Container, for transporting and storing low- and intermediate-level radioactive waste, comprising a metal composite coating layer, and method for manufacturing same

Abstract

The present invention relates to: a container for transporting and storing low- and intermediate-level radioactive waste, the container comprising a base layer and a metal composite coating layer that is disposed on the base layer and is formed from a metal composite powder comprising 35 to 85 wt% of tungsten (W), 3 to 7 wt% of carbon (C), 5 to 20 wt% of nickel (Ni), and 5 to 45 wt% of chromium (Cr); and a method for manufacturing a container for transporting and storing low- and intermediate-level radioactive waste, the method comprising a base layer-providing step of preparing a base layer and a first coating step of forming a metal composite coating layer by coating the base layer with a metal composite powder comprising 35 to 85 wt% of tungsten (W), 3 to 7 wt% of carbon (C), 5 to 20 wt% of nickel (Ni), and 5 to 45 wt% of chromium (Cr).

Description

A container for transporting and storing low- and intermediate-level radioactive waste including a metal composite coating layer, and a method for manufacturing the same

[0001] The present invention relates to a container for transporting and storing intermediate- and low-level radioactive waste comprising a metal composite coating layer, and a method for manufacturing the same. The invention relates to a container for transporting and storing intermediate- and low-level radioactive waste comprising a metal composite coating layer that significantly improves corrosion resistance, mechanical properties, and radiation shielding performance, and ensures the integrity and safety of the container, and a method for manufacturing the same.

[0002]

[0003] Radioactive waste is classified into high-level radioactive waste (spent nuclear fuel) and low- and intermediate-level radioactive waste according to risk level.

[0004] The above spent nuclear fuel is disposed of by storing it in a water storage tank next to the reactor for a certain period to reduce heat and radioactivity, and then burying it at a depth of 500 m underground.

[0005] Depending on the state of the material, the above low- and intermediate-level radioactive waste is processed by capturing radioactive materials within the waste using a high-performance gas collection filter in the case of gas, filtering radioactive materials using various filters and ion exchange resins in the case of liquid, and then solidifying it using cement; in the case of solid, it is compressed to reduce volume. After undergoing these processes, all waste is stored in a stable solid form in 200 L and 320 L commercial low- and intermediate-level radioactive waste transport / storage containers. It is then transported to a storage facility by a special vehicle, loaded into drums within the facility for temporary storage, and once a disposal drum is selected, it is transported to a disposal site by vehicle and shipment for permanent disposal.

[0006] During the transportation process, the aforementioned radioactive waste transport / storage containers may be worn down by physical phenomena such as acceleration, vibration, and resonance, or damaged by impact during loading, and there are potential risks such as overturning, collision, and fire during transport.

[0007] Domestic commercial transport and storage containers for low- and intermediate-level radioactive waste are manufactured by applying an anti-corrosion primer to the outer surface of cold-rolled steel sheets. Although the aforementioned cold-rolled steel sheets have excellent mechanical properties, they are vulnerable in terms of corrosion resistance due to the characteristics of carbon steel, which is primarily composed of iron. The anti-corrosion primer is applied thinly with a thickness of 10 to 36 μm, making it susceptible to damage from external impacts during transport and stacking of the containers. If the thickness is increased to improve this, the coating thickness becomes uneven and prone to cracking. In this case, electrochemical pitting corrosion occurs in the exposed areas of the steel sheets, and in particular, the corrosion of the transport and storage containers is accelerated by galvanic corrosion.

[0008] There have been reports of cases in the past at the radioactive waste disposal facility in Gyeongju, North Gyeongsang Province, where holes were punctured in the steel plates of storage containers for low- and intermediate-level radioactive waste due to corrosion.

[0009] Meanwhile, according to the "Safety Regulations on the Transport of Radioactive Materials, etc.," the maximum permissible radiation dose rate on the outer surface of a transport container is stipulated to be 10 mSv / h or less. This means that if the dose exceeds the maximum permissible limit when the maximum amount of waste is contained in the container, it cannot be transported.

[0010] In addition, the aforementioned radioactive waste transport / storage containers currently in commercial use have insufficient radiation shielding performance, so they are disposed of by being repackaged with a polymer composite concrete overlay during final disposal. At this time, the thickness of the overlay varies depending on the dose of the radioactive waste, but is typically 300 mm.

[0011] Accordingly, there is a need to develop radioactive waste transport / storage containers with improved radiation shielding efficiency in terms of strengthening the durability of the transport / storage containers, increasing the load capacity by mitigating radiation dose on the surface, enhancing safety regarding worker exposure, and securing disposal space by reducing the thickness of the overlay.

[0012] In particular, low- and intermediate-level radioactive waste is continuously generated during the operation and decommissioning of nuclear facilities, and as a large amount of radioactive waste is expected to be generated in a short period, especially during the decommissioning of multi-unit nuclear power plants, the demand for the development of radioactive waste transport / storage containers with such enhanced performance is increasing.

[0013] Patent Document 1 relates to a radioactive waste packaging container, a method for manufacturing a radioactive waste packaging container, and a plated steel plate, and discloses a radioactive waste packaging container comprising a steel plate, a plating layer plated on the steel plate, and a coating layer coated on the plating layer, the coating layer comprising a urethane resin layer and silica particles dispersed in the urethane resin layer, wherein the surface of the silica particles is hydrophobically treated.

[0014] Prior art refers to technical information that the inventor possessed for the derivation of the present invention or acquired during the process of deriving the present invention, and it cannot necessarily be considered publicly known technology disclosed to the general public prior to the filing of the present invention.

[0015]

[0016] <Prior Art Literature>

[0017] (Patent Document 1) Republic of Korea Registered Patent No. 10-2076694 (Registered on Feb. 6, 2020)

[0018]

[0019] In resolving the aforementioned problems, the objective of the present invention is to provide a container for transporting and storing low- and intermediate-level radioactive waste comprising a metal composite coating layer that significantly improves corrosion resistance, mechanical properties, and radiation shielding performance, and ensures the integrity and safety of the container.

[0020] In addition, the objective of the present invention is to provide a container for transporting and storing low- and intermediate-level radioactive waste that includes a metal composite coating layer which can increase the load capacity by mitigating radiation dose on the surface of the container and is also advantageous in terms of securing disposal space by reducing the thickness of the overlay.

[0021] In addition, the objective of the present invention is to provide a method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste that can improve the adhesion and strength of the coating layer and increase wear resistance and corrosion resistance.

[0022] The problems that the present invention aims to solve are not limited to those mentioned above, and other problems not mentioned will be clearly understood by a person skilled in the art to which the present invention belongs from the description below.

[0023]

[0024] A transport and storage container for low- and intermediate-level radioactive waste according to an embodiment of the present invention comprises a substrate layer and a metal composite coating layer disposed on the substrate layer and formed from a metal composite powder comprising 35 to 85 wt% tungsten (W), 3 to 7 wt% carbon (C), 5 to 20 wt% nickel (Ni), and 5 to 45 wt% chromium (Cr).

[0025] At this time, the metal composite coating layer may have a thickness in the range of 100 to 1000 μm.

[0026] In addition, the metal composite powder may have a particle size in the range of 10 to 60 μm.

[0027] In addition, the metal composite coating layer can be formed by a High Velocity Oxygen Fuel (HVOF) process.

[0028] Meanwhile, the above-mentioned low- and intermediate-level radioactive waste transport and storage container is disposed on the metal composite coating layer and may further include an outer coating layer comprising an anti-corrosion primer.

[0029] In this case, the anti-corrosion primer may include melamine resin.

[0030] In addition, the outer coating layer may have a thickness in the range of 5 to 40 μm.

[0031] The above low- and intermediate-level radioactive waste transport and storage container may have a gamma ray shielding performance improvement rate of 30% or more compared to the case where the metal composite coating layer is not formed.

