WO2021201725A2

WO2021201725A2 - Method and apparatus for dismantling large components of nuclear power plants using laser cutting

Info

Publication number: WO2021201725A2
Application number: PCT/RU2021/050080
Authority: WO
Inventors: Azamat Yuryevich BEDANOKOV; Aleksander Grigorievich KRASYUKOV; Dmitriy Vladimirovich MARKOV
Original assignee: Joint Stock Company "State Scientific Center Of The Russian Federation Troitsk Institute For Innovative And Fusion Research" (Jsc "Ssc Rf Trinity")
Priority date: 2020-03-30
Filing date: 2021-03-25
Publication date: 2021-10-07
Also published as: WO2021201725A3; RU2756175C1

Abstract

A method and apparatus for dismantling the nuclear power plant (NPP) components are provided. The method comprises: producing a focused laser beam (6) with a maximum output power of more than 20 kW by a laser module containing an ytterbium fiber laser (1), an optical fiber (2) and a cutting head (3). The method also comprises: laser cutting of the largest metal component (5) of NPP, related to reactor vessels, steam generators and heat exchangers; moving the cutting head by a robotic arm (11), removing the cut-out fragments (13) by auxiliary robotic arm (12) and cleaning of an air around the metal component from radioactive aerosols and volatile products of laser cutting using an anti-pollution equipment (9) configured to provide an enclosed space (10) around the metal component (5). The cutting is performed depending on the wall thickness in at least two different modes.

Description

METHOD AND APPARATUS FOR DISMANTLING LARGE COMPONENTS OF NUCLEAR POWER PLANTS USING LASER CUTTING

FIELD OF INVENTION

[0001] The present invention relates to the dismantling large-sized components, namely the vessels of nuclear reactors, steam generators and heat exchangers of decommissioned nuclear power plant (NPP) units, mainly by laser cutting. More specifically, the invention relates to the dismantling of water- water power reactors (VVER).

PRIOR ART

[0002] The urgency of the problem of remote cutting of nuclear reactor vessels and other thick- walled metal components with a large surface area (about 100 m² or more) into fragments results from the growing need to decommission them after 30 years of operation. Water-water power nuclear reactors with pressurized water are one of the most successful branches of the development of nuclear power plants, which have become widespread in the world. The common name of this type of reactor in other countries is PWR (pressurized water reactor); they are the basis of the world's nuclear energy. VVER are Russian representatives of this type of the most common reactors. They have a body diameter of 4.5 m, a height of about 11 m and a wall thickness of 199.5 mm (in thinnest part of the vessel) and more. The large mass of the reactor vessel and the high level of radiation necessitate its dismantling at the installation site without taking out whole.

[0003] Fragmentation of NPP radioactive components by mechanical methods, known, for example, from the patent RU 2687048, published on 07.05.2019, is considered ineffective due to the necessity of frequent replacement of cutting tools (diamond saws, disc cutters, hydraulic shear, etc.) in hard-to-reach conditions of radiation exposure.

[0004] Traditional thermal methods, such as gas cutting, plasma or spark cutting, etc., also have the disadvantage of a high labor intensity, long duration of equipment preparation and working process.

[0005] Mobile laser systems, known, for example, from the patent RU 2485287, published on 20.06.2013, have an optimally high power and allow laser cutting of metal components at a large (up to 70 m) distance of the focusing lens from the cutting object. This makes these laser systems highly efficient means for eliminating accidents, for example, in oil and gas fields. However, they are not designed for high-performance cutting of radioactive components, which should ensure compliance to the environmental safety standards. [0006] The device and the method for underwater laser cutting of radioactive long-length elements of a nuclear reactor, known from patent application JP 200315693, published on 30.05.2003, are partially free from this disadvantage. However, the solution disclosed in this invention is not applicable for dismantling a nuclear reactor vessel at the installation site due to the impossibility of filling it with water due to its leakage and the threat of converting a large volume of water into liquid radioactive waste.

