High-level radioactive matter processing system, and high-level radioactive matter processing method

Abstract

To enable reducing of a generation amount of waste fluid in extraction and back-extraction operation of minor actinoid.SOLUTION: A high-level radioactive matter processing method includes: an extraction unit that uses an organic solvent serving as a diluted solution and an extraction agent to extract minor actinoid and lanthanoid from liquid containing high-level radioactive matter to the organic solvent; a concentration processing unit that reduces the organic solvent of the organic solvent including the minor actinoid and lanthanoid generated by the extraction unit, and raises concentration of the actinoid and lanthanoid of the organic solvent; and a back-extraction unit that mixes the organic solvent including the minor actinoid and lanthanoid concentrated by the concentration processing unit, and a diluted solution of a liquid phase including a back-extraction agent of the liquid phase, and generates liquid making the minor actinoid and lanthanoid move to the diluted liquid including the back-extraction agent of the liquid phase.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a high-level radioactive material processing system and a high-level radioactive material processing method. [Background technology]

[0002] 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 (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-185338 A Summary of the Invention [Problem to be solved by the invention]

[0004] By extracting minor actinides from high-level radioactive materials, the extracted minor actinides can be reused as fuel for fast breeder reactors and the like. In addition, by removing the minor actinides, it becomes possible to reduce the waste treatment load. Here, when performing a stripping process to move the extracted minor actinides from the organic phase to the aqueous phase, the higher the extraction capacity of the extractant used for minor actinides, the more it is necessary to reduce the aqueous phase concentration during stripping, which results in a problem that a large amount of treatment liquid is used and a large amount of waste liquid is also generated.

[0005] The present disclosure has been made in consideration of the above, and has an object to provide a high-level radioactive material treatment system and a high-level radioactive material treatment method that can reduce the amount of waste liquid generated in extraction and stripping operations of minor actinides. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the present disclosure provides a high-level radioactive material treatment device, comprising: an extraction unit that extracts the minor actinides and the lanthanoids from a liquid containing high-level radioactive material into an organic solvent using an organic solvent that is a diluent and an extractant; a concentration treatment unit that reduces the organic solvent containing the minor actinides and the lanthanoids produced in the extraction unit and increases the concentrations of the minor actinides and the lanthanoids in the organic solvent; and a back-extraction unit that mixes the organic solvent containing the minor actinides and the lanthanoids concentrated in the concentration treatment unit with a liquid-phase diluent containing a liquid-phase stripping agent, and generates a liquid in which the minor actinides and the lanthanoids have been transferred to the diluent containing a liquid-phase stripping agent.

[0007] In order to solve the above-mentioned problems and achieve the object, the present disclosure provides a method for treating high-level radioactive material, the method including: an extraction step of extracting the minor actinides and the lanthanoids from a liquid containing high-level radioactive material into an organic solvent using an organic solvent as a diluent and an extractant; a concentration step of reducing the organic solvent containing the minor actinides and the lanthanoids produced in the extraction step and increasing the concentrations of the minor actinides and the lanthanoids in the organic solvent; and a stripping step of mixing the organic solvent containing the minor actinides and the lanthanoids concentrated in the concentration step with a liquid-phase diluent containing a liquid-phase stripping agent, to generate a liquid in which the minor actinides and the lanthanoids have been transferred to the diluent containing a liquid-phase stripping agent. Effect of the Invention

[0008] According to the present disclosure, it is possible to reduce the amount of waste liquid generated in the extraction and stripping operations of minor actinides. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of a high-level radioactive material treatment apparatus according to this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, 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. Furthermore, when lanthanides are contained in the high-level radioactive material, the high-level radioactive material treatment device extracts lanthanides as well as minor actinides. In the present disclosure, "MA (minor actinides)" refers to transuranium elements belonging to 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 (lanthanoids)" is a general term for elements with atomic numbers from 57 to 71.

[0011] FIG. 1 is a schematic diagram showing a schematic configuration of a 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. The treatment device 10 may further include a mechanism for treating the radioactive material extracted by the extraction device 12. The treatment device 10 of this embodiment will be described as using high-level radioactive liquid waste (hereinafter also referred to as "HALW") as the high-level radioactive material, similar to the treatment device 10. The waste liquid is, for example, a liquid remaining after U (uranium) and Pu (plutonium) are recovered from a solution of spent nuclear fuel in the reprocessing of spent nuclear fuel discharged from a light water reactor. The high-level radioactive waste contained in the waste liquid includes fission products (hereinafter also referred to as "FP"), MA, and lanthanoids. Specifically, the HALW is a waste liquid generated in reprocessing by 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.