[0032] A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste according to an embodiment of the present invention may include a step of providing a substrate layer for preparing a substrate layer, and a first coating step of forming a metal composite coating layer by coating a metal composite powder comprising 35 to 85 wt% tungsten (W), 3 to 7 wt% carbon (C), 5 to 20 wt% nickel (Ni), and 5 to 45 wt% chromium (Cr) onto the substrate layer.

[0033] In addition, the first coating step may be performed such that the metal composite coating layer has a thickness in the range of 100 to 1000 μm.

[0034] At this time, the metal composite powder may have a particle size in the range of 10 to 60 μm.

[0035] In addition, the first coating step can be performed by a High Velocity Oxygen Fuel (HVOF) process.

[0036] In this case, the high-speed flame spraying process can be carried out under process conditions of an oxygen flow rate of 100 to 200 psi, a hydrogen flow rate of 40 to 70 psi, an air flow rate of 20 to 50 psi, and a powder feed rate of 20 to 30 g / min.

[0037] Meanwhile, the method for manufacturing the above-mentioned low- and intermediate-level radioactive waste transport and storage container may further include a second coating step of forming an outer coating layer containing an anti-corrosion primer on the metal composite coating layer.

[0038] At this time, the second coating step may be performed such that the outer coating layer has a thickness in the range of 5 to 40 μm.

[0039] In addition, the above anti-corrosion primer may include melamine resin.

[0040] Meanwhile, the method for manufacturing the above-mentioned low- and intermediate-level radioactive waste transport and storage container may further include a pretreatment step for surface modification of the substrate layer prior to the first coating step.

[0041] At this time, the pretreatment step may be performed to remove oxides formed on the surface of the substrate layer and to increase the surface area of ​​the substrate layer.

[0042] In addition, the above pretreatment step may include a grit blasting process.

[0043] In this case, the grit blasting process can be carried out under process conditions of a blasting distance of 4 to 8 inches, a blasting pressure of 25 to 35 psi, and a blasting angle of 45° to 90°.

[0044] Meanwhile, the method for manufacturing the above-mentioned low- and intermediate-level radioactive waste transport and storage container may further include a post-processing step for enhancing the adhesion and physical properties of the metal composite coating layer after the first coating step.

[0045] At this time, the above post-processing step may include a heat treatment process and a polishing process.

[0046] In addition, the heat treatment process may be performed to relieve residual stress generated in the first coating step, improve the microstructure, and strengthen the inter-particle bonding force within the metal composite coating layer, and the polishing process may be performed to reduce the surface roughness of the metal composite coating layer.

[0047]

[0048] As described above, according to the low- and intermediate-level radioactive waste transport and storage container comprising a metal composite coating layer according to the present invention, corrosion resistance, mechanical properties, and radiation shielding performance can be significantly improved simultaneously.

[0049] In addition, according to the low- and intermediate-level radioactive waste transport and storage container comprising a metal composite coating layer according to the present invention, the integrity of the container can be ensured during transport, loading, and movement of the low- and intermediate-level radioactive waste container, and can contribute to the safety of workers from radioactive gamma ray sources outside the container.

[0050] In addition, according to the low- and intermediate-level radioactive waste transport and storage container including a metal composite coating layer according to the present invention, the loading capacity can be increased by mitigating the radiation dose on the surface of the container, and it is also advantageous in terms of securing disposal space by reducing the thickness of the overlay.

[0051] In addition, according to the method for manufacturing a transport and storage container for intermediate and low-level radioactive waste according to the present invention, by performing a pretreatment process and a posttreatment process before and after the formation of a metal composite coating layer, respectively, the adhesion and strength of the metal composite coating layer, as well as the wear resistance and corrosion resistance of the container, can be improved.

[0052] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by a person skilled in the art to which the present invention pertains from the description below.

[0053]

[0054] FIG. 1 is a schematic diagram showing the appearance of a low-to-medium level radioactive waste transport and storage container according to an embodiment of the present invention.

[0055] FIG. 2 is a schematic diagram showing a transport and storage container for low- and intermediate-level radioactive waste according to an embodiment of the present invention.

[0056] FIG. 3 is a flowchart illustrating a method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste according to an embodiment of the present invention.

[0057] FIG. 4a is a graph showing the results of the corrosion characteristics evaluation of a specimen of a low-to-medium level radioactive waste transport and storage container according to an embodiment and a comparative example of the present invention under 60% relative humidity conditions, and FIG. 4b is a graph showing the results of the corrosion characteristics evaluation of a specimen of a low-to-medium level radioactive waste transport and storage container according to an embodiment and a comparative example of the present invention under 40% relative humidity conditions.

[0058] Figure 5 is a graph showing the results of the hardness characteristic evaluation of specimens of low- and intermediate-level radioactive waste transport and storage containers according to the embodiments and comparative examples of the present invention.

[0059] Figures 6a and 6b are graphs showing the results of evaluating the wear resistance characteristics of specimens of low- and intermediate-level radioactive waste transport and storage containers according to the embodiments and comparative examples of the present invention.

[0060] Figure 7 is a graph showing the results of evaluating the adhesion strength characteristics of specimens of low- and intermediate-level radioactive waste transport and storage containers according to the embodiments and comparative examples of the present invention.

[0061] FIGS. 8a and FIGS. 8b are graphs showing the radiation shielding rate and the shielding performance improvement rate of specimens of low- and intermediate-level radioactive waste transport and storage containers according to the embodiments and comparative examples of the present invention, respectively.

[0062] FIGS. 9a and FIGS. 9b are graphs showing the corrosion rate test results and the hardness characteristic change test results of a specimen of a low-to-medium level radioactive waste transport and storage container according to Example 1 of the present invention, respectively.

[0063] Figure 10 is a graph showing the results of evaluating the shielding performance improvement rate according to the coating thickness of a specimen of a low-to-medium level radioactive waste transport and storage container according to Example 1 of the present invention.

[0064] Figure 11 is a graph showing the results of the hardness characteristic evaluation according to the coating thickness of a specimen of a low-to-medium level radioactive waste transport and storage container according to Example 1 of the present invention.

[0065] FIG. 12 is a graph showing the results of evaluating adhesion strength characteristics according to the coating thickness of a specimen of a low-to-medium level radioactive waste transport and storage container according to Example 1 of the present invention.

[0066]

[0067] <Explanation of Symbols>

[0068] 1: Transport and storage container for low- and intermediate-level radioactive waste including a metal composite coating layer

[0069] 10: Base layer

[0070] 20: First coating layer

[0071] 30: Second coating layer

[0072]

[0073] In the present invention, the attached drawings may be illustrated with exaggerated expressions to distinguish it from the prior art, ensure clarity, and facilitate the understanding of the technology. Furthermore, the terms described below are defined considering their functions in the present invention; since these terms may vary depending on the intentions or conventions of the user or operator, their definitions should be based on the technical content throughout this specification. Meanwhile, the embodiments are merely exemplary details of the components presented in the claims of the present invention and do not limit the scope of the rights of the present invention; the scope of rights should be interpreted based on the technical concept throughout the specification of the present invention.

[0074] Throughout the specification, when a configuration is described as "including" a configuration, this means that, unless specifically stated otherwise, it does not exclude other configurations but may include additional configurations.

[0075] Furthermore, when it is said that one configuration is "connected," "connected," or "combined" with another configuration, this means that it is not only "directly connected," "directly connected," or "directly combined," but also that there may be cases where it is "connected with another configuration interposed," "connected with another configuration interposed," or "combined with another configuration interposed." On the other hand, when it is said that one configuration is "directly connected," "directly connected," or "directly combined" with another configuration, it should be understood that there is no other configuration in between.

[0076] In addition, when directional terms such as "front," "back," "up," "down," "left," "right," "first end," "other end," and "both ends" are used, they are used exemplarily in relation to the orientation of the disclosed drawings and should not be interpreted restrictively, and when terms such as "first" and "second" are used, they are terms used to distinguish each configuration and should not be interpreted restrictively.

