JP2003194996A - Underwater laser cutting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To securely cut an end of an object to be cut or a region of it whose thickness varies in an underwater environment. <P>SOLUTION: If an end of the object 3 or a region of it whose thickness varies is cut, a cutting nozzle 4 is shuttled back and forth and is scanned so as to overlap the object 3 while emitting laser light and a gas 13 from the cutting nozzle 4. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underwater laser cutting method for cutting highly radioactive solid waste such as a spent control rod and a spent fuel channel box generated from a nuclear power plant in water.

[0002]

2. Description of the Related Art In recent years, for example, reduction of the volume of highly radioactive solid waste such as control rods and fuel channel boxes that have been used in nuclear power plants, or application to preventive maintenance of nuclear reactor internals, etc. As a purpose, a technique for performing laser cutting in an underwater environment is being developed.

At this time, a technique is adopted in which an assist gas is ejected from a cutting nozzle to form a partial dry area in the laser irradiation portion. Further, in order to improve the cutting quality, underwater laser cutting technology is being developed for the purpose of controlling the components of the atmospheric gas used during laser cutting and utilizing the cooling effect of water.

For example, in reducing the volume of a control rod used in a boiling water (BWR) nuclear power plant, a control rod having a cross-shaped cross section is cut in the axial direction to form a hook-shaped "C" shape. A method of improving the utilization efficiency of the storage space by dividing the above-mentioned cut pieces into a rectangular cut piece and accommodating the cut pieces having the substantially same shape in an overlapping manner has been studied. In this case, the material of the cut portion of the object to be cut is stainless steel, and it is necessary to cut the end portion having a thickness of 20 mm or more and the portion where the thickness is rapidly increasing.

[0005]

However, it is difficult to collect the laser beam and to secure the gas flow rate at the end of the thick material of the object to be cut or in the portion where the thickness increases rapidly due to diffusion near the back surface. In addition, the inertial force of water is an obstacle to control the gas flow, and the central axis of the gas flow and the central axis of the laser beam are easily displaced, so that an uncut portion is easily formed on the back surface side. . Therefore, when the object to be cut is a thick material, there is a demand for a method for surely cutting the end portion of the thick material or the rapidly increased thickness portion, but means for realizing such a request are known. Absent.

The present invention has been made in view of the above circumstances, and an object thereof is to change the end portion of the object to be cut or the thickness of the object to be cut in underwater laser cutting in an underwater environment. An object of the present invention is to provide an underwater laser cutting method capable of reliably cutting an existing portion.

[0007]

In order to achieve the above object, an underwater laser cutting method according to the invention of claim 1 is
In the method of laser cutting an object to be cut in water, when cutting an end portion of the object to be cut or a portion where the thickness of the object to be cut is changed, a cutting nozzle for emitting laser light and gas is used. It is characterized in that the object to be cut is reciprocally scanned.

The underwater laser cutting method according to a second aspect of the present invention is a method of laser cutting an object to be cut in water, wherein an end portion of the object to be cut or the thickness of the object to be cut is changed. When cutting the part, the scanning speed of the cutting nozzle for emitting laser light and gas with respect to the object to be cut is switched to high speed scanning after low speed scanning.

The underwater laser cutting method according to the invention of claim 3 is a method of laser cutting an object to be cut in water, wherein when it is determined that the object has an uncut portion,
A cutting nozzle that emits laser light and gas scans the object to be cut in a direction opposite to the cutting direction, and reciprocally scans in a region including the uncut portion.

According to a fourth aspect of the present invention, in the underwater laser cutting method according to the first to third aspects, the laser oscillator is Nd: YAG.
It is a laser, and an optical fiber is used as a means for transmitting the laser light. According to a fifth aspect of the present invention, in the underwater laser cutting method according to the first to third aspects, the object to be cut is a highly radioactive solid waste.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In addition, the same components in the drawings will be denoted by the same reference numerals, and redundant description will be omitted. A first embodiment of the underwater laser cutting method according to the present invention will be described with reference to FIG.

FIG. 1 is an apparatus block diagram of a first embodiment of an underwater laser cutting method according to the present invention. This underwater laser cutting device includes a water tank 1, a holder 2, a cutting nozzle 4 and a drive mechanism 5 installed in the water tank 1, and a YAG laser oscillator 8 connected to the cutting nozzle 4 via an optical fiber 6. It comprises a compressor 9 connected to the cutting nozzle 4 via a gas tube 7, a driver 10 connected to the drive mechanism 5, a laser oscillator 8, a compressor 9 and a controller 11 for controlling the driver 10.

