How to recycle carbon steel scrap

Abstract

To provide a specific method for reusing carbon steel scrap generated in nuclear facility.SOLUTION: A method for reusing carbon steel scrap generated in nuclear facility is provided, including: melting the carbon steel scrap using a melting device; taking a sample from molten material of the carbon steel scrap; measuring the copper content and the tin content of the sample; and casting the molten material of the carbon steel scrap into an ingot, wherein when the copper content of the measured sample is 0.50 mass% or less and the tin content thereof is 0.03 mass% or less, the ingot is reused for special steel excellent in low-temperature strength.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recycling carbon steel scrap generated in nuclear facilities. [Background technology]

[0002] During the decommissioning of nuclear facilities, such as the decommissioning of nuclear reactors at nuclear power plants, large amounts of metal waste, or scrap, are generated by the dismantling of the facilities. If the scrap generated at nuclear facilities is disposed of as radioactive waste, costs are incurred for transportation and burial, and furthermore, environmental burdens are generated.

[0003] Therefore, scrap whose radioactivity concentration exceeds the national standard must be disposed of as radioactive waste, but scrap whose radioactivity concentration is below the national standard should be reused as a raw material for valuable materials such as steel.

[0004] The materials and chemical composition of scrap generated within nuclear facilities are the same as those of general scrap generated outside nuclear facilities. Therefore, scrap generated within nuclear facilities whose radioactivity concentration is below the national standard can be cut or crushed into manageable sizes, separated by chemical composition, melted in an electric furnace at a metal processing plant, refined, cast, and processed into steel and other products that meet specified standards, making it possible to reuse it as valuable material.

[0005] The majority of scrap generated within nuclear facilities is carbon steel, such as general structural rolled steel generated during the renewal and decommissioning of nuclear facilities. Such carbon steel scrap (hereinafter also referred to as "carbon steel scrap") is generally reused as raw material for general structural rolled steel, which is also a carbon steel product, specifically rebar or steel frame.

[0006] The reason for this is that while carbon steel chemical composition standards do not specify elements such as copper (Cu), tin (Sn), cobalt (Co), molybdenum (Mo), arsenic (As), and tungsten (W), special steel standards often specify upper limits for these elements as impurities. Furthermore, these elements may be present in carbon steel scrap and are difficult to remove during melting and refining. Therefore, if carbon steel scrap is used as a raw material for special steel, the content of these impurity elements may exceed the specified value. If the content of the mixed impurity elements exceeds the specified value for special steel, the entire steel will be deemed non-conforming, resulting in significant losses.

[0007] However, depending on the location of a nuclear facility, there are often no metal processing plants or users of carbon steel products such as rebar and steel frames near the facility, and there is not much demand for carbon steel scrap generated at nuclear facilities as a raw material for carbon steel.

[0008] Therefore, if carbon steel scrap generated in nuclear facilities could be used to make special steel products, particularly special steel products used in nuclear facilities, it is believed that this would increase demand for carbon steel scrap generated in nuclear facilities and promote reuse.

[0009] One example of a special steel product used in nuclear facilities is a radioactive waste storage container. Radioactive waste storage containers must be sound not only during storage but also during transportation, and stringent requirements include performance such as soundness at low temperatures of -20°C. For this reason, special steels that can ensure these performances are used for radioactive waste storage containers, and strict standards are required for regulations on chemical composition and quality, making it difficult to reuse carbon steel scrap.

[0010] Therefore, special steels have been developed that have relatively loose regulations regarding chemical composition, allowing the inclusion of elements such as copper (Cu) and tin (Sn), which have previously been considered impurities and were not assumed to be present. For example, Patent Document 1 specifies the chemical composition of large steel castings for welded structures that can be used as shielding for radioactive materials as follows: Cu: 0.01% by mass to 0.5% by mass, and Sn: 0.03% by mass or less.

[0011] Recently, a public standard has been established that specifies a manufacturing method for a special alloy that can ensure soundness at low temperatures of -20°C, a typical performance requirement for storage containers for radioactive waste (Non-Patent Document 1). This standard specifies that the chemical composition of the special alloy should be copper: 0.50% or less, and tin: 0.03% or less.

