JP2021156851A - System and method for processing high-level radioactive material - Google Patents

Abstract

To reduce a process load and to extract a minor actinide with high workability.SOLUTION: Disclosed is a high-level radioactive material processing device which performs processing on the high-level radioactive material containing a minor actinide. The device includes: a liquid supply part for supplying liquid containing the high-level radioactive material; an extraction agent supply part for supplying an extraction agent of an organic phase; a diluent liquid supply part for supplying the dilution liquid; and an MA extraction liquid generation part for mixing the liquid, the extraction agent, and the dilution liquid, and extracting one of the minor actinide and lanthanoid contained in the high-level radioactive material into the extraction agent. The dilution liquid has a boiling point of 100°C or lower.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to high-level radioactive material treatment systems and high-level radioactive material treatment methods.

As a treatment of high-level radioactive waste, there is a method of extracting a minor actinide which is a radioactive substance from a high-level radioactive substance (for example, Patent Document 1 and Patent Document 2).

JP-A-2018-63198 Japanese Unexamined Patent Publication No. 2019-15533

By extracting minor actinides from high-level radioactive substances, the extracted minor actinides can be reused as fuel for fast breeder reactors and the like. In addition, by removing minor actinides, it is possible to reduce the waste treatment load. Here, since the treatment devices of References 1 and 2 use octanol or dodecane having a flash point (flammable liquid) as the diluent, the treatment device is used from the viewpoint of safety when treating minor actinides. The process load and work load become high because it is necessary to scaveng or depressurize the inside and treat it outside the combustion range. Similarly, when collecting and reusing the diluted solution or separating the minor actinide as a solid, it is necessary to perform the treatment in a non-flammable atmosphere from the viewpoint of safety. The process load and work load will increase due to the need for collection and solidification processing.

The present disclosure has been made in view of the above, and it is possible to extract a minor actinide, reuse a diluted solution, and solidify the minor actinide with reduced process load and high workability. It is an object of the present invention to provide a high-level radioactive material treatment system and a high-level radioactive material treatment method.

In order to solve the above-mentioned problems and achieve the object, the present disclosure is a high-level radioactive substance processing apparatus for treating a high-level radioactive substance containing a minor actinoid, and supplies a liquid containing the high-level radioactive substance. The liquid supply unit, the extractant supply unit that supplies the extractant of the organic phase, the diluent supply unit that supplies the diluent, the liquid, the extractant, and the diluent are mixed, and the height is increased. The diluted solution contains a MA extract generator that extracts at least one of the minor actinoid and the lanthanoid contained in the level radioactive substance into the extractant, and the diluted solution has a boiling point of 100 ° C. or lower. Further, it is preferable that the diluted solution does not have a flash point or has a flash point of 150 ° C. or higher.

In order to solve the above-mentioned problems and achieve the object, the present disclosure is a high-level radioactive substance treatment method for treating a high-level radioactive substance containing a minor actinide, for a liquid containing a high-level radioactive substance. The step of adding the organic phase extractant and the diluent having a boiling point of 100 ° C. or lower and having no ignition point or 150 ° C. or higher, the liquid, the extractant, and the diluent And the step of extracting at least one of the minor actinide and the lanthanoid contained in the high level radioactive substance into the extractant.

According to the present disclosure, minor actinides can be extracted, diluted solutions can be reused, and minor actinides can be solidified with reduced process load and high workability.

FIG. 1 is a schematic diagram showing a schematic configuration of a high-level radioactive material processing apparatus of the present embodiment.

Hereinafter, embodiments of the high-level radioactive material treatment apparatus according to the present disclosure will be described in detail with reference to the drawings. The high-level radioactive material processing apparatus of the present disclosure extracts MA (minor actinide) from the high-level radioactive material, vitrifies it, and stabilizes it. The high-level radioactive material treatment apparatus also extracts lanthanoids as well as minor actinides when the high-level radioactive material contains lanthanoids. In the present disclosure, "MA (minor actinide)" is an element excluding Pu from the transuranium elements belonging to actinides. "Actinide" is a general term for elements having atomic numbers 89 to 103. Minor actinides include, for example, Np (neptunium), Am (americium), and Cm (curium). "Ln (lanthanoid)" is a general term for elements having atomic numbers 57 to 71.