[0077] In order to more clearly explain the features of the embodiments of the present invention, detailed descriptions of matters widely known to those skilled in the art to which the following embodiments pertain are omitted. Additionally, detailed descriptions of parts in the drawings that are unrelated to the description of the embodiments are omitted.

[0078] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[0079]

[0080] FIG. 1 is a schematic diagram showing the external appearance of a low-to-intermediate level radioactive waste transport and storage container according to an embodiment of the present invention; FIG. 2 is a schematic diagram showing a low-to-intermediate level radioactive waste transport and storage container according to an embodiment of the present invention; FIG. 3 is a flowchart showing a method for manufacturing a low-to-intermediate level radioactive waste transport and storage container according to an embodiment of the present invention; FIG. 4a is a graph showing the results of evaluating corrosion characteristics of a low-to-intermediate level radioactive waste transport and storage container specimen according to an embodiment and a comparative example of the present invention under 60% relative humidity conditions; FIG. 4b is a graph showing the results of evaluating corrosion characteristics of a low-to-intermediate level radioactive waste transport and storage container specimen according to an embodiment and a comparative example of the present invention under 40% relative humidity conditions; FIG. 5 is a graph showing the results of evaluating hardness characteristics of a low-to-intermediate level radioactive waste transport and storage container specimen according to an embodiment and a comparative example of the present invention; and FIG. 6a and FIG. 6b show the wear resistance characteristics of a low-to-intermediate level radioactive waste transport and storage container specimen according to an embodiment and a comparative example of the present invention. This is a graph showing evaluation results; FIG. 7 is a graph showing the evaluation results of adhesion strength characteristics of a specimen of a low-to-medium level radioactive waste transport and storage container according to an embodiment and a comparative example of the present invention; FIG. 8a and FIG. 8b are graphs showing the radiation shielding rate and shielding performance improvement rate of a specimen of a low-to-medium level radioactive waste transport and storage container according to an embodiment and a comparative example of the present invention, respectively; FIG. 9a and FIG. 9b are graphs showing the corrosion rate test results and hardness characteristic change test results of a specimen of a low-to-medium level radioactive waste transport and storage container according to Embodiment 1 of the present invention, respectively; FIG. 10 is a graph showing the evaluation results of the shielding performance improvement rate according to the coating thickness of a specimen of a low-to-medium level radioactive waste transport and storage container according to Embodiment 1 of the present invention; FIG. 11 is a graph showing the evaluation results of hardness characteristics according to the coating thickness of a specimen of a low-to-medium level radioactive waste transport and storage container according to Embodiment 1 of the present invention.FIG. 12 is a graph showing the results of evaluating adhesion strength characteristics according to the coating thickness of a specimen of a low-to-medium level radioactive waste transport and storage container according to Example 1 of the present invention.

[0081]

[0082] Referring to FIGS. 1 and 2, a medium-to-low level radioactive waste transport and storage container (1, hereinafter also referred to as "container") according to an embodiment of the present invention comprises a substrate layer (10) and a metal composite coating layer (20). Additionally, the medium-to-low level radioactive waste transport and storage container (1) according to an embodiment of the present invention may further comprise an outer coating layer (30).

[0083] The above substrate layer (10) has excellent mechanical properties and can serve as a structural framework for the above medium-to-low level radioactive waste transport and storage container (1).

[0084] The above substrate layer (10) may include a raw material applied to a commercial low-to-medium level radioactive waste storage container. For example, the above substrate layer (10) may include a cold-rolled steel sheet that satisfies the KS D 3512-SPCC standard.

[0085] The above substrate layer (10) may have a thickness of 0.5 to 1.5 mm, and preferably may have a thickness of about 1.2 mm.

[0086] The metal composite coating layer (20) can improve corrosion resistance, radiation shielding performance, and mechanical properties, thereby enabling the integrity and safety of the medium- and low-level radioactive waste transport and storage container (1).

[0087] The metal composite coating layer (20) can be disposed on the substrate layer (10). That is, the metal composite coating layer (20) can be formed on the outer surface of the substrate layer (10).

[0088] The metal composite coating layer (20) may include metal composite powder.

[0089] The metal composite powder may comprise 35 to 85 wt% tungsten (W), 3 to 7 wt% carbon (C), 5 to 20 wt% nickel (Ni), and 5 to 45 wt% chromium (Cr); preferably, it may comprise 50 to 80 wt% tungsten (W), 4 to 7 wt% carbon (C), 5 to 20 wt% nickel (Ni), and 5 to 25 wt% chromium (Cr); more preferably, it may comprise 60 to 80 wt% tungsten (W), 4 to 6 wt% carbon (C), 5 to 15 wt% nickel (Ni), and 5 to 20 wt% chromium (Cr); and even more preferably, it may comprise 78 to 80 wt% tungsten (W), 4.5 to 6 wt% carbon (C), 10 to 12 wt% nickel (Ni), and 5 to 6 wt% chromium (Cr).

[0090] The composition of the metal composite powder is set so that the low-to-medium level radioactive waste transport and storage container (1) can exhibit optimized characteristics by comprehensively considering the effects on corrosion resistance, hardness, wear resistance, adhesion strength, and gamma ray shielding performance. The inventors considered a number of materials known to be excellent in terms of durability and gamma ray shielding performance, and as a result of an in-depth evaluation of candidate compositions evaluated as particularly excellent among them, confirmed that the metal composite powder having the specified composition can exhibit the best performance overall in terms of required characteristics when applied to the low-to-medium level radioactive waste transport and storage container (1).

[0091] If the above metal composite powder does not have the above-specified composition, any one of the performances of corrosion resistance, hardness, wear resistance, adhesion strength, and gamma ray shielding performance may be excellent, but other performances are significantly reduced, and consequently, when considering the above characteristics comprehensively, it cannot exhibit satisfactory performance as a medium-to-low level radioactive waste transport and storage container (1).

[0092] The metal composite coating layer (20) can be formed by a High Velocity Oxygen Fuel (HVOF) process. Therefore, compared to the case where it is formed by a plasma spray process, the metal composite coating layer (20) can have excellent film characteristics and a large film thickness. Specifically, compared to the case where it is formed by a plasma spray process, the metal composite coating layer (20) has a high density, low porosity and oxidation rate, excellent bonding strength, hardness and wear resistance characteristics, and can have a large thickness.

[0093] The above metal composite powder is a powder suitable for the above HVOF process, and when a coating layer is formed by the above HVOF process compared to other coating processes, it exhibits significantly superior performance, thereby improving the characteristics of the above low- and intermediate-level radioactive waste transport and storage container (1) and ensuring soundness and safety.

[0094] The metal composite powder may have a particle size in the range of 10 to 60 μm. If the particle size of the metal composite powder exceeds the above range, sufficient bonding between the metal composite powder particles may not occur when forming the metal composite coating layer (20), and cracks may occur inside the metal composite coating layer (20).

[0095] When the metal powder particles have a smaller particle size, most of the particles do not directly collide with the substrate layer due to the reduced spraying speed, but instead scatter and fly around the substrate layer, degrading the coating quality. When the particle size is larger, the melting time increases; therefore, if the particle size is inappropriately large, the melting time is prolonged, and the particles may collide with the substrate layer (10) in a solid state when forming the metal composite coating layer (20). In this case, cracks may occur inside the coating because sufficient bonding between the powder particles is not achieved. The metal composite powder included in the metal composite coating layer (20) is a high-melting-point cermet-based powder mixed with carbide powder and metal powder, and since its thermal conductivity is lower than that of general metal powder, it is necessary to pay more attention to the particle size. Additionally, since the metal composite coating layer (20) is formed by an HVOF process, it is desirable for the metal composite powder to have a particle size in the range of 10 to 60 μm, taking into account the particle velocity and flame temperature in the process.

[0096] The metal composite layer (20) may have a thickness in the range of 100 to 1000 μm, preferably in the range of 200 to 600 μm, and more preferably in the range of 250 to 550 μm. If the thickness of the metal composite layer (20) is less than the above range, the corrosion resistance, hardness, wear resistance, adhesion strength, and gamma ray shielding performance are insufficient, so the performance as a medium-to-low level radioactive waste transport and storage container (1) cannot be secured, and if it exceeds the above range, the gamma ray shielding efficiency may increase with increasing thickness, but there is a concern about deterioration of physical properties and burden of process costs.

