JP7660438B2 - High-level radioactive material processing system and method - Google Patents

Description

This disclosure relates to a high-level radioactive material processing system and a high-level radioactive material processing method.

As a method for treating high-level radioactive waste, there is a method for extracting minor actinides, which are radioactive substances, from high-level radioactive materials (e.g., Patent Document 1 and Patent Document 2). In addition, there is a solidification method as a treatment method for storing spent fuel in a recyclable form (e.g., Patent Document 3).

JP 2018-63198 A JP 2019-15533 A Patent No. 6037168

By extracting minor actinides from high-level radioactive materials, the extracted minor actinides can be reused as fuel for fast breeder reactors and other reactors. In addition, removing the minor actinides can reduce the burden of waste disposal. However, in order to reuse minor actinides as fuel, minor actinide combustion technology is required. Furthermore, in situations where reuse technology has not yet been put to practical use, the separated minor actinides must be stored stably for long periods of time.

The present disclosure has been made in consideration of the above, and aims to provide a high-level radioactive material processing system and a high-level radioactive material processing method that can convert minor actinides into a solid in a more stable state.

In order to solve the above-mentioned problems and achieve the object, the present disclosure provides a radioactive material treatment device that includes a uranium supply unit that supplies uranium to a liquid from which at least one of minor actinides and lanthanides has been extracted, a solidification process in which the liquid from which uranium is supplied and from which the minor actinides and lanthanides have been extracted is heated to evaporate some of the liquid, and then further heated to create a solidified body, and a stabilization process in which the solidified body thus created is sintered to remove some or all of the carbon, hydrogen, oxygen, and nitrogen components, and a fluorite structure of uranium dioxide having the minor actinides and lanthanides incorporated therein is created.

In order to solve the above-mentioned problems and achieve the object, the present disclosure provides a high-level radioactive material processing method, which includes the steps of: supplying uranium to a liquid from which at least one of minor actinides and lanthanides has been extracted; performing a solidification process in which the liquid from which uranium has been supplied and from which the minor actinides and lanthanides have been extracted is heated to evaporate some of the liquid, and then further heated to create a solidified body; and performing a stabilization process in a single apparatus to sinter the solidified body, remove some or all of the carbon, hydrogen, oxygen, and nitrogen components, and create a fluorite structure of uranium dioxide incorporating the minor actinides and the lanthanides.

This disclosure makes it possible to convert minor actinides into more stable solids.

FIG. 1 is a schematic diagram showing a schematic configuration of a high-level radioactive material treatment apparatus according to this embodiment. FIG. 2 is a schematic diagram showing a schematic configuration of a high-level radioactive material treatment apparatus according to another embodiment. FIG. 3 is a schematic diagram showing an example of the solidification stabilization processing unit. FIG. 4 is a schematic diagram showing another example of the solidification stabilization processing unit.

Below, an embodiment of the high-level radioactive material treatment device according to the present disclosure will be described in detail with reference to the drawings. The high-level radioactive material treatment device according to the present disclosure extracts MA (minor actinides) from high-level radioactive material and stabilizes it by vitrification. Furthermore, when lanthanides are contained in the high-level radioactive material, the high-level radioactive material treatment device extracts the lanthanides as well as the minor actinides. In this disclosure, "MA (minor actinides)" refers to transuranium elements belonging to the actinides, excluding Pu. "Actinides" is a general term for elements with atomic numbers from 89 to 103. Minor actinides include, for example, Np (neptunium), Am (americium), and Cm (curium). "Ln (lanthanoid)" is a general term for elements with atomic numbers from 57 to 71.

1 is a schematic diagram showing the schematic configuration of the high-level radioactive material treatment device of this embodiment. The high-level radioactive material treatment device (treatment device) 10 shown in FIG. 1 includes an extraction device 12, a solidification and stabilization device 13, and a storage device 18. The solidification and stabilization device 13 includes a solidification device 14 and a stabilization device 16. The treatment device of this embodiment will be described as a case in which high-level radioactive waste (hereinafter also referred to as "HALW") is used as the high-level radioactive material. The waste liquid is, for example, a liquid obtained after U (uranium) and Pu (plutonium) are recovered from the solution of spent nuclear fuel discharged from a light water reactor in the reprocessing of spent nuclear fuel. The high-level radioactive waste contained in the waste liquid includes fission products (hereinafter also referred to as "FP"), MA, and lanthanides. Specifically, the high-level radioactive waste (hereinafter also referred to as "HALW") is waste liquid generated by reprocessing using the PUREX method. In the Purex process, a nitric acid solution containing U and Pu is contacted and mixed with tributyl phosphate (TBP) and an organic solvent such as dodecane. As a result, U and Pu in the nitric acid solution form complexes with TBP and move to the organic solvent. Meanwhile, FP, MA, and Ln remain in the nitric acid solution (waste liquid). The nitric acid solution containing FP, MA, and Ln becomes the waste liquid to be treated.

The extraction device 12 extracts MA components from the waste liquid. The extraction device 12 includes a waste liquid supply unit 22, an extractant supply unit 24, a diluent supply unit 26, and an MA extract liquid production unit 28. The waste liquid supply unit 22 stores HALW, which is liquid high-level radioactive waste, and supplies it to the MA extract liquid production unit 28. In this embodiment, the extractant supply unit 24 and the diluent supply unit 26 are provided, but the extractant supply unit 24 and the diluent supply unit 26 may be combined into a single device to supply a liquid phase organic solvent in which the extractant is dissolved.

