JP2020067456A - Metal melting method and metal melting system - Google Patents

Abstract

To provide a metal melting technique capable of melting and recycling metal waste including a radioactive substance.SOLUTION: A metal melting method includes: a radiation information acquisition process for measuring concentration of a first type radionuclide included in an object 2 for including metal and a radioactive substance, and acquiring radiation information of the object 2; a melting process for melting the object 2 for which radiation information is acquired in a furnace 24; an evaluation process for estimating concentration of a second type radionuclide that is included in the object 2 after melting and differs from the first type radionuclide based on concentration of the first type radionuclide; and a clearance determination process for determining whether a value calculated from the concentration of a radioactive substance of the object 2 is equal to or less than a reference value.SELECTED DRAWING: Figure 8

Description

  Embodiments of the present invention relate to a metal melting method and a metal melting system.

  Nuclear power plants affected by the earthquake, nuclear facilities where decommissioning will be performed, and radiation medical facilities generate a large amount of radioactively contaminated metals or activated metals. These metals are radioactive wastes and require long-term storage and management. However, the amount of radioactive waste is enormous, and it is difficult to secure a disposal site or a storage site. Therefore, a technique for reducing or reusing radioactive waste is known.

JP, 2003-307591, A Japanese Patent No. 3861286

  In order to secure the reuse destination of 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 controlling the components in the metal during melting to perform quality control. Here, in order to reuse the radioactive waste, it is necessary to reduce the concentration of the radioactive substance contained in the radioactive waste. In particular, when a metal is melted using an arc furnace, a large amount of metal fumes are generated. Therefore, when melting radioactive waste, it is necessary to prevent secondary pollution by the metal fumes.

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

  A metal melting method according to an embodiment of the present invention includes a radioactivity information acquisition step of measuring the concentration of a first-type radionuclide contained in an object containing a metal and a radioactive substance and acquiring radioactivity information of the object. A melting step of melting the object from which the radioactivity information has been obtained in a furnace, and a concentration of a second type radionuclide contained in the object after the melting and different from the first type radionuclide. An evaluation step of estimating based on the concentration of the first type radionuclide, and a clearance determination step of determining whether or not a value calculated from the concentration of the radioactive substance of the object is equal to or less than a reference value. Including.

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

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 a material selection process. The conceptual diagram which shows a radioactivity information acquisition process. The conceptual diagram which shows the determination process of the input object for carbon concentration reduction. The conceptual diagram which shows the determination process of the input object for cesium concentration reduction. 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, an embodiment of a metal melting method will be described in detail with reference to the drawings.

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

  In this embodiment, the radioactive waste is the target 2 that is the target of the recycling process. This object 2 is an article contaminated with radioactive substances (radionuclides) generated from a nuclear power plant that has been hit by the earthquake, a nuclear facility where decommissioning will be performed, and a radiation medical facility.

  The objects 2 include, for example, demolition waste from a nuclear power plant, debris scattered by a disaster such as a tsunami or an earthquake, and consumable items brought from outside the power plant. Further, the object 2 includes carbon steel, cast iron, and alloy steel contaminated with radioactive materials. Further, the object 2 includes non-metal or non-ferrous metal in addition to metal waste. Examples include medical waste, PCB contaminants, asbestos, aluminum and the like. That is, the object 2 includes hazardous waste that can be detoxified by high temperature. Here, the detoxification treatment refers to deactivating the effect of a substance that causes harm by high temperature.

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

  As shown in FIGS. 1 and 2, the metal melting system 1 performs a material selection unit 3 that executes a material selection process, a radioactivity information acquisition unit 4 that executes a radioactivity information acquisition process, and a decontamination process. A decontamination unit 5, a melting unit 6 that executes a melting process, a casting unit 7 that executes a casting process, a clearance judgment unit 8 that executes a clearance judgment 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 selection unit 3 selects the target 2 based on the properties of the target 2, such as the contamination history of the target 2, the shape of the target 2, the material of the target 2, and the like. In addition, the contamination history is a history indicating a situation in which the object 2 has been used, and includes a history of a radioactive substance attached or a history of activation. The material sorting unit 3 includes a magnetic force sorter 11 that sorts the target 2 using magnetic force, a wind power sorter 12 that sorts the target 2 using wind force, and a fluorescent X-ray that analyzes the properties of the target 2. And an analyzer 13.