[0012] The extraction apparatus 12 extracts MA components from the waste liquid. The extraction apparatus 12 includes a waste liquid supply unit 22, an extractant supply unit 24, a dilution liquid supply unit 26, an MA extract liquid production unit 28, a concentration treatment unit 29, an MA strip-extraction liquid production unit 30, a strip-extraction agent supply unit 32, and a separation unit 36. 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.

[0013] 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 cheaper than the complexing agent that selectively forms a complex with MA. Examples of the extractant 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). It is preferable to use a DGA-based material (complexing agent) as the extractant. Specific examples of the complexing agent include N,N,N',N'-tetraoctyl-3-oxapentanediamide (TODGA), tetra(2-ethylhexyl)diglycolamide (T2EHDGA), etc. The extracting agent may be used alone or in combination of two or more kinds.

[0014] The diluent supply unit 26 supplies the diluent (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 the 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 organic solvent serving as the diluent is separated from the MA in the MA stripping liquid production unit 30 and then made into a reusable liquid.

[0015] 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 are brought 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 is a liquid in which the extractant that has captured MA and Ln is mixed with an organic solvent that is a diluent. The MA extract generating unit 28 may be a continuous type in which each material is continuously supplied to generate the MA extract, or a batch type in which each material is intermittently supplied to generate the MA extract. 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.

[0016] The concentration processor 29 reduces the organic solvent in the MA extract produced in the MA extract production unit 28, thereby increasing the concentrations of MA and Ln in the MA extract. The concentration processor 29 in this embodiment is a distillation apparatus that heats the MA extract to evaporate the organic solvent, i.e., performs distillation. The concentration processor 29 supplies the MA extract from which the organic solvent has been reduced, i.e., from which MA and Ln have been concentrated, to the MA strip-extract production unit 30. The concentration processor 29 may use a method in which the organic solvent in the MA extract is separated using a filter that allows the organic solvent to pass but does not allow MA, Ln, etc. to pass, thereby increasing the concentrations of MA, Ln, etc.

[0017] The MA stripping liquid production unit 30 is supplied with the MA extract from the MA extract production unit 28 and with the stripping agent from the stripping agent supply unit 32 .

[0018] The stripping agent supply unit 32 supplies a substance that transfers MA and Ln from the MA extraction liquid to the liquid phase as a stripping agent. The stripping agent is, for example, nitric acid. The stripping agent is diluted with a liquid diluent, for example, water.

[0019] The MA stripping solution 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 extractor 12 may reuse the organic solvent (extractant and diluent) in the MA extract after treatment. The MA stripping solution generator 30 controls the acid concentration of the liquid and the amount of stripping solution to set the component ratio during treatment in the solidification process 14 to a predetermined ratio.

[0020] The separation unit 36 ​​recovers the organic solvent separated from the MA extract in the concentration treatment unit 29, and supplies it to the diluent supply unit 26. The separation unit 36 ​​in this embodiment liquefies the organic solvent vaporized in the concentration treatment unit 29, and removes impurities.

[0021] In the processing device 10 of this embodiment, an MA extract is produced in the extraction device 12, and then a concentration process is performed in the concentration processing unit 29 to reduce the amount of organic solvent in the MA extract. This makes it possible to reduce the amount of MA extract supplied to the MA strip-extraction production unit 30, and therefore the amount of organic solvent that comes into contact with the aqueous phase in the MA strip-extraction production unit 30. Furthermore, because the amount of MA extract supplied to the MA strip-extraction production unit 30 can be reduced and the concentration of MA is high, stripping can be performed efficiently and the amount of dilution liquid for the liquid phase can be reduced. The amount of liquid used in the extraction device 12 can be reduced, and therefore the amount of liquid discharged as waste liquid can be reduced.

[0022] Specifically, the stripping process performed in the MA stripping solution generating unit 30 of the extraction device 12 utilizes distribution equilibrium to transfer MA and La in the organic phase (org) to the aqueous phase (aq). org / C aq The organic solvent and water are set in a combination that maximizes the concentration of solutes (C) (C is the total concentration of the solute), but there are limitations. In addition, MA, etc. can be transferred to the aqueous phase by increasing the amount of contact aqueous phase, but this increases the amount of aqueous phase. In response to this, the treatment device 10 is provided with a concentration treatment unit 29, and by increasing the concentration of the MA, etc. to be extracted in the MA extract, it is possible to increase the amount of MA, etc. transferred to the aqueous phase without increasing the amount of aqueous phase in contact with the organic phase. This makes it possible to reduce the amounts of both the organic solvent, which is the diluent for the organic phase, and the diluent (water, etc.) for back extraction.