The extractant supply unit 24 supplies the extractant to the MA extractant generating unit 28. The extractant captures MA and Ln. The extractant is a liquid that migrates to the dilution liquid and mixes uniformly. For example, a complexing agent that forms a complex with MA or Ln can be used as the extractant. The complexing agent is preferably less expensive than a complexing agent that selectively forms a complex with MA. Examples of extractants include n-octyl(phenyl)-N,N'-diisobutylcarbamoylmethylphosphine oxide-tributyl phosphate mixture (CMPO-TBP mixture), diisodecyl phosphate, 6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2'-bipyridine (BTBP), and N,N'-dibutyl-N,N'-dimethyltetradecylmalonamide (DMDBTDMA). As the extractant, it is preferable to use a DGA-based material (complexing agent). Specific examples of complexing agents include N,N,N',N'-tetraoctyl-3-oxapentanediamide (TODGA), tetra(2-ethylhexyl)diglycolamide (T2EHDGA), etc. The extractant may be used alone or in combination of two or more.

The dilution liquid supply unit 26 supplies the dilution liquid to the MA extraction liquid generation unit 28. The dilution liquid is an organic phase material (organic solvent) that is insoluble in the liquid components of the waste liquid. The organic solvent can be appropriately selected depending on the extractant used. It is desirable that the organic solvent is reusable, inexpensive, and resistant to radiation deterioration. The dilution liquid is an organic phase material that is insoluble in the liquid components of the waste liquid. The dilution liquid has a property of eluting the extractant from the liquid of the waste liquid. The dilution liquid preferably has a boiling point of 30°C or more and 100°C or less. In addition, it is preferable that the dilution liquid does not have a flash point or has a flash point of 150°C or more. By using a liquid that satisfies the above range as the dilution liquid, the processing load in the solidification processing unit can be reduced. In addition, the dilution liquid is preferably a material that is less deteriorated by heat or radiation even when reused, and is preferably a solvent having a hydrocarbon structure that is less deteriorated by heat or radiation even when reused. Here, the phrase "there is little deterioration due to heat or radiation even when reused" means that even if the material is exposed to heat or radiation energy and becomes a low molecular weight structure, it has the property of being difficult to form a complex with a metal ion. As the diluent, for example, a hydrofluorocarbon (HFC) is preferably used. The organic solvent may be used alone or in combination of two or more kinds. In addition, it is preferable that the diluent is separated from the MA in the solidification device 14 and then made into a liquid that can be reused.

The MA extract generating unit 28 is supplied with waste liquid, an extractant, and a diluent. When the MA and Ln in the waste liquid come into contact with the extractant by the solvent extraction method, the MA and Ln migrate to the extractant side. The extractant that has captured MA and Ln is encapsulated in the diluent. After the extraction process, the MA extract generating unit 28 separates the diluent from the waste liquid to generate an MA extract in which the extractant that has captured MA and Ln is encapsulated in the diluent. The MA extract generating unit 28 may be a continuous type in which each material is continuously supplied and an MA extract is generated, or a batch type in which each material is intermittently supplied and an MA extract is generated. The MA extract generating unit 28 may selectively capture MA with the extractant, or may simultaneously capture and process MA and Ln.

Next, the solidification stabilization processing device 13 will be described. The solidification stabilization processing device 13 includes a solidification device 14 and a stabilization device 16. The solidification stabilization processing device 13 performs the heat treatment of the solidification device 14 and the stabilization device 16 in a single device. The configuration of the device that performs the heat treatment of the solidification stabilization processing device 13 will be described later.

The solidification device 14 mixes uranium with the MA extract, removes the liquid components of the mixed liquid, and produces a solidified body. The solidification device 14 includes a solidification processing unit 40 and a uranium supply unit 44. The uranium supply unit 44 supplies uranium to the MA extract in the solidification processing unit 40. The uranium supply unit 44 supplies a uranium-containing substance that is uniformly soluble in the diluent (organic solvent) that constitutes the MA extract, such as an organic U complex, specifically a uranium complex of dipivaloylmethane. The uranium in the organic U complex is contained in a valence state of tetravalent or hexavalent.

The solidification treatment section 40 includes a distillation section 45, a heat treatment section 46, a dilution liquid recovery section 47, an oxidation gas supply section 48, and an exhaust gas recovery section 49. The distillation section 45 heats the MA extract mixed with uranium to, for example, 50°C to 100°C to evaporate the dilution liquid. The heat treatment section 46 is an apparatus integrated with the distillation section 45, and further heats the object from which the dilution liquid has been evaporated, for example to 300°C, to thermally decompose the residue and convert it to oxide. The dilution liquid recovery section 47 is connected to the distillation section 45 and recovers the dilution liquid evaporated in the dilution section 45. The dilution liquid recovery section 47 supplies the recovered dilution liquid to the dilution liquid supply section 26 for reuse. The oxidation gas supply section 48 supplies an oxidizing gas, for example, oxygen or air, to the heat treatment section 46. The exhaust gas supply section 49 recovers the exhaust gas discharged from the heat treatment section 46.

