High-level radioactive material treatment system and high-level radioactive material treatment method

Abstract

To solidify a larger amount of minor actinoids with high workability.SOLUTION: A high-level radioactive substance treatment device performs treatment of a high-level radioactive substance containing minor actinoids, and includes a liquid supply unit that supplies liquid containing the high-level radio active substance, an extractant supply unit that supplies an organic phase extractant, a diluent supply unit that supplies diluent; and an MA extract generation unit that mixes the liquid, extractant, and diluent and extracts at least one of the minor actinoids and lanthanoid included in the high-level radio active substance into an extract. When the liquid containing the high-level radioactive substance includes neptunium, the MA extract generation unit performs oxidation-reduction treatment to adjust the valence of neptunium to quadrivalence or hexavalence. The extractant is a material composed of C, H, O, N.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a high-level radioactive substance treatment system and a high-level radioactive substance treatment method.

Background Art

[0002] As a method for treating high-level radioactive waste, there is a method of extracting minor actinides, which are radioactive substances, from high-level radioactive substances (for example, Patent Document 1, Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By extracting minor actinides from high-level radioactive substances, the extracted minor actinides can be reused as fuel in a fast breeder reactor or the like. Further, by removing minor actinides, it becomes possible to reduce the treatment load of waste. Here, minor actinides have different properties with respect to solvent extraction depending on the valence, but it is required to extract them efficiently and in a simple process.

[0005] The present disclosure has been made in view of the above, and an object thereof is to provide a high-level radioactive substance treatment system and a high-level radioactive substance treatment method that have high workability and can solidify more minor actinides.

Means for Solving the Problems

[0006] To solve the above-mentioned problems and achieve the objective, this disclosure provides a high-level radioactive material processing apparatus for processing high-level radioactive materials containing minor actinides, comprising: a liquid supply unit for supplying a liquid containing the high-level radioactive material; an extractant supply unit for supplying an organic phase extractant; a diluent supply unit for supplying a diluent; and an MA extractant generation unit for mixing the liquid, the extractant, and the diluent, and extracting at least one of the minor actinides and lanthanides contained in the high-level radioactive material into the extractant, wherein the MA extractant generation unit adjusts the valence of neptunium to tetravalent or hexavalent by redox treatment if the liquid containing the high-level radioactive material contains neptunium, and the extractant is a material composed of the four elements C, H, O, and N.

[0007] To solve the above-mentioned problems and achieve the objective, this disclosure provides a method for processing high-level radioactive materials containing minor actinides, comprising the steps of: adjusting the valence of neptunium to tetravalent or hexavalent by redox treatment when the liquid containing the high-level radioactive material contains neptunium, and adding an organic phase extractant and a diluent; mixing the liquid, the extractant and the diluent, and extracting at least one of the minor actinides and lanthanides contained in the high-level radioactive material into the extractant, wherein the extractant is a material composed of the four elements C, H, O, and N. [Effects of the Invention]

[0008] According to this disclosure, a larger number of minor actinides can be solidified with high workability. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram showing the general configuration of the high-level radioactive material processing device of this embodiment. [Figure 2] Figure 2 is a schematic diagram showing the test conditions for the isolation of neptunium, one of the minor actinides. [Figure 3]Figure 3 is a graph showing an example of the separation results for neptunium among the minor actinides. [Modes for carrying out the invention]

[0010] Embodiments of the high-level radioactive material processing apparatus according to this disclosure will be described in detail below with reference to the drawings. The high-level radioactive material processing apparatus of this disclosure extracts MA (minor actinides) from high-level radioactive materials and stabilizes them by vitrification. In addition, if the high-level radioactive material contains lanthanides, the high-level radioactive material processing apparatus also extracts lanthanides along with the minor actinides. In this disclosure, "MA (minor actinides)" refers to transuranic elements belonging to actinides, excluding Pu. "Actinides" is a general term for elements with atomic numbers 89 to 103. Minor actinides include, for example, Np (neptunium), Am (americium), and Cm (curium). "Ln (lanthanides)" is a general term for elements with atomic numbers 57 to 71.