  As shown in FIG. 4, a predetermined unit 31 of the object 2 is brought into the material selection unit 3 in the material selection process. 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 sorted for each contamination history unit 32.

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

  If the object 2 is formed 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. When the object 2 is managed and stored for each contamination history, the selection may be omitted. Further, when the preselected object 2 is brought into the metal melting system 1, the execution of the material selecting step may be omitted.

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

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

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

  As shown in FIGS. 1 and 2, the radioactivity information acquisition unit 4 includes a radioactivity measuring device 16 that measures the radiation emitted from the object 2 and a weight measuring device 17 that measures the weight of the object 2. Prepare The radioactivity information acquisition unit 4 executes a radioactivity information acquisition step of acquiring radioactivity information that serves as an index for identifying the decontamination method for 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, acquisition of radioactivity information includes acquisition of information indicating the radioactivity amount of the target object 2. In addition to acquiring information indicating that the target object 2 is not contaminated with radioactive substances, acquiring information indicating that the target object 2 is not contaminated with radioactive substances is also a Included in acquisition. In the present embodiment, the measurement of the radioactivity of the object 2 includes the radiochemical analysis of the radionuclide 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 the radioactivity information is not limited to the measurement of the radioactivity of the target object 2 by the radioactivity measuring device 16, and may be other modes. For example, the object 2 previously measured using the radioactivity measuring device 16 has been stored for a long period of time, and acquiring the storage history includes acquiring information indicating the amount of radioactivity of the object 2. That is, when the radioactivity of the target object 2 is known in advance, the measurement of the radioactivity of the target object 2 by the radioactivity measuring device 16 may be omitted.

  As shown in FIG. 5, in the radioactivity information acquisition step, the radioactivity of the target object 2 is measured according to the contamination history, shape, and material of the target object 2 selected for each selection unit 33 in the material selection 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 and the weight may be measured.

  For example, when there is a contamination history mainly composed of γ-ray nuclides, the radioactivity may be measured using a basket-type γ-ray measuring device regardless of the shape of the object 2. In addition, when there is a contamination history mainly composed of β nuclides and when the contamination history is surface contamination, if the target object 2 has a flat plate shape, the radioactivity measurement is performed using a tray type β ray measuring device. To do. Further, if the shape of the object 2 is other than the flat shape, the radioactivity is measured using a GM tube type survey meter.

  In the material selection step, the contamination history, shape, and material of the target object 2 are selected, and the information is managed in association with each target object 2, so that the state of the target object 2 is determined in the radioactivity information acquisition step. 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 selection step and the radioactivity concentration and weight information associated in the radioactivity information acquisition step. Then, the radioactivity information recording step of recording the radioactivity information and the object 2 in association with each other in the management computer 10 (see FIG. 3) is executed.

  In addition, among the objects 2 whose radioactivity information has been acquired in the radioactivity information acquisition step, the charging target object determination step of determining the target object 2 to be charged into the arc furnace 24 in the melting step is executed. Here, the type, the attribute, and the amount of the object 2 to be charged into the arc furnace 24 are determined. The determination of the object 2 to be 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). Note that the worker may determine the target object 2 to be input based on the design information, the contamination history, the selection information, and the radioactivity information. This input object determination step may be performed before the decontamination step or may be performed before the melting step.

  As shown in FIG. 1 and FIG. 2, the decontamination part 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. Run. In this embodiment, at least one of mechanical decontamination, chemical decontamination, and melt decontamination is performed in the decontamination step. By doing so, the optimum decontamination method can be specified based on the radioactivity information. Note that a plurality of decontamination methods may be used together. Further, the specification of the decontamination method includes a mode of specifying that the decontamination is not performed when the concentration of the radioactive substance in the object is low and the decontamination is not necessary. That is, the decontamination process may be omitted for the object 2 having a low degree of contamination and the process may proceed to the melting process.

  The decontamination section 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 section 5 includes a mechanical decontamination device 20 used for mechanical decontamination and a chemical decontamination device 21 used for chemical decontamination.