The solidification processing unit 40 distills the MA extract mixed with uranium in the distillation unit 45 to remove the dilution liquid components. By removing the dilution liquid, the solidification processing unit 40 leaves a solidified residue containing the extractant, MA, Ln, and uranium as a complex. The solidification processing unit 40 also recovers the gas discharged during distillation in the distillation unit 45 in the dilution liquid recovery unit 47. The solidification processing unit 40 heats the object obtained by distilling the dilution liquid in the heat treatment unit 46 while supplying an oxidizing gas from the oxidizing gas supply unit 48, thereby removing the components of the extractant, specifically, C, N, O, and H, and generating a solidified body. The solidified body becomes an oxide. The solidification processing unit 40 can use known evaporation methods such as a batch type (batch type) and a continuous type (plate tower or packed tower) for distillation and heat treatment. It is preferable that the distillation unit 45 sets the processing temperature to a boiling point of the diluted solution of the MA extract solution based on the boiling point of the diluted solution, and the boiling point of the diluted solution is -10°C or more and +20°C or less, and below the flash point. The heat treatment unit 46 is at a temperature at which thermal decomposition and oxide conversion processes occur, for example, 300°C or higher.

The stabilization device 16 performs a stabilization process to remove some or all of the carbon, hydrogen, oxygen, and nitrogen components from the solidified body. The stabilization device 16 has a stabilization processing section 50.

The stabilization treatment section 50 includes a reduction section 52, a reduction gas supply section 54, and an exhaust gas recovery section 56. The reduction section 52 heats the solidified body in a reducing atmosphere and calcines and sinters it. The reduction section 52 is an apparatus integrated with the distillation section 45 and the heat treatment section 46. The reduction gas supply section 54 supplies a reducing gas, such as hydrogen, to the reduction section 52. The exhaust gas recovery section 56 recovers the exhaust gas discharged from the reduction section 52.

The stabilization treatment unit 50 supplies reducing gas from the reducing gas supply unit 54 to the reducing unit 52 while heating, calcining, and sintering the solidified body in the reducing unit 52, thereby removing some or all of the carbon, hydrogen, oxygen, and nitrogen components from the treatment target and solidifying it into a fluorite structure. Specifically, the stabilization treatment unit 50 sinters the solidified body to perform denitration and pyrolysis treatment, remove impurity components (organic components, nitric acid components, moisture) in the solidified body, i.e., CHON components, and then sinters it. The sintering temperature is, for example, 600°C or higher and 800°C or lower.

The stabilization treatment unit 50 removes impurity components from the solidified body containing uranium, and then sinters the solidified body in a reducing atmosphere, thereby obtaining uranium oxide having a fluorite structure in which MA and Ln are dissolved. As an example, by distillation, a solidified matter consisting of [M3 ⁺ .( _NO3- ⁾ _3.m (extractant)] + ([U4 ⁺ .( _NO3- ) _4.n (ligand)] or [M3 ⁺ .( ^NO3- _{) 3.m} (extractant)] + ([ _UO22 ⁺ .( _NO3- ^{) 2.n} (ligand)] is generated. Here, M is MA or Ln. By heat treating this solidified matter and removing _the CHON component, it becomes M _aOb + U ₃ O ₈ + ( _αCO2 + _βH2O + _γNOx ), and ( _αCO2 + _βH2O + _γNOx ) is removed. Furthermore, by sintering M _aOb + U ₃ O ₈ , _it becomes an oxide with a fluorite structure _, UM _RM O _y is formed. RM is M(Ln or MA)/U, which is the equivalent ratio of Ln or MA to U. The stabilization device 16 removes some or all of the carbon, hydrogen, oxygen, and nitrogen components that may gasify during storage, and forms a fluorite structure of uranium dioxide containing MA and Ln, thereby producing a solidified body with high thermal and chemical stability.

The storage device 18 stores the stabilized treated material. The storage device 18 includes a storage section 60. The storage section 60 stores the stabilized MA-containing material in a solid state. The storage section 60 is, for example, a cask. The storage section 60 may also be provided underground, and the stabilized treated material may be buried underground.

The MA-containing material stored in the storage section 60 of the processing system 10 can be used as fuel for a nuclear power generation system. When burning MA as fuel, the stored solidified body with a fluorite structure is melted to produce a solution containing U, MA, and Ln (solidified body melting). Next, the resulting solution is subjected to a purification process for U and MA (MA purification). In MA purification, for example, U and MA in the resulting solution are separated from Ln, and highly exothermic MA is separated from MA as necessary. Next, the resulting U and MA (Np, Am, etc.) are mixed with U and Pu to obtain a mixed oxide, thereby producing fuel (MA fuel production). The resulting fuel is burned in a fast breeder reactor or the like (MA combustion).

In the processing device 10 of this embodiment, an extractant and a diluent are added to the waste liquid in the extraction device 12, and then mixed to perform a separation process to separate MA from the waste liquid together with Ln, thereby producing an MA extract. Next, in the solidification device 14, the processing device 10 distills the diluent from the MA extract and supplies U to produce a solidified body containing U, MA, and Ln. Next, in the stabilization device 16, the processing device 10 forms a fluorite structure by removing organic components (CHON) from the solidified body containing MA. The processing device 10 stores the processed product with the fluorite structure in the storage device 18.

The processing device 10 can simplify the device configuration by performing the heat treatment of the solidification stabilization device 13 in a single device. In addition, the processing device 10 can perform multiple processes in a single device, reducing the number of times radioactive materials need to be transported, making processing safer.

