Method for solidifying radioactive waste, solidified radioactive waste, and method for burying solidified radioactive waste

Abstract

To provide, a solidification treatment method of a radioactive waste which can suppress outflow of a radioactive waste.SOLUTION: A solidified matter 3 of a radioactive waste includes: an including resin solidified matter 1 obtained by mixing a treatment object of a radioactive waste and an including resin including the treatment object; and a coating resin layer 2 formed of a coating resin coating the including resin solidified matter. A solidification treatment method of a radioactive waste includes: an including resin solidified matter formation step of mixing a molten including resin with a treatment object of a radioactive waste included in the including resin, and forming an including resin solidified matter; and a radioactive waste solidified matter formation step of allowing the including resin solidified matter to form a coating resin layer using the coating resin coating the including resin solidified matter, and forming a radioactive waste solidified matter composed of the including resin solidified matter and the coating resin layer.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The technical field of the present specification relates to a method for solidifying radioactive waste generated from nuclear facilities and the like, a solidified radioactive waste product obtained by the solidification treatment, and a method for burying the solidified radioactive waste product. [Background technology]

[0002] BACKGROUND ART Conventionally, a known method for solidifying radioactive waste involves filling the radioactive waste together with a hydraulic material such as cement into a container such as a drum and solidifying the waste (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-064334 [Patent Document 2] Japanese Patent Publication No. 2020-187030 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional methods for solidifying radioactive waste involve directly solidifying the radioactive waste using hydraulic materials such as cement, which poses the risk of radioactive waste leaking out when the hardened cement (mortar) corrodes due to reaction with the radioactive waste or neutralization.

[0005] The problem that the technology of this specification aims to solve has been made in consideration of the above points, and its object is to provide a method for solidifying and treating radioactive waste that can suppress the outflow of radioactive waste. [Means for solving the problem]

[0006] The radioactive waste solidification treatment method according to an embodiment of the present specification includes: a process of forming a solidified product made of encapsulating resin by mixing the molten encapsulating resin with the radioactive waste to be encapsulated in the encapsulating resin; a radioactive waste solidification process in which a coating resin layer is formed on the encapsulating resin solidified material using a coating resin that coats the encapsulating resin solidified material, thereby forming a radioactive waste solidified material consisting of the encapsulating resin solidified material and the coating resin layer; The present invention is characterized by having the following.

[0007] According to the radioactive waste solidification treatment method of the embodiment of this specification, the radioactive waste to be treated is mixed with an encapsulating resin to form an encapsulating resin solidified material, and is fixed in the encapsulating resin. The encapsulating resin solidified material is coated with a coating resin to form a coating resin layer. Because the radioactive waste to be treated is fixed in the encapsulating resin and further coated with the coating resin, it is possible to suppress leakage from the solidified radioactive waste.

[0008] Here, in the radioactive waste solidification treatment method, the radioactive waste is an acidic wastewater solution, Before the step of forming the encapsulated resin solidified product, a neutralization step of neutralizing the wastewater solution; a salting-out step of heating the neutralized wastewater solution to precipitate salt as the treatment target; The present invention can be applied to a semiconductor device having a semiconductor substrate.

[0009] This makes it possible to reduce the amount of acidic wastewater solution of radioactive waste that is to be treated.

[0010] In the radioactive waste solidification treatment method, the wastewater solution may be the same hydrochloric acid solution used in Sr (strontium) analysis.

[0011] This allows for suitable treatment of the hydrochloric acid solution used in Sr analysis.

[0012] In the radioactive waste solidification treatment method, the encapsulating resin may be paraffin.

[0013] This allows the paraffin used as the encapsulating resin to be easily melted.

[0014] In the radioactive waste solidification treatment method, the coating resin may be an epoxy resin.

[0015] According to this, since the epoxy resin has excellent hardening characteristics, the encapsulating resin solidified matter can be adequately coated.

