JPH11183693A - Method and device for decontamination - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decontaminate surfaces of structural materials and equipment in contact with a radioactive fluid through laser irradiation while preventing radioactive adherents from scattering and suppress or reduce the readhesion of radioactivity after the decontamination. SOLUTION: A large area of a surface of an object 4 is irradiated with a laser 6 at a homogenized low energy density to remove a radioactive substance adhering to the surface by exfoliating it and suppress the readhesion of the radioactive substance through the modification of the surface of a base material. The laser irradiation can be done in water or a liquid containing chemicals such as an oxidizer and a reductant, which makes it possible both to prevent the diffusion and emission of the exfoliated radioactive substances into the air and to accelerate the modification of the surface of the base material. By using a double pulse laser or that of two or more waves, moreover, even the timing and period of each laser irradiation can be controlled through the decontamination and surface modification.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for decontamination by laser, and more particularly, to a method for adhering to a structural material or equipment that comes into contact with a radioactive fluid in a facility for handling radioactivity such as a nuclear power plant. The present invention relates to a method for decontaminating a radioactive substance by removing and removing the radioactive substance by irradiation with a laser, modifying a surface of the radioactive substance to suppress re-adhesion of the radioactive substance, and an apparatus therefor.

[0002]

2. Description of the Related Art In a facility for handling radioactivity such as a nuclear power plant or a spent fuel reprocessing plant, a pipe constituting a flow path of a fluid having a radioactivity (liquid), a device installed in the flow path, and the like. A film such as a metal oxide is formed on the surface, and the radioactive substance is incorporated therein. In such plants, in order to prevent workers from being exposed during overhaul for maintenance and management of structural materials such as pipes and equipment, in order to prevent workers from being exposed, the attached metal oxide film with radioactivity was removed in advance. (Decontamination) has become important.

In a nuclear power plant or the like, when decontaminating the entire system, it is desirable to employ a chemical decontamination method in which a decontamination agent is circulated to chemically dissolve the oxide film. When decontaminating a small range of structural materials or a single device such as the above, the chemical decontamination method requires a partition for creating a circulating system in each device, a decontamination seat for taking in and out the decontamination agent, etc. It is necessary to set up a light emitting device, which in turn causes exposure to reduce the exposure of workers, resulting in a problem of poor decontamination efficiency. Therefore, in actuality, mechanical decontamination such as wiping a metal oxide film adhered to the surface of these structural materials or devices with a rag or a brush has been implemented.

Therefore, as a method for easily performing decontamination of a small area of a single device such as a pump or a valve or a structural material in a short time, a decontamination method by laser irradiation has been proposed. For example, Japanese Patent Publication No. 1-45039 discloses a method in which a laser is scanned by a reflection mirror, and the scanned laser beam spot is irradiated into a nuclear reactor to remove an oxide film. JP-168400 discloses a method in which a laser beam having a circular cross section is condensed in one axial direction by a cylindrical lens, and this elongated linear beam spot is irradiated to perform decontamination. Also,
Japanese Patent Application Laid-Open No. 7-225300 discloses that a pulsed laser is condensed linearly, and a removal accelerating liquid (water, detergent, rust remover, organic solvent, etc.) is applied to the surface deposits before or during laser irradiation. Is disclosed. further,
JP-A-8-110396 discloses that after decontamination by irradiation with a first laser in a dry environment, surface irradiation is performed by irradiation with a second laser and supply of a modifier such as an oxidizing agent. A method for forming a layer is disclosed.

[0005]

However, these conventional decontamination methods have the following problems. In other words, a method of focusing a high-power laser in a point or line shape and scanning such a laser beam on the surface of a member to be decontaminated with a uniform energy density requires a precise scanning control mechanism. If the control is not sufficient, the surface of the device or the like after the adhered substance is removed may be irradiated with a high-power laser, and the device itself may be damaged. In addition, in the conventional decontamination method, since all lasers are irradiated in the air, the adhered material that has been peeled off and scattered may scatter, causing exposure of workers, or damage to the lens and surrounding equipment. There is a problem that it adheres and generates new contamination. Further, after decontamination, the radioactive substance may adhere to the surface of the device or the like again.

