Contaminant removal device and contaminant removal method using same

Abstract

A contaminant removal device according to the present invention removes a surface contaminant by irradiating a contaminated surface with a nanopulse laser beam oscillated from a pulse oscillator, the contaminant removal device comprising: a means for converting a Gaussian-shaped beam nanopulse laser beam (40) oscillated from the pulse oscillator into a square flat-top-shaped nanopulse laser beam (44) by a flat beam shaver; and a means for irradiating the contaminated surface with the square flat-top-shaped nanopulse laser beam (44), wherein the surface contaminant is removed in a solid state of 0.15 μm or greater. Thus, provided are a contaminant removal device that removes a contaminant without causing damage to a substrate and without volatilizing the contaminant, and a contaminant removal method using the same.

Description

Contaminant removal device and method for removing contaminants using the same

[0001] The present invention relates to a contaminant removal device and a contaminant removal method using the same.

[0002] Radioactive contaminants such as cesium oxides and strontium oxides, or chemical contaminants such as polychlorinated biphenyls (PCBs) and dioxins, are generally harmful to the human body and living organisms on Earth and need to be removed. Patent Document 1 proposes irradiating radioactive contaminants present on the surface of a metal substrate with laser light to evaporate or volatilize the radioactive contaminants along with the surface layer of the metal substrate and remove them. Patent Document 2 proposes irradiating with laser light at a scanning speed sufficiently faster than the heat generated by the energy transfer of a pulsed laser, thereby evaporating or removing the substance from the irradiated area.

[0003] Japanese Patent Publication No. 2020-016530 Japanese Patent Publication No. 2007-315995

[0004] However, the aforementioned conventional technology has the problem that, because the radioactive contaminants evaporate or volatilize due to the ultra-high temperature caused by the laser light, they cannot be captured even by current high-performance filters such as HEPA and ULPA. This results in the contaminants simply diffusing into the air without being essentially removed, and it also damages the substrate. In other words, the collection limit of air filters is 0.15 μm, and methods that create a large number of particles smaller than 0.15 μm, such as CW lasers and short-time pulsed lasers (picosecond, femtosecond pulses), cannot be captured by air filters. For example, the collection limit of ULPA filters is 0.15 μm, and the collection efficiency of ULPA filters decreases significantly at 0.1 μm.

[0005] To solve the aforementioned conventional problems, the present invention provides a contaminant removal device that removes contaminants without damaging the substrate and without volatilizing the contaminants, and a contaminant removal method using the same.

[0006] One embodiment of the present invention relates to a contaminant removal apparatus that removes surface contaminants by irradiating a contaminated surface with nanopulse laser light emitted from a pulse oscillator, and includes means for converting Gaussian-shaped beam nanopulse laser light emitted from the pulse oscillator into rectangular flat-top shaped nanopulse laser light using a flat beam shaver, and means for irradiating the contaminated surface with the rectangular flat-top shaped nanopulse laser light, and removes the surface contaminants in a solid state of 0.15 μm or larger.

[0007] Another embodiment of the present invention relates to a method for removing contaminants using the above-described contaminant removal apparatus, comprising means for converting nanopulse laser light in a Gaussian shape beam emitted from a pulse oscillator into a rectangular flat-top shape nanopulse laser light using a flat beam shaver, and means for irradiating the contaminated surface with the flat-top shape nanopulse laser light, and is a method for removing surface contaminants in a solid state of 0.15 μm or larger without damaging the substrate or causing the contaminants to volatilize.

[0008] The present invention includes means for converting a Gaussian-shaped nanopulse laser beam emitted from a pulse oscillator into a rectangular flat-top nanopulse laser beam using a flat beam shaver, and means for irradiating the contaminated surface with the rectangular flat-top nanopulse laser beam. By maximizing the ablation effect of nanopulse light and minimizing thermal effects, the invention can efficiently remove surface contaminants in a solid state of 0.15 μm or larger without damaging the substrate or causing the contaminants to volatilize. If the contaminants are in a solid state of 0.15 μm or larger, they can be collected by a ULPA filter.

[0009] Figure 1 is a schematic diagram of a nanopulse laser oscillator according to one embodiment of the present invention. Figure 2 is a schematic diagram of a nanopulse laser irradiation device according to one embodiment of the present invention. Figure 3 shows a schematic waveform diagram of a conventional Gaussian-shaped beam nanopulse laser light (left) and a schematic waveform diagram of a rectangular flat-top beam nanopulse laser light according to one embodiment of the present invention (right). Figure 4A is a schematic top view showing the irradiation situation with a rectangular flat-top beam shape according to one embodiment of the present invention, and Figure 4B is a schematic side cross-sectional view thereof. Figure 5A is a schematic top view showing the irradiation situation with a conventional Gaussian beam shape, and Figure 5B is a schematic side cross-sectional view thereof. Figure 6A is a schematic energy distribution diagram of a flat-top beam laser light, and Figure 6B is a schematic energy distribution diagram of a Gaussian beam laser light. Figure 7 shows the contamination status of the primary systems of BWR and PWR type nuclear reactors as published by the IAEA. Figure 8 is a cross-sectional view showing an example of the contamination status of radioactively contaminated metal structures within the Fukushima Daiichi Nuclear Power Plant site. Figure 9 is a cross-sectional view showing an example of the contamination status of radioactively contaminated metal structures within the Fukushima Daiichi Nuclear Power Plant. Figure 10 is a cross-sectional view showing an example of the contamination status of radioactively contaminated metal structures within the Fukushima Daiichi Nuclear Power Plant. Figure 11 is a cross-sectional view showing an example of the contamination status of radioactively contaminated metal structures within the Fukushima Daiichi Nuclear Power Plant. Figure 12 is a cross-sectional photograph before etching and before laser cleaning according to one embodiment of the present invention. Figure 13 is a cross-sectional photograph after etching and before laser cleaning according to one embodiment 1 of the present invention. Figure 14 is a schematic cross-sectional explanatory diagram of a state in which sodium bicarbonate is added to an aqueous solution of polyvinyl alcohol resin and coated according to one embodiment of the present invention. Figure 15 is a schematic cross-sectional explanatory diagram after the resin coating has been dried. Figure 16 is a schematic perspective view of a state during irradiation with nanopulse laser light according to one embodiment of the present invention. Figure 17 is a schematic perspective view of a state in which the resin coating has been peeled off according to one embodiment of the present invention. Figure 18 is a schematic explanatory diagram of an ultrasonic cleaning apparatus according to one embodiment of the present invention. Figure 19 is a schematic side view of a contaminated object before and after cleaning according to Embodiment 3 of the present invention. Figure 20 is a schematic side view of the contaminated object before and after cleaning according to Embodiment 4 of the present invention.

