Decontamination method using laser decontamination device

Abstract

To realize decontamination in a corner part such as internal corner of a structure by an optical system of a decontamination device and simple setting.SOLUTION: The decontamination method performs decontamination by irradiating an irradiation target member, that is, surfaces of a wall part 3 and a floor part 4 orthogonal to one another and a junction 5 at an internal corner part with a laser beam L emitted from a laser head 20 of a laser decontamination device at an irradiation angle 45°. The decontamination method includes adjusting a focal distance of the laser beam L in an optical system 30 of the laser head 20 in accordance with irradiation angle θv changing when the laser beam L is deflected and scanned, and emitting the laser beam L while focusing the laser beam L on the surfaces of the wall part 3 and the floor part 4 to cut the member surface for decontamination.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a decontamination method using a laser decontamination apparatus, and more particularly to a decontamination method using a laser decontamination apparatus that realizes decontamination work at a corner portion such as a corner of a structure with a simple setting of an optical system and operation of the decontamination apparatus.

Background Art

[0002] In the dismantling of facilities such as nuclear reactors, reprocessing plants, and accelerators in accordance with the decommissioning measures of nuclear facilities and radiation utilization facilities, decontamination devices using laser light have been proposed as devices for reliably and efficiently decontaminating structures themselves contaminated with radioactive isotopes (hereinafter abbreviated as RI), members and parts generated by dismantling, and the like.

[0003] The laser decontamination apparatus disclosed in Patent Document 1 is provided with a surface shape measuring apparatus having a distance meter using measurement laser light irradiated along the optical path of the processing laser light. Based on the surface shape data obtained by this surface shape measuring apparatus, the focusing distance to the member surface position is fed back to the focus position control unit, and the processing laser light is scanned by a galvanometer scanner provided with a mirror controllable with respect to the XY axes.

[0004] In the apparatus disclosed in Patent Document 1, it is possible to scan the processing laser light along a surface shape having irregularities as shown in FIGS. 1 and 2 in Patent Document 1. However, there are problems in that the equipment configuration and system configuration of the apparatus are complicated, the apparatus is expensive, and it lacks practicality at the current technical level.

[0005] Therefore, the applicant has proposed a laser decontamination technology that can efficiently decontaminate the surfaces of members such as concrete structures with many planar shapes and steel plates and steel materials of steel structures in consideration of the shape characteristics of structures and members to be decontaminated (Non-Patent Document 1).

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-108977 [Non-Patent Document]

[0007] [Non-Patent Document 1] Seiichiro Tanaka, et al., "Development of Remote-Controlled Laser Decontamination Technology", [online], February 28, 2022, Ando Hazama Research Annual Report Vol. 9 2021, [searched on September 20, 2023], Internet <https: / / www.ad-hzm.co.jp / trr / 2021 / jp / papers.html> [Summary of the Invention] [Problems to be Solved by the Invention]

[0008] According to the decontamination technology disclosed in Non-Patent Document 1, it has been confirmed that a flat part of a member can be divided into a plurality of decontamination areas, and each decontamination area can be efficiently and sequentially decontaminated by a decontamination device mounted on a cart. However, in an actual structure, there are wall rising parts, corner parts, and direct joining parts between members. In order to decontaminate RI adhering to and penetrating these parts, a step of changing the orientation of the laser head of the decontamination device is required in addition to decontaminating each part, resulting in a decrease in decontamination efficiency.

[0009] Therefore, an object of the present invention is to solve the problems of the above-described conventional technology and to provide a decontamination method using a laser decontamination device that can efficiently perform laser decontamination in the vicinity of a corner part (hereinafter, collectively referred to as a corner part) formed by two members whose surfaces are substantially at right angles, such as a corner part. [Means for Solving the Problems]

[0010] The decontamination method using the laser decontamination apparatus of the present invention is a decontamination method in which laser light emitted from a laser head of the laser decontamination apparatus is irradiated onto a surface to be decontaminated at a predetermined irradiation angle toward a corner portion where two orthogonal surfaces face inward to perform decontamination. In this method, according to the irradiation angle that changes when the laser light is deflected and scanned, the focal length in the optical system of the laser light is adjusted so that the laser light is focused on the surface to be decontaminated to perform decontamination on the surface to be decontaminated.