[0012] It is believed that special steels and special alloys (hereinafter collectively referred to as "special steels") having the chemical compositions described in Patent Document 1 and Non-Patent Document 1 can be manufactured using carbon steel scrap generated within nuclear facilities. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Publication No. 2018-178145 [Non-patent literature]

[0014] [Non-Patent Document 1] Japan Steel Casting and Forging Association Standard JCSS C-1 "Casting Steel Products for Low-Temperature Welding Structures", 2019 Summary of the Invention [Problem to be solved by the invention]

[0015] As described above, an environment is being developed for recycling carbon steel scrap generated at nuclear facilities into special steel or special steel products used in nuclear facilities. However, neither Patent Document 1 nor Non-Patent Document 1 discloses specific means for actually recycling carbon steel scrap generated at nuclear facilities.

[0016] The present invention has been made in view of the above problems, and has an object to provide a specific method for recycling carbon steel scrap generated in nuclear facilities. [Means for solving the problem]

[0017] As a result of extensive investigations, the present inventors have found that the above object can be achieved by the following invention.

[0018] A method for recycling carbon steel scrap according to one aspect of the present invention is a method for recycling carbon steel scrap generated at a nuclear facility, comprising the steps of: melting the carbon steel scrap using a melting device; taking a sample from the melt of carbon steel scrap; measuring the copper and tin content of said sample; and casting the melt of carbon steel scrap into an ingot; When the measured copper content of the sample is 0.50 mass % or less and the tin content is 0.03 mass % or less, the ingot is reused to produce special steel with excellent low-temperature strength. [Effects of the Invention]

[0019] According to the present invention, a specific method for recycling carbon steel scrap generated in nuclear facilities can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, a method for recycling carbon steel scrap according to an embodiment of the present invention will be described.

[0021] [First embodiment] A method for recycling carbon steel scrap according to a first embodiment of the present invention is a method for recycling carbon steel scrap generated at a nuclear facility, comprising melting the carbon steel scrap using a melting apparatus, taking a sample from the molten carbon steel scrap, measuring the copper and tin contents of the sample, and casting the molten carbon steel scrap into an ingot, and if the measured copper content of the sample is 0.50% by mass or less and the tin content is 0.03% by mass or less, the ingot is recycled into special steel with excellent low-temperature strength. This method is highly useful industrially because it allows the carbon steel scrap generated at a nuclear facility to be recycled and enables the production of valuable special steel.

[0022] <Carbon steel scrap> The carbon steel scrap according to the present embodiment is scrap made of carbon steel generated during the decommissioning or refurbishment of nuclear facilities. Nuclear facilities according to the present embodiment include, for example, smelting and processing facilities for nuclear fuel materials such as uranium and thorium, nuclear reactor facilities for research or power generation, and spent fuel reprocessing facilities. Furthermore, the carbon steel scrap according to the present embodiment has a radioactivity concentration below the national standard and is therefore not considered radioactive waste. Such carbon steel scrap may be, for example, scrap originally with a low radioactivity concentration within a nuclear facility or scrap whose radioactivity concentration has been reduced by decontamination. Decontamination refers to the removal of trace amounts of radioactive material adhering to the surface of the carbon steel scrap, and can be performed by spraying abrasive grains or water onto the carbon steel scrap.

[0023] In this embodiment, carbon steel refers to an iron alloy with a carbon content of 2.0 mass% or less, a low content of alloying elements, and does not fall under the category of special steel, while special steel refers to an iron alloy containing a predetermined amount or more of one or more alloying elements other than carbon (C), with the balance being iron (Fe) and unavoidable impurities. Usable alloying elements include, for example, nickel (Ni), chromium (Cr), silicon (Si), manganese (Mn), molybdenum (Mo), tungsten (W), vanadium (V), cobalt (Co), titanium (Ti), boron (B), and niobium (Nb).

[0024] In this embodiment, carbon steel scrap is classified according to its copper (Cu) content and tin (Sn) content. Carbon steel scrap with a copper content of 0.50% by mass or less and a tin content of 0.03% by mass or less is reused as a raw material for special steel with excellent low-temperature strength. Other carbon steel scrap can be reused as a raw material for structural carbon steel, for example.

[0025] Special steel with excellent low-temperature strength is, for example, a special steel that can maintain soundness at low temperatures of -20°C, as specified by the aforementioned Japan Steel Casting and Forging Association standard JCSS C-1 "Casting Steel for Low-Temperature Welding Structures." This special steel is preferably used for storage containers for radioactive waste, transport containers for radioactive materials, radiation shielding, etc. Because of the large quantities required, it is even more preferable to use it as a storage container for radioactive waste. Soundness at low temperatures of -20°C means that the yield point or 0.2% proof stress, tensile strength, elongation, and Charpy absorbed energy exceed the standard values.

