U.S. patent application number 10/680162 was filed with the patent office on 2004-06-03 for manufacturing method and device of control rods for nuclear reactors.
Invention is credited to Araya, Masashirou, Kimura, Seiichiro, Suenaga, Toshihiro, Tamura, Masataka, Tongu, Yuichi, Yamada, Yuji.
Application Number | 20040105519 10/680162 |
Document ID | / |
Family ID | 26411080 |
Filed Date | 2004-06-03 |
United States Patent
Application |
20040105519 |
Kind Code |
A1 |
Yamada, Yuji ; et
al. |
June 3, 2004 |
Manufacturing method and device of control rods for nuclear
reactors
Abstract
A method for manufacturing a control rod of a nuclear reactor,
the control rod comprising a blade including neutron absorbers and
a sheath, a tie rod for fixing the blade, a handle and a lower
blade fixed to the tie rod and the blade. The method comprises a
first step for cutting weep holes for water to cool the neutron
absorbers in the sheath and cutting a periphery of the sheath, a
second step for bending the sheath cut in the first step to a
C-shape, a third step for inserting the neutron absorbers in a bent
portion of the sheath formed by bending in the second step, a
fourth step for successively welding the blade to the tie rod, the
blade to the handle and the blade to the lower blade, and a fifth
step for finishing portions welded in the fourth step.
Inventors: |
Yamada, Yuji; (Ayase-shi,
JP) ; Tamura, Masataka; (Yokohama-shi, JP) ;
Kimura, Seiichiro; (Inagi-shi, JP) ; Suenaga,
Toshihiro; (Yokohama-shi, JP) ; Araya,
Masashirou; (Yokohama-shi, JP) ; Tongu, Yuichi;
(Yokohama-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
26411080 |
Appl. No.: |
10/680162 |
Filed: |
October 8, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10680162 |
Oct 8, 2003 |
|
|
|
09525941 |
Mar 15, 2000 |
|
|
|
6647082 |
|
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Current U.S.
Class: |
376/260 |
Current CPC
Class: |
Y02E 30/39 20130101;
G21C 7/113 20130101; G21C 21/18 20130101; Y02E 30/30 20130101 |
Class at
Publication: |
376/260 |
International
Class: |
G21C 019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 16, 1999 |
JP |
11-069908 |
Feb 28, 2000 |
JP |
2000-051799 |
Claims
What is claimed is:
1. A method for manufacturing a control rod of a nuclear reactor,
the control rod comprising a blade including neutron absorbers and
sheathes, a tie rod for fixing the blade, a handle and a lower
blade fixed to the tie rod and the blade, said method comprising: a
first step for cutting weep holes for water to cool the neutron
absorbers in the sheath and cutting a periphery of the sheath; a
second step for bending the sheath cut in the first step to a
C-shape; a third step for inserting the neutron absorbers in a bent
portion of the sheath formed by bending in the second step; a
fourth step for successively welding the blade to the tie rod, the
blade to the handle and the blade to the lower blade; and a fifth
step for finishing portions welded in the fourth step.
2. A method for manufacturing a control rod of a nuclear reactor
according to claim 1, wherein in the fourth step for successively
welding the blade to the tie rod, the blade to the handle and the
blade to the lower blade, one of a YAG laser beam and a CO.sub.2
laser beam is irradiated through an optical system on one of a
position located immediately above a bevel and a position deviated
in parallel from the bevel within a range of 2 mm.
3. A method for manufacturing a control rod of a nuclear reactor
according to claim 2, wherein when one of a YAG laser beam and a
CO.sub.2 laser beam is irradiated through an optical system on one
of a position located immediately above a bevel and a position
deviated in parallel from the bevel within a range of 2 mm, the
laser beam is irradiated several times so as to lap over one
another, shifted within a range of 0.1 to 2.0 mm from one of a
first pass and a first pass target position.
4. A method for manufacturing a control rod of a nuclear reactor
according to claim 2, wherein when one of a YAG laser beam and a
CO.sub.2 laser beam is irradiated through an optical system on one
of a position located immediately above a bevel and a position
deviated in parallel from the bevel within a range of 2 mm, the
laser beam is irradiated while traveling forward with circular
motion in a diameter within 2 mm.
5. A method for manufacturing a control rod of a nuclear reactor
according to claim 2, wherein when one of a YAG laser beam and a
CO.sub.2 laser beam is irradiated through an optical system on one
of a position located immediately above a bevel and a position
deviated in parallel from the bevel within a range of 2 mm, a prism
is inserted before a condenser lens contained in the optical
system, and the laser beam is irradiated on the prism while the
prism is rotating about an axis of the laser beam, so that a focus
position of the laser beam is rotating relative to the condenser
lens.
6. A method for manufacturing a control rod of a nuclear reactor
according to claim 1, wherein in the fourth step for successively
welding the blade to the tie rod, the blade to the handle and the
blade to the lower blade, TIG welding is performed on one of a
position located immediately above a bevel and a position deviated
in parallel from the bevel within a range of 3 mm.
7. A method for manufacturing a control rod of a nuclear reactor
according to claim 1, wherein the first step for cutting weep holes
and a periphery of the sheath is carried out by laser cutting with
high-pressure nitrogen gas.
8. A method for manufacturing a control rod of a nuclear reactor
according to claim 1, wherein the third step, raggedness of end
faces of the sheath which are connected to the tie rod is aligned
by laser cutting with high-pressure nitrogen gas.
9. A method for manufacturing a control rod of a nuclear reactor
according to claim 1, wherein in the third step, raggedness of end
faces of the sheath which are connected to the tie rod is aligned
by shear cutting.
10. A method for manufacturing a control rod of a nuclear reactor
according to claim 1, wherein in the fourth step for welding the
blade to the tie rod, the blade to the handle or the blade to the
lower blade, two slits are provided in one of the tie rod, the
handle and the lower blade, projections of the blade is inserted in
the slits, and the laser beam is irradiated on one of a boundary
between the blade and the tie rod and a boundary between the blade
and the lower blade.
11. An apparatus for manufacturing a control rod of a nuclear
reactor, the control rod comprising a blade including neutron
absorbers inserted in a recess portion of a sheath formed by
bending, a tie rod for fixing the blade, a handle fixed to the tie
rod and an upper end of the blade, and a lower blade fixed to the
tie rod and a lower end of the blade, said apparatus comprising a
welding apparatus for welding the blade to the tie rod, the blade
to the handle and the blade to the lower blade, said welding
apparatus comprising: a work head on which an image pickup
apparatus is mounted; a moving apparatus for moving the work head
to a bevel position as designed in each of welding portions; an
image processing apparatus for processing an image signal picked up
by the image pickup means; a detecting apparatus for detecting an
actual bevel position based on image data processed by the image
processing apparatus; arithmetic processing apparatuses for
comparing the actual bevel position detected by the detecting
apparatus with a bevel position as designed, and calculating
deviation of the work head from the bevel position; a control
apparatus for providing the moving apparatus with a control command
to move the work head by a distance corresponding to an amount of
the deviation of the work head calculated by the arithmetic
processing apparatus plus an amount of an offset of the work head
and the image pickup apparatus; and an apparatus for starting
welding after completion of movement of the work head.
12. An apparatus for manufacturing a control rod of a nuclear
reactor, the control rod comprising a blade including neutron
absorbers inserted in a recess portion of a sheath formed by
bending, a tie rod for fixing the blade, a handle fixed to the tie
rod and an upper end of the blade, and a lower blade fixed to the
tie rod and a lower end of the blade, said apparatus comprising a
welding apparatus for welding the blade to the tie rod, the blade
to the handle and the blade to the lower blade, said welding
apparatus comprising a fixing jig for fixing the blade by chillers
worked so as to be externally accessible at a welding bevel, said
fixing jig including bulk or two metal plates containing a cooling
mechanism therein, and a space between the metal plates in which
the blade including the neutron absorbers and the sheath is
inserted.
