JP6918076B2 - Metal melting method and metal melting system - Google Patents

Description

Embodiments of the present invention relate to metal melting methods and metal melting systems.

Nuclear power plants that have been hit by the earthquake, decommissioned nuclear facilities, and radiation medical facilities generate large amounts of radioactively contaminated or activated metals. These metals are radioactive waste and require long-term storage and management. However, the amount of radioactive waste is enormous, and it is difficult to secure a disposal place or storage place. Therefore, a technique for reducing or reusing the volume of radioactive waste is known.

Japanese Unexamined Patent Publication No. 2003-307591 Japanese Patent No. 3861286

In order to secure a reuse destination for radioactive waste, it is desirable to use standard products such as building materials such as reinforcing bars. Therefore, it is preferable to use an arc furnace capable of melting a large amount of metal and adjusting the components in the metal during melting to perform quality control. Here, in order to reuse radioactive waste, it is necessary to reduce the concentration of radioactive substances contained in the radioactive waste. In particular, when melting metal using an arc furnace, a large amount of metal fume is generated. Therefore, when melting radioactive waste, it is necessary to prevent secondary contamination by the metal fume.

An embodiment of the present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a metal melting technique capable of melting and reusing a metal waste containing a radioactive substance.

The metal melting method according to the embodiment of the present invention includes a radioactivity information acquisition step of measuring the concentration of a type 1 radioactive nuclei contained in an object containing a metal and a radioactive substance and acquiring the radioactivity information of the object. A melting step of melting the object from which the radioactivity information has been acquired in a furnace, a casting step of casting a metal block of the object after the melting step, and the target to be melted in the furnace. Input target determination step of determining the melting unit, which is a combination of the objects to be charged into the furnace, based on the radioactivity information so that the value calculated from the concentration of the contained radioactive substance is equal to or less than the reference value. When the included in the object of the melt after, and the concentration of the first type radionuclide second type radionuclides different from the evaluation step of estimating, based on the concentration of the first type radionuclide, wherein see containing and a clearance determination step of determining the whether the value calculated from the concentration of radioactive material is less than the reference value of the object at the closing object determination step, the metal block that satisfies clearance level Or the amount of the metal ingot that does not satisfy the clearance level is predicted .

Embodiments of the present invention provide a metal melting technique capable of melting and reusing metal waste containing radioactive substances.

The block diagram which shows the metal melting system of this embodiment. The block diagram which shows the metal melting system of this embodiment. The block diagram which shows the metal melting system of this embodiment. The conceptual diagram which shows the material sorting process. The conceptual diagram which shows the radioactivity information acquisition process. The conceptual diagram which shows the determination process of the input object for reducing the carbon concentration. The conceptual diagram which shows the determination process of the input object for reducing the cesium concentration. The flowchart which shows the metal melting method of this embodiment. The flowchart which shows the metal melting method of the modification 1. The flowchart which shows the metal melting method of the modification 2.

Hereinafter, embodiments of the metal melting method will be described in detail with reference to the drawings.

Reference numeral 1 in FIG. 1 is the metal melting system of the present embodiment. This metal melting system 1 is used to regenerate radioactive waste as a reusable standard product. The standard product refers to an product in which the components in the metal are adjusted and quality control is performed to comply with a predetermined standard.

In the present embodiment, the radioactive waste is the object 2 to be reclaimed. This object 2 is an article contaminated with radioactive substances (radionuclides) generated from a nuclear power plant that was hit by an earthquake, a nuclear facility that is being decommissioned, and a radiological medical facility.

Object 2 includes, for example, dismantled waste from a nuclear power plant, rubble scattered due to a disaster such as a tsunami or an earthquake, and consumables brought in from outside the power plant. In addition, the object 2 includes carbon steel, cast iron, and alloy steel contaminated with radioactive substances. Further, the object 2 includes a non-metal or a non-ferrous metal in addition to the metal waste. For example, medical waste, PCB contaminants, asbestos, aluminum and the like are included. That is, the object 2 contains hazardous waste that can be detoxified by high temperature. Here, the detoxification treatment means that the effect is deactivated by altering a substance that causes harm due to high temperature.

The object 2 includes not only a metal to which a radioactive substance is attached, but also a metal in which a part of the metal is activated to become a radioactive substance. Examples of radioactive substances include substances such as radioactive isotopes cesium, cobalt, strontium, and uranium. Further, the metal of the present embodiment means a metal other than a radioactive substance that can be reused.

As shown in FIGS. 1 and 2, the metal melting system 1 executes a material sorting unit 3 that executes a material sorting process, a radioactivity information acquisition unit 4 that executes a radioactivity information acquisition process, and a decontamination process. It includes a decontamination unit 5, a melting unit 6 that executes a melting process, a casting unit 7 that executes a casting process, a clearance determination unit 8 that executes a clearance determination process, and a processing unit 9 that executes a processing process. Further, the metal melting system 1 includes a management computer 10 (see FIG. 3).

The material sorting unit 3 sorts the object 2 based on the properties of the object 2, such as the contamination history of the object 2, the shape of the object 2, and the material of the object 2. The contamination history includes a history showing a situation in which the object 2 has been used, a history in which a radioactive substance is attached, or a history in which the object 2 is activated. The material sorting unit 3 includes a magnetic force sorter 11 that sorts the object 2 using magnetic force, a wind power sorter 12 that sorts the object 2 using wind power, and a fluorescent X-ray that analyzes the properties of the object 2. It is provided with an analyzer 13.

As shown in FIG. 4, in the material sorting step, the object 2 of the predetermined unit 31 is brought into the material sorting unit 3. Further, the contamination history of the object 2 is managed by the management computer 10 (see FIG. 3). Based on this contamination history, the object 2 is sorted in the material sorting step. Here, the object 2 is selected for each contamination history unit 32.

Further, the design information indicating the shape and material of the object 2 is managed by the management computer 10. Based on this design information, the object 2 is sorted in the material sorting step. Here, the object 2 is sorted by the sorting unit 33 for each shape or material. As described above, in the material sorting step, the object 2 is sorted based on a predetermined condition.

When the object 2 is composed of a single shape and material, the selection may be omitted. When the object 2 is handled for each shape and material, the selection may be omitted. If the object 2 is managed and stored for each contamination history, the selection may be omitted. Further, when the pre-sorted object 2 is brought into the metal melting system 1, the execution of the material sorting step may be omitted.

In the material sorting unit 3, the object 2 having a shape or material that cannot be reused is discarded as waste 14. Further, the contaminated object 2 that cannot be reused even after decontamination is discarded as waste 15.

Further, in the material sorting step, sorting information indicating the sorting state of the object 2 is acquired. Then, the sorting information recording step of associating the sorting information with the object 2 and recording the sorting information on the management computer 10 (see FIG. 3) is executed. The selection information may include the contamination history acquired before the selection of the object 2.

In the present embodiment, the object 2 is provided with object identification information (object ID) capable of identifying each object 2. When the management computer 10 (see FIG. 3) records the object 2 in association with other information, the object identification information and the other information are associated and recorded. When the object identification information is given to the object 2, a tag recording the object identification information may be directly attached to the object 2, or this tag may be attached to the container in which the object 2 is housed. You may.

As shown in FIGS. 1 and 2, the radioactivity information acquisition unit 4 includes a radioactivity measuring device 16 for measuring the radiation emitted from the object 2 and a weight measuring device 17 for measuring the weight of the object 2. Be prepared. The radioactivity information acquisition unit 4 executes a radioactivity information acquisition step of acquiring radioactivity information as an index for specifying the decontamination method of the object 2.

As the radioactivity measuring device 16, for example, a γ-ray measuring device that measures γ-rays emitted from the object 2 is exemplified. The radioactivity information acquisition unit 4 may include a radioactivity measuring device 16 other than the γ-ray measuring device. For example, the radioactivity information acquisition unit 4 may include a β-ray measuring device or a GM tube type survey meter.

In the present embodiment, the acquisition of radioactivity information includes the acquisition of information indicating the amount of radioactivity of the object 2. In addition to acquiring information indicating that the object 2 is contaminated with radioactive substances, it is also possible to acquire information indicating that the object 2 is not contaminated with radioactive substances. Included in acquisition. In the present embodiment, the measurement of the radioactivity of the object 2 includes a radiochemical analysis of the radionuclides contained in the object 2. The suitable decontamination method differs depending on the radionuclide, the contamination status, the contamination history, the shape of the object 2, or the material of the object 2.

Further, the acquisition of radioactivity information is not limited to measuring the radioactivity of the object 2 with the radioactivity measuring device 16, but may be in other aspects. For example, the object 2 measured in advance using the radioactivity measuring device 16 is stored for a long period of time, and by acquiring the storage history, information indicating the radioactivity amount of the object 2 is acquired. That is, when the radioactivity of the object 2 is known in advance, it may be omitted to measure the radioactivity of the object 2 by the radioactivity measuring device 16.

As shown in FIG. 5, in the radioactivity information acquisition step, the radioactivity of the object 2 is measured according to the contamination history, shape, and material of the object 2 sorted for each sorting unit 33 in the material sorting step. Here, the object 2 may be selected for each measurement unit 34 according to the performance of the radioactivity measuring device 16, and then the radioactivity concentration of the specified radioactive substance may be measured and the weight may be measured.

For example, when there is a history of contamination mainly consisting of γ-ray nuclides, radioactivity may be measured using a basket-type γ-ray measuring device regardless of the shape of the object 2. Further, in the case of a contamination history in which β-nuclide is the main component and a contamination history in which surface contamination is present, if the shape of the object 2 is a flat plate, radioactivity measurement is performed using a tray-type β-ray measuring device. conduct. Further, if the shape of the object 2 is other than the flat plate shape, the radioactivity is measured using a GM tube type survey meter.

In the material sorting process, the contamination history, shape, and material of the object 2 are sorted, and the information is associated and managed for each object 2, so that the state of the object 2 is restored in the radioactivity information acquisition process. In addition, it can be measured using an appropriate radioactivity measuring device 16.

Further, the radioactivity information including the radioactivity concentration measurement result and the weight measurement result is recorded in the management computer 10 (see FIG. 3) in association with each measurement unit 34. That is, the measurement unit 34 that has undergone the radioactivity information acquisition step includes information on the shape and material associated in the material sorting step and information on the radioactivity concentration and weight associated in the radioactivity information acquisition step. Then, the radioactivity information recording step of associating the radioactivity information with the object 2 and recording the radioactivity information on the management computer 10 (see FIG. 3) is executed.

Of the objects 2 whose radioactivity information has been acquired in the radioactivity information acquisition step, the input object determination step of determining the object 2 to be charged into the arc furnace 24 in the melting process is executed. Here, the type, attribute, and input amount of the object 2 to be charged into the arc furnace 24 are determined. The determination of the object 2 for input is made based on the design information, the contamination history, the selection information, and the radioactivity information recorded in the management computer 10 (see FIG. 3). The worker may determine the object 2 to be input based on the design information, the contamination history, the selection information, and the radioactivity information. This input target determination step may be executed before the decontamination step or may be executed before the melting step.

As shown in FIGS. 1 and 2, the decontamination unit 5 performs a decontamination step of decontaminating the object 2 by a decontamination method specified based on the radioactivity information acquired in the radioactivity information acquisition step. Execute. In the present embodiment, at least one of mechanical decontamination, chemical decontamination, and melt decontamination is performed in the decontamination step. In this way, the optimum decontamination method can be specified based on the radioactivity information. A plurality of decontamination methods may be used in combination. Further, the specification of the decontamination method includes an aspect of specifying that decontamination is not performed when the concentration of the radioactive substance of the object is low and decontamination is not necessary. That is, the object 2 having a low degree of contamination may skip the decontamination step and proceed to the melting step.

The decontamination unit 5 includes a high-frequency induction furnace 18 as an electric furnace used for melt decontamination and a bottom-pouring type ladle 19. Further, the decontamination unit 5 includes a mechanical decontamination device 20 used for mechanical decontamination and a chemical decontamination device 21 used for chemical decontamination.

The mechanical decontamination apparatus 20 performs mechanical decontamination by shot blasting, for example, by spraying particles composed of an iron abrasive or the like onto the object 2. Decontamination is performed by peeling off the surface of the object 2 by shot blasting. The object 2 may be mechanically decontaminated with a drill or other equipment. In this way, it is possible to decontaminate the object 2 having properties suitable for mechanical decontamination.

The chemical decontamination apparatus 21 performs chemical decontamination by, for example, immersing (contacting) formic acid as a decontamination liquid in the object 2. Decontamination is performed by dissolving the surface of the object 2 with formic acid. In this way, the object 2 having properties suitable for chemical decontamination can be decontaminated.

The high-frequency induction furnace 18 heats and melts the object 2 to decompose or oxidize the radioactive substance to transfer it to the gas or slag 22. The gas is released from the melt and the slag 22 floats on the surface of the melt. Melt decontamination is performed by separating these gases or slag 22 from the melt.

The high-frequency induction furnace 18 used in the decontamination step of the present embodiment is characterized in that it can be melted more gently than the arc furnace 24 and less metal fume is generated. Therefore, there is little possibility of secondary contamination by the metal fume containing radioactive substances, and the radioactive substances contained in the object 2 can be removed.

It should be noted that a certain amount of slag 22 needs to be present in order to facilitate separation and recovery of the radioactive substance after it has been oxidized and transferred to the slag 22. Therefore, when performing melt decontamination, for example, a substance (slag-forming agent) that becomes slag 22 such as silicon dioxide, calcium oxide, and iron oxide is put into the high-frequency induction furnace 18 together with the object 2 to be melted. Therefore, if a non-radioactive slag-forming agent is added for each treatment, the amount of secondary waste in which the slag-forming agent becomes radioactive slag 22 increases.

Therefore, in the present embodiment, when the decontamination step is performed a plurality of times, the slag 22 generated in the high frequency induction furnace 18 when the previous decontamination step is performed is recovered, and the high frequency is generated when the next decontamination step is performed. It is put into the induction furnace 18. That is, the slag 22 separated and recovered after transferring the radioactive substance from the object 2 in the decontamination step is reused in the subsequent decontamination step. By using the slag 22 separated and recovered in the decontamination step instead of the non-radioactive slag-forming agent, the amount of secondary waste can be reduced.

In the present embodiment, after the object 2 is melt-decontaminated in the high-frequency induction furnace 18, the molten metal is transferred to the bottom-pouring type ladle 19. Then, the molten metal and the slag 22 are separated by specific gravity in the bottom pouring type ladle 19, and only the molten metal is discharged from the bottom of the ladle 19. Then, the slag 22 is separated and recovered, and the slag 22 is reintroduced into the high frequency induction furnace 18. In this way, the slag 22 generated by melt decontamination can be reused, so that the amount of secondary waste generated can be suppressed.

Further, during melt decontamination using an electric furnace, for example, medical waste, PCB contaminants, asbestos, aluminum and other wastes are detoxified by heating. In this way, the hazardous waste can be detoxified simply by raising the temperature. Therefore, it is not necessary to perform detoxification treatment separately.

In the decontamination step, the object 2 suitable for melt decontamination can be decontaminated by performing melt decontamination that separates the radioactive substance contained in the object 2 from the metal using an electric furnace. In addition, the radioactive waste 23 generated by decontamination in the decontamination unit 5 is discarded.

In the decontamination step, a plurality of mechanical decontaminations and a plurality of chemical decontaminations may be used in combination. Further, in the decontamination step, mechanical decontamination, chemical decontamination and melt decontamination may be used in combination.

The melting unit 6 includes an arc furnace 24 as an electric furnace and a ladle 25. The melting unit 6 executes a melting step of melting the object 2 decontaminated in the decontamination step in the arc furnace 24. When the object 2 is melted using the arc furnace 24, a large amount of metal fume is generated. In this embodiment, the decontamination step is executed before the melting step. In this way, since the object 2 is decontaminated and then melted, it is possible to suppress secondary contamination by the metal fume generated in the melting step.

In the melting step, the object 2 is melted using the arc furnace 24. Further, in the melting step, the components of the object 2 are adjusted during melting in the arc furnace 24 so that the specific element contained in the object 2 has a target concentration.

Component adjustment is, for example, adding elements such as carbon, silicon, and manganese as ferroalloys. Further, by blowing oxygen, a predetermined element is reduced. Further, elements such as phosphorus and sulfur are reduced by adding calcium oxide.

In principle, it is difficult for the high-frequency induction furnace to increase the size and the refractory material to be thick, whereas in the arc furnace 24, these are easy. Therefore, the arc furnace 24 can process a large amount of metal. Further, in the arc furnace 24, it is possible to adjust the components by blowing oxygen having a high erosion property of the refractory material or adding calcium oxide. In this way, the components of the object 2 can be appropriately adjusted in the melting step and reused as a standard product.

Further, in the melting step, the object 2 is sorted for each measurement unit 34 appropriately so as to be within the range in which the component can be adjusted by using the sorting information associated with each measurement unit 34 in the material sorting step. Melt in various combinations. In this way, the object after the melting step can be adjusted before the melting step so as to satisfy the clearance.

In the present embodiment, the object 2 to be charged into the arc furnace 24 based on the selection information so that the concentration of the specific element contained in the object 2 before being charged into the arc furnace 24 becomes a value whose component can be adjusted. To determine. This determination is made in the input target determination process. Here, the object 2 is sorted for each melting unit 35. In this way, a value of a concentration that allows the composition of a specific element to be adjusted is set in advance in the arc furnace, and the object 2 containing the specific element having a concentration equal to or lower than this value is charged into the arc furnace 24. Therefore, the components can be appropriately adjusted in the arc furnace 24.

As shown in FIG. 6, for example, regarding component adjustment regarding carbon concentration, it is necessary to set the carbon concentration to 0.6% or less in order to produce a reusable standard product. In the melting step, in order to reduce the carbon concentration to this concentration in a realistic treatment time, the carbon concentration needs to be about 4% or less. That is, the upper limit of the range in which the carbon concentration can be reduced in the arc furnace 24 is about 4%. Therefore, the carbon concentration in the combination of the objects 2 (melting unit 35) to be charged into the arc furnace 24 in one melting step is 4% or less by using the material information and the weight information for each measurement unit 34 of the object 2. It is necessary to limit it so that it becomes.

In the present embodiment, the arc furnace 24 is based on the radioactivity information so that the value calculated from the concentration of the radioactive substance contained in the object 2 melted in the arc furnace 24 in the melting step is equal to or less than the reference value. The object 2 to be put into is determined. This determination is made in the input target determination process. Here, the object 2 is sorted for each melting unit 35. In this way, it is possible to suppress secondary contamination by metal fume generated during melting in the arc furnace 24. Further, it is possible to assume that the object 2 after melting in the arc furnace 24 is satisfied with the clearance level.

The combination of the objects 2 to be charged into the arc furnace 24 (melting unit 35) is determined by using the radioactivity information associated with each measurement unit 34 in the radioactivity information acquisition step. For example, the value calculated from the radioactive concentration of the specified radioactive substance in the melting unit 35 of the object 2 decontaminated by the decontamination step is adjusted to be equal to or less than the reference value. By selecting each measurement unit 34 for the object 2 and making an appropriate combination, it is possible to reduce the influence of the radioactivity of the object 2 melted in the melting step.

As shown in FIG. 7, for example, the specified radioactive substance is Cs-137, the value calculated from this radioactive concentration is the value obtained by dividing the radioactive concentration by 0.1, and the reference value is 1. Then, the decontamination coefficient of Cs-137 in the decontamination step is set to 100. For example, when decontamination with a decontamination coefficient of 100 is performed, the concentration of radioactive substances is reduced to 1/100 after decontamination. Here, in order for the melting unit 35 after decontamination to satisfy the reference value, the radioactivity concentration of Cs-137 in the melting unit 35 needs to be 10 Bq / g. Therefore, it is necessary to limit the radioactivity concentration of Cs-137 in the melting unit 35 to 10 Bq / g or less by using the radioactivity concentration information and the weight information for each measurement unit 34.

In addition, at least one of mechanical decontamination and chemical decontamination may be performed in the decontamination step, and melt decontamination may be performed in the melting step. In that case, melt decontamination and component adjustment are performed using the arc furnace 24. The object 2 is a metal whose radioactivity concentration has been reduced by mechanical decontamination or chemical decontamination, and even if it is put into the arc furnace 24, secondary contamination is suppressed. Further, it is possible to further reduce the contamination level of the melting target in the arc furnace 24.

As shown in FIGS. 1 and 2, the waste 26 generated in the arc furnace 24 is discarded in the melting step. When melt decontamination is performed in the melting step, radioactive waste 26 is generated in the arc furnace 24, and these are also discarded.

The casting section 7 includes a continuous casting machine 27 that continuously casts using the object 2 melted in the arc furnace 24. The casting unit 7 executes the casting process using the continuous casting machine 27. For example, the continuous casting machine 27 can produce a metal ingot 2A having a certain shape in the process of solidifying the molten iron in the arc furnace 24. In this way, the object 2 can be processed into a recycled product.

In the casting step, casting may be performed using a machine other than the continuous casting machine 27. For example, the metal ingot 2A may be manufactured by casting by pouring the molten object 2 into a pig iron machine, an ingot case, or the like.

The clearance determination unit 8 includes a clearance measuring device 28. The concentration of the radioactive substance contained in the metal block 2A is measured using this clearance measuring device 28, and whether or not the value calculated from the concentration of the radioactive substance is equal to or less than the reference value, that is, the metal block 2A determines the clearance level. A clearance determination step for determining whether or not the condition is satisfied is executed.

In the clearance determination step, the radioactivity concentration of the specified radioactive substance contained in the metal ingot 2A produced in the casting step is measured, and it is confirmed that the value calculated from this radioactivity concentration is equal to or less than the reference value. In this way, it is possible to determine whether or not the metal block 2A satisfies the clearance level. In the present embodiment, the measurement of the concentration of the radioactive substance contained in the object 2 includes a radiochemical analysis of the radionuclide contained in the object 2. The metal ingot 2A satisfying the clearance level is conveyed to the processing section 9. On the other hand, the metal block 2A that does not satisfy the clearance level is discarded as waste 29.

The amount of metal ingot 2A that satisfies the clearance level or the amount of metal ingot 2A that does not satisfy the clearance level can be predicted by the above-mentioned step of determining the input target. The parameters used for determining the input target 2 in the input target determination step may be changed based on the actual amount of the metal ingot 2A generated. By repeating the change of this parameter, it is possible to improve the accuracy when the actual amount of the metal ingot 2A generated is predicted based on the amount of the object 2 for charging.

The clearance measuring device 28 of the present embodiment includes, for example, a γ-ray measuring device, a γ-ray spectrum measuring device, a device for radiochemical analysis, and the like. The type of the clearance measuring device 28 may be appropriately changed according to the radioactive substance to be measured.

Further, a judgment result information recording process is performed in which the judgment is performed in the clearance judgment step, and the judgment result information indicating the judgment result is associated with the metal block 2A (object 2) and recorded in the management computer 10 (see FIG. 3). Will be executed.

In the present embodiment, an evaluation step of estimating the concentration of the type 2 radionuclide different from the type 1 radionuclide contained in the object 2 is executed based on the selection information and the radioactivity information. The first type radionuclide is an easy-to-measure nuclide that is easy to measure. The second type radionuclide is a difficult-to-measure nuclide that is difficult to measure. The easy-to-measure nuclide is a nuclide that emits γ-rays such as cesium, which is easy to measure. Gamma rays have strong penetrating power and are easy to measure even if there is a shield. On the other hand, difficult-to-measure nuclides are nuclides that emit α-rays that are difficult to measure, such as uranium, and nuclides that emit β-rays, such as strontium, that are difficult to measure. α-rays and β-rays have weak penetrating power and are difficult to measure if there is a shield.

The concentration of the Type 2 radionuclide can be estimated and evaluated based on the measurement results of the Type 1 radionuclide. For example, it is estimated by the radionuclide composition ratio method or the average radioactivity concentration method. In the radionuclide composition ratio method, it is estimated that there is a correlation between the concentration of the type 2 radionuclide and the concentration of the type 1 radionuclide, and the concentration of the type 2 radionuclide is calculated from the measurement results of the type 1 radionuclide. presume. In the average radioactivity concentration method, it is estimated that the concentration of the type 2 radionuclide is substantially constant regardless of the concentration of the type 1 radionuclide, and the concentration of the type 2 radionuclide is estimated.

By accumulating this information, the radionuclide composition ratio or average radioactivity concentration for each contamination history of the object 2 is estimated, and the second type radionuclide measurement result is used in the clearance determination step. The radioactivity concentration of the species radionuclide can be estimated and evaluated.

For example, when the radionuclide composition ratio of the first type radionuclide and the second type radionuclide is known for a certain pollution history, the γ-ray of the object 2 of the certain pollution history is measured in the radioactivity information acquisition process. Thereby, the concentration of the first-class radionuclide is measured. In addition, the concentration of the type 2 radionuclide is estimated from the measured concentration of the type 1 radionuclide using a known radionuclide composition ratio. After that, the concentration of the first-class radionuclide is measured by measuring the γ-rays of the object 2 in the clearance determination step, and the concentration of the second-class radionuclide is analyzed. Furthermore, the concentrations of the first-class radionuclide and the second-class radionuclide measured or estimated in the radioactivity information acquisition process should be compared with the concentrations of the first-class radionuclide and the second-class radionuclide measured in the clearance determination step. Therefore, the decontamination status of radionuclides can be estimated, and the composition ratio of radionuclides after decontamination can be estimated. Here, after estimating the radionuclide composition ratio after decontamination, the concentration of the radionuclide type 2 at the time of clearance determination is measured by using the radionuclide composition ratio with respect to the measurement result. Can be evaluated.

The evaluation step may be performed after the sorting information recording step and the radioactivity information recording step. Preferably, in the present embodiment, it is configured to be carried out after the sorting information recording step and the radioactivity information recording step and before the clearance determination step.

In the material sorting step, the target object 2 is sorted based on the contamination history of the target object 2. Then, in the sorting information recording process, the sorting information is recorded in association with the object 2. Next, in the radioactivity information acquisition step, the concentration of the first-class radionuclide contained in the object 2 is measured. Then, in the radioactivity information recording process, the radioactivity information is recorded in association with the object 2. By repeating the treatment of the object 2 and accumulating this information, the radionuclide composition ratio or the average radioactivity concentration in the object 2 in a certain contamination history is estimated. After estimating the radionuclide composition ratio or average radionuclide concentration, in the evaluation process, the concentration of the type 2 radionuclide different from the type 1 radionuclide contained in the object is determined based on the selection information and the radioactivity information. evaluate.

In the clearance determination step, it may be necessary to determine not only the type 1 radionuclide but also the type 2 radionuclide. In that case, if the evaluation step is not executed before the clearance determination step, the measurement of the type 2 radionuclide is indispensable in the clearance determination step.

If it is necessary to determine the type 2 radionuclide in the clearance determination process and the evaluation process is performed before the clearance determination process, use the concentration of the type 2 radionuclide evaluated in the evaluation process. Therefore, the measurement of the second type radionuclide in the clearance determination step can be omitted.

The clearance determination step may be performed in a melting step before the casting step. For example, the concentration of the radioactive substance may be measured with respect to the sampled melt such as the molten metal taken out from the arc furnace 24, and it may be determined whether or not the value calculated from this concentration is equal to or less than the reference value. In this way, it is possible to determine whether or not the object 2 being melted in the arc furnace 24 satisfies the clearance level.

The processing unit 9 includes a rolling mill 30 that rolls the metal ingot 2A produced in the casting process. The processing unit 9 executes a processing step of processing the metal ingot 2A to produce the processed product 2B. For example, the metal ingot 2A is processed by rolling, forging, cutting, or the like. The clearance determination step described above may be performed on the processed product 2B manufactured in the processing step. The processed product 2B processed by the processing unit 9 is a reusable standard product.

In the present embodiment, by using the arc furnace 24, a large amount of radioactive waste can be recycled as a standard product that can be efficiently reused. Further, by using the arc furnace 24, carbon, phosphorus and sulfur can be removed by adding oxygen or calcium oxide to the molten metal. Further, since the decontamination step is performed before the object 2 is charged into the arc furnace 24 (before the melting step), the possibility of secondary contamination is low even when the arc furnace 24 is used.

Further, when melt decontamination is performed using the high frequency induction furnace 18 in the decontamination step, the concentration of the radioactive substance contained in the object 2 after decontamination is uniform as compared with mechanical decontamination and chemical decontamination. Therefore, the measurement becomes easy.

In addition, a large amount of waste is generated when radioactive materials are released to the outside of a nuclear reactor due to a serious accident at a nuclear power plant. For example, wastes that are required to be properly treated by law and wastes that are difficult to solidify with cement-based fillers are contaminated by the adhesion of radioactive substances. Such waste cannot be carried out of the premises of a nuclear power plant. Therefore, it is necessary to process it on the premises. Of these wastes, those that can be detoxified by heating are treated at the same time as melt decontamination, so that it is not necessary to install new equipment for treatment.

Further, the object 2 of the measurement unit 34 that has undergone the material selection step and the radioactivity information acquisition step is associated with the radioactivity concentration and weight information. Therefore, by selecting and combining the objects 2 for each measurement unit 34 in consideration of the decontamination effect of the decontamination step, it is possible to obtain a radioactivity concentration that has little influence in the melting step after decontamination.

Further, the object 2 of the measurement unit 34 that has undergone the material selection step and the radioactivity information acquisition step is associated with the material and weight information. Therefore, by selecting and combining the objects 2 of the measurement unit 34 in the range in which the components of the melting step can be adjusted, the metal after melting can have an arbitrary component concentration.

From the data that shows the concentration of radioactive substances before and after the decontamination process and the accumulated sorting information in the material selection process, the radioactivity information acquisition process, and the clearance determination process, from the measurement results of easily measured nuclides in the clearance determination process. The concentration of difficult-to-measure nuclides can be evaluated and estimated. Therefore, the measurement of difficult-to-measure nuclides, which requires time or man-hours for measurement, can be replaced by the measurement of easy-to-measure nuclides.

As shown in FIG. 3, the metal melting system 1 includes a management computer 10 for managing each process. In the management of each process using the management computer 10, information output from the management computer 10 is given to the operator who operates the equipment used in each process, and the operator controls the equipment based on this information. Includes aspects to control. The management computer 10 may be connected to the equipment used in each process, and the management computer 10 may directly control the equipment.

The management computer 10 includes a main control unit 36, an information input / output unit 37, a decontamination method specifying unit 38, an evaluation unit 39, an input target determination unit 40, and a management database 41. These are realized by executing the program stored in the memory or the HDD by the CPU. The management database 41 includes a design information recording unit 42, a contamination history recording unit 43, a selection information recording unit 44, a radioactivity information recording unit 45, and a determination result information recording unit 46.

The main control unit 36 comprehensively manages the management computer 10. Further, information acquired by an operator who operates the equipment used in each process is input to the information input / output unit 37. Further, the information input / output unit 37 outputs information for controlling each process to the operator. The information input / output to / from the information input / output unit 37 includes design information, contamination history, selection information, radioactivity information, and determination result information. The information input / output unit 37 has a function of controlling devices such as a communication unit, a keyboard, a mouse, a display, a selection input unit displayed on the display, and a printer.

The decontamination method specifying unit 38 specifies the decontamination method based on various information input to the information input / output unit 37. In addition, the evaluation unit 39 evaluates the concentration of the radioactive substance in the object 2 after decontamination. Further, the object to be input determination unit 40 determines the object 2 to be charged into the arc furnace 24 in the melting step.

The management database 41 records various information used in each process. The management computer 10 including the management database 41 functions as a part of the material sorting unit 3, a part of the radioactivity information acquisition unit 4, or a part of the clearance determination unit 8. May be done.

The design information recording unit 42 records design information indicating the shape and material of the object 2. The design information includes information on the design drawing such as CAD data used before the decommissioning of the predetermined facility where the object 2 was used.

The contamination history recording unit 43 records the contamination history of the object 2. This contamination history may be information already recorded before starting the metal melting method using the metal melting system 1.

The sorting information recording unit 44 records the sorting information acquired in the material sorting step in association with the object 2. In this way, it is possible to verify the relationship between the clearance level of the object 2 after the melting step and the sorting information based on the information recorded in the sorting information recording unit 44.

The radioactivity information recording unit 45 records the radioactivity information acquired in the radioactivity information acquisition step in association with the object 2. The determination result information recording unit 46 records the determination result information indicating the determination result performed in the clearance determination step in association with the object 2. In this way, it is possible to verify the relationship between the radioactivity information of the object 2 acquired before the melting step and the clearance level of the object 2 acquired after the melting step.

Next, the metal melting method executed by the metal melting system 1 of the present embodiment will be described with reference to the flowchart of FIG. It should be noted that FIGS. 1 to 7 described above are referred to as appropriate.

As shown in FIG. 8, first, in step S11, the material sorting unit 3 determines the object 2 based on the properties of the object 2, such as the contamination history of the object 2, the shape of the object 2, and the material of the object 2. Perform a material sorting process.

In the next step S12, the sorting information recording unit 44 executes a sorting information recording step of recording the sorting information acquired in the material sorting step in association with the object 2.

In the next step S13, the radioactivity information acquisition unit 4 executes the radioactivity information acquisition step of acquiring the radioactivity information as an index for specifying the decontamination method of the object 2 selected in the material selection step.

In the next step S14, the radioactivity information recording unit 45 executes a radioactivity information recording step of associating and recording the radioactivity information acquired in the radioactivity information acquisition step with the object 2.

In the next step S15, the charging target determination unit 40 determines the charging target 2 to be charged into the arc furnace 24 in the melting step among the objects 2 whose radioactivity information has been acquired in the radioactivity information acquisition step. Perform the object determination process.

In the next step S16, the decontamination unit 5 executes a decontamination step of decontaminating the object 2 by a decontamination method specified based on the radioactivity information acquired in the radioactivity information acquisition step.

In the next step S17, the melting unit 6 executes a melting step of melting the object 2 determined to be charged in the charging target determination step in the arc furnace 24.

In the next step S18, the casting unit 7 casts the object 2 melted in the arc furnace 24 in the melting step, and executes the casting step of producing the metal ingot 2A.

In the next step S19, the evaluation unit 39 executes an evaluation step of evaluating the concentration of the radioactive substance in the object 2 after decontamination, which is the metal block 2A.

In the next step S20, the clearance determination unit 8 executes a clearance determination step of determining whether or not the metal ingot 2A cast in the casting step satisfies the clearance level.

In the next step S21, the determination result information recording unit 46 performs a determination result information recording step of recording the determination result information indicating the determination result performed in the clearance determination step in association with the object 2 which is the metal block 2A. Execute.

In the next step S22, the processing unit 9 executes a processing step of processing the metal ingot 2A cast in the casting process to produce the processed product 2B. Then, the process ends.

Next, the metal melting method executed by the metal melting system 1 of the modification 1 will be described with reference to FIG. In the metal melting method of the modified example 1, only the steps from step S17A to step S21A are different from the above-mentioned metal melting method (see FIG. 8), and the other steps are the same steps.

As shown in FIG. 9, in the first modification, the evaluation step is executed in step S17A after the decontamination step is executed in step S16. In the next step S18A, the clearance determination step is executed.

In the next step S19A, the determination result information recording step is executed. In the next step S20A, the melting step is executed. In the next step S21A, the casting step is executed. In the next step S22, the processing step is executed. Then, the process ends.

In the first modification, since the clearance determination step is executed before the melting step, it is possible to prevent the object 2 having insufficient decontamination from being accidentally thrown into the arc furnace 24. Therefore, it is possible to suppress secondary contamination by metal fume generated in the melting process.

Next, the metal melting method executed by the metal melting system 1 of the modification 2 will be described with reference to FIG. In the metal melting method of the modification 2, the decontamination step of step S16 of the metal melting method (see FIG. 8) described above is omitted. Further, the melting step of step S17B is different from the above-mentioned metal melting method, and the other steps are the same steps.

As shown in FIG. 9, in the second modification, the melting step is executed in step S17B after the input target determination step is executed in step S15. In this melting step, melt decontamination, which is a decontamination method specified based on the radioactivity information acquired in the radioactivity information acquisition step, is executed. In this melt decontamination, the radioactive substance contained in the object 2 is separated from the metal by using the arc furnace 24.

In the second modification, the object 2 can be melt-decontaminated in the melting step. That is, it can be considered that the melting process includes the decontamination process.

In the present embodiment, the determination of an arbitrary value using the reference value may be a determination of "whether or not the arbitrary value is equal to or greater than the reference value" or "whether or not the arbitrary value exceeds the reference value". May be judged. Alternatively, it may be determined "whether or not the arbitrary value is less than or equal to the reference value" or "whether or not the arbitrary value is less than the reference value". Further, the reference value is not fixed but may change. Therefore, a value in a predetermined range may be used instead of the reference value to determine whether or not an arbitrary value falls within the predetermined range. Further, the error generated in the apparatus may be analyzed in advance, and a predetermined range including the error range centered on the reference value may be used for the determination.

Although the flowchart of the present embodiment illustrates a mode in which each step is executed in series, the context of each step is not necessarily fixed, and even if the context of some steps is exchanged. good. Also, some steps may be executed in parallel with other steps.

The management computer 10 of the present embodiment includes a control device in which a dedicated chip, a controller such as an FPGA (Field Programmable Gate Array), a GPU (Graphics Processing Unit), or a CPU (Central Processing Unit) is highly integrated, and a ROM (ROM). Storage devices such as Read Only Memory) or RAM (Random Access Memory), external storage devices such as HDD (Hard Disk Drive) or SSD (Solid State Drive), display devices such as displays, and input such as mouse or keyboard. It includes a device and a communication interface. The management computer 10 can be realized by a hardware configuration using a normal computer.

In the present embodiment, the radioactivity information acquisition step is executed after the material selection step, but the radioactivity information acquisition step may be executed before the material selection step.

In the melting step, the arc furnace 24, which is an electric furnace, may be used to heat the object 2 to perform melt decontamination to detoxify the hazardous waste.

The management computer 10 may be a computer equipped with artificial intelligence (AI) that performs machine learning. Then, the management computer 10 may include a deep learning unit that extracts a specific pattern from a plurality of patterns based on deep learning. Then, the management computer 10 is made to machine-learn the relationship between the determination of the object 2 for input in the process of determining the object to be input and the actual amount of the metal ingot 2A generated, and based on this machine learning, the following The object 2 for input may be determined. Further, the evaluation in the clearance determination step may be performed by artificial intelligence.

For example, the radioactivity measuring device 16 may have a function of measuring the weight of the object 2. In that case, the radioactivity measuring device 16 can execute the function of the weight measuring device 17, and the configuration of the weight measuring device 17 can be omitted.

According to the embodiment described above, by providing the melting step of melting the object for which the radioactivity information has been acquired in an arc furnace, the metal waste containing a radioactive substance can be melted and reused.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Metal melting system, 2 ... Object, 2A ... Metal ingot, 2B ... Processed product, 3 ... Material sorting section, 4 ... Radioactivity information acquisition section, 5 ... Decontamination section, 6 ... Melting section, 7 ... Casting section , 8 ... Clearance judgment unit, 9 ... Processing unit, 10 ... Management computer, 11 ... Magnetic sorter, 12 ... Wind sorter, 13 ... Fluorescent X-ray analyzer, 14, 15 ... Waste, 16 ... Radioactivity measuring device , 17 ... Weight measuring device, 18 ... High frequency induction furnace, 19 ... Pot, 20 ... Mechanical decontamination device, 21 ... Chemical decontamination device, 22 ... Slag, 23 ... Radioactive waste, 24 ... Arc furnace, 25 ... Taking Pot, 26 ... Waste, 27 ... Continuous casting machine, 28 ... Clearance measuring device, 29 ... Waste, 30 ... Rolling machine, 31 ... Predetermined unit, 32 ... Contamination history unit, 33 ... Sorting unit, 34 ... Measurement unit, 35 ... Melting unit, 36 ... Main control unit, 37 ... Information input / output unit, 38 ... Decontamination method identification unit, 39 ... Evaluation unit, 40 ... Input target determination unit, 41 ... Management database, 42 ... Design information recording unit , 43 ... Contamination history recording unit, 44 ... Sorting information recording unit, 45 ... Radioactivity information recording unit, 46 ... Judgment result information recording unit.

Claims (15)

A radioactivity information acquisition step of measuring the concentration of a type 1 radionuclide contained in an object containing a metal and a radioactive substance and acquiring the radioactivity information of the object, and
A melting step of melting the object from which the radioactivity information has been acquired in a furnace, and
After the melting step, a casting step of casting a metal block of the object and a casting step of casting the metal block of the object.
It is a combination of the objects to be charged into the furnace based on the radioactivity information so that the value calculated from the concentration of the radioactive substance contained in the object melted in the furnace is equal to or less than the reference value. The process of determining the input target to determine the melting unit and
An evaluation step of estimating the concentration of a type 2 radionuclide contained in the object after melting and different from the type 1 radionuclide based on the concentration of the type 1 radionuclide.
A clearance determination step for determining whether or not the value calculated from the concentration of the radioactive substance of the object is equal to or less than the reference value, and
Including
In the process of determining the object to be charged, the amount of the metal ingot that satisfies the clearance level or the amount of the metal ingot that does not satisfy the clearance level is predicted.
Metal melting method. A radioactivity information acquisition step of measuring the concentration of a type 1 radionuclide contained in an object containing a metal and a radioactive substance and acquiring the radioactivity information of the object, and
A melting step of melting the object from which the radioactivity information has been acquired in a furnace, and
After the melting step, a casting step of casting a metal block of the object and a casting step of casting the metal block of the object.
It is a combination of the objects to be charged into the furnace based on the radioactivity information so that the value calculated from the concentration of the radioactive substance contained in the object melted in the furnace is equal to or less than the reference value. The process of determining the input target to determine the melting unit and
An evaluation step of estimating the concentration of a type 2 radionuclide contained in the object after melting and different from the type 1 radionuclide based on the concentration of the type 1 radionuclide.
A clearance determination step for determining whether or not the value calculated from the concentration of the radioactive substance of the object is equal to or less than the reference value, and
A step of causing a computer to machine-learn the relationship between the determination of the object to be charged into the furnace in the process of determining the object to be charged and the amount of the metal ingot generated in the casting process.
Including
In the process of determining the object to be charged, the object to be charged into the furnace is determined based on the machine learning.
Metal melting method. In the radioactivity information acquisition step, the radioactivity information recording step of measuring the concentration of the type 1 radionuclide contained in the object and recording the radioactivity information based on this measurement in association with the object. ,
An evaluation step of estimating the concentration of the Type 2 radionuclide contained in the object based on the radioactivity information based on the concentration of the Type 1 radionuclide, and an evaluation step.
In the clearance determination step, the concentration of the type 1 radionuclide contained in the object is measured, and the determination result information relating to the type 1 radionuclide and the type 2 radionuclide is associated with the object. Judgment result information recording process to be recorded and
The metal melting method according to claim 1 or 2, wherein the metal melting method comprises. In the evaluation step, according to any one of claims 1 to 3, the concentration of the type 2 radionuclide is estimated based on the concentration of the type 1 radionuclide using a known radionuclide composition ratio. The metal melting method described. In the evaluation step, any one of claims 1 to 4 in which the concentration of the type 2 radionuclide is estimated based on the concentration of the type 1 radionuclide using the radionuclide composition ratio corresponding to the contamination history. The metal melting method according to item 1. The metal melting method according to any one of claims 1 to 5, wherein the type 1 radionuclide is a nuclide that emits γ-rays. The metal melting method according to any one of claims 1 to 6, wherein the type 2 radionuclide is a nuclide that emits β rays. Based on the radioactivity information, at least one of mechanical decontamination, chemical decontamination, and melt decontamination is specified, and a decontamination step of decontaminating the object by the specified decontamination method is performed. The metal melting method according to any one of claims 1 to 7, which includes. The metal melting method according to claim 8, wherein in the decontamination step, the melt decontamination is performed by using an electric furnace to separate the radioactive substance contained in the object from the metal. The metal melting method according to any one of claims 1 to 9, wherein in the melting step, the furnace is used to perform melt decontamination to separate the radioactive substance contained in the object from the metal. The metal melting method according to any one of claims 1 to 10, further comprising a material sorting step of sorting the object based on its properties before the melting step. The metal melting method according to any one of claims 1 to 11, wherein the furnace is an arc furnace. A melting process in which an object containing metal and radioactive substances is melted in a furnace,
After the melting step, a casting step of casting a metal block of the object and a casting step of casting the metal block of the object.
A process of determining an object to be charged, which determines a combination of the objects to be charged into the furnace, and a step of determining the object to be charged.
A clearance determination step for determining whether or not the value calculated from the concentration of the radioactive substance of the object is equal to or less than the reference value, and
Including
In the process of determining the object to be charged, the amount of the metal ingot that satisfies the clearance level or the amount of the metal ingot that does not satisfy the clearance level is predicted.
Metal melting method. A melting process in which an object containing metal and radioactive substances is melted in a furnace,
After the melting step, a casting step of casting a metal block of the object and a casting step of casting the metal block of the object.
A process of determining an object to be charged, which determines a combination of the objects to be charged into the furnace, and a step of determining the object to be charged.
A clearance determination step for determining whether or not the value calculated from the concentration of the radioactive substance of the object is equal to or less than the reference value, and
A step of causing a computer to machine-learn the relationship between the determination of the object to be charged into the furnace in the step of determining the object to be charged and the amount of the metal ingot generated in the casting process.
Including
In the process of determining the object to be charged, the object to be charged into the furnace is determined based on the machine learning.
Metal melting method. A radioactivity information acquisition unit that measures the concentration of type 1 radionuclides contained in an object containing metals and radioactive substances and acquires the radioactivity information of the object.
A melting part that melts the object from which the radioactivity information has been acquired in a furnace, and
A casting part for casting a metal block of the object after melting in the melting part, and a casting part.
It is a combination of the objects to be charged into the furnace based on the radioactivity information so that the value calculated from the concentration of the radioactive substance contained in the object melted in the furnace is equal to or less than the reference value. The input target determination unit that determines the melting unit and
An evaluation unit that estimates the concentration of a type 2 radionuclide contained in the object after melting and different from the type 1 radionuclide based on the concentration of the type 1 radionuclide.
A clearance determination unit that determines whether or not the value calculated from the concentration of the radioactive substance of the object is equal to or less than the reference value.
With
The input target determination unit predicts the amount of the metal ingot that satisfies the clearance level or the amount of the metal ingot that does not satisfy the clearance level.
Metal melting system.

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