[0011] With the laser head including the optical system fixed, it is preferable to cut a decontamination target range near the corner portion into a thin layer by deflecting and scanning the laser light.

[0012] The laser light preferably has an initial irradiation angle of 45° with respect to the orthogonal surfaces, and the focal length of the optical system is adjusted according to the change in the irradiation angle over the range of the surface to be decontaminated.

[0013] The adjustment of the focal length in the optical system preferably includes deflecting and scanning the laser light by a galvanometer scanner.

[0014] For the decontamination target range near the corner portion, with the laser head including the optical system fixed, every time the operation of cutting the decontamination target range near the corner portion into a thin layer by deflecting and scanning the laser light is completed, the laser head is preferably moved along the extension direction of the corner portion to be cut in a strip shape.

Effect of the Invention

[0015] According to the present invention, when the decontamination target is a corner portion such as an inner corner, with the orientation of the laser head of the laser decontamination apparatus kept constant, a predetermined range of the corner portion can be irradiated with laser light by setting the laser optical system, and the effect of efficiently performing decontamination can be achieved.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

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Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0017] Hereinafter, as an embodiment for carrying out the decontamination method by the laser decontamination apparatus of the present invention, the configuration of the laser decontamination apparatus and the decontamination method for the corner portions and the like of the structure will be described with reference to the accompanying drawings.

[0018] FIG. 1 shows a laser decontamination apparatus 10 (hereinafter referred to as the decontamination apparatus 10) according to an embodiment of the present invention. This decontamination apparatus 10 is used in the dismantling work of nuclear facilities and radiation utilization facilities, etc. In areas with high radiation doses where direct work by workers is difficult, and in complex and narrow areas with intricate shapes, the surface of the concrete and steel materials of the structure 1 contaminated with radioactive substances is cut by irradiating with a laser beam L by remote operation so as to peel off a thin layer for decontamination. The present invention, as shown in FIGS. 1 and 2, can efficiently irradiate and cut the surface of the member in the vicinity of the corner portion 2 formed by the wall surface 3 and the floor surface 4, where the surfaces of the two members are substantially at right angles, especially in the corner portions and the like of the structure 1. The optical system of the laser beam L irradiated from the laser head described later and the movement operation of the self-propelled mechanism 13 of the decontamination apparatus 10 main body are controlled.

[0019] As a method and procedure for irradiating the laser beam L to the corner portion 2 according to the present invention, as shown in FIGS. 1 to 3, along a straight line or a curve that is the boundary line between the wall surface 3 and the floor surface 4 as an example constituting the corner portion 2, from the decontamination device 10 to the corner portion 2, with the reference line S having an inclination of 45° from the floor surface 4 (or the wall surface 3) (hereinafter referred to as the 45° line S) as the center, within a predetermined angle range (hereinafter, this range is referred to as the cutting area A), the laser beam L is deflected and scanned in a predetermined pattern to perform decontamination within the cutting area A. Also, by continuously irradiating the laser beam L so that the respective cutting areas A are adjacent to each other, the surface of the member near the corner portion 2 is continuously cut, and the corner portion 2 contaminated with RI can be decontaminated in a band shape with a predetermined width. For example, when performing decontamination within the pit P shown in FIG. 2(a), decontamination of a portion composed of a wide plane such as each of the wall surface 3 and the floor surface 4 can be performed by a decontamination method using a laser decontamination device disclosed in Non-Patent Document 1.