13. An apparatus for manufacturing a control rod of a nuclear
reactor, the control rod comprising a blade including neutron
absorbers and a sheath, a tie rod for fixing the blade, a handle
and a lower blade fixed to the tie rod and the blade, said
apparatus comprising: a work table on which objects to be welded
constituting the control rod are set and welding is carried out; a
laser oscillator for outputting one of a YAG laser beam and a
CO.sub.2 laser beam; a work head comprising an optical system for
transmitting the laser beam oscillated by the laser oscillator and
converging it to the objects to be welded by a condenser lens; an
image pickup apparatus, mounted on the work head, for picking up
images of a portion near a bevel of the objects to be welded; an
image processing apparatus for detecting a bevel position from the
image picked up by the image pickup apparatus; an arithmetic
processing apparatus for comparing the bevel position obtained by
the image processing apparatus with a bevel position as designed,
and calculating deviation therebetween; a servo motor for moving
one of the work head and the work table by a distance corresponding
to an amount of the deviation of the bevel position calculated by
the arithmetic processing apparatus plus an amount of an offset of
the work head and the image pickup apparatus; and a control
apparatus for driving and controlling the servo motor, said
apparatus comprising at least two work heads and two work tables
and a movable mirror between the laser oscillator and the work
heads.
14. An apparatus for manufacturing a control rod of a nuclear
reactor, the control rod comprising a blade including neutron
absorbers and a sheath, a tie rod for fixing the blade, a handle
and a lower blade fixed to the tie rod and the blade, said
apparatus comprising: a work table on which objects to be welded
constituting the control rod are set and welding is carried out; a
TIG welding torch; an image pickup apparatus, mounted on the work
head, for picking up images of a portion near a bevel of the
objects to be welded; an image processing apparatus for detecting a
bevel position from the image picked up by the image pickup
apparatus; an arithmetic processing apparatus for comparing the
bevel position obtained by the image processing apparatus with a
bevel position as designed, and calculating deviation therebetween;
a servo motor for moving one of the TIG welding torch and the work
table by a distance corresponding to an amount of the deviation of
the bevel position calculated by the arithmetic processing
apparatus plus an amount of an offset of the welding torch and the
image pickup apparatus; and a control apparatus for driving and
controlling the servo motor, said apparatus comprising at least two
TIG welding torches and two work tables, which simultaneously or
alternately perform welding.
Description
BACKGROUND OF THE INVENTION
[0001] This application is based on Japanese Patent Application No.
11-69908 filed Mar. 16, 1999, and No. 2000-51779 filed Feb. 28,
2000, the contents of which are cited herein by reference.
[0002] The present invention relates to a method and apparatus for
manufacturing a control rod for a nuclear reactor, the parts of the
control rod are adhered to one another by laser welding or TIG
welding.
[0003] FIG. 1 schematically shows an example of the internal
structure of a reactor pressure vessel (RPV) of a boiling water
reactor (BWR).
[0004] Referring to FIG. 1, water as a coolant is heated and
boiled, while flowing upward from a bottom portion of a reactor
core through a gap between fuel rods 1 containing fuel. Power of
the reactor varies in accordance with withdrawal or insertion of a
control rod 2. The reactivity is increased when the control rod 2
is withdrawn. The reactivity is decreased when the control rod 2 is
inserted.
[0005] An example of the structure of the control rod 2 will be
described with reference to a schematic perspective view of FIG.
2A. As shown in FIG. 2A, the control rod 2 mainly comprises blades
3, a handle 4 attached to the upper ends of the blades 3 and lower
blades 5 attached to the lower ends of the blades 3. More
specifically, the blade 3 comprises neutron absorbers 6, a sheath 7
housing them and insertion pieces 8 inserted for the purpose of
securing a portion to allow water to flow between the neutron
absorbers 6 in the sheath 7.
[0006] Four of the blades 3 make a set, and the adhesion ends of
the respective blades are connected to a tie rod so as to form a
cross shape as a whole.
[0007] Conventionally, the control rod 2 of the reactor is
manufactured by the following method. FIGS. 3A and 3B show examples
of processes for manufacturing the control rod 2.
[0008] First, a process for manufacturing the control rod 2 using
boron carbide (B.sub.4C) as the neutron absorbers 6 will be
described with reference to the flowchart of FIG. 3A.
[0009] In this case, first, the periphery of the sheath 7 is cut
(S1), and weep holes are formed by cutting (S2). Thereafter, the
sheath 7 is bent like a C-shape (S3). After the ends of the
C-shaped sheath 7 are aligned, a tube containing boron carbide as
the neutron absorbers 6 is inserted in the sheath 7 (S4). Thus, the
blade 3 is assembled.
[0010] The blades 3 are fixed to the tie rod 9, with the result
that the control rod 2 is assembled (S5). Thereafter, welding of
the tie rod 9 (S6) and welding of the handles 4 and the lower
blades 5 (S7) are carried out. Finally, the control rod 2 is
smoothed by finishing with a wire brush or the like (S8).
[0011] No insertion piece 8 is employed in the control rod 2 which
uses B.sub.4C as the neutron absorbers 6.
[0012] In the above case, B.sub.4C is used as the neutron absorbers
6. Next, the control rod 2 using hafnium (Hf) as the neutron
absorbers 6 will be described.
[0013] In this case, as shown in FIG. 3B, the periphery of the
sheath 7 is cut first (S11), and weep holes are formed by cutting
(S12). Thereafter, the sheath 7 is bent like a C-shape (S13). After
the ends of the C-shaped sheath 7 are aligned, piece-inserting
holes through which the insertion pieces 8 are inserted inside the
C shape is formed by cutting (S14). Thereafter, an Hf plate as the
neutron absorbers 6, and the insertion pieces 8 are inserted in the
sheath 7, thereby assembling the blade 3 (S15). The sheath 7 and
the insertion pieces 8 are welded together (S16) and finishing with
a wire brush is carried out (S17), thus producing the blade 3.
[0014] Further, the tie rod 9, the handles 4 and the lower blades 5
are combined with the blades 3 produced by the above method, with
the result that the control rod 2 is assembled (S18). Thereafter,
welding of the tie rod 9 (S19) and welding of the handles 4 and the
lower blades 5 (S20) are carried out. Finally, the control rod 2 is
finished with a wire brush (S21).
[0015] In the case where the control rod 2 of the reactor is
manufactured as described above, first, the sheath 7 is cut and
bent, and thereafter the blade 3 is assembled. Then, the frames of
the tie rod 9, the handles 4 and the lower blades 5 are assembled.
Further, welding of the blades 3, the tie rod 9, the handles 4 and
the lower blades 5 and welding of the sheath 7 and the insertion
pieces 8 are carried out.
[0016] Conventionally, welding of these parts is performed by
manual TIG welding. The TIG welding is a method in which arc is
generated between a nonconsumable tungsten electrode and a base
material in an inert gas atmosphere for the purpose of melting.
[0017] According to the manual TIG welding, since heat input is
great, deformation after the process is great, and in particular,
welding deformation is considerable. Therefore, welding is
frequently performed while the deformation is corrected. In
addition, since the process speed of welding is low, the
productivity is low.
BRIEF SUMMARY OF THE INVENTION
[0018] An object of the present invention is to provide a method
and apparatus for manufacturing a control rod for a nuclear
reactor, by reducing heat input to suppress deformation after the
process and increasing welding speed to improve the
productivity.
[0019] The above object is obtained by the invention as described
below.
[0020] (1) In a method for manufacturing a control rod for a
nuclear reactor comprising blades including neutron absorbers,
insertion pieces and a sheath, weep holes and piece-inserting holes
are formed in the sheath by cut working and the periphery is cut.
Thereafter, the neutron absorbers and the insertion pieces are
inserted in a recess portion formed by bending the sheath. The
piece-inserting holes and the insertion pieces are welded together
by a laser beam, thereby forming an integral blade. The blades and
handles are welded by a laser beam, and subsequently, the blades
and lower blades are welded by a laser beam. Then, the welded
portions are surface-finished by a wire brush or the like.
[0021] (2) In a method for manufacturing a control rod for a
nuclear reactor comprising blades including neutron absorbers and a
sheath, weep holes are formed in the sheath by cut working. After
the periphery is cut, the neutron absorbers are inserted in a
recess portion formed by bending the sheath, thereby forming an
integral blade. The blades and handles are welded by a laser beam,
and subsequently, the blades and lower blades are welded by a laser
beam. Then, the welded portions are surface-finished by a wire
brush or the like.
[0022] With the method for manufacturing a control rod described
above, the heat input in the welding time is kept low and the
deformation after the process is suppressed. Moreover, since the
process speed of welding is increased, the productivity can be
improved.
[0023] (3) In the welding time, to reliably melt a bevel line and
secure the penetration bead on the rear surface of the sheath, a
YAG laser beam or a CO.sub.2 laser beam is irradiated on a position
located immediately above a bevel position or a position deviated
in parallel from the bevel position within a range of 2 mm. The
laser beam may be irradiated several times so as to lap over one
another, shifted within a range of 0.1 to 2.0 mm from a first pass
or a first pass target position. Alternatively, the laser beam is
irradiated while traveling forward with circular motion in a
diameter within 2 mm. To produce circular motion of the laser beam,
a prism is inserted before a condenser lens, and while the prism is
rotating on an axis of the laser beam, the laser beam is irradiated
on the rotating prism. As a result, the laser beam is incident on
the condenser lens, while rotating.