The object to be cut 3 is, for example, a highly radioactive solid waste such as a control rod or a fuel channel box which has been used in a nuclear power plant, and is fixed by a holder 2 and stretched inside the water tank 1. It is immersed in water 12.

The laser light emitted from the Nd: YAG laser oscillator 8 is transmitted through the inside of the optical fiber 6 and is emitted from the cutting nozzle 4 to the object 3 to be cut. The gas compressed by the compressor 9 passes through the gas tube 7 and the cutting nozzle 4
Is ejected onto the object to be cut 3. The drive mechanism 5 is the driver 1
The cutting nozzle 4 is caused to scan the object to be cut 3 by operating 0. The controller 11 is an Nd: YAG laser oscillator 8,
The operation of the compressor 9 and the driver 10 is controlled.

FIG. 2 is a process diagram showing a method of cutting the end portion of the object 3 by the cutting nozzle 4 using the underwater laser cutting device shown in FIG. That is, as shown in step (I) in FIG. 2, while the laser light and the gas are supplied from the gas tube 6 and the optical fiber 7 to the cutting nozzle 4 and the laser light and the gas 13 are emitted from the cutting nozzle 4, The cutting nozzle 4 is caused to scan downward from the position a to the position b above the cutting object 3 as indicated by the white arrow.

Next, as shown in the step (II), while the laser beam and the gas 13 are being emitted, the position b to the position a
The cutting nozzle 4 is caused to scan upward as indicated by the outline arrow. Finally, as shown in step (III), the cutting nozzle 4 is again scanned downward from the position a as indicated by the white arrow while the laser light and the gas 13 are being emitted.

Next, the operation of this underwater laser cutting method will be described. When the object to be cut 3 has a certain thickness or more, first, as shown in step (I), while the laser beam and the gas 13 are emitted, the cutting nozzle 4 is moved from the position a to the position b above the object to be cut 3. When scanned downward, near the back surface of the edge (α part)
Then, it is difficult to collect the laser beam and secure the gas flow rate because of the diffusion. In addition to this, the inertial force of water interferes with the control of the gas flow, and the central axis of the gas flow and the central axis of the laser light are easily misaligned. There is an uncut part that cannot be separated.

Next, as shown in the step (II), the cutting nozzle 4 is kept in a state where the laser beam and the gas 13 are emitted.
Is scanned upward from the position b to the position a, and further, the cutting nozzle 4 is reciprocally scanned downward again from the position a as shown in step (III). Then, the workpiece 3 is formed in the step (I). By the groove, it becomes easy to collect the laser beam and secure the gas flow rate up to the vicinity of the back surface of the object to be cut 3, and it becomes possible to separate the uncut portion formed in the α portion.

According to the embodiment of the present invention, when cutting the end portion of the object to be cut 3, the laser beam and the gas 13 are emitted from the cutting nozzle 4 while the cutting nozzle 4 is directed to the object to be cut three times.
Since the reciprocating scanning is performed so as to overlap, even when an uncut portion is formed in the vicinity of the back surface of the object to be cut in the first scanning, the back surface of the object 3 to be cut is formed by the groove formed in the first scanning during the return scanning. It is easy to collect the laser light and secure the gas flow rate up to the vicinity. Therefore, it becomes possible to separate the uncut portion formed in the vicinity of the back surface of the object 3 to be cut.
It is possible to reliably cut the end portion of the object to be cut 3.

In the present embodiment, the case of cutting along the downward direction has been described, but the same action and effect can be obtained with downward cutting or horizontal cutting. Also,
The laser oscillator 8 may be a CO ₂ laser or a semiconductor laser. Mirror transmission may be adopted as the laser light transmission means. A high-pressure gas cylinder may be used as the assist gas supply means. Further, as the assist gas, air, oxygen, nitrogen or a mixed gas of nitrogen and oxygen is used.

Next, a second embodiment of the underwater laser cutting method according to the present invention will be described with reference to FIG. In this embodiment, the underwater laser cutting device shown in FIG. 1 is used as in the first embodiment. FIG. 3 shows a step of cutting a portion of the object to be cut 3 where the thickness changes, by using the underwater laser cutting apparatus shown in FIG.

That is, in step (I) in FIG.
The object to be cut 3 is thin above the position c and thick below the position c. First, as shown in step (I),
While the laser light and the gas 13 are being emitted, the cutting nozzle 4 is scanned downward from a position a where the object 3 is thin to a position b where the object 3 is thick.