[0016] Here, the radioactive waste solidified body according to an embodiment of this specification is characterized by comprising an encapsulating resin solidified material in which the radioactive waste to be treated and an encapsulating resin that encapsulates the treated material are mixed, and a coating resin layer formed from a coating resin that coats the encapsulating resin solidified material.

[0017] According to the radioactive waste solidification body of the embodiment of this specification, the radioactive waste to be treated is fixed in the encapsulating resin and further coated with the coating resin, thereby preventing leakage from the radioactive waste solidification body.

[0018] In the solidified radioactive waste, the radioactive waste may be an acidic wastewater solution, and the material to be treated may be a salt precipitated from a neutralized aqueous solution of the acidic wastewater solution.

[0019] This makes it possible to reduce the amount of acidic wastewater solution of radioactive waste that is to be treated.

[0020] In the solidified radioactive waste, the wastewater solution may be an aqueous hydrochloric acid solution used in Sr (strontium) analysis.

[0021] This allows the salt precipitated from the hydrochloric acid solution used in the Sr analysis to be properly solidified.

[0022] In the solidified radioactive waste, the encapsulating resin may be paraffin.

[0023] According to this, since the paraffin used as the enveloping resin is hydrophobic, it is possible to prevent the object to be treated from leaking into the water.

[0024] In the solidified radioactive waste, the coating resin may be an epoxy resin.

[0025] According to this, since the epoxy resin has high strength, the solidified radioactive waste can be made to have excellent impact resistance.

[0026] Here, a method for burying radioactive waste according to an embodiment of the present specification is a method for burying a solidified radioactive waste formed by the above-mentioned method for solidifying radioactive waste, or the above-mentioned solidified radioactive waste, comprising the steps of: an encapsulation step of transporting the solidified radioactive waste into a metal container and encapsulating it by injecting a binder; a burying step of burying the metal container in which the solidified radioactive waste is sealed in the ground; The present invention is characterized by having the following.

[0027] This makes it possible to bury the solidified radioactive waste while preventing the radioactive waste from leaking out.

[0028] In the method for burying solidified radioactive waste, the binder may contain Portland cement (JIS R 5210-2019).

[0029] This makes it possible to suppress corrosion of the metal container.

[0030] Furthermore, in the above-mentioned method for burying solidified radioactive waste, the burial process can be pit disposal (pit disposal as defined in the regulations concerning the business of burying Type 2 waste from nuclear fuel materials or materials contaminated by nuclear fuel materials).

[0031] This allows radioactive waste to be disposed of appropriately. [Effects of the Invention]

[0032] According to the radioactive waste solidification treatment method of this specification, the radioactive waste to be treated is fixed in the encapsulating resin and coated with the coating resin, thereby preventing leakage from the solidified radioactive waste body. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a flow diagram of a process for forming an encapsulated resin solidified material in a radioactive waste solidification treatment method according to an embodiment. [Figure 2] FIG. 2 is a flow chart of the radioactive waste solidification body forming process of the solidification treatment method. [Figure 3] 3A is a perspective view of the solidified radioactive waste, and FIG. 3B is a cross-sectional view taken along line IIIB-IIIB in FIG. 3A. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, a radioactive waste solidification treatment method and a radioactive waste solidified body according to an embodiment of the present specification will be described. Note that the scope of the present invention is not limited to the scope disclosed in the embodiment. As shown in Fig. 3, a radioactive waste solidified body 3 according to an embodiment includes an encapsulating resin solidified material 1 in which a radioactive waste to be treated and an encapsulating resin that encapsulates the treatment object are mixed, and a coating resin layer 2 formed from a coating resin that coats the encapsulating resin solidified material 1.

[0035] The radioactive waste in this embodiment is radioactive waste generated from a nuclear facility or the like. In another embodiment, it may be low-level radioactive waste, and in yet another embodiment, it may be waste liquid with a relatively low level of radioactivity. The waste liquid (wastewater solution) may be radioactive waste liquid, for example, a highly concentrated hydrochloric acid solution used in Sr (strontium) analysis.