The present invention has been made to solve these problems, and decontaminates the surface of a structural material or equipment that comes into contact with a radioactive fluid while preventing scattering of radioactive deposits. An object of the present invention is to provide a laser decontamination method and an apparatus for suppressing and reducing the reattachment of radioactivity.

[0007]

According to the decontamination method of the present invention, a laser having a controlled energy density is applied to the surface of a structural material or equipment which comes into contact with a radioactive fluid, and adheres to the surface of the structural material or equipment. The radioactive material is peeled off and removed, and a surface-modified layer in which the radioactive material is prevented from adhering is formed.

Further, the decontamination apparatus of the present invention irradiates a laser having a controlled energy density to a surface of a structural material or a device which comes into contact with a radioactive fluid, and removes a radioactive substance attached to the surface of the structural material or a device. Peel and remove,
A decontamination device that forms a surface modified layer in which the adhesion of the radioactive substance is suppressed, a laser oscillation section, an optical transmission system that transmits a laser oscillated from the oscillation section, and a laser transmission section that is transmitted by the optical transmission system. And an optical irradiation system for shaping and irradiating the laser beam into a parallel beam.

According to the present invention, in a facility for handling radioactivity such as a nuclear power plant, a laser beam is made uniform over a relatively large area on the surface of a structural material such as a pipe or a device such as a valve which comes into contact with a radioactive fluid. Irradiation at a low energy density removes and removes the radioactive oxide film attached to the surface by ablation without changing the basic properties of the base material, and smoothes the surface of the metal base material. Alternatively, by thermally melting or amorphizing the surface, it is possible to form a surface-modified layer in which re-adhesion of a radioactive substance is suppressed.

[0010] In the decontamination method and decontamination apparatus of the present invention, laser irradiation can be performed in water or in a liquid containing a desired drug, in addition to air. By irradiating a laser in water or a liquid containing a drug, a radioactive metal oxide separated from the surface of a structural material or a device to be decontaminated (hereinafter, referred to as a member to be decontaminated) is converted into water or water. Since the radioactive contaminants are diffused and held in the liquid containing the drug, the radioactive contaminants can be prevented from being diffused and released into the air. In addition, when the laser is irradiated in water or in a liquid containing a drug, in addition to the ablation effect, the surface of the base material is modified by the interaction between the metal base material and water or the drug on the irradiated surface. Is promoted. As the agent, permanganic acid or hydrogen peroxide as an oxidizing agent, and oxalic acid as a reducing agent can be used.

In the present invention, the laser to be irradiated may be a solid laser oscillated from a solid element such as Nd: YAG, Er: YAG, alexandrite, ruby, glass or the like, or an excited state of ArF, KrF or XeCl molecules. An excimer laser or a semiconductor laser can be used.

In addition, two or more of these lasers are combined, that is, a combination of a laser suitable for removing radioactive oxide and a laser suitable for forming a surface-modified layer is applied. By the synergistic effect, decontamination and surface modification can be performed more efficiently. Furthermore, a pulsed laser may be used instead of a continuous wave laser, and the pulsed laser may be oscillated and irradiated with its timing and interval adjusted. Further, in the irradiation of such a double-pulse laser or two or more lasers, decontamination and surface modification are performed by adjusting the irradiation time of each laser, so that decontamination and surface modification can be performed. It can be performed more efficiently.

The decontamination apparatus according to the present invention includes a laser oscillating section, an optical transmission system, and an optical irradiation system. As the optical transmission system for transmitting a laser, an optical fiber such as a multi-bundle fiber may be used. it can. In the optical irradiation system, the laser beam narrowed down by the optical transmission system or the like is expanded again to be shaped into a parallel beam, and the energy density is smooth distribution close to Gaussian shape (normal distribution) or distribution close to flat top shape. The optical element which adjusts is built in.

In the present invention, the energy density of the laser to be irradiated is controlled to a uniform and low level by such an optical irradiation system, so that precise scanning control is not required. Uniform decontamination and surface modification can be performed over a wide range of the surface of the target member.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a view schematically showing a first embodiment of a decontamination apparatus according to the present invention. The decontamination device is a device for decontaminating a contaminated portion of a valve installed in a pipe of a nuclear power plant, and the valve is illustrated with a lid, a handle, and a shaft removed.