[0024] With the above method, in any case, the bevel line is
reliably melted and the penetration bead on the rear surface is
secured.
[0025] (4) As another method, in the step for welding the blade to
the tie rod, the blade to the handle or the blade to the lower
blade, two slits are provided in the tie rod, the handle or the
lower blade, and projections of the blade is inserted in the slits.
The laser beam is irradiated on a boundary between the blade and
the tie rod, a boundary between the blade and the handle or a
boundary between the blade and the lower blade.
[0026] With the above method, in any case, the bevel line is
reliably melted and the penetration bead on the rear surface is
secured. In addition, the bevel line is not deviated due to the
work accuracy of the blade. Therefore, the laser beam is reliably
irradiated on the bevel line.
[0027] (5) A CCD camera is mounted on the work head, and the CCD
camera in its entirety is moved to the bevel position as designed.
An image near the welding portion is picked up by the CCD camera.
The image processing apparatus detects the actual bevel position
from the image, i.e., the coordinates of the center of the
insertion piece from the bevel position in the case of welding the
piece-inserting hole of the sheath and the insertion piece. In the
case of welding the blades and the tie rod, welding of the blades
and the handles or welding of the blades and the lower blades, the
work start and end points of the welding are detected from the
bevel position. The arithmetic processing apparatus compares the
actual bevel position with the bevel position as designed, and
calculates the deviation of the irradiation position of the laser
beam. After the work head is moved by a distance corresponding to
the amount of the deviation of the irradiation position of the
laser beam plus the amount of the offset of the work head and the
CCD camera, the laser beam is irradiated.
[0028] With the above apparatus for manufacturing a control rod,
even if there is a difference between the bevel position as
designed and the actual bevel position, the bevel line is melted
reliably, the penetration bead on the rear surface of the sheath is
secured, and the welding process can be automated.
[0029] In addition, since the heat input in the welding time is
kept low, the deformation after the process is suppressed.
Moreover, since the process speed of welding is increased, the
productivity can be improved.
[0030] (6) In an apparatus for manufacturing a control rod of a
nuclear reactor, the control rod comprising blades including
neutron absorbers, an insertion pieces and a sheath or blades
including neutron absorbers and a sheath, a tie rod for fixing the
blade, a handle and a lower blade fixed to the tie rod and the
blade, there is provided a work table, a laser oscillator, a work
head, a CCD camera, an image processing apparatus, an arithmetic
processing apparatus, a servo motor and control means. The above
apparatus comprises at least two work heads and two work tables and
a movable mirror between the laser oscillator and the work
heads.
[0031] The work table is used to set objects to be welded
constituting the control rod and carry out welding. The laser
oscillator outputs a YAG laser beam or CO.sub.2 laser beam. The
work head has an optical system for transmitting the laser beam
oscillated by the laser oscillator and converging it to the objects
to be welded by a condenser lens. The CCD camera, mounted on the
work head, picks up an image of a portion near a bevel of the
objects to be welded. The image processing apparatus detects a
bevel position from the image picked up by the CCD camera. The
arithmetic processing apparatus compares the bevel position
obtained by the image processing apparatus with a bevel position as
designed, and calculates deviation therebetween. The servo motor
moves the work head or the work table by a distance corresponding
to an amount of the deviation of the bevel position calculated by
the arithmetic processing means plus an amount of the offset of the
work head and the CCD camera. The control means drives and controls
the servo motor.
[0032] With the above apparatus for manufacturing a control rod,
the welding process can be automated. Further, since the bevel
position is adjusted, the bevel line is reliably melted, the
penetration bead on the rear surface of the sheath is secured and
the welding process can be automated. In addition, the heat input
is kept low and the deformation after the process is suppressed.
Moreover, since the process speed of welding is increased, the
productivity can be improved.
[0033] (7) In a method for manufacturing a control rod for a
nuclear reactor, weep holes and piece-inserting holes are formed in
the sheath by cut working and the periphery is cut. Thereafter, the
neutron absorbers and the insertion pieces are inserted in a recess
portion formed by bending the sheath. The piece-inserting holes and
the insertion pieces are welded together by TIG welding, thereby
forming an integral blade. The blades and handles are welded by TIG
welding, and subsequently the blades and lower blades are welded by
TIG welding. Then, the welded portions are surface-finished by a
wire brush or the like.
[0034] With the method for manufacturing a control rod described
above, the heat input in the welding time is kept low and the
deformation after the process is suppressed. Further, if two
welding torches are used simultaneously, the productivity can be
improved.
[0035] (8) In the welding time, to reliably melt a bevel line and
secure the penetration bead on the rear surface of the sheath,
automatic TIG welding is carried out at a position located
immediately above a bevel or a position deviated in parallel from
the bevel within a range of 3 mm.
[0036] With the above method, in any case, the bevel line is
reliably melted and the penetration bead on the rear surface of the
sheath is secured.
[0037] (9) A CCD camera is mounted on the work head, and the CCD
camera in its entirety is moved to the bevel position as designed.
An image near the welding portion is picked up by the CCD camera.
The image processing apparatus detects the actual bevel position
from the image, i.e., the coordinates of the center of the
insertion piece from the bevel position in the case of welding the
piece-inserting hole of the sheath and the insertion piece. In the
case of welding the blades and the tie rod, welding of the blades
and the handles or welding of the blades and the lower blades, the
work start and end points of the welding are detected from the
bevel position. The arithmetic processing apparatus compares the
actual bevel position with the bevel position as designed, and
calculates the deviation of the welding torch. After the welding
torch is moved by a distance corresponding to the amount of the
deviation of the welding torch plus the amount of the offset of the
welding torch and the CCD camera, TIG welding is carried out.
[0038] With the above apparatus for manufacturing a control rod,
even if there is a difference between the bevel position as
designed and the actual bevel position, the bevel line is melted
reliably, the penetration bead on the rear surface of the sheath is
secured, and the welding process can be automated.
[0039] In addition, since the welding speed is stabilized, the heat
input in the welding time is kept low, with the result that the
deformation after the process is suppressed. Moreover, when two
welding torches are used simultaneously, the productivity can be
improved.
[0040] (10) In an apparatus for manufacturing a control rod of a
nuclear reactor, the control rod comprising blades including
neutron absorbers, insertion pieces and a sheath, a tie rod for
fixing the blade, a handle and a lower blade fixed to the tie rod
and the blade, the blade is sandwiched between chillers made of two
metal plates having openings only at welding bevel portions so that
a TIG welding torch can access thereto. With this structure, since
heat generated by welding is absorbed, welding deformation can be
considerably suppressed.
[0041] (11) In an apparatus for manufacturing a control rod of a
nuclear reactor, the control rod comprising a blade including
neutron absorbers, insertion pieces and a sheath, a tie rod for
fixing the blade, a handle and a lower blade fixed to the tie rod
and the blade, there is provided a work table, a TIG torch, a CCD
camera, an image processing apparatus, an arithmetic processing
apparatus, a servo motor and control means. The above apparatus
comprises at least two TIG torches and two work tables.
[0042] The work table is used to set objects to be welded
constituting the control rod and carry out welding. The CCD camera,
mounted on the TIG welding torch, picks up an image of a portion
near a bevel of the objects to be welded. The image processing
apparatus detects a bevel position from the image picked up by the
CCD camera. The arithmetic processing apparatus compares the bevel
position obtained by the image processing apparatus with a bevel
position as designed, and calculates deviation therebetween. The
servo motor moves the work head or the work table by a distance
corresponding to an amount of the deviation of the bevel position
calculated by the arithmetic processing means plus an amount of the
offset of the work head and the CCD camera. The control means
drives and controls the servo motor.
[0043] With the above apparatus for manufacturing a control rod,
the welding process can be automated. Further, since the bevel
position is adjusted, the bevel line is reliably melted, the
penetration bead on the rear surface is secured and the welding
process can be automated. In addition, the heat input is kept low
and the deformation after the process is suppressed. Moreover, if
the two TIG torches are used simultaneously, the productivity can
be improved.
[0044] (12) In the process of bending the sheath, since the end
face of the side of the sheath that is connected to the tie rod
tends to be ragged, the ragged portion is removed by laser cutting
with high-pressure nitrogen gas, which can perform a process at a
higher work speed than machining with a work accuracy equivalent to
that of the machining. As a result, the productivity can be
considerably improved.