[0011] Figure 1 is a schematic diagram showing the general configuration of the high-level radioactive material processing device of this embodiment. The high-level radioactive material processing device (processing device) 10 shown in Figure 1 includes an extraction device 12, a solidification device 14, a stabilization device 16, and a storage device 18. The processing device of this embodiment will be described assuming that high-level radioactive waste (hereinafter also referred to as "HALW") is used as the high-level radioactive material. The waste liquid is, for example, the liquid remaining after recovering U (uranium) and Pu (plutonium) from the spent nuclear fuel solution 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"), as well as MA and lanthanides. Specifically, high-level radioactive waste (hereinafter also referred to as "HALW") includes the waste liquid produced in reprocessing by the PUREX method. In the PUREX process, a nitric acid solution containing uranium (U) and pulp (Pu) is brought into contact with and mixed with tributyl phosphate (TBP) and an organic solvent such as dodecane. This causes the U and Pu in the nitric acid solution to form complexes with TBP and migrate to the organic solvent side. Meanwhile, fission products (FP), mineral admixture (MA), and linum (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 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 extractant generation unit 28. The waste liquid supply unit 22 stores HALW, which is liquid high-level radioactive waste, and supplies it to the MA extractant generation unit 28. In this embodiment, an extractant supply unit 24 and a 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 an organic solvent in the liquid phase in which the extractant is dissolved.

[0013] The extractant supply unit 24 supplies the extractant to the MA extract solution generation unit 28. The extractant captures MA and Ln. The extractant is also a liquid that migrates to the diluent and mixes uniformly. As the extractant, for example, a complexing agent that forms a complex with MA and Ln can be used. It is preferable that the complexing agent is less expensive than a complexing agent that selectively forms a complex with MA. As the extractant, a material composed of the four elements C, H, O, and N is preferred. It is more preferable to use a diglycolamide (DGA)-based material (complexing agent) as the extractant. Specific examples of complexing agents include N,N,N',N'-tetraoctyl-3-oxapentanediamide (TODGA) and tetra(2-ethylhexyl)diglycolamide (T2EHDGA). The extractant may be used alone or in combination of two or more types.

[0014] The diluent supply unit 26 supplies the diluent to the MA extractant generation unit 28. The diluent is an organic phase material insoluble in the liquid components of the waste liquid. The diluent has the property of eluting the extractant from the liquid of the waste liquid. The diluent has a boiling point of 100°C or less. Preferably, the diluent has no flash point or a flash point of 150°C or higher. Furthermore, it is preferable that the diluent is a material that does not degrade easily due to heat or radiation even when reused, and preferably a solvent having a hydrocarbon structure that does not degrade easily due to heat or radiation even when reused. Here, "not degrading easily due to heat or radiation even when reused" means that even if it becomes a low molecular weight structure due to the energy of heat or radiation, it has the property of not easily forming complexes with metal ions. Furthermore, it is preferable that the diluent has a low environmental impact, such as a global warming potential and ozone depletion potential. Specifically, it is preferable that the diluent has a global warming potential of 2000 or less and an ozone depletion potential of 0.01 or less. For example, hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs) can be used as diluents.

[0015] The MA extract generation unit 28 is supplied with waste liquid, extractant, and diluent. If the waste liquid contains neptunium, the MA extract generation unit 28 processes the waste liquid. , return The valence of MA was adjusted by the original treatment, and pentavalent neptunium was 4 price The MA extract generation unit 28 reduces pentavalent neptunium to tetravalent neptunium, for example, by electrolysis and the addition of a reducing agent. Here, it is preferable to add hydrazine during the valency adjustment process in the MA extract generation unit 28. By adding hydrazine, the valency of neptunium can be stabilized. It is also preferable to perform the necessary valency adjustment for other MAs.