[0010] The present invention relates to a contaminant removal device that removes surface contaminants by irradiating a contaminated surface with nanopulse laser light emitted from a pulse oscillator. Examples of contaminated surfaces include radioactive contaminants and / or chemical contaminants containing chlorine components, metals and / or inorganic materials. The surface contaminant removal device of the present invention includes means for converting Gaussian-shaped beam nanopulse laser light emitted from a pulse oscillator into rectangular flat-top shaped nanopulse laser light using a flat beam shaver, and means for irradiating the contaminated surface with the rectangular flat-top shaped nanopulse laser light, thereby removing the surface contaminants in a solid state of 0.15 μm or larger. If the contaminants are in a solid state of 0.15 μm or larger, they can be collected by an air filter made of nonwoven fabric or the like: HEPA (High Efficiency Particulate Air Filter) ULPA filter. More preferably, the surface contaminants are removed in a solid state of 1 μm or larger. If the contaminants are in a solid state of 1 μm or larger, a large amount of contaminants can be collected by a regenerated air filter, reducing the burden on HEPA and ULPA filters. More preferably, the surface contaminants are removed in a solid state of 10 μm or larger. If they are in a solid state of 10 μm or larger, they can be easily collected by a regenerated air filter with an even higher collection efficiency. Specifically, ULPA filters can collect 99.9995% or more of 0.15 μm particles, and HEPA filters can collect 99.97% or more of 0.3 μm particles. If the surface contaminants are in a solid state or spray state of less than 0.1 μm, it becomes difficult to collect them with an air filter, and the contaminants volatilize into the atmosphere, causing damage to the surrounding area, which becomes a serious problem.

[0011] The nanopulse laser beam from the rectangular flat-top shaped laser that irradiates the contaminated surface has an energy density of 1 J / cm² per unit area. 2 It is preferable that the J / cm² be greater than or equal to 1 to 10 J / cm², and more preferably 1 to 10 J / cm². 2 And more preferably 5 to 10 J / cm 2 And more preferably 7 to 10 J / cm 2Therefore, by irradiating the substrate with nanopulse laser light having an energy density higher than the van der Waals forces and hydrogen bonds (which are the adhesion energies at the interface between the steel surface to which the contaminants are attached) and the contaminants, and lower than the metallic and covalent bond energies of the substrate, the ablation effect of the pulsed laser light can be utilized to efficiently remove the contaminants without damaging the substrate or causing them to volatilize. To achieve the aforementioned energy density, it is preferable to adjust the average output, pulse width, repetition frequency, laser scanning speed, and the focal diameter of the square flat-top shape in combination.

[0012] Preferably, the focal diameter of the rectangular flat-top nanopulse laser beam irradiated onto the contaminated surface can be adjusted between 1 mm and 1.8 mm. This not only allows for a smaller focal diameter and higher energy density, but also allows for adjustment of the depth of focus by combining the rectangular flat-top shape of the laser beam with the focal diameter, thereby reducing the influence of fluctuations in the energy density of the laser beam due to the unevenness of the substrate.

[0013] The aforementioned contaminant removal device preferably includes a pulse oscillator of an Nd:YAG laser that emits light of a single wavelength controlled to be between 1064 nm and 1070 nm. In nanopulse lasers, where the pulse width is in the nanosecond range, the generation of spectral dispersion hinders the uniform energy transfer to the irradiated surface. Therefore, it is preferable to employ a MOPA-type pulse oscillator of an Nd:YAG laser that emits light of a single wavelength with extremely high precision controlled to be between 1064 nm and 1070 nm.

[0014] The pulse width of the pulse oscillator is preferably 10 ns or more and 500 ns or less. This allows the energy density of the focusing surface (J / cm²) to be such that when the focusing shape of the pulsed light is flat top. ２ This allows for increasing the intensity of the pulse and adjusting the range of energy density per pulse by varying the pulse width.

[0015] The frequency of the pulse oscillator is preferably between 10 kHz and 50 kHz. This allows the energy density of the irradiated surface to be adjusted by combining the scanning speed of the laser light (m / s) and the oscillation frequency of the flat-top pulse light (kHz).

[0016] Preferably, the nanopulse laser light oscillated by the pulse oscillator has a minimum average output of 500 W or more and a maximum output of 2.5 M W or more. This allows the energy density at the top surface of the laser light (J / cm²) to be such that when the focusing shape of the pulse light is a flat top, the oscillation frequency is 20 kHz or higher. ２ ) and power density (W / cm²) ２ This can enhance the ablation effect of nanopulse laser light.

[0017] Preferably, the system includes means for transmitting the nanopulse laser light emitted by the pulse oscillator to the irradiation device via a fiber cable with a length of 10 m to 150 m. This allows the oscillator to be placed in a safe location over a wide area such as a large structure, and the irradiation device alone can be mounted on a remotely operated robot or the like, making it mobile.

[0018] The present invention's method for removing contaminants includes the following steps: (1) Flat-top nanopulse laser light conversion step: A flat beam shaver converts the Gaussian-shaped nanopulse laser light emitted from a pulse oscillator into flat-top nanopulse laser light. (2) Nanopulse laser light irradiation step on the contaminated surface: The flat-top nanopulse laser light is irradiated onto the contaminated surface. The flat-top nanopulse laser light has a threshold value set at the maximum power intensity (W) of the pulsed light to prevent damage to the substrate surface, and the energy density (J / cm²) of the pulsed light is set to prevent damage to the substrate surface. ２ This makes it possible to concentrate the light (see Figure 3 for the pulsed light shape). As a result, contaminants can be removed without damaging the substrate or causing them to volatilize.

[0019] The method for removing contaminants of the present invention is suitable for removing radioactive contaminants and / or chemical contaminants containing chlorine components. Furthermore, the contaminants may also contain metals and / or inorganic substances.

[0020] The method for removing contaminants according to one embodiment of the present invention includes the following steps: (1) Water-soluble resin solution coating step In this step, a water-soluble resin solution, which has been adjusted in advance to match the chemical properties of the contaminants adhering to the surface of the substrate, is coated using an airless spray, brush, roll coater, etc. For example, if the adhering substance is radioactive Cs chloride, radioactive Sr chloride, or oil, an alkaline water-soluble resin coating material is used to rapidly ionize the contaminants in water using OH groups in the water and disperse them in the fine particle polymer of the water-soluble resin. For metal oxides, etc., a water-soluble resin coating material containing organic acids, inorganic acids, etc. is used to ionize the metal molecules and disperse them as solid fine particles of oxides and chlorides between the fine particle polymer when the water-soluble resin dries. It is preferable to add an alkaline substance such as sodium bicarbonate and an acidic substance such as ascorbic acid to the water-soluble resin solution. The amount added is preferably 1 to 20 parts by mass per 100 parts by mass of the water-soluble resin solution. This makes it possible to dissolve the contaminants in water and to atomize and disperse the contaminants in the aqueous resin when the water evaporates. The amount of coating is preferably such that the film thickness after evaporation of moisture is 0.1 mm to 2 mm in a dry state, more preferably 0.1 to 1.5 mm, and even more preferably 0.1 to 1 mm. (2) Drying process Drying is preferably done by natural drying or low-temperature hot air dehumidification drying at about 20 to 40°C. The low-temperature hot air dehumidification effect allows for gradual evaporation of moisture in the coating film from the lower layer to the upper layer, which is sufficient to evaporate and remove moisture interposed between the resin polymer particles, and also allows for film formation without the volatilization of contaminants with low evaporation temperatures. High-temperature air drying is undesirable because it rapidly forms a dried film on the surface of the coating film, leaving moisture in the film. In this way, a dried film of water-soluble resin coating containing adhering contaminants on the substrate surface is formed. (3) Nanopulse laser light irradiation process This process will be explained in detail later. To explain the key points, by irradiating the rectangular flat-top shaped device of the present invention with laser light having a nanopulse width of 20 nm to 100 nm at an appropriate repetition frequency (kHz) and scanning speed, the dried coating film is peeled off from the substrate surface by the ablation effect of the nanopulse laser without thermal damage.Therefore, the dried coating film can be easily peeled off from the surface of the metal substrate afterward. (4) Coating film peeling process When the nanopulse laser light is irradiated under the above conditions, a very high vibration phenomenon occurs on the coating film and the metal substrate surface due to the ablation effect, and a minute separation space is created at the interface between the coating film and the metal substrate, so in some cases it can be peeled off more easily by air blowing. At this time, the dried coating film is not destroyed by the air pressure of the air blow, so the contaminants do not diffuse, the coating film can be peeled off in a film form, and the contaminants can be safely disposed of.