[0023] Moreover, in the processing device 10 of this embodiment, the concentration processing unit 29 is a distillation process that evaporates the organic solvent, specifically, a heating mechanism that heats the organic solvent containing minor actinides and lanthanides. In this way, by concentrating the MA extract (processing to reduce the amount of organic solvent) by distillation, the concentration can be performed by a simple process. In addition, since the concentration can be performed by a heating process, a filter used for filtration, etc. is not required, and it is possible to suppress the generation of radioactive waste due to contact with radioactive materials.

[0024] The organic solvent used as the diluent in this embodiment preferably has a boiling point of 50° C. or more and 120° C. or less, and the extractant preferably has a thermal decomposition temperature of the diluent organic solvent or more. By using the organic solvent and extractant having the above characteristics, concentration can be suitably performed.

[0025] The concentration treatment unit 29 preferably heats the organic solvent containing the minor actinide and the lanthanide to a temperature equal to or higher than the boiling point of the organic solvent and equal to or lower than the thermal decomposition temperature of the extractant. As an example, the concentration treatment unit 29 preferably heats the organic solvent containing the minor actinide and the lanthanide to a temperature equal to or higher than 50° C. and equal to or lower than 120° C. By carrying out the heating treatment at the above temperatures, the organic solvent can be distilled while suppressing deterioration of the extraction performance and alteration of the extractant.

[0026] Moreover, the concentration processor 29 preferably reduces the amount of the organic solvent so that the concentrations of minor actinides and rhamnoides in the organic solvent become 2 to 10 times higher. By reducing the concentration by 2 or more, the amount of the MA strip-extraction solution during stripping can be suitably reduced, and by reducing the concentration by 10 or less, a reduction in the performance of transporting the MA extract to the MA strip-extraction solution generator 30 can be suppressed.

[0027] In addition, the organic solvent is preferably a flame-retardant solvent with low heat of vaporization, and the extractant is preferably an extractant composed of the elements C, H, N, and O. Furthermore, the organic solvent is preferably a hydrofluorocarbon, and the extractant is preferably N,N,N',N'-tetraoctyl-3-oxapentanediamide (TODGA) or tetra(2-ethylhexyl)diglycolamide (T2EHDGA). By using the above combination of organic solvent and extractant, the concentration treatment can be performed favorably, and the extraction of MA can be performed favorably.

[0028] The processing device 10 is provided with a separation section 36, and the organic solvent separated from the MA extract (an organic solvent containing minor actinides and the lanthanides) in the concentration processing section 29 is recovered in the separation section 36 and supplied to the diluent supply section 26, thereby making it possible to reuse the organic solvent and reduce the generation of waste liquid.

[0029] Here, the concentration processing unit 29 may perform the concentration process for reducing the dilution liquid of the MA extract and increasing the concentration of MA as a batch process or as a continuous process.

[0030] In addition, the processing apparatus 10 of the present embodiment may supply uranium, solidify it, and perform a stabilization process after stripping MA, after stripping MA, but the process after stripping MA is not limited to this.

[0031] Although the present invention has been described above by showing the embodiments, the present disclosure is not limited to the above embodiments. Each configuration and their combination in the above embodiments is an example, and addition, omission, substitution, and other modifications of the configuration are possible within the scope of the gist of the present invention.

[0032] The present disclosure discloses the following inventions, but is not limited to the following. (1) an extraction unit that extracts the minor actinides and the lanthanides from a liquid containing high-level radioactive materials into an organic solvent that is a diluent and an extractant; a concentration treatment unit that reduces the concentration of the organic solvent containing the minor actinides and the lanthanides produced in the extraction unit and increases the concentrations of the minor actinides and the lanthanides in the organic solvent; a stripping unit that mixes the organic solvent containing the minor actinide and the lanthanide concentrated in the concentration treatment unit with a liquid-phase dilution liquid containing a liquid-phase stripping agent, and generates a liquid in which the minor actinide and the lanthanide have been transferred to the dilution liquid containing the liquid-phase stripping agent.

[0033] (2) The high-level radioactive material treatment system according to (1), wherein the concentration treatment unit evaporates the organic solvent.

[0034] (3) The high-level radioactive material processing system according to (2), wherein the enrichment treatment unit is a heating mechanism that heats the organic solvent containing the minor actinide and the lanthanide.

[0035] (4) A high-level radioactive material treatment system as described in (3), wherein the organic solvent has a boiling point of 50°C or higher and 120°C or lower, and the extractant has a thermal decomposition temperature equal to or higher than the boiling point of the organic solvent used as a diluent.

