Pollutant removal methods

Abstract

Provided is a method for removing contaminants that removes contaminants without damaging a substrate and without volatilizing the contaminants. [Solution] The system includes a means for converting nano-pulse laser light 40, which is a Gaussian-shaped beam emitted from a pulse oscillator, into nano-pulse laser light 44 with a square flat-top shape using a flat beam shaver, and a means for irradiating the nano-pulse laser light with the square flat-top shape onto the contaminated surface, thereby removing the contaminants without damaging the substrate and without volatilizing them.

Description

[Technical field]

[0001] The present invention relates to a method for removing contaminants. [Background technology]

[0002] Radioactive contaminants such as cesium oxide and strontium oxide, or chemical contaminants such as polychlorinated biphenyls (PCBs) and dioxins, are generally harmful to humans and terrestrial organisms and must be removed. Patent Document 1 proposes irradiating a radioactive contaminant present on the surface of a metal substrate with a laser beam to burn, evaporate or volatilize the radioactive contaminant together with the surface layer of the metal substrate and remove it. Patent Document 2 proposes irradiating a laser beam at a scanning speed sufficiently faster than the generation of heat, etc., caused by energy transmission from a pulsed laser, to evaporate or remove the substance from the irradiated area. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-016530 A [Patent Document 2] JP 2007-315995 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned conventional technology, radioactive contaminants are evaporated or volatilized by the ultra-high temperature caused by the laser light, making it difficult or impossible to capture them even with current high-performance filters such as HEPA and ULPA. There were also problems in that the contaminants were simply dispersed into the air, and were not essentially removed, and that the base material was damaged.

[0005] In order to solve the above-mentioned problems of the conventional art, the present invention provides a method for removing contaminants that does not damage the substrate and does not volatilize the contaminants. [Means for solving the problem]

[0006] One embodiment of the present invention relates to a method for removing contaminants, which includes a means for converting a Gaussian-shaped beam of nano-pulse laser light emitted from a pulse oscillator into a square, flat-top shaped nano-pulse laser light using a flat beam shaver, and a means for irradiating a contaminated surface with the square, flat-top shaped nano-pulse laser light, and which utilizes the ablation effect of the nano-pulse laser to remove the contaminants without damaging the substrate and without volatilizing the contaminants. Effect of the Invention