[0021] Any water-soluble resin can be used, but examples include polyvinyl alcohol, polyvinyl acetal, polyvinyl acetate, polyvinylpyrrolidone, polyethylene oxide, phenolic hydroxyl group-containing resins, and carboxyl group-containing resins. Among these, polyvinyl alcohol is preferred in terms of handling, safety, and cost.

[0022] In the aforementioned polyvinyl alcohol water-soluble resin solution, it is preferable to dissolve 100 parts by mass of polyvinyl alcohol resin in 1,000 to 10,000 parts by mass of water. Water is safe as a solvent and easy to handle. Furthermore, the adhesion energy of the dried coating film using polyvinyl alcohol resin to the metal substrate surface due to van der Waals forces is extremely low, and the magnitude of the van der Waals force is usually around 2 kJ to 4 kJ / mol.

[0023] A method for removing contaminants according to one embodiment of the present invention includes the following steps: (1) Ultrasonic cleaning step in an organic acid cleaning solution In this step, a thick-film contaminated object to which contaminants are attached is ultrasonically cleaned in a weakly acidic organic acid cleaning solution. The weakly acidic organic acid cleaning solution is preferably an aqueous solution of citric acid, ascorbic acid, glycolic acid, malonic acid, acetic acid, or oxalic acid. The organic acid is weakly acidic and does not corrode the metal substrate. It also has a chelating effect and a high metal ion capture effect. The processing temperature may be 30 to 60°C. The deposited material to be removed by the weakly acidic organic acid cleaning solution readily absorbs water. Taking advantage of this water absorption, the target metal product is immersed in the acidic cleaning solution, and ultrasonic energy is used to absorb water into the gaps between the deposited particles and to promote the removal of the deposited material. By employing this method, weakly acidic organic acids that have entered the gaps in thick film deposits are vibrated within the gaps by the propagation of ultrasonic vibrations, thereby separating the adhesion between the thick film deposits. This allows for the removal of thick film deposits on metal parts of nuclear equipment in a much shorter time than conventional methods that sequentially remove them from the surface only using nanopulse lasers. Furthermore, by ultrasonically vibrating the cleaning water, a water flow is created in the cleaning water on the contaminated metal surface, making it possible to immediately remove contaminants precipitated in the cleaning water from the metal surface. As described above, rust can be removed from the surface of metal structures using a weakly acidic organic acid cleaning solution. (2) Ultrasonic cleaning process in alkaline neutralization solution In this process, ultrasonic cleaning is performed using an alkaline neutralization solution such as an aqueous solution of sodium metasilicate or sodium bicarbonate, followed by neutralization treatment. The treatment temperature can be 5 to 35°C. It is preferable to mix and neutralize the wastewater after the organic acid cleaning treatment and the wastewater after the alkaline neutralization treatment, and then heat and distill this neutralized water to concentrate the contaminants before landfill disposal. The boiling points of citric acid, ascorbic acid, ascorbic acid, glycolic acid, glycolic acid, malonic acid, malonic acid, malonic acid, acetic acid, acetic acid, and oxalic acid are all higher than the boiling point of water (100°C), and the evaporation process can be easily performed by using organic acids with high boiling points. (3) Drying process Drying can be done by air drying or by removing water with air, but in cold seasons hot air may be blown on.(4) Nanopulse laser light irradiation process A nanopulse laser with a rectangular flat top shape is irradiated onto the contaminated surface to remove the contaminants from the surface. This process will be explained in detail later. An important point is that if the contaminated metal structure is numerous and covers a large area, the decontamination efficiency can be further improved by adding acid ultrasonic cleaning as a pretreatment step for nanopulse laser decontamination, considering the efficiency of rust removal.

[0024] The ultrasonic cleaning frequency in the organic acid cleaning solution and the ultrasonic frequency in the neutralization solution are preferably 15 to 40 kHz, and more preferably 26 to 38 kHz. It is also preferable to install a cleaning solution stirring and circulation pump to ensure consistent cleaning conditions within the cleaning tank. Furthermore, it is preferable to install a cyclone-type particulate removal device to purify the cleaning solution in the cleaning tank, to remove coarse particles with a particle size of 10 μm or more removed from the metal surface by ultrasonic cleaning, and to prevent damage to the cleaning tank due to contact resonance with the oscillator plate vibrating by the ultrasonic waves. After removing contaminants to a thin film thickness (20 μm or less) by ultrasonic cleaning in the organic acid cleaning solution, any remaining contaminants on the substrate metal surface are removed by nanopulse laser irradiation.

[0025] In addition, in the present invention, a step of applying a water-soluble resin solution such as polyvinyl alcohol to the contaminated surface and forming a coating film may be added between the ultrasonic cleaning step in the alkaline neutralization solution of (2) and the drying step of (3). This allows the contaminants to be peeled off the contaminated surface together with the water-soluble resin coating film, and can be efficiently removed without damaging the substrate or causing the contaminants to volatilize.

[0026] Next, the following will be explained using the drawings. In the following, the same reference numerals in the drawings indicate the same component. Figure 1 is a schematic diagram of a nanopulse laser oscillator 1 according to one embodiment of the present invention. The nanopulse laser oscillator 1 generates pulses with a pulse generator 2. Preferably, an Nd:YAG fiber laser is used as the pulse generator. This is an infrared laser with a single wavelength of 1064 nm, and when the average output is 500 watts or more, the fiber cable can be extended up to 150 m in the case of 2 kW. Therefore, in large structures and other areas with a wide surface area, the oscillator can be placed in a safe location, and only the irradiation device can be mounted on a remotely operated robot or the like, making it movable. Preferably, the pulse oscillator 1 uses a MOPA type pulse oscillator that can oscillate pulsed light with a pulse width of nanoseconds at a stable maximum output and frequency. It is necessary to irradiate the interface between the surface contaminant and the metal surface with single-wavelength light with high precision and minimal spectral dispersion. Conventionally, CW lasers with a large wavelength tolerance of 1070 nm ± 50 nm have been used. However, in nanopulse lasers with pulse widths in the nanosecond range, the generation of spectral dispersion hinders the uniform energy delivery to the irradiated surface. Therefore, it is preferable to employ a MOPA-type pulse oscillator of an Nd:YAG laser that emits extremely precise single-wavelength light controlled between 1064 nm and 1070 nm. The pulses generated by the pulse generator 2 are converted into picosecond or sub-nanosecond pulsed laser light by the seed LD 3.