In addition, by using a diluent with a boiling point between 30°C and 100°C, or with no flash point or with a flash point of 150°C or higher, the diluent can be easily recovered in the solidification process and the required energy can be reduced.

The processing device 10 separates, solidifies, and stabilizes MA along with Ln. This allows MA to be efficiently extracted from liquid high-level radioactive waste, reducing the waste disposal burden and solidifying it. Furthermore, by extracting MA and Ln and turning them into a stabilized substance, the MA can be stored stably even when it is stored for reuse as fuel. Furthermore, when it is to be reused, it can be made reusable by simply dissolving the solidified body.

In addition, by processing MA and Ln without separating them, the process of separating MA and Ln is unnecessary, and the processing load can be reduced.

In addition, when producing an MA extract from highly radioactive materials containing nitric acid-based substances, the processing device 10 preferably uses an extractant that does not form a third phase. Specifically, it is preferable to use a DGA-based material. One example is T2EHDGA. Furthermore, it is preferable that the extractant be a material that can be removed during processing in the stabilization device 16, specifically a material composed only of carbon, hydrogen, nitrogen, and oxygen. Furthermore, it is preferable that the extractant does not contain any corrosive components.

In addition, the processing device 10 supplies uranium to a liquid containing MA and Ln in the uranium supply unit 44, generates a solidified body, and then sinters it in the stabilization device 16, thereby forming a fluorite structure of uranium dioxide in which MA and Ln are fixed. This allows the solid to have a long-term stable crystal structure after stabilization processing, and MA can be stored stably. Specifically, trivalent MA and Ln can be dissolved in the fluorite structure, and a stable fluorite structure can be obtained compared to a mixture of MA and Ln or an oxide structure of only one of them. Furthermore, by forming a crystal structure using uranium, when a solid containing MA is reprocessed and used, it is possible to obtain a structure that is free of unnecessary components such as Si, Na, Ca, etc. This allows the substance to be stabilized in a state that is easy to use when reprocessing.

The uranium supply unit 44 preferably supplies uranium in the form of an organic substance complex. This makes it easier to dissolve the uranium in the diluent. Here, it is preferable to use a ligand that is coordinated to the organic U complex and that is composed only of carbon, hydrogen, nitrogen, and oxygen. It is also preferable that the ligand that is coordinated to the organic U complex is easy to stabilize (thermally decompose) and does not contain corrosive components, etc. This allows it to be suitably removed during the stabilization process, and the MA-containing substance can be made into a stabilized substance, which can be stored stably.

In the above embodiment, the extraction device 12 produces an MA extract by extraction with an organic solvent and performs a solidification process, but this is not limited to the above. The processing device may produce a stripped liquid in which MA is extracted into a liquid phase, solidify it, and stabilize it.

Figure 2 is a schematic diagram showing the general configuration of a high-level radioactive material treatment device of another embodiment. The high-level radioactive material treatment device (treatment device) 10A shown in Figure 2 includes an extraction device 12A, a solidification and stabilization device 13A, and a storage device 18. The solidification and stabilization device 13A includes a solidification device 14A and a stabilization device 16A. The treatment device 10A of this embodiment will be described as a case in which high-level radioactive waste (hereinafter also referred to as "HALW") is used as the high-level radioactive material, similar to the treatment device 10.

The extraction device 12A extracts MA components from the waste liquid. The extraction device 12A includes a waste liquid supply unit 22, an extractant supply unit 24, a diluent supply unit 26, an MA extract liquid production unit 28, an MA stripping liquid production unit 30, a stripping agent supply unit 32, and a diluent supply unit 34. The waste liquid supply unit 22 stores HALW, which is a liquid high-level radioactive waste, and supplies it to the MA extract liquid production unit 28.

The extractant supply unit 24 supplies the extractant to the MA extractant generating unit 28. The extractant captures MA and Ln. The extractant is a liquid that transfers to the dilution liquid. For example, a complexing agent that forms a complex with MA or Ln can be used as the extractant. The complexing agent is preferably less expensive than a complexing agent that selectively forms a complex with MA. Examples of extractants include n-octyl(phenyl)-N,N'-diisobutylcarbamoylmethylphosphine oxide-tributyl phosphate mixture (CMPO-TBP mixture), diisodecyl phosphate, 6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2'-bipyridine (BTBP), and N,N'-dibutyl-N,N'-dimethyltetradecylmalonamide (DMDBTDMA). As the extractant, it is preferable to use a DGA-based material (complexing agent). Specific examples of complexing agents include N,N,N',N'-tetraoctyl-3-oxapentanediamide (TODGA), tetra(2-ethylhexyl)diglycolamide (T2EHDGA), etc. The extractant may be used alone or in combination of two or more.

The diluent supply unit 26 supplies the diluent to the MA extract production unit 28. The diluent is an organic phase material (organic solvent) that is insoluble in the liquid components of the waste liquid. The organic solvent can be appropriately selected depending on the extractant used. It is desirable that the organic solvent is reusable, inexpensive, and resistant to radiation degradation. A specific example of an organic solvent is n-dodecane. One type of organic solvent may be used alone, or two or more types may be used in combination. In addition, it is preferable that the diluent is separated from MA in the MA stripping production unit 30 and then made into a reusable liquid.