[0007] The present invention includes a means for converting a Gaussian-shaped beam of nano-pulse laser light emitted from a pulse oscillator into a square, flat-top shaped nano-pulse laser light using a flat beam shaver, and a means for irradiating the square, flat-top shaped nano-pulse laser light onto a contaminated surface. This makes maximum use of the ablation effect of the nano-pulse light and minimizes the thermal effects, thereby enabling efficient removal of contaminants without damaging the substrate and without volatilizing them. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic explanatory diagram of a nano-pulse laser oscillator according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic explanatory diagram of a nanopulse laser irradiation device according to one embodiment of the present invention. [Diagram 3] FIG. 3 shows a schematic waveform diagram (left) of a conventional nano-pulse laser beam having a Gaussian shape, and a schematic waveform diagram (right) of a nano-pulse laser beam having a square flat-top shape according to one embodiment of the present invention. [Figure 4] FIG. 4A is a schematic top view showing an irradiation state with a square flat-top beam shape according to one embodiment of the present invention, and FIG. 4B is a schematic side cross-sectional view of the same. [Diagram 5] FIG. 5A is a schematic top view showing an irradiation state with a conventional Gaussian beam shape, and FIG. 5B is a schematic side cross-sectional view of the same. [Figure 6] FIG. 6A is a schematic energy distribution diagram of laser light having a flat-top beam shape, and FIG. 6B is a schematic energy distribution diagram of laser light having a Gaussian beam shape. [Figure 7] Figure 7 shows the contamination status of the primary systems of BWR and PWR reactors announced by the IAEA. [Figure 8] FIG. 8 is a cross-sectional view of an example showing the contamination state of a radioactively contaminated metal structure within the Fukushima Daiichi Nuclear Power Plant site. [Figure 9] FIG. 9 is a cross-sectional view of an example showing the contamination state of a radioactively contaminated metal structure within the Fukushima Daiichi Nuclear Power Plant site. [Figure 10] FIG. 10 is a cross-sectional view of an example showing the contamination state of a radioactively contaminated metal structure within the Fukushima Daiichi Nuclear Power Plant site. [Figure 11] FIG. 11 is a cross-sectional view of an example showing the contamination state of a radioactively contaminated metal structure within the Fukushima Daiichi Nuclear Power Plant site. [Figure 12] FIG. 12 is a cross-sectional photograph of Example 1 of the present invention before and after laser cleaning and before etching. [Figure 13] FIG. 13 is a cross-sectional photograph of Example 1 of the present invention before and after laser cleaning and etching. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention uses a contaminant removal device that irradiates a contaminated surface with nano-pulse laser light oscillated from a pulse oscillator to remove surface contaminants, such as radioactive contaminants and / or chemical contaminants containing chlorine components, metals and / or inorganic substances. The contaminant removal device includes a means for converting a Gaussian-shaped nano-pulse laser beam emitted from a pulse oscillator into a square-shaped flat-top nano-pulse laser beam by a flat beam shaver, and a means for irradiating the square-shaped flat-top nano-pulse laser beam onto a contaminated surface. This allows efficient removal of contaminants without damaging the substrate and without volatilizing them. Damage to the substrate can compromise safety in nuclear power-related equipment, and volatilizing contaminants into the atmosphere can cause damage to the surrounding area, both of which are important issues. The phrase "removing contaminants without damaging the substrate and without volatilizing them" refers to decontaminating both the attached contaminants and the substrate surface at the same temperature as the ambient temperature, 5 to 45°C.

[0010] The square flat-top nano-pulse laser light irradiated to the contaminated surface has an energy density per unit area of ​​1 J / cm 2 More preferably, it is 1 to 10 J / cm 2 and more preferably 5 to 10 J / cm 2 and more preferably 7 to 10 J / cm 2 By irradiating the steel surface to which the contaminants are adhered with nano-pulse laser light having an energy density higher than the van der Waals force and hydrogen bond, which are the adhesion energy of the boundary surface between the contaminants and the steel surface to which the contaminants are adhered, and lower than the metallic bond and covalent bond energy of the substrate, the ablation effect of the pulse laser light is utilized, and the contaminants can be efficiently removed without damaging the substrate and without volatilizing them. To achieve the above energy density, it is preferable to adjust the average output, pulse width, repetition frequency, laser light scanning speed, and focal diameter of the square flat top shape in combination. In addition, if the amount of contaminants adhering to the substrate surface is large, the energy density of one nano-pulse laser irradiation (J / cm 2 ) is insufficient, a certain cooling time is allowed to prevent the pollutants from burning, evaporating, or volatilizing due to an excessive rise in temperature, and the pollutants are removed by multiple nano-pulse laser irradiations.

[0011] The focal diameter of the nano-pulse laser beam having the square flat-top shape irradiated to the contaminated surface is preferably adjustable from 1 mm to 1.8 mm, which not only reduces the focal diameter of the laser beam and increases the energy density, but also adjusts the focal depth by combining the square 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 unevenness of the base material.

[0012] The pollutant removal device preferably includes a pulsed Nd:YAG laser oscillator that oscillates light of a single wavelength controlled to a wavelength of 1064 nm or more and 1070 nm or less. Since the occurrence of splitting in a nano-pulse laser with a pulse width in the nanosecond range prevents uniform energy deposition on the irradiated surface, it is preferable to employ a MOPA type pulsed Nd:YAG laser oscillator that oscillates light of a single wavelength with extremely high accuracy controlled to a wavelength between 1064 nm and 1070 nm.