FIG. 1 is a schematic diagram showing a schematic configuration of a high-level radioactive material processing apparatus of the present embodiment. The high-level radioactive material treatment device (treatment device) 10 shown in FIG. 1 includes an extraction device 12, a solidification device 14, a stabilization device 16, and a storage device 18. The processing apparatus of the present embodiment will be described as a case where high-level radioactive waste (hereinafter, also referred to as “HALW”) is used as the high-level radioactive substance. The waste liquid is, for example, a liquid after recovering U (uranium) and Pu (plutonium) from the spent nuclear fuel solution in the reprocessing of the spent nuclear fuel discharged from the light water reactor. The high-level radioactive waste contained in the effluent includes fission products (hereinafter, also referred to as “FP”), MA, and lanthanoids. Specific examples of high-level radioactive waste (hereinafter, also referred to as “HALW”) include waste liquid generated by reprocessing by the PUREX method. In the Purex method, a nitric acid solution containing U or Pu, tributyl phosphate (TBP), and an organic solvent such as dodecane are contact-mixed. As a result, U and Pu in the nitric acid solution form a complex with TBP and move to the organic solvent side. On the other hand, FP, MA and Ln remain on the nitric acid solution (waste liquid) side. The nitric acid solution containing FP, MA, and Ln becomes the waste liquid to be treated.

The extraction device 12 extracts the MA component 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 generation unit 28. The waste liquid supply unit 22 stores HALW, which is a high-level radioactive waste of liquid, and supplies it to the MA extract generation unit 28. In the present 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 are used as one device to form a liquid phase in which the extractant is dissolved. An organic solvent may be supplied.

The extractant supply unit 24 supplies the extractant to the MA extract generation unit 28. The extractant captures MA and Ln. The extractant is a liquid that is transferred to a diluted solution and uniformly mixed. As the extractant, for example, a complexing agent that forms a complex with MA or Ln can be used. The complexing agent is preferably cheaper than the complexing agent that selectively forms a complex with MA. Examples of extracts include n-octyl (phenyl) -N, N'-diisobutylcarbamoylmethylphosphine oxide-tributylphosphate mixture (CMPO-TBP mixture), diisodecylphosphate, 6,6'-bis (5,5). 5,8,8-Tetramethyl-5,6,7,8-Tetrahydro-1,2,4-benzotriazine-3-yl) -2,2'-bipyridine (BTBP), N, N'-dibutyl- It is preferable to use a diglycolamide (DGA) -based material (complexing agent) as the extractant, which contains N, N'-dimethyltetradecylmalonamide (DMDBTDMA). Specific examples of the complexing agent include N, N, N', N'-tetraoctyl-3-oxapentanediamide (TODGA), 2-ethylhexyldiglycolamide (2EHDGA) and the like. One type of extractant may be used alone, or two or more types may be used in combination.

The diluent supply unit 26 supplies the diluent to the MA extract generation unit 28. The diluent is an organic phase material that is insoluble in the liquid components of the waste liquid. The diluent has the property of eluting the extractant from the waste liquid. The diluted solution has a boiling point of 100 ° C. or lower. Further, the diluent preferably has no flash point or has a flash point of 150 ° C. or higher. Further, the diluent is preferably a material that is less deteriorated by heat or radiation even if reused, and is preferably a solvent having a hydrocarbon-based structure that is less deteriorated by heat or radiation even if reused. .. Here, the fact that there is little deterioration due to heat or radiation even when reused means that even if the structure has a low molecular weight due to the energy of heat or radiation, it has the property that it is difficult to form a complex with metal ions. be. Further, it is preferable that the diluent has a low environmental load such as a global warming potential and an ozone depletion potential. Specifically, the diluent preferably has a global warming potential of 2000 or less and an ozone depletion potential of 0.01 or less. As the diluent, for example, hydrofluorocarbon (HFC), hydrofluoroolefin (HFO) and the like can be used.