[0026] Specifically, with regard to Charpy absorbed energy, the above-mentioned JCSS C-1 stipulates that for each of the "cast steel products for low-temperature welding structures" JCWL410, JCWL440, and JCWL500, the average Charpy absorbed energy of three samples must be 18J or more, 23J or more, and 27J or more, respectively, and the individual Charpy absorbed energies must be 13J or more, 16J or more, and 19J or more, respectively, and that two of the three samples must exceed the aforementioned average Charpy energy.

[0027] The chemical composition of the cast steel product specified in the above-mentioned JCSS C-1 is: C: 0.22% by mass or less, Si: 0.80% by mass or less, Mn: 1.50% by mass or less, P: 0.025% by mass or less, S: 0.015% by mass or less, Cu: 0.50% by mass or less, Ni: 2.50% by mass or less, Cr: 1.00% by mass or less, Mo: 0.30% by mass or less, V: 0.20% by mass or less, Sn: 0.03% by mass or less, C-carbon equivalent: 0.50% by mass or less, with the remainder being Fe and unavoidable impurities. The C-carbon equivalent (Ceq (mass%)) is a value calculated using the following formula (1). In formula (1), [C], [Si], [Mn], [Ni], [Cr], [Mo], and [V] represent the contents of C, Si, Mn, Ni, Cr, Mo, and V, respectively, expressed in mass%. Ceq=[C]+[Si] / 24+[Mn] / 6+[Ni] / 40+[Cr] / 5+[Mo] / 4+[V] / 14 …(1)

[0028] Structural carbon steel refers to carbon steel used for building and construction materials such as reinforcing bars and steel frames, and more specifically, carbon steel used for general structural rolled steel materials specified in JIS G3101:2020.

[0029] <How to reuse carbon steel scrap> In the scrap recycling method according to this embodiment, first, carbon steel scrap generated at a nuclear power facility is melted using a melting device. Even if the chemical compositions of each scrap differ, the chemical compositions can be made uniform by mixing and melting them. As described below, the chemical compositions of the homogenized carbon steel scrap can be measured using samples taken from the melted scrap. A general electric furnace, a high-frequency induction furnace, or the like can also be used as the melting device. The size and capacity of the melting device, such as an electric furnace, can be determined depending on the amount of carbon steel scrap to be melted.

[0030] The melting equipment may be installed at the nuclear facility where the carbon steel scrap is generated, or if the nuclear facility where the carbon steel scrap is generated does not have a melting equipment, a melting equipment installed at another nuclear facility may be used. However, in order to simplify the transportation work and reduce the human burden, such as the burden on workers during transportation, it is preferable to use the melting equipment installed at the nuclear facility where the carbon steel scrap is generated.

[0031] Next, a sample is taken from the melted carbon steel scrap (hereinafter also referred to as "molten scrap"), and the copper content and tin content of the taken sample are measured. The measurement of the copper content and tin content can be performed at a nuclear facility equipped with a melting device, at another nuclear facility, or outside a nuclear facility. However, it is preferable to perform the measurement at a nuclear facility equipped with a melting device in order to avoid the trouble of transporting the carbon steel scrap outside the nuclear facility as radioactive waste and to perform the measurement quickly.

[0032] The copper content and tin content can be measured by a general elemental analysis method such as ICP emission spectrometry, atomic absorption spectrometry, etc. At this time, the contents of elements other than copper and tin may also be measured.

[0033] The molten scrap from which the sample was taken is cast into an ingot. The casting of the molten scrap is carried out at a nuclear facility equipped with a melting apparatus. The size and shape of the ingot may be determined depending on the intended use of the ingot. The casting of the molten scrap may be carried out simultaneously with, before, or after the measurement of the copper and tin contents of the sample.

[0034] Next, the cast ingots are classified into uses according to the copper and tin contents of the molten scrap samples used in the ingots. If the copper content of the measured sample is 0.50% by mass or less and the tin content is 0.03% by mass or less, the ingots are recycled into special steel with excellent low-temperature strength. Otherwise, the ingots can be recycled into, for example, structural carbon steel.