[0013] The pulse width of the pulse oscillator is preferably 20 ns to 500 ns, so that when the focused shape of the pulsed light is a flat top, the energy density at the focused surface can be increased and the range of the energy density per pulsed light can be adjusted by varying the pulse width.

[0014] The frequency of the pulse oscillator is preferably 20 kHz or more and 50 kHz or less, so that the energy density of the irradiated surface can be adjusted by the combination of the scanning speed (m / s) of the laser light and the oscillation frequency (kHz) of the flat-top pulse light.

[0015] The nano-pulse laser light oscillated by the pulse oscillator preferably has a minimum average output of 500 W or more and a maximum output of 2.5 Mw or more. This makes it possible to increase the energy density (J) and energy intensity (W) at the top surface of the laser light at an oscillation frequency of 20 kHz or more when the focused shape of the pulse light is flat-topped, thereby enhancing the ablation effect of the nano-pulse laser light.

[0016] It is preferable to include a means for transmitting the nano-pulse laser light generated by the pulse oscillator to the irradiation device via a fiber cable having a length of 10 m to 150 m. This makes it possible to place the oscillator at a safe location in a wide area such as a large structure, and to mount only the irradiation device on a remote-controlled robot or the like for movement.

[0017] The method for removing contaminants of the present invention comprises the following steps. (1) Flat-top nano-pulse laser light conversion process The flat beam shaver converts the Gaussian-shaped nano-pulse laser beam emitted from a pulse oscillator into a flat-top nano-pulse laser beam. (2) Irradiating the contaminated surface with nanopulse laser light The flat-top shaped nano-pulse laser light is irradiated onto the contaminated surface. This allows the contaminants to be removed without damaging the substrate and without volatilizing the contaminants.

[0018] The method for removing contaminants of the present invention is suitable for removing radioactive contaminants and / or chemical contaminants containing chlorine components. The contaminants may also contain metals and / or inorganic substances.

[0019] Next, the description will be given with reference to the drawings. In the following, the same reference numerals in the drawings indicate the same objects. FIG. 1 is a schematic diagram of a nano-pulse laser oscillator 1 according to one embodiment of the present invention. The nano-pulse laser oscillator 1 generates pulses using a pulse generator 2. The pulse generator preferably uses a Nd:YAG fiber laser. This is an infrared laser with a single wavelength of 1064 nm, and when the average output is set to 500 w or more, the fiber cable can be extended up to 150 m in the case of 2 kW. Therefore, in a wide area such as a large structure, the oscillator can be placed at a safe location, and only the irradiation device can be mounted on a remote-controlled robot or the like and moved.

[0020] The pulse generator 1 is preferably a MOPA type pulse generator capable of oscillating pulsed light with a nanosecond pulse width at a stable maximum output and frequency. It is necessary to irradiate the adhesion interface between the surface contaminant and the metal surface with light of a single wavelength with high precision and little splitting. Conventionally, a CW laser with a large wavelength tolerance of 1070nm±50nm has been used, but in the case of a nano-pulse laser with a pulse width in the nanosecond range, splitting prevents uniform energy transfer to the irradiated surface, so it is preferable to adopt a MOPA type pulse generator of a Nd:YAG laser that oscillates light of a single wavelength with extremely high precision controlled between 1064nm and 1070nm. The pulse generated by the pulse generator 2 is converted into picosecond or subnanosecond pulsed laser light by the seed LD 3.

[0021] Next, the isolator 4 in the preamplifier 8 prevents signal leakage, protects the equipment, and reduces the effects of noise. The semiconductor laser excitation light is input from the excitation LD 6 to the rare earth doped fiber cable 7 via the coupler 5 . Next, the isolator 9 in the main amplifier 13 prevents signal leakage, protects the equipment, and reduces the effects of noise, and the bandpass filter 10 extracts physical phenomena in a specific frequency band. The semiconductor laser excitation light is then input from the excitation LD 11 to the rare-earth doped fiber cable 7 via the coupler 12. The fiber cable 7 is connected to the nano-pulse laser irradiation device 20.