[0045] (13) In the process of bending the sheath, since the end
face of the side of the sheath that is connected to the tie rod
tends to be ragged, the ragged portion is removed by shearing,
which can perform processing by machining in a short period of
time. As a result, the productivity can be considerably
improved.
[0046] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0047] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred embodiments of the invention, and together with the
general description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
[0048] FIG. 1 is a bird's eye view showing an example of the
internal structure of a reactor pressure vessel of a boiling water
reactor;
[0049] FIG. 2A is a perspective view for explaining the structure
of a control rod;
[0050] FIG. 2B is a cross sectional view of a blade;
[0051] FIGS. 3A and 3B are flowcharts for explaining examples of
processes of manufacturing a control rod for a nuclear reactor of
the prior art;
[0052] FIG. 4 is a flowchart for explaining a method for
manufacturing a control rod for a nuclear reactor according to a
first embodiment of the present invention;
[0053] FIGS. 5A and 5B are diagrams for explaining laser beam
oscillating conditions;
[0054] FIG. 6A is a front view showing a laser irradiation position
or a TIG welding torch position;
[0055] FIG. 6B is a cross-sectional view showing a laser
irradiation position or a TIG welding torch position;
[0056] FIG. 6C is a front view showing a laser irradiation position
or a TIG welding torch position;
[0057] FIG. 6D is a cross-sectional view showing a laser
irradiation position or a TIG welding torch position;
[0058] FIG. 6E is a front view showing a laser irradiation position
or a TIG welding torch position;
[0059] FIG. 6F is a cross-sectional view showing a laser
irradiation position or a TIG welding torch position;
[0060] FIG. 7A is a front view showing a laser irradiation
position, when the laser beam is rotated;
[0061] FIG. 7B is a cross-sectional view showing a laser
irradiation position, when the laser beam is rotated;
[0062] FIG. 8 is a cross-sectional view showing a schematic
structure of an apparatus for rotating a YAG laser beam by means of
a prism in the first embodiment;
[0063] FIG. 9 is a cross-sectional view showing a schematic
structure of an apparatus for rotating a CO.sub.2 laser beam by
means of a prism in the first embodiment;
[0064] FIG. 10A is a plan view showing a fixing jig for use in
welding in the first embodiment;
[0065] FIG. 10B is a cross-sectional view showing a fixing jig for
use in welding in the first embodiment;
[0066] FIG. 11A is a perspective view showing a set state of the
entire fixing jigs;
[0067] FIG. 11B is a cross sectional view of an example of the
control rod to which fixing jigs are set;
[0068] FIG. 11C is a cross sectional view of another example of the
control rod to which fixing jigs are set;
[0069] FIG. 11D is a detailed diagram showing an example of a
portion A;
[0070] FIG. 11E is a detailed diagram showing another example of
the portion A;
[0071] FIG. 12 is a plan view showing a fixing jig of a state in
which the blades and the tie rod are fixed thereto;
[0072] FIG. 13 is a plan view showing a system structure used in a
case where the blades are welded to a tie rod by means of two
welding machines;
[0073] FIG. 14 is a flowchart for explaining a method for
manufacturing a control rod for a nuclear reactor according to a
second embodiment of the present invention;
[0074] FIG. 15 is a flowchart for explaining a method for
manufacturing a control rod for a nuclear reactor according to a
third embodiment of the present invention;
[0075] FIG. 16 is a schematic structural diagram showing an
apparatus used in welding of insertion pieces of an apparatus for
manufacturing a control rod for a nuclear reactor according to a
fourth embodiment of the present invention;
[0076] FIG. 17 is a block diagram showing a drive control system in
the fourth embodiment;
[0077] FIG. 18 is a diagram showing a sequence of automatic
insertion piece welding in the fourth embodiment;
[0078] FIG. 19 is a diagram showing a sequence of automatic tie rod
welding in the fourth embodiment;
[0079] FIG. 20 is a schematic structural diagram showing an
apparatus used in welding of insertion pieces according to a fifth
embodiment of the present invention;
[0080] FIG. 21 is a flowchart for explaining a method for
manufacturing a control rod for a nuclear reactor according to a
sixth embodiment of the present invention;
[0081] FIG. 22 is a diagram showing an example of conditions for
welding insertion pieces and a sheath by an automatic TIG welding
machine according to the sixth embodiment;
[0082] FIG. 23 is a flowchart for explaining a method for
manufacturing a control rod for a nuclear reactor according to a
seventh embodiment of the present invention;
[0083] FIG. 24 is a diagram showing a sequence of performing
insertion piece welding by means of an automatic TIG welding
machine according to an eighth embodiment of the present
invention;
[0084] FIG. 25 is a diagram showing a sequence of performing tie
rod welding by means of the automatic TIG welding machine according
to the eighth embodiment of the present invention; and
[0085] FIG. 26 is a schematic structural diagram showing an
apparatus used in welding of insertion pieces according to a ninth
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0086] Embodiments of the present invention will be described with
reference to the drawings.
[0087] (First Embodiment)
[0088] FIG. 4 is a flowchart for explaining a method for
manufacturing a control rod for a nuclear reactor according to a
first embodiment of the present invention. Components of a control
rod 2 are described with reference to FIG. 2. In this embodiment,
Hf is used as neutron absorbers 6.
[0089] First, weep holes for cooling the neutron absorbers 6 (S30)
and holes for setting insertion pieces 8 to secure a space between
the neutron absorbers 6 and a sheath 7 (S31) are formed by cutting
the sheath 7 by a laser beam. Thereafter, the periphery of the
sheath 7 is cut (S32).
[0090] The laser beam is used to cut the periphery of the sheath
and the holes in order to keep the accuracy high. Holes may be made
by punching or shearing instead of using a laser beam. After the
cutting, it is preferable that scribing is performed by means of a
laser beam to confirm the bent position.
[0091] Then, the sheath 7 is C-shaped by bending (S33). The
insertion pieces 8 and the neutron absorbers 6 are inserted into
the C shape, thereby assembling a blade 3 (S34). Thereafter, the
insertion pieces 8 and the sheath 7 are welded by a laser beam
(S35).
[0092] In this case, the insertion pieces 8 are used to fix the
neutron absorbers 6 and secure a space between the sheath 7 and the
neutron absorbers 6.
[0093] Examples of conditions for processing the insertion pieces 8
and the sheath 7 with a laser beam will be described with reference
to FIGS. 5A and 5B.
[0094] FIG. 5A shows conditions in the case of pulse amplitude
oscillation, and FIG. 5B shows conditions in the case of continuous
oscillation. A YAG laser is used in both cases. Although welding
tends to be stable in continuous oscillation, either oscillation
may be applied.
[0095] FIGS. 6A to 6F schematically show laser irradiation
positions. As indicated by the arrows in FIGS. 6A and 6B, the laser
irradiation position is basically located immediately above a bevel
of the sheath 7 with which the insertion piece 8 is fit. However,
it may be deviated from the bevel within a range of 0.1 to 2.0 mm
as indicated by the arrows in FIGS. 6C and 6D to secure a
penetration bead.
[0096] If the bead width is small, laser beams may be irradiated
several times so as to lap over one another, immediately above the
bevel or in a range within 2 mm from the bevel, as indicated by the
arrows in FIGS. 6E and 6F. In this case, the laser beam is passed
several times to lap over one another, shifted within a range of
0.1 to 2.0 mm from the first pass or the first pass target
position.
[0097] FIGS. 7A and 7B schematically shows a laser irradiation
position for radiating a laser beam with circular motion. As
indicated by the arrows in FIGS. 7A and 7B, the sheath 7 in which
the insertion pieces 8 are inserted is radiated with the laser beam
traveling forward with circular motion in a diameter within 2
mm.
[0098] Through the methods shown in FIGS. 6A to 6F and FIGS. 7A and
7B, a wide and stable bead is obtained, the bevel line is reliably
melted, and the penetration bead on the rear surface is
secured.
[0099] As another method for giving the circular motion to the
laser beam, a work head or a work table may be mechanically
rotated. However, when this mechanical method is employed and the
process speed is increased to about several meters per minute, the
circular motion may be distorted.
[0100] FIG. 8 shows a schematic structure of an apparatus for
rotating a laser beam by means of a prism.