[0035] Specifically, if the measured sample has a copper content of 0.50% by mass or less and a tin content of 0.03% by mass or less, the ingot is used as a raw material for special steel with excellent low-temperature strength. The produced special steel is preferably used as a material for special steel products used in nuclear facilities, such as storage containers for radioactive waste, transport containers for radioactive materials, and radiation shielding. The production of special steel using this ingot may be carried out in a nuclear facility equipped with a melting device, but is preferably carried out by a metal processing company or special steel manufacturer outside the nuclear facility that has dedicated equipment.

[0036] In other cases, i.e., when the copper content of the measured sample exceeds 0.50% by mass or when the tin content exceeds 0.03% by mass, the ingot can be used, for example, as a raw material for structural carbon steel. The produced structural carbon steel can be used, for example, for building and construction materials such as reinforcing bars and steel frames, and may be used both in nuclear facilities and outside nuclear facilities. The production of structural carbon steel using this ingot may be carried out in a nuclear facility equipped with a melting device, but is preferably carried out by a metal processing company outside a nuclear facility with dedicated equipment.

[0037] In this embodiment, two or more samples may be collected. In this case, at least one sample may be used to measure the copper content and the tin content, and at least one remaining sample may be used to measure the content of elements other than copper and tin. Examples of elements other than copper and tin that may be measured include manganese, phosphorus, sulfur, niobium, chromium, molybdenum, and vanadium. The content of these elements may be measured for the purpose of determining the amount of elements to be added during recycling. The content of elements other than copper and tin may be measured at a nuclear facility equipped with a melting device, or at a metal processing company outside the nuclear facility.

[0038] Metal processing companies outside nuclear facilities can measure the chemical composition of ingots in more detail than the copper and tin content measurements for the purpose of classifying ingots, in order to produce special steel with specified chemical compositions. By shipping pre-collected samples to the company along with the ingots and using these samples to measure the chemical composition at the company, the company does not need to collect new samples, and carbon steel scrap can be reused efficiently.

[0039] In this embodiment, the ingot may be stored within a nuclear facility before being recycled into special steel or structural carbon steel. Specifically, if the measured sample has a copper content of 0.50% by mass or less and a tin content of 0.03% by mass or less, the ingot is stored in a designated area within the nuclear facility; otherwise, the ingot is stored in another area within the nuclear facility. The area in which the ingot is stored is preferably an area other than the controlled area within the nuclear facility. The stored ingot is reused as described above when an opportunity for reuse arises.

[0040] The nuclear facility where the carbon steel scrap is stored shall be the nuclear facility where the melting equipment is installed if the nuclear facility where the carbon steel scrap is generated is the same as the nuclear facility where the melting equipment is installed. If the nuclear facility where the carbon steel scrap is generated is different from the nuclear facility where the melting equipment is installed, either nuclear facility may be used, but the nuclear facility where the melting equipment is installed is preferred in order to simplify the transportation work and reduce the human burden on workers during transportation.

[0041] [Second embodiment] A method for recycling carbon steel scrap according to a second embodiment of the present invention will be described. The first embodiment deals with carbon steel scrap whose radioactivity concentration is below the national standard and does not fall under the category of radioactive waste. In contrast, the present embodiment also deals with carbon steel scrap whose radioactivity concentration exceeds the national standard and falls under the category of radioactive waste. This embodiment differs from the first embodiment in that it is similar to the first embodiment in terms of melting carbon steel scrap, collecting samples, casting the melt into ingots, casting the ingots, and storing the ingots. Therefore, the following description will mainly focus on the differences between the first embodiment and the present embodiment in the method for recycling carbon steel scrap.

[0042] In this embodiment, carbon steel scrap classified as radioactive waste is also included, so any carbon steel scrap generated within a nuclear facility is acceptable, regardless of its radioactivity concentration or whether it has been decontaminated. However, it is preferable to decontaminate the carbon steel scrap by spraying it with abrasive grains or water before melting it.

[0043] In this embodiment, as in the first embodiment, the melting apparatus for melting the carbon steel scrap may be installed at the nuclear facility where the carbon steel scrap was generated, or may be installed at another nuclear facility. However, in this embodiment, when a melting apparatus installed at another nuclear facility is used, the carbon steel scrap is placed in a predetermined container and transported from the nuclear facility where the carbon steel scrap was generated to the other nuclear facility. This is because the radioactivity concentration of the carbon steel scrap is unknown before melting, and the carbon steel scrap must be treated as radioactive waste when transported outside the nuclear facility.

[0044] In this embodiment, when measuring the copper content and tin content of a sample taken from the molten scrap, the radioactivity concentration of the sample is also measured. "When measuring the copper content and tin content of a sample, the radioactivity concentration of the sample is also measured" means that the copper content and tin content of the sample are measured at the same time. The measurement of the copper content and tin content of the sample and the measurement of the radioactivity concentration of the sample are preferably performed in the same workplace, and more preferably by the same worker.

[0045] Examples of radioactive substances that can be measured include Co-60, Mn-54, Sr-90, Cs-134, Cs-137, Eu-152, Eu-154, and H-3. The radioactivity concentration of radioactive substances that are easy to measure with gamma rays, such as Co-60, Mn-54, and Cs-137, can be measured with a germanium semiconductor detector. On the other hand, the radioactivity concentration of radioactive substances that are difficult to measure with gamma rays can be measured by dissolving a portion of the sample in a reagent and measuring the beta rays in the liquid with a liquid scintillation detector, or by drying the liquid in which a portion of the sample is dissolved and measuring the alpha rays with a silicon surface barrier semiconductor detector. The radioactivity concentration of radioactive substances that are difficult to measure with gamma rays can also be estimated based on the gamma ray measurement results of the above-mentioned radioactive substances that are easy to measure with gamma rays.

[0046] If the radioactivity concentration of the sample evaluated by such measurements does not meet the standards set by the government, the ingots cast from the molten scrap are classified as radioactive waste and stored in a designated area using a designated method.

[0047] The standard set by the government means that the sum of the ratios (D / C) of the radioactivity concentration (D) of each radioactive substance evaluated as described above to the standard value (C) set by the government must be less than or equal to 1. More specifically, if the radioactivity concentration of the measured radioactive substance j is Dj and the standard value of the radioactivity concentration of radioactive substance j set by the government is Cj, the following formula (1) must be satisfied. Σ(Dj / Cj)≦1 …(1)

[0048] If the radioactivity concentration of the sample evaluated by measurement etc. does not satisfy the above formula (1), the ingot is classified as radioactive waste. The standard value C of radioactivity concentration set by the government is 0.1 Bq / g for both Co-60 and Mn-54.

[0049] When carbon steel scrap is decontaminated as described above, the amount of radioactive material adhering to the carbon steel scrap can be reduced, and the amount of ingots classified as radioactive waste can be reduced. Therefore, it is preferable to decontaminate the carbon steel scrap before melting it in a melting device.

[0050] If the radioactivity concentration of the measured sample is below the national standard, and if the copper content of the measured sample is 0.50% by mass or less and the tin content is 0.03% by mass or less, the ingot can be reused as a raw material for special steel with excellent low-temperature strength, as in the first embodiment. If the copper content and tin content of the measured sample are outside the above range, the ingot can be reused as a raw material for structural carbon steel, for example.

[0051] [Summary of the disclosed technology] As described above, this specification discloses various aspects of the technology, the main aspects of which are summarized below.

[0052] As described above, a method for recycling carbon steel scrap according to one aspect of the present invention is a method for recycling carbon steel scrap generated at a nuclear facility, comprising: melting the carbon steel scrap using a melting device; taking a sample from the molten carbon steel scrap; measuring the copper content and tin content of the sample; and casting the molten carbon steel scrap into an ingot; and if the measured copper content of the sample is 0.50% by mass or less and the tin content is 0.03% by mass or less, the ingot is recycled into special steel with excellent low-temperature strength.

[0053] As mentioned above, carbon steel does not have a regulated content of elements considered impurities in the special steel standards, unlike copper and tin. Furthermore, special steel requires strict standards for chemical composition and quality, making it difficult to recycle carbon steel scrap into special steel. However, this configuration makes it possible to provide metal processors or special steel manufacturers with carbon steel scrap whose copper and tin content is clear. This allows metal processors or special steel manufacturers to consider using carbon steel scrap as a raw material for special steel, thereby promoting the reuse of carbon steel scrap.

[0054] Furthermore, if the carbon steel scrap has a copper content of 0.50% by mass or less and a tin content of 0.03% by mass or less, the manufacturer can prevent excessive contamination of copper and tin when using the carbon steel scrap as a raw material to produce special steel, allowing the manufacturer to produce special steel of the specified composition, thereby enabling efficient reuse of carbon steel scrap.

[0055] Furthermore, by forming carbon steel scrap into ingots, the volume of the ingots can be reduced compared to recovered carbon steel scrap, making transportation and management of the carbon steel scrap easier. Therefore, the above configuration allows for the reuse of carbon steel scrap generated within nuclear facilities. In addition, the retention of carbon steel scrap within nuclear facilities can be reduced.

[0056] In the method for recycling carbon steel scrap having the above configuration, the melting device may be provided within the nuclear facility.

[0057] According to this configuration, the carbon steel scrap can be melted at the nuclear facility where the carbon steel scrap is generated, which simplifies the labor required for transporting the carbon steel scrap and reduces the burden on workers and other personnel involved in transporting the carbon steel scrap.

[0058] In the method for recycling carbon steel scrap having the above configuration, the special steel may be used for a radioactive waste storage container.

[0059] According to this configuration, carbon steel scrap generated within nuclear facilities can be made into special steel products used within nuclear facilities, thereby promoting the reuse of carbon steel scrap generated within nuclear facilities.

[0060] In the method for recycling carbon steel scrap having the above configuration, if the copper content of the sample measured before recycling the ingot is 0.50 mass% or less and the tin content is 0.03 mass% or less, the ingot may be stored in a predetermined area within the nuclear facility, or in other cases, the ingot may be stored in another area within the nuclear facility.

[0061] According to this configuration, by forming the carbon steel scrap into ingots, the volume can be reduced compared to carbon steel scrap in its recovered state, allowing for more effective use of the space in the narrow nuclear facility than if the scrap was stored in its recovered state.

[0062] In the method for recycling carbon steel scrap having the above configuration, two or more samples may be collected, one of the samples may be used to measure the copper content and the tin content, and the other of the samples may be used to measure the content of elements other than copper and tin.

[0063] According to this configuration, the metal processing company or special steel manufacturer that provided the carbon steel scrap does not need to collect new samples to measure the chemical composition of the carbon steel scrap, and the carbon steel scrap can be reused efficiently.

[0064] In the method for recycling carbon steel scrap having the above configuration, the radioactivity concentration of the sample may also be measured when measuring the copper content and the tin content of the sample.

[0065] According to this configuration, the measurement of the radioactivity concentration of carbon steel scrap, which has conventionally been performed at nuclear facilities, can be performed in conjunction with the measurement of the copper and tin contents of molten scrap samples, thereby reducing the human and financial burden of the new task of measuring the copper and tin contents of molten scrap samples.

Claims

1. A method for recycling carbon steel scrap generated at a nuclear facility, the carbon steel scrap being scrap, comprising: melting the carbon steel scrap using a melting device; taking a sample from the melt of carbon steel scrap; measuring the copper and tin content of said sample; and casting the melt of carbon steel scrap into an ingot; If the measured copper content of the sample is 0.50% by mass or less and the tin content is 0.03% by mass or less, the ingot is reused for special steel with excellent low-temperature strength, The carbon steel is an iron alloy having a carbon content of 2.0% by mass or less, The special steel is a special steel that can ensure soundness at low temperatures of -20°C, as specified by the Japan Steel Casting and Forging Society standard JCSS C-1 "Cast Steel for Low-Temperature Welding Structures," The method for recycling carbon steel scrap, wherein the melting device is installed within the nuclear facility.

2. 2. The method for recycling carbon steel scrap according to claim 1, wherein the special steel is for use in a radioactive waste storage container.

3. 2. The method for recycling carbon steel scrap according to claim 1, wherein, before recycling the ingot, if the measured copper content of the sample is 0.50% by weight or less and the measured tin content is 0.03% by weight or less, the ingot is stored in a predetermined area within the nuclear facility, and otherwise, the ingot is stored in another area within the nuclear facility.

4. 2. The method for recycling carbon steel scrap according to claim 1, wherein two or more samples are collected, one of the samples is used to measure the copper content and the tin content, and the other of the samples is used to measure the content of elements other than copper and tin.

5. 5. The method for recycling carbon steel scrap according to claim 1, wherein the radioactivity concentration of the sample is also measured when the copper content and tin content of the sample are measured.