[0016] In the MA extract generation unit 28, when MA and Ln in the waste liquid, whose neptunium valency has been adjusted by solvent extraction, come into contact with the extractant, 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 generation unit 28 separates the diluent from the waste liquid to produce an MA extract in which the extractant containing MA and Ln is encapsulated in the diluent. The MA extract generation unit 28 may be a continuous type in which each material is continuously supplied to produce the MA extract, or a batch type in which each material is supplied intermittently to produce the MA extract. Furthermore, the MA extract generation unit 28 may selectively capture MA with the extractant, or capture and process MA and Ln simultaneously.

[0017] The solidification unit 14 removes the liquid component of the MA extract and produces a solidified body. The solidification unit 14 includes a solidification section 40 and a recovery section 42. The solidification section 40 distills the MA extract to remove the diluent component. By distilling the diluent, the solidification section 40 leaves a solidified residue containing the extractant and MA as a complex. The residue becomes a solidified body. The solidified body is an organometallic complex of the substance containing MA and the extractant. The solidification section 40 can use known evaporation methods such as batch or continuous (tray column or packed column) for the distillation process. The recovery section 42 collects the diluent distilled in the solidification section 40, cools it, and liquefies it to recover the diluent. The recovery section 42 supplies the recovered diluent to the diluent supply section 26. The recovery section 42 may also perform a removal process if impurities are mixed in the diluent.

[0018] The stabilization device 16 performs a stabilization treatment to remove some or all of the carbon, hydrogen, oxygen, and nitrogen components from the solidified body. The stabilization device 16 has a stabilization treatment unit 50. The stabilization treatment unit 50 oxidizes the object to be treated by heating, calcining, and sintering the solidified body. The stabilization device 16 stabilizes the solidified body by removing some or all of the carbon, hydrogen, oxygen, and nitrogen components, which may gasify during storage.

[0019] The storage device 18 stores the processed material after the stabilization treatment. The storage device 18 includes a storage unit 60. The storage unit 60 stores the substance containing the stabilized MA in a solid state. The storage unit 60 is, for example, a cask. Alternatively, the storage unit 60 may be provided underground, and the processed material after the stabilization treatment may be buried underground.

[0020] The substance containing MA stored in the storage unit 60 of the processing system 10 can be used as fuel for a nuclear power generation system. When MA is burned as fuel, the stored oxide solidified body is dissolved to generate a solution containing MA and Ln (solidified body dissolution). Next, a purification process for MA is performed on the obtained solution (MA purification). In MA purification, for example, MA and Ln in the obtained solution are separated, and if necessary, highly exothermic MA is separated from MA. Next, the obtained MA (Np, Am, etc.) is mixed with U and Pu to obtain a mixed oxide, thereby manufacturing fuel (MA fuel manufacturing). The obtained fuel is burned in a fast breeder reactor or the like (MA combustion).

[0021] The processing device 10 of the present embodiment performs a separation process in the extraction device 12 to separate MA by allowing the coexistence of Ln in the waste liquid by adding an extractant and a diluent to the waste liquid and mixing them, thereby generating an MA extract. Next, the processing device 10 generates a solidified body containing MA by distilling the diluent from the MA extract in the solidification device 14. Next, the processing device 10 removes the organic components (CHON) from the solidified body containing MA in the stabilization device 16 to stabilize it. The processing device 10 stores the stabilized processed material in the storage device 18.

[0022] The processing device 10 adjusts the valence of neptunium to 4 Value and Furthermore, by using a material composed of the four elements C, H, O, and N, preferably a diglycolamide (DGA)-based material, as the extractant, MA containing neptunium can be efficiently transferred to the extractant and diluent side.

[0023] Figure 2 is a schematic diagram showing the test conditions for a test to separate neptunium from the minor actinides. Figure 3 is a graph showing an example of the separation results for neptunium from the minor actinides. Figure 3 measures the migration rate of tetravalent neptunium to the extractant layer. For comparison, the migration rate of pentavalent neptunium to the extractant layer was also measured. As shown in Figure 2, the test used tetra(2-ethylhexyl)diglycolamide (T2EHDGA), a DGA-based extractant, and HFC as a diluent. The extractant concentration was set to 0.1 to 10 mmol / l, and the nitric acid concentration in the liquid phase (aqueous phase) was set to 1 to 6 mol / l (3 mol / l and 5 mol / l in the test shown in the graph in Figure 3). The metal ion (neptunium) concentration was set to 0.05 mmol / l. 100 mmol / l of hydrazine was added.