[0036] The radioactive waste to be treated is the radioactive waste that is actually encapsulated in an encapsulating resin and solidified, such as solid radioactive waste itself, or non-volatile matter obtained by volatilizing water from liquid radioactive waste (e.g., wastewater solution), or salt.

[0037] The encapsulating resin in the embodiment is a resin that encapsulates the radioactive waste to be treated. Examples of encapsulating resins that can be used include paraffin (aliphatic saturated hydrocarbon), polypropylene, polyethylene, ethylene-propylene copolymer resin, polyamide, polystyrene, acrylic resin, methacrylic resin, acrylamide resin, PET (polyethylene terephthalate), ABS resin (acrylonitrile, butadiene, styrene copolymer), vinyl chloride resin, epoxy resin, and urethane resin. In another embodiment, paraffin can be used as the encapsulating resin. This is because paraffin has excellent radiation shielding properties and is hydrophobic, preventing the material to be treated from leaking into water and rendering the material to be treated harmless in the metal container described below.

[0038] The dropping point of the encapsulating resin can be set to 80 to 150°C. This is because it can suitably encapsulate the radioactive waste to be treated. If the dropping point of the encapsulating resin is less than 80°C, there is a risk that the resin will soften when encapsulated in concrete (cement), as described below. On the other hand, if the dropping point is greater than 150°C, there is a risk that energy is required to melt the resin, resulting in poor thermal efficiency. In another embodiment, the dropping point of the encapsulating resin can be set to 90 to 130°C, and in yet another embodiment, the dropping point of the encapsulating resin can be set to 100 to 120°C.

[0039] In one embodiment, the mixing ratio of the object to be treated to the encapsulating resin can be 200 to 400 parts by mass of the object to be treated to 100 parts by mass of the encapsulating resin. This is because the object to be treated can be suitably encapsulated. If the ratio of the object to be treated to 100 parts by mass of the encapsulating resin is less than 200 parts by mass, there is a risk of incurring too little object to be treated, which may be uneconomical. On the other hand, if the ratio of the object to be treated to 100 parts by mass of the encapsulating resin exceeds 400 parts by mass, there is a risk of the object to be treated precipitating on the surface of the encapsulating resin solidified material 1. In another embodiment, the mixing ratio of the object to be treated to 100 parts by mass of the encapsulating resin can be 250 to 360 parts by mass of the object to be treated to 100 parts by mass of the encapsulating resin. In yet another embodiment, the ratio of the object to be treated to 100 parts by mass of the encapsulating resin can be 300 to 340 parts by mass of the object to be treated to 100 parts by mass of the encapsulating resin.

[0040] The coating resin in this embodiment is a resin that coats the encapsulated resin solidified material 1, which is a mixture of the radioactive waste to be treated and the encapsulated resin. Examples of the coating resin that can be used include epoxy resin, urethane resin, acrylic resin, methacrylic resin, acrylamide resin, PET (polyethylene terephthalate), ABS resin (acrylonitrile, butadiene, styrene copolymer), vinyl chloride resin, paraffin (aliphatic saturated hydrocarbon), polypropylene, polyethylene, ethylene-propylene copolymer resin, polyamide, and polystyrene. In another embodiment, a reactive curing resin such as epoxy resin, urethane resin, or acrylic resin can be used as the coating resin. This is because reactive curing resins have strength and can adequately protect the encapsulated resin solidified material 1. In yet another embodiment, an epoxy resin can be used as the coating resin. This is because epoxy resin has a pot life (usable time) of approximately 10 minutes and excellent curing characteristics.