[0097] The above outer coating layer (30) can further improve the corrosion resistance of the above medium-to-low level radioactive waste transport and storage container (1).

[0098] The outer coating layer (30) may be disposed on the metal composite coating layer (20). That is, the outer coating layer (30) may be formed on an outer surface facing the bonding surface of the metal composite coating layer (20) with the substrate layer (10).

[0099] The above outer coating layer (30) may include an anti-corrosion primer. The anti-corrosion primer is a material applied to protect the metal surface and can primarily serve to prevent corrosion of the metal surface.

[0100] In one embodiment, the anti-corrosion primer may include melamine resin.

[0101] The outer coating layer (30) may have a thickness in the range of 5 to 40 μm. If the thickness of the outer coating layer (30) is less than the above range, it is difficult to sufficiently exhibit the corrosion prevention effect, and if it exceeds the above range, there is a problem that the thickness of the outer coating layer (30) is formed unevenly and is prone to breaking.

[0102] The medium-to-low level radioactive waste transport and storage container (1), in which the metal composite coating layer (20) is formed to a thickness of about 250 μm or more, may have a gamma ray shielding performance improvement rate of at least 30% compared to the case where the metal composite coating layer (20) is not formed, i.e., the case where only the substrate layer (10) and the outer coating layer (30) formed on the substrate layer (10) are included.

[0103] A low-to-medium level radioactive waste transport and storage container (1) according to an embodiment of the present invention may have significantly improved corrosion resistance, mechanical properties, and radiation shielding performance, and may ensure the integrity of the container (1) and contribute to the safety of workers from radioactive gamma ray sources outside the container (1). In particular, the low-to-medium level radioactive waste transport and storage container (1) according to an embodiment of the present invention may be applied as a high-integrity container. The "high-integrity container" refers to a waste packaging container capable of maintaining integrity for more than 300 years under general underground environments and disposal conditions in Korea.

[0104] In addition, according to the low- and intermediate-level radioactive waste transport and storage container (1) according to the embodiment of the present invention, the loading capacity can be increased by mitigating the radiation dose on the surface of the container (1), and it is also advantageous in terms of securing disposal space by reducing the thickness of the overlay.

[0105]

[0106] Next, with reference to FIG. 3, a method for manufacturing a transport and storage container for intermediate-level radioactive waste according to an embodiment of the present invention will be described. The method for manufacturing a transport and storage container for intermediate-level radioactive waste illustrated in FIG. 3 is a method for manufacturing a transport and storage container for intermediate-level radioactive waste (1) according to the aforementioned embodiment illustrated in FIG. 1 and FIG. 2. Accordingly, in this embodiment, in order to avoid repetition, a detailed description of the contents described in relation to the embodiment illustrated in FIG. 1 and FIG. 2 is omitted.

[0107] A method for manufacturing a transport and storage container for intermediate-to-low level radioactive waste according to an embodiment of the present invention may include a step of providing a substrate layer and a first coating step (S20). Additionally, a method for manufacturing a transport and storage container for intermediate-to-low level radioactive waste according to an embodiment of the present invention may further include a pretreatment step (S10), a posttreatment step (S30), and a second coating step (S40).

[0108] The step of providing the above substrate layer is a step of preparing a substrate layer (10) that forms the structural framework of the above low- and intermediate-level radioactive waste transport and storage container (1).

[0109] The above substrate layer (10) may include a cold-rolled steel sheet that satisfies the KS D 3512-SPCC standard, which is a raw material applied to commercial low- and intermediate-level radioactive waste storage containers.

[0110] The above substrate layer (10) may have a thickness of 0.5 to 1.5 mm, and preferably may have a thickness of about 1.2 mm.

[0111] The above pretreatment step (S10) is a step for surface modification of the substrate layer that can be performed before the above first coating step (S20).

[0112] The above pretreatment step (S10) may be performed to remove oxides formed on the surface of the substrate layer (10) and to increase the surface area of ​​the substrate layer (10). By the above pretreatment step (S10), the adhesion of the metal composite coating layer (20) formed in the subsequent process, the first coating step (S20), can be significantly improved.

[0113] The above pretreatment step (S10) may include a grit blasting process.

[0114] The grit blasting process described above is a process that uses high-pressure air or water to spray abrasive particles onto a surface at high speed to remove contaminants, create texture, or roughen the surface for further processing.

[0115] The above grit blasting process can be performed using aluminum oxide as abrasive particles.

[0116] The grit blasting process described above can be carried out under process conditions of a blasting distance of 4 to 8 inches, a blasting pressure of 25 to 35 psi, and a blasting angle of 45° to 90°. The grit blasting process conditions are selected to optimize the adhesion between the substrate layer (10) and the metal composite coating layer (20) by considering the material of the substrate layer (10), the composition of the metal composite powder, the microstructure and thickness of the metal composite coating layer (20), etc.

[0117] The first coating step (20) above is a step of forming the metal composite coating layer (20) by coating the metal composite powder on the substrate layer (10).

[0118] The first coating step (20) above can be performed by a High Velocity Oxygen Fuel (HVOF) process.

[0119] General surface coating technologies include thermal spraying, chemical vapor deposition (CVD), physical vapor deposition (PVD), and laser cladding, depending on the operating temperature, material, and method. Furthermore, the aforementioned thermal spraying coating technology can be classified into flame, arc, plasma, and explosive spraying based on the heat source, and the applicable technology may vary depending on the coating material. When the coating material is a metal, ceramic, or cermet, the aforementioned high-speed flame spraying and plasma spraying technologies may be applied.

[0120] The above high-speed flame spraying technology is a surface treatment technology that uses a high-temperature, high-speed flame to melt powder-form coating materials and spray them onto a target surface. A mixture of fuel and oxygen is heated to a high temperature to generate a flame, coating powder is injected into the generated flame to melt it rapidly, and then the molten powder particles are sprayed onto the target surface to collide and cool, thereby forming a coating layer.

[0121] The above plasma spraying technology is a surface treatment technology that involves melting a coating material using a high-temperature plasma heat source and spraying it onto a target surface. It forms a coating layer by exposing a gas to high voltage to ionize it into a plasma state, injecting coating powder into a generated plasma arc to melt it rapidly, and then spraying the molten and accelerated powder particles onto the target surface to collide with and cool them.

[0122] Since these thermal spray coatings exhibit different characteristics depending on the individual techniques and powders used, it is important to apply a technique that enables optimal performance based on the powder used as the coating material.

[0123] The inventors applied the thermal spraying technology to the metal composite powder included in the metal composite coating layer (20) to compare their respective characteristics, and applied the high-speed flame spraying process to the first coating step (S20) in terms of optimal performance. Specifically, compared to the layer formed using the plasma spraying technology, the metal composite coating layer (20) formed using the high-speed flame spraying technology had fewer pores, a dense structure, and was relatively superior in hardness, porosity, and oxidation rate. In particular, compared to the layer formed using the plasma spraying technology, the metal composite coating layer (20) formed using the high-speed flame spraying technology exhibited wear resistance characteristics approximately four times higher.

[0124] Accordingly, by applying the high-speed thermal spraying process in the first coating step (S20), the metal composite coating layer (20) can have a high density, low porosity and oxidation rate, excellent bonding strength, hardness and wear resistance characteristics, and a large thickness.

[0125] In one embodiment, the high-speed flame spraying process may be carried out under process conditions of an oxygen flow rate of 100 to 200 psi, a hydrogen flow rate of 40 to 70 psi, an air flow rate of 20 to 50 psi, and a powder feed rate of 20 to 30 g / min. The high-speed flame spraying process conditions are selected to optimize the characteristics of the metal composite coating layer (20) by taking into account the composition of the metal composite powder.