Next, as shown in the step (II), while the laser beam and the gas 13 are being emitted, the position b to the position a
The cutting nozzle 4 is scanned upward until. Finally the process (II
As shown in I), the cutting nozzle is reciprocally scanned downward again from the position a while the laser beam and the gas 13 are being emitted.

Next, the operation of this underwater laser cutting method will be described. If there is a step over the thickness of the object to be cut 3,
First, as shown in the step (I), while the laser beam and the gas 13 are being emitted, the laser beam and the gas 13 are emitted from the position a above the object 3 to the position b.
When the cutting nozzle 4 is scanned downwards up to, the vicinity of the back surface where the thickness changes (β portion) makes it difficult to collect laser light and secure the gas flow rate due to diffusion, and Due to the fact that the inertial force interferes with the control of the gas flow, and the central axis of the gas flow and the central axis of the laser light are easily misaligned, a groove is formed but it cannot be completely cut. The part is made.

Then, as shown in step (II), the cutting nozzle 4 is moved to the position b while the laser beam and the gas 13 are being emitted.
From the position a to the position a, and further, step (III)
When the cutting nozzle 4 is again reciprocally scanned downward from the position a as shown in FIG. 3, the groove formed in the object to be cut 3 in the step (I) causes the laser light to be condensed to the vicinity of the back surface of the object to be cut 3. It becomes easier to secure the gas flow rate, and it becomes possible to separate the uncut portion formed in the β portion.

According to the embodiment of the present invention, when cutting the portion of the cut object 3 where the thickness is changed, the cutting nozzle 4 is made to eject the laser light and the gas 13 while cutting the cut nozzle 4 to be cut. With respect to No. 3, reciprocating scanning is performed so as to overlap. As a result, even when an uncut portion is formed near the back surface of the object to be cut 3 in the first scanning, the laser beam is emitted to the vicinity of the back surface of the object to be cut 3 by the groove formed in the first scanning during the return scanning. It becomes easy to collect the light and secure the gas flow rate. for that reason,
The uncut portion formed in the vicinity of the back surface of the object to be cut 3 can be cut off, so that the end portion of the object to be cut 3 can be reliably cut.

Next, a third embodiment of the underwater laser cutting method according to the present invention will be described with reference to FIG. In this embodiment, as in the first embodiment, the underwater laser cutting device shown in FIG. 1 is used. FIG. 4 is a process chart according to the third embodiment of the present invention, which shows a process of cutting an end portion of an object to be cut using the underwater laser cutting device shown in FIG.

First, as shown in step (I), while the laser beam and the gas 13 are being emitted, the cutting nozzle 4 is caused to scan downward from the position a above the object 3 to the position b. At this time, the cutting nozzle 4 is normally scanned at a speed V1 (V1 <V2) lower than the speed V2 at which the object 3 other than the initial end can be cut. Next, as shown in step (II),
While the laser light and the gas 13 are being emitted, the cutting nozzle is scanned downward from the position b at a speed of V2.

Next, the operation of this underwater laser cutting method will be described. When the thickness of the object to be cut 3 is more than a certain value, first, as shown in step (I), the cutting nozzle 4 is moved from the position a above the object 3 to the position b while emitting the laser beam and the gas 13. Scan down. In this case, normally, when scanning is performed at a cutting speed V2 other than the first end of the object 3 to be cut, near the rear surface of the end (α portion), the laser light is condensed and the gas flow rate is reduced due to diffusion. It is difficult to secure. In addition to this, the inertial force of water becomes an obstacle to control the gas flow, and the center axis of the gas flow and the center axis of the laser beam are easily displaced from each other, so that the groove is formed. There is an uncut part that cannot be completely separated.

However, the speed: V2 is lower than the speed: V2
By scanning the cutting nozzle at 1 (V1 <V2), sufficient heat can be obtained up to the vicinity of the back surface of the object to be cut 3 and, at the same time, the melt can be sufficiently removed. It can be separated.

According to the present embodiment, when cutting the end portion of the object 3 to be cut, while the laser beam and the gas 13 are being emitted from the cutting nozzle 4, the scanning speed of the cutting nozzle 4 with respect to the object 3 to be cut is After switching to low speed for a while, it switches to high speed,
Sufficient heat input can be obtained up to the vicinity of the back surface of the object to be cut 3 and, at the same time, the melted material can be sufficiently removed, so that the end portion of the object to be cut 3 can be reliably cut.

Next, a fourth embodiment of the underwater laser cutting method according to the present invention will be described with reference to FIG. In this embodiment, the underwater laser cutting device shown in FIG. 1 is used as in the first embodiment. FIG. 5 is a process chart for explaining the present embodiment, and shows a process of cutting a portion of the object to be cut 3 where the thickness changes, using the underwater laser cutting device shown in FIG.