[0020] Depending on the laser decontamination device disclosed in Non-Patent Document 1, in the linear corner portion 2 at the boundary between the wall surface 3 and the floor surface 4 that is difficult to decontaminate, decontamination can be performed by cutting the surface of the member with the laser beam L along a narrow band-shaped range as shown in the figure by the decontamination method according to the present invention. Also, in the corner portion 2 formed by the boundary between the wall surface 3 and the floor surface 4 having a curved surface shape such as a tank as shown in FIGS. 2(b) and 2(c), by the procedure of moving the laser head 20 of the decontamination device 10 (FIG. 1) along the φ direction, the cutting areas A can be made continuous in a polygonal shape along the range of the corner portion 2 formed by a narrow band-shaped curved surface to cut the surface of the member. In each of the diagrams in FIG. 2, the horizontally extending corner portion 2 formed by the boundary between the wall surface 3 and the floor surface 4 is described as an example, but it goes without saying that the present invention is also applicable to a corner portion extending in the vertical direction as the boundary between two wall surfaces.

[0021] Hereinafter, the decontamination device 10 used in the laser decontamination method of the present invention will be described with reference to the attached drawings. [Configuration of Decontamination Device 10] As shown in Fig. 1, the decontamination device 10 of the present invention is composed of a known CW laser oscillator 11 as a light source of the laser beam L, a laser head 20 that emits the laser beam L guided from the laser oscillator 11 through an optical fiber cable 12 in a predetermined direction, and a self-propelled mechanism 13 that can move the laser head 20 in a predetermined direction.

[0022] The laser oscillator 11 can be installed at a location away from the RI contamination area or the high-dose area. The specifications of the laser oscillator 11 used in this embodiment are a CW (continuous wave) single-mode fiber laser (oscillation wavelength 1080 nm), and the maximum output is 500 W.

[0023] (Configuration of the laser head 20) The laser head 20 is composed of a variable-focus concave lens 31 that can slide in the Z-axis direction to change the focal length of the incident laser beam L, a condenser lens 32 located behind the variable-focus concave lens 31 on the optical axis, and a Z-axis focus adjustment unit 30. A galvanometer scanner 40 (the configuration will be described later) that can deflect and scan the laser beam L from the condenser lens 32 of the Z-axis focus adjustment unit 30 in a predetermined direction (angle), and a laser beam L that is two-dimensionally deflected by the galvanometer scanner 40 and emitted from the laser head 20 toward the irradiation target. An fθ lens 21 that can be focused on the surface of the irradiation target regardless of the deflection angle, and a control driver 22 that controls the slide amount and rotation angle of the mirror groups of the Z-axis focus adjustment unit 30 and the galvanometer scanner 40. The laser head 20 is mounted on the self-propelled mechanism 13 and can irradiate the laser beam L while moving according to a predetermined control mode with respect to the laser oscillator 11 connected by the optical fiber cable 12 to perform a cutting operation on the irradiation target. In Fig. 1, for the sake of simplicity of the figure, only the optical axis of the laser beam L is drawn. However, as shown in Figs. 3 and 4, the laser beam L passes through each lens on the optical path, so that the light diameter is controlled, deflected by the galvanometer scanner 40, etc., and emitted from the laser head 20, and is focused on the surface of the irradiation target with the minimum spot diameter.

[0024] (Configuration and operation of the Z-axis focus adjustment unit 30) The variable-focus concave lens 31 of the Z-axis focus adjustment unit 30 is held slidably in the Z-axis direction on the optical axis by a voice coil motor 23 controlled by a control driver 22. Therefore, the degree of divergence of the laser beam L guided into the laser head 20 is changed after passing through the variable-focus concave lens 31 by the sliding operation of the variable-focus concave lens 31. Further, a condenser lens 32 (convex lens) is fixedly arranged behind the variable-focus concave lens 31 on the optical path. As shown in FIGS. 1, 3, and 4, this condenser lens 32 has a focal length F at which the minimum spot diameter is obtained on the surface of the irradiation target after the optical path is deflected by the galvanometer scanner 40. The focal length F changes with the change in the position of the variable-focus concave lens 31 on the optical axis.

[0025] (Configuration and operation of the galvanometer scanner 40) The galvanometer scanner 40 has two mirrors that can deflect and scan the laser beam L around two axes, the X-axis and the Y-axis (see FIG. 1). The first mirror 41 is pivotally supported on a support shaft 43a extending the rotation axis (Y-axis) of the motor 43, and the second mirror 42 is pivotally supported on a support shaft 44a extending the rotation axis (X-axis) of the motor 44. Both are controlled in conjunction by the control driver 22 so that the rotation angles are controlled, and the respective mirror surfaces (reflective surfaces) can be set to form a predetermined reflection angle. Thereby, the optical path of the laser beam L can be two-dimensionally deflected through the respective reflective surfaces of the first mirror 41 and the second mirror 42, and the laser beam L can be scanned in a predetermined direction (angle).