The MA extract generation unit 28 is supplied with a waste liquid, an extractant, and a diluent. When the MA extract generation unit 28 contacts the MA and Ln in the waste liquid with the extractant by the solvent extraction method, the MA and Ln are transferred to the extractant side. The extractant that captures MA and Ln is encapsulated in the diluent. After the extraction treatment, the MA extract generation unit 28 separates the diluent from the waste liquid to generate an MA extract containing an extractant that collects MA and Ln in the diluent. The MA extract generation unit 28 may be a continuous type in which each material is continuously supplied to generate an MA extract, or a batch type in which each material is intermittently supplied to generate an MA extract. Further, the MA extract generator 28 may selectively capture MA with an extractant, or may simultaneously capture and process MA and Ln.

The solidifying device 14 removes the liquid component of the MA extract to produce a solidified body. The solidification device 14 includes a solidification processing unit 40 and a recovery processing unit 42. The solidification treatment unit 40 distills the MA extract to remove the diluent component. The solidification treatment unit 40 distills the diluted solution, so that the solidification residue containing the extractant and MA remains as a complex. The residue becomes a solidified body. The solidified product is an organometallic complex of a substance containing MA and an extractant. The solidification treatment unit 40 can use a known evaporation method such as a batch type or a continuous type (shelf-stage column or packed column) as the distillation process. The recovery processing unit 42 collects the diluted liquid distilled by the solidification processing unit 40, cools it, and liquefies it to recover the diluted liquid. The recovery processing unit 42 supplies the recovered contract liquid to the diluent supply unit 26. If impurities are mixed in the diluent, the recovery processing unit 42 may perform a removal treatment.

The stabilizer 16 performs a stabilization treatment for removing a part or all of carbon, hydrogen, oxygen, and nitrogen components from the solidified body. The stabilizer 16 has a stabilization processing unit 50. The stabilization treatment unit 50 heats the solidified body, calcins it, and sinters it to oxidize the object to be treated. The stabilizer 16 stabilizes the solidified body by removing a part or all of carbon, hydrogen, oxygen, and nitrogen components which are components that may be gasified during storage.

The storage device 18 stores the stabilized processed product. The storage device 18 includes a storage unit 60. The storage unit 60 stores the stabilized MA-containing substance in a solid state. The storage unit 60 is, for example, a cask. Further, the storage unit 60 may be provided in the ground, and the stabilized processed material may be buried in the ground.

The substance containing MA stored in the storage unit 60 of the processing system 10 can be used as fuel for the nuclear power generation system. When MA is burned as fuel, the stored oxide solidified body is dissolved to produce a solution containing MA and Ln (solidified body dissolved). Next, the obtained solution is subjected to MA purification treatment (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 producing a fuel (MA fuel production). The obtained fuel is burned in a fast breeder reactor or the like (MA combustion).

The processing device 10 of the present embodiment is an extraction device 12, which performs a separation process of adding an extractant and a diluent to the waste liquid and mixing them to allow Ln to accompany the waste liquid and separate the MA. Produce an extract. Next, the processing device 10 produces a solidified product containing MA by distilling the diluted solution from the MA extract in the solidifying device 14. Next, the processing device 10 removes the organic component (CHON) from the solidified body containing MA in the stabilizing device 16 and stabilizes it. The processing device 10 stores the stabilized processed material in the storage device 18.

The processing apparatus 10 separates, solidifies, and stabilizes MA together with Ln. As a result, MA can be efficiently extracted from the liquid high-level radioactive waste, the disposal load of the waste can be reduced, and the solid can be solidified. Further, by extracting MA and Ln and using them as stabilized substances, stable storage is possible even when MA and Ln are stored for reuse as fuel.

Further, by processing without separating MA and Ln, the process of separating MA and Ln becomes unnecessary, and the processing load can be reduced.

Further, in the treatment apparatus 10 of the present embodiment, by using an organic solvent having a boiling point of 100 ° C. or lower as the diluent, the load of the treatment of distilling the diluent in the solidification treatment unit 40 can be reduced. As a result, the process load can be reduced.

Further, the diluent preferably 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 that the diluent is ignited or burned during the work can be reduced. As a result, the processing in the processing system 10 can be performed more stably with high workability.

Further, the diluted solution preferably has a temperature difference of 50 ° C. or more between the boiling point and the flash point. This makes it possible to improve workability.