[0041] The thickness of the coating resin layer 2 formed from the coating resin can be 0.5 to 2.0 cm. This is because it can adequately coat the encapsulated resin solidified material 1. If the thickness of the coating resin layer 2 is less than 0.5 cm, the strength of the coating resin layer 2 is insufficient, and cracks may occur in the coating resin layer 2 when the solidified radioactive waste 3 is subjected to an impact. On the other hand, if the thickness of the coating resin layer 2 exceeds 2.0 cm, the thickness is excessive and may be uneconomical. In another embodiment, the thickness of the coating resin layer 2 formed from the coating resin can be 0.7 to 1.5 cm, and in yet another embodiment, 0.8 to 1.2 cm. Note that when the encapsulated resin solidified material 1 shown in the examples weighs 390 g, the coating resin used (total amount of base resin and curing agent) can be 130 to 600 g. In another embodiment, the coating resin used can be 180 to 400 g, and in yet another embodiment, 200 to 330 g.

[0042] Next, a method for burying solidified radioactive waste will be described. In the method for burying solidified radioactive waste, a metal container is a drum (200 L open-head drum) and a binder is a mortar slurry (a mixture of Portland cement (JIS R 5210-2019), sand, and water).

[0043] The method for burying solidified radioactive waste in this embodiment comprises an encapsulation step of transporting the solidified radioactive waste 3 into a drum and injecting mortar slurry into it to encapsulate it, and an burial step of burying the drum containing the solidified radioactive waste 3 in the ground by pit disposal (regulations regarding the business of burying type 2 waste from nuclear fuel material or material contaminated by nuclear fuel material).

[0044] In the encapsulation process, the solidified radioactive waste 3 was carried into a drum and laid out, and mortar slurry was poured into the gaps between the solidified radioactive waste 3 to encapsulate it. At this time, it is expected that the temperature inside the drum will rise to about 80°C due to the heat of hydration of the Portland cement in the mortar slurry, but if the dropping point of paraffin is 80°C or higher, there is little risk of the paraffin melting.

[0045] In the burial process for pit disposal, the drums were buried underground in accordance with the regulations for Category II waste disposal of nuclear fuel materials or materials contaminated by nuclear fuel materials. The binder used in this process is a mortar slurry mainly made of Portland cement, which can prevent the drums from corroding in the long term. [Example]

[0046] The solidified radioactive waste form 3 of the example was prepared as follows: In the radioactive waste solidification treatment method of the example (method for preparing the solidified radioactive waste form 3), the radioactive waste used was an aqueous hydrochloric acid solution (concentration: approximately 18%) that was used in Sr (strontium) analysis, the encapsulating resin was paraffin (dropping point: approximately 110°C), and the coating resin was epoxy resin.

[0047] The radioactive waste solidified body 3 of the embodiment was produced through the following steps: 1. a neutralization process for neutralizing a hydrochloric acid aqueous solution; 2. a salting-out process for precipitating salt from the neutralized aqueous solution; 3. an encapsulating resin solidified body formation process for mixing an encapsulating resin with salt to form an encapsulating resin solidified body; and 4. a radioactive waste solidified body formation process for coating the encapsulating resin solidified body with a coating resin to form a radioactive waste solidified body.

[0048] 1. In the neutralization process, an alkaline solution (aqueous sodium hydroxide solution) was added dropwise to the hydrochloric acid solution to neutralize it until the pH reached 6 or higher. The hydrochloric acid solution used in the Sr (strontium) analysis was discharged according to the Atomic Energy Society's analytical standard (ion exchange method) added in 2011, and was generated from nuclear facilities across the country.

[0049] 2. In the salting out step, the hydrochloric acid solution neutralized in the neutralization step was heated to volatilize the water and precipitate the salt.

[0050] 3. In the process of forming the encapsulated resin solidified product, as shown in Figure 1, paraffin was heated and melted in a heating container. The salt obtained in the salting-out process was mixed with the molten paraffin, and the salt-mixed paraffin was poured into a silicone container and allowed to solidify, forming encapsulated resin solidified product 1. LICOLUB H4 (Clariant Japan Co., Ltd.) was used as the paraffin. The mixture was 90 g of paraffin and 300 g of salt. The paraffin and salt mixture poured into the silicone container (encapsulated resin solidified product 1) took 2–3 hours to solidify. After solidification, it was removed from the silicone container, and the excess paraffin that had solidified on the edge of the silicone container due to surface tension was scraped off. Because salt does not dissolve in paraffin, the salt precipitates, and the paraffin powder solidified on the edge does not contain salt. By scraping off the excess paraffin that solidified on the edge, the amount of coating resin used in the next process can be reduced.