As shown in FIG. 1, the decontamination apparatus according to the first embodiment includes a laser oscillation unit 1 having a laser oscillator such as an Nd: YAG laser, a vacuum unit, a power supply unit, and a control unit. A decontamination object (consisting of a connection hose part 2 connected to the laser oscillation unit 1 and an irradiation head unit 3 connected to the other end of the connection hose part 2 and fixed in a pipe of a plant ( A liquid (e.g., an aqueous solution) that is installed movably with respect to the valve 4 and contains water or a drug.
5 is configured to irradiate a laser 6. As the chemical, an oxidizing agent such as permanganic acid or hydrogen peroxide or a reducing agent such as oxalic acid is used.

The connection hose section 2 contains an optical fiber and a power cable, and the laser oscillated from the laser oscillation unit 1 is transmitted to the irradiation head unit 3 by the optical fiber. As the optical fiber, a multi-bundle type optical fiber (multi-bundle fiber) in which many optical fiber elements are converged is used. For multi-bundle fiber,
By reducing the transmission energy per fiber, the fiber is prevented from being damaged.

In order to make the laser oscillated from the laser oscillation unit 1 efficiently enter such a multi-bundle fiber, a multi-lens (not shown) formed by combining a plurality of lenses is used to enter the optical fiber. At the exit end, at the exit end, the focused optical fiber elements are rearranged to exhibit an elongated cross-sectional shape such as an oval, linear, or rectangular shape to facilitate shaping the laser beam shape. ing. Instead of rearranging the optical fiber elements as described above, a multi-lens having a plurality of lenses arranged perpendicular to the laser optical axis, a homogenizer combining a prism and a mirror, or the like is provided at the emission end of the optical fiber. Alternatively, the laser beam may be shaped.

The irradiation head unit 3 has a built-in irradiation optical system 7, and the irradiation optical system 7 expands a laser beam and irradiates the object 4 as a parallel beam. Here, the irradiation optical system 7 is formed by one optical lens inserted into the unit or a combination of two optical lenses. By controlling the irradiation optical system 7, the irradiation optical system 7 can be used. It is also possible to configure so that the energy density can be adjusted.

In the first embodiment of the decontamination method according to the present invention, the laser 6 having a controlled energy density and irradiated from the irradiation head unit 3 of the decontamination apparatus is used as a valve to be decontaminated. Irradiate the inner surface of Laser 6
Irradiation, contaminants adhering to the inner surface of the bulb,
In other words, the metal oxide film containing radioactivity is ablated by the heat of laser or energy of impact vibration, and is peeled and removed in a fine particle state. At this time, at the same time as removing and removing the contaminated metal oxide film,
The surface of the base material of the object to be decontaminated is smoothed, or the surface of the base material is thermally melted or amorphized to form a surface modified layer in which reattachment of radioactivity is suppressed.

Next, another embodiment of the decontamination apparatus of the present invention will be described.
These are shown in FIGS. 2 to 5, respectively. In these drawings, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

In the decontamination apparatus of the second embodiment, as shown in FIG. 2, two laser oscillation units 1a and 1b each having a built-in laser oscillator are provided in parallel. One irradiation head unit 3 via connection hoses 2a and 2b containing fibers
It is connected to the. The irradiation head unit 3 has a mechanism (not shown) for alternately selecting and irradiating two lasers (pulse lasers) 6 transmitted from the respective laser oscillators.

In the second embodiment of the decontamination method of the present invention using such a decontamination apparatus, a laser which is most effective for decontamination and formation of a surface-modified layer is selected, and a laser is applied to an object. Since irradiation is performed, both decontamination and surface modification can be performed most efficiently.

In the decontamination apparatus according to the third embodiment, as shown in FIG. 3, a plurality of mirrors 8 are used instead of optical fibers as transmission means of the laser oscillated from the laser oscillation unit 1. Each of these mirrors 8 is installed in a movable arm cover 9. The movable arm cover 9 which can move itself allows the irradiation head unit 3 to move with respect to the object 4 to be decontaminated.