[0126] The metal composite powder may comprise 35 to 85 wt% tungsten (W), 3 to 7 wt% carbon (C), 5 to 20 wt% nickel (Ni), and 5 to 45 wt% chromium (Cr); preferably, it may comprise 50 to 80 wt% tungsten (W), 4 to 7 wt% carbon (C), 5 to 20 wt% nickel (Ni), and 5 to 25 wt% chromium (Cr); more preferably, it may comprise 60 to 80 wt% tungsten (W), 4 to 6 wt% carbon (C), 5 to 15 wt% nickel (Ni), and 5 to 20 wt% chromium (Cr); and even more preferably, it may comprise 78 to 80 wt% tungsten (W), 4.5 to 6 wt% carbon (C), 10 to 12 wt% nickel (Ni), and 5 to 6 wt% chromium (Cr).

[0127] The above metal composite powder is a powder suitable for the above HVOF process, and when applied to the above HVOF process compared to other coating processes, it exhibits significantly superior performance, thereby improving the characteristics of the above low- and intermediate-level radioactive waste transport and storage container (1) and ensuring soundness and safety.

[0128] The metal composite powder may have a particle size in the range of 10 to 60 μm. If the particle size of the metal composite powder exceeds the above range, sufficient bonding between the metal composite powder particles is not achieved when forming the metal composite coating layer (20), and cracks may occur inside the metal composite coating layer (20).

[0129] The first coating step (S20) above may be performed such that the metal composite layer (20) has a thickness in the range of 100 to 1000 μm, preferably in the range of 200 to 600 μm, and more preferably in the range of 250 to 550 μm. If the thickness of the metal composite layer (20) is less than the above range, the corrosion resistance, hardness, wear resistance, adhesion strength, and gamma ray shielding performance are insufficient, so the performance as a medium-to-low level radioactive waste transport and storage container (1) cannot be secured, and if it exceeds the above range, the gamma ray shielding efficiency may increase with increasing thickness, but there is a concern regarding the deterioration of physical properties and the burden of process costs.

[0130] The above post-processing step (S30) is a step for strengthening the adhesion and physical properties of the metal coating layer that can be performed after the above first coating step (S20).

[0131] The above post-processing step (S30) may include a heat treatment process and a polishing process.

[0132] The above heat treatment process can be performed to relieve residual stress generated in the first coating step (S20), improve the microstructure, and strengthen the inter-particle bonding force within the metal composite coating layer (20).

[0133] The above heat treatment process can be performed at a temperature in the range of 400 to 700°C for 1 to 5 hours. If the temperature of the above heat treatment process exceeds the above range, caution is required as it may promote the decomposition of carbides and oxidation reactions. In addition, if the heat treatment process time is too short, the effects of microstructure stabilization and residual stress relief may be negligible, and if the heat treatment process time is excessive, the coating layer may be destroyed due to embrittlement.

[0134] By the above heat treatment process, the adhesion and strength of the outer coating layer (30) formed in the subsequent second coating step (S40) can be significantly improved.

[0135] The above polishing process may be performed to reduce the surface roughness of the metal composite coating layer (20). By the above polishing process, the wear resistance and corrosion resistance of the metal composite coating layer (20) may be further improved.

[0136] The above heat treatment process and the above polishing process may be carried out by selecting an appropriate method among the methods known in the relevant technical field.

[0137] The second coating step (S40) is a step of forming the outer coating layer (30) on the metal composite coating layer (20).

[0138] The second coating step (S40) above can be performed using an anti-corrosion primer. The anti-corrosion primer is a material applied to protect the metal surface and primarily serves to prevent corrosion of the metal surface.

[0139] In one embodiment, the anti-corrosion primer may include melamine resin.

[0140] The second coating step (S40) above may be performed such that the outer coating layer (30) has a thickness in the range of 5 to 40 μm. If the thickness of the outer coating layer (30) is less than the above range, it is difficult to sufficiently exhibit the corrosion prevention effect, and if it exceeds the above range, there is a problem that the thickness of the outer coating layer (30) is formed unevenly and is prone to cracking.

[0141] According to the method for manufacturing a medium-to-low level radioactive waste transport and storage container according to an embodiment of the present invention, the characteristics of the metal composite coating layer (20) can be significantly improved by forming the metal composite coating layer (20) by an HVOF process selected from the perspective of performance optimization. In addition, according to the method for manufacturing a medium-to-low level radioactive waste transport and storage container according to the present invention, by performing a pretreatment step and a posttreatment step before and after the formation of the metal composite coating layer (20), respectively, the adhesion and strength of the metal composite coating layer (20), as well as the wear resistance and corrosion resistance of the container (1), can be improved.

[0142]

[0143] The present invention will be explained in more detail below through examples. However, the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited to the following examples.

[0144]

[0145] [Example]

[0146] 1. Preparation of specimens for transport and storage containers for low- and intermediate-level radioactive waste

[0147] (1) Materials

[0148] - Base layer: A 1.2 mm thick cold-rolled steel sheet (KS D 3512-SPCC), which is the raw material for commercial low- and intermediate-level radioactive waste transport and storage containers (200 L, 320 L), was used as the base layer. For coating and performance testing, a steel sheet of the KS D 3512-SPCC standard, supplied in bulk, was reprocessed into a square plate specimen with dimensions of 100 mm × 100 mm × 1.2 T.

[0149] - Metal composite coating layer (hereinafter referred to as "coating layer"):

[0150] A metal composite powder having the composition shown in Table 1 below was used as the material for the metal composite coating layer. The metal composite powder used was manufactured through an aggregation / sintering process or an atomization process.

[0151] Particle Size (㎛) Chemical Composition (wt%) WCNiCrCoSiFe Example 1 15-4579.25.410.25.2--- Example 2 16-4566.75.97.419.90.1-- Example 3 10-5359.56.416.317.7--0.1 Example 4 16-4535.33.618.143--- Comparative Example 1 5-45-0.0579.120.70.04-- Comparative Example 2 16-45-0.150.846-1.91.2 Comparative Example 3 10-53-3.421.578.5---

[0152]

[0153] (2) Manufacturing process

[0154] - Pretreatment step: A grit blasting process was performed as a pretreatment process on the substrate layer specimen of (1) above. Foreign substances on the metal composite coating layer formation surface of the substrate layer specimen were checked and, if necessary, cleaned with acetone or ethyl alcohol. After tape masking the fixture before the grit blasting process, the grit blasting process was performed according to the working conditions listed in Table 2 below.

[0155] Item Parameters Grit Type: Brown Aluminum Oxide, 60 Mesh Blasting Distance: 6 ± 2" Blasting Pressure: 30 ± 5 PSI Blasting Angle: 45°-90° Passes: 2-6 Nozzle Size: 1 / 4". STD

[0156]

[0157] - Coating step: A metal composite coating layer was formed by coating the metal composite powder of (2) onto the substrate specimen using HVOF (High Velocity Oxygen Fuel). A high-output HVOF spray nozzle of 250 kW or more was mounted on a motion-controlled robot, and the metal composite powder was sprayed and deposited onto the surface of the substrate specimen while the robot moved the HVOF spray nozzle left and right. The coating thicknesses were set to 250 μm, 350 μm, 450 μm, and 550 μm, respectively. The main process conditions required for the HVOF process are as shown in Table 3 below.

[0158] Key Process Conditions Process Values Oxygen Flow Rate (psi) 100 - 200 Hydrogen Flow Rate (psi) 40 - 70 Air Flow Rate (psi) 20 - 50 Powder Feed Rate (g / min) 25 ± 5

[0159]

[0160] 2. Manufacture of transport and storage containers for low- and intermediate-level radioactive waste

[0161] A low-to-medium level radioactive waste transport and storage container according to the present invention was manufactured by forming a substrate layer and a metal composite coating layer in a manner similar to that of 1 above, in accordance with the specifications of a commercial low-to-medium level radioactive waste transport and storage container (200 L, 320 L), and forming an outer coating layer by coating a melamine resin with a thickness of 10 to 36 μm on the metal composite coating layer.