[0024] Here, the chemical equilibrium that occurs during extraction from the waste liquid to the extractant layer is given by the following equation.

number

[0025] Furthermore, the distribution ratio is defined by the following formula.

number

[0026] The test results are shown in Figure 3. Figure 3 shows the distribution ratio (percentage of migration) D and the concentration of the extractant, diglycolamide (DGA), on a logarithmic axis. A higher value of D (logD) indicates a greater amount of migration to the extractant layer. As shown in Figure 3, it can be seen that when neptunium is in the tetravalent state, a higher rate of migration occurs to the extractant layer compared to when it is in the pentavalent state.

[0027] Here, the MA extract generation unit 28 preferably measures whether the waste liquid contains neptunium, performs valency adjustment only if the waste liquid contains neptunium, and does not perform valency adjustment if the waste liquid does not contain neptunium. Furthermore, the MA extract generation unit 28 may adjust the content of the valency adjustment process to be performed according to the distribution of the valency of neptunium contained in the waste liquid, for example, , return It is preferable to adjust the amount of the drug introduced at the source. The MA extract generation unit 28 may always perform the same valency adjustment process without measuring whether or not the waste liquid contains neptunium.

[0028] Furthermore, the processing device 10 separates, solidifies, and stabilizes Ln and MA. This allows for efficient extraction of MA from liquid high-level radioactive waste, reducing the waste disposal burden and enabling solidification. Additionally, by extracting and stabilizing MA and Ln into a stable substance, MA can be stored stably even when it is intended for reuse as fuel.

[0029] Furthermore, by processing MA and Ln without separating them, the process of separating MA and Ln becomes unnecessary, thus reducing the processing load.

[0030] Furthermore, in this embodiment, the processing apparatus 10 uses an organic solvent with a boiling point of 100°C or lower as the diluent, thereby reducing the processing load of distilling the diluent in the solidification processing unit 40. This reduces the process load.

[0031] Furthermore, it is preferable that the diluent has no flash point or has a flash point of 150°C or higher. By setting the flash point within the above range, the working conditions of the solidification processing unit 40 can be relaxed, and the possibility of ignition or combustion of the diluent during operation can be reduced. As a result, processing in the processing system 10 can be carried out more stably with high workability.

[0032] Furthermore, it is preferable that the diluent has a temperature difference of 50°C or more between its boiling point and flash point. This improves workability.

[0033] Furthermore, the diluent preferably has a hydrocarbon-based structure that is less susceptible to degradation by heat and radiation. This allows for the reuse of the recovered diluent, thereby increasing the economic efficiency of the extraction process. The diluent also preferably has a global warming potential of 2000 or less and an ozone depletion potential of 0.01 or less. This reduces the environmental burden when processing the used diluent. More preferably, the diluent contains at least one of hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs), as described above. Using the above substances as the diluent allows for easy mixing of the extractant and the diluent, making it easier to separate the liquid components of the wastewater. While the diluent preferably has the above components as its main components, it may also contain organic solvents such as alcohols with boiling points within the above range as secondary components.

[0034] Furthermore, the processing apparatus 10 of this embodiment is equipped with a recovery processing unit 42, which recovers the diluted solution evaporated during processing in the solidification processing unit 40 and supplies it to the diluted solution supply unit 26, thereby enabling the reuse of the diluted solution. In addition, as described above, by using a diluted solution with a boiling point within the above range, the processing load on the recovery processing unit 42 can be reduced.

[0035] Furthermore, the processing apparatus 10 preferably uses an extractant that does not form a third phase when producing an MA extract from highly radioactive materials containing nitrate-based substances. Specifically, it is preferable to use a DGA-based material. One example is T2EHDGA. In addition, it is preferable that the extractant be a material that can be removed during processing in the stabilization apparatus 16, specifically a material composed only of carbon, hydrogen, nitrogen, and oxygen. Furthermore, it is preferable that the extractant does not contain corrosive components.