The irradiation head unit 3 includes a plurality of movable mirrors 10 as shown in an enlarged view in FIG. A laser transmission window 11 made of a transparent material such as glass is formed on the front surface of the irradiation head unit 3.

In the third embodiment of the present invention using such a decontamination apparatus, the angle of the movable mirror 10 incorporated in the irradiation head unit 3 with respect to the laser optical axis is adjusted, so that the irradiation head unit 3 is controlled. The laser 6 can be irradiated to a certain area on the surface of the decontamination target 4 without moving the whole. The irradiation head unit 3
However, the laser irradiation can be performed even when the irradiation head unit 3 is immersed in water or a liquid 5 containing a chemical, since it has a watertight structure and is provided with a laser transmission window 11 on the front surface.

The decontamination apparatus according to the fourth embodiment is provided with a circulation line 13 having a circulation pump 12 as shown in FIG.
Is circulated through the circulation line 13 by being sucked by the circulation pump 12. Further, in order to improve the decontamination efficiency, a purification filter 14 for removing suspended matters and the like in the circulating liquid is inserted in the circulation line 13. Further, the circulation line 13 including the circulation pump 12 and the purification filter 14 is configured to move in conjunction with the irradiation head unit 3.

In the fourth embodiment of the present invention using such a decontamination apparatus, the radiation released from the surface of the object 4 to be decontaminated by the irradiation of the laser 6 from the irradiation head unit 3 is used. The metal oxide film (not shown) is forcibly circulated while suspended in the liquid 5 containing water or a chemical, and is removed by the purification filter 14 in the circulation line 13. Therefore, such contaminated suspended matter does not hinder laser irradiation, and efficient laser irradiation can be performed continuously.

In the fourth embodiment, the laser
The configuration in which the liquid 5 containing water or medicine near the irradiation field is sucked and circulated by the circulation pump 12 has been described, but the circulation direction by the circulation pump 12 is reversed to include the water or medicine circulated through the circulation line 13. The liquid 5 may be blown out near the decontamination target 4.

Further, when the object to be decontaminated is removable from the structural material or the main body of the equipment, the decontamination and surface modification are carried out as follows by using the decontamination apparatus of the above embodiment. be able to.

That is, as shown in FIG. 6, a glass water tank 15 filled with a liquid 5 containing water or a chemical is installed opposite to the fixed irradiation head unit 3, and the bulb removed from the apparatus body or the like is installed. Such an object 4 to be decontaminated is suspended in a glass water tank 15 by a suspension handle 16 provided with a drive mechanism, and is immersed in the liquid 5 containing water or a drug. Then, while driving the suspension handle 16 in conjunction with the laser oscillation from the oscillation unit 1, the irradiation head unit 3
Laser irradiation. Thus, the decontamination object 4
Can be efficiently irradiated with the laser 6 to perform decontamination and surface modification.

In the above embodiment, decontamination is performed by irradiating the surface of the contaminated object with a laser, and the surface modification layer is formed to suppress reattachment of radioactivity after decontamination. Before the operation of the plant, the surface of structural materials and equipment that come into contact with the radioactive fluid was irradiated with a laser to modify the surface of the base material regardless of decontamination, and to emit radiation at the time of new use. It is also possible to suppress or reduce functional adhesion.

Next, as a specific example of the decontamination method of the present invention, decontamination by laser irradiation was performed using a test piece made of SUS304 steel.

Embodiments 1 and 2 First, the formation of a preliminary oxide film simulating an actual machine was performed under the normal water quality conditions of a BWR primary system (temperature 285 ° C., dissolved oxygen concentration 200 ppb) using a high-temperature high-pressure loop test apparatus. This was performed by soaking for 500 hours.

On the surface of the test piece on which the preliminary oxide film was formed, a second harmonic (wavelength: 532 nm) of an Nd: YAG laser was applied.
m) is changed to a condition with a lower energy density than before (laser output intensity 132mJ / pulse, beam diameter 5mm,
Irradiation was performed in the air and in water at a scanning speed of 25 mm / s) to remove the oxide film.