[0022] 2 is a schematic diagram of a nano-pulse laser irradiation device 20 according to one embodiment of the present invention. First, the laser light is collimated by a collimator 14. Next, a Gaussian-shaped beam, which is a typical pulsed laser beam shape, is converted by a flat-beam shaver 15 into a flat-top beam shape when it reaches the irradiation surface. Next, the flat-top-shaped nano-pulse laser light passes through optical system focus adjusters 16a and 16b, a scan head 17, and a laser profiler 18, and is irradiated onto an irradiation target (contaminated surface) 19.

[0023] FIG. 3 is a schematic waveform diagram (left) of a nano-pulse laser beam of a Gaussian-shaped beam 40 according to an embodiment of the present invention, and a schematic waveform diagram (right) of a nano-pulse laser beam of a square flat-top-shaped beam 44. By flattening the laser beam shape into a trapezoidal shape like the square flat-top-shaped beam 44, the thermal effect on the irradiated surface is reduced, and only the ablation effect, which is the vibration abrasion effect, can be utilized, thereby reducing the melting and oxidation of the substrate surface. However, in this case, the excess energy part of a general pulse laser beam is flattened to an irradiation intensity up to a line where the irradiation intensity reaches a slightly upper part of the ablation threshold 47, so the irradiation intensity area at the ablation threshold 47 is expanded. However, as described above, in order to obtain a separation speed that satisfies the cleaning speed of a metal structure, the van der Waals force, which is the adhesion energy, and the several J / cm, which is the irradiation intensity line of the ablation threshold that breaks hydrogen bonds at an appropriate range and speed, are required. 2 It is necessary to raise the line, and for that purpose, it is preferable to use an irradiation device having an optical system that stably outputs pulsed light of Nd:YAG fiber laser light (wavelength 1064 nm) with an average output of 500 w or more, a maximum output of 1.25 Mw or more, a pulse width of 10 ns to 500 ns, an oscillation frequency of 20 to 50 kHz, and a laser light scanning speed of 1 to 10 m / s, and that makes the pulsed light into a square flat-top shape. In FIG. 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 square flat-top shaped beam 44, and 45 is the thermal energy of the skirt. Its width is extremely narrow compared to the thermal energy 43 of the Gaussian-shaped beam 40.

[0024] Fig. 4A is a schematic top view showing the irradiation state with the square flat-top beam shape of one embodiment of the present invention, and Fig. 4B is a schematic side cross-sectional view of the same. Fig. 5A is a schematic top view showing the irradiation state with a conventional Gaussian beam shape, and Fig. 5B is a schematic side cross-sectional view of the same. In Figs. 4A-B and 5A-B, it is assumed that the contaminant is red rust (Fe2O3) that has occurred on the surface of a steel material, and that the red rust layer is about 500 μm thick. In order to remove this red rust, the adhesion energy of the boundary surface between the steel material surface to which the contaminant is adhered and the contaminant itself is the van der Waals force, and its magnitude is 1 cm 2 Since the energy density is 2 to 4 kJ / mol per mole, it is estimated that the atoms are fixed at the following energy density: A Adhesion energy (J / cm 2 ) Calculation example 1. Red rust (Fe2O3) (1) Calculate the molecular weight per mole of attached red rust: 160g / mol (2) Thickness of attached red rust: 500 μm (3) Adhesion surface area: 1 cm 2 Weight of rust per unit: 5.24g / cm 2 (Density of Fe2O3) x 1 / 20 = 0.262g (4) 1 cm 2 Number of moles of red rust per mole: 0.262g ÷ 160g / mol = 0.0016375mol (5) Van der Waals bond strength of 0.0016375 mol of red rust: 3.275 J / cm 2 ~6.55J / cm 2