The MA extract generating unit 28 is supplied with waste liquid, an extractant, and a diluent. When the MA and Ln in the waste liquid come into contact with the extractant by the solvent extraction method, the MA and Ln migrate to the extractant side. The extractant also migrates to the diluent side. The MA extract generating unit 28 separates the diluent from the waste liquid after the extraction process to generate an MA extract, which is an extractant that has captured MA and Ln. The MA extract generating unit 28 may be a continuous type in which each material is continuously supplied and an MA extract is generated, or a batch type in which each material is intermittently supplied and an MA extract is generated. In this embodiment, the extractant supply unit 24 and the diluent supply unit 26 are provided, but the extractant supply unit 24 and the diluent supply unit 26 may be combined into one device to supply an organic solvent in a liquid phase in which the extractant is dissolved.

The MA back-extraction liquid generation unit 30 is supplied with the MA extract from the MA extract generation unit 28 and with the back-extraction agent from the back-extraction agent supply unit 32.

The back extraction agent supply unit 32 supplies a substance that transfers MA and Ln from the MA extract to the liquid phase as a back extraction agent. The back extraction agent is, for example, nitric acid. The back extraction agent is diluted with a diluent of the liquid phase, for example, water. The hydrothermal treatment promoter supply unit 34 supplies the hydrothermal treatment promoter to the MA back extraction liquid production unit 30. The hydrothermal treatment promoter is a neutral to basic liquid and is a reducing agent composed of CNOH, for example, an aldehyde compound, an amine compound, etc. Here, the preparation of the mixture of the MA extract, the back extraction agent, and the hydrothermal treatment promoter is not limited to this embodiment. The hydrothermal treatment promoter supply unit 34 may supply the back extraction agent to the MA extract and supply the hydrothermal treatment promoter to the MA back extraction liquid.

The MA stripping liquid generator 30 brings the MA extract into contact with a diluent containing a stripping agent, and transfers the MA and Ln contained in the organic phase MA extract to the diluent containing a stripping agent. The extraction device 12A may reuse the organic solvent (extractant and diluent) in the MA extract after processing. The MA stripping liquid generator 30 controls the acid concentration of the liquid and the amount of stripping agent to set the component ratio during processing in the solidification process 14A to a predetermined ratio.

Next, the solidification stabilization processing device 13A will be described. The solidification stabilization processing device 13A includes a solidification device 14A and a stabilization device 16A. The solidification stabilization processing device 13A performs the heat treatment of the solidification device 14A and the stabilization device 16A in a single device. The configuration of the device that performs the heat treatment of the solidification stabilization processing device 13A will be described later.

The solidification device 14A supplies uranium to the MA stripping liquid, removes the liquid components of the mixed liquid, and produces a solidified body. The solidification device 14A includes a solidification processing unit 40A and a uranium supply unit 44A. The uranium supply unit 44A supplies uranium to the MA stripping liquid of the solidification processing unit 40A. The uranium supply unit 44A supplies a uranium-containing material that is homogeneously soluble in the liquid phase solvent that constitutes the MA stripping liquid. Uranium dissolves in the liquid phase in a valence state of tetravalent or hexavalent.

The solidification treatment section 40A includes a hydrothermal treatment section 45A, a heat treatment section 46A, an exhaust gas recovery section 47A, an oxidizing gas supply section 48A, and an exhaust gas recovery section 49A. The hydrothermal treatment section 45A heats the MA stripping liquid mixed with uranium to, for example, 80°C to 150°C, causing hydrothermal treatment and oxide conversion treatment, and evaporating the liquid components. The liquid components also include a hydrothermal treatment promoter. The heat treatment section 46A is an apparatus integrated with the hydrothermal treatment section 45A, and further heats the object from which the liquid has been evaporated, for example to 300°C, to thermally decompose the residue. The exhaust gas recovery section 47A is connected to the hydrothermal treatment section 45A and recovers the exhaust gas evaporated by the hydrothermal treatment section 45A. The oxidizing gas supply section 48A supplies an oxidizing gas, for example, oxygen or air, to the heat treatment section 46A. The exhaust gas supply section 49A recovers the exhaust gas discharged from the heat treatment section 46A.

The solidification treatment section 40A performs hydrothermal synthesis of the MA stripping solution mixed with uranium in the hydrothermal treatment section 45A to form a solidified material containing MA and uranium. The liquid component is removed by solid-liquid separation of the solidified body and the dilution liquid component. In addition, the hydrothermal reaction can be promoted by adding a hydrothermal treatment promoter. The solidification treatment section 40A heats the object from which the liquid has been removed and which has been oxidized while supplying an oxidizing gas from the oxidizing gas supply section 48A in the heat treatment section 46A, thereby removing the components of the extractant, specifically, C, N, O, H, and generating a solidified body. The solidified body contains U, MA, and Ln. Specifically, the solidified body contains _UO2 and an M oxide precursor. The M oxide precursor is MOOH, M(OH) ₃ , etc. M is at least one of MA and Ln. The hydrothermal treatment treatment section 45A is exemplified by a treatment temperature of 80°C or more and 150°C or less, and a treatment time of 0.5h or more and 20h or less. The heat treatment section 46 is heated to a temperature equal to or higher than the temperature at which pyrolysis occurs, for example, 300° C. or higher.

The stabilization device 16A performs a stabilization process to remove some or all of the carbon, hydrogen, oxygen, and nitrogen components from the solidified body and generate a solidified body with a fluorite structure. The stabilization device 16A has a stabilization processing unit 50A.