Next, the test piece after decontamination was placed in water adjusted to a Co-60 concentration of 0.02 Bq / ml under the conditions of BWR hydrogen injection water (temperature 285 ° C., dissolved oxygen concentration 10 ppb, dissolved hydrogen concentration 50 ppb). After immersion for 500 hours, the radioactivity (C
o-60) The adhesion amount was measured by a Ge detector. For comparison, the oxide film formed on the surface of the SUS304 steel test piece was mechanically decontaminated by Emery No. 500, and the amount of Co-60 radioactivity deposited on the test piece after decontamination was measured. It measured like Example. Table 1 shows the measurement results.

[0038]

[Table 1] As is clear from the table, when the amount of radioactivity attached to the test piece after decontamination is set to 1 in the case of the comparative example in which mechanical decontamination was performed, Example 1 in which the laser treatment was performed in air was performed. 0.51 in Example 2, and 0.2 in Example 2 where laser processing was performed in water.
The result was 46, and it was confirmed that in the examples, the decontamination effect and the effect of suppressing the adherence of radioactivity after decontamination were confirmed.

When the appearance of the test piece after the radioactivity reattachment test was visually observed, in the comparative example in which laser treatment was not performed, the entire surface was covered with a black oxide film. Example 2 with laser treatment in water
It was found that there was no oxide film adhered and the film exhibited metallic luster. Further, photographs (SEM photographs) of the surfaces of these test pieces were taken with an electron microscope. FIG. 7 shows a surface SEM photograph of Example 2, and FIG. 8 shows a surface SEM photograph of Comparative Example.

As is clear from these photographs, the test piece obtained in the comparative example has magnetite crystals, which are spinel-type oxides grown to 1 μm or more, and its surface is tightly covered. In the test piece obtained in Example 2, it was confirmed that these oxide crystals hardly adhered, and the generation and growth of crystals were significantly suppressed.

[0041]

As is evident from the above description, in the present invention, a laser having a relatively low energy density which is uniform over a wide area of the surface of the object to be decontaminated is irradiated.
Decontamination can be performed without the need for precise scanning control and without adversely affecting the properties of the base material of the object to be decontaminated. At the same time, the surface is modified to suppress the adhesion of radioactivity after decontamination. can do.

In addition, it is possible to simply and efficiently decontaminate a single device such as a pump and a valve without using a large-scale apparatus as in systematic chemical decontamination.

Further, by irradiating a laser beam in water or a liquid containing a drug, it is possible to prevent contamination due to the diffusion of the separated radioactive material into the air and promote the modification of the surface of the object to be decontaminated. it can.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of a decontamination apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram showing a second embodiment of the decontamination apparatus according to the present invention.

FIG. 3 is a schematic configuration diagram showing a third embodiment of the decontamination apparatus according to the present invention.

FIG. 4 is an enlarged view showing a structure of an irradiation head unit in a third embodiment.

FIG. 5 is a schematic configuration diagram showing a fourth embodiment of the decontamination apparatus according to the present invention.

FIG. 6 is a diagram showing a schematic configuration of a fifth embodiment of the decontamination method of the present invention.

FIG. 7 is a surface SEM photograph of the test piece of Example 2 after the radioactivity reattachment test.

FIG. 8 shows the surface S of the test piece of the comparative example after the radioactivity reattachment test.
EM photograph.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser oscillation unit 2 ... Connection hose part 3 ... Irradiation head unit 4 ... Object to be decontaminated 5 ... Water or liquid containing chemicals 6 ... Laser 7 ... Irradiation optics System 8 Mirror 9 Movable arm cover 10 Movable mirror 11 Laser transmission window 12 Circulation pump 13 Circulation line 14 Purification filter 15 … Glass tank 16 …… Hanging handle

Continuing from the front page (72) Inventor Takuji Fukasawa 1st office, Toshiba R & D Center, Komukai Toshiba, Kawasaki City, Kanagawa Prefecture Inside Engineering Co., Ltd.

