300 without slipping with
respect to the guide thimble flange 300.
[0058] The structure of the flow plate of the embodiment of the
present invention is almost the same as that of the conventional
flow plate. However, unlike the conventional flow plate, as stated
above, the flow plate of the present invention includes the
rotation-preventing portion 711 which has a cross-sectional shape
corresponding to that of the rotation-preventing surface 455, so
that when the inner-extension tube body 451 is joined with the flow
plate 700, the rotation-preventing surface 455 is put into close
contact with the rotation-preventing portion 711, thus preventing
the inner-extension tube 450 from undesirably rotating. The present
invention is not limited to this rotation-preventing structure.
FIG. 9 illustrates another example of the rotation-preventing
structure. As show in FIG. 9, the number of rotation-preventing
surfaces 455a can be determined arbitrarily. Also, a
rotation-preventing portion 711a has an inner surface corresponding
to the shape of the rotation-preventing surfaces 455a.
[0059] Hereinafter, the operation and effect of the embodiment of
the present invention will be described with reference to FIG. 7.
FIG. 7 illustrates the joint structure among the outer guide post
441, the inner-extension tube body 451, the inner-extension tube
head 456, the flow plate 700 and the guide thimble flange 300.
[0060] First, a process of assembling the embodiment of the present
invention will be explained.
[0061] The outer guide post 441 is joined with the hold-down spring
(not shown) and the flow plate 700. The wedge 200 is disposed
between the inner-extension tube body 451 and the guide thimble
flange 300, and then the guide thimble flange 300 is threadedly
coupled to the inner-extension tube body 451. Subsequently, the
wedge 200 is welded to the inner-extension tube body 451. The
inner-extension tube body 451, which has been joined with the guide
thimble flange 300 and to which the wedge 200 is welded, is
inserted into the outer guide post 441. Thereafter, the
inner-extension tube head 456 is coupled to the inner-extension
tube body 451, thus completing the assembly.
[0062] A process of disassembling the joint structure of the
present invention is conducted in the reverse order of the
above-mentioned assembly.
[0063] First, the inner-extension tube head 456 is rotated and
removed from the inner-extension tube body 451. Subsequently, the
integrated top nozzle, which includes the outer guide post 441, the
flow plate 700, the hold-down spring (not shown) and the hold-down
plate (not shown), is separated from the nuclear fuel assembly.
[0064] In the disassembly process, in detail, when the
inner-extension tube head 456 is separated from the inner-extension
tube body 451, there is a likelihood of the lower thread 454 of the
inner-extension tube body 451 becoming undesirably loosened from
the internal thread 310 of the guide thimble. However, in the
present invention, because the stop protrusion 201 provided on the
wedge 200 which is welded to the inner-extension tube body 451 is
blocked in a stop protrusion receiving depression 302 formed in the
upper end of the guide thimble flange 300, the inner-extension tube
body 451 can be prevented from becoming loosened from the guide
thimble flange 300.
[0065] As described above, in the present invention, a threaded
portion guide is formed in each of an inner-extension tube head and
an inner-extension tube body, thus making it easy to carry out the
assembly or disassembly remotely.
[0066] Furthermore, in the present invention, a wedge is provided
between an inner-extension tube of a top nozzle and a guide
thimble, so that when the integrated top nozzle is separated from
the guide thimble, rotation of an inner-extension tube head can be
prevented from causing an inner-extension tube to become loosened
from the guide thimble.
[0067] Moreover, an area of a contact portion between elements that
rotate can be minimized. The assembly or disassembly of the top
nozzle can be facilitated, thus reducing the time required to
assemble or disassemble it.
[0068] Although the preferred embodiment of the present invention
has been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions of the joint structure between the top nozzle and the
guide thimble are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
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