The stabilization treatment section 50A includes a reduction section 52A, a reduction gas supply section 54A, and an exhaust gas recovery section 56A. The reduction section 52A heats the solidified body in a reducing atmosphere and calcines and sinters it. The reduction section 52A is an integrated device with the distillation section 45A and the heat treatment section 46A. The reduction gas supply section 54A supplies a reducing gas, such as hydrogen, to the reduction section 52A. The exhaust gas recovery section 56A recovers the exhaust gas discharged from the reduction section 52.

The stabilization treatment unit 50A supplies reducing gas from the reducing gas supply unit 54 to the reduction unit 52A while heating, calcining, and sintering the solidified body in the reduction unit 52A, solidifying the object to be treated into a fluorite structure. Specifically, the stabilization treatment unit 50A sinters the solidified body to perform denitration and pyrolysis treatment, remove impurity components (organic components, nitric acid components, moisture) in the solidified body, i.e., CHON components, and then sinters it. The sintering temperature is, for example, 600°C or higher and 800°C or lower.

The stabilization processing section 50A removes impurity components from the solidified body containing uranium, and then sinters it to obtain uranium oxide with a fluorite structure containing MA and Ln in solid solution. The stabilization device 16A removes some or all of the carbon, hydrogen, oxygen, and nitrogen components that may gasify during storage, and creates a fluorite structure of uranium dioxide containing MA and Ln, resulting in a solidified body with high thermal and chemical stability.

The storage device 18 stores the stabilized treated material. The storage device 18 includes a storage section 60. The storage section 60 stores the stabilized MA-containing material in a solid state. The storage section 60 is, for example, a cask. The storage section 60 may also be provided underground, and the stabilized treated material may be buried underground.

In the processing device 10A of this embodiment, extraction and back-extraction are performed in the extraction device 12A, a solution containing MA in the liquid phase is processed, uranium is supplied, and a fluorite structure of uranium dioxide with MA and Ln fixed therein is formed in the stabilization device 16A.

The processing device 10A can simplify the device configuration by performing the heat treatment of the solidification stabilization device 13 in a single device. In addition, since the processing device 10A can perform multiple processes in a single device, it is possible to reduce the transportation of radioactive materials, making processing safer.

In addition, even when performing back extraction, by forming a fluorite structure, it is possible to obtain a long-term stable crystal structure as a solid after stabilization processing, and MA can be stored stably. Specifically, trivalent MA and Ln can be dissolved in the fluorite structure, making the stable fluorite structure even more stable. Furthermore, by forming a crystal structure using uranium, it is possible to obtain a structure that is free of unnecessary components such as Si, Na, Ca, etc., when the solid containing MA is reprocessed and used. This makes it possible to obtain a substance that is stabilized in a state that is easy to use when reprocessing. Furthermore, the processing device 10A can obtain various effects similar to those of the processing device 10.

It is preferable that the uranium supply unit 44 of the processing device 10, 10A supplies uranium in an amount equal to or greater than the total molar amount of minor actinides and lanthanides contained in the liquid extracted by the extraction device. This allows for a more stable structure than the fluorite structure of the solid material during storage.

Next, an example of a solidification stabilization processing unit will be described with reference to FIG. 3. FIG. 3 is a schematic diagram showing an example of a solidification stabilization processing unit. The solidification stabilization processing unit 100 shown in FIG. 3 is a unit in the solidification stabilization device that performs processing after adding uranium, i.e., heating processing. In other words, the solidification stabilization processing unit 100 is the portion of the solidification device 14 (14A) and stabilization device 16 (16A) excluding the uranium supply unit 40.

The solidification stabilization processing unit 100 (hereinafter also referred to as the processing unit 100) processes the target material in a continuous manner to produce a stabilized solid material. The processing unit 100 includes a rotating drum 102, a heating furnace 104, a supply unit 106, a circulating gas supply unit 108, and a combustion air supply unit 110. The supply unit 106 supplies the target material to the rotating drum 102, i.e., the liquid extracted by the extraction devices 12, 12A and the uranium supplied from the uranium supply units 44, 44A.

The rotating drum 102 is a so-called rotary kiln that conveys the object toward the heating furnace 104 while rotating. The rotating drum 102 is rotated by a drive source around the center of the drum as an axis. The rotating drum 102 conveys the object to be treated from one side to the other. The rotating drum 102 has an object conveying area that is divided into a distillation section 130 (hydrothermal treatment section 130A), a heat treatment section 132, and a reduction section 134 from the upstream side to the downstream side in the conveying direction. The treatment section 100 becomes the distillation section 130 when producing an MA extract as shown in FIG. 1, and becomes the hydrothermal treatment section 130A when producing an MA stripping agent as shown in FIG. 2. The position at which it is divided is not particularly limited. The rotating drum 102 passes the object through the distillation section 130 (hydrothermal treatment section 130A), the heat treatment section 132, and the reduction section 134 by moving the object from the upstream side to the downstream side. In addition, the rotating drum 102 has a structure in which the area corresponding to the distillation section 130 (hydrothermal treatment section 130A) can transport liquid.