The object 3 is thin above the position c and thick below the position c. First, as shown in step (I), while the laser light and the gas 13 are being emitted, the cutting nozzle 4 is scanned downward from a position a where the object 3 is thin to a position b where the object 3 is thick. At this time, usually, the thick portion of the object to be cut 3 can be cut at a point other than the thickness change point, which is lower than the speed V2: V1 (V1 <V2)
To scan the cutting nozzle. Next, as shown in step (II), the cutting nozzle is scanned downward from position b at a speed of V2 while the laser light and the gas 13 are being emitted.

Next, the operation of this underwater laser cutting method will be described. If there is a step over the thickness of the object to be cut 3,
First, as shown in the step (I), while the laser beam and the gas 13 are being emitted, there is a portion where the thickness of the object to be cut 3 is thick from the position a where the thickness of the object to be cut 3 is thin. The cutting nozzle 4 is scanned downward to the position b. In this case, normally, when a thick portion of the object to be cut 3 is scanned at a speed V2 at which cutting is possible at a point other than the thickness change point, the laser beam is diffused near the back surface (β portion) where the thickness changes, due to diffusion. In addition to difficulty in collecting light and securing the gas flow rate, it is difficult to control the gas flow due to the inertial force of water, and the central axis of the gas flow and the central axis of the laser light are easily misaligned. As a result, a groove is formed, but an uncut portion that cannot be completely separated is formed.

However, lower speed: V than speed: V2
By scanning the cutting nozzle 4 at 1 (V1 <V2), sufficient heat can be obtained up to the vicinity of the back surface of the object to be cut 3 and, at the same time, the melt can be sufficiently removed. It is possible to separate it.

According to the present embodiment, when cutting the portion of the cut object 3 where the thickness changes, the cut nozzle 4 emits the laser beam and the gas 13 while cutting the cut object of the cut nozzle 4. Since the scanning speed for 3 is temporarily lowered and then switched to high speed, sufficient heat input can be obtained up to the vicinity of the back surface of the object to be cut 3 and, at the same time, the melt can be sufficiently removed. It is possible to reliably cut the portion where the thickness of the is changed.

Next, a fifth embodiment of the underwater laser cutting method according to the present invention will be described with reference to FIG. The underwater laser cutting apparatus shown in the same drawing is different from the underwater laser cutting apparatus shown in FIG. 1 in that the cutting nozzle 4 has a second optical fiber 6a.
Is connected, the photosensor 14, the amplifier 15, and the determination unit 16 are connected to the second optical fiber 6a, and the determination unit 16 is connected to the control device 11.

The photosensor 14 converts the intensity of light in the visible wavelength range into an electric signal (voltage). The amplifier 15 amplifies the voltage output from the photo sensor 14 so that it has a voltage value suitable for the determination unit 16. The determination unit 16 compares the input voltage with the reference voltage value and determines whether the voltage is higher than the reference voltage value.

This underwater laser cutting apparatus has the following functions in addition to the underwater laser cutting apparatus shown in FIG. That is, collecting the plasma light generated from the processing part during cutting,
The signal is transmitted through the optical fiber 6, and the photosensor 14 converts the intensity in the visible wavelength range into an electric signal (voltage). The electric signal is amplified by the amplifier 15 and then compared with the reference voltage value determined in advance by the determination unit 16.

This reference voltage value is a reference for determining whether or not the cut object 3 is cut. If the input voltage is higher than the reference voltage value, the cut cannot be made. It is judged that excessive photoreaction occurs in the processed part without coming out to the side.

On the other hand, when the input voltage is lower than the reference voltage value, good cutting is performed, so that the laser light escapes to the back surface side of the workpiece 3 and the photoreaction in the processed portion is within an appropriate range. It is judged to be suppressed. When the input voltage is higher than the reference voltage value, that is, when it is determined that the object 3 is not cut, a signal is input to the control device 11.

Next, a method of cutting the object 3 using the underwater laser cutting device shown in FIG. 6 will be described. When the determination unit 16 determines that the object to be cut 3 is uncut, the signal is input to the control device 11, and the first and second laser cutting methods according to the present invention are instructed by the control device 11.
1 or 3 in the embodiment, that is, while the laser beam and the gas are emitted from the cutting nozzle 4, the cutting nozzle 4 is once moved in the opposite direction to the object to be cut 3. Scanning is performed so that the area including the uncut portion is folded and scanned so as to overlap.