[0025] From the above, it takes 1 cm to remove red rust with a thickness of 500 μm. 2 7J / cm per 2 It is theoretically possible to dissociate pollutants by irradiating them with pulsed laser light with a certain energy density. However, the energy density of the nano-pulse laser is 7 J / cm 2 The energy density converted into ablation effect is 7J / cm 2The ablation effect is reduced by a certain percentage of the total surface area of ​​the red rust, and a certain amount of energy is absorbed by the free electrons in the base metal. The boundary surface between the surface where the red rust actually occurs and the steel material is not flat, but has irregularities caused by corrosion, increasing the area of ​​the boundary surface. The distance from the laser light emitting lens to the boundary surface changes slightly due to the irregularities from the boundary surface. In addition, the thickness of the actual red rust layer is not constant. Therefore, the following points must be kept in mind when removing red rust from steel materials by irradiating them with pulsed laser light. (1) The pulsed light is 1cm 2 7J / cm per 2 It is preferable to use a laser with an energy density equivalent to 1000μm. With this energy density, red rust with a theoretical thickness of 500μm cannot be removed with a single irradiation, but with several round-trip irradiations, the contaminants can be separated without evaporating or vaporizing them, and without damaging the base material, by the ablation effect of the nano-pulse laser alone. When irradiating back and forth in this way, care must be taken not to overheat the contaminants and the base metal due to the ablation effect. If the amount of attached contaminants is sufficiently small, it is possible to separate the contaminants by a single irradiation with an energy density close to the theoretical value. Conversely, if the amount of attached contaminants is large, the energy density (J / cm) of the nano-pulse laser is 2 ) is set to a certain limit, and a certain cooling time is taken to prevent the pollutants from burning, evaporating, or volatilizing due to excessive temperature rise, and the pollutants are removed by multiple nano-pulse laser irradiation. In other words, the ablation effect of nano-pulse lasers utilizes the repetition of the generation and extinction of plasma generated by the pulse oscillation of nano-pulse laser light at microsecond intervals. The number of times this repetition occurs can be controlled by the repetition frequency of the pulse light. The ablation effect that occurs as a result can destroy the van der Waals forces and hydrogen bond energy that hold contaminants together. However, if the contaminant is deposited in a thick layer, it may be as low as 7 J / cm 2As mentioned above, even if pulse energy with an energy density of 1000 nm is applied, not all of the energy is converted into mechanical energy, which is called the ablation effect, and some of the energy is consumed as thermal energy. This cannot be specified because it depends on the characteristics of the contaminant, whether it is a metal oxide or an organic substance, and the electrical resistance of the base metal. Therefore, in many cases, it is difficult to completely remove the contaminant by irradiating a nano-pulse laser with an energy density calculated by theoretical calculation. Therefore, 7 J / cm2 is used to prevent damage to the substrate surface. 2 By using a nano-pulse laser with an energy density of 1000 nm to gradually remove contaminants from the surface, it is possible to remove the contaminants without evaporating or vaporizing them and without damaging the substrate. (2) To meet this requirement, the threshold of pulsed light irradiation intensity is 7 J / cm 2 The flat-top beam in Fig. 4A is more effective than the Gaussian beam in Fig. 5 in irradiating the target with less gaps if the oscillation frequency and scanning speed of the pulsed light are the same. (3) It is preferable that the irradiation pitch is appropriate under the condition (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 on the left side of Figure 4, the scanning speed and repetition frequency settings are well-balanced, so there are no gaps on the irradiated surface, making it possible to remove the contaminants reliably. However, if the scanning speed is too fast compared to the repetition frequency conditions, as in the right side of Figure 4, gaps will appear on the irradiated surface, and these will remain unremoved. Also, the unit area (cm2) of the contaminant 2 If the number of adhering moles per unit area is not constant but increases or decreases, the combination of the scanning speed and repetition frequency of the laser light and the irradiation overlap rate of the pulsed light can be changed to remove the contaminants without leaving any residue.