[0036] Furthermore, although the processing apparatus of this embodiment underwent a stabilization treatment, it may also be stored without undergoing a stabilization treatment.

[0037] Although the present invention has been described above with reference to embodiments, this disclosure is not limited to the above embodiments. The configurations and combinations thereof in the above embodiments are examples, and additions, omissions, substitutions, and other modifications are possible without departing from the spirit of the present invention. [Explanation of Symbols]

[0038] 10. Processing System (High-Level Radioactive Material Processing System) 12 Extraction device 14 Solidification equipment 16 Stabilizer 18 Storage device 22 Wastewater supply section 24 Extractant supply unit 26 Diluent supply unit 28 MA extract generation section 40 Solidification Processing Unit 42 Recovery Processing Unit 50 Stabilization Processing Unit 60 Storage Department

Claims

1. A high-level radioactive material processing system for processing high-level radioactive materials containing minor actinides, This is the liquid remaining after recovering uranium and plutonium from the solution of spent nuclear fuel. A liquid supply unit that supplies the liquid containing the aforementioned high-level radioactive material, An extractant supply unit that supplies organic phase extractants, A diluent supply unit that supplies the diluent, The system includes an MA extractant generation unit that mixes the liquid, the extractant, and the diluent to extract the minor actinides contained in the high-level radioactive material into the extractant, The MA extract generating unit, when the liquid containing the high-level radioactive material contains neptunium, adds hydrazine as a valency stabilizer and then performs a reduction treatment to adjust the valency of neptunium so that its main valency becomes 4. When the liquid containing the high-level radioactive material does not contain neptunium, no valency adjustment is performed. The extractant is a material composed of four elements C, H, O, and N, and is a diglycolamide (DGA) type material, in a high-level radioactive material processing system.

2. The high-level radioactive material processing system according to claim 1, wherein the diluent has a boiling point of 100°C or less.

3. The high-level radioactive material treatment system according to claim 1 or claim 2, wherein the diluent has no flash point or has a flash point of 150°C or higher.

4. The high-level radioactive material treatment system according to any one of claims 1 to 3, wherein the diluent contains a solvent having a hydrocarbon structure that makes it difficult for decomposition products due to heat or radiation to form complexes with metal ions.

5. The diluent has a global warming potential of 2000 or less and an ozone depletion potential of 0.01 or less, according to any one of claims 1 to 3.

6. The high-level radioactive material treatment system according to any one of claims 1 to 5, wherein the diluent contains at least one of hydrofluorocarbon and hydrofluoroolefin.

7. The high-level radioactive material processing system according to any one of claims 1 to 6, wherein the MA extractant generation unit is continuously supplied with a liquid containing high-level radioactive material, an organic phase extractant, and a diluent, and continuously generates an MA extractant in which the minor actinides have been extracted into the extractant.

8. A solidification processing unit which evaporates a diluent from the MA extract produced in the MA extract production unit to produce a solid containing MA, A high-level radioactive material processing system according to any one of claims 1 to 6, further comprising a solidification apparatus having a recovery processing unit that recovers the diluent evaporated in the solidification processing unit and supplies it to the diluent supply unit.

9. A method for processing high-level radioactive materials containing minor actinides, The liquid obtained after recovering uranium and plutonium from the solution of spent nuclear fuel contains high-level radioactive material. If the liquid contains neptunium, hydrazine is added as a valence stabilizer, and the valence of neptunium is adjusted by reduction treatment so that its main valence is 4. Then, an organic phase extractant and a diluent are added. If the liquid containing high-level radioactive material does not contain neptunium, no valence adjustment is performed, and the organic phase extractant and a diluent are added. The step includes mixing the liquid, the extractant, and the diluent to extract the minor actinides contained in the high-level radioactive material into the extractant, A method for treating high-level radioactive materials, wherein the extractant is a material composed of four elements C, H, O, and N, and is a diglycolamide (DGA) type material.

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