Claims (24)

[Claims] 1. A surface of a structural material or a device that comes into contact with a radioactive fluid is irradiated with a laser having a controlled energy density to remove and remove a radioactive substance attached to the surface of the structural material or a device, A decontamination method comprising forming a surface-modified layer in which adhesion of a substance is suppressed. 2. The decontamination method according to claim 1, wherein the laser irradiation on the surface of the structural material or the device is performed in water or a liquid containing a drug. 3. The decontamination method according to claim 2, wherein the chemical is permanganic acid or hydrogen peroxide as an oxidizing agent. 4. The decontamination method according to claim 2, wherein the chemical is oxalic acid as a reducing agent. 5. The decontamination method according to claim 1, wherein the laser is a solid-state laser oscillated from a solid-state device. 6. The laser according to claim 1, wherein the laser is excited ArF, K
3. The decontamination method according to claim 1, wherein the decontamination method is an excimer laser using rF or XeCl molecules as an oscillator. 7. The decontamination method according to claim 1, wherein the laser is a semiconductor laser. 8. The decontamination method according to claim 1, wherein the surface of the structural material or the device is irradiated with two or more lasers. 9. The laser according to claim 1, wherein the laser is a pulse laser.
3. The decontamination method according to claim 1, wherein timing and interval of irradiation of the pulse laser are adjusted. 10. The irradiation of a double-pulse laser or two or more lasers, wherein the irradiation time of each laser is changed to separate and remove the radioactive material and to form a surface-modified layer, respectively. 8 or 9
The decontamination method described. 11. The decontamination method according to claim 1, wherein the surface-modified layer is a layer whose surface roughness is reduced and smoothed. 12. The decontamination method according to claim 1, wherein the surface modification layer is a layer in which a surface of a metal layer is thermally melted or amorphized. 13. A method for irradiating a surface of a structural material or a device that comes into contact with a radioactive fluid with a laser having a controlled energy density to peel off and remove a radioactive substance attached to the surface of the structural material or a device. A decontamination apparatus for forming a surface-modified layer in which adhesion of a substance is suppressed, a laser oscillation unit, an optical transmission system for transmitting a laser oscillated from the oscillation unit, and a laser transmitted by the optical transmission system. A decontamination apparatus, comprising: an optical irradiation system for shaping the light into a parallel beam for irradiation. 14. The laser oscillator according to claim 1, wherein the laser oscillator includes a solid-state device that oscillates a solid-state laser.
3. The decontamination apparatus according to 3. 15. The solid-state device according to claim 1, wherein the garnet crystal (Nd: YAG) of yttrium / aluminum doped with neodymium ion, and the Y doped with erbium ion.
The decontamination apparatus according to claim 14, wherein the rod is a rod made of a solid material selected from AG (Er: YAG), alexandrite, ruby, and glass. 16. The optical transmission system includes an optical fiber,
16. The optical fiber according to claim 13, further comprising a multi-lens having a plurality of lenses arranged perpendicular to a laser optical axis at an input end and an output end of the optical fiber. Decontamination equipment. 17. An optical irradiation system comprising an optical element for shaping a laser beam shape and adjusting an energy density to a smooth distribution close to a Gaussian shape or a distribution close to a flat top shape. Item 14. The decontamination apparatus according to Item 13. 18. The decontamination apparatus according to claim 13, wherein the optical irradiation system is incorporated in a head unit provided with a laser irradiation unit. 19. The apparatus according to claim 18, wherein a mirror having a driving function is provided in the head unit, and laser irradiation can be performed on a fixed area by the fixed head unit. Dyeing equipment. 20. The head unit according to claim 18, wherein the head unit has a watertight structure, and the laser irradiation from the head unit is performed in water or a liquid containing a drug. Decontamination equipment. 21. A circulating mechanism for aspirating and circulating a liquid containing water or a medicine near the irradiation field irradiated with the laser, or a circulating mechanism for ejecting and circulating a liquid containing a water or medicine near the irradiation field. The decontamination apparatus according to claim 20, comprising: 22. The decontamination apparatus according to claim 21, wherein the circulation mechanism includes a device for purifying suspended matters. 23. The apparatus according to claim 18, further comprising a mechanism for driving the head unit, wherein the laser is scanned by driving the head unit with the driving mechanism. The decontamination apparatus according to claim 1. 24. A mechanism for driving the detached structural member or device in a state of being immersed in water or a liquid containing a drug, and fixed to a surface of the structural member or device driven by the driving mechanism. 23. The decontamination apparatus according to claim 18, wherein the head unit is configured to irradiate a laser.