[0026] (Configuration and operation of the emission-side lens) An fθ lens 21 is disposed on the laser head 20 at the side from which the laser light L is emitted. By disposing the fθ lens 21 on the emission side, the laser light L that passes through the fθ lens 21 and is irradiated onto the surface of the irradiation target can be focused with a circular minimum spot diameter on the surface of the irradiation target even if the scanning angle at the time of emission changes. The function of the fθ lens 21 is exerted even when the angle θv changes and the focal position is controlled by the Z-axis focus adjustment unit 30 and the mirror control by the galvano scanner 40 is performed. It is preferable to use a cylindrical lens as the lens constituting the fθ lens 21. It is also possible to use a toroidal lens having a lens surface with different curvatures in two axial directions.

[0027] (Installation of a removed material recovery device) The laser head 20 is preferably provided with a gas ejection device (not shown) that blows away the cutting waste (removed material) with an inert gas, and a removed material recovery device (not shown) that sucks up and collects the removed material containing RI. This allows the laser light L to use an inert gas to collect and remove the removed material containing RI on the surface of the irradiation target contaminated with RI. Alternatively, a device may be used that installs a hood covering the irradiation section and sucks up and collects the removed material using negative pressure.

[0028] (Configuration of the self-propelled mechanism 13) As the self-propelled mechanism 13, various types of traveling devices such as a crawler traveling carriage on which the laser head 20 can be directly mounted, a tire traveling carriage, etc., as shown in FIG. 1, can be used. Each traveling carriage is equipped with a support mechanism that can adjust the inclination of the supported laser head 20, the irradiation direction and angle of the laser light L. It is also preferable to mount a robot arm or the like that can be controlled to various support states. The self-propelled mechanism 13 can travel at a set speed along a course and route that are preprogrammed by a driving control unit (not shown), but an operator may remotely control it via a controller or the like based on a real image of the irradiation location.

[0029] [Laser light irradiation method within cutting area A] A laser decontamination method for a corner portion 2 by irradiating a laser beam L using the decontamination apparatus 10 described in the present invention will be described with reference to FIGS. 3 to 5. FIG. 3 is an explanatory diagram showing a schematic configuration inside the laser head 20 of the decontamination apparatus 10 shown in FIG. 1 and a state in which the light beam of the laser beam L emitted from the laser head 20 is scanned on the surface of the corner portion 2 to be irradiated. FIG. 4 is an optical path diagram in which the optical path of the laser beam L two-dimensionally deflected and scanned by the mirrors 41 and 42 and irradiated on the corner portion 2 is drawn in a plane for explanation. FIG. 5 is an explanatory diagram showing the scanning pattern of the laser beam L in the cutting area A of the corner portion 2 and the continuous state of the cutting area A.

[0030] Hereinafter, the relationship between the irradiation angle θv and the irradiation distance f of the laser beam L at the initial position of the laser head 20 in the cutting area A will be described based on the geometric relationship in the explanatory diagrams shown in FIGS. 3 and 4. The initial position of the laser head 20 of the decontamination apparatus 10 is set at a position where the emitted laser beam L is irradiated along a reference line S (45° line S) forming θ = 45° toward the joint point 5 between the orthogonal floor surface 4 and wall surface 3, as shown in FIG. 3. Here, in FIGS. 3 and 4, the distances, positions, etc. of each part are defined as follows. a: The distance from the joint point 5 between the floor surface 4 and the wall surface 3 of the corner portion 2 to the range where cutting is performed b: The horizontal distance between the joint point 5 and the support shaft 44a of the second mirror 42 of the galvanometer scanner 40 θv: An arbitrary irradiation angle of the laser beam L irradiated within the range of the 45° line and the distance a F: The focal length from the condenser lens 32 to the surface to be irradiated F 0 : The distance from the condenser lens 32 to the reflecting surface of the second mirror 42 (fixed value) f: The irradiation distance from the reflecting surface of the second mirror 42 to the surface to be irradiated

[0031] That is, as described above, it is clear from the geometric shape shown in FIG. 3 that the relationship between the irradiation angle θv and the irradiation distance f is in the following relationship of Equation 1.