  The mechanical decontamination device 20 performs mechanical decontamination by, for example, shot blasting in which a granular material composed of an iron abrasive or the like is sprayed on the object 2. The surface of the object 2 is peeled off by shot blasting for decontamination. The object 2 may be mechanically decontaminated with a drill or other equipment. By doing so, it is possible to decontaminate the object 2 having a property suitable for mechanical decontamination.

  The chemical decontamination apparatus 21 performs chemical decontamination by, for example, immersing (contacting) the target 2 with formic acid as a decontaminating solution. Decontamination is performed by dissolving the surface of the object 2 with formic acid. By doing so, it is possible to decontaminate the object 2 having a property suitable for chemical decontamination.

  The high-frequency induction furnace 18 heats and melts the object 2, and decomposes or oxidizes the radioactive substance to transfer it to the gas or the 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 process of the present embodiment is characterized by being capable of gentle melting as compared with the arc furnace 24 and generating less metal fume. Therefore, there is little possibility of secondary contamination by the metal fumes containing the radioactive substance, and the radioactive substance contained in the object 2 can be removed.

  In addition, after oxidizing the radioactive substance and transferring it to the slag 22, a certain amount of the slag 22 must be present in order to facilitate the separation and recovery thereof. Therefore, when melt decontamination is performed, for example, a substance (a slag forming agent) such as silicon dioxide, calcium oxide, and iron oxide that becomes the slag 22 is introduced into the high-frequency induction furnace 18 together with the object 2 and melted. Therefore, if a non-radioactive slag-forming agent is added for each treatment, the amount of the secondary waste in which the slag-forming agent becomes the radioactive slag 22 increases.

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

  In the present embodiment, after melting and decontaminating the object 2 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 subjected to specific gravity separation in the bottom pouring type ladle 19, and only the molten metal is tapped from the bottom of the ladle 19. Then, the slag 22 is separated and recovered, and the slag 22 is re-charged to the high frequency induction furnace 18. In this way, the slag 22 generated by the melt decontamination can be reused, so that the amount of secondary waste generated can be suppressed.

  Furthermore, during melt decontamination using an electric furnace, for example, waste such as medical waste, PCB contaminants, asbestos, and aluminum is rendered harmless by heating. By doing so, it is possible to render the hazardous waste harmless simply by raising it to a high temperature. Therefore, it is not necessary to perform a detoxification process separately.

  In the decontamination step, the decontamination of the target 2 suitable for the melt decontamination can be performed by performing the melt decontamination for separating the radioactive substance contained in the target 2 from the metal by using the electric furnace. Further, the radioactive waste 23 generated by the decontamination in the decontamination section 5 is discarded.

  In the decontamination step, a plurality of mechanical decontaminations and a plurality of chemical decontaminations may be used in combination. Furthermore, 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 process of melting the object 2 decontaminated in the decontamination process in the arc furnace 24. When the object 2 is melted using the arc furnace 24, a large amount of metal fumes are generated. In the present embodiment, the decontamination process is executed before the melting process. In this way, the object 2 is decontaminated and then melted, so that it is possible to suppress secondary contamination by the metal fumes 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 target object 2 are adjusted during melting in the arc furnace 24 so that the specific element contained in the target object 2 has a target concentration.

  Component adjustment is, for example, addition of an element such as carbon, silicon, or manganese as an iron alloy thereof. Moreover, it is to reduce a predetermined element by blowing oxygen. Further, it is to reduce elements such as phosphorus and sulfur by adding calcium oxide.

  In principle, it is difficult to increase the size of the high-frequency induction furnace and to thicken the refractory material, whereas the arc furnace 24 is easy to do so. Therefore, the arc furnace 24 can process a large amount of metal. Further, in the arc furnace 24, it is possible to adjust the composition by blowing oxygen, which has a high erosion resistance of the refractory material, or by adding calcium oxide. By doing so, the components of the object 2 can be appropriately adjusted in the melting step and reused as a standard product.