[0007] In a substantial way, these disadvantages are not present in the device and method for dismantling reactor equipment by laser cutting in a high-speed assist gas stream, coaxial with a laser beam, known from patent application JP 2001166090, published on 22.06.2001. Laser cutting of metal is a process in which a focused laser beam is concentrated on a small area of the surface. Next are the melting, burning, evaporation and the blowing of the molten material by the assist gas stream. High purity of the assist gas is necessary because exceeding the permissible value of impurities adversely affects the focusing lens of the laser cutting head. The specified method and device are designed for high-performance cutting of in-reactor equipment having different thicknesses.

[0008] However, the optimal laser cutting modes of the reactor vessels themselves and other large-sized objects have not been determined. The disadvantage related to cutting thick-walled objects is a necessity of a high flow rate (~ 5001/min or more) of pure assist gas to be injected into the cutting zone coaxially with the laser beam, which can be burdensome for cutting big NPP metal components. Moreover, there is a problem of localization and / or trapping of radioactive aerosols and volatile compounds blown off the cutting zone (which may also be termed work zone or processing zone).

SUMMARY

[0009] The technical task and technical result of the invention is to create a highly efficient technology for dismantling nuclear power plant power units by laser cutting to ensure the safety of work and the localization of radioactive contamination.

[0010] Achievement of the purpose is possible by means of method for dismantling components of NPP comprising fragmentation of a metal component with a focused laser beam and moving cut fragments out of a cutting zone.

[0011] The method is characterized in that it comprises steps of providing a focused laser beam with a maximum output power of more than 20 kW by a laser module containing an ytterbium fiber laser, an optical fiber and a cutting head; providing a laser cutting of the largest metal components of nuclear power plants, related to reactor vessels, steam generators and heat exchangers of nuclear power plants; moving the cutting head by a robotic arm during a laser cutting and removing the cut-out fragments by at least one auxiliary robotic arm; providing a cleaning of an air around the metal component from radioactive aerosols and volatile products of laser cutting using an anti -pollution equipment (which may also be termed means for radioactive debris protection) providing an enclosed space around the metal component.

[0012] In an embodiment of the invention, metal component with a wall thickness of 30 mm to 440 mm is cut and laser cutting is performed depending on the wall thickness, in at least two modes that differ in the cut width (which may also be termed kerf width).

[0013] In an embodiment, the cutting is performed at a laser power density (measured as p = P/S, where p is the laser power density, P - power of laser radiation, S is the laser spot area at cutting zone, S= D²/4, D is laser beam spot size) of more than 1.5- 10⁵ BT/CM² and a focused laser beam spot size (measured as laser beam diameter D defined by multiplied by 2 the distance from the point of maximum laser power density p_max in the laser power distribution, at the center of the beam, to the point where the laser power density equals p_max / e²) of not more than 5 mm.

[0014] In a preferred embodiment of the invention, a jet of pure assist gas directed into the cutting zone coaxially with the focused laser beam is used.

[0015] In a preferred embodiment of the invention, the cutting of the thickest components, with the wall thickness of about 200 mm to 440 mm, is performed at the laser power density of not more than 1.5-10⁵ W/cm² and the focused laser beam spot size of not less than 5 mm. [0016] In a preferred embodiment of the invention, a high-speed air jet directed into the cutting zone at an angle to the axis of the focused laser beam is formed.

[0017] The cutting may be provided with at least two laser modules operating in various modes.

[0018] The cutting out the thickest fragments may be provided from two sides: from the inside and from the outside.

[0019] In a preferred embodiment of the invention, the cut-out fragments are transported outside of the enclosed space.

[0020] The cut-out fragments may be transported through the technological channels of NPP reactor unit.

[0021] In another aspect, the invention relates to an apparatus for implementing the method of dismantling components of nuclear power plants, said apparatus comprising: a laser module consisting of a laser with an optical fiber that transports a laser-radiation to a cutting head equipped with a focusing lens that forms a focused laser beam.

[0022] The apparatus for dismantling components of nuclear power plants is characterized in that the laser module is arranged to cut the largest metal components of nuclear power plants including reactor vessels, steam generators and heat exchangers; the laser is a fiber ytterbium laser with an average radiation power of more than 20 kW; the cutting head is placed on a robotic arm; at least one an auxiliary robotic arm is arranged to move the cut-out fragments, and an anti-pollution equipment providing an enclosed space around the metal component to prevent a release of cutting by-products beyond its limits is used, said equipment includes an enclosed-space air cleaning system fitted with replaceable air filters for removal of radioactive aerosols and other by-products of laser cutting.

