Method for solidifying radioactive waste by recycling already solidified radioactive waste

Abstract

The present invention relates to a method for solidifying a radioactive waste by recycling an already solidified radioactive waste, the method comprising the steps of: (c) mixing a solidification medium, a radioactive waste, and water to generate a mixture; and (d) curing the mixture of step (c), wherein the solidification medium is a solidified radioactive waste for a solidification medium, which is an already solidified radioactive waste.

Description

Radioactive waste solidification method for recycling radioactive waste solidified in an already solidified state

[0001] The present invention relates to a method for solidifying new radioactive waste by recycling a solidified radioactive waste body that has already solidified, wherein instead of cement as a solidification medium, a solidified radioactive waste body that has already solidified with cement is utilized in a powdered state as a solidification medium to solidify new radioactive waste.

[0002]

[0003] Non-fixed materials or highly radioactive materials generated at nuclear power plants, such as concentrated waste liquid, waste resin, and spent filters, are solidified using solidifying agents like cement, polymers, paraffin, and asphalt to be safely stored in a fixed form and placed in storage drums.

[0004] Radioactive waste solidification technologies currently under research and use include cement solidification, asphalt solidification, geopolymer solidification, and glass solidification. The radioactive waste solidified bodies produced by these technologies must satisfy various acceptance criteria (strength, durability, leakage rate, radiation dose, etc.) required by the radioactive waste disposal facility for final disposal.

[0005]

[0006] Meanwhile, the reality is that most radioactive waste in Korea is disposed of in a solidified state using cement as a solidification medium. In other words, it is being disposed of as a solidified radioactive waste body generated by curing a mixture of commercially available cement, radioactive waste, and water.

[0007] However, in reality, solidified radioactive waste solidified with cement does not meet the acceptance criteria of radioactive waste disposal facilities and is therefore not disposed of in facilities but is being disposed of in temporary storage areas; consequently, urgent measures are required to address this situation.

[0008] Furthermore, even if such cement-solidified radioactive waste is disposed of in a radioactive waste disposal facility, there is an urgent need for technology that can minimize the amount and volume of radioactive waste ultimately disposed of, as the area of ​​radioactive waste disposal facilities in Korea is limited.

[0009]

[0010] (Patent Document 1) KR 10-1641281 B

[0011]

[0012] In order to solve the problems associated with the aforementioned conventional technology, we propose a method for solidifying radioactive waste using a solidification medium for disposal, which increases resource recyclability while simultaneously minimizing the amount and volume of radioactive waste ultimately disposed of.

[0013]

[0014] In order to solve the problems according to the prior art described above, the radioactive waste solidification method according to the present invention comprises: (c) a step in which a solidification medium, radioactive waste, and water are mixed to form a mixture; and (d) a step in which the mixture from step (c) is cured.

[0015] The above solidification medium may be a radioactive waste solidification medium that is already in a solidified state.

[0016]

[0017] Preferably, the method further comprises: (a) a step in which the radioactive waste solidified body for the solidification medium is crushed to produce a radioactive waste solidified body for the solidification medium in powder form; and (b) a step in which the radioactive waste solidified body for the solidification medium in powder form is heated.

[0018] After step (b) above, step (c) above may be performed.

[0019]

[0020] Preferably, the radioactive waste solidified body for the solidification medium that is crushed in step (a) above may be a radioactive waste solidified body solidified with cement.

[0021]

[0022] Preferably, in step (b), the solidified radioactive waste in powder form for the solidification medium may be heated at 550 to 750°C for 1 to 2 hours.

[0023]

[0024] Preferably, one or more of cement, calcium hydroxide (Ca(OH)2), calcium oxide (CaO), and silicon oxide (SiO2) may be added to the mixture produced in step (c).

[0025]

[0026] By recycling solidified radioactive waste disposed of in a temporary storage area due to failing to meet the acceptance criteria of a radioactive waste disposal facility, or by recycling solidified radioactive waste disposed of in a facility, the amount and volume of the radioactive waste ultimately disposed of can be minimized while minimizing the amount of cement that can be utilized during the solidification of radioactive waste.

[0027]

[0028] FIG. 1 is a flowchart of a method for solidifying radioactive waste according to the present invention.

[0029]

[0030] Hereinafter, preferred embodiments according to the present invention will be described with reference to the accompanying drawings. The terms described below are defined considering their functions in the present invention, and these may vary depending on the intention or practice of the user or operator. Therefore, the definitions of these terms should be based on the content throughout this specification.