[0027] Next, an isolator 4 in the preamplifier 8 prevents signal interference, protects the equipment, and reduces the effects of noise, and the semiconductor laser excitation light from the excitation LD 6 is input to the rare-earth doped fiber cable 7 via the coupler 5. Then, an isolator 9 in the main amplifier 13 prevents signal interference, protects the equipment, and reduces the effects of noise, and a bandbus filter 10 extracts physical phenomena in a specific frequency band, and the semiconductor laser excitation light from the excitation LD 11 is input to the rare-earth doped fiber cable 7 via the coupler 12. The fiber cable 7 is connected to a nanopulse laser irradiation device 20.

[0028] FIG. 2 is a schematic explanatory diagram of a nanosecond laser irradiation device 20 according to an embodiment of the present invention. First, the laser beam is collimated by a collimator 14. Next, a flat beam shaper 15 converts a Gaussian-shaped beam, which is a typical pulse laser beam shape, into a flat-top beam shape when it reaches the irradiation surface. Then, it passes through optical system focus adjusters 16a and 16b, a scan head 17, and a laser profiler 18, and irradiates an object to be irradiated (contaminated surface) 19 with a flat-top-shaped nanosecond laser beam.

[0029] FIG. 3 is a schematic waveform diagram (left side) of nanosecond laser light of a Gaussian-shaped beam 40 and a schematic waveform diagram (right side) of nanosecond laser light of a rectangular flat-top beam 44 according to an embodiment of the present invention. By flattening the laser beam shape into a trapezoidal shape like the rectangular flat-top beam 44, the thermal influence on the irradiation surface is reduced, and only the ablation effect, which is a vibration wear effect, can be utilized to reduce the melting and oxidation of the base material surface. However, in this case, in order to flatten the excess energy part of the general pulse laser light to the irradiation intensity up to the line where the irradiation intensity reaches just above the ablation threshold 47, the irradiation intensity area at the ablation threshold 47 expands. However, as described above, in order to achieve a deviation speed that satisfies the cleaning speed of the metal structure for the contaminants adhering to the surface of the metal base material, it is the irradiation intensity line of the ablation threshold that breaks the van der Waals force and hydrogen bond, which are the adhesion energies, within an appropriate range and speed. The number of J / cm 2It is necessary to raise the beam to the line, and for this purpose, an irradiation device is preferred that stably outputs pulsed light of an Nd:YAG fiber laser (wavelength 1064 nm) with an average output of 500 W or more, a maximum output of 1.25 M W or more, a pulse width of 10 ns to 500 ns, an oscillation frequency of 10 to 50 kHz, and a laser light scanning speed of 1 to 10 m / s, and has an optical system that produces pulsed light with a rectangular flat-top shape. In Figure 3, 41 is the excess energy of the Gaussian-shaped beam 40, 42 is the irradiation diameter, and 43 is the thermal energy. Also, 45 is the irradiation diameter of the rectangular flat-top shaped beam 44, and 45 is the thermal energy of the tail. Its width is extremely narrow compared to the thermal energy 43 of the Gaussian-shaped beam 40.

[0030] Figure 4A is a schematic top view showing the irradiation situation with a rectangular flat-top beam shape according to one embodiment of the present invention, and Figure 4B is a schematic side cross-sectional view thereof. Figure 5A is a schematic top view showing the irradiation situation with a conventional Gaussian beam shape, and Figure 5B is a schematic side cross-sectional view thereof. In Figures 4A-B and 5A-B, it is assumed that the contaminant is red rust (Fe2O3) generated on the surface of the steel material, and that the red rust layer is approximately 500 μm thick. To remove this red rust, the adhesion energy at the interface between the steel material surface to which the contaminant is attached and the contaminant is a van der Waals force, and its magnitude is 1 cm 2 Since the energy density is 2-4 kJ / mol per unit area, it is estimated that the material is fixed at the following energy density: Adhesion energy of red rust (Fe2O3) (J / cm²) 2 Calculation Example (1) Determine the molecular weight per mole of attached red rust: 160 g / mol (2) Thickness of attached red rust: 500 μm (3) Surface area of ​​attachment 1 cm 2 Weight of red rust per unit area: 5.24 g / cm 2 (Density of Fe2O3) × 1 / 20 = 0.262 g (4) 1 cm 2 Number of moles of red rust attached to the surface: 0.262 g ÷ 160 g / mol = 0.0016375 mol (5) Van der Waals bond strength of 0.0016375 mol of red rust: 3.275 J / cm 2 ~6.55 J / cm 2

[0031] From the above, to remove red rust with a thickness of 500 μm, 1 cm 2 7 J / cm 2 Theoretically, it can be interpreted that pollutants can be separated by irradiating them with pulsed laser light that has energy density. However, the energy density of a nanopulse laser is 7 J / cm². 2 Of this, the energy density converted into the ablation effect is 7 J / cm². 2 Within this, a certain proportion is present, and the ablation effect is reduced as a certain amount of energy is absorbed by the free electrons of the base metal. Furthermore, the actual interface between the rust-generating surface and the steel is not flat, but rather has irregularities due to corrosion, increasing the interface area. In addition, the distance from the laser beam emission lens to the interface surface changes subtly due to the irregularities of the interface surface. Moreover, the actual thickness of the rust layer is not constant. Therefore, the following points must be taken into consideration when removing rust from steel by pulsed laser beam irradiation: (1) The pulsed light to be irradiated should be 1 cm 2 7 J / cm 2 A laser with an energy density equivalent to the above is preferable. While this energy density cannot remove a theoretical thickness of 500 μm of rust in a single irradiation, several back-and-forth irradiations allow for the removal of contaminants solely through the ablation effect of the nanopulse laser, without vaporizing or volatilizing the contaminants, and without damaging the substrate. During these back-and-forth irradiations, care must be taken to avoid overheating of the contaminants and the substrate metal due to the ablation effect. Furthermore, if the amount of contaminant adhesion is sufficiently small, removal of the contaminants is possible with a single irradiation at an energy density close to the theoretical value. In other words, the ablation effect of the nanopulse laser utilizes the repeated generation and extinction of plasma generated by the pulse oscillation of the nanopulse laser light at microsecond intervals. The number of repetitions can be controlled by the pulse frequency of the pulse light. This ablation effect can break the van der Waals forces and hydrogen bond energy, which are the adhesive forces of the contaminants. However, if the contaminants are attached as a thick layer, 7 J / cm² is required. 2Even if the pulse energy of the energy density is given, as described above, not all the energy is converted into mechanical energy called ablation effect, and a certain percentage of the energy is consumed as thermal energy. This cannot be specified because it depends on the characteristics of the contaminant such as whether the contaminant is a metal oxide or an organic substance and the electrical resistance of the base metal, etc. Therefore, in many cases, it is difficult to completely remove by irradiating with a nanosecond laser having an energy density calculated by theoretical calculation. Thus, by gradually separating and removing from the surface layer of the contaminant with a nanosecond laser having an energy density of 7 J / cm 2 without causing evaporation or volatilization of the contaminant and without damaging the base material, the contaminant can be separated. (2) To satisfy this requirement, it is advantageous to irradiate with a flat-top shaped beam whose threshold value of the irradiation intensity of the pulsed light is 7 J / cm 2 . In the flat-top light of FIG. 4A, if the oscillation frequency and the scanning speed of the pulsed light are the same as those of the Gaussian beam light of FIG. 5, it can be irradiated without gaps. (3) Based on the conditions of (1) above, it is preferable that the irradiation pitch is appropriate. The appropriate irradiation pitch is determined by the combination of the scanning speed and the repetition frequency of the laser light. In the irradiation condition setting on the left side in FIG. 4, since the scanning speed and the repetition frequency are set in harmony, there are no gaps in the irradiation surface, so reliable contaminant removal is possible. However, if the scanning speed is too fast compared to the repetition frequency condition as on the right side in FIG. 4, gaps will appear in the irradiation surface, and that part will remain unremoved. Also, when the number of moles of adhesion per unit area (cm 2 ) of the contaminant is not constant but increases or decreases, the contaminant can be removed without leaving any residue by changing the combination of the scanning speed and the repetition frequency of the laser light and changing the irradiation repetition rate of the pulsed light.