[0023] In a preferred embodiment of the invention, the apparatus for dismantling components of NPP is configured to cut the metal component with a wall thickness varying from 20 to 440 mm.

[0024] In an embodiment, the apparatus for dismantling metal components of NPP is designed to perform cutting at a laser power density of more than 1.5-10⁵ W/cm² and a cut width of not more than 5 mm.

[0025] In an embodiment, the apparatus for dismantling metal components of NPP additionally comprises a gas system arranged for supplying pure assist gas directed into the cutting zone coaxially with the focused laser beam, wherein said assist gas belongs to a group of gases comprising: oxygen, air, nitrogen, inert gases, carbon dioxide and their mixtures. [0026] In a preferred embodiment of the invention, the apparatus for dismantling metal components of NPP is configured to perform cutting at the laser power density of not more than 1.5- 10⁵ W/cm² and the cut width of not less than 5 mm.

[0027] In a preferred embodiment of the invention, the apparatus for dismantling metal components of NPP is equipped by an air flow system comprising a compressor and a nozzle for producing an air jet with high flow rate, more than 500 1/min, directed to the cutting zone. An air intake arranged to collect the cutting by-products may be placed in the path of a high speed air jet outgoing from the cutting zone.

[0028] The cutting head may be equipped with an automated changer for an optical filter arranged to protect the focusing lens against contamination.

[0029] In an embodiment, laser cutting may be performed from inside to outside and / or from outside to inside, wherein auxiliary robotic arms are placed both outside and inside the metal component.

[0030] In a preferred embodiment of the invention, the robotic arms are installed on one or more mobile devices.

[0031] In a preferred embodiment of the invention, the apparatus for dismantling metal components of NPP further comprises a system for transporting cut-out fragments outside the enclosed space.

[0032] In method and apparatus for dismantling NPP metal components as proposed are achieved the following technical results:

[0033] - highly efficient remote cutting of the radioactive metal components of various thickness up to 440 mm;

[0034] - elimination of radiation pollution of the surrounding air with aerosols related to laser cutting of metal components;

[0035] - protection of the cutting head optics from splashes of heated metal and slag flowing out of the cutting zone;

[0036] - ensuring radiation safety of work,

[0037] - elimination of the burdensome need for a high flow rate (~ 5001/min or more) of pure assist gas for its injection into the cutting zone coaxially with the laser beam.

[0038] The mentioned advantages are realized through the following solutions.

[0039] - Use of the continuous wave (CW) fiber ytterbium laser, allowing to generate and transmit by the optical fiber high, more than 20 kW, laser radiation power required for cutting metal components of large thickness with the highest efficiency.

[0040] - Robotization of a dismantling complex, remote control and management.

[0041] - Creation of an enclosed air space around a large-sized NPP component with the use of a cleaning ventilation system; ability to capture aerosols and slags coming out of the cutting zone.

[0042] - The molten metal removal from the cutting zone when cutting thick-walled components, stimulated by an increase in the power density of the laser beam to 1.5· 10⁵ W/cm² or more, which causes the boiling of the melt and its removal by the vapor recoil pressure.

[0043] - An increase (up to 5 mm or more) in the cutting width, which actuates the removal of metal from the cut caused by the fact that the gravity forces of the molten metal exceed the surface tension forces, and contributes to the fact that the assist gas jet blowing out the melt, reaches the far wall of the deep cut without significant pressure loss. [0044] - The use of ambient air as an assist gas, which solves the problem of long-term operation with a high gas flow rate (more than 500 1/min), necessary for cutting thick-walled components. Equipping the cutting head with an additional nozzle with a powerful air compressor to create a high flow rate jet of compressed air directed into the cutting zone at an optimal angle, about ~ 40°, to the axis of the laser beam.

[0045] - Protection of the focusing optics of the cutting head from debris by means of a replaceable optical filter, in combination with a pure assist gas flow coaxed with the laser beam.

[0046] It should be clear that the features of the above embodiments can be combined with each other. In particular, it is to be understood that the features mentioned above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without leaving the scope of the present invention.