[0162]

[0163] 3. Characterization of Specimens for Transport and Storage Containers for Low- and Intermediate-Level Radioactive Waste

[0164] Tests for characteristic evaluation were conducted on the specimen of the low- and intermediate-level radioactive waste transport and storage container manufactured in 1 above as follows.

[0165] (1) Evaluation of porosity, oxidation rate, and presence of defects regarding cracking / scraping

[0166] The metal composite coating layers of Examples 1 to 4 and Comparative Examples 1 to 3 all exhibited a porosity of less than 1% and an oxidation rate of less than 2%, and no defects related to cracking and peeling were observed.

[0167] (2) Evaluation of corrosion characteristics (corrosion resistance)

[0168] The actual environment for the transportation, storage, and disposal of commercial storage containers is an atmospheric environment with appropriate humidity (RH 40-60%) rather than an aqueous environment, and the corrosion characteristics of metal composite coating materials in an atmospheric environment depend significantly on relative humidity. Therefore, a relative humidity influence assessment model was established to more accurately predict the corrosion rate in an atmospheric environment that simulates the actual environment.

[0169] The modeling procedure is as follows.

[0170] - Collection of a database on corrosion rates based on relative humidity

[0171] - Convert the above data into a percentage decrease rate and analyze

[0172] - Derivation of a trend line representing the relationship between relative humidity and corrosion rate based on converted data

[0173] - Non-linear models (Power, Exponential, Cubic polynomial) that represent abrupt changes at specific points in time are used to derive trend lines.

[0174] Exponential: y = 0.0125 × 1.0389 x

[0175] Power: y = 9.9313 × 10 -7 × x 2.9917

[0176] Cubic polynomial: y = 0.0067x - (1.8042 × 10 -4 )x 2 + (2.1044 × 10 -6 )x 3

[0177] - R to evaluate the accuracy of the derived model 2 Using metrics and the Root Mean Square Error (RMSE) statistical indicator, R used as an evaluation metric 2 It means that the closer it is to 1, and the smaller the RMSE, the better the model's performance.

[0178] - Selection of the optimal relative humidity impact assessment model by comparing these indicators; among the three prediction models, the Exponential model is R 2 Shows the best results in both and RMSE indicators

[0179] - Using the optimal trend equation selected in this way, the corrosion rate of the aqueous solution environment was applied as a constant, and a relative humidity effect evaluation model was established as shown in Equation 1 below.

[0180] <Equation 1>

[0181] Corrosion rate under x% relative humidity conditions = 0.0215C measured × 1.039 x

[0182] (C measured : Corrosion rate measured in an aqueous environment)

[0183] Using the model established in this way, the expected corrosion rates of Examples 1 to 4 and Comparative Examples 1 to 3 were calculated under relative humidity conditions of 60% and 40%, and the results are shown in FIG. 4a and FIG. 4b. FIG. 4a shows the results of the corrosion characteristic evaluation under 60% relative humidity conditions, and FIG. 4b shows the results of the corrosion characteristic evaluation under 40% relative humidity conditions.

[0184] As shown in FIGS. 4a and 4b, Comparative Example 2 exhibited the best corrosion resistance. However, despite the conservative evaluation method, Examples 1 to 4 and Comparative Examples 1 to 3 all satisfied a corrosion rate of less than 1 μm per year (< 1 μm / year) in terms of corrosion resistance.

[0185] (3) Evaluation of hardness characteristics

[0186] To evaluate hardness characteristics closely related to wear resistance, the ASTM E384-22 (Knoop and Vickers Hardness of Materials) Vickers hardness test method was adopted, and the test load was set to 300g for micro-area measurement. The results of the hardness characteristic evaluation are shown in Table 4 and Figure 5 below. In Table 4 and Figure 5, Comparative Example 4 represents the original material, that is, a substrate layer specimen without a coating layer formed thereon.

[0187] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 1 time 11 12 10 10 836 88 44 16 44 17 75 11 3 2 times 10 19 10 339 358 6 44 23 42 17 72 11 5 3 times 10 6 7 11 268 68 87 340 74 217 84 11 2 4 times 11 75 11 318 438 78 41 54 36 79 51 13 5 times 10 8 41 117 9 338 9 14 24 4 237 74 11 3 Average 10 91.4 10 83.4 8 838 78 41 74 28.4 7 80 11 3.2

[0188] As shown in Table 4 and Figure 5 above, Examples 1 to 4 and Comparative Example 3 all satisfied the performance indicator criteria, and Examples 1 to 4 exhibited superior hardness characteristics compared to Comparative Example 3. In particular, Example 1, which had the highest average hardness value, showed a hardness property 9.6 times higher than that of a commercial storage container.

[0189] (4) Evaluation of wear resistance characteristics

[0190] To evaluate wear resistance characteristics, the flat plate rotational abrasion test (hereinafter referred to as the Taber abrasion test), which is widely used in industry and research due to its suitability for the shape and size of the test specimen, high reproducibility, and smooth control of test parameters, was selected as the evaluation method. The Taber abrasion test was performed in accordance with ASTM D4060 (Organic Coatings by the Taber Abraser), and the degree of wear (amount of thickness reduction) was measured by measuring the coating thickness with a micrometer during the test. The results of evaluating wear resistance characteristics by the Taber abrasion test for 5,000 cycles and 30,000 cycles are shown in Table 5, Fig. 6a and Table 6, Fig. 6b below. In Tables 5 and 6, Comparative Example 4 represents the original material, that is, a substrate layer specimen in which the metal composite coating layer is not formed, and the amount of thickness reduction of Comparative Example 4 is indicated as the average amount of thickness reduction of the original material in Figs. 6a and 6b.

[0191] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 1st time 18 29 18 45 10 0 7 9 5 3 12 6 2nd time 26 19 29 38 10 6 7 4 4 8 11 6 3rd time 22 22 16 38 10 6 8 4 4 3 12 4 Average 22 23 21 40 10 4 7 9 4 8 12 2 Error (+) 46 85 25 5 4 Error (-) 44 5 34 5 5 6

[0192] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 1st time 29 40 33 7 12 7 4 15 4 8 8 60 7 2nd time 31 28 38 6 12 5 4 17 18 46 0 6 3rd time 28 30 23 6 22 5 5 16 9 7 7 6 47 Average 29 32 31 6 5 26 11 6 48 36 20 Error (+) 17 6 ​​7 13 7 5 27 Error (-) 14 8 47 11 6 14

[0193] As shown in Tables 5 and 6, and Figures 6a and 6b, it was confirmed that Examples 1 to 4 exhibited excellent wear resistance by showing a smaller thickness reduction compared to Comparative Examples 1 to 3. In the case of Comparative Example 4, which is the raw material, it showed a thickness reduction of 50% or more (600 μm or more). (5) Evaluation of adhesion strength characteristics

[0194] To evaluate the adhesion strength characteristics, an adhesion strength test was performed using a universal tensile testing machine in accordance with ASTM C633 (Adhesion or Cohesion Strength of Thermal Spray Coatings). The results of the adhesion strength evaluation, measured five times, are shown in Table 7 and Figure 7 below.

[0195] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 1 time 825376677261692 time 856576765876713 time 807282686570764 time 826977797863745 time 82677670517275 Average 82.265.277.47264.868.473

[0196] According to international standards (ISO 2063, NQRSOK M-501, AWC C2. 18-93), a coating agent is classified as a material with excellent adhesion when its adhesion strength is 10.3 MPa or higher. As shown in Table 7 and Figure 7 above, Examples 1 to 4 and Comparative Examples 1 to 3 all exhibited high adhesion characteristics of an average of 60 MPa or higher, which significantly exceeds the international standards. In particular, Example 1 showed the highest adhesion strength.