  In addition, in the melting step, the object 2 is selected for each measurement unit 34 by using the selection information associated with each measurement unit 34 in the material selection step so that the range of component adjustment is possible, And combine them to melt. In this way, the object after the melting step can be adjusted before the melting step so that the clearance satisfies 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 at which the composition can be adjusted. To decide. This determination is performed in the input object determination step. Here, the objects 2 are sorted by the melting unit 35. In this way, the value of the concentration at which the composition of the specific element can be adjusted in the arc furnace is set in advance, and the object 2 containing the specific element with the concentration of this value or less 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 the component adjustment relating to the carbon concentration, the carbon concentration needs to be 0.6% or less in order to manufacture a reusable standard product. In the melting step, in order to reduce the carbon concentration to this concentration within a realistic processing time, the carbon concentration needs to be approximately 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, using the material information and the weight information for each measurement unit 34 of the object 2, the carbon concentration in the combination (melting unit 35) of the objects 2 to be charged into the arc furnace 24 in one melting step is 4% or less. Must be restricted to

  In the present embodiment, in the melting step, 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 becomes equal to or less than the reference value. The object 2 to be thrown into is determined. This determination is performed in the input object determination step. Here, the objects 2 are sorted by the melting unit 35. By doing so, it is possible to suppress the secondary contamination by the metal fumes generated during melting in the arc furnace 24. Further, the object 2 after melting in the arc furnace 24 can be made to have a clearance level satisfied.

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

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

  Note that 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, the melt decontamination and the component adjustment are performed using the arc furnace 24. The target object 2 is a metal whose radioactivity concentration has been lowered by mechanical decontamination or chemical decontamination, and secondary contamination is suppressed even when it is put into the arc furnace 24. 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 process. When the melt decontamination is performed in the melting process, radioactive waste 26 is generated in the arc furnace 24 and these are also discarded.

  The casting unit 7 includes a continuous casting machine 27 that performs continuous casting 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 the 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 reused product.

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

  The clearance determination unit 8 includes a clearance measuring device 28. The clearance measuring device 28 is used to measure the concentration of the radioactive substance contained in the metal lump 2A, and whether or not the value calculated from the concentration of the radioactive substance is less than or equal to the reference value, that is, the metal lump 2A has the clearance level. A clearance determination step of 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 lower than the reference value. By doing so, it is possible to determine whether or not the metal ingot 2A satisfies the clearance level. In the present embodiment, the measurement of the concentration of the radioactive substance contained in the object 2 includes the radiochemical analysis of the radionuclide contained in the object 2. The metal ingot 2A that satisfies the clearance level is conveyed to the processing section 9. On the other hand, the metal ingot 2A that does not satisfy the clearance level is discarded as the waste 29.

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

  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 determination result information recording step of performing determination in the clearance determination step and recording the determination result information indicating the determination result and the metal ingot 2A (object 2) in the management computer 10 (see FIG. 3) in association with each other. To be executed.

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

  By accumulating such information, the radionuclide composition ratio or the average radioactivity concentration for each contamination history of the object 2 is estimated, and in the clearance determination step, based on the measurement result of the type 1 radionuclide, the second Species Radionuclide radioactivity concentrations can be estimated and evaluated.

  For example, if the radionuclide composition ratio of the first and second radionuclides for a certain contamination history is known, the γ-ray of the object 2 with a certain contamination history is measured in the radioactivity information acquisition step. By doing so, the concentration of the type 1 radionuclide is measured. Further, the concentration of the second type radionuclide is estimated from the measured concentration of the first type radionuclide using a known radionuclide composition ratio. After that, the concentration of the first-type radionuclide is measured by measuring the γ-ray of the object 2 in the clearance determination step, and the concentration of the second-type radionuclide is analyzed. Furthermore, compare the concentrations of the 1st and 2nd radionuclides measured or estimated in the radioactivity information acquisition process with the 1st and 2nd radionuclide concentrations measured in the clearance determination process. Thus, the decontamination status of the radionuclide can be estimated, and further the radionuclide composition ratio after decontamination can be estimated. Here, after estimating the radionuclide composition ratio after decontamination, by using the radionuclide composition ratio for the measurement result of the concentration of the 1st type radionuclide at the time of clearance determination, the concentration of the 2nd type radionuclide Can be evaluated.

  The evaluation process may be performed after the selection information recording process and the radioactivity information recording process. Preferably, the present embodiment is configured to be performed after the selection information recording step and the radioactivity information recording step and before the clearance determination step.