[0047] The advantages and features of the present invention will become more apparent from the following non-limiting description of exemplary embodiments thereof, given by way of example with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS [0048] Embodiments of the invention are explained with reference to the drawings, wherein: [0049] Fig. 1, Fig. 2 - Schematic diagram of an apparatus for dismantling NPP large-sized metal components in accordance with the embodiments,

[0050] Fig. 3 - Schematic diagram a part of the apparatus near the laser cutting zone in accordance with an embodiment of the invention.

[0051] In the drawings, the matching elements of the apparatus have the same reference numbers indicating the following:

[0052] 1- laser [0053] 2- optical fiber [0054] 3- cutting head [0055] 4- focusing lens [0056] 5- metal component [0057] 6- focused laser beam [0058] 7- air cleaning system [0059] 8- remote-control system [0060] 9- anti-pollution equipment [0061] 10- enclosed space [0062] 11- robotic arm

[0063] 12- auxiliary robotic arm

[0064] 13- cut-out fragments

[0065] 14- replaceable air filters

[0066] 15- system for transporting cut-out fragments

[0067] 16- gas system components

[0068] 17- air flow system

[0069] 18- compressor

[0070] 19- nozzle

[0071] 20- high flow rate air jet

[0072] 21- cutting zone

[0073] 22- auxiliary robotic arm

[0074] 23- air intake

[0075] 24- optical filter

[0076] 25- automated changer for an optical filter [0077] 26- mobile devices [0078] 27- cover.

[0079] These drawings do not cover and, moreover, do not limit the entire scope of options for implementing this technical solution, and they are only illustrative examples of particular cases of its implementation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0080] Figure 1 illustrates an embodiment of an apparatus for dismantling the metal components of nuclear power plants that are being decommissioned. The apparatus includes a laser module containing a fiber Yb- laser 1 with the output of laser radiation into the optical fiber 2, to the distal end of which a cutting head 3 with a focusing lens 4, forming a focused laser beam 6, is connected.

[0081] The laser module is designed to cut the largest metal components 5 related to the reactor vessels (wall thickness variable from 199.5 up to 440 mm, weight 324.4 tons), as shown in Fig. 1, steam generators (wall thickness 105-171 mm, weight about 400 tons) and heat exchangers (wall thickness 20-30 mm) of nuclear power plants. According to the invention, higher efficiency in laser cutting of metal components with a wall thickness varying from 20 to 440 mm is achieved by using a fiber Yb- laser with a central laser wavelength of 1070-1080 nm and an output power of continuous laser radiation of more than 20 kW, preferably from 30 to 50 kW.

[0082] To ensure the safety of work, the laser 1 is located at long, up to 100 m, range from the radioactive cutting object. For the same purpose, automated technologies and robotics are used; in particular, the cutting head 3 is placed on a robotic arm 11, which ensures the cutting of metal components in an automated mode according to a preset program.

[0083] The apparatus for dismantling the NPP metal components also contains anti-pollution equipment 9, designed to provide an enclosed space 10, in which the metal component 5 is placed, and to prevent the release of cutting by-products from the enclosed space 10. Figure 1 illustrates an embodiment with using for this purpose a temporary equipped dome over a concrete shaft, in which the nuclear reactor vessel is located. Anti-pollution equipment 9 includes a cleaning air system 7 of the enclosed space 10, fitted with replaceable air filters 14 for capturing radioactive aerosols and volatile laser cutting by-products.

[0084] At least one auxiliary robotic arm 12 is introduced to separate and move the cut-out fragments 13.

[0085] The robotic arms 11, 12 should preferably be installed on mobile devices 26, which can be in the form of robotic vehicles, or mobile platforms.

[0086] To remove the cut-out fragments 13, a system 15 for transporting them outside the enclosed airspace 10 is introduced. The transporting system 15 may be equipped with atmospheric airlocks that prevent the release of radioactive aerosols.

[0087] The apparatus, which is essentially a robotic laser complex for dismantling the NPP metal components, is operated by a remote-control system 8, which can be placed in the same box with the laser 1.

[0088] The characteristic surface area of the metal component 5 to be cut by a robotic laser complex is at least 100 m². In case where the object of cutting is the VVER 1000 11-m-high reactor vessel, it is located in the reactor shaft of about 20 m deep.