[0032] TIFF2025077607000002.tif29136 Therefore, as shown in FIGS. 3 and 4, when rotating the second mirror 42 in the laser head 20 to deflect and scan the laser beam L and irradiate the surface of the object to be irradiated within the range a with the laser beam L, the irradiation distance f from the reflecting surface of the second mirror 42 to the surface of the object to be irradiated is the value set at the initial position (θv = 0°) of the laser head 20 as θv increases.

[0033] TIFF2025077607000003.tif35116 becomes shorter. In response to this change, in the present invention, the irradiation distance f is adjusted by simply moving the Z-axis position of the variable-focus concave lens 31 of the Z-axis focus adjustment unit 30 by several millimeters on the optical axis, so that the laser beam L is focused on the surface of the object to be irradiated, and irradiation with the laser beam L at the minimum spot diameter can be performed. The adjustment of the laser optical system such as the control of the Z-axis position of the variable-focus concave lens 31 of the Z-axis focus adjustment unit 30 and the mirror control of the galvanometer scanner 40 is designed to be executed according to a command from the control driver 22 (FIG. 1) provided in the laser head 20.

[0034] Further, since the laser beam L passes through the fθ lens 21 on the emission side of the laser head 20, even if the optical axis of the laser beam L is deflected by θ, the laser beam L can be focused into a circular shape with the minimum spot diameter on the surface of the object to be irradiated. According to the optical design performed by the applicant, it was confirmed that by adjusting the position of the variable-focus concave lens 31 of the Z-axis focus adjustment unit 30 by approximately 6.6 mm in the Z-axis direction, a change amount of the focal length F of approximately 80 mm can be obtained.

[0035] In the description of FIG. 3, the deflection scanning of the laser beam L by changing the irradiation angle θv over the range a of the floor surface 4 to the range a of the wall surface 3 was described. In contrast, FIG. 5 shows the scanning pattern of the laser beam L within the cutting area A. FIG. 5 shows a cutting area A where the cutting of the range a of the wall surface 3 and the floor surface 4 and the range of width B of the surface to be irradiated has been completed by the irradiation of the laser beam L, and a state where the laser beam L reciprocally scans within an area adjacent to the cutting area A to cut the surface of the member. The cutting in one cutting area A shown in the figure can be realized only by controlling the slide operation on the optical axis (Z-axis) of the variable-focus concave lens 31 of the Z-axis focus adjustment unit 30 within the laser head 20 without moving the laser head 20, and by controlling the reflection angles of the first mirror 41 and the second mirror 42 of the galvanometer scanner 40. The scanning pattern of the laser beam L within this cutting area A is in a zigzag shape that reciprocates while shifting the width B of the cutting area A (in the y-axis direction) in the cutting progress direction. When reciprocally scanning in the zigzag shape, the zigzag scanning pattern, the laser output, and the beam spot diameter are set so that the cutting operation in the cutting area A can be performed evenly.

[0036] Based on the above-described irradiation (cutting) method using the laser beam L, the procedure of the decontamination operation of the decontamination method by the laser decontamination apparatus 10 of the present invention will be described with reference to FIGS. 6, 1, 2(a), and 5. For example, when performing the decontamination operation using the laser beam L over the entire length in the extension direction (y direction) of the joint portion (corner portion 2) between the floor surface 4 and the wall surface 3 of the long side of the pit P shown in FIG. 2(a), the moving direction of the laser head 20 that coincides with the extension direction (y direction) of the pit P, that is, the traveling direction of the decontamination apparatus 10, and the cutting distance on the member surface are set. Next, the support position and angle of the laser head 20 are set so that the laser beam L forms a 45° angle with the floor surface 4 (or the wall surface 3) of the corner portion 2 to be irradiated (coincides with the assumed 45° line: irradiation angle θv = 0°). At the same time, the Z-axis direction position of the variable focal concave lens 31 of the Z-axis focus adjustment unit 30 of the control driver 22 in the laser head 20, the rotation angles of the mirrors of the galvanoscanner 40, etc. are initialized, and the laser specifications, scanning speed, scanning pattern, etc. of the laser beam L in one cutting area A are set as scanning conditions.