[0032] Figure 6A shows a schematic energy distribution diagram of a flat-top beam laser beam, and Figure 6B shows a schematic energy distribution diagram of a Gaussian beam laser beam. Compared to the Gaussian beam shown in Figure 6A, the flat-top beam shown in Figure 6B has a wider optimal energy density zone in both the focal length direction and the focal diameter. Within this optimal zone, the energy necessary for separation can be appropriately supplied. Furthermore, within this optimal zone, the energy supplied is greater than that that can break the van der Waals forces and hydrogen bonds that adhere to the contaminants, but not enough energy to break the metallic bonding energy of the base metal, so the steel material will not be damaged. From the above, it can be concluded that to reliably remove contaminants such as radioactive contaminants from the surface of metal structures without damaging the base material, a flat-top beam nanopulse laser beam can be irradiated onto the interface between the contaminant and the base material with an appropriate repetition frequency, scanning speed, and focal diameter, thereby supplying an energy density that can resist van der Waals forces and hydrogen bonds.

[0033] Figure 7 shows the contamination status of the primary systems of boiling water reactors (BWRs) and pressurized water reactors (PWRs), as previously announced by the International Atomic Energy Agency (IAEA). On a base metal 21 such as stainless steel, a lower layer 22 made of a base alloy of Fe, Cr, Ni, etc., an intermediate layer 23 with deposited chromium-rich contaminants such as FeCr2O4 and Cr2O3, and an outer layer 24 with deposited ion-rich contaminants such as Fe2O3 are stacked. As can be seen from Figure 7, the base metal 21 is stainless steel containing a large amount of Cr, Ni, etc. for corrosion prevention, and its radioactive contamination layer is roughly classified into three layers. The outer layer 24 is mainly a layer of Fe oxides, the intermediate layer 23 is a layer of deposited contaminants (Cs, Sr oxides, etc.) mainly composed of Cr oxides, and the lower layer 22 is a SUS alloy layer of the base metal. Furthermore, excluding the activated base metal portion in the lower layer, the contamination layer consists of a maximum thickness of 15 μm of base metal oxides, radioactive nuclide oxides, and, in some cases, their respective chlorides, deposited on the base metal surface.

[0034] Figures 8 to 11 are cross-sectional views showing an example of the contamination status of radioactively contaminated metal structures within the Fukushima Daiichi Nuclear Power Plant. Figure 8 shows a base metal 25 with minor radioactive contamination, on which a metal oxide layer 26 (radioactive contamination layer) containing Cr etc. with a thickness of several μm and a layer 27 (radioactive contamination layer) containing Fe oxide and chloride with a thickness of several μm are deposited. Figure 9 shows a base metal 28 with minor radioactive contamination, on which a protective coating layer 29 of acrylic resin, urethane resin etc. with a thickness of several tens of μm, a radioactive contamination film 30 on which deteriorated coating particles, sludge etc. are mixed with a thickness of several tens of μm, and a resin deterioration part 31 located in the thickness direction of the protective coating layer 29. The radioactive contamination film 30 and the resin deterioration part 31 contain Fe oxide, Fe chloride, sea salt, Ce oxide, Sr oxide, Ce chloride, Sr chloride etc. Figure 10 shows a base steel material 32 with minor radioactive contamination, on which is a layer 33 containing a mixture of Ce oxide, Sr oxide, Ce chloride, Sr chloride, sludge, etc., with a thickness of several tens to several hundreds of micrometers, and on top of that is a contaminated layer 34 containing Fe oxide, Fe chloride, sea salt, etc. Figure 11 shows a base steel material 35 with minor radioactive contamination, on which is an epoxy resin layer 36 with a thickness of several hundreds of micrometers to several millimeters, and on top of that is a layer 37 of Ce and Sr chloride fine particles with a thickness of several micrometers. The epoxy resin layer 36 contains tritium on its surface, is water-absorbing, and is radioactively contaminated.

[0035] As shown in Figures 8 to 11, the contamination levels of metal structures within the Fukushima Daiichi Nuclear Power Plant vary depending on the base metal, the treatment of the metal surface, and whether the structure existed before or after the accident. In addition to these differences in contamination levels, there are also differences in the shape, dimensions, installation, and storage conditions of the metal structures.

[0036] Figure 8 shows items that have already been dismantled and removed and stored in casks, separated and stored according to their level of contamination. Figure 9 shows large structures with low levels of radioactive contamination that are installed or stored outdoors. Figure 10 shows jigs, tools, and equipment used in dismantling work, etc., that have been separated and stored. Figure 11 shows items that have not yet been dismantled or removed and are installed in high-radiation areas. The contaminant removal method of the present invention can be applied to any form of contamination.

[0037] Figure 12 shows cross-sectional photographs of the first embodiment of the present invention before and after laser cleaning and etching. In the left side of Figure 12, before laser cleaning, contaminants 52 such as red rust (Fe2O3), salt (NaCl), and sand are adhering to the surface of the iron substrate 51 in the cross-sectional section 50. However, after laser cleaning, the surface of the iron substrate 51 in the cross-sectional section 53 has been cleanly removed, exposing the fine irregularities of the iron substrate surface. This shows that the contaminants have been almost completely removed. Figure 13 shows cross-sectional photographs of the first embodiment of the present invention before and after laser cleaning and etching. In the left side of Figure 13, before laser cleaning, contaminants 52 such as red rust (Fe2O3), salt (NaCl), and sand are adhering to the surface of the iron substrate 51 in the cross-sectional section 54. However, after laser cleaning, the surface of the iron substrate 51 in the cross-sectional section 55 has been cleanly removed, exposing the fine irregularities of the iron substrate surface. This shows that the contaminants have been almost completely removed without damaging the iron substrate.