[0089] To optimize the laser cutting process and protect the optics of the cutting head 3 from the cutting by-products, a system 16 for supplying pure assist gas coaxially with the focused laser beam 6 is preferably used.

[0090] The pure assist gas supply system 16 may contain a gas cylinder with a gas reducer and a flexible hose laid to the gas inlet to the cutting head 3.

[0091] The assist gas jet emerges from a nozzle of the cutting head coaxially with the focused laser beam to the molten metal in the cutting zone 21.

[0092] Fig. 2 shows a schematic diagram of apparatus for dismantling NPP big components in accordance with an embodiment of invention, wherein a cover 27 installed above the room, is used to provide an enclosed air space 10. In particular, the cover 27 is installed above the concrete shaft where reactor vessel is placed.

[0093] For the system 15 for transporting cut-out fragments 13, the technological channels of the NPP reactor unit can be used as shown in Fig. 2. In this regard, in the embodiments of the invention, the surface area of the cut-out fragments is limited so that to ensure their transportation through the technological channels with a limited flow section.

[0094] One of the used cutting mode is characterized by a power density of the laser beam in the focus above 1.5· 10⁵ W/cm² and a laser beam diameter in the cutting zone of no more than 5 mm. Using this mode, the boiling of the melt is achieved and its removal improved due to the vapors recoil pressure. The laser beam focus preferably is located about 1/2 the thickness of the metal component 5. In this mode of operation, a high-speed jet of pure assist gas is used, directed into the laser cutting zone coaxially with the focused laser beam 6. Pure assist gas refers to a group of gases that include oxygen, air, nitrogen, inert gases, carbon dioxide and their mixtures. The use of pure assist gas helps both to remove the melt from the cutting zone and protects the focusing lens 4 of the cutting head 3 against contamination.

[0095] The use of active assist gas, in particular oxygen, contributes to improving the cutting speed. In this case, metal heating by a laser beam to a temperature of more than 1000 °C, provides the metal burning in the zone of exposure to the oxygen jet and laser radiation, which boosts the cutting efficiency.

[0096] For the thickest walls of the cutting object, that reach about 400 mm, the cutting mode providing a laser beam power density of not more than 1.5· 10⁵ W/cm² and a laser beam diameter in the cutting zone of not less than 5 mm is used. In this mode, the removal of metal from the cutting zone is caused by the fact that the gravity forces of the molten metal exceed the surface tension forces. Increasing the cutting width to 5 mm or more ensures that the gas jet blowing out the melt reaches the far wall of the cut or kerf without significant pressure loss. However, the required gas consumption becomes very large (about 500 1/min and more) and expensive in case of pure assist gas use.

[0097] To solve this problem, in the embodiments of the invention, the laser cutting apparatus is equipped with an air flow system containing a compressor 18 and a nozzle 19 fixed on a robotic arm 11 to form a high flow rate air jet 20 directed into the cutting zone 21. In the embodiment of the invention shown in Fig. 2, the compressor 18 can be placed outside the enclosed space 10.

[0098] The formation of a high flow rate assist gas jet using the ambient air environment makes it possible to create a high-performance technology for dismantling large NPP components using laser cutting.

[0099] In the embodiment of invention an air intake 23 is placed in the path of a high flow rate air jet outgoing from the cutting zone, said air intake is arranged to collect the cutting by products, which include aerosols and sedimented slag.

[0100] As shown in Fig. 2, the air intake 23, placed on the robotic arm 22, can be connected to one of the channels of the air cleaning system 7 fitted with replaceable air filters 14.

[0101] Fig. 3 shows a layout of the apparatus near the laser cutting zone. In the embodiment of the invention shown in Fig. 3, the compressor 18 is fixed on the same mobile device 26 as the robotic arm 11. The air intake to the compressor 18 is carried out either from an enclosed space 10 or from a clean environment by a corrugated hose, the length of which from the intake point to the cutting point can exceed 20 m.

[0102] The high flow rate air jet 20, when interacting with the cutting zone, branches into two jets 20a and 20b, which are involved in the cutting processes and the removal of cutting by products from the cut kerf. At the same time, the jet 20b helps to protect the focusing lens 4 by deflecting debris particles that may move in their direction from the cutting zone.