[0031]

[0032] This will be explained with reference to Fig. 1.

[0033] S100: Step in which a solidified radioactive waste body in powder form for a solidification medium is generated

[0034] In this document, a radioactive waste solidified body for solidification medium refers to a radioactive waste solidified body that has already been solidified with a specific solidification medium. For example, it may be a radioactive waste solidified body that has been solidified with cement, which is the solidification medium.

[0035] The present invention relates to a method for solidifying radioactive waste that minimizes the amount and volume of radioactive waste to be finally disposed of while minimizing the amount of commercially available cement that can be used during radioactive waste solidification, by manufacturing a new radioactive waste solidification body using a radioactive waste solidification body as a solidification medium.

[0036] In other words, this invention relates to a radioactive waste solidification method that manufactures a new radioactive waste solidification body containing new radioactive waste by utilizing a powdered radioactive waste solidification medium capable of performing the same function as cement, instead of solidifying radioactive waste using commercially available cement.

[0037]

[0038] In this stage, the radioactive waste solidified body for the solidification medium may be crushed to produce a radioactive waste solidified body for the solidification medium in powder form. Here, the radioactive waste solidified body for the solidification medium may be a radioactive waste solidified body that has already been solidified with cement. That is, the radioactive waste solidified body for the solidification medium may be an existing radioactive waste solidified body in which the radioactive waste has been solidified using cement as the solidification medium.

[0039] First of all, this solidified radioactive waste for solidification media can be crushed using a jaw crusher or the like. In the crushed state, fine aggregate is separated, and the remainder is sieved to a diameter of less than a certain size through ball milling or the like to produce a solidified radioactive waste for solidification media in powder form.

[0040] In the case of solidified radioactive waste solidified into powdered cement, since it is solidified using cement as a solidification medium, its chemical composition can be considered similar to that of Portland cement. Therefore, solidified radioactive waste solidified into powdered cement containing calcium oxide (CaO) or silicon oxide (SiO2) can perform the function of a solidification medium similar to commercially available cement.

[0041] However, in the case of a solidified radioactive waste body solidified in the form of cement powder, since it is solidified while containing radioactive waste, the content of constituent components such as calcium oxide (CaO) or silicon oxide (SiO2) may be insufficient or unevenly distributed in order to perform the function as a solidification medium. Accordingly, one or more of cement, calcium hydroxide (Ca(OH)2), calcium oxide (CaO), and silicon oxide (SiO2) may be added to the mixture in the S300 step described below.

[0042]

[0043] S200: Step in which a solidified radioactive waste in powder form for solidification medium is heated

[0044] A solidified radioactive waste material in powder form for solidification media can be heated at 550 to 750°C for 1 to 2 hours. That is, it can undergo a calcination process to produce tricalcium silicate (alite, C3S) or dicalcium silicate (belite, C2S), which can undergo a hydration reaction through reaction with water. Of course, when a solidified radioactive waste material in powder form for solidification media is heated under the calcination conditions described above, tricalcium silicate (alite, C3S) or dicalcium silicate (belite, C2S) can be produced.

[0045]

[0046] S300: A step in which a mixture is formed by mixing a solidified radioactive waste body in powder form for a solidification medium, radioactive waste, and water.

[0047] A mixture may be formed by mixing the solidified radioactive waste body for the solidification medium, which has been calcined in the S200 stage, (new) radioactive waste to be solidified, and water. The radioactive waste constituting the mixture is new radioactive waste different from the radioactive waste solidified in the solidified radioactive waste body for the solidification medium, and may be radioactive waste of the same type as the radioactive waste solidified in the solidified radioactive waste body for the solidification medium, or radioactive waste of a different type.

[0048] As described above, one or more of cement, calcium hydroxide (Ca(OH)2), calcium oxide (CaO), and silicon oxide (SiO2) may be added to the mixture.

[0049] Furthermore, it goes without saying that fly ash, blast furnace slag, sand, and admixtures may be added to the mixture to maintain properties such as compressive strength, similar to concrete.

[0050]

[0051] S400: A step in which the mixture is cured to create a new radioactive waste solidified body

[0052] The mixture can be cured to produce a radioactive waste solidified body for solidification media and other new radioactive waste solidified bodies.