[0038] Figure 14 is a schematic cross-sectional diagram illustrating a state in which sodium bicarbonate is added to an aqueous solution of polyvinyl alcohol resin according to one embodiment of the present invention and used for coating. Chloride particles 57 such as Cs, Sr, and Na, oil molecules 58 such as PCB contaminants, and water-insoluble fine particulate matter 59 are attached to the surface of the SUS substrate 56. In the wet state, the coating film 60 contains dissolved polyvinyl alcohol resin 61 and sodium ions (Na + ), hydroxide ion (OH - ), carbonate ions (CO3 2- ) and others exist.

[0039] Figure 15 is a schematic cross-sectional diagram illustrating the resin coating after drying. The space between the SUS substrate 56 and the polyvinyl alcohol resin coating 62 is a weak adhesive surface 66 due to van der Waals forces. The polyvinyl alcohol resin coating 62 contains fine particles 64 that have been micronized and trapped within the polyvinyl alcohol resin coating, as well as sodium bicarbonate (NaHCO3) fine particles 63, etc. Arrow 65 indicates the direction of low-temperature evaporation of water.

[0040] Figure 16 is a schematic perspective view of an embodiment of the present invention during nanopulse laser light irradiation. Nanopulse laser light 68 is irradiated from a laser irradiation device 67 onto a polyvinyl alcohol resin coating 62 coated on the surface of a SUS substrate 56.

[0041] Figure 17 is a schematic perspective view of the resin coating of one embodiment of the present invention after it has been peeled off. When air 70 is blown from an air duster (air knife) 69 between the SUS substrate 56 and the polyvinyl alcohol resin coating 62, the resin coating 62 can be easily peeled off and disposed of as a standalone unit.

[0042] Figure 18 is a schematic diagram illustrating an ultrasonic cleaning apparatus 71 according to one embodiment of the present invention. In this ultrasonic cleaning apparatus 71, ultrasonic oscillators 73a-73d are directly connected to a cleaning tank 72 and emit ultrasonic waves with a frequency of 20 to 40 kHz. Contaminated objects 74 are immersed inside the cleaning tank 72. A cleaning liquid circulation circuit 80 is provided outside the cleaning tank 72, and this circuit 80 is equipped with a circulation pump 77, a cyclone 7+6, and a fine bubble generator 56 to circulate the cleaning liquid 57. The cyclone 55 removes particles 79 with an average diameter of 10 μm or more, for example, and removes them from the bottom of the cyclone. The fine bubble generator 77 generates a mixed fluid of organic acid cleaning liquid, bubbles containing fine bubbles, and water, and returns it to the cleaning tank 72. This cleaning tank 72 can also be used as an ultrasonic cleaning tank in an alkaline neutralizing solution. The material of the cleaning tank 72 may be SUS, but it is preferable to paint it with a protective coating.

[0043] The following will be explained using examples. The present invention is not limited to these examples. (Example 1) (1) Contaminant removal apparatus The apparatus shown in Figures 1 and 2 was used. The nanopulse laser oscillator 1 was manufactured by Narran, product name "ROD 1000W". This product is an Nd:YAG fiber laser, average output 1000W, optical wavelength 1064-1070nm, frequency 10-50kHz, transmission fiber length 15-100m, irradiator weight 2.5kg, ambient temperature 5-45℃, weight 245kg, power consumption 5kW. The flat beam shaver 15 was also manufactured by Narran. The waveform of the rectangular flat-top shaped nanopulse laser light irradiated onto the contaminated surface is as shown on the right side of Figure 3, with an energy density per unit area of ​​7 J / cm². 2 The focal diameter was 1 mm and the pulse width was 40 ns. (2) Object to be cleaned After spraying salt water onto a steel plate, the surface was cleaned using the contaminant removal device to remove the red rust (Fe2O3) that had formed due to natural exposure. The reason for verifying the removal of red rust formed by salt water spraying was, firstly, to resolve the question of whether red rust formed on a steel plate containing salt water could be removed by a laser. Secondly, to resolve the question of whether NaCl (salt), an impurity other than red rust, could be removed. Since Na belongs to the same alkali metals as the radioactive nuclide Cs, it is presumed that if Na can be removed, Cs can also be removed. (3) Results of contaminant removal The results of elemental analysis before and after laser cleaning are shown in Table 1 below, cross-sectional photographs before etching before and after laser cleaning are shown in Figure 12, and cross-sectional photographs after etching before and after laser cleaning are shown in Figure 13.

[0044]

[0045] As is clear from Table 1, approximately 94% of Na was removed, leaving approximately 1 / 20 of the original amount. From this experimental result, it can be inferred that Cs, which belongs to the same alkali metal as Na, can be removed in a similar manner. Furthermore, as shown in Figure 12, the adhering contaminants such as red rust (Fe2O3), salt (NaCl), and sand in the upper left of the iron substrate before laser cleaning were completely removed after laser cleaning, exposing the fine irregularities on the surface of the iron substrate. Similarly, the cross-sectional photograph after etching in Figure 13 also showed the fine irregularities on the surface of the iron substrate. Moreover, with the energy density of the contaminant removal device in this embodiment, both the adhering contaminants and the substrate surface were heated to approximately +30°C (i.e., 5-75°C) even when the ambient temperature was higher than 5-45°C. The contaminants were able to detach from the substrate surface mainly as solid particles of 0.5 μm or larger, without volatilization or evaporation, without damaging the metal surface of the substrate, and could be collected by the air filter. The fact that the particles were solid particles of 0.5 μm or larger was confirmed by observing the particles collected in the air filter under a microscope. From the above, it was confirmed that the contaminant removal device of this embodiment can remove contaminants without damaging the substrate and without volatilizing them.