[0101] Referring to FIG. 8, an optical fiber 10 for guiding a laser
beam from a laser oscillator is connected to a laser incident
portion of a work head 20. In the work head 20, a long focus lens
11, a prism 12 and a condenser lens 13 are held by holding members
at suitable distances in this order from a laser input side to a
laser output side. In this case, the holding member for holding the
prism 12 is rotatably supported by a rotary member comprising a
toothed portion on its circumferential surface. A gear 14 is
rotated by a motor 15 mounted on the circumferential surface of the
work head 20. The rotation can be transmitted to the rotary body
via the toothed portion which meshes with the gear 14. The rotation
speed of the prism 12 is controlled by a controller 27.
[0102] In this laser beam rotating apparatus, in the case of a YAG
laser, a YAG laser beam is guided to the work head 20 through the
optical fiber 10. In the work head 20, the laser beam is converted
to a parallel beam by the long focus lens 11, guided to the prism
12 and then irradiated on the work surface through the condenser
lens 13.
[0103] At this time, the prism 12 is rotated by rotating the gear
14 by means of the motor 15. As a result, the focus position is
rotated at a high speed of several meters per minute within a range
of several millimeters.
[0104] The structure in the case of a YAG laser is described above.
In the case of a CO.sub.2 laser also, the laser beam can be given
circular motion by a similar laser beam rotating apparatus.
[0105] FIG. 9 shows an example of the structure of a CO.sub.2
laser, which is different from the structure of the YAG laser in
that it does not have a long focus lens 11. The other portions of
the structure is the same as those shown in FIG. 8.
[0106] A jig used in welding will be described with reference to
FIGS. 10A and 10B.
[0107] The jib in its entirety is formed of copper, as shown in
FIGS. 10A and 10B. The jigs are arranged so as to sandwich the
sheath 7 on the upper and lower surfaces thereof, and used as
chillers 16 in the laser welding time. Inverted cone-shaped holes
16s are provided on both surfaces of the chillers 16 at positions
corresponding to the positions of the insertion pieces 8, so that
the work head 20 shown in FIG. 8 or 9 can access thereto when the
insertion pieces 8 are welded.
[0108] The chillers 16 are also used in welding of a tie rod 9
(described later).
[0109] When the welding of the sheath 7 and the insertion pieces 8
is completed, the surface of the bead is smoothed with a wire brush
(S36).
[0110] An integral structure storing the neutron absorbers 6 and
the insertion pieces 8 in the sheath 7 is called a blade 3.
[0111] Then, four blades 3 are set to the tie rod 9, and handles 4
and lower blades 5 are also set.
[0112] FIGS. 11A to 11C show a state in which these elements are
set to fixing jigs 17.
[0113] As shown in FIGS. 11A to 1C, the blades 3, the handles 4 and
the lower blades 5 are set to the tie rod 9 with at least three
fixing jigs 17. Thus, the control rod 2 is assembled (S37). In this
case, the fixing jig 17 is divided into two equal parts of upper
and lower portions, as shown in FIG. 12. The four blades 3 are set
in the upper half portion 17a and the lower half portion 17b and
the crisscross tie rod 9 is set at the center of the portions. The
fixing jig 17 near the handles 4 has a toothed portion on its
circumferential surface. The toothed portion meshes with a gear 18
which is connected to a motor 19. Turning force is transmitted to
the fixing jig 17 by the motor 19, so that the work position can be
changed.
[0114] The tie rod 9 and the blades 3 are not entirely beveled
along their overall lengths. As shown in FIG. 1D, the length of the
welding bevel is about 3 to 8 cm. In the portions which are not
welded, the sheath 7 and the tie rod 9 are separated to allow water
to flow, i.e., coolant.
[0115] Further, as shown in the cross-sectional view of FIG. 11B,
the tie rod 9 has sockets 35 to make the positioning with the
sheath 7 easy. The position indicated by the arrow in the drawing
is beveled.
[0116] According to another method, as shown in FIG. 1C, the tie
rod 9 may have two slits 36. In this method, when the blade 3 and
the tie rod 9 are welded by a laser beam, the laser beam is
irradiated in a state where projected portions of the blade 3 is
inserted in the sits 36. In this case, as shown in FIG. 1C, the
laser beam is radiated, targeted at the position indicated by the
arrow, i.e., the boundary between the blade 3 and the tie rod
9.
[0117] With this method, since the blade 3 and the tie rod 9 are
fixed securely, the bevel line is prevented from deviating and the
laser beam can be irradiated to the bevel line easily and
reliably.
[0118] FIG. 13 is a plan view showing a system structure of the
components of the control rod 2 set as described above, used in a
case where the blades 3 are welded to the tie rod 9 by means of two
welding machines.
[0119] In FIG. 13, a head drive mechanism 51 drives the work head
20 in radial and longitudinal directions. A welding machine 52
welds the end face of the blade 3 to the tie rod 9 via the head
drive mechanism 51. A control apparatus 53 controls the welding
machine 52 and the head drive mechanism 51.
[0120] Next, the tie rod 9 is welded (S38). The welding conditions
are the same as those shown in FIGS. 5A and 5B. The irradiation
position of the laser beam is basically located immediately above
the bevel. However, it may be deviated from the bevel within a
range of 2.0 mm to secure a penetration bead.
[0121] If the bead width is small, laser beams may be irradiated
several times so as to lap over one another, immediately above the
bevel or in a range within 2 mm from the bevel. Further, to
increase the bead width, the laser beam may be moved circularly. In
either case, the method of welding is the same as the welding of
the insertion piece 8 shown in FIGS. 6A, 7A and 7B. Therefore, the
description thereof is omitted.
[0122] To reduce the welding deformation, the chillers 16 are set
to positions which do not interfere with the work heads 20. In this
case, they are set to the blades 3 located in upper and lower
portions along the vertical direction.
[0123] The handles 4 and the lower blades 5 are also welded by
means of the laser beam at the same time (S39). The welded surfaces
are smoothed with the wire brush (S40). Thus, production of the
control rod 2 is completed.
[0124] As described above, according to the first embodiment of the
present invention, in the method for manufacturing the control rod
2 of the nuclear reactor, the sheath 7 is bent, after the weep
holes, the piece-inserting holes and the periphery of the sheath
are cut. The neutron absorbers 6 and the insertion pieces 8 are
inserted in the bent sheath 7. The piece-inserting holes and the
insertion pieces 8 are welded together by the laser beam, thereby
forming an integral blade 3. The blades 3 and the tie rod 9 are
welded together by the laser beam. Thereafter, the blades 3 and the
handles 4 are also welded by the laser beam. Further, after the
blades 3 and the lower blades 5 are welded by the laser beam, the
welded portions are finished with a wire brush.
[0125] Thus, the YAG laser beam is used to weld the control rods 2
of the nuclear reactor, thereby suppressing the heat input in the
welding time and the deformation after the process. Moreover, since
the process speed of welding can be increased as compared to the
TIG welding, the productivity can be improved.
[0126] (Second Embodiment)
[0127] FIG. 14 is a flowchart for explaining a method for
manufacturing a control rod 2 for a nuclear reactor according to a
second embodiment of the present invention. Components of the
control rod 2 are described with reference to FIG. 2. In this
embodiment, Hf is used as neutron absorbers 6.
[0128] First, weep holes for cooling the neutron absorbers 6 (S41)
and holes for setting insertion pieces 8 to secure a space between
the neutron absorbers 6 and a sheath 7 (S42) are formed by cutting
the sheath 7 by the laser beam. Thereafter, the periphery of the
sheath 7 is also cut by the laser beam (S43).
[0129] The laser beam is used to cut the periphery of the sheath
and the holes in order to keep the accuracy high. Holes may be made
by punching or shearing instead of using a laser beam. After the
cutting, it is preferable that scribing is performed by means of a
laser beam to confirm the bent position.
[0130] Then, the sheath 7 is C-shaped by bending (S44). The
insertion pieces 8 and the neutron absorbers 6 are inserted inside
the C shape, thereby assembling a blade 3 (S45). Unlike in the
first embodiment, however, the insertion pieces 8 are not welded by
the laser beam, but only provisional TIG welding is carried
out.
[0131] In this state, four blades 3 are set to the tie rod 9.
Handles 4 and lower blades 5 are also set. The set state is as
shown in FIGS. 11A to 1C. The blades 3, the handles 4 and the lower
blades 5 are set to the tie rod 9 with at least three fixing jigs
17. Thus, the control rod 2 is assembled (S46). In this case, the
fixing jig 17 is divided into two equal parts of upper and lower
portions, as shown in FIG. 12. The respective parts are set between
the upper half portion 17a and the lower half portion 17b.