[0051] 4. In the radioactive waste solidification process, the encapsulating resin solidified material 1 was coated with a coating resin to form a radioactive waste solidified material 3, following the procedure shown in Figure 2. In the radioactive waste solidification process, a polypropylene container (PP container) slightly larger than the silicone container used in the encapsulating resin solidification process was used, and the coating resin that coated the encapsulating resin solidified material 1 was applied in the following order: bottom, front, back, left, and right sides, and top. The coating resin used was a two-component reaction-curing epoxy resin (main agent (EPOXY RESIN XNR7425) and hardener (HARDNER HY956) (both manufactured by Nagase ChemteX Corporation)), and 260 g (total amount of main agent and hardener) was used for 390 g of encapsulating resin solidified material 1. The mixing ratio of main agent to hardener was 5:1. The curing conditions of the coating resin are in accordance with the curing conditions of the coating resin, but in an embodiment, based on the results of the heat resistance test described later, after the coating resin is poured into the PP container, it can be cooled in cold water for 15 hours or more, and then heat cured (at 40°C or higher for 5 hours or more).

[0052] The solidified radioactive waste 3 thus produced was subjected to a salt elution test, a compressive strength test and a heat resistance test, and the results were evaluated.

[0053] Salt elution test The salt elution test was carried out on the solidified radioactive waste 3 prepared as described above and on the solidified radioactive waste 3 not coated with a coating resin (that is, the resin-encapsulated solidified matter 1).

[0054] The salt elution test for the solidified radioactive waste 3 was carried out by submerging the solidified radioactive waste 3 in 1 L of demineralized water for 100 hours. The test liquid was quantified as chloride ions using ion chromatography. The test results are shown in Table 1. As a result of the test, 0.1 to 0.4 mg / L of chloride ions were detected, but it is presumed that this salt content originates from the release agent used in resin molding and components contained in the epoxy resin. The inner surface of drums to be disposed of as radioactive waste originally has a salt content of several mg / m due to the influence of salt from the sea breeze. 2 As the contents contain 100% chloride, the salt content in this test is considered to be no problem. As a result, the hydrophobic effect of paraffin and the protection provided by the resin have completely embedded the salt in the contents, making it harmless.

[0055] To test the salt elution of the encapsulated resin-solidified material 1, three pieces of the encapsulated resin-solidified material 1 were submerged in 2.5 L of demineralized water and subjected to a 100-hour salt elution test. The test was evaluated based on the weight before and after. The test results are shown in Table 2. As a result of the test, the salt elution rate was 3.3-4.0%. After the test, all of the paraffin-solidified materials retained their original shape and most of the salt, demonstrating that the hydrophobic properties of paraffin were working effectively.

[0056] [Table 1]

[0057] [Table 2] Compression Strength Test The compressive strength test was carried out on the solidified radioactive waste form 3 prepared as described above. The results are shown in Table 3.

[0058] [Table 3] Compression strength test: 92.4~311.0N / cm 2 If the solidified radioactive waste 3 is placed at the bottom of the drum, the head pressure from the weight of the mortar slurry is 1.8 N / cm 2 Therefore, it can be said that it has sufficient strength.

[0059] Heat Resistance Test For the heat resistance test, the radioactive waste solidified body 3 prepared as described above was subjected to a high temperature test (80°C, 5 hours) simulating the heat of hydration of Portland cement in the mortar slurry during the encapsulation process, and a low temperature test (-18°C, 80 hours) simulating pit disposal in a cold region, and the occurrence of abnormalities such as deformation or cracks was confirmed.