Further, the diluent preferably has a hydrocarbon-based structure that is less deteriorated by heat or radiation. As a result, the recovered diluent can be reused, and the economic efficiency of the extraction process can be improved. The diluent preferably has a global warming potential of 2000 or less and an ozone depletion potential of 0.01 or less. This makes it possible to reduce the environmental load when processing the diluted solution after use. Further, it is more preferable that the diluent contains at least one of HFC and HFO as described above. By using the above substance as a diluent, the extractant and the diluent can be easily mixed, so that the liquid component of the waste liquid can be easily separated. The diluent preferably contains the above components as the main component, but may contain an organic solvent such as alcohol having a boiling point in the above range as a sub component.

Further, the processing apparatus 10 of the present embodiment is provided with a recovery processing unit 42, collects the diluted solution evaporated in the treatment of the solidification processing unit 40, and supplies the diluted solution to the diluted solution supply unit 26 to reuse the diluted solution. can do. Further, as described above, the processing load in the recovery processing unit 42 can be reduced by using the diluted solution having the boiling point in the above range.

Further, it is preferable that the processing apparatus 10 uses an extractant that does not form a third phase when producing an MA extract for a highly radioactive substance containing a nitric acid-based substance. Specifically, it is preferable to use a DGA-based material. One example is 2EHDGA. Further, the extractant is preferably a material that can be removed during the treatment with the stabilizer 16, specifically, a material composed of only carbon, hydrogen, nitrogen, and oxygen. Moreover, it is preferable that the extractant does not contain a corrosive component.

Further, although the processing apparatus of the present embodiment has undergone stabilization treatment, it may be stored without performing stabilization treatment.

Although the present invention has been described above with reference to embodiments, the present disclosure is not limited to the above embodiments. Each configuration in the above embodiment and a combination thereof are examples, and the configuration can be added, omitted, replaced, and other changes can be made without departing from the spirit of the present invention.

10 Treatment system (high-level radioactive material treatment system)
12 Extractor 14 Solidification device 16 Stabilization device 18 Storage device 22 Waste liquid supply unit 24 Extractor supply unit 26 Diluting liquid supply unit 28 MA Extract generation unit 40 Solidification processing unit 42 Recovery processing unit 50 Stabilization processing unit 60 Storage unit

Claims (8)

A high-level radioactive material processing device that processes high-level radioactive materials containing minor actinides.
A liquid supply unit that supplies a liquid containing the high-level radioactive substance, and
An extractor supply unit that supplies an extractant for the organic phase,
The diluent supply unit that supplies the diluent and
It contains an MA extract generator that mixes the liquid, the extractant, and the diluent and extracts at least one of the minor actinides and lanthanides contained in the high-level radioactive substance into the extractant.
The diluent is a high-level radioactive material treatment system having a boiling point of 100 ° C. or lower. The high-level radioactive material treatment system according to claim 1, wherein the diluent does not have a flash point or is at least 150 ° C. The high-level radioactive substance treatment system according to claim 1 or 2, wherein the diluent contains a solvent having a hydrocarbon-based structure in which decomposition products due to heat or radiation do not easily form a complex with metal ions. The high-level radioactive substance treatment system according to claim 1 or 2, wherein the diluent has a global warming potential of 2000 or less and an ozone depletion potential of 0.01 or less. The high-level radioactive substance treatment system according to any one of claims 1 to 4, wherein the diluent contains at least one of HFC and HFO. The high-level radioactive substance treatment system according to any one of claims 1 to 5, wherein the extractant is a DGA-based material. A solidification treatment unit that evaporates the diluent from the MA extract produced by the MA extract generation unit to generate an oxide of MA, and a solidification treatment unit.
The height according to any one of claims 1 to 6, further comprising a solidification device having a recovery processing unit for recovering the diluted solution evaporated in the solidification processing unit and supplying it to the diluent supply unit. Level radioactive material processing system. A high-level radioactive material treatment method for treating high-level radioactive materials containing minor actinides.
A step of adding an organic phase extractant and a diluent having a boiling point of 100 ° C. or lower and having no flash point or 150 ° C. or higher to a liquid containing a high-level radioactive substance.
A method for treating a high-level radioactive substance, which comprises a step of mixing the liquid, the extractant, and the diluent and extracting at least one of a minor actinide and a lanthanoid contained in the high-level radioactive substance into the extractant. ..

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