[0036] (5) The high-level radioactive material processing system according to (4), wherein the enrichment treatment unit heats the organic solvent containing the minor actinide and the lanthanide to a temperature of 50° C. or higher and 120° C. or lower.

[0037] (6) A high-level radioactive material processing system according to any one of (1) to (5), wherein the concentration treatment unit reduces an amount of the organic solvent such that the concentrations of the minor actinides and the rhamnoides in the organic solvent are increased by a factor of 2 to 10.

[0038] (7) A high-level radioactive material treatment system described in any of (1) to (6), wherein the organic solvent is a solvent having flame retardant and low heat of vaporization properties, and the extractant is an extractant composed of the elements C, H, N, and O.

[0039] (8) A high-level radioactive material processing system according to any one of (1) to (7), further comprising a separation section that supplies to the extraction section an organic solvent separated from the organic solvent containing the minor actinide and the lanthanide in the enrichment treatment section.

[0040] (9) an extraction step of extracting the minor actinides and the lanthanides from a liquid containing high-level radioactive materials into an organic solvent as a diluent and an extractant; a concentrating step of reducing the organic solvent of the organic solvent containing the minor actinides and the lanthanides produced in the extraction step and increasing the concentrations of the minor actinides and the lanthanides in the organic solvent; a stripping step of mixing the organic solvent containing the minor actinide and the lanthanide concentrated in the concentrating step with a liquid-phase diluting solution containing a liquid-phase stripping agent, and generating a liquid in which the minor actinide and the lanthanide have been transferred to the diluting solution containing the liquid-phase stripping agent. [Explanation of symbols]

[0041] 10 Processing system (high-level radioactive material processing system) 12 Extraction device 22 Waste liquid supply section 24 Extractant supply section 26 Diluent supply section 28 MA extract generation section 29 Concentration processing section 30 MA reverse extraction liquid generation section 34 Hydrothermal Treatment Accelerator Supply Section 36 Separation part

Claims

1. an extraction unit that extracts minor actinides and lanthanides from a liquid containing highly radioactive materials into an organic solvent that is a diluent and an extractant; a concentration treatment unit that reduces the amount of organic solvent in the organic solvent containing the minor actinides and the lanthanoids produced in the extraction unit, thereby increasing the concentrations of the minor actinides and the lanthanoids in the organic solvent; a stripping unit that mixes the organic solvent containing the minor actinides and the lanthanoids concentrated in the concentration treatment unit with a liquid-phase dilution solution containing a liquid-phase stripping agent, and generates a liquid in which the minor actinides and the lanthanoids have been transferred to the dilution solution containing the liquid-phase stripping agent.

2. The high-level radioactive material processing system according to claim 1 , wherein the concentration treatment unit evaporates the organic solvent.

3. 3. The high-level radioactive material processing system according to claim 2, wherein the enrichment treatment unit is a heating mechanism that heats the organic solvent containing the minor actinides and the lanthanides.

4. The organic solvent has a boiling point of 50°C or higher and 120°C or lower, 4. The high-level radioactive material processing system according to claim 3, wherein the extractant has a thermal decomposition temperature equal to or higher than the boiling point of the organic solvent used as the diluent.

5. 5. The high-level radioactive material processing system according to claim 4, wherein the enrichment treatment unit heats the organic solvent containing the minor actinides and the lanthanides to a temperature of 50°C or higher and 120°C or lower.

6. 2. The high-level radioactive material processing system according to claim 1, wherein the concentration treatment unit reduces the amount of the organic solvent so that the concentrations of the minor actinides and the lanthanoids in the organic solvent are increased by a factor of 2 to 10.

7. The organic solvent is a flame-retardant solvent with a low heat of vaporization, 2. The high-level radioactive material processing system according to claim 1, wherein the extractant is an extractant composed of C, H, N, and O elements.

8. 2. The high-level radioactive material processing system according to claim 1, further comprising a separation section that supplies the organic solvent separated from the organic solvent containing the minor actinides and the lanthanoids in the enrichment processing section to the extraction section.

9. an extraction step of extracting minor actinides and lanthanides from a liquid containing highly radioactive materials into an organic solvent as a diluent and an extractant; a concentration step of reducing the organic solvent in the organic solvent containing the minor actinides and the lanthanoids produced in the extraction step, thereby increasing the concentrations of the minor actinides and the lanthanoids in the organic solvent; a stripping step of mixing the organic solvent containing the minor actinide and the lanthanide concentrated in the concentration step with a liquid-phase dilution solution containing a liquid-phase stripping agent, and producing a liquid in which the minor actinide and the lanthanide have been transferred to the dilution solution containing the liquid-phase stripping agent.

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