The heating furnace 104 is a heat source for the processing section 100, and is connected to the end of the outlet side of the rotating drum 102. The heating gas supply section 110 supplies gas, such as heated air or nitrogen, that heats the rotating drum 102. The heating furnace 104 may supply air and fuel to be burned in the heating furnace 104 from the heating gas supply section 110 and burn them in the heating furnace 104. The heating furnace 104 increases the temperature inside the furnace with the heating gas, and radiant heat 112 from the furnace walls and structures arranged in the furnace is supplied to the rotating drum 102. The heating furnace 104 supplies heat to each of the distillation section 130 (hydrothermal processing section 130A), heat treatment section 132, and reduction section 134 of the rotating drum 102, and heats the treatment object in each area to a predetermined temperature. In addition, the heating furnace 104 discharges the heating gas and the gas that has passed through the rotating drum 102 as exhaust gas 114.

The circulating gas supply unit 108 supplies gas into the rotating drum 102, with the gas flowing from the supply unit 106 toward the heating furnace 104. The circulating gas is preferably an inert gas.

The rotary drum 102 is also provided with a diluted gas recovery section 120, an oxidizing gas supply section 122, a reducing gas supply section 126, and an exhaust gas recovery section 128. The diluted gas recovery section 120 is connected to the downstream end of the distillation section 130 of the rotary drum 102. The diluted gas recovery section 120 is used when an MA extract is used. The diluted gas recovery section 120 recovers gas containing the components of the diluted liquid that have been heated and evaporated in the distillation section 130. The diluted gas recovery section 120 recovers the components of the diluted liquid from the recovered gas. When a portion of the upstream side of the rotary drum 102 is used as the hydrothermal treatment section 130A, the rotary drum 102 can be configured without the diluted gas recovery section 120. The oxidizing gas supply section 122 is disposed at the upstream end of the thermal treatment section 132 of the rotary drum 102, and supplies oxidizing gas to the rotary drum 102. The reducing gas supply section 126 is disposed at the upstream end of the reducing section 134 of the rotating drum 102 and supplies reducing gas to the rotating drum 102. The exhaust gas recovery section 128 recovers the exhaust gas discharged from the heating furnace 104.

The processing section 100 transports the object to be processed on the rotating drum 102 while heating it in each area, and further supplies and collects the necessary gas in each area, allowing the solidification and stabilization of the object to be processed to be performed in a single device in a continuous manner. This allows the heat source within the device to be used effectively, and eliminates the need to transport the object to be processed separately for each process.

In addition, the processing unit 100 processes the object to be processed while rotating it on the rotating drum 102, and the supply unit 106 can suitably attach the solidified material formed by evaporating the dilution liquid to the uranium particles supplied to the rotating drum 102 together with the liquid extracted by the extraction devices 12 and 12A, thereby making the processed material with a fluorite structure into granules. This allows the product to have a granular structure that is easy to manage.

The processing unit 100 may extract components to be used as a diluent from the gas recovered by the exhaust gas recovery unit 128 without providing the diluent gas recovery unit 120.

Here, the solidification and stabilization processing unit 100 shown in FIG. 3 is a rotary kiln, but the structure is not limited to this. In addition, the heat source may be a heating element wrapped around a rotating drum, or heated inert gas may be supplied.

Here, in FIG. 3, an example of a solidification stabilization processing unit that performs continuous processing has been described, but a batch-type processing may also be performed. An example of a batch-type solidification stabilization processing unit will be described using FIG. 4. FIG. 4 is a schematic diagram showing an example of a solidification stabilization processing unit.

The solidification and stabilization processing unit 200 (hereinafter also referred to as processing unit 200) shown in FIG. 4 processes the target object in a batch manner to produce a stabilized solid object. The processing unit 200 includes a base unit 212, a support unit 214, a drive unit 216, a container 218, and a heat source 220.

The base 212 is a base formed at a position where the processing unit 200 is installed. The support 214 is fixed to the base 212 and supports the drive unit 216 and the container 218. The support 214 supports the drive unit 216 and the container 218 in a state where they can rotate freely around the rotation axis of the drive unit 216. The support 214 may also support the drive unit 216 and the container 218 so that they can rotate around an axis perpendicular to the rotation axis of the drive unit 216. The drive unit 216 is fixed to the support 214 and rotates the container 218. The container 218 is introduced with the object to be processed. The container 218 is provided with a lid, and the inside can be sealed. The inner surface of the container 218 is a curved surface that is convex to the bottom surface. The container 218 is supported by the support 214 with the central axis from the bottom of the container to the lid inclined relative to the vertical direction. The heat source 220 heats the container 218. The heat source 220 is disposed vertically below the container 218 and heats the container 218 from the outer periphery of the container 218.

In addition, the container 218 is connected to an exhaust gas recovery unit 120A, an oxidizing gas supply unit 122A, a reducing gas supply unit 126A, and an exhaust gas recovery unit 128A. The exhaust gas recovery unit 120A recovers gas containing components of the liquid evaporated by the hydrothermal reaction. The oxidizing gas supply unit 122A supplies an oxidizing gas to the container 218. The reducing gas supply unit 126A supplies a reducing gas to the container 218. The exhaust gas recovery unit 128A recovers the exhaust gas discharged from the container 218.

The processing unit 200 starts processing by introducing the object to be processed, that is, the liquid extracted by the extraction device 12, 12A, and the uranium supplied from the uranium supply unit 44, 44A, into the container 218. The processing unit 200 may be equipped with a device for introducing the object to be processed and a device for opening and closing the lid of the container. The processing unit 200 puts the object to be processed into the container 218, closes the lid, and then heats the container 218 with the heat source 220 while rotating it with the drive unit 216. The processing unit 200 performs each process by switching the temperature and the gas supplied for each of the heating process, pyrolysis process, and reduction process.