Next, the operation of this underwater laser cutting method will be described. At the end of the object to be cut 3 and the change in the thickness, it is difficult to collect the laser beam and secure the gas flow rate due to diffusion near the back surface of the object to be cut, and the inertial force of water is It is difficult to control the gas flow, and the center axis of the gas flow and the center axis of the laser beam are easily misaligned, which may cause a groove to be formed, but not completely separated. There is a nature.

When such an uncut portion is formed, it is detected, and while the cutting nozzle 4 emits the laser beam and the gas, the cutting nozzle 4 scans the object 3 in the opposite direction once. Then, by folding and scanning so as to overlap in the area including the uncut portion, the groove formed on the cut object in the first scan causes the laser light to be collected and the gas flow rate up to the vicinity of the back surface of the cut object. Can be secured easily, and the uncut portion can be cut off.

According to this embodiment, a cutting possibility sensor for judging in real time whether or not the cutting object 3 is cut is provided, and when the cutting possibility sensor judges that the cutting object 3 is not cut, While injecting the laser beam and the gas 13 from the cutting nozzle 4, the cutting nozzle 4 is moved to the object 3 to be cut.
It scans in the opposite direction once, and it folds back and scans so that it overlaps in the area including the uncut portion, so the uncut portion is automatically detected and the cut object is formed by the groove formed in the first scan at this portion. Since it is easy to collect the laser light and secure the gas flow rate up to the vicinity of the back surface of the, the uncut portion can be separated. Therefore, the object to be cut can be reliably cut off.

In the above-mentioned embodiment, the case of the sensor for monitoring the plasma light generated in the cutting portion to judge whether or not the cutting is possible has been described. However, the same action and effect can be obtained even when another cutting possibility sensor is used. Can be obtained.

[0047]

According to the present invention, in underwater laser cutting in an underwater environment, it is possible to reliably cut the end portion of the object to be cut or the portion where the thickness of the object to be cut changes.

[Brief description of drawings]

FIG. 1 is an apparatus configuration diagram for explaining a first embodiment of an underwater laser cutting method according to the present invention.

FIG. 2 is a process diagram illustrating a first embodiment of an underwater laser cutting method according to the present invention.

FIG. 3 is a process diagram illustrating a second embodiment of the underwater laser cutting method according to the present invention.

FIG. 4 is a process diagram illustrating a third embodiment of the underwater laser cutting method according to the present invention.

FIG. 5 is a process diagram illustrating a fourth embodiment of the underwater laser cutting method according to the present invention.

FIG. 6 is an apparatus configuration diagram for explaining a fifth embodiment of the underwater laser cutting method according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Water tank, 2 ... Holder, 3 ... Cut object, 4 ... Cutting nozzle, 5 ... Drive mechanism, 6 ... Optical fiber, 6a ... 2nd optical fiber, 7 ... Gas tube, 8 ... Nd: YAG laser oscillator ,
9 ... Compressor, 10 ... Driver, 11 ... Control device,
12 ... Water, 13 ... Laser light / gas, 14 ... Photo sensor, 15 ... Amplifier, 16 ... Judgment part.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B23K 26/08 B23K 26/08 K 26/12 26/12 26/14 26/14 Z G21C 19/37 G21C 19/36 B 19/375 C (72) Inventor Seiichiro Kimura 2-4 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa F-term (reference) 4E068 AE01 CE02 CE08 CH01 CH08 CJ07 DA00 at Toshiba Keihin Plant

Claims (5)

[Claims] 1. A method of laser cutting an object to be cut in water, wherein a laser beam and a gas are emitted when cutting an end portion of the object to be cut or a portion where the thickness of the object to be cut is changed. Underwater laser cutting method, characterized in that the cutting nozzle is reciprocally scanned with respect to the object to be cut. 2. A method of laser cutting an object to be cut in water, wherein laser light and gas are emitted when cutting an end of the object to be cut or a portion where the thickness of the object to be cut is changed. The underwater laser cutting method, wherein the scanning speed of the cutting nozzle for the object to be cut is switched to high speed scanning after low speed scanning. 3. A method of laser cutting an object to be cut in water, wherein when it is determined that the object to be cut has an uncut portion, a cutting nozzle for emitting a laser beam and a gas is provided to the object to be cut. An underwater laser cutting method, characterized in that scanning is performed in a direction opposite to a cutting direction, and reciprocating scanning is performed in a region including the uncut portion. 4. The underwater laser cutting method according to claim 1, wherein the laser oscillator is an Nd: YAG laser, and an optical fiber is used as a means for transmitting the laser light. 5. The underwater laser cutting method according to claim 1, wherein the object to be cut is a highly radioactive solid waste.