[0046] (Example 2) (1) Water-soluble resin Polyvinyl alcohol was used as the water-soluble resin. Polyvinyl alcohol is soluble in water, with a melting point of 200°C and a density of 1.19 g / cm³. 3, boiling point: 340°C. This polyvinyl alcohol (10% by mass), sodium bicarbonate (5% by mass), and the remaining 85% by mass being water were mixed to make a coating solution. (2) Coating Using an airless gun, the contaminated surface was spray-coated and air-dried at 25°C. The coating amount was 0.2 mm in thickness after drying. The contaminated surface was a SUS substrate with sea salt and other trace contaminants (including oils and fats, trace amounts of metal oxides) and chlorides of Cs and Sr radioactive nuclides attached to the surface. By applying this aqueous solution, the sea salt and Cs and Sr chlorides dissolve in the water in the polyvinyl alcohol aqueous solution, and trace amounts of water-insoluble fine particles are mixed into the coating during the drying and film formation process and are contained in the coating. (3) Cleaning method After the water evaporates from the applied aqueous solution and the film is completely formed, the surface of the coating is irradiated with a nanopulse laser, and the coating is peeled off by blowing air between the coating and the interface between the coating and the SUS substrate. This cleaning method utilizes the effect of easily removing surface contaminants from the substrate by incorporating contaminants into the film during the film-forming process caused by the evaporation of water in a weakly alkaline polyvinyl alcohol aqueous solution, and by utilizing the film-forming strength and heat resistance of the formed film. Because the van der Waals force, which is the adhesion force of the polyvinyl alcohol coating to the SUS substrate, is very low, the processing speed of nanopulse laser irradiation is improved, and even on curved SUS substrates, contaminants on deeper curves can be removed in film form, thus preventing the scattering of fine dust contaminants into the atmosphere. (4) Contaminant removal apparatus The apparatus shown in Figures 1 and 2 was used. The nanopulse laser oscillator 1 was manufactured by Narran, product name "ROD 500W". This product is an Nd:YAG fiber laser with an average output of 500W, an optical wavelength of 1064-1070nm, a frequency of 10-50kHz, a transmission fiber length of 15-100m, an irradiator weight of 2.5kg, an ambient temperature of 5-45℃, a total weight of 195kg, and a power consumption of 3.5kW. The flat beam shaver 15 used is also manufactured by Narran, product name "ROD500". The waveform of the rectangular flat-top nanopulse laser light irradiated onto the contaminated surface is shown on the right side of Figure 3, with an energy density of 1 J / cm² per unit area. 2The focal diameter was 1.8 mm and the pulse width was 20 ns. (5) Coating film removal process After irradiation with a square flat-top nanopulse laser beam, as shown in Figure 17, air was blown from an air duster (air knife) between the substrate and the polyvinyl alcohol resin coating to remove the resin coating. This allowed the contaminants to be removed together with the resin coating without diffusion, and the contaminants could be safely disposed of. Furthermore, the contaminants were separated from the substrate surface as solid particles of 0.5 μm or larger, and did not volatilize or evaporate, and there was no damage to the metal surface of the substrate. The fact that the particles were solid particles of 0.5 μm or larger was confirmed by observing the particles adhering to the polyvinyl alcohol resin coating under a microscope.

[0047] (Example 3) (1) After spraying salt water onto a contaminated steel plate, the surface was cleaned using the contaminant removal device to remove the red rust (Fe2O3) that had formed due to natural exposure. The reason for verifying the removal of red rust formed by salt water spraying was, firstly, to resolve the question of whether red rust formed on a steel plate containing salt water could be removed by a laser. Secondly, to resolve the question of whether NaCl (salt), an impurity other than red rust, could be removed. Since Na belongs to the same alkali metal as the radioactive nuclide Cs, it is presumed that if Na can be removed, Cs can also be removed. (2) Protective coating of the inner surface of the ultrasonic cleaning tank As a protective coating for the inner surface of the ultrasonic cleaning tank, a two-component curing acrylic urethane paint with uniformly dispersed 7 nm size silica was used, and the coating was applied to a dry film thickness of 20 μm. This formed a coating film with high acid resistance, alkali resistance, heat resistance, and adhesion resistance, preventing damage to the stainless steel (SUS) forming the cleaning tank. The performance of this coating film is shown in Table 2.

[0048]

[0049] (3) Ultrasonic cleaning process in organic acid cleaning solution Using the ultrasonic cleaning apparatus 50 shown in Figure 18 (however, it is not equipped with a fine bubble generator 56), a 5% by mass aqueous solution of ascorbic acid was prepared, and a contaminated object having rust and radioactive contaminants on the surface of the steel plate was placed in this aqueous solution, and the ultrasonic frequency was set to 26 kHz to 38 kHz. The processing temperature was set to 40°C. A cleaning solution stirring and circulation pump was installed to ensure that the cleaning conditions in the cleaning tank were the same. In addition, a cyclone-type particulate removal device was attached to purify the cleaning solution in the cleaning tank, removing coarse particles with a particle size of 10 μm or more that were removed from the metal surface by ultrasonic cleaning, and preventing damage to the cleaning tank due to contact resonance with the oscillator plate vibrating by the ultrasonic waves. As a result, the contaminants were reduced to a thin film (20 μm or less).

[0050] (4) Ultrasonic cleaning process in alkaline neutralization solution A solution was prepared by adding 10% by mass of sodium bicarbonate, and the contaminated object was placed in this solution and ultrasonically cleaned to neutralize it. The treatment temperature was 25°C. The wastewater after the organic acid cleaning treatment and the wastewater after the alkaline neutralization treatment were mixed and neutralized, and this neutralized water was heated and distilled at 100°C or below to concentrate the contaminants before being disposed of in a landfill.

[0051] (5) Drying process: Drying was carried out by air drying at room temperature (5-35°C).

[0052] (6) Contaminant removal apparatus The apparatus shown in Figures 1 and 2 was used. The nanopulse laser oscillator 1 is a Nd:YAG fiber laser manufactured by Narran, trade name "ROD 1000W". Average power: 1000W, optical wavelength: 1064-1070nm, frequency: 10kHz, pulse width: 20ns, size: 400%, focus: 172, speed: 6000mm / s, energy density per unit area: 1.5J / cm² 2 The specifications were: focal diameter: 1 mm, transmission fiber length: 15 m, irradiator weight: 2.5 kg, ambient temperature: 5-45°C, weight: 245 kg, power consumption: 5 kW. A flat beam shaver 15 manufactured by Narran was also used. The waveform of the rectangular flat-top nanopulse laser light irradiated onto the contaminated surface was as shown on the right side of Figure 3.

[0053] (7) Contaminant removal results Figure 19 is a schematic side view of photographs of the contaminated object (pipe) 81 before and after cleaning. Contaminants have accumulated in the untreated central section 83, but the contaminants have been almost completely removed from the section 82 on the left that was ultrasonically treated in an organic acid. In the section 84 on the right that was treated with a nanopulse laser, some contaminants were visible, but they were mostly removed. Furthermore, the contaminants could be separated from the substrate surface as solid particles of 0.5 μm or larger, and they did not volatilize or evaporate, did not damage the metal surface of the substrate, and could be collected by the air filter. The fact that they were solid particles of 0.5 μm or larger was confirmed by observing the particles collected in the air filter under a microscope.

[0054] (Example 4) The procedure was carried out in the same manner as in Example 1, except that an ultrasonic cleaning device 71 incorporating a fine bubble generator 77 was used. The fine bubble generator used was manufactured by OK Engineering Co., Ltd., and its product name is "OK Nozzle". This fine bubble generator is a device that generates microbubbles of several tens to 100 μm and ultrafine bubbles (UFB) of several tens to 100 nm. Figure 20 is a schematic side view of photographs of the contaminated object (pipe) 85 before and after cleaning. The untreated portion 83 and the portion 82 treated ultrasonically in organic acid are substantially the same as in Figure 19, but the portion 85 treated with a nanopulse laser on the right side had all the contaminants and even the black rust completely removed, revealing the base metal. Furthermore, the contaminants could be separated from the substrate surface as solid particles of 0.5 μm or larger, did not volatilize or evaporate, did not damage the metal surface of the substrate, and could be collected by an air filter. The fact that the particles were solid particles of 0.5 μm or larger was confirmed by observing the particles collected in the air filter under a microscope. Furthermore, because there was no oil or grease present, there was no smoke during pulse cleaning, and the dust collection filter did not become clogged. From the above, it was confirmed that the contaminant removal device of this embodiment can remove contaminants without damaging the substrate and without volatilizing them.