[0103] In embodiments of the invention, to increase the reliability and ensure the smooth operation of the complex, a cassette system 25 for changing optical filters 24, designed to further protect the focusing lens 4 from debris is introduced, Fig. 3.

[0104] In embodiments of the invention, the diameter of the laser beam in the cutting zone is varied by changing the distance between the cutting head and the cutting front, which makes it possible to perform laser cutting with different cutting widths.

[0105] In embodiments of the invention, at least two laser modules are used, which may be configured to operate in at least two different cutting modes.

[0106] The cutting head 3 can be used for cutting from inside to outside, Fig. 1, Fig. 2.

[0107] In other embodiments of the invention, the cutting head 3 can be used for cutting from outside to inside.

[0108] In another embodiment two laser modules may provide cutting the thickest fragments from both sides: from inside and from outside of the NPP component.

[0109] Auxiliary robotic arms 12 can be placed both outside and inside the cutting object. [0110] Fig. 2 shows the attachment of robotic arms, mainly onto one or more mobile devices 26, which may be suspended platforms. In this case, the mobile devices 26 can move linearly along two axes or rotate.

[0111] A method for dismantling the NPP components, realized in particular by an apparatus schematically shown in FIG. 1, comprises: producing a focused laser beam 6 with a maximum output power of more than 20 kW by a laser module containing an ytterbium fiber laser 1, an optical fiber 2 and a cutting head 3. The method further comprises: laser cutting of the largest metal component 5 of nuclear power plant, related to reactor vessels, steam generators and heat exchangers; moving the cutting head 3 by a robotic arm 11 during a laser cutting and removing the cut-out fragments 13 by at least one auxiliary robotic arm 12, and cleaning of an air around the metal component from radioactive aerosols and volatile products of laser cutting using an anti-pollution equipment 9 arranged to provide an enclosed space 10 around the metal component 5 of nuclear power plant.

[0112] The anti-pollution equipment 9, comprising an air cleaning system 7 with replaceable air filters 14, prevents the release of radioactive aerosols and volatile laser cutting by-products outside the enclosed space 10.

[0113] The cut-out fragments 13 are transported outside the enclosed space 10 using, in the embodiment shown in Fig. 2, the technological channels of the NPP power unit.

[0114] The dismantling is carried out using the remote-control system 8.

[0115] Depending on the wall thickness of the metal component 5, cutting is performed in at least two different modes that differ in the cut width.

[0116] In a one mode the cutting is carried out at a laser beam power density in focus spot above 1.5-10⁵ W/cm² and a cutting width of less than 5 mm. In this case, a high flow rate jet of pure assist gas is used, directed into the laser cutting zone coaxially with the focused laser beam 6.

[0117] In another mode, cutting of the thickest walls of the metal component 5 is carried out at a laser beam power density at the focus of no more than 1.5· 10⁵ W/cm² and a cutting width of at least 5 mm.

[0118] In this mode, using an air flow system 17, a high flow rate air jet 20 is formed, directed into the laser cutting zone 21 at an angle to the axis of the focused laser beam 6.

[0119] In an embodiment of the invention, cutting is performed by at least two laser modules that perform cutting in different modes.

[0120] In another embodiment laser cutting the thickest fragments is performed from inside and from outside preferably by two laser modules.

[0121] In the course of approbation of the proposed solutions, samples of reactor steel with a thickness of 440 mm were cut. The cutting was performed with a laser output power of 30 kW. Cutting was carried out on one side. If necessary, the proposed implementation of cutting on both sides will significantly increase the cutting thickness. Successful laser cutting of reinforced concrete supports of large NPP components was also demonstrated.

INDUSTRIAL APPLICABILITY

[0122] The proposed method and apparatus are intended for a variety of applications, including dismantling large-sized metal components of decommissioning nuclear power plants.

Claims

1. A method for dismantling components of nuclear power plants (NPP) characterized by fragmentation of a metal component with a focused laser beam and moving cut fragments out of a cutting zone, said method comprising: producing a focused laser beam with a maximum output power of more than 20 kW by a laser module containing an ytterbium fiber laser, an optical fiber and a cutting head; laser cutting of the largest metal components of nuclear power plant, related to reactor vessels, steam generators and heat exchangers, moving the cutting head by a robotic arm during a laser cutting and removing the cut-out fragments by at least one auxiliary robotic arm; cleaning of an air around the metal component from radioactive aerosols and volatile products of laser cutting using anti-pollution equipment arranged to provide an enclosed space around the metal component of nuclear power plant.