[0053]

[0054] experiment

[0055] The first experiment, in which radioactive waste was solidified with commercial cement, and the second experiment, in which radioactive waste was solidified into a powder-form radioactive waste solidification medium, were conducted.

[0056] The radioactive waste used in Experiment 1 and Experiment 2 is a simulated radioactive waste sample, which is a powder-form radioactive concentrated waste liquid sample produced by drying radioactive concentrated waste liquid.

[0057] The solidification medium used in the second experiment is a solidified radioactive waste material in powder form, produced by heating and crushing an existing solidified radioactive waste material in which radioactive concentrated waste liquid has been solidified with cement. In other words, to solidify a new radioactive concentrated waste liquid in the form of a dried powder, a solidified radioactive waste material in which radioactive concentrated waste liquid had been previously solidified was crushed into a powder form to serve as the solidification medium, and this was then used as the solidification medium to solidify the new powdered radioactive concentrated waste liquid.

[0058] In both the first and second experiments, experiments were conducted with different loading rates of radioactive waste (0%, 30%, 40%, 50%).

[0059] The mixing ratios for each experiment are as shown in the table below. In the table below, Falkland cement refers to commercially available cement.

[0060]

[0061] [0% Immersion of Radioactive Waste (Powdered Concentrated Radioactive Waste Liquid)] Material Solidification Medium Radioactive Waste Total Input Amount (g) Experiment 1 (Solidification Medium: Portland Cement) 183.266 1.740 245.00 Experiment 2 (Solidification Medium: Solidified Radioactive Waste for Solidification Medium) 183.266 1.740 245.00

[0062]

[0063] [30% Immersion in Radioactive Waste (Powdered Concentrated Radioactive Waste Liquid)] Material Solidification Medium Radioactive Waste Total Input Amount (g) Experiment 1 (Solidification Medium: Portland Cement) 109.766 1.747 3.50 245.00 Experiment 2 (Solidification Medium: Solidified Radioactive Waste for Solidification Medium) 109.766 1.747 3.50 245.00

[0064]

[0065] [40% Immersion in Radioactive Waste (Powdered Concentrated Radioactive Waste Liquid)] Material Solidification Medium Radioactive Waste Total Input Amount (g) Experiment 1 (Solidification Medium: Portland Cement) 94.08 52.92 98.00 245.00 Experiment 2 (Solidification Medium: Solidified Radioactive Waste for Solidification Medium) 94.08 52.92 98.00 245.00

[0066]

[0067] [50% Immersion in Radioactive Waste (Powdered Concentrated Radioactive Waste Liquid)] Material Solidification Medium Radioactive Waste Total Input Amount (g) Experiment 1 (Solidification Medium: Portland Cement) 69.58 52.92 12 2.50 245.00 Experiment 2 (Solidification Medium: Solidified Radioactive Waste for Solidification Medium) 69.58 52.92 12 2.50 245.00

[0068] The mixture was mixed according to the mixing ratios for each experiment described above, sealed in a zipper bag, and cured at room temperature for 28 days.

[0069]

[0070] Experimental results

[0071] The experimental results regarding the acceptance criteria for the low- and intermediate-level radioactive waste disposal facility are as follows.

[0072]

[0073] The compressive strength after curing is as shown in Table 5 below.

[0074] Solidification Medium Compressive Strength (MPa) Radioactive Waste (Radioactive Concentrated Liquid) 0% Supported Radioactive Waste (Radioactive Concentrated Liquid) 30% Supported Radioactive Waste (Radioactive Concentrated Liquid) 40% Supported Radioactive Waste (Radioactive Concentrated Liquid) 50% Supported Portland Cement 30.34 13.40 12.70 11.57 Radioactive Waste Solidification Medium 26.45 12.27 11.97 11.08

[0075]

[0076] The compressive strength after the thermal cycling test (compressive strength after 30 cycles between -40℃ and 60℃) is as shown in Table 6 below.

[0077] Solidification Medium Compressive Strength (MPa) Radioactive Waste (Radioactive Concentrated Liquid) 0% Supported Radioactive Waste (Radioactive Concentrated Liquid) 30% Supported Radioactive Waste (Radioactive Concentrated Liquid) 40% Supported Radioactive Waste (Radioactive Concentrated Liquid) 50% Supported Portland Cement 31.21 13.26 12.89 11.13 Radioactive Waste for Solidification Medium Solidified Body 26.18 12.62 12.05 11.20

[0078]

[0079] The results of the rational number experiment regarding how much water is contained in the solidified body are as shown in Table 7 below.