As a result, the processing section 200 can perform solidification and stabilization processing of the processing object in a single device, and in a batch manner. This allows for efficient use of a single heat source, and eliminates the need to transport the processing object for each process.

In addition, by rotating the object to be treated in the container 218 while treating it, the treatment section 200 can favorably attach the solidified material formed by evaporating the dilution liquid to the uranium particles contained in the object to be treated, and can turn the treated material with a fluorite structure into granules. This allows the product to have a granular structure that is easy to manage.

Although the present invention has been described above with reference to the embodiments, the present disclosure is not limited to the above embodiments. Each configuration and their combinations in the above embodiments are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible without departing from the spirit of the present invention.

10, 10A Processing system (high-level radioactive material processing system)
12, 12A Extraction device 13, 13A Solidification and stabilization device 14, 14A Solidification device 16, 16A Stabilization device 18 Storage device 22 Waste liquid supply section 24 Extractant supply section 26 Dilution liquid supply section 28 MA extract liquid production section 30 MA stripping liquid production section 34 Hydrothermal treatment accelerator supply section 40, 40A Solidification treatment section 44, 44A Uranium supply section 45, 45A Distillation section 46, 46A Heat treatment section 47, 47A Dilution liquid recovery section 48, 48A Oxidizing gas supply section 49, 49A Exhaust gas recovery section 50, 50A Stabilization treatment section 52, 52A Reduction section 54, 54A Reduction gas supply section 56, 56A Exhaust gas recovery section 60 Storage section 100, 200 Solidification and stabilization section REFERENCE SIGNS LIST 102 Rotating drum 104 Heating furnace 106 Supply section 108 Circulating gas supply section 110 Heating gas supply section 112 Radiant heat 120, 120A Diluted gas recovery section 122, 122A Oxidizing gas supply section 126, 126A Reducing gas supply section 128, 128A Exhaust gas recovery section 130 Distillation section 130A Hydrothermal treatment section 132 Heat treatment section 134 Reduction section 212 Foundation section 214 Support section 216 Drive section 218 Container 220 Heat source

Claims (12)

a uranium supply unit that supplies uranium to the liquid from which at least one of minor actinides and lanthanides has been extracted;
a solidification and stabilization treatment section which performs, in a single apparatus, a solidification treatment in which uranium is supplied, the liquid from which the minor actinides and the lanthanoids have been extracted is heated to evaporate a portion of the liquid, and then further heated to create a solidified body; and a stabilization treatment in which the solidified body thus created is sintered to remove some or all of the carbon, hydrogen, oxygen, and nitrogen components, and a fluorite structure of uranium dioxide having the minor actinides and the lanthanoids incorporated therein is created. The high-level radioactive material processing system according to claim 1, wherein the solidification and stabilization processing unit performs solidification and stabilization processing in a batch manner. The high-level radioactive material processing system according to claim 1, wherein the solidification and stabilization processing unit performs solidification and stabilization processing in a continuous manner. The high-level radioactive material processing system according to any one of claims 1 to 3, wherein the solidification and stabilization processing unit is provided with an oxidizing gas supply unit that supplies oxygen or air during the solidification process. The high-level radioactive material processing system according to any one of claims 1 to 4, wherein the solidification and stabilization processing unit is provided with a reducing gas supply unit that supplies reducing gas during stabilization processing. The high-level radioactive material processing system according to any one of claims 1 to 5, wherein the uranium supply unit supplies uranium in an amount equal to or greater than the total molar amount of the minor actinides and the lanthanides contained in the extracted liquid. an extraction device that uses an organic solvent liquid to extract the minor actinides and the lanthanides from a liquid containing a high-level radioactive material, extracts the organic solvent containing the minor actinides and the lanthanides, and supplies a dilution liquid to produce a diluted liquid;
The high-level radioactive material processing system according to claim 1 , wherein the uranium supply unit adds a uranium complex that dissolves in the organic solvent to the liquid. The high-level radioactive material processing system according to claim 7, wherein the diluting liquid has a boiling point of 30°C or higher and 100°C or lower. The high-level radioactive material processing system according to claim 7 or claim 8, wherein the diluting liquid has no flash point or has a flash point of 150°C or higher. an extraction device for extracting the minor actinides and the lanthanides from a liquid containing high-level radioactive materials using an organic solvent liquid, and then mixing the extracted organic solvent with a diluent containing a liquid-phase stripping agent to generate a liquid in which the minor actinides and the lanthanides have been transferred to the diluent containing the liquid-phase stripping agent;
7. The high-level radioactive material processing system according to claim 1, wherein the uranium supply unit adds uranium ions that dissolve in a liquid phase to the liquid. The high-level radioactive material processing system according to claim 10 , wherein the solidification and stabilization processing section creates a solidified body by a heat treatment. Supplying uranium to the liquid from which at least one of minor actinides and lanthanides has been extracted;
A high-level radioactive material processing method comprising the steps of: a solidification treatment in which uranium is supplied, and a liquid from which the minor actinides and the lanthanoids have been extracted is heated to evaporate a portion of the liquid, and then further heated to create a solidified body; and a stabilization treatment in which the solidified body thus created is sintered to remove some or all of the carbon, hydrogen, oxygen, and nitrogen components, and to create a fluorite structure of uranium dioxide having the minor actinides and the lanthanoids incorporated therein, in a single apparatus.

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