[0060] The results varied depending on the curing conditions of the coating resin. In a high-temperature test of a test specimen in which the coating resin was poured into a PP container and then cooled in cold water for 15 hours, cracks appeared inside the coating resin layer 2. This is thought to be due to insufficient hardening of the coating resin. In a test specimen in which the coating resin was poured into a PP container and then cooled in cold water for 15 hours, and then heat-cured (40°C for 5 hours), no abnormalities such as deformation or cracks were found in either the high-temperature or low-temperature test. Therefore, it was confirmed that by heat curing, no abnormalities would occur in the radioactive waste solidified body 3 due to the heat of hydration of Portland cement during the encapsulation process, and that no abnormalities would occur even when the solidified body is disposed of in a cold region. [Explanation of symbols]

[0061] 1...Encapsulated resin solidified material, 2...Coating resin layer, 3...Solidified radioactive waste body.

Claims

1. a process of forming a solidified product made of encapsulating resin by mixing the molten encapsulating resin with the radioactive waste to be encapsulated in the encapsulating resin; and a radioactive waste solidification process for forming a radioactive waste solidification product comprising the encapsulating resin solidification product and the coating resin layer by forming a coating resin layer on the encapsulating resin solidification product, and a salting-out step of heating the radioactive waste to precipitate salt as the treatment target prior to the resin-containing solidification step. A method for solidifying radioactive waste.

2. the radioactive waste is a wastewater solution; Before the salting out step, 2. The method for solidifying radioactive waste according to claim 1, further comprising a neutralization step of neutralizing the wastewater solution.

3. A method for solidifying and treating radioactive waste as described in claim 2, characterized in that the wastewater solution is acidic.

4. 4. The method for solidifying radioactive waste according to claim 3, wherein the wastewater solution is a hydrochloric acid solution used in Sr (strontium) analysis.

5. A method for solidifying radioactive waste as described in claim 1, characterized in that the encapsulating resin has a dropping point of 80 to 150°C.

6. A method for solidifying radioactive waste as described in claim 1, characterized in that the encapsulating resin is hydrophobic.

7. 7. The method for solidifying radioactive waste according to claim 1, wherein the coating resin is an epoxy resin.

8. The method comprises: a resin-containing solidified material obtained by mixing a radioactive waste to be treated with an encapsulating resin that encapsulates the radioactive waste; and a coating resin layer formed from a coating resin that coats the resin-containing solidified material; The object to be treated is a salt precipitated by heating the radioactive waste.

9. 9. The solidified radioactive waste form according to claim 8, wherein the radioactive waste is a wastewater solution, and the salt is a salt precipitated from a neutralized aqueous solution of the wastewater solution.

10. A radioactive waste solidified body as described in Claim 9, characterized in that the wastewater solution is acidic.

11. 11. The solidified radioactive waste form according to claim 10, wherein the wastewater solution is a hydrochloric acid solution used in Sr (strontium) analysis.

12. The solidified radioactive waste body according to claim 8, characterized in that the encapsulating resin has a dropping point of 80 to 150°C.

13. A radioactive waste solidified body as described in claim 8, characterized in that the encapsulating resin is hydrophobic.

14. 14. The solidified radioactive waste form according to claim 8, wherein the coating resin is an epoxy resin.

15. A method for burying solidified radioactive waste, comprising: a resin-containing solidified product obtained by mixing a radioactive waste to be treated with a resin-containing material that contains the radioactive waste; and a coating resin layer formed from a resin that coats the resin-containing solidified product, an encapsulation step of transporting the solidified radioactive waste into a metal container and injecting a binder thereinto to encapsulate the solidified radioactive waste; a burying step of burying the metal container in which the solidified radioactive waste is sealed in the ground; A method for burying solidified radioactive waste, comprising:

16. The method for burying solidified radioactive waste according to claim 15, characterized in that the binder contains Portland cement (JIS R 5210-2019).

17. A method for burying solidified radioactive waste bodies as described in claim 15 or 16, characterized in that the burial process is pit disposal (pit disposal as prescribed in the regulations regarding the business of Type 2 waste burial of nuclear fuel materials or materials contaminated by nuclear fuel materials).

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