[0037] From this state, cutting of the surface of the member within the cutting area A by irradiation with the laser beam L is started. The laser beam L is scanned back and forth in a zigzag shape within one cutting area A, for example, as shown in FIG. 5, to thinly peel off the surface of the member for cutting and remove the surface portion contaminated with RI. As described above, the cutting operation within one cutting area A can be performed only by controlling the position of the variable focus concave lens 31 of the Z-axis focus adjustment unit 30 in the Z-axis direction and controlling the rotation angle of each mirror of the galvanometer scanner 40 without moving the laser head 20. When the cutting operation within one cutting area A is completed, the laser head 20 is moved along the y-direction by the width (B) of one cutting area A. At this time, the injection nozzle of the laser beam L or the like is reset to the initial position at the start of scanning. Therefore, the cutting operation in the new cutting area A can be performed continuously with the cutting area A where the cutting operation has already been completed. The cutting operation by the laser beam L for each cutting area A is repeated until the cutting for the set cutting distance is completed. Each process of the cutting operation can be stored and executed by the control driver 22, but it is also possible to perform the operation while the operator checks the cutting status based on the real-time video obtained by a monitoring camera or the like mounted on the laser head 20.

[0038] In the above description, it has been described that the surface of the irradiation target contaminated with RI can be decontaminated using a laser beam, but the present invention is also applicable to the field of material processing using a laser beam. For example, in the manufacture of a stepped shaft used as an automotive part, it can be applied to a technique such as laser hardening treatment aimed at improving the strength of a portion such as a corner where stress concentration is expected.

[0039] Note that the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in each claim. That is, embodiments obtained by combining technical means appropriately modified within the scope shown in the claims are also included in the technical scope of the present invention.

Description of Reference Numerals

[0040] 1 Structure 2 Corner part 10 Laser decontamination device 11 Laser oscillator 13 Self-propelled mechanism 20 Laser head 21 fθ lens 22 Control driver 23 Voice coil motor 30 Z-axis focus adjustment unit 31 Variable focus concave lens 32 Condensing lens 40 Galvanometer scanner 41 First mirror 42 Second mirror A Cutting area L Laser beam S 45° reference line (45° line)

Claims

1. A decontamination method for decontaminating a surface to be decontaminated by irradiating a laser beam emitted from a laser head of a laser decontamination apparatus onto a corner having two orthogonal surfaces facing inward at a predetermined irradiation angle, A decontamination method using a laser decontamination apparatus, characterized in that a focal length within an optical system of the laser light is adjusted in accordance with the irradiation angle that changes when the laser light is deflected and scanned, and the laser light is focused on the surface to be decontaminated, thereby decontaminating the surface to be decontaminated.

2. 2. A decontamination method using a laser decontamination apparatus according to claim 1, wherein the decontamination target area near the corner is cut into a thin layer by deflection scanning of the laser light while the laser head including the optical system is fixed.

3. 3. A decontamination method using a laser decontamination apparatus according to claim 1 or claim 2, wherein an initial irradiation angle of the laser light is 45° with respect to the perpendicular plane, and a focal length of the optical system is adjusted in response to changes in the irradiation angle over the range of the surface to be decontaminated.

4. 2. The decontamination method using a laser decontamination apparatus according to claim 1, wherein adjustment of the focal length in the optical system includes deflection scanning of the laser light using a galvano scanner.

5. A decontamination method using a laser decontamination device, in which the decontamination target area near the corner is cut in a strip shape by moving the laser head along the extension direction of the corner each time the cutting described in claim 2 is completed.

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