[0132] The tie rod 9 has sockets 35 to make the positioning with
the sheath 7 easy. The boundary between the tie rod 9 and the
sheath 7 is beveled.
[0133] Next, the tie rod 9 is welded by a laser (S47). The welding
conditions are the same as those shown in FIGS. 5A and 5B. The
irradiation position of the laser beam is basically located
immediately above the bevel. However, it may be deviated from the
bevel within a range of 2.0 mm to secure a penetration bead.
[0134] If the bead width is small, laser beams may be irradiated
several times so as to lap over one another, immediately above the
bevel or in a range within 2 mm from the bevel. Further, to
increase the bead width, the laser beam may be moved circularly. In
either case, the method of welding is the same as that described
with reference to FIGS. 5A and 5B and 6A to 6F. Therefore, the
description thereof is omitted.
[0135] To reduce the welding deformation, the chillers 16 are set
to positions of the blades 3 which do not interfere with the work
heads 20.
[0136] The handles 4 and the lower blades 5 are also welded by
means of the laser beam at the same time (S48). Then, the welded
surfaces are smoothed with a wire brush (S49). Thereafter, the
insertion pieces 8 are welded by the laser beam (S50), and the
welded surface is smoothed with the wire brush (S51). Thus,
production of the control rod 2 is completed.
[0137] According to the second embodiment of the present invention,
the same effect and advantage as those of the first embodiment can
be obtained.
[0138] (Third Embodiment)
[0139] FIG. 15 is a flowchart for explaining a method for
manufacturing a control rod 2 for a nuclear reactor according to a
third embodiment of the present invention.
[0140] Components of the control rod 2 are described with reference
to FIG. 2. In this embodiment, B.sub.4C is used as neutron
absorbers 6. The control rod 2 using B.sub.4C is characterized in
that an insertion piece 8 to keep constant the gap between the
sheath 7 is not used.
[0141] First, weep holes for cooling the neutron absorbers 6 are
formed by cutting the sheath 7 by a laser beam. Thereafter, the
periphery of the sheath 7 is cut (S61).
[0142] The laser beam is used to cut the periphery of the sheath 7
and the holes in order to keep the accuracy high. Holes may be made
by punching or shearing instead of using a laser beam. After the
cutting, it is preferable that scribing is performed by means of a
laser beam to confirm the bent position.
[0143] Then, the sheath 7 is C-shaped by bending (S62). The neutron
absorbers 6 are inserted inside the C shape, thereby assembling a
blade 3 (S63).
[0144] In this state, four blades 3 are set to the tie rod 9.
Handles 4 and lower blades 5 are also set. The set state is as
shown in FIGS. 11A to 11C. The blades 3, the handles 4 and the
lower blades 5 are set to the tie rod 9 with at least three fixing
jigs 17. In this case, the fixing jig 17 is divided into two equal
parts of upper and lower portions, as shown in FIG. 12. The
respective parts are set between the upper half portion 17a and the
lower half portion 17b. Thus, the control rod 2 is assembled
(S64).
[0145] The tie rod 9 has sockets 35 to make the positioning with
the sheath 7 easy. The boundary between the tie rod 9 and the
sheath 7 is beveled.
[0146] Next, the tie rod 9 is welded (S65). The welding conditions
are the same as those shown in FIGS. 5A and 5B. The irradiation
position of the laser beam is basically located immediately above
the bevel. However, it may be deviated from the bevel within a
range of 2.0 mm to secure a penetration bead.
[0147] If the bead width is small, laser beams may be irradiated
several times so as to lap over one another, immediately above the
bevel or in a range within 2 mm from the bevel. Further, to
increase the bead width, the laser beam may be moved circularly. In
either case, the method of welding is the same as that described
with reference to FIGS. 6A to 6F and FIGS. 7A and 7B. Therefore,
the description thereof is omitted.
[0148] To reduce the welding deformation, the chillers 16 are set
to positions of the blades 3 which do not interfere with the work
heads 20.
[0149] The handles 4 and the lower blades 5 are also welded by
means of the laser beam at the same time. Then, the welded surfaces
are smoothed with a wire brush (S66). Thus, production of the
control rod 2 is completed.
[0150] According to the third embodiment of the present invention,
the same effect and advantage as those of the first and second
embodiments can be obtained.
[0151] (Fourth Embodiment)
[0152] FIG. 16 schematically shows an apparatus used in welding of
insertion pieces according to a fourth embodiment of the present
invention.
[0153] As shown in FIG. 16, an insertion piece 8 can be seen
through a piece-inserting hole 37 from above the sheath 7.
Therefore, the piece-inserting hole 37 is confirmed through a CCD
camera 21 mounted on the work head 20.
[0154] FIG. 17 is a block diagram showing an automatic insertion
piece welding apparatus. Image information of the piece-inserting
hole 37 recognized by a CCD camera 21 as shown in FIG. 16 is first
converted to shape information by an image processing apparatus 22,
and the coordinates of the center of a circle are recognized.
Coordinate information is input to an arithmetic processing
apparatus 23. The arithmetic processing apparatus 23 compares the
coordinates with coordinates of the center of the piece-inserting
hole 37 prestored as work data, so that the amount of deviation of
the holes is detected. The information is fed back to a numerical
control apparatus 25 via an operation computer 24, thereby driving
an NC servo motor 26.
[0155] FIG. 18 shows a sequence of automatic insertion piece
welding.
[0156] Referring to FIG. 18, first, the work head 20 is moved (S71)
and the work start point is determined (S72). The work start point
of the CCD camera 21 is also determined. The work head 20 is moved
to the center of an insertion piece 8 (S73), and positional
deviation is detected by the CCD camera 21, the image processing
apparatus 22 and the arithmetic processing apparatus 23 (S74). The
work head 20 is moved by a distance corresponding to the amount of
this positional deviation plus the offset of the work head 20 and
the CCD camera 21 (S75).
[0157] In this state, the work head 20 starts rotating and moving
(S76). When irradiation of the beam is started (S77), welding is
started. When the welding is ended, beam irradiation is stopped
(S78) and rotation and movement of the work head 20 is also stopped
(S79).
[0158] When the welding of the insertion pieces 8 on one surface of
the blade 3 is completed, the surfaces of the blade 3 are changed
and the insertion pieces 8 on the other surface is welded. This
operation is repeated, until that the insertion pieces 8 on all
surfaces of the blades 3 are welded (S80).
[0159] Welding of the insertion pieces 8 is described above.
Welding of the tie rod 9 is carried out in the same manner by means
of the aforementioned apparatus shown in FIGS. 16 and 17.
[0160] FIG. 19 shows a sequence of automatic tie rod welding.
[0161] Referring to FIG. 19, first, the work head 20 is moved (S91)
and the work start point is determined (S92). Then, as shown in the
enlarged views of FIGS. 11B and 11C, at the welding portion between
the 10, tie rod 9 and the sheath 7, projections are formed on the
sheath 7 side and sockets 35 are formed on the tie rod 9 side. The
work head 20 is moved to one end of the projections of the sheath
7, i.e., the work start point (S93). The positional deviation of
the work start point is detected by the CCD camera 21, the image
processing apparatus 22 and the arithmetic processing apparatus 23
(S94). In the same manner, the work head 20 is moved to the other
end of the projections of the sheath 7, i.e., the work end point
(S95). The positional deviation of the work end point is detected
by the CCD camera 21, the image processing apparatus 22 and the
arithmetic processing apparatus 23 (S96).
[0162] Then, the work head 20 is moved by a distance corresponding
to the amount of deviation of the work start point and the offset
of the work head 20 and the CCD camera 21 (S97).
[0163] In this state, movement of the work head 20 is started
(S98). When irradiation of the beam is started, welding is started
(S99). When the welding is ended, beam irradiation is stopped
(S100) and movement of the work head 20 is also stopped (S101).
[0164] When the welding of the tie rod 9 on one surface of the
blade 3 is completed, the surfaces of the blade 3 are exchanged
(S102) and welding of the other seven surfaces of the tie rod 3 is
successively performed.
[0165] In the first and second embodiments descried above, in the
case of welding of a comparatively narrow bead width of 0.1 to 2.0
mm, when the laser irradiation position is greatly deviated from
the bevel position, it becomes difficult to carry out welding by
means of a laser beam.
[0166] According to the fourth embodiment, to solve this problem,
the bevel position is detected by the CCD camera 21 and the image
processing apparatus 22 mounted on the work head 20, thereby
correcting the laser beam irradiating position. As a result, the
welding of the insertion pieces 8 and the tie rod 9 can be
automatically carried out with high accuracy.