[0080] Solidification Medium Glass Water % Radioactive Waste (Radioactive Concentrated Waste Liquid) 0% Supported Radioactive Waste (Radioactive Concentrated Waste Liquid) 30% Supported Radioactive Waste (Radioactive Concentrated Waste Liquid) 40% Supported Radioactive Waste (Radioactive Concentrated Waste Liquid) 50% Supported Portland Cement 0000 Radioactive Waste Solidified Body for Solidification Medium 0000

[0081]

[0082] The test results for compressive strength after flooding (compressive strength after 90 days of flooding) are as shown in Table 8 below.

[0083] Solidification Medium Compressive Strength (MPa) Radioactive Waste (Radioactive Concentrated Liquid) 0% Supported Radioactive Waste (Radioactive Concentrated Liquid) 30% Supported Radioactive Waste (Radioactive Concentrated Liquid) 40% Supported Radioactive Waste (Radioactive Concentrated Liquid) 50% Supported Portland Cement 29.45 13.14 12.22 11.24 Radioactive Waste for Solidification Medium Solidified Body 25.37 12.05 11.53 10.89

[0084]

[0085] The leaching index based on the leaching experiment (the leaching index of the acceptance criteria for Co, Sr, and Cs must be 6 or higher) is as shown in Table 9 below.

[0086] Solidification Medium Radionuclide Leaching Index Radioactive Waste (Radioactive Concentrated Liquid) 30% Supported Radioactive Waste (Radioactive Concentrated Liquid) 40% Supported Radioactive Waste (Radioactive Concentrated Liquid) 50% Supported Portland Cement CO16.49 15.37 14.83 Sr10.28 10.03 9.92 Cs12.41 11.83 10.92 Radioactive Waste for Solidification Medium Solidified Body CO16.32 15.82 14.97 Sr10.47 10.34 10.01 Cs12.38 12.04 11.86

[0087]

[0088] Upon examining the experimental results regarding the aforementioned compressive strength, compressive strength after thermal cycling, compressive strength after immersion, free water, and leaching index, it can be seen that even when a powdered radioactive waste solidification medium is used as the solidification medium, there is almost no difference in effect compared to that of a radioactive waste solidification medium using commercially available cement (Portland cement) as the solidification medium.

[0089] In other words, even if solidified radioactive waste that has already been disposed of is manufactured into a powder form and recycled as a solidification medium, there is no significant difference compared to the effect of solidified waste solidified with commercial cement. Therefore, by recycling solidified radioactive waste that has already been disposed of and using it to solidify new radioactive waste, it is possible to minimize the amount and volume of the radioactive waste ultimately disposed of while minimizing the amount of cement that can be utilized during radioactive waste solidification.

[0090]

[0091] For the time being, the present specification has been described with reference to embodiments illustrated in the drawings so that those skilled in the art can easily understand and reproduce the present invention; however, this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible from the embodiments of the present invention. Accordingly, the scope of protection of the present invention should be determined by the claims.

Claims

1. (c) A step in which a solidification medium, radioactive waste, and water are mixed to produce a mixture; and (d) includes a step in which the mixture of step (c) above is cured, and The above solidification medium is a radioactive waste solidification medium that is already in a solidified state, and is a radioactive waste solidification method.

2. In Paragraph 1, (a) a step in which the radioactive waste solidification body for the solidification medium is crushed to produce a radioactive waste solidification body for the solidification medium in powder form; and (b) further comprising a step in which the solidified radioactive waste in powder form for the solidification medium is heated, and A radioactive waste solidification method in which step (c) is performed after step (b) above.

3. In Paragraph 2, A radioactive waste solidification method in which the radioactive waste solidified body for the solidification medium crushed in step (a) above is a radioactive waste solidified body solidified with cement.

4. In Paragraph 3, A method for solidifying radioactive waste in which, in step (b) above, the solidified radioactive waste in powder form for the solidification medium is heated at 550 to 750°C for 1 to 2 hours.

5. In Paragraph 4, A method for solidifying radioactive waste in which one or more of cement, calcium hydroxide (Ca(OH)2), calcium oxide (CaO), and silicon oxide (SiO2) are added to the mixture produced in step (c) above.

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