[0055] The contaminant removal apparatus and method of the present invention are useful for removing harmful substances including radioactive contaminants such as cesium oxides and strontium oxides, and / or chemical contaminants such as polychlorinated biphenyls (PCBs) and dioxins. Furthermore, they are also useful in nuclear-related facilities, waste incineration facilities, and the like.

[0056] 1 Nanopulse laser oscillator 2 Pulse generator 3 Seed LD3 4,9 Isolator 5,12 Coupler 6,11 Excitation LD 7 Fiber cable 8 Preamplifier 10 Bandbus filter 13 Main amplifier 14 Collimator 15 Flat beam shaver 16a,16b Optical system focus adjuster 17 Scan head 18 Laser profiler 19 Irradiation target (contaminated surface) 20 Nanopulse laser irradiation device 21 Base metal 22 Lower layer 23 Intermediate layer 24 Outer layer 25,28 Base metal 26,27 Radioactive contamination layer 29 Protective coating layer 30 Radioactive contamination film 31 Resin degradation part 32,35 Base steel material 33 Mixed layer of oxides, chlorides, sludge, etc. 34 Contaminated layer of oxides, chlorides, sea salt, etc. 36 Epoxy resin layer 40 Gaussian-shaped beam 41 Excess energy of Gaussian-shaped beam 42 Irradiation diameter of Gaussian-shaped beam 43 Thermal energy of Gaussian-shaped beam 44 Rectangular flat-top beam 45 Irradiation diameter of rectangular flat-top beam 46 Thermal energy of rectangular flat-top beam 47 Ablation threshold 50, 54 Cross-section before laser cleaning 51 Iron substrate 52 Contaminants 53, 55 Cross-section after laser cleaning 56 SUS substrate 57 Chloride particles 58 Oil molecules such as PCB contaminants 59 Water-insoluble particulate matter adhering to the surface 60 Wet coating 61 Polyvinyl alcohol resin 62 Polyvinyl alcohol resin coating 63 Sodium bicarbonate (NaHCO3) fine particles 64 Fine particles trapped within the resin coating 65 Low-temperature evaporation direction of water 66 Surface with weak adhesion force 67 Laser irradiation device 68 Nanopulse laser light 69 Air duster (air knife) 70 Air 71 Ultrasonic cleaning device 72 Cleaning tank 73a-73d Ultrasonic oscillator 74 Contaminated object 75 Circulation pump 76 Cyclone 77 Fine bubble generator 78 Cleaning solution 79 Particles 80 Circulation circuit 81 Contaminated object (pipe) 82 Part treated ultrasonically in organic acid 83 Untreated part 84, 85 Part treated with nanopulse laser

Claims

1. A surface contaminant removal device for removing surface contaminants by irradiating a contaminated surface with nanopulse laser light emitted from a pulse oscillator, comprising means for converting Gaussian-shaped beam nanopulse laser light emitted from the pulse oscillator into rectangular flat-top shaped nanopulse laser light using a flat beam shaver, and means for irradiating the contaminated surface with the rectangular flat-top shaped nanopulse laser light, characterized in that the surface contaminants are removed in a solid state of 0.15 μm or larger.

2. The contaminant removal device according to claim 1, wherein the nanopulse laser light emitted by the pulse oscillator has a minimum average output of 500 watts or more and a maximum output of 2.5 MW or more.

3. The contaminant removal device according to claim 1 or 2, wherein the pulse width of the pulse oscillator is 10 ns or more and 500 ns or less.

4. The contaminant removal device according to any one of claims 1 to 3, wherein the frequency of the pulse oscillator is 10 kHz or more and 50 kHz or less.

5. The contaminant removal device according to any one of claims 1 to 4, wherein the focal diameter of the rectangular flat-top shaped nanopulse laser beam irradiated onto the contaminated surface can be adjusted to be between 1 mm and 1.8 mm.

6. The nanopulse laser beam from the rectangular flat-top shaped laser irradiated onto the contaminated surface has an energy density of 1 to 10 J / cm² per unit area. 2 The contaminant removal device according to any one of claims 1 to 5.

7. The contaminant removal device according to any one of claims 1 to 6, wherein the pulse oscillator is an Nd:YAG laser pulse oscillator.

8. The contaminant removal device according to any one of claims 1 to 7, wherein the pulse oscillator is a pulse oscillator that emits light of a single wavelength controlled to have a wavelength of 1064 nm or more and 1070 nm or less.

9. A contaminant removal device according to any one of claims 1 to 8, comprising means for transmitting nanopulse laser light oscillated by the pulse oscillator to an irradiation device via a fiber cable with a length of 10 m to 150 m.

10. A method for removing contaminants using a contaminant removal apparatus according to any one of claims 1 to 9, comprising means for converting nanopulse laser light of a Gaussian-shaped beam emitted from a pulse oscillator into flat-top shaped nanopulse laser light using a flat beam shaver, and means for irradiating a contaminated surface with the flat-top shaped nanopulse laser light, characterized in that the surface contaminants are removed in a solid state of 0.15 μm or larger without damaging the substrate and without volatilizing the contaminants.

11. A method for removing contaminants according to claim 10, wherein the contaminated surface is pre-coated with a water-soluble resin solution and dried, and then a square-shaped, flat-top nanopulse laser beam is irradiated onto the dried film containing the contaminant, thereby peeling off the contaminant together with the water-soluble resin coating film from the substrate surface without heating and volatilizing it.

12. The method for removing contaminants according to claim 11, wherein the water-soluble resin is a solution obtained by dissolving at least one selected from polyvinyl alcohol, polyvinyl acetal, polyvinyl acetate, polyvinylpyrrolidone, polyethylene oxide, phenolic hydroxyl group-containing resin, and carboxyl group-containing resin in 1,000 to 10,000 parts by mass of water per 100 parts by mass of the water-soluble resin.

13. The method for removing contaminants according to claim 11 or 12, wherein an alkaline substance and / or an acidic substance are added to the water-soluble resin solution to dissolve the contaminant in water, and the contaminant is atomized and dispersed in the aqueous resin when the water evaporates.

14. A method for removing contaminants according to any one of claims 10 to 13, wherein the contaminated object is first ultrasonically cleaned in a washing tank in a weakly acidic organic acid washing solution which is an aqueous solution of at least one selected from the group consisting of citric acid, ascorbic acid, glycolic acid, malonic acid, acetic acid, and oxalic acid, then ultrasonically cleaned in an alkaline neutralizing solution, dried or drained, and then irradiated onto the contaminated surface with nanopulse light from a square flat-top shaped laser to peel off the contaminant from the contaminated surface.

15. The method for removing contaminants according to any one of claims 10 to 14, wherein the ultrasonic cleaning frequency in the organic acid cleaning solution and the ultrasonic frequency in the neutralizing solution are 15 to 40 kHz.

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