[0197] (6) Evaluation of radiation shielding properties

[0198] To evaluate radiation shielding characteristics, a verification test using radioactive isotopes was performed by applying KS C IEC 61331-1:2014 as the standard test specification. Cs-137 was selected as a gamma ray source suitable for evaluating shielding characteristics. The shielding rate data for Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 8 and Figure 8a below. In Table 8 below, Comparative Example 4 represents the original material, that is, a substrate layer specimen without a coating layer formed thereon.

[0199] Thickness (mm) | Shielding Rate (%) | Attenuation Ratio Substrate Layer | Coating Layer Example 1: 1.20.25 | 9.57 | 1.110 Example 2: 2.20.25 | 8.97 | 1.102 Example 3: 3.1.20.25 | 8.27 | 1.100 Example 4: 4.1.20.25 | 8.78 | 1.100 Comparative Example 1: 1.20.25 | 3.80 | 1.095 Comparative Example 2: 2.20.25 | 2.60 | 1.093 Comparative Example 3: 3.20.25 | 2.00 | 1.093 Comparative Example 4: 4.1.26 | 6.65 | 1.070

[0200] As shown in Table 8, FIG. 8a, and FIG. 8b above, Examples 1 to 4 and Comparative Examples 1 to 3 showed improved shielding rates compared to commercial storage containers. Examples 1 to 4 exhibited superior shielding rates compared to Comparative Examples 1 to 3, with Example 1 showing the highest shielding rate. Additionally, the shielding performance improvement rates of Examples 1 to 4 and Comparative Examples 1 to 3 compared to commercial storage containers were calculated and are shown in Table 9 and FIG. 8b below.

[0201] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Shielding performance improvement rate (%) 4 3.89 3 4.94 3 2.72 3 2.01 2 6.00 2 4.19 2 3.29

[0202] As shown in Table 9 and Figure 8b above, the shielding performance improvement rates of Examples 1 to 4 and Comparative Examples 1 to 3 showed a similar trend to the shielding rates. Examples 1 to 4 had higher shielding performance improvement rates than Comparative Examples 1 to 3, and in particular, Example 1 showed the highest shielding performance improvement rate.

[0203] As a result of evaluating the corrosion resistance, hardness, wear resistance, adhesion strength, and gamma ray shielding performance, it was confirmed that Examples 1 to 4 are suitable as storage containers for low- and intermediate-level radioactive waste compared to Comparative Examples 1 to 3, when considering each characteristic overall.

[0204] In particular, Example 1 exhibited the best characteristics in terms of hardness, wear resistance, adhesion strength, and gamma ray shielding performance, and also satisfied the requirements of the performance evaluation indicators for corrosion resistance. Compared to a commercial storage container, Example 1 showed a hardness increase of approximately 9.6 times, a wear rate decrease of approximately 21 times, and a shielding rate increase of approximately 44%.

[0205] Accordingly, regarding Example 1, an integrity evaluation test regarding corrosion characteristics and hardness characteristics due to aging and changes in physical properties, and an evaluation test of the shielding performance of the inspection line due to increased thickness were additionally carried out as follows.

[0206]

[0207] 4. Characterization of Example 1

[0208] (1) Evaluation of corrosion characteristics and hardness characteristics due to aging

[0209] In order to predict the life of the material, an accelerated aging test, commonly used in industry and academia, was performed to evaluate the corrosion characteristics and hardness characteristics according to the aging of Example 1.

[0210] The accelerated aging test was based on the assumption that the chemical reaction related to the decomposition of the material follows the Arrhenius reaction rate function, and that the chemical reaction rate doubles when the temperature increases by 10℃, and the accelerated aging time was derived through Equation 2 below.

[0211] <Equation 2>

[0212] AAF = Q 10 [(TAA-TRT) / 10]

[0213] - AAF (Accelerated Aging Factor): Accelerated aging factor, the time rate estimated to obtain material property changes equivalent to the state in an actual storage environment.

[0214] - Q 10 (Aging coefficient at a 10℃ increase in temperature): Aging coefficient when the temperature increases by 10℃

[0215] - TAA (Accelerated aging temperature): The temperature used for accelerated aging, which is the temperature of the constant temperature and humidity chamber where aging tests are performed.

[0216] - TRT (Ambient temperature): Ambient temperature, the actual environment temperature in which the target material is used.

[0217] - AAT (Accelerated aging time): The time during which the accelerated aging test is conducted.

[0218] Based on these basic concepts, the accelerated aging factor required for the test was derived as follows.

[0219] - Accelerated Aging Temperature (TAA): 60℃ (considering material damage and deformation)

[0220] - Ambient Temperature (TRT): 25℃ (Room Temperature)

[0221] - Q 10 : 2.0 (Industrial normal constant)

[0222] - Accelerated Aging Factor (AAF): 11.313

[0223] The accelerated aging test time calculated based on the derived accelerated aging coefficient is as shown in Table 10 below.

[0224] Classification Temperature (°C) AAF Aging Test Time (Days) Aging Time (Years) 160 11.3 13 32.3 126 4.5 239 6.83

[0225] The accelerated aging test was performed using a chamber capable of maintaining constant temperature and humidity conditions. The aging temperature condition was selected as 60°C within the range of -40°C to 70°C specified in Article 25, Subparagraph 5 of the “Regulations on Packaging and Transport of Radioactive Materials, etc.”, and the humidity was set to 50%, which is the intermediate value within the range of RH 40% to 60%. The results of the corrosion rate test and the change in hardness characteristics according to the aging of Example 1 are shown in Figures 9a and 9b, respectively.

[0226] As shown in Fig. 9a, it was observed that there was no significant difference in the corrosion rate between the specimen before aging and the specimen to which an accelerated aging time of 1 to 3 years was applied. From this, it can be confirmed that in the case of Example 1, corrosion resistance is well maintained despite long-term aging.

[0227] As shown in Fig. 9b, it was observed that there was no significant difference in hardness between the specimen before aging and the specimen to which an accelerated aging time of 3 years was applied. From this, it can be confirmed that in the case of Example 1, the hardness characteristics are well maintained despite long-term aging.

[0228] Based on the results of the corrosion rate test and the change in hardness characteristics due to aging, it is determined that Example 1 can ensure aging integrity as there are no significant changes in corrosion characteristics and hardness characteristics in an aging environment of 3 years or less.

[0229] (2) Evaluation of properties according to coating thickness

[0230] 1) Evaluation of shielding performance improvement rate according to coating thickness

[0231] To evaluate the effect of coating thickness on the improvement rate of gamma ray shielding performance of Example 1, the shielding characteristics were evaluated while increasing the coating thickness from 0.25 mm to 0.55 mm in increments of 0.1 mm, and the results are shown in Table 11 and Figure 10 below.

[0232] Thickness (mm) Measured Value (mSy / h) Shielding Rate (%) Shielding Performance Improvement Rate Compared to Commercial Storage Containers (%) Substrate Layer Coating Layer After Initial Transmission 11.20.25 2.55 22.31 79.21 38.45 21.20.35 2.54 62.28 610.21 53.54 31.20.45 2.55 12.25 611.56 73.87 41.20.55 2.55 12.22 912.62 89.78

[0233] As shown in Table 11 and Fig. 10 above, in the case of Example 1, the improvement rate of gamma ray shielding performance increased linearly as the coating thickness increased. When the coating thickness was increased to 0.35 mm, the gamma ray shielding performance improved by 53.54% compared to a commercial storage container, satisfying the evaluation criterion (50%). Here, the evaluation criterion was set as the final goal by the inventors, and even at a thickness of 0.25 mm, an improved shielding rate compared to a commercial storage container was observed.2) Results of shape and composition analysis according to coating thickness

[0234] In the case of Example 1, the test results regarding porosity, oxidation rate, cracking, and peeling according to the increase in coating thickness showed that all coating conditions were good, similar to the results for a coating thickness of 250 μm. In addition, the results of the fine particle component analysis according to the increase in coating thickness showed that there was no significant difference in particle distribution and binder component content with increasing thickness.