[0026] Figure 6A is a schematic energy distribution diagram of a laser beam with a flat-top beam shape, and Figure 6B is a schematic energy distribution diagram of a laser beam with a Gaussian beam shape. Compared to the Gaussian beam shown in Figure 6A, the optimum energy density of the flat-top beam shown in Figure 6B can be set in a wider optimum energy density zone in both the focal length direction and focal diameter. Within this optimum zone, the energy required for separation can be appropriately applied. Also, within the optimum zone, energy is applied that is greater than the energy required to break the van der Waals force and hydrogen bonds that are the adhesive force of the contaminants, but energy that breaks the metal bond energy of the base metal is not applied, so the steel part will not be destroyed. From the above, in order to reliably remove contaminants such as radioactive contaminants from the surface of a metal structure, etc., without damaging the substrate, it is possible to achieve this by irradiating the interface between the contaminant and the substrate with a flat-top beam-shaped nano-pulse laser light at an appropriate repetition frequency, appropriate scanning speed, and appropriate focal diameter, thereby providing an energy density that resists van der Waals forces and hydrogen bonds.

[0027] Figure 7 shows the contamination status of the primary system of a boiling water reactor (BWR) and a pressurized water reactor (PWR) previously announced by the International Atomic Energy Agency (IAEA). On top of a base metal 21 such as stainless steel, a lower layer 22 made of a base alloy such as Fe, Cr, Ni, etc., an intermediate layer 23 in which contaminants from the chromium-rich layer such as FeCr2O4 and Cr2O3 have accumulated, and an outer layer 24 in which contaminants from the ion-rich layer such as Fe2O3 have accumulated are layered. As can be seen from Figure 7, the base metal 21 is stainless steel that contains a large amount of Cr, Ni, etc. to prevent corrosion, and its radioactively contaminated layer is roughly divided into three layers. The outer layer 24 is a layer mainly composed of Fe oxides, the intermediate layer 23 is a layer of contaminants (Cs, Sr oxides, etc.) mainly composed of Cr oxides, and the lower layer 22 is a SUS alloy layer of the base metal. The thickness of the contamination layer, excluding the activated portion of the base metal in the lower layer, is a maximum of 15 μm, consisting of base metal oxides, radioactive nuclide oxides, and in some cases chlorides of each, deposited on the surface of the base metal.

[0028] 8 to 11 are cross-sectional views of an example showing the contamination state of a radioactively contaminated metal structure on the premises of the Fukushima Daiichi Nuclear Power Plant. In Fig. 8, a metal oxide layer 26 (radioactively contaminated layer) containing Cr and the like and a layer 27 (radioactively contaminated layer) containing Fe oxide and chloride and having a thickness of several µm are deposited on a base metal 25 that is lightly radioactively contaminated. In Figure 9, on top of a base metal 28 with only slight radioactive contamination, there is a protective coating layer 29 made of acrylic resin, urethane resin, etc. with a thickness of several tens of microns, a radioactively contaminated film 30 on top of that which is several tens of microns thick and contains a mixture of deteriorated coating particles, sludge, etc., and a resin deteriorated part 31 existing in the thickness direction of the protective coating layer 29. The radioactively contaminated film 30 and the resin deteriorated part 31 contain Fe oxides, Fe chlorides, sea salt, Ce oxides, Sr oxides, Ce chlorides, Sr chlorides, etc. In FIG. 10, on top of a base steel material 32 with only slight radioactive contamination is a layer 33 several tens to several hundreds of μm thick containing a mixture of Ce oxides, Sr oxides, Ce chlorides, Sr chlorides, sludge, etc., and on top of that is a contaminated layer 34 containing Fe oxides, Fe chlorides, sea salt, etc. In Fig. 11, an epoxy resin layer 36 having a thickness of several hundred µm to several mm is placed on a base steel material 35 with only slight radioactive contamination, and a Ce, Sr chloride fine particle layer 37 having a thickness of several µm is placed on the epoxy resin layer 36. The epoxy resin layer 36 contains tritium in the surface layer, is water absorbent, and is radioactively contaminated.

[0029] As shown in Figures 8 to 11, the contamination status of metal structures within the Fukushima Daiichi Nuclear Power Plant varies depending on the base metal, the treatment of the metal surface, and the differences between structures before and after the accident. In addition to these differences in contamination status, there are also differences in the shape, dimensions, installation, and storage conditions of the metal structures.

[0030] Figure 8 shows items that have already been dismantled and removed and stored in casks, separated by level of contamination. Figure 9 shows large structures with a low level of radioactive contamination that are installed or stored outdoors. Figure 10 shows items such as tools and equipment used in dismantling work that are stored separately. Figure 11 shows items that have not yet been dismantled or removed and are still installed in high radiation areas. The method for removing pollutants of the present invention can be applied to any form of contamination.

[0031] Fig. 12 shows cross-sectional photographs of Example 1 of the present invention before and after laser cleaning and before etching. Contaminants 52 such as red rust (Fe2O3), salt (NaCl), and sand are adhered to the surface of the iron substrate 51 of the cross-section 50 before laser cleaning on the left side of Fig. 12. However, the surface of the iron substrate 51 of the cross-section 53 after laser cleaning has been completely removed, and the fine irregularities of the surface of the iron substrate are exposed. This shows that the contaminants have been almost completely removed. Fig. 13 is a cross-sectional photograph of Example 1 of the present invention before and after laser cleaning and etching. Contaminants 52 such as red rust (Fe2O3), salt (NaCl), and sand are adhered to the surface of the iron substrate 51 at the cross-section 54 before laser cleaning on the left side of Fig. 13. However, the surface of the iron substrate 51 at the cross-section 55 after laser cleaning has been completely removed, exposing the fine irregularities on the surface of the iron substrate. This shows that the contaminants have been almost completely removed without damaging the iron substrate. EXAMPLES

[0032] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Example 1 (1) Pollutant removal equipment The apparatus shown in Figures 1 and 2 was used. The nano-pulse laser oscillator 1 used was manufactured by Narran and has the product name "ROD 1000W". This product has an Nd:YAG fiber laser, an average output of 1000W, an optical wavelength of 1064-1070nm, a frequency of 20-50kHz, a transmission fiber length of 15-100m, an irradiator weight of 2.5kg, an ambient temperature of 5-45°C, a weight of 245kg, and a power consumption of 5kW. The Flat Beam Shaver 15 was also made by Narran. The waveform of the nano-pulse laser light with a square flat top shape irradiated onto the contaminated surface is shown on the right side of Figure 3, and the energy density per unit area is 7 J / cm. 2 , focal diameter: 1 mm, pulse width: 40 ns. (2) Cleaning object After salt spraying on a steel plate, the red rust (Fe2O3) that had developed through natural exposure was cleaned using the above-mentioned contaminant removal device. The reasons for verifying the removal of red rust that had developed through salt spraying were, firstly, to resolve the question of whether red rust that had developed on steel plates containing salt water can be removed by laser. Secondly, to resolve the question of whether NaCl (salt), an impurity other than red rust, can be removed. Since Na belongs to the same alkali metal group as Cs, a radioactive nuclide, it is presumed that if Na can be removed, Cs can also be removed. (3) Pollutant removal results The results of elemental analysis before and after laser cleaning are shown in Table 1 below. Cross-sectional photographs before and after laser cleaning and etching are shown in FIG. 12, and cross-sectional photographs before and after laser cleaning and etching are shown in FIG.

[0033] [Table 1]

[0034] As is clear from Table 1, about 94% of Na was removed, and the remaining amount was about 1 / 20. From this experimental fact, it is presumed that Cs, which belongs to the same alkali metal as Na, can also be removed in the same way. In addition, as shown in FIG. 12, the adhering contaminants such as red rust (Fe2O3), salt (NaCl), and sand on the upper left of the iron substrate before laser cleaning were completely removed after laser cleaning, and the iron substrate surface was exposed with fine irregularities. In addition, the cross-sectional photograph after etching in FIG. 13 also shows that the iron substrate surface was exposed with fine irregularities. Furthermore, with the energy density of the contaminant removal device of this embodiment, both the adhering contaminants and the substrate surface were heated to about +30°C, and the contaminants were mainly detached from the substrate surface in particles of 0.5 μm or more, and did not volatilize or evaporate, and no damage was caused to the substrate metal surface. From the above, it was confirmed that the contaminant removal device of this embodiment can remove contaminants without damaging the substrate and without volatilizing the contaminants. [Industrial Applicability]

[0035] The contaminant removal device and the contaminant removal method of the present invention are useful for removing harmful substances including radioactive contaminants such as cesium oxide, strontium oxide, etc., and / or chemical contaminants such as polychlorinated biphenyls (PCBs), dioxins, etc. Furthermore, they are also useful in nuclear power-related facilities, waste incineration facilities, etc. [Explanation of symbols]

[0036] 1. Nano-pulse laser oscillator 2 Pulse generator 3 Seed LD3 4,9 Isolator 5,12 Coupler 6,11 Excitation LD 7 Fiber optic cable 8. Preamplifier 10 Bandpass Filters 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 Nano-pulse laser irradiation device 21 Base metal 22 Lower layer 23 Middle Class 24 Outer layer 25,28 Base metal 26,27 Radioactive Contamination Layer 29 Protective Coating Layer 30 Radioactive Contaminated Membrane 31 Resin deterioration part 32,35 Base steel 33 Mixed layer of oxides, chlorides, sludge, etc. 34 Contamination layers such as oxides, chlorides, sea salt, etc. 36 Epoxy resin layer 40 Gaussian Shaped Beam 41 Excess energy in Gaussian-shaped beams 42 Irradiation diameter of Gaussian beam 43 Thermal Energy of Gaussian Shaped Beam 44 Square flat top beam 45 Square flat top beam diameter 46 Thermal energy of a rectangular flat-top beam 47 Ablation Threshold 50,54 Cross section before laser cleaning 51 Iron base material 52 Contaminants 53,55 Cross section after laser cleaning

Claims

1. The method includes: a means for converting a Gaussian-shaped nano-pulse laser beam emitted from a pulse oscillator into a square-shaped flat-top nano-pulse laser beam by a flat beam shaver; and a means for irradiating the square-shaped flat-top nano-pulse laser beam onto a contaminated surface, A method for removing contaminants that utilizes the ablation effect of a nano-pulse laser to remove the contaminants without damaging the substrate or volatilizing the contaminants.

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

3. The method for removing contaminants according to claim 1 or 2, wherein the contaminants include metals and / or inorganic substances.

4. 3. The method for removing pollutants according to claim 1 or 2, wherein the nano-pulse laser light oscillated by the pulse oscillator has a minimum average output of 500 W or more and a maximum output of 2.5 Mw or more.

5. 3. The method for removing pollutants according to claim 1, wherein the pulse width of the pulse oscillator is 10 ns or more and 500 ns or less.

6. 3. The method for removing pollutants according to claim 1, wherein the frequency of the pulse oscillator is in the range of 20 kHz to 50 kHz.

7. 3. The contaminant removal method according to claim 1, wherein a focal diameter of the nano-pulse laser light having a square flat-top shape that is irradiated onto the contaminated surface is adjustable within a range of 1 mm or more and 1.8 mm or less.

8. The square flat-top nano-pulse laser light irradiated to the contaminated surface has an energy density per unit area of ​​1 to 10 J / cm 2 3. The method for removing pollutants according to claim 1 or 2,

9. 3. The method for removing pollutants according to claim 1, wherein the pulse oscillator is a Nd:YAG laser pulse oscillator.

10. 3. The contaminant removal method according to claim 1, wherein the pulse oscillator is a pulse oscillator that oscillates light of a single wavelength that is controlled to be equal to or greater than 1064 nm and equal to or less than 1070 nm.

11. 3. The method for removing pollutants according to claim 1, further comprising a means for transmitting the nano-pulse laser light oscillated by the pulse oscillator to an irradiation device via a fiber cable having a length of 10 m or more and 150 m or less.

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