2. The method according to claim 1, wherein the metal components with a wall thickness of 30 mm to 440 mm is cut and laser cutting is performed depending on the wall thickness, in at least two modes that differ in the cut width.

3. The method according to any one of the claims 1 or 2, wherein the cutting is performed at a laser power density of more than 1.5· 10⁵ W/cm² and a laser beam spot size in cutting zone of not more than 5 mm.

4. The method according to any one of the preceding claims, further comprising: providing a jet of pure assist gas directed into the cutting zone coaxially with the focused laser beam.

5. The method according to any one of the preceding claims, wherein the cutting of the thickest walls, with a thickness of about 200 mm to 440 mm, is performed at the laser power density of not more than 1.5-10⁵ W/cm² and the laser beam spot size in cutting zone of not less than 5 mm.

6. The method according to any one of the preceding claims, further comprising: providing a high-speed air jet directed into the cutting zone at an angle to the axis of the focused laser beam.

7. The method according to any one of the preceding claims, wherein the cutting is performed with at least two laser modules.

8. The method according to any one of the preceding claims, wherein the cutting out the thickest fragments is provided from two sides: from the inside and from the outside.

9. The method according to any one of the preceding claims, further comprising: transporting the cut-out fragments outside of the enclosed space.

10. The method according to any one of the preceding claims, wherein the cut-out fragments are transported through the technological channels of NPP reactor unit.

11. An apparatus for dismantling components of nuclear power plants comprising a laser module consisting of a laser (1) with an optical fiber (2) that transports a laser-radiation to a cutting head (3) equipped with a focusing lens (4) that forms a focused laser beam (6), characterized in that the laser module is arranged to cut the largest metal components of nuclear power plant including reactor vessels, steam generators and heat exchangers, the laser is a fiber ytterbium laser with an average radiation power of more than

20 kW; the cutting head (3) is placed on a robotic arm (11); at least one an auxiliary robotic arm (12) is arranged to move the cut-out fragments (13), and an anti-pollution equipment (9) providing an enclosed space (10) around the metal component to prevent a release of cutting by-products beyond its limits is used, said equipment includes an enclosed-space air cleaning system (7) fitted with replaceable air filters (14) for removal of radioactive aerosols and other by-products of laser cutting.

12. The apparatus according to claim 11, designed to cut the metal components with a wall thickness varying from 20 to 440 mm.

13. The apparatus according to any one of claims 11 or 12, arranged to perform cutting at a laser power density of more than 1.5· 10⁵ W/cm² and a cut width of not more than 5 mm.

14. The apparatus according to any one of claims 11 to 13, further comprising a gas system (16) arranged for supplying pure assist gas directed into the cutting zone coaxially with the focused laser beam, while said assist gas belongs to a group consisting of oxygen, air, nitrogen, inert gases, carbon dioxide and their mixtures.

15. The apparatus according to any one of claims 11-14, arranged to perform cutting at the laser power density of not more than 1.5· 10⁵ W/cm² and the cut width of not less than 5 mm.

16. The apparatus according to any one of claims 11 to 15, further comprising an air flow system (17) with a compressor (18) and a nozzle (19) and configured to provide an air jet (20a) with high flow rate, more than 500 1/min, directed to the cutting zone (21).

17. The apparatus according to claim 16, further comprising an air intake (23) for collecting the cutting by-product placed in the path of a high-speed air jet outgoing from the cutting zone.

18. The apparatus according to any one of the claims 11-17, wherein the cutting head (3) is equipped with an automated changer (25) for an optical filter (24) arranged to protect the focusing lens (4) against contamination.

19. The apparatus according to any one of the claims 11-18, arranged to perform laser cutting from inside to outside and/or from outside to inside.

20. The apparatus according to any one of the claims 11-19, wherein robotic arms are installed on one or more robotic mobile devices (26).

21. The apparatus according to any one of the claims 11-20, further comprising a system (15) for transporting the cut-out fragments outside the enclosed space (10).