[0167] As described above, according to the fourth embodiment of
the present invention, the CCD camera 21 is mounted on the work
head 20 and the CCD camera 21 in its entirety is moved by numerical
control (NC) to the bevel position as designed. An image near the
welding portion is picked up by the CCD camera 21. The image
information is supplied to the image processing apparatus 22. The
image processing apparatus 22 detects the actual bevel position
from the image, i.e., the coordinates of the center of the
insertion piece 8 from the bevel position in the case of welding
the piece-inserting hole 37 of the sheath 7 and the insertion piece
8.
[0168] In the case of welding the blades 3 and the tie rod 9,
welding of the blades 3 and the handles 4 or welding of the blades
3 and the lower blades 5, the work start and end points of the
welding are detected from the bevel position. The arithmetic
processing apparatus 23 compares the actual bevel position with the
bevel position as designed. As a result, the positional deviation
of the laser beam irradiation is calculated based on the above.
After the work head 20 is moved by a distance corresponding to the
amount of the positional deviation of the laser beam irradiation
plus the offset of the work head 20 and the CCD camera 21, the
laser beam is irradiated.
[0169] Therefore, even if there is a difference between the bevel
position as designed and the actual bevel position, the bevel line
is melted reliably, the penetration bead on the rear surface is
secured, and the welding process is performed automatically. As a
result, since the heat input in the welding time is kept low, the
deformation after the process is suppressed. Moreover, since the
process speed of welding is increased, the productivity can be
improved.
[0170] (Fifth Embodiment)
[0171] FIG. 20 schematically shows an apparatus used in welding of
insertion pieces 8 according to a fifth embodiment of the present
invention. Since the structure of the work head 20 is the same as
that shown in FIG. 16, the same component is identified by the same
reference symbol.
[0172] As shown in FIG. 20, when insertion pieces 8 are welded to
sheathes 7 mounted on at least two work tables 28, the work heads
20 are set on the respective sheathes 7.
[0173] The laser beam output from a laser oscillator 29 provided as
a welding machine is reflected by a variable mirror 30 arranged in
the optical path thereof. The laser beam is guided to one of the
work heads 20 through an optical fiber 31. Then, the laser beam is
irradiated on a welding position from the work head 20.
[0174] To guide the laser beam to the other work head 20, the
variable mirror 30 is moved to a position which does not interfere
with the laser beam, so that the laser beam is reflected by a fixed
mirror 32 arranged in the laser optical path and guided to the
other work head 20 through an optical fiber 31. Then, the laser
beam is irradiated on a welding portion by the work head 20.
[0175] In this case, if so-called time sharing light division is
feasible, that is, the laser beam of one laser oscillator 29 is
used for at least two work heads 20 in different time period, the
laser oscillator 29 can be efficiently utilized.
[0176] The structure for automatically welding an insertion piece 8
based on the image information of the piece inserting-hole 37,
recognized by the CCD camera 21 mounted on each work head 20, is
the same as that of the third embodiment shown in FIGS. 17 and 18.
Therefore, the description thereof is omitted.
[0177] With the above apparatus, the welding process can be
automatically performed. In addition, the bevel line can be melted
reliably by adjusting the bevel position, and the penetration bead
on the rear surface is secured. Further, the welding process can be
automatically performed.
[0178] (Sixth Embodiment)
[0179] FIG. 21 is a flowchart for explaining a method for
manufacturing a control rod 2 for a nuclear reactor according to a
sixth embodiment of the present invention. Components of the
control rod 2 are described with reference to FIG. 2. In this
embodiment, Hf is used as neutron absorbers 6.
[0180] First, the periphery of a sheath 7 is cut by a laser beam
(S111). Thereafter, weep holes for cooling the neutron absorbers 6
are formed by cutting the sheath 7 by a laser beam (S112).
[0181] The laser beam is used to cut the periphery of the sheath
and the holes in order to keep the accuracy high. Holes may be made
by punching or shearing instead of using a laser beam. After the
cutting, it is preferable that scribing is performed by means of a
laser beam to confirm the bent position.
[0182] Then, the sheath 7 is C-shaped by bending (S113).
[0183] At this time, since the end face of the side of the sheath 7
which is connected to the tie rod 9 tends to be ragged, the ragged
portion is cut and removed by the laser beam, thus aligning the end
face of the sheath 7 (S114). Alignment may be achieved by shearing
instead of using a laser beam.
[0184] Then, piece-inserting holes 37 through which insertion
pieces 8 are inserted into the internal portion of the C shape are
cut (S115). The insertion pieces 8 and the neutron absorbers 6 are
inserted into the sheath 7, thereby assembling a blade 3 (S116).
Thereafter, the insertion pieces 8 and the sheath 7 are welded by
an automatic TIG welding machine (S117).
[0185] In this case, the insertion pieces 8 are used to fix the
neutron absorbers 6 and secure a space between the sheath 7 and the
neutron absorbers 6.
[0186] FIG. 22 shows examples of conditions for welding the
insertion pieces 8 and the sheath 7 with an automatic TIG welding
machine.
[0187] AS in the case of the first embodiment shown in FIGS. 6A and
6B, the torch position of the TIG welding machine is basically
located immediately above a bevel of the sheath 7 corresponding to
the insertion piece 8. However, it may be deviated from the bevel
within a range of 0.1 to 3.0 mm as shown in FIGS. 6C and 6D to
secure a penetration bead.
[0188] Through the methods shown in FIGS. 6A to 6F, a stable bead
is obtained, the bevel line is reliably melted and the penetration
bead on the rear surface is secured.
[0189] The jig used in the TIG welding is the same as that shown in
FIGS. 10A and 10B, and the description thereof is omitted.
[0190] Then, the surface of the welded bead is smoothed with a wire
brush (S118).
[0191] The neutron absorbers 6 and the insertion pieces 8 are
stored in the sheath 7 and integrated with a blade 3. Thereafter,
four blades 3 are set to a tie rod 9 and handles 4 and lower blades
5 are also set, thereby assembling the control rod 2 (S119).
[0192] Since the state in which the control rod 2 thus assembled is
set to fixing jigs 17 is the same as that shown in FIGS. 11A and
12, the description thereof is omitted.
[0193] The tie rod 9 and the blades 3 are not entirely 41-beveled
along their overall lengths. As shown in the enlarged views of in
FIGS. 11D and 11E, the length of the welding bevel is about 3 to 8
cm. In the portions which are not welded, the sheath 7 and the tie
rod 9 are separated to allow water as a coolant to flow.
[0194] Further, as shown in the cross-sectional view of FIG. 11C,
the tie rod 9 has sockets 35 to make the positioning with the
sheath 7 easy. The position indicated by the arrow in the drawing
is beveled.
[0195] As regards the components of the control rod 2 set as
described above, the system structure used in the case of welding
the blades 3 to the tie rod 9 by two TIG welding machines is the
same as that shown in FIG. 13.
[0196] The tie rod 9 is welded by means of the TIG welding machines
(S120). The welding conditions are the same as those shown in FIG.
22. The position of a TIG welding torch 20 is basically located
immediately above a bevel. However, it may be deviated from the
bevel within a range of 3.0 mm to secure a penetration bead.
[0197] To reduce the welding deformation, chillers 16 are set to
positions which do not interfere with the welding torch 20. In this
case, they are set to the blades 3 located in upper and lower
portions along the vertical direction.
[0198] Then, the handles 4 and the lower blades 5 are also welded
in the same manner (S121). The welded surfaces are smoothed with a
wire brush (S122).
[0199] As described above, according to the sixth embodiment of the
present invention, in the method for manufacturing a control rod of
a nuclear reactor, after the periphery of the sheath 7 is cut and
the weep holes and piece-inserting holes are cut, the sheath 7 is
bent. The neutron absorbers 6 and the insertion pieces 8 are
inserted in the bent sheath 7. The piece-inserting holes 37 of the
sheath 7 and the insertion pieces 8 are welded by the TIG welding
machines, thereby forming an integral blade 3.
[0200] The blades 3 and the tie rod 9 are welded by the TIG welding
machines, and subsequently, the blades 3 and the handles 4 are also
welded by the TIG welding machines. Further, the blades 3 and the
lower blades 5 are welded by the laser beam. Thereafter, the welded
portions are smoothed with a wire brush or the like.
[0201] Thus, when the control rod 2 of the nuclear reactor is
welded, since the heat input in the welding time is kept low by
using the two automatic TIG welding machines, the deformation after
the process is suppressed. Further, since the TIG welding torches
are simultaneously used in place of the two work heads, the
productivity can be improved.