[0235] From this, it can be confirmed that in the case of Example 1, when a coating layer of 550 μm or less is formed, it can be applied as a storage container for low- and intermediate-level radioactive waste without problems in terms of porosity, oxidation rate, cracking and peeling, fine particle distribution, and component ratio.

[0236] 3) Results of hardness characteristic evaluation according to coating thickness

[0237] The hardness characteristics according to the increase in coating thickness of Example 1 are shown in FIG. 11.

[0238] As shown in Fig. 11, in the case of Example 1, there was no change in hardness value with increasing coating thickness.

[0239] Therefore, it was observed that there was no significant difference in terms of hardness even when applying the coating thickness increase conditions as described above.

[0240] 4) Evaluation results of adhesion strength characteristics according to coating thickness

[0241] The adhesion strength characteristics according to the increase in coating thickness of Example 1 are shown in FIG. 12.

[0242] As shown in Fig. 12, in the case of Example 1, there were differences in adhesion strength according to coating thickness, but no trend was observed with increasing thickness. The difference in adhesion strength according to coating thickness can be interpreted as a difference arising from the adhesive curing conditions. However, all tested adhesion strengths according to coating thickness showed values ​​exceeding the evaluation indicator.

[0243] Therefore, it was observed that there was no significant difference in terms of adhesion strength even when applying the coating thickness increase conditions as described above.

[0244]

[0245] 5. Conclusion

[0246] As a result of evaluating the corrosion resistance, hardness, wear resistance, adhesion strength, and gamma ray shielding performance, when judging the overall characteristics comprehensively, Examples 1 to 4 exhibited superior characteristics as storage containers for low- and intermediate-level radioactive waste compared to Comparative Examples 1 to 3.

[0247] In addition, through further evaluation of Example 1, which exhibited the best characteristics, it was confirmed that aging integrity could be ensured as there were no significant changes in corrosion characteristics and hardness characteristics in an aging environment of 3 years or less.

[0248] In addition, under the tested conditions of increased coating thickness, it can be confirmed that there are no significant differences in terms of porosity, oxidation rate, cracking and delamination, fine particle distribution and component ratio, hardness, and adhesion strength depending on the coating thickness.

[0249]

[0250] As described above, the low-to-intermediate level radioactive waste transport and storage container including a metal composite coating layer according to the present invention can simultaneously and significantly improve corrosion resistance, mechanical properties, and radiation shielding performance, and can ensure the integrity of the container during transport, loading, and movement of the low-to-intermediate level radioactive waste container, and contribute to the safety of workers from radioactive gamma ray sources outside the container. Furthermore, the low-to-intermediate level radioactive waste transport and storage container including a metal composite coating layer according to the present invention can increase the loading capacity by mitigating the radiation dose on the container surface, and is also advantageous in terms of securing disposal space by reducing the thickness of the overlay. In addition, according to the method for manufacturing the low-to-intermediate level radioactive waste transport and storage container according to the present invention, the characteristics of the metal composite coating layer can be significantly improved by forming the metal composite coating layer using an HVOF process selected from the perspective of performance optimization. In addition, according to the method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste according to the present invention, by performing a pretreatment process and a posttreatment process before and after the formation of the metal composite coating layer, respectively, the adhesion and strength of the metal composite coating layer, as well as the wear resistance and corrosion resistance of the container, can be improved.

[0251]

[0252] As described above, the present invention has been explained with reference to the embodiments illustrated in the drawings, but this is merely illustrative, and it should be understood that various modifications and equivalent alternative embodiments are possible based on the ordinary knowledge of the art to which the art belongs. Accordingly, the true technical scope of protection of the present invention is defined by the claims described below and should be determined based on the specific details of the invention described above.

[0253]

[0254] The present invention relates to a container for transporting and storing low- and intermediate-level radioactive waste comprising a metal composite coating layer and a method for manufacturing the same, and is applicable to industrial fields related to radioactive waste.

Claims

1. Substrate layer; and A metal composite coating layer disposed on the above substrate layer and formed of a metal composite powder comprising 35-85 wt% tungsten (W), 3-7 wt% carbon (C), 5-20 wt% nickel (Ni), and 5-45 wt% chromium (Cr); A transport and storage container for low- and intermediate-level radioactive waste including 2. In claim 1, the metal composite coating layer is, A transport and storage container for low- and intermediate-level radioactive waste characterized by having a thickness in the range of 100 to 1000 μm.

3. In paragraph 1, the metal composite powder is, A transport and storage container for low- and intermediate-level radioactive waste characterized by having a particle size in the range of 10 to 60 µm.

4. In claim 1, the metal composite coating layer is, A low- and intermediate-level radioactive waste transport and storage container characterized by being formed by a High Velocity Oxygen Fuel (HVOF) process.

5. In Paragraph 1, A low- and intermediate-level radioactive waste transport and storage container characterized by further comprising an outer coating layer disposed on the metal composite coating layer and including an anti-corrosion primer.

6. In paragraph 5, the above-mentioned anti-corrosion primer is, A container for transporting and storing low- and intermediate-level radioactive waste characterized by containing melamine resin.

7. In paragraph 5, the outer coating layer is, A transport and storage container for low- and intermediate-level radioactive waste characterized by having a thickness in the range of 5 to 40 μm.

8. In Paragraph 5, A low- and intermediate-level radioactive waste transport and storage container characterized by a gamma ray shielding performance improvement rate of 30% or more compared to the case where the above-mentioned metal composite coating layer is not formed.

9. A step of providing a base layer for preparing a base layer; and A first coating step of forming a metal composite coating layer by coating a metal composite powder comprising 35-85 wt% tungsten (W), 3-7 wt% carbon (C), 5-20 wt% nickel (Ni), and 5-45 wt% chromium (Cr) onto the substrate layer; A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste including 10. In claim 9, the first coating step is, A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste, characterized in that the metal composite coating layer has a thickness in the range of 100 to 1000 μm.

11. In claim 9, the metal composite powder is, A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste, characterized by having a particle size in the range of 10 to 60 μm.

12. In claim 9, the first coating step is, A transport and storage container for low- and intermediate-level radioactive waste characterized by being carried out by a High Velocity Oxygen Fuel (HVOF) process.

13. In Clause 12, the high-speed flame spraying process is, A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste, characterized by being carried out under process conditions of an oxygen flow rate of 100 to 200 psi, a hydrogen flow rate of 40 to 70 psi, an air flow rate of 20 to 50 psi, and a powder feed rate of 20 to 30 g / min.

14. In Paragraph 9, A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste, characterized by further including a second coating step of forming an outer coating layer containing an anti-corrosion primer on the metal composite coating layer.

15. In paragraph 14, the second coating step is, A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste, characterized in that the outer coating layer has a thickness in the range of 5 to 40 μm.

16. In Clause 14, the above-mentioned anti-rust primer is, A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste characterized by including melamine resin.

17. In Paragraph 9, A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste, characterized by further including a pretreatment step for surface modification of the substrate layer prior to the first coating step.

18. In Clause 17, the above preprocessing step is, A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste, characterized by removing oxides formed on the surface of the substrate layer and increasing the surface area of ​​the substrate layer.

19. In Clause 17, the above preprocessing step is, A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste, characterized by including a grit blasting process.

20. In Clause 17, the grit blasting process is, A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste, characterized by being carried out under process conditions of a blasting distance of 4 to 8 inches, a blasting pressure of 25 to 35 psi, and a blasting angle of 45° to 90°.

21. In Paragraph 9, A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste, characterized by further including a post-treatment step for enhancing the adhesion and physical properties of the metal composite coating layer after the first coating step.

22. In paragraph 21, the above post-processing step is, Heat treatment process; and Polishing process; A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste, characterized by including 23. In Paragraph 22, The above heat treatment process is performed to relieve residual stress generated in the first coating step, improve the microstructure, and strengthen the interparticle bonding force within the metal composite coating layer. A method for manufacturing a transport and storage container for low- and intermediate-level radioactive waste, characterized in that the above polishing process is performed to reduce the surface roughness of the metal composite coating layer.

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