Methods for removing contaminants

Abstract

The present invention provides a method for removing contaminants without damaging the substrate and without causing the contaminants to volatilize. [Solution] A water-soluble resin solution is coated onto the contaminated surface and dried. A square-shaped, flat-top nanopulse laser beam is then irradiated onto the dried film 36 containing the contaminants, and the contaminants are peeled off and removed from the substrate surface along with the water-soluble resin coating film 36 without heating and volatilizing. Polyvinyl alcohol is preferred as the water-soluble resin. The resin film, attached contaminants, and substrate surface can be decontaminated at 75°C or below.

Description

[Technical Field]

[0001] This invention relates to a method for removing contaminants using a water-soluble resin coating film. [Background technology]

[0002] Radioactive contaminants such as radioactive cesium oxides, chlorides, radioactive strontium oxides, and chlorides, as well as chemical contaminants such as polychlorinated biphenyls (PCBs) and dioxins, which adhere to structures, are generally harmful to humans and living organisms on Earth, and therefore need to be safely removed or collected from the surface of structures. As a means of removal, a method has been proposed in which energy-controlled laser light is irradiated onto the surface of a structure to which contaminants are attached in order to remove the contaminants. Patent Document 1 proposes irradiating radioactive contaminants present on the surface of a metal substrate with CW laser light and pulsed laser light to melt, evaporate or volatilize the radioactive contaminants together with the surface layer of the metal substrate and remove them. In this case, the high heat generated by the laser irradiation causes all of the radioactive contaminants to become dust (particle size 1-150 μm) or fumes (particle size 0.2-1 μm) and scatter. Therefore, a large number of filters would be used to collect a large amount of scattered fine particles, which would in turn generate a large amount of contaminated waste. Patent Document 2 proposes using a short-time pulsed laser characterized by a pulse width in picoseconds and femtoseconds to irradiate the contaminants within the irradiation area for a sufficiently short time in picoseconds and femtoseconds, without the heat generated by the energy transfer of the laser light affecting surrounding molecules, thereby evaporating or removing the contaminants at the molecular level. In this case, fumes (particle size 0.2 to 1 μm) or smaller, i.e., ultrafine particles at the molecular and atomic level, are scattered into the atmosphere, making them more difficult to collect than the fine dust particles generated in Patent Document 1. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-016530 [Patent Document 2] Japanese Patent Publication No. 2007-315995 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The aforementioned conventional technologies all operate on the principle of applying the high-temperature or ultra-high-temperature energy of laser light to the contaminant for a very short time, thereby minimizing thermal effects on the surrounding environment and melting, vaporizing, or volatilizing only the contaminant. Consequently, it is extremely difficult to collect particles with a diameter of 0.2 to 1 μm or less that are removed and scattered by any of these methods. For example, if radioactive contaminants or PCBs contained in organic materials such as oils and fats that vaporize and burn at several hundred degrees Celsius are removed from the surface of a substrate using the aforementioned conventional technologies, the contaminants will burn or vaporize / volatilize due to the high heat, and the contaminants will simply diffuse into the air, resulting in a problem of not being essentially removed and of damaging the substrate.

[0005] To solve the problems of the prior art described above, the present invention provides a method for removing contaminants that does not damage the substrate and does not burn or volatilize the contaminants due to the high temperature generated when the contaminants are irradiated with laser light. [Means for solving the problem]

[0006] One embodiment of the present invention is a method for removing contaminants by irradiating a contaminated surface with nanopulse laser light emitted from a pulse oscillator, wherein the contaminated surface is coated with a water-soluble resin solution and dried, This invention relates to a method for removing contaminants by irradiating a dried film containing contaminants with a square, flat-top shaped nanopulse laser beam, thereby removing the contaminants together with the water-soluble resin coating film from the substrate surface without heating and volatilizing them. [Effects of the Invention]

[0007] This invention involves coating a contaminated surface with a water-soluble resin solution to encapsulate the contaminants in the gaps between resin polymer particles, drying the solution, and then irradiating the contaminated surface from the surface of the dried film with nanopulse laser light from a rectangular flat-top shaped laser. This provides energy to ablate the contaminants along with the dried film from the substrate surface, resisting the van der Waals forces that hold the dried film in place, and causing vibration peeling. This allows for efficient peeling and removal of the contaminants without damaging the substrate and without burning or volatilizing the dried film containing the encapsulated contaminants at low temperatures. As a result, the contaminants can be removed in film form, eliminating the need for high-performance filters as in conventional technologies. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram illustrating a nanopulse laser oscillator according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram illustrating a nanopulse laser irradiation device according to one embodiment of the present invention. [Figure 3] Figure 3 shows a schematic waveform of a conventional Gaussian-shaped beam nanopulse laser (left) and a schematic waveform of a rectangular flat-top shaped beam nanopulse laser according to one embodiment of the present invention (right). [Figure 4] Figure 4A is a schematic top view showing the irradiation situation with a rectangular flat-top beam shape of one embodiment of the present invention, and Figure 4B is a schematic side cross-sectional view thereof. [Figure 5] 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 of the same. [Figure 6] Figure 6A shows a schematic energy distribution diagram of a flat-top beam laser, and Figure 6B shows a schematic energy distribution diagram of a Gaussian beam laser. [Figure 7] Figure 7 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. [Figure 8] Figure 8 is a schematic cross-sectional diagram illustrating the resin coating after drying. [Figure 9] FIG. 9 is a schematic perspective view during irradiation with a nanosecond pulsed laser beam according to an embodiment of the present invention. [Figure 10] FIG. 10 is a schematic perspective view of a state in which a resin film according to an embodiment of the present invention is peeled off.

Embodiment for Carrying Out the Invention

[0009] A method for removing contaminants according to an embodiment of the present invention includes the following steps. (1) Water-soluble resin solution coating step In this step, a water-soluble resin solution adjusted in advance according to the chemical properties of contaminants adhering to the surface of the substrate is coated by airless spraying, brushing, roll coater, etc. For example, if the adhering substances are radioactive Cs chloride, radioactive Sr chloride or oils and fats, an alkaline water-soluble resin coating material is used to quickly ionize the contaminants in water by OH groups in 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 an organic acid, an inorganic acid, etc. is used to ionize metal molecules and disperse them as solid fine particles of oxides and chlorides between the fine particle polymers when the water-soluble resin dries. It is preferable to add an alkaline substance such as sodium hydrogen carbonate and an acidic substance such as ascorbic acid to the water-soluble resin solution. The addition amount is preferably 1 to 20 parts by mass with respect to 100 parts by mass of the water-soluble resin solution. Thereby, it becomes possible to dissolve the contaminants in water and atomize and disperse the contaminants in the aqueous resin when the water evaporates. The coating amount is preferably such that the film thickness after moisture evaporation and drying is 0.1 mm to 2 mm in the dry state, more preferably 0.1 to 1.5 mm, and even more preferably 0.1 to 1 mm. (2) Drying step Drying is preferably done by natural drying or low-temperature hot air dehumidification drying at around 20-40°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, ensuring sufficient evaporation and removal of moisture interposed between resin polymer particles, while also allowing for film formation without the volatilization of contaminants with low evaporation temperatures. High-temperature air drying is undesirable because it rapidly forms a dry film on the coating film surface, leaving moisture within the film. In this way, a dry 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 a laser beam 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 metal substrate surface afterward. (4) Coating film removal process When nanopulse laser light is irradiated under the aforementioned conditions, a very high vibration phenomenon occurs between the coating film and the metal substrate surface due to the ablation effect, creating a minute separation space at the interface between the coating film and the metal substrate, which in some cases allows for easier removal by air blowing. At this time, the dried coating film is not destroyed by the air pressure of the air blow, so the coating film can be removed in a film-like manner without the diffusion of contaminants, and the contaminants can be safely disposed of.

[0010] 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.

[0011] 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.

[0012] Next, we will explain the nanopulse laser light irradiation process. The surface contaminant removal apparatus used in 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. This allows for efficient removal without damaging the substrate or volatilizing the contaminants. Damaging the substrate could compromise safety in the case of nuclear-related equipment, and volatilizing contaminants into the atmosphere could cause damage to the surrounding area; both are important issues. Nanopulse laser light, emitted from a pulse oscillator capable of emitting high-precision pulsed laser light with minimal spectral dispersion when passing through a lens using a single-wavelength laser beam, is irradiated onto the contaminated surface. The contaminants are removed at low temperatures by utilizing the ablation effect, which is the vibrational effect of the nanopulse laser light. In other words, the dried film containing the contaminants is given energy exceeding the van der Waals force, which is the binding energy between the contaminated surface and the dried film, mainly by the ablation effect of the nanolaser light, causing it to peel off from the substrate surface as a film, thereby removing the contaminants from the substrate surface without scattering them as particulate matter. In the present invention, "without heating and volatilization" means decontaminating the resin coating, attached contaminants, and substrate surface at a temperature of 75°C or lower.

[0013] Typically, the nanopulse laser beam from the rectangular flat-top shaped laser irradiated onto the contaminated surface has an energy density of 1 J / cm² per unit area. 2Preferably, the J / cm² is greater than or equal to 1 to 10 J / cm². 2 And more preferably 5-10 J / cm² 2 The ideal J / cm² is 7-10 J / cm², and more preferably 7-10 J / cm². 2 However, as a dried coating film containing dissolved or encapsulated contaminants, the van der Waals force on the contaminated surface, which is the polyvinyl alcohol resin film, is 1 J / cm² if the thickness is 0.2 mm, and the adhesion energy at the interface between the metal substrate surface to which the coating film is fixed and the dried coating film is 1 J / cm². 2 The energy density is approximately (J), and by irradiating with nanopulse laser light having an energy density greater than or equal to this, the substrate can be efficiently removed by ablation without damaging it or volatilizing contaminants. To achieve the aforementioned energy density, it is preferable to adjust the combination of the maximum output power (kW) of the pulsed light, pulse width, repetition frequency, laser light scanning speed, and the focal diameter of the square flat-top shape. Polyvinyl alcohol has a concentration of 44.05 g / mol, and the van der Waals force of a 0.2 mm thick polyvinyl alcohol layer is approximately 1 J / cm². 2 It has a heat resistance of over 300°C and is not susceptible to thermal damage.

[0014] 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 allows for a smaller focal diameter of the laser beam, a higher energy density (J), and the deep depth of focus (several centimeters to tens of centimeters) characteristic of rectangular flat-top laser beams. Furthermore, because there are fewer gaps during laser beam scanning compared to round flat-top lasers, uniform energy application to the uneven surface of the irradiation area is possible at high scanning speeds.

[0015] The aforementioned contaminant removal device preferably includes a pulse oscillator of an Nd:YAG laser that emits light of a single wavelength controlled to a wavelength between 1064 nm and 1070 nm. In nanopulse lasers with pulse widths 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 a wavelength between 1064 nm and 1070 nm.

[0016] The pulse width of the pulse oscillator is preferably 20 ns or more and 500 ns or less. This makes it possible to increase the energy density (J) of the flat-top focusing surface of a relatively low-power nanopulse laser with an average output of 500 W when the focusing shape of the pulsed light is a rectangular flat top. The frequency of the pulse oscillator is preferably between 10 kHz and 50 kHz. This makes it possible to deliver energy to the irradiation surface without gaps, even when the scanning speed of the laser beam is increased, when the focusing shape of the pulsed light is a square flat top.

[0017] The nanopulse laser light emitted by the pulse oscillator preferably has a minimum average output of 500 W or more and a maximum output of 2.5 M W or more. This makes it possible to increase the energy density (J) of the focusing surface when the focusing shape of the pulse light is a rectangular flat top. Incidentally, the energy density per pulse of a pulsed laser can be calculated by dividing the average power output (W) by the oscillation repetition rate. Furthermore, the maximum power output can be determined by dividing the energy density per pulse by the pulse width.

[0018] 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.

[0019] The nanopulse laser light emitted by the pulse oscillator is preferably used to decontaminate the resin coating, attached contaminants, and substrate surface at a temperature of 75°C or lower, more preferably 65°C or lower, and even more preferably 55°C or lower. This allows for the removal of contaminants without damaging the substrate and without burning or volatilizing them.

[0020] The present invention's method for removing contaminants is suitable for removing contaminants compatible with water-soluble resin coating materials, such as fine particles of sea salt containing radioactive contaminants Cs, Sr and / or chloride components including Na, Ca, etc., and / or oils and fats, particulate metal oxides, inorganic substances, etc.

[0021] 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 1067 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 spanning a wide 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 mobile. Preferably, the pulse oscillator 1 uses a MOPA type pulse oscillator capable of oscillating 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 highly accurate, low-spectrum single-wavelength light. Conventionally, CW lasers with a large wavelength tolerance of 1070 nm ± 50 nm have been used. However, in nanopulse lasers, where the pulse width is in the nanosecond range, the generation of spectroscopy 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 pulse generator 2 are converted into picosecond or sub-nanosecond pulsed laser light by seed LD3.

[0022] Next, the 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. Next, an isolator 9 in the main amplifier 13 prevents signal interference, protects equipment, and reduces the effects of noise. A bandbus filter 10 extracts physical phenomena in a specific frequency band, and 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.

[0023] Figure 2 is a schematic diagram of a nanopulse laser irradiation device 20 according to one embodiment of the present invention. First, the laser light is made parallel by the collimator 14. Next, the flat beam shaver 15 converts the Gaussian beam, which is the beam shape of a typical pulsed laser, into a flat-top beam shape when it reaches the irradiation surface. Then, the nanopulse laser light, which has a rectangular flat-top shape, is passed through the optical focus adjusters 16a, 16b, scan head 17, and laser profiler 18 and irradiated onto the target object (contaminated surface) 19.

[0024] Figure 3 shows schematic waveform diagrams of nanopulse laser light from a Gaussian-shaped beam 21 (left) and a rectangular flat-top shaped beam 25 (right) according to one embodiment of the present invention. By flattening the laser beam shape into a trapezoidal shape, as in the rectangular flat-top shaped beam 25, the thermal effects on the irradiation surface are reduced, and only the ablation effect, which is a vibrational abrasion effect, can be utilized, thereby reducing the melting of contaminants. However, in this case, the excess energy portion of a typical pulsed laser beam is flattened to an irradiation intensity that reaches a line where the irradiation intensity reaches just above the ablation threshold 28, so the irradiation intensity area at the ablation threshold 28 is expanded. However, as mentioned above, in order to achieve a separation rate that satisfies the cleaning rate of metal structures for contaminants adhering to the surface of a metal substrate, the irradiation intensity line of the ablation threshold, which is several J / cm, is required to destroy the van der Waals forces, which are the adhesion energy, within an appropriate range and speed. 2 It is necessary to raise the beam to the line, and for this purpose, an irradiation device is preferred that can stably output pulsed light of Nd:YAG fiber laser light (wavelength 1064 nm) with an average output of 500 watts or more, a maximum output of 1.25 MW or more, a pulse width of 10 ns to 500 ns, and an optical system that produces a beam shape of a rectangular flat top. In Figure 3, 22 is the excess energy of the Gaussian-shaped beam 21, 23 is the irradiation diameter, and 24 is the thermal energy. Also, 26 is the irradiation diameter of the rectangular flat top-shaped beam 25, and 26 is the thermal energy of the tail. The width of the Gaussian-shaped beam 21 is extremely narrow compared to the width of the thermal energy 24.

[0025] Figure 4A is a schematic top view showing the irradiation situation of the rectangular flat-top beam shape according to an 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 of the conventional Gaussian beam shape, and Figure 5B is a schematic side cross-sectional view thereof. In Figures 4A-B and Figures 5A-B, it is assumed that the generated red rust (Fe2O3) is a polyvinyl alcohol film containing contaminants adhering to the surface of the steel material, and the thickness of the red rust layer is about 500 μm. To remove this red rust, the adhesion energy at the interface between the steel material surface to which the contaminants are adhered and the contaminants is the van der Waals force, and its magnitude is 1 cm 2 per 2 to 4 kj / mol, and it is estimated that it adheres at the following energy density. A Adhesion energy (J / cm 2 ) Calculation example (1) Red rust (Fe2O3) (1) Determine the molecular weight per mole of the adhering red rust: 160 g / mol (2) Thickness of the adhered red rust: 500 μm (3) Red rust weight per 1 cm 2 of the adhered surface area: 5.24 g / cm 2 (Density of Fe2O3) × 1 / 20 = 0.262 g (4) Number of moles of red rust adhered per 1 cm 2 of the adhered surface area: 0.262 g ÷ 160 g / mol = 0.0016375 mol (5) Van der Waals binding force of 0.0016375 mol of red rust: 3.275 J / cm 2 ~6.55 J / cm 2 From the above, to remove the red rust with a thickness of 500 μm, 7 J / cm 2 per 1 cm 2Theoretically, it is believed that irradiating a surface with pulsed laser light containing high energy density can detach contaminants. However, the actual interface between the rust-affected surface and the steel is not flat; corrosion creates irregularities, increasing the interface area. Furthermore, the distance from the laser emission lens to the interface changes subtly due to the irregularities of the interface. In addition, the actual thickness of the rust layer is not constant. For these reasons, the following points must be considered when removing rust from steel using pulsed laser light. (1) The pulsed light to be irradiated is 1 cm 2 7 J / cm² 2 A material with an energy density equivalent to this is preferable. To meet this requirement, the pulsed light irradiation intensity threshold must be 7 J / cm². 2 The advantage lies in the irradiation of a flat-top shaped beam. The flat-top light in Figure 4A can irradiate more seamlessly than the Gaussian beam light in Figure 5. (2) It is preferable that the irradiation pitch is appropriate based on the conditions in (1) above. The appropriate irradiation pitch is determined by the combination of the scanning speed and repetition frequency of the laser light. In the irradiation condition setting shown on the left in Figure 4, the scanning speed and repetition frequency are well-balanced, resulting in no gaps on the irradiation surface and ensuring reliable removal of contaminants. However, as shown on the right in Figure 4, if the scanning speed is too fast compared to the repetition frequency, gaps will form on the irradiation surface, resulting in remaining contaminants in those areas.

[0026] 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 supplied energy does not exceed the energy required to break the van der Waals forces, so the steel material will not be destroyed. Based on the above, it can be reliably removed from the surface of metal structures and other materials without damaging the substrate by irradiating the interface between the contaminant and the substrate with a flat-top beam-shaped nanopulse laser beam at an appropriate repetition frequency, scanning speed, and focal diameter, thereby providing an energy density that can overcome the van der Waals forces.

[0027] Figure 7 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 31 such as Cs, Sr, and Na, oil molecules 32 such as PCB contaminants, and water-insoluble particulate matter 33 are attached to the surface of the SUS substrate 30. The wet coating film 34 contains dissolved polyvinyl alcohol resin 35 and sodium ions (Na + ), hydroxide ion (OH - ), carbonate ions (CO3 2- ) and others exist. Figure 8 is a schematic cross-sectional diagram illustrating the resin coating after drying. A weak adhesive surface 40 exists between the SUS substrate 30 and the polyvinyl alcohol resin coating 36 due to van der Waals forces. The polyvinyl alcohol resin coating 36 contains fine particles 38 and sodium bicarbonate (NaHCO3) fine particles 37, which have been micronized and trapped within the polyvinyl alcohol resin coating. Arrow 39 indicates low-temperature evaporation of water.

[0028] Figure 9 is a schematic perspective view of one embodiment of the present invention during nanopulse laser light irradiation. Nanopulse laser light 42 is irradiated from a laser irradiation device 41 onto a polyvinyl alcohol resin coating 36 coated on the surface of a SUS substrate 30.

[0029] Figure 10 is a schematic perspective view of the present invention in which the resin coating has been peeled off. When air 44 is blown from an air duster (air knife) 43 between the SUS substrate 30 and the polyvinyl alcohol resin coating 36, the resin coating 36 peels off and can be disposed of as a standalone unit. [Examples]

[0030] The present invention will be described below using examples. However, the present invention is not limited to these examples. (Example 1) (1) Water-soluble resin Polyvinyl alcohol was used as the water-soluble resin. Polyvinyl alcohol is soluble in water, has a melting point of 200°C, and a density of 1.19 g / cm³. 3 Its boiling point is 340°C. This polyvinyl alcohol (10% by mass), sodium bicarbonate (5% by mass), and the remaining 85% by mass being water were mixed to form a coating solution. (2) Coating The contaminated surface was spray-coated using an airless gun and air-dried at room temperature (25°C). The coating thickness after drying was 0.2 mm. The contaminated surface was a SUS substrate with sea salt and other trace contaminants (including oils and trace amounts of metal oxides) and chlorides of Cs and Sr radioactive nuclides attached to the surface. By applying this aqueous solution, sea salt and Cs and Sr chlorides dissolve in the water in the polyvinyl alcohol aqueous solution, while trace amounts of water-insoluble fine particles become mixed into the coating during the drying and film formation process and are contained within the coating. (3) Cleaning method After the water evaporated from the applied aqueous solution and the film was completely formed, the film surface was irradiated with a nanopulse laser, and the film was peeled off by blowing air between the film and the SUS substrate interface. 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 taking advantage of 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 device 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, optical wavelength of 1064-1070nm, frequency of 10-50kHz, transmission fiber length of 15-100m, irradiator weight of 2.5kg, ambient temperature of 5-45℃, weight of 245kg, and power consumption of 5kW. The flat beam shaver 15 used was also manufactured by Narran, and the product name was "ROD500". The waveform of the square-shaped, flat-top nanopulse laser beam 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. 2 The focal diameter was 1.8 mm and the pulse width was 20 ns. (5) Coating film removal process After irradiation with a square-shaped, flat-top nanopulse laser beam, air was blown from an air duster (air knife) between the substrate and the polyvinyl alcohol resin coating, as shown in Figure 10, to peel off the resin coating. This allowed the contaminants to be peeled off together with the resin coating without diffusion, and the contaminants could be disposed of safely. [Industrial applicability]

[0031] 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. [Explanation of Symbols]

[0032] 1. Nanopulse laser oscillator 2. Pulse Generator 3rd Seed LD3 4.9 Isolator 5,12 Coupler 6,11 Excited LD 7 Fiber optic cables 8 Preamplifier 10-bandbus filter 13 Main Amplifier 14 Collimator 15 Flat Beam Shaver 16a,16b Optical system focus adjuster 17 Scanhead 18 Laser Profilers 19. Object to be irradiated (contaminated surface) 20 Nanopulse Laser Irradiation Device 21 Gaussian-shaped beam 22. Excess energy of Gaussian-shaped beams 23. Irradiation diameter of a Gaussian-shaped beam 24 Thermal energy of a Gaussian-shaped beam 25-sided flat-top beam 26. Irradiation diameter of a square flat-top beam 27 Thermal energy of a rectangular flat-top beam 28 Ablation threshold 30 SUS base material 31 Chloride particles 32 Oil molecules 33 Particulate deposits 34 Coating film 35 Polyvinyl alcohol resin 36 Polyvinyl alcohol resin coating 37. Sodium bicarbonate (NaHCO3) fine particles 38. Fine particles trapped within the resin coating 39 Low-temperature evaporation of moisture 40 Weak adhesive surface 41 Laser irradiation device 42 Nanopulse laser light 43. Air duster (air knife) 44 Air

Claims

1. A method for removing contaminants by irradiating a contaminated surface with nanopulse laser light emitted from a pulse oscillator, wherein the contaminated surface is coated with a water-soluble resin solution and dried, A method for removing contaminants, characterized by irradiating a dried film containing contaminants with a square-shaped, flat-top nanopulse laser beam, and peeling off the contaminants together with the water-soluble resin coating film from the substrate surface without heating and volatilizing them.

2. The method for removing contaminants according to claim 1, wherein the water-soluble resin is at least one selected from polyvinyl alcohol, polyvinyl acetal, polyvinyl acetate, polyvinylpyrrolidone, polyethylene oxide, phenolic hydroxyl group-containing resin, and carboxyl group-containing resin.

3. The method for removing contaminants according to claim 1 or 2, wherein the water-soluble resin solution is a solution obtained by adding 1,000 to 10,000 parts by mass of water to 100 parts by mass of water and dissolving it.

4. A method for removing contaminants according to claim 1 or 2, 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.

5. The nanopulse laser beam from the rectangular flat-top shaped laser that irradiates the contaminated surface has an energy density of 1 to 10 J / cm² per unit area. 2 The method for removing pollutants according to claim 1 or 2.

6. The method for removing contaminants according to claim 1 or 2, 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.

7. The method for removing contaminants according to claim 1 or 2, wherein the contaminant removal device includes a pulse oscillator of an Nd:YAG laser that emits light of a single wavelength controlled to have a wavelength of 1064 nm or more and 1070 nm or less.

8. The method for removing contaminants according to claim 1 or 2, wherein the pulse width of the pulse oscillator is 20 ns or more and 500 ns or less.

9. The method for removing contaminants according to claim 1 or 2, wherein the frequency of the pulse oscillator is 10 kHz or more and 50 kHz or less.

10. The method for removing contaminants according to claim 1 or 2, 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.

11. The method for removing contaminants according to claim 1 or 2, 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.

12. The method for removing contaminants according to claim 1 or 2, wherein the nanopulse laser light emitted by the pulse oscillator decontaminates the resin coating, attached contaminants, and substrate surface at a temperature of 75°C or lower.

13. The method for removing contaminants according to claim 1 or 2, wherein the contaminant is a radioactive contaminant and / or a chemical contaminant containing a chlorine component.

14. The method for removing contaminants according to claim 1 or 2, wherein the contaminant comprises a metal and / or an inorganic substance.

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