[0202] (Seventh Embodiment)
[0203] FIG. 23 is a flowchart for explaining a method for
manufacturing a control rod 2 for a nuclear reactor according to a
seventh embodiment of the present invention. Components of the
control rod 2 are described with reference to FIG. 2. In this
embodiment, Hf is used as neutron absorbers 6.
[0204] First, the periphery of a sheath 7 is cut by a laser beam
(S131). Thereafter, weep holes for cooling the neutron absorbers 6
are formed by cutting the sheath 7 by a laser beam (S132).
[0205] The laser beam is used to cut the periphery of the sheath
and the holes in order to keep the accuracy high. Holes may be made
by punching or shearing instead of using a laser beam. After the
cutting, it is preferable that scribing is performed by means of a
laser beam to confirm the bent position.
[0206] Then, the sheath 7 is C-shaped by bending (S133).
[0207] At this time, since the end face of the side of the sheath 7
which is to be connected to the tie rod 9 tends to be ragged, the
ragged portion is cut and removed by the laser beam, thus aligning
the end face of the sheath 7 (S134). Alignment may be achieved by
shearing instead of using a laser beam.
[0208] Then, piece-inserting holes are formed by cutting (S135).
Insertion pieces 8 and the neutron absorbers 6 are inserted into
the sheath 7, thereby assembling a blade 3 (S136). However, the
seventh embodiment is different from the sixth embodiment in that
welding of the insertion pieces 8 by a laser beam is not carried
out but only provisional TIG welding is carried out.
[0209] In this state, four blades 3 are set to the tie rod 9, and
handles and lower blades 5 are also set, thereby assembling a
control rod 2 (S137).
[0210] Since the state in which the four blades are set to the tie
rod 9 and the handles 4 and the lower blades 5 are set and fixed by
fixing jigs 17 is the same as that shown in FIGS. 11A and 12, the
description thereof is omitted.
[0211] Then, the tie rod 9 is welded (S138). The welding conditions
are the same as those shown in FIG. 22. The position of a TIG
welding torch 20 is basically located immediately above a bevel.
However, it may be deviated from the bevel within a range of 3.0 mm
to secure a penetration bead.
[0212] To reduce the welding deformation, chillers 16 are set to
positions which do not interfere with the welding torch 20.
[0213] The handles 4 and the lower blades 5 are also welded
simultaneously by the laser beam (S139). After the welding, the
welded surfaces are smoothed with a wire brush (S140).
Subsequently, the insertion pieces 8 are welded by the laser beam
(S141), and then the surfaces thereof are smoothed (S142).
[0214] Thus, in the seventh embodiment of the present invention,
the same effect and advantage as those of the sixth embodiment can
be obtained.
[0215] (Eighth Embodiment)
[0216] FIG. 24 shows a sequence of insertion piece welding by means
of an automatic TIG welding machine according to an eighth
embodiment of the present invention.
[0217] The structure of the automatic insertion piece welding
apparatus and the control device thereof are the same as those
shown in FIGS. 16 and 17. Therefore, the descriptions thereof are
omitted.
[0218] Referring to FIG. 24, first, a welding torch 20 in place of
the work head is moved (S151) and the work start point is
determined (S152). The work start point of the CCD camera 21 is
also determined. The welding torch 20 is moved to the center of an
insertion piece 8 (S153), and positional deviation is detected by
the CCD camera 21, the image processing apparatus 22 and the
arithmetic processing apparatus 23 as shown in FIG. 17 (S154). The
welding torch 20 is moved by a distance corresponding to the amount
of this positional deviation plus the offset of the welding torch
20 and the CCD camera 21 (S155).
[0219] In this state, the welding torch 20 starts rotating and
moving (S156) and TIG welding is started (S157). When the welding
is ended, welding arc is stopped (S158) and rotation and movement
of the welding torch is also stopped (S159).
[0220] When the welding of the insertion pieces 8 on one surface of
the blade 3 is completed, the surfaces of the blade 3 are changed
and the insertion pieces 8 on the other surface is welded. This
operation is repeated, until the insertion pieces 8 on all surfaces
of the blades 3 are welded (S160).
[0221] Welding of the insertion pieces 8 is described above.
Welding of the tie rod 9 is also carried out in the same
manner.
[0222] FIG. 25 shows a sequence of welding the tie rod 9 by an
automatic TIG welding machine.
[0223] Referring to FIG. 25, first, the welding torch 20 in place
of the work head is moved (S171) and the work start point is
determined (S172). Then, as shown FIG. 11B, at the welding portion
between the tie rod 9 and the sheath 7, projections are formed on
the sheath 7 side and sockets 35 are formed on the tie rod 9 side.
The welding torch 20 is moved to one end of the projections of the
sheath 7, i.e., the work start point (S173). The positional
deviation of the work start point is detected by the CCD camera 21,
the image processing apparatus 22 and the arithmetic processing
apparatus 23 (S174).
[0224] In the same manner, the welding torch 20 is moved to the
other end of the projections of the sheath 7, i.e., the work end
point (S175). The positional deviation of the work end point is
detected by the CCD camera 21, the image processing apparatus 22
and the arithmetic processing apparatus 23 (S176). Then, the
welding torch 20 is moved by a distance corresponding to the amount
of deviation of the work start point and the offset of the work
head 20 and the CCD camera 21 (S177).
[0225] In this state, movement of the welding torch 20 is started
(S178) and TIG welding is started (S179). When the welding is
ended, welding arc is stopped (S180) and movement of the welding
torch 20 is also stopped (S181).
[0226] When the welding of the tie rod 9 on one surface of the
blade 3 is completed, welding of the other seven surfaces of the
tie rod 9 is successively performed. This operation is repeated,
until that the welding of all surfaces of the blades 3 is completed
(S182).
[0227] In the sixth and seventh embodiments descried above, when
the welding torch position is greatly deviated from the bevel
position, welding itself becomes difficult.
[0228] According to the eighth embodiment, to solve this problem,
the bevel position is detected by the CCD camera 21 and the image
processing apparatus 22 mounted on the welding torch 20, so that
the position of the welding torch can be corrected. As a result,
the welding of the insertion pieces 8 and the tie rod 9 can be
automatically carried out with high accuracy.
[0229] As described above, according to the eighth embodiment of
the present invention, the CCD camera 21 is mounted on the welding
torch 20 and the CCD camera 21 in its entirety is moved by
numerical control (NC) to the bevel position as designed. An image
near the welding portion is picked up by the CCD camera 21.
[0230] The image information is supplied to the image processing
apparatus 22. The image processing apparatus 22 detects the actual
bevel position, i.e., the coordinates of the center of the
insertion piece 8 to be welded. In the case of welding the blades 3
and the tie rod 9, welding of the blades 3 and the handles 4 or
welding of the blades 3 and the lower blades 5, the work start and
end points of the welding are detected from the bevel position. The
arithmetic processing apparatus 23 compares the actual bevel
position with the bevel position as designed. As a result, the
positional deviation of the TIG welding torch is calculated. After
the welding torch is moved by a distance corresponding to the
amount of the positional deviation of the position of the welding
torch plus the TIG welding is carried out.
[0231] Therefore, even if there is a difference between the bevel
position as designed and the actual bevel position, the bevel line
is melted reliably, the penetration bead on the rear surface is
secured, and the welding process is performed automatically. As a
result, since the heat input in the welding time is kept low, the
deformation after the process is suppressed. Moreover, since the
two welding torches are simultaneously used, the productivity can
be improved.
[0232] (Ninth Embodiment)
[0233] FIG. 26 schematically shows an apparatus used in welding of
insertion pieces according to a ninth embodiment of the present
invention. Since the structure of the work head is the same as that
shown in FIG. 20, the same component is identified by the same
reference symbol.
[0234] As shown in FIG. 26, when insertion pieces 8 are welded to
sheathes 7 mounted on at least two work tables 28, welding torches
20 of TIG welding machines are set on the respective sheathes
7.
[0235] The structure for automatically welding an insertion piece 8
based on the image information of a hole, recognized by the CCD
camera 21 mounted on each welding torch, is the same as that of the
eighth embodiment shown in FIGS. 17 and 24. Therefore, the
description thereof is omitted.
[0236] With the above apparatus, the welding process can be
automatically performed. In addition, the bevel line can be melted
reliably by adjusting the bevel position, and the penetration bead
on the rear surface is secured. Further, the welding process can be
automatically performed.
[0237] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *