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] The method includes means for converting a Gaussian-shaped nanopulse laser beam 40 emitted from a pulse oscillator into a rectangular flat-top shaped nanopulse laser beam 44 using a flat beam shaver, and means for irradiating the contaminated surface with the rectangular flat-top shaped nanopulse laser beam, thereby removing contaminants without damaging the substrate or causing them to volatilize.

Description

[Technical Field]

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

[0002] Radioactive contaminants such as cesium oxides and strontium oxides, as well as chemical contaminants such as polychlorinated biphenyls (PCBs) and dioxins, are generally harmful to the human body and living organisms on Earth, and therefore need to be removed. Patent Document 1 proposes irradiating radioactive contaminants present on the surface of a metal substrate with laser light to burn, 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 to evaporate or remove the material from the irradiated area. [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 project] [Problems that the invention aims to solve]

[0004] However, the aforementioned conventional technology had the problem that, because the radioactive contaminants evaporated or volatilized due to the ultra-high temperature caused by the laser light, they were difficult or impossible to capture even with current high-performance filters such as HEPA and ULPA. As a result, the contaminants were merely dispersed into the air and did not achieve essential removal, and there was also the problem of damaging the substrate.

[0005] To solve the aforementioned conventional problems, the present invention provides a method for removing contaminants that does not damage the substrate and does not cause the contaminants to volatilize. [Means for solving the problem]

[0006] One embodiment of the present invention relates to a method for removing contaminants, which 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 a contaminated surface with the rectangular flat-top nanopulse laser beam, and which removes the contaminants by utilizing the ablation effect of the nanopulse laser without damaging the substrate or volatilizing the contaminants. [Effects of the Invention]

[0007] 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 enables efficient removal without damaging the substrate or volatilizing contaminants. [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 is a schematic energy distribution diagram of laser light with a flat-top beam shape, and Figure 6B is a schematic energy distribution diagram of laser light with a Gaussian beam shape. [Figure 7] Figure 7 shows the contamination status of the primary system of BWR and PWR reactors announced by the IAEA. [Figure 8] Figure 8 is a cross-sectional view showing an example of the contamination status of radioactive contaminated metal structures within the Fukushima Daiichi Nuclear Power Plant site. [Figure 9] Figure 9 is a cross-sectional view showing an example of the contamination status of radioactive contaminated metal structures within the Fukushima Daiichi Nuclear Power Plant site. [Figure 10] Figure 10 is a cross-sectional view showing an example of the contamination status of radioactive contaminated metal structures within the Fukushima Daiichi Nuclear Power Plant site. [Figure 11] Figure 11 is a cross-sectional view showing an example of the contamination status of radioactive contaminated metal structures within the Fukushima Daiichi Nuclear Power Plant site. [Figure 12] Figure 12 is a cross-sectional photograph before etching before and after laser cleaning in Example 1 of the present invention. [Figure 13] Figure 13 is a cross-sectional photograph after etching before and after laser cleaning in Example 1 of the present invention.

Mode for Carrying Out the Invention

[0009] The present invention uses a contaminant removal device that irradiates nanopulse laser light oscillated from a pulse oscillator onto a contaminated surface to remove surface contaminants. Examples of the contaminated surface include radioactive contaminants and / or chemical contaminants containing chlorine components, metals and / or inorganic substances, etc. The aforementioned contaminant removal device 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 of contaminants without damaging the substrate or causing them to volatilize. 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 significant problems. "Removing contaminants without damaging the substrate or causing them to volatilize" means decontaminating both the attached contaminants and the substrate surface at the same ambient temperature of 5 to 45°C.

[0010] 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 Preferably, 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 Therefore, 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. Furthermore, if the amount of contaminants adhering to the substrate surface is large, the energy density of a single nanopulse laser irradiation (J / cm²) 2 If the pollutants are insufficient, a certain cooling period is allowed to prevent combustion, evaporation, or volatilization of the pollutants due to excessive temperature rise, and they are removed by multiple nanopulse laser irradiations.

[0011] Preferably, the focal diameter of the rectangular flat-top nanopulse laser beam irradiated onto the contaminated surface is adjustable 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 and focal diameter of the laser beam, thereby reducing the influence of fluctuations in the energy density of the laser beam due to irregularities in the substrate.

[0012] 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.

[0013] The pulse width of the pulse oscillator is preferably 20 ns or more and 500 ns or less. This allows for an increase in the energy density of the focusing surface when the focusing shape of the pulsed light is flat top, and the range of energy density per pulse can be adjusted by changing the pulse width.

[0014] The frequency of the pulse oscillator is preferably between 20 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).

[0015] Preferably, the nanopulse laser light oscillated by the pulse oscillator has a minimum average output of 500W or more and a maximum output of 2.5MW or more. This allows for an increase in the energy density (J) and energy intensity (W) at the top surface of the laser light when the pulse light is focused into a flat top shape, thereby enhancing the ablation effect of the nanopulse laser light at oscillation frequencies of 20kHz or higher.

[0016] 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.

[0017] The present invention's method for removing contaminants includes the following steps. (1) Flat-top nanopulse laser light conversion process The flat beam shaver converts the Gaussian-shaped nanopulse laser beam emitted from the pulse oscillator into a flat-top shaped nanopulse laser beam. (2) Nanopulse laser light irradiation process on the contaminated surface The flat-top nanopulse laser beam is irradiated onto the contaminated surface. This allows for removal without damaging the substrate or causing contaminants to volatilize.

[0018] 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.

[0019] Next, we will explain 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 for 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 mobile.

[0020] It is preferable to use a MOPA-type pulse oscillator for pulse oscillator 1, which is 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, single-wavelength light with minimal spectral dispersion. Conventionally, CW lasers with a large wavelength tolerance of 1070 nm ± 50 nm have been used, but in nanopulse lasers with a pulse width in the nanosecond range, the generation of spectral dispersion hinders uniform energy delivery to the irradiated surface. Therefore, it is preferable to employ a MOPA-type pulse oscillator of an Nd:YAG laser that oscillates highly accurate 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.

[0021] 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 LD6 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.

[0022] Figure 2 is a schematic diagram of a nanopulse laser irradiation device 20 according to one embodiment of the present invention. First, the laser beam 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 flat-top nanopulse laser light 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.

[0023] Figure 3 shows schematic waveform diagrams of nanopulse laser light from a Gaussian-shaped beam 40 (left) and a rectangular flat-top shaped beam 44 (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 44, 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 melting oxidation of the substrate surface. 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 47, thus expanding the irradiation intensity area at the ablation threshold 47. However, as mentioned above, in order to achieve a decontamination rate that satisfies the cleaning rate of metal structures by removing contaminants attached to the surface of a metal substrate, the irradiation intensity line of the ablation threshold, which is several J / cm², is required to break the van der Waals forces and hydrogen bonds, which are the adhesion energy, within an appropriate range and at an appropriate speed. 2 It 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 watts 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 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.

[0024] Figure 4A is a schematic top view showing the irradiation situation of the square 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 contaminant is red rust (Fe2O3) generated on the surface of the steel material, and the red rust layer is about 500 μm. To remove this red rust, the adhesion energy at the interface between the steel material surface where the contaminant adheres and the contaminant is the van der Waals force, and its magnitude is 2 - 4 kj / mol per 1 cm 2 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) Weight of red rust per 1 cm of the adhesion surface area 2 : 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 : 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

[0025] From the above, to remove red rust with a thickness of 500 μm, it is theoretically interpreted that if pulsed laser light with an energy density of 7 J / cm 2 per 1 cm is irradiated, the contaminants can be separated. However, among the energy density of the nanosecond pulsed laser of 7 J / cm 2 , the energy density converted into the ablation effect is 7 J / cm 2 of which 2Within 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 considered when removing rust from steel using pulsed laser beam irradiation. (1) The pulsed light to be irradiated is 1 cm 2 7 J / cm² 2 A laser with an energy density equivalent to the above is preferred. With this energy density, a theoretical thickness of 500 μm of red rust cannot be removed in a single irradiation, but by irradiating back and forth several times, the contaminants can be separated solely by the ablation effect of the nanopulse laser without vaporizing or volatilizing the contaminants, and without damaging the substrate. During this back and forth irradiation, care must be taken to avoid overheating of the contaminants and the substrate metal caused by the ablation effect. Furthermore, if the amount of contaminant adhesion is sufficiently small, it is possible to separate the contaminant with a single irradiation at an energy density close to the theoretical value. Conversely, if the amount of contaminant adhesion is large, the energy density of the nanopulse laser (J / cm²) 2 The temperature is kept within a certain limit, and a certain cooling time is taken to prevent combustion, evaporation, volatilization, etc., of the pollutants due to excessive temperature rise, and the pollutants are removed by multiple nanopulse laser irradiations. In other words, the ablation effect of nanopulse lasers utilizes the repeated generation and extinction of plasma, which is produced by the pulse oscillation of nanopulse laser light, at microsecond intervals. The number of repetitions can be controlled by the repetition frequency of the pulse light. The resulting ablation effect can break the van der Waals forces and hydrogen bond energy that are the adhesive forces of contaminants. However, if the contaminants are attached as a thick layer, the radiation level may be 7 J / cm². 2Even when pulsed energy with a certain energy density is applied, as mentioned above, not all of the energy is converted into mechanical energy in the form of ablation; some of the energy is consumed as thermal energy. This cannot be determined because it varies depending on the characteristics of the contaminant, such as whether it is a metal oxide or an organic substance, and the electrical resistance of the base metal. Therefore, in many cases, complete removal is difficult by irradiating with a nanopulse laser at an energy density calculated by theoretical calculations. Therefore, 7 J / cm² is used to avoid damaging the substrate surface. 2 By using a nanopulse laser with a high energy density, contaminants can be gradually separated and removed from the surface without vaporizing or volatilizing them, and without damaging the substrate. (2) To satisfy this requirement, the pulsed light irradiation intensity threshold must be 7 J / cm 2 The advantage lies in the irradiation of a flat-top shaped beam. With the flat-top light in Figure 4A, irradiation can be performed without gaps, even if the pulsed light oscillation frequency and scanning speed are the same, compared to the Gaussian beam light in Figure 5. (3) 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 on the left side of 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 side of 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. Also, the unit area (cm²) of contaminants... 2 If the number of fixed moles per unit area is not constant but fluctuates, the irradiation pitch can be changed by altering the combination of the laser light scanning speed and repetition frequency, thereby changing the overlap rate of pulsed light irradiation, and the contaminants can be removed without leaving any residue.

[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 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 portion 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 van der Waals forces and hydrogen bonds.

[0027] Figure 7 shows the contamination status of the primary systems of boiling water reactors (BWRs) and pressurized water reactors (PWRs), as previously published by the International Atomic Energy Agency (IAEA). On a base metal 21 such as stainless steel, there are layers: 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. 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 can be broadly classified into three layers. The outer layer 24 is mainly composed of Fe oxides, the intermediate layer 23 is a deposit layer of contaminants (Cs, Sr oxides, etc.) mainly composed of Cr oxides, and the lower layer 22 is the 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.

[0028] 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 site. Figure 8 shows a base metal 25 with minor radioactive contamination, on which a metal oxide layer 26 (radioactive contamination layer) containing Cr etc., several micrometers thick, and a layer 27 (radioactive contamination layer) containing Fe oxide and chloride, several micrometers thick, are deposited. Figure 9 shows a base metal 28 with minor radioactive contamination, a protective coating layer 29 made of acrylic resin, urethane resin, etc., several tens of micrometers thick, a radioactive contamination film 30 several tens of micrometers thick on top of the protective coating layer 29 containing deteriorated coating particles, sludge, etc., and a resin deterioration section 31 located in the thickness direction of the protective coating layer 29. The radioactive contamination film 30 and the resin deterioration section 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 top of 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 hundred μm to several mm, and on top of that is a layer of Ce, Sr chloride particulate matter 37 with a thickness of several μm. The epoxy resin layer 36 contains tritium on its surface, is water-absorbing, and is radioactively contaminated.

[0029] 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.

[0030] 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 tools, equipment, etc., used in dismantling work, which are stored separately. Figure 11 shows items that have not yet been dismantled or removed and are installed in high-radiation areas. The pollutant removal method of the present invention can be applied to any form of contamination.

[0031] Figure 12 shows cross-sectional images of Example 1 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 area 50. However, the surface of the iron substrate 51 in the cross-sectional area 53 after laser cleaning has been cleaned, and the fine irregularities of the iron substrate surface are exposed. This shows that the contaminants have been almost completely removed. Figure 13 shows cross-sectional images of the first embodiment of the present invention before and after etching with laser cleaning. On 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 (cross-section 54). However, after laser cleaning, the surface of the iron substrate 51 (cross-section 55) is cleanly removed, exposing the fine irregularities of the iron substrate surface. This indicates that the contaminants were almost completely removed without damaging the iron substrate. [Examples]

[0032] The present invention will be described below using examples. However, the present invention is not limited to these examples. (Example 1) (1) 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 1000W". This product is an Nd:YAG fiber laser with 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℃, a total weight of 245kg, and a power consumption of 5kW. I also used a Narran flatbeam shaver 15. 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 7 J / cm² per unit area. 2 The focal diameter was 1 mm and the pulse width was 40 ns. (2) Cleaning object After spraying saltwater onto the steel plate, the surface was cleaned using the aforementioned contaminant removal device to remove the red rust (Fe2O3) that had formed due to natural exposure. The reasons for verifying the removal of red rust formed by saltwater spraying were, firstly, to answer the question of whether red rust formed on a steel plate containing saltwater can be removed by laser. Secondly, to answer the question of whether impurities other than red rust, such as NaCl (salt), can 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 images before etching are shown in Figure 12, and cross-sectional images after etching are shown in Figure 13.

[0033] [Table 1]

[0034] 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 red rust (Fe2O3), salt (NaCl), sand, and other contaminants adhering to 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, causing the contaminants to detach from the substrate surface mainly as particles of 0.5 μm or larger, without volatilization or evaporation, and without damage to the metal surface of the substrate. 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. [Industrial applicability]

[0035] 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]

[0036] 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 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 contamination membrane 31. Degraded resin section 32,35 Base steel 33. Mixed layer containing oxides, chlorides, sludge, etc. 34. Contamination layers containing oxides, chlorides, sea salt, etc. 36 Epoxy resin layer 40 Gaussian-shaped beam 41. Excess energy of Gaussian-shaped beams 42. Irradiation diameter of a Gaussian-shaped beam 43 Thermal energy of a Gaussian-shaped beam 44 square flat-top beams 45-square flat-top beam irradiation diameter Thermal energy of a 46-sided 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 system 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. A method for removing contaminants that utilizes the ablation effect of a nanopulse laser to remove them without damaging the substrate or causing the contaminants to volatilize.

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

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

4. 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.

5. The method for removing contaminants according to claim 1 or 2, wherein the pulse width of the pulse oscillator is 10 ns or more and 500 ns or less.

6. The method for removing contaminants according to claim 1 or 2, wherein the frequency of the pulse oscillator is 20 kHz or more and 50 kHz or less.

7. 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.

8. 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.

9. The method for removing contaminants according to claim 1 or 2, wherein the pulse oscillator is an Nd:YAG laser pulse oscillator.

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

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

Images