  In the material selection step, the target object 2 is selected based on the contamination history of the target object 2. Then, in the selection information recording step, the selection information is recorded in association with the object 2. Next, in the radioactivity information acquisition step, the concentration of the type 1 radionuclide contained in the object 2 is measured. Then, in the radioactivity information recording step, the radioactivity information is recorded in association with the object 2. By repeating the processing of the object 2 and accumulating such information, the radionuclide composition ratio or the average radioactivity concentration in the object 2 having a certain contamination history is estimated. After estimating the radionuclide composition ratio or average radioactivity concentration, in the evaluation process, based on the selection information and the radioactivity information, determine the concentration of the second radionuclide different from the first radionuclide contained in the object. evaluate.

  In the clearance determination step, it may be necessary to determine not only the first-type radionuclide but also the second-type radionuclide. In that case, if the evaluation step is not performed before the clearance determination step, the measurement of the second radionuclide is essential in the clearance determination step.

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

  The clearance determination step may be performed in the melting step before the casting step. For example, the concentration of the radioactive substance in the sampled melt such as the molten metal taken out from the arc furnace 24 may be measured, and it may be determined whether or not the value calculated from this concentration is equal to or lower than the reference value. By doing so, 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 manufactured in the casting process. The processing unit 9 executes a processing step of processing the metal ingot 2A to manufacture the processed product 2B. For example, the metal block 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 efficiently recycled as a standard product that can be reused. Further, by using the arc furnace 24, it is possible to add oxygen or calcium oxide to the molten metal to remove carbon, phosphorus and sulfur. Further, since the decontamination step is performed before the object 2 is put 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 becomes more uniform as compared with mechanical decontamination and chemical decontamination. Therefore, the measurement becomes easy.

  Also, when radioactive materials are released outside the reactor due to a serious accident at a nuclear power plant, a large amount of waste is generated. For example, wastes that are legally required to be properly treated and wastes that are difficult to solidify with cement-based fillers are contaminated by the deposition of radioactive substances. Such waste cannot be transported outside the nuclear power plant. Therefore, it is necessary to process on the premises. By treating the wastes that can be detoxified by heating at the time of melt decontamination, it is not necessary to install new equipment for the 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 a small influence in the melting step after decontamination.

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

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

  As shown in FIG. 3, the metal melting system 1 includes a management computer 10 for managing each process. The management of each process using the management computer 10 means that an operator who operates a device used in each process is given information output from the management computer 10, and based on this information, the worker manages the device. Including a control mode. 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 object determination unit 40, and a management database 41. These are realized by the CPU executing a program stored in the memory or the HDD. 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 centrally manages the management computer 10. Further, the information input / output unit 37 is input with the information acquired by the operator who operates the device used in each process. Further, the information input / output unit 37 outputs information for controlling each process to the worker. 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 identification unit 38 identifies 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 decontaminated object 2. In addition, the input target determination unit 40 determines the target 2 to be input into the arc furnace 24 in the melting process.

  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 selection section 3, a part of the radioactivity information acquisition section 4, or a part of the clearance determination section 8. There is a case.

  The design information recording unit 42 records design information indicating the shape and material of the object 2. The design information includes design drawing information 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 selection information recording unit 44 records the selection information acquired in the material selection process in association with the object 2. By doing so, it is possible to verify the relationship between the clearance level of the object 2 after the melting process and the selection information based on the information recorded in the selection 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 and the object 2 in association with each other. By doing so, 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 can be verified.

  Next, a 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 the above-mentioned FIGS. 1 to 7 are appropriately referred to.

  As shown in FIG. 8, first, in step S11, the material selection unit 3 determines the target object 2 based on the properties of the target object 2 such as the contamination history of the target object 2, the shape of the target object 2, and the material of the target object 2. The material selection step of selecting is performed.

  In the next step S12, the selection information recording unit 44 executes the selection information recording step of recording the selection information acquired in the material selection 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 radioactivity information that serves as an index for identifying the decontamination method of the objects 2 selected in the material selection step.

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

  In the next step S15, the input target determination unit 40 determines the target 2 to be charged into the arc furnace 24 in the melting process among the targets 2 whose radioactivity information was acquired in the radioactivity information acquisition process. The target object determination step is executed.

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

  In the next step S <b> 17, the melting unit 6 executes a melting step of melting the target object 2 whose input has been determined in the input target determination step in the arc furnace 24.

  In the next step S18, the casting unit 7 performs the casting process of casting the object 2 melted in the arc furnace 24 in the melting process to produce 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 decontaminated object 2 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 the determination result information recording step of recording the determination result information indicating the determination result performed in the clearance determination step and the object 2 which is the metal lump 2A in association with each other. Run.

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

  Next, a metal melting method executed by the metal melting system 1 of Modification 1 will be described with reference to FIG. The metal melting method of the first modification differs from the above-described metal melting method (see FIG. 8) only in steps S17A to S21A, and the other steps are the same.

  As shown in FIG. 9, in the modified example 1, the evaluation step is executed in step S17A after the decontamination step is executed in step S16. In the next step S18A, a clearance determination step is executed.

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

  In the first modification, the clearance determination step is executed before the melting step, so that it is possible to prevent the object 2 whose decontamination is insufficient from being mistakenly thrown into the arc furnace 24. Therefore, it is possible to suppress the secondary contamination due to the metal fumes generated in the melting process.

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

  As shown in FIG. 9, in the second modification, the melting step is executed in step S17B after the insertion target object determining step is executed in step S15. In this melting step, melting decontamination that is a decontamination method specified based on the radioactivity information acquired in the radioactivity information acquisition step is executed. In this melt decontamination, the arc furnace 24 is used to separate the radioactive substance contained in the object 2 from the metal.

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

  In the present embodiment, the determination of the arbitrary value using the reference value may be the determination of "whether the arbitrary value is the reference value or more", or "whether the arbitrary value exceeds the reference value. It is also possible to judge. Alternatively, the determination may be “whether or not an arbitrary value is less than or equal to a reference value” or “determined whether or not an arbitrary value is less than a reference value”. Further, the reference value may not be fixed but may be changed. 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. Alternatively, an error generated in the device may be analyzed in advance, and a predetermined range including the error range centered on the reference value may be used for the determination.

  In the flowchart of the present embodiment, the mode in which the steps are executed in series is illustrated, but the context of each step is not necessarily fixed, and the context of some steps may be interchanged. good. Also, some steps may be executed in parallel with other steps.

  The management computer 10 according to the present embodiment includes a dedicated chip, a field programmable gate array (FPGA), a graphics processing unit (GPU), a CPU (central processing unit), or other control device having a highly integrated processor, and a ROM ( Storage device such as Read Only Memory) or RAM (Random Access Memory), external storage device such as HDD (Hard Disk Drive) or SSD (Solid State Drive), display device such as display, input such as mouse or keyboard A device and a communication interface are provided. 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 addition, in the melting step, melt decontamination may be performed in which the object 2 is heated by using the electric arc furnace 24, which is an electric furnace, to render harmful wastes harmless.

  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 caused to perform machine learning of the relationship between the determination of the target object 2 for input in the input target object determination step and the actual generation amount of the metal ingot 2A, and based on this machine learning, the following The object 2 to be input may be determined. Further, artificial intelligence may be used to perform the evaluation in the clearance determination step.

  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 perform 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 a melting step of melting an object for which radioactivity information has been acquired in an arc furnace, it is possible to melt and recycle metal waste containing radioactive material.

  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 spirit of the invention. These embodiments and their modifications are included in the invention described in the claims and the equivalents thereof as well as included in the scope and the gist of the invention.

DESCRIPTION OF SYMBOLS 1 ... Metal melting system, 2 ... Target, 2A ... Metal lump, 2B ... Processed product, 3 ... Material selection part, 4 ... Radioactivity information acquisition part, 5 ... Decontamination part, 6 ... Melting part, 7 ... Casting part , 8 ... Clearance determination part, 9 ... Processing part, 10 ... Management computer, 11 ... Magnetic force sorter, 12 ... Wind force sorter, 13 ... Fluorescent X-ray analyzer, 14, 15 ... Waste, 16 ... Radioactivity measuring device , 17 ... Weight measuring device, 18 ... High frequency induction furnace, 19 ... Ladle, 20 ... Mechanical decontamination device, 21 ... Chemical decontamination device, 22 ... Slag, 23 ... Radioactive waste, 24 ... Arc furnace, 25 ... 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 ... Measuring unit, 35 ... Melting unit, 36 ... Main control unit, 37 ... Information input / output unit, 3 Decontamination method specifying unit, 39 ... Evaluation unit, 40 ... Input object determining unit, 41 ... Management database, 42 ... Design information recording unit, 43 ... Contamination history recording unit, 44 ... Selection information recording unit, 45 ... Radioactivity Information recording unit, 46 ... Determination result information recording unit.

Claims (15)

A radioactivity information acquisition step of measuring the concentration of a first-type radionuclide contained in an object containing a metal and a radioactive substance and acquiring radioactivity information of the object;
A melting step of melting the object for which the radioactivity information has been acquired in a furnace,
An evaluation step of estimating the concentration of the second type radionuclide contained in the object after the melting and different from the first type radionuclide based on the concentration of the first type radionuclide,
A clearance determination step of determining whether the value calculated from the concentration of the radioactive substance of the object is less than or equal to a reference value,
A method of melting a metal, comprising: In the radioactivity information acquisition step, a radioactivity information recording step of measuring the concentration of the first type 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 second type radionuclide contained in the object based on the radioactivity information, based on the concentration of the first type radionuclide;
In the clearance determination step, the concentration of the first type radionuclide contained in the object is measured, and the determination result information related to the first type radionuclide and the second type radionuclide is associated with the object. A determination result information recording step of recording,
The metal melting method according to claim 1, further comprising:   The metal melting method according to claim 1 or 2, wherein in the evaluation step, a known radionuclide composition ratio is used to estimate the concentration of the second type radionuclide based on the concentration of the first type radionuclide. .   The said evaluation process estimates the density | concentration of the said 2nd type radionuclide based on the density | concentration of the said 1st type radionuclide using the radionuclide composition ratio corresponding to a contamination history. The metal melting method according to item 1.   The metal melting method according to any one of claims 1 to 4, wherein the first type radionuclide is a nuclide that emits γ-rays.   The metal melting method according to any one of claims 1 to 5, wherein the second type radionuclide is a nuclide that emits β-rays.   A decontamination step of identifying at least one of mechanical decontamination, chemical decontamination, and melt decontamination based on the radioactivity information, and decontaminating the object by the identified decontamination method. The metal melting method according to any one of claims 1 to 6, which comprises.   The metal melting method according to claim 7, wherein in the decontamination step, the melt decontamination is performed in which the radioactive substance contained in the object is separated from the metal by using an electric furnace.   The metal melting method according to any one of claims 1 to 8, wherein in the melting step, melt decontamination for separating the radioactive substance contained in the object from the metal is performed using the furnace.   The metal melting method according to claim 1, further comprising a material selection step of selecting the object based on a property before the melting step.   A combination of the objects to be put 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 a reference value. The metal melting method according to any one of claims 1 to 10, further comprising a step of determining an input object for determining a melting unit. After the melting step, including a casting step of casting a metal mass of the object,
The metal melting method according to claim 11, wherein the generation amount of the metal lump satisfying the clearance level or the generation amount of the metal lump not satisfying the clearance level is predicted in the input object determination step. A casting step of casting a metal ingot of the object after the melting step,
A step of causing a computer to machine-learn the relationship between the determination of the target to be charged into the furnace in the input target determination step and the generation amount of the metal ingot in the casting step;
Including,
The metal melting method according to claim 11 or 12, wherein in the step of determining an object to be charged, the object to be charged into the furnace is determined based on the machine learning.   The metal melting method according to any one of claims 1 to 13, wherein the furnace is an arc furnace. A radioactivity information acquisition unit that measures the concentration of the type 1 radionuclide contained in the object containing metal and radioactive material and acquires the radioactivity information of the object;
A melting part for melting the object from which the radioactivity information has been acquired in a furnace,
An evaluation unit that estimates the concentration of a second-type radionuclide that is contained in the object after the melting and that is different from the first-type radionuclide, based on the concentration of the first-type radionuclide,
A clearance determination unit that determines whether or not the value calculated from the concentration of the radioactive substance of the object is less than or equal to a